Exelon (EXC) 10-K 10 Feb 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Jan. 31, 2016
Entity Registrant Name	EXELON CORP
Entity Central Index Key	1,109,357
Document Type	10-K
Document Period End Date	Dec. 31, 2015
Amendment Flag	false
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock Shares Outstanding		919,924,742
Entity Public Float	$ 27,049,825,290
Exelon Generation Co L L C [Member]
Entity Registrant Name	EXELON GENERATION CO LLC
Entity Central Index Key	1,168,165
Entity Filer Category	Non-accelerated Filer
Commonwealth Edison Co [Member]
Entity Registrant Name	COMMONWEALTH EDISON CO
Entity Central Index Key	22,606
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding		127,016,973
PECO Energy Co [Member]
Entity Registrant Name	PECO ENERGY CO
Entity Central Index Key	78,100
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding		170,478,507
Baltimore Gas and Electric Company [Member]
Entity Registrant Name	BALTIMORE GAS AND ELECTRIC
Entity Central Index Key	9,466
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding		1,000

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income (Unaudited) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Operating revenues [Abstract]
Revenues	$ 29,447	$ 27,429		$ 24,888
Operating revenues	18,395	16,637		14,277
Electric Revenue	9,876	9,467		9,365
Gas Domestic Regulated Revenue	1,176	1,325		1,246
Operating revenues from affiliates	9	23		70
Regulated Operating Revenue	11,052	10,792		10,611
Reclassifications from accumulated OCI to net income	18,395	16,637		14,277
Operating expenses
Rate-regulated utility purchased power and fuel	3,077	3,103		2,540
Purchased power	10,007	9,369		6,928
Purchased power and fuel from affiliates	0	531		1,256
Operating and maintenance	8,322	8,568		7,270
Depreciation and amortization	2,450	2,314		2,153
Taxes other than income	1,200	1,154		1,095
Total operating expenses	25,056	25,039		21,242
Equity in (losses) earnings of unconsolidated affiliates		(20)		10
Gain on sales of assets	18	437		13
Gain on consolidation and acquisition of businesses	0	289		0
Operating Income (Loss)	4,409	3,096		3,669
Other income and (deductions)
Interest expense, net	(992)	(1,024)		(1,315)
Interest expense to affiliates, net	(41)	(41)		(41)
Other, net	(46)	455		460
Total other income and (deductions)	(1,079)	(610)		(896)
Income before income taxes	3,330	2,486		2,773
Income before income taxes	3,330	2,486		2,773
Income taxes	1,073	666		1,044
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	(7)	(20)		10
Net income	2,250	1,820		1,729
Net income (loss) attributable to noncontrolling interest and preference stock dividends	19	(197)		(10)
Net income attributable to common shareholders	2,269	1,623		1,719
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost, net of tax	(46)	(30)		0
Actuarial loss reclassified to periodic cost, net of tax	220	147		208
Pension and non-pension postretirement benefit plans valuation adjustment, net of tax	(99)	(497)		669
Unrealized gain (loss) on cash flow hedges, net of taxes	9	(148)		(248)
Unrealized gain (loss) on marketable securities, net of taxes	0	1		2
Unrealized gain (loss) on equity investments, net of taxes	(3)	8		106
Unrealized gain (loss) on foreign currency translation, net of taxes	(21)	(9)		(10)
Reversal of CENG equity method AOCI, net of taxes	0	(116)		0
Other comprehensive income (loss)	60	(644)	[1]	727
Comprehensive income	$ 2,310	$ 1,176		$ 2,456
Average shares of common stock outstanding:
Basic	890	860		856
Diluted	893	864		860
Earnings per average common share:
Basic (in usd per share)	$ 2.55	$ 1.89		$ 2.01
Diluted (in usd per share)	2.54	1.88		2
Dividends per common share (in usd per share)	$ 1.24	$ 1.24		$ 1.46
Exelon Generation Co L L C [Member]
Operating revenues [Abstract]
Revenues	$ 19,135	$ 17,393		$ 15,630
Operating revenues	18,386	16,614		14,207
Operating revenues from affiliates	749	779		1,423
Reclassifications from accumulated OCI to net income	18,386	16,614		14,207
Operating expenses
Rate-regulated utility purchased power and fuel	10,007	9,368		6,927
Purchased power and fuel from affiliates	14	557		1,270
Operating and maintenance	4,688	4,943		3,960
Operating and maintenance from affiliates	620	623		574
Depreciation and amortization	1,054	967		856
Taxes other than income	489	465		389
Total operating expenses	16,872	16,923		13,976
Equity in (losses) earnings of unconsolidated affiliates	8	(20)		10
Gain on sales of assets	12	437		13
Gain on consolidation and acquisition of businesses	0	289		0
Operating Income (Loss)	2,275	1,176		1,677
Other income and (deductions)
Interest expense, net	(322)	(303)		(298)
Interest expense to affiliates, net	(43)	(53)		(59)
Other, net	(60)	406		355
Total other income and (deductions)	(425)	50		(2)
Income before income taxes	1,850	1,226		1,675
Income taxes	502	207		615
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	(8)
Net income	1,340	1,019		1,060
Net income (loss) attributable to noncontrolling interests	(32)	184		(10)
Net income attributable to membership interest	1,372	835		1,070
Pension and non-pension postretirement benefit plans:
Unrealized gain (loss) on cash flow hedges, net of taxes	(3)	(132)		(398)
Unrealized gain (loss) on marketable securities, net of taxes	0	(1)		2
Unrealized gain (loss) on equity investments, net of taxes	(3)	8		107
Unrealized gain (loss) on foreign currency translation, net of taxes	(21)	(9)		(10)
Reversal of CENG equity method AOCI, net of taxes	0	(116)		0
Other comprehensive income (loss)	(27)	(250)	[1]	(299)
Comprehensive income	1,313	769		761
Commonwealth Edison Co [Member]
Operating revenues [Abstract]
Revenues	4,905	4,564		4,464
Electric operating revenues	4,901	4,560		4,461
Operating revenues from affiliates	4	4		3
Operating expenses
Rate-regulated utility purchased power and fuel	1,301	1,001		662
Purchased power from affiliate	18	176		512
Operating and maintenance	1,372	1,263		1,211
Operating and maintenance from affiliates	195	166		157
Depreciation and amortization	707	687		669
Taxes other than income	296	293		299
Total operating expenses	3,889	3,586		3,510
Equity in (losses) earnings of unconsolidated affiliates	0	0		0
Gain on sales of assets	1	2		0
Operating Income (Loss)	1,017	980		954
Other income and (deductions)
Interest expense, net	(319)	(308)		(566)
Interest expense to affiliates, net	(13)	(13)		(13)
Other, net	21	17		26
Total other income and (deductions)	(311)	(304)		(553)
Income before income taxes	706	676		401
Income taxes	280	268		152
Net income	426	408		249
Pension and non-pension postretirement benefit plans:
Other comprehensive income (loss)				7,528
Comprehensive income	426	408		249
PECO Energy Co [Member]
Operating revenues [Abstract]
Revenues	3,032	3,094		3,100
Electric Revenue	2,485	2,446		2,499
Gas Domestic Regulated Revenue	545	646		600
Operating revenues from affiliates	2	2		1
Operating expenses
Rate-regulated utility purchased power and fuel	235	327		296
Purchased power	735	740		612
Purchased power from affiliate	220	194		392
Operating and maintenance	684	767		647
Operating and maintenance from affiliates	110	99		101
Depreciation and amortization	260	236		228
Taxes other than income	160	159		158
Total operating expenses	2,404	2,522		2,434
Gain (Loss) on Disposition of Other Assets	2	0		0
Equity in (losses) earnings of unconsolidated affiliates	0	0		0
Operating Income (Loss)	630	572		666
Other income and (deductions)
Interest expense, net	(102)	(101)		(103)
Interest expense to affiliates, net	(12)	(12)		(12)
Other, net	5	7		6
Total other income and (deductions)	(109)	(106)		(109)
Income before income taxes	521	466		557
Income taxes	143	114		162
Net income	378	352		395
Preferred security dividends and redemption	0	0		(7)
Net income attributable to common shareholders	378	352		388
Pension and non-pension postretirement benefit plans:
Comprehensive income	378	352		395
Baltimore Gas and Electric Company [Member]
Operating revenues [Abstract]
Revenues	3,135	3,165		3,065
Electric Revenue	2,490	2,460		2,405
Gas Domestic Regulated Revenue	631	680		647
Operating revenues from affiliates	14	25		13
Operating expenses
Purchased power from affiliate	498	382		452
Utilities Operating Expense, Purchased Power	602	733		676
Utilities Operating Expense, Fuel Used	205	302		293
Operating and maintenance	565	614		551
Operating and maintenance from affiliates	118	103		83
Depreciation and amortization	366	371		348
Taxes other than income	224	221		213
Total operating expenses	2,578	2,726		2,616
Gain (Loss) on Disposition of Other Assets	1	0		0
Equity in (losses) earnings of unconsolidated affiliates	0	0		0
Operating Income (Loss)	558	439		449
Other income and (deductions)
Interest expense, net	(83)	(90)		(106)
Interest expense to affiliates, net	(16)	(16)		(16)
Other, net	18	18		17
Total other income and (deductions)	(81)	(88)		(105)
Income before income taxes	477	351		344
Income taxes	189	140		134
Net income	288	211		210
Preferred security dividends and redemption	(13)	(13)		(13)
Net income attributable to common shareholders	275	198		197
Pension and non-pension postretirement benefit plans:
Comprehensive income	$ 288	$ 211		$ 210
[1]	All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.

Consolidated Statements of Ope3

Consolidated Statements of Operations and Comprehensive Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commonwealth Edison Co [Member]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$ 0	$ 0	$ 0
PECO Energy Co [Member]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$ 0	$ 0	$ 0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities
Net income	$ 2,250	$ 1,820	$ 1,729
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization, depletion and accretion, including nuclear fuel and energy contract amortization	3,987	3,868	3,779
Impairment of long-lived assets	36	687	171
Gain on consolidation and acquisition of businesses	0	(296)	0
Gain on sales of assets	(18)	(437)	(13)
Gain on sales of assets	(18)	(437)	(13)
Deferred income taxes and amortization of investment tax credits	752	502	119
Net fair value changes related to derivatives	(367)	716	(445)
Net realized and unrealized losses (gains) on nuclear decommissioning trust fund investments	131	(210)	(170)
Other non-cash operating activities	1,109	1,054	718
Changes in assets and liabilities:
Accounts receivable	240	(318)	(97)
Inventories	4	(380)	(100)
Accounts payable and accrued expenses	(121)	49	(116)
Option premiums received (paid), net	58	38	(36)
Collateral received (posted), net	347	(1,719)	215
Income taxes	97	(143)	883
Pension and non-pension postretirement benefit contributions	(502)	(617)	(422)
Other assets and liabilities	(387)	(157)	128
Net cash flows provided by operating activities	7,616	4,457	6,343
Cash flows from investing activities
Capital expenditures	(7,624)	(6,077)	(5,395)
Proceeds from termination of direct financing lease investment	0	335	0
Proceeds from nuclear decommissioning trust fund sales	6,895	7,396	4,217
Investment in nuclear decommissioning trust funds	(7,147)	(7,551)	(4,450)
Acquisitions of businesses	(40)	(386)	0
Proceeds from sales of long-lived assets	147	1,719	32
Proceeds from sales of investments	0	7	22
Cash and restricted cash acquired from consolidations and acquisitions	0	140	0
Purchases of investments	0	(3)	(4)
Change in restricted cash	66	(104)	(43)
Distribution from CENG	0	13	115
Other investing activities	(119)	(88)	112
Net cash flows used in investing activities	(7,822)	(4,599)	(5,394)
Cash flows from financing activities
Payment of accounts receivable agreement	0	0	(210)
Issuance of long-term debt	6,709	3,463	2,055
Retirement of long-term debt	(2,687)	(1,545)	(1,589)
Redemption of preferred securities	0	0	(93)
Distribution to noncontrolling interest of consolidated VIE	0	(421)	0
Dividends paid on common stock	(1,105)	(1,065)	(1,249)
Proceeds from employee stock plans	32	35	47
Other financing activities	67	178	119
Contributions from parent			0
Net cash flows provided by (used in) financing activities	4,830	411	(826)
Proceeds from Issuance of Common Stock	1,868	0	0
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	80	122	332
Increase in cash and cash equivalents	4,624	269	123
Cash and cash equivalents at beginning of period	1,878	1,609	1,486
Cash and cash equivalents at end of period	6,502	1,878	1,609
Parent Company [Member]
Cash flows from operating activities
Net income	2,269	1,623	1,719
Changes in assets and liabilities:
Net cash flows provided by operating activities	3,071	806	1,053
Cash flows from investing activities
Capital expenditures	0	1	0
Proceeds from termination of direct financing lease investment	0	335	0
Change in restricted cash	0	0	38
Other investing activities	(55)	(126)	15
Changes in Exelon intercompany money pool	(1,217)	(83)	(60)
Net cash flows used in investing activities	(934)	57	439
Cash flows from financing activities
Issuance of long-term debt	4,200	1,150	0
Retirement of long-term debt	(2,263)	(23)	(450)
Dividends paid on common stock	(1,105)	(1,065)	(1,249)
Proceeds from employee stock plans	32	35	47
Other financing activities	58	84	6
Contribution from member	3,209	1,370	1,175
Net cash flows provided by (used in) financing activities	2,674	13	(1,648)
Proceeds from Issuance of Common Stock	1,868	0	0
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	0	0	10
Increase in cash and cash equivalents	4,811	876	(156)
Cash and cash equivalents at beginning of period	879	3	159
Cash and cash equivalents at end of period	5,690	879	3
Exelon Generation Co L L C [Member]
Cash flows from operating activities
Net income	1,340	1,019	1,060
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization, depletion and accretion, including nuclear fuel and energy contract amortization	2,589	2,519	2,559
Impairment of long-lived assets	12	663	157
Gain on consolidation and acquisition of businesses	0	(296)	0
Gain on sales of assets	(12)	(437)	(13)
Gain on sales of assets	(12)	(437)	(13)
Deferred income taxes and amortization of investment tax credits	49	(198)	315
Net fair value changes related to derivatives	(249)	635	(448)
Net realized and unrealized losses (gains) on nuclear decommissioning trust fund investments	131	(210)	(170)
Other non-cash operating activities	268	346	270
Changes in assets and liabilities:
Accounts receivable	194	(215)	109
Receivables from and payables to affiliates, net	15	15	2
Inventories	16	(359)	(88)
Accounts payable and accrued expenses	(149)	29	(160)
Option premiums received (paid), net	58	38	(36)
Collateral received (posted), net	407	(1,748)	162
Income taxes	(18)	265	402
Pension and non-pension postretirement benefit contributions	(245)	(297)	(149)
Other assets and liabilities	(207)	57	(85)
Net cash flows provided by operating activities	4,199	1,826	3,887
Cash flows from investing activities
Capital expenditures	(3,841)	(3,012)	(2,752)
Proceeds from nuclear decommissioning trust fund sales	6,895	7,396	4,217
Investment in nuclear decommissioning trust funds	(7,147)	(7,551)	(4,450)
Acquisitions of businesses	(40)	(386)	0
Proceeds from sales of long-lived assets	147	1,719	32
Cash and restricted cash acquired from consolidations and acquisitions	0	140	0
Change in restricted cash	35	(87)	(64)
Distribution from CENG	0	13	115
Other investing activities	(118)	(43)	30
Changes in Exelon intercompany money pool	0	44	(44)
Net cash flows used in investing activities	(4,069)	(1,767)	(2,916)
Cash flows from financing activities
Issuance of long-term debt	1,309	1,112	854
Retirement of long-term debt	(89)	(586)	(570)
Repayments of Related Party Debt	(550)
Changes in Exelon intercompany money pool	1,252	0	0
Distribution to noncontrolling interest of consolidated VIE	0	(421)	0
Other financing activities	(26)	67	82
Distribution to member	(2,474)	(645)	(625)
Contribution from member	47	53	26
Contributions from parent			0
Net cash flows provided by (used in) financing activities	(479)	(537)	(384)
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	0	17	13
Increase in cash and cash equivalents	(349)	(478)	587
Cash and cash equivalents at beginning of period	780	1,258	671
Cash and cash equivalents at end of period	431	780	1,258
Commonwealth Edison Co [Member]
Cash flows from operating activities
Net income	426	408	249
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization, depletion and accretion, including nuclear fuel and energy contract amortization	707	687	669
Gain on sales of assets	(1)	(2)	0
Deferred income taxes and amortization of investment tax credits	353	433	(57)
Other non-cash operating activities	416	255	28
Changes in assets and liabilities:
Accounts receivable	(93)	(121)	(12)
Receivables from and payables to affiliates, net	(19)	(11)	(12)
Inventories	(40)	(16)	(18)
Accounts payable and accrued expenses	68	95	91
Collateral received (posted), net	(33)	2	53
Income taxes	192	(159)	178
Pension and non-pension postretirement benefit contributions	(150)	(248)	(122)
Other assets and liabilities	69	1	171
Net cash flows provided by operating activities	1,896	1,326	1,218
Cash flows from investing activities
Capital expenditures	(2,398)	(1,689)	(1,433)
Proceeds from sales of investments	0	7	7
Purchases of investments	0	(3)	(4)
Change in restricted cash	2	(2)	(2)
Other investing activities	34	32	45
Net cash flows used in investing activities	(2,362)	(1,655)	(1,387)
Cash flows from financing activities
Issuance of long-term debt	850	900	350
Retirement of long-term debt	(260)	(617)	(252)
Dividends paid on common stock	(299)	(307)	(220)
Other financing activities	16	10	1
Contributions from parent	202	273	176
Net cash flows provided by (used in) financing activities	467	359	61
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	(10)	120	184
Increase in cash and cash equivalents	1	30	(108)
Cash and cash equivalents at beginning of period	66	36	144
Cash and cash equivalents at end of period	67	66	36
PECO Energy Co [Member]
Cash flows from operating activities
Net income	378	352	395
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization, depletion and accretion, including nuclear fuel and energy contract amortization	260	236	228
Deferred income taxes and amortization of investment tax credits	90	88	20
Net realized and unrealized losses (gains) on nuclear decommissioning trust fund investments	2
Other non-cash operating activities	70	92	108
Changes in assets and liabilities:
Accounts receivable	37	(16)	(79)
Receivables from and payables to affiliates, net	3	(6)	(18)
Inventories	10	2	2
Accounts payable and accrued expenses	(25)	58	31
Income taxes	(9)	(57)	87
Pension and non-pension postretirement benefit contributions	(40)	(16)	(31)
Other assets and liabilities	(4)	(21)	4
Net cash flows provided by operating activities	770	712	747
Cash flows from investing activities
Capital expenditures	(601)	(661)	(537)
Change in restricted cash	(1)	0	(2)
Other investing activities	14	12	8
Net cash flows used in investing activities	(588)	(649)	(531)
Cash flows from financing activities
Payment of accounts receivable agreement	0	0	(210)
Issuance of long-term debt	350	300	550
Retirement of long-term debt	0	(250)	(300)
Redemption of preferred securities	0	0	(93)
Dividends paid on common stock	(279)	(320)	(332)
Other financing activities	4	4	2
Contributions from parent	16	24	27
Dividends paid on preferred securities	0	0	(1)
Net cash flows provided by (used in) financing activities	83	(250)	(361)
Increase in cash and cash equivalents	265	(187)	(145)
Cash and cash equivalents at beginning of period	30	217	362
Cash and cash equivalents at end of period	295	30	217
Baltimore Gas and Electric Company [Member]
Cash flows from operating activities
Net income	288	211	210
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization, depletion and accretion, including nuclear fuel and energy contract amortization	366	371	348
Deferred income taxes and amortization of investment tax credits	165	116	125
Other non-cash operating activities	137	180	153
Changes in assets and liabilities:
Accounts receivable	84	46	(127)
Receivables from and payables to affiliates, net	(2)	(1)	(14)
Inventories	18	(6)	1
Accounts payable and accrued expenses	(3)	(75)	(6)
Collateral received (posted), net	(27)	27	0
Income taxes	(54)	45	(33)
Pension and non-pension postretirement benefit contributions	(17)	(16)	(24)
Other assets and liabilities	(173)	(158)	(72)
Net cash flows provided by operating activities	782	740	561
Cash flows from investing activities
Capital expenditures	(719)	(620)	(587)
Change in restricted cash	26	(22)	2
Other investing activities	18	20	14
Net cash flows used in investing activities	(675)	(622)	(571)
Cash flows from financing activities
Issuance of long-term debt	0	0	300
Retirement of long-term debt	(75)	(70)	(467)
Dividends paid on common stock	(158)	0	0
Other financing activities	13	(13)	3
Contributions from parent	7	0	0
Dividends paid on preferred securities	(13)	(13)	(13)
Net cash flows provided by (used in) financing activities	(162)	(85)	(48)
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	90	(15)	135
Increase in cash and cash equivalents	(55)	33	(58)
Cash and cash equivalents at beginning of period	64	31	89
Cash and cash equivalents at end of period	$ 9	$ 64	$ 31

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Current assets
Cash and cash equivalents		$ 6,502	$ 1,878
Cash and cash equivalents		6,502	1,878
Restricted cash and cash equivalents		205	271
Accounts receivable, net
Customer		3,187	3,482
Other		912	1,227
Mark-to-market derivative assets		1,365	1,279
Unamortized energy contract assets		86	254
Inventories, net
Fossil fuel		462	579
Materials and supplies		1,104	1,024
Regulatory assets		759	847
Assets held for sale		4	147
Other		748	865
Total current assets		15,334	11,853
Property, plant and equipment, net		57,439	52,170
Deferred debits and other assets
Regulatory assets		6,065	6,076
Nuclear decommissioning trust funds		10,342	10,537
Investments		639	544
Goodwill		2,672	2,672
Mark-to-market derivative assets		758	773
Unamortized energy contract assets		484	549
Pledged assets for Zion Station decommissioning		206	319
Other		1,445	923
Total deferred debits and other assets		22,611	22,393
Total assets	[1]	95,384	86,416
Current liabilities
Short-term borrowings		533	460
Long-term debt due within one year		1,500	1,802
Accounts payable		2,883	3,048
Accrued expenses		2,376	1,539
Payables to affiliates		8	8
Accounts Payable, Related Parties, Current		8	8
Mark-to-market derivative liabilities		205	234
Unamortized energy contract liabilities		100	238
Energy Marketing Accounts Payable		302	192
Regulatory liabilities		369	310
Other		842	931
Total current liabilities		9,118	8,762
Long-term debt		23,645	19,212
Long-term debt to financing trusts	[2]	641	641
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		13,776	12,778
Asset retirement obligations		8,585	7,295
Pension obligations		3,385	3,366
Non-pension postretirement benefit obligations		1,618	1,742
Spent nuclear fuel obligation		1,021	1,021
Regulatory liabilities		4,201	4,550
Mark-to-market derivative liabilities		374	403
Unamortized energy contract liabilities		117	211
Payable for Zion Station decommissioning		90	155
Other		1,491	2,147
Total deferred credits and other liabilities		34,658	33,668
Total liabilities	[1]	68,062	62,283
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount		28	0
Shareholders’ equity
Common stock		18,676	16,709
Treasury stock, at cost (35 shares at December 31, 2015 and 2014, respectively)		(2,327)	(2,327)
Retained earnings		12,068	10,910
Accumulated other comprehensive loss, net		(2,624)	(2,684)	[3]
Total shareholders’ equity		25,793	22,608
BGE preference stock not subject to mandatory redemption		193	193
Noncontrolling interest		1,308	1,332
Total equity		27,294	24,133
Total liabilities and shareholders’ equity		95,384	86,416
Member’s equity
Accumulated other comprehensive loss, net		(2,624)	(2,684)	[3]
Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure [Member]
Deferred debits and other assets
Total assets		8,268	8,159
Deferred credits and other liabilities
Total liabilities		3,264	2,728
Commonwealth Edison Co [Member]
Current assets
Cash and cash equivalents		67	66
Restricted cash and cash equivalents		2	4
Accounts receivable, net
Customer		533	477
Other		272	648
Receivables from affiliates		199	14
Inventories, net
Inventories, net		164	125
Regulatory assets		218	349
Other		63	40
Total current assets		1,518	1,723
Property, plant and equipment, net		17,502	15,793
Deferred debits and other assets
Regulatory assets		895	852
Investments		6	6
Goodwill		2,625	2,625
Receivable from affiliates		2,172	2,571
Prepaid pension asset		1,490	1,551
Other		324	237
Total deferred debits and other assets		7,512	7,842
Total assets		26,532	25,358
Current liabilities
Short-term borrowings		294	304
Long-term debt due within one year		665	260
Accounts payable		660	598
Accrued expenses		706	331
Accounts Payable, Related Parties, Current		62	84
Mark-to-market derivative liabilities		23	20
Customer deposits		131	128
Regulatory liabilities		155	125
Other		70	73
Total current liabilities		2,766	1,923
Long-term debt		5,844	5,665
Long-term debt to financing trusts		205	205
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		4,914	4,561
Asset retirement obligations		111	103
Non-pension postretirement benefit obligations		259	263
Regulatory liabilities		3,459	3,655
Mark-to-market derivative liabilities		224	187
Other		507	889
Total deferred credits and other liabilities		9,474	9,658
Total liabilities		18,289	17,451
Shareholders’ equity
Common stock		1,588	1,588
Other paid-in capital		5,677	5,468
Retained earnings		978	851
Total shareholders’ equity		8,243	7,907
Total liabilities and shareholders’ equity		26,532	25,358
Exelon Generation Co L L C [Member]
Current assets
Cash and cash equivalents		431	780
Cash and cash equivalents		431	780
Restricted cash and cash equivalents		123	158
Accounts receivable, net
Customer		2,095	2,295
Other		360	318
Mark-to-market derivative assets		1,365	1,276
Receivables from affiliates		83	113
Unamortized energy contract assets		86	254
Inventories, net
Fossil fuel		384	465
Materials and supplies		880	847
Assets held for sale		4	147
Other		531	658
Total current assets		6,342	7,311
Property, plant and equipment, net		25,843	23,028
Deferred debits and other assets
Nuclear decommissioning trust funds		10,342	10,537
Investments		210	104
Goodwill		47	47
Mark-to-market derivative assets		733	771
Prepaid pension asset		1,689	1,704
Unamortized energy contract assets		484	549
Deferred income taxes		6	3
Pledged assets for Zion Station decommissioning		206	319
Other		627	578
Total deferred debits and other assets		14,344	14,612
Total assets	[4]	46,529	44,951
Current liabilities
Short-term borrowings		29	36
Long-term debt due within one year		90	58
Accounts payable		1,583	1,759
Accrued expenses		935	886
Payables to affiliates		0	556
Accounts Payable, Related Parties, Current		104	107
Mark-to-market derivative liabilities		182	214
Unamortized energy contract liabilities		100	238
Energy Marketing Accounts Payable		302	192
Other		356	413
Exelon Money Pool Borrowing Current		1,252	0
Total current liabilities		4,933	4,459
Long-term debt		7,936	6,639
Long-term debt to financing trusts		933	943
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		5,845	5,707
Asset retirement obligations		8,431	7,146
Non-pension postretirement benefit obligations		924	915
Spent nuclear fuel obligation		1,021	1,021
Mark-to-market derivative liabilities		150	105
Unamortized energy contract liabilities		117	211
Payable for Zion Station decommissioning		90	155
Other		602	719
Due to Affiliate, Noncurrent		2,577	2,880
Total deferred credits and other liabilities		19,757	18,859
Total liabilities	[4]	33,559	30,900
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount		28
Shareholders’ equity
Accumulated other comprehensive loss, net		(63)	(36)	[3]
Noncontrolling interest		1,307	1,333
Member’s equity
Membership interest		8,997	8,951
Undistributed earnings		2,701	3,803
Accumulated other comprehensive loss, net		(63)	(36)	[3]
Total member’s equity		11,635	12,718
Total equity		12,942	14,051
Total liabilities and equity		46,529	44,951
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure [Member]
Deferred debits and other assets
Total assets		8,235	8,118
Deferred credits and other liabilities
Total liabilities		3,135	2,512
PECO Energy Co [Member]
Current assets
Cash and cash equivalents		295	30
Restricted cash and cash equivalents		3	2
Accounts receivable, net
Customer		258	320
Other		146	141
Receivables from affiliates		2	3
Inventories, net
Fossil fuel		43	57
Materials and supplies		26	22
Prepaid utility taxes		11	10
Regulatory assets		34	29
Other		24	31
Total current assets		842	645
Property, plant and equipment, net		7,141	6,801
Deferred debits and other assets
Regulatory assets		1,583	1,529
Investments		28	31
Receivable from affiliates		405	490
Prepaid pension asset		347	344
Other		21	20
Total deferred debits and other assets		2,384	2,414
Total assets		10,367	9,860
Current liabilities
Long-term debt due within one year		300	0
Accounts payable		281	337
Accrued expenses		109	91
Accounts Payable, Related Parties, Current		55	52
Customer deposits		58	52
Regulatory liabilities		112	90
Other		29	31
Total current liabilities		944	653
Long-term debt		2,280	2,232
Long-term debt to financing trusts		184	184
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		2,792	2,602
Asset retirement obligations		27	29
Non-pension postretirement benefit obligations		287	287
Regulatory liabilities		527	657
Mark-to-market derivative liabilities		12
Other		90	95
Total deferred credits and other liabilities		3,723	3,670
Total liabilities		7,131	6,739
Shareholders’ equity
Common stock		2,455	2,439
Retained earnings		780	681
Accumulated other comprehensive loss, net		1	1	[3]
Total shareholders’ equity		3,236	3,121
Total liabilities and shareholders’ equity		10,367	9,860
Member’s equity
Accumulated other comprehensive loss, net		1	1	[3]
Baltimore Gas and Electric Company [Member]
Current assets
Cash and cash equivalents		9	64
Restricted cash and cash equivalents		24	50
Accounts receivable, net
Customer		300	390
Other		112	82
Inventories, net
Fossil fuel		36	57
Materials and supplies		33	30
Prepaid utility taxes		61	59
Regulatory assets		267	214
Other		3	5
Total current assets		845	951
Property, plant and equipment, net		6,597	6,204
Deferred debits and other assets
Regulatory assets		514	510
Investments		12	12
Prepaid pension asset		319	370
Other		8	9
Total deferred debits and other assets		853	901
Total assets	[5]	8,295	8,056
Current liabilities
Short-term borrowings		210	120
Long-term debt due within one year		378	75
Accounts payable		209	215
Accrued expenses		110	131
Accounts Payable, Related Parties, Current		52	66
Customer deposits		102	92
Regulatory liabilities		38	44
Other		35	51
Total current liabilities		1,134	794
Long-term debt		1,480	1,857
Long-term debt to financing trusts		252	252
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		2,081	1,911
Asset retirement obligations		17	17
Non-pension postretirement benefit obligations		209	212
Regulatory liabilities		184	200
Other		61	60
Total deferred credits and other liabilities		2,552	2,400
Total liabilities	[5]	5,418	5,303
Shareholders’ equity
Common stock		1,367	1,360
Retained earnings		1,320	1,203
Total shareholders’ equity		2,687	2,563
BGE preference stock not subject to mandatory redemption		190	190
Total equity		2,877	2,753
Total liabilities and shareholders’ equity		8,295	8,056
Baltimore Gas and Electric Company [Member] | Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure [Member]
Deferred debits and other assets
Total assets		26	24
Deferred credits and other liabilities
Total liabilities		122	$ 197
Constellation Energy Group LLC [Member]
Deferred debits and other assets
Total assets		$ 187
[1]	Exelon’s consolidated assets include $8,268 million and $8,159 million at December 31, 2015 and December 31, 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,264 million and $2,728 million at December 31, 2015 and December 31, 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.
[2]	Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets.
[3]	All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.
[4]	Generation’s consolidated assets include $8,235 million and $8,118 million at December 31, 2015 and 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,135 million and $2,512 million at December 31, 2015 and 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities.
[5]	BGE’s consolidated assets include $26 million and $24 million at December 31, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE that can only be used to settle the liabilities of the VIE. BGE’s consolidated liabilities include $122 million and $197 million at December 31, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. See Note 2 - Variable Interest Entities.

Consolidated Balance Sheets (U6

Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Common stock, par value	$ 0	$ 0
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common Stock, Shares, Outstanding	919,924,742	859,833,343
Treasury Stock, Shares held	35,000,000	35,000,000
Commonwealth Edison Co [Member]
Common stock, shares authorized	250,000,000
Common Stock, Shares, Outstanding	127,016,973	127,016,947
PECO Energy Co [Member]
Common stock, shares authorized	500,000,000
Common Stock, Shares, Outstanding	170,478,507	170,478,507
Baltimore Gas and Electric Company [Member]
Common stock, shares authorized	175,000,000
Common Stock, Shares, Outstanding	1,000	1,000

Consolidated Statement of Chang

Consolidated Statement of Changes in Shareholders Equity (Unaudited) - USD ($) shares in Thousands, $ in Millions		Total	Common Stock [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interest [Member]	Preference Stock Not Subject To Mandatory Redemption [Member]	PECO Energy Co [Member]	PECO Energy Co [Member]Common Stock [Member]	PECO Energy Co [Member]Retained Earnings [Member]	PECO Energy Co [Member]Accumulated Other Comprehensive Income (Loss) [Member]	Exelon Generation Co L L C [Member]	Exelon Generation Co L L C [Member]Accumulated Other Comprehensive Income (Loss) [Member]	Exelon Generation Co L L C [Member]Noncontrolling Interest [Member]	Exelon Generation Co L L C [Member]Membership Interest [Member]	Exelon Generation Co L L C [Member]Undistributed Earnings [Member]	Commonwealth Edison Co [Member]	Commonwealth Edison Co [Member]Common Stock [Member]	Commonwealth Edison Co [Member]Other Paid-In Capital [Member]	Commonwealth Edison Co [Member]Retained Deficit Unappropriated [Member]	Commonwealth Edison Co [Member]Retained Earnings Appropriated [Member]	Baltimore Gas and Electric Company [Member]	Baltimore Gas and Electric Company [Member]Common Stock [Member]	Baltimore Gas and Electric Company [Member]Retained Earnings [Member]	Baltimore Gas and Electric Company [Member]Membership Interest [Member]	Baltimore Gas and Electric Company [Member]Preference Stock Not Subject To Mandatory Redemption [Member]
Beginning Balance at Dec. 31, 2012		$ 21,730	$ 16,632	$ (2,327)	$ 9,893	$ (2,767)	$ 106	$ 193															$ 2,358	$ 1,360	$ 808	$ 2,168	$ 190
Beginning Balance (in shares) at Dec. 31, 2012		889,525
Beginning Balance at Dec. 31, 2012									$ 2,982	$ 2,388	$ 593	$ 1						$ 7,323	$ 1,588	$ 5,014	$ (1,639)	$ 2,360
Beginning Balance at Dec. 31, 2012													$ 12,665	$ 513	$ 108	$ 8,876	$ 3,168
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		$ 1,729			1,719		(10)	20	395		395		1,060		(10)		1,070	249			249		210		210	210
Long-term incentive plan activity, shares		1,445
Long-term incentive plan activity		$ 81	81
Employee stock purchase plan issuances		$ 28	28
Employee stock purchase plan issuances, shares		1,064
Common stock dividends		$ (1,254)			(1,254)			(6)	(332)		(332)							(220)				(220)
Common stock issuance Constellation merger, shares		0
Consolidated VIE dividend to noncontrolling interest		$ (63)	0				(63)
Deconsolidation of VIE		(18)	0				(18)						(19)		(18)	(1)
Redemption of preferred securities		(6)						0	(6)		(6)
Preferred and preference stock dividends		(14)						(14)	(1)		(1)												(13)		(13)	(13)
Other comprehensive income, net of income taxes		727											(299)	(299)				7,528
Acquisition of noncontrolling interest													(63)		(63)
Tax benefit on stock compensation		44
Acquisition of noncontrolling interest													3			3
Other comprehensive loss, net of income taxes		727				727
Distribution to member													(625)				(625)
Allocation of tax benefit from member													26			26
Parent tax matter indemnification									27	27								176		176
Appropriation of retained earnings for future dividends																					(249)	249
Ending Balance at Dec. 31, 2013		$ 22,940	16,741	(2,327)	10,358	(2,040)	15	193															2,555	1,360	1,005	2,365	190
Ending Balance (in shares) at Dec. 31, 2013		892,034
Ending Balance at Dec. 31, 2013									3,065	2,415	649	1							1,588	5,190	(1,639)	2,389
Ending Balance at Dec. 31, 2013													12,742	214	17	8,898	3,613
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Allocated Share-based Compensation Expense, Net of Tax		$ 74
Net income		$ 1,820			1,623		184	13	352		352		1,019		184		835	408			408		211		211	211
Long-term incentive plan activity, shares		1,574
Long-term incentive plan activity		$ 72	72
Employee stock purchase plan issuances		$ 35	35
Employee stock purchase plan issuances, shares		960
Common stock dividends					0				(320)		(320)							(307)				(307)
Consolidated VIE dividend to noncontrolling interest													421		421
Deconsolidation of VIE													(1,548)		(1,548)
Preferred and preference stock dividends		$ (131)						0															(13)		(13)	(13)
Other comprehensive income, net of income taxes	[1]	(644)											(250)
Acquisition of noncontrolling interest		(421)				0	(421)
Common stock dividends		(1,071)			(1,071)		0
Preferred and preference stock dividends		(13)						(13)
Tax benefit on stock compensation		47
Acquisition of noncontrolling interest		4	(2)				6						(5)		(5)
Fair value of financing contract payments			(131)
Transfer of CENG pension and non-pension postretirement benefit obligations		(2)	(2)
Reversal of CENG equity method AOCI, net of income taxes		(116)
Other comprehensive loss, net of income taxes		(528)				(528)							(134)	(134)
Distribution to member													(645)				(645)
Allocation of tax benefit from member													53			53
Noncontrolling interest acquired		(1,548)					(1,548)						(116)	116
Parent tax matter indemnification									24	24								5		5
Appropriation of retained earnings for future dividends																					(408)	408
Contribution from parent		273																		273
Ending Balance at Dec. 31, 2014		$ 24,133	16,709	(2,327)	10,910	(2,684)	1,332	193															2,753	1,360	1,203	2,563	190
Ending Balance (in shares) at Dec. 31, 2014		894,568
Ending Balance at Dec. 31, 2014		$ 22,608							3,121	2,439	681	1						7,907	1,588	5,468	(1,639)	2,490	2,563
Ending Balance at Dec. 31, 2014													14,051	(36)	1,333	8,951	3,803
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options		(8)	8
Allocated Share-based Compensation Expense, Net of Tax		80
Net income		$ 2,250			2,269		(32)	13	378		378		1,340		(32)		1,372	426			426		288		288	288
Long-term incentive plan activity, shares		1,430
Long-term incentive plan activity		$ 70	70
Employee stock purchase plan issuances		$ 32	32
Employee stock purchase plan issuances, shares		1,170
Common stock dividends		$ (1,111)			(1,111)				(279)		(279)							(299)				(299)	(158)		(158)	(158)
Preferred and preference stock dividends		(13)						(13)															(13)		(13)	(13)
Other comprehensive income, net of income taxes		60											(27)
Tax benefit on stock compensation		46
Acquisition of noncontrolling interest		(4)	0				(4)						(1)		(2)	1
Temporary Equity, Other Changes		4					4						4		4
Other comprehensive loss, net of income taxes		60				60							(27)	(27)
Distribution to member													(2,474)				(2,474)
Allocation of tax benefit from member													47			47
Noncontrolling interest acquired													(32)
Parent tax matter indemnification									16	16								7		7			7	7		7
Appropriation of retained earnings for future dividends																					(426)	426
Contribution from parent		202																		202
Ending Balance at Dec. 31, 2015		$ 27,294	18,676	$ (2,327)	$ 12,068	$ (2,624)	$ 1,308	$ 193															2,877	$ 1,367	$ 1,320	$ 2,687	$ 190
Ending Balance (in shares) at Dec. 31, 2015		954,668
Ending Balance at Dec. 31, 2015		$ 25,793							$ 3,236	$ 2,455	$ 780	$ 1						$ 8,243	$ 1,588	$ 5,677	$ (1,639)	$ 2,617	$ 2,687
Ending Balance at Dec. 31, 2015													$ 12,942	$ (63)	$ 1,307	$ 8,997	$ 2,701
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, New Issues		57,500
Stock Issued During Period, Value, New Issues		$ 1,868	$ 1,868
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options		(3)
Allocated Share-based Compensation Expense, Net of Tax		$ 73
[1]	All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.

Consolidated Statement of Chan8

Consolidated Statement of Changes in Shareholders Equity (Unaudited) (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2013USD ($)
Other comprehensive income, income taxes	$ (468)
Exelon Generation Co L L C [Member]
Other comprehensive income, income taxes	190
PECO Energy Co [Member]
Other comprehensive income, income taxes	0
Commonwealth Edison Co [Member]
Other comprehensive income, income taxes	$ 0

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Significant Accounting Policies (Exelon, Generation, ComEd, PECO and BGE)	(Exelon, Generation, ComEd, PECO and BGE) Description of Business (Exelon, Generation, ComEd, PECO and BGE) Exelon is a utility services holding company engaged through its principal subsidiaries in the energy generation and energy delivery businesses. On April 1, 2014, Generation assumed the operating licenses and corresponding operational control of CENG’s nuclear fleet. As a result, Exelon and Generation consolidated CENG’s financial position and results of operations into their businesses. Prior to April 1, 2014, Exelon and Generation accounted for CENG as an equity method investment. Refer to Note 5 — Investment in Constellation Energy Nuclear Group, LLC for further information regarding the integration transaction. The energy generation business includes: • Generation : Physical delivery and marketing of owned and contracted electric generation capacity and provision of renewable and other energy-related products and services, and natural gas exploration and production activities. Generation has six reportable segments consisting of the Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. The energy delivery businesses include: • ComEd : Purchase and regulated retail sale of electricity and the provision of distribution and transmission services in northern Illinois, including the City of Chicago. • PECO : Purchase and regulated retail sale of electricity and the provision of distribution and transmission services in southeastern Pennsylvania, including the City of Philadelphia, and the purchase and regulated retail sale of natural gas and the provision of distribution services in the Pennsylvania counties surrounding the City of Philadelphia. • BGE : Purchase and regulated retail sale of electricity and the provision of distribution and transmission services in central Maryland, including the City of Baltimore, and the purchase and regulated retail sale of natural gas and the provision of distribution services in central Maryland, including the City of Baltimore. Basis of Presentation (Exelon, Generation, ComEd, PECO and BGE) This is a combined annual report of Exelon, Generation, ComEd, PECO and BGE. The Notes to the Consolidated Financial Statements apply to Exelon, Generation, ComEd, PECO and BGE as indicated above in the Index to Combined Notes to Consolidated Financial Statements and parenthetically next to each corresponding disclosure. When appropriate, Exelon, Generation, ComEd, PECO and BGE are named specifically for their related activities and disclosures. Each of the Registrant’s Consolidated Financial Statements includes the accounts of its subsidiaries. All intercompany transactions have been eliminated. As a result of the Registrants' 2014 divestiture of certain unconsolidated affiliates considered integral to their operations and the consolidation of CENG during 2014, all Equity in earnings (losses) from unconsolidated affiliates have been presented below Income taxes in the Registrants' Consolidated Statements of Operations and Comprehensive Income starting in the first quarter of 2015. Through its business services subsidiary, BSC, Exelon provides its subsidiaries with a variety of support services at cost, including legal, human resources, financial, information technology and supply management services. The costs of BSC, including support services, are directly charged or allocated to the applicable subsidiaries using a cost-causative allocation method. Corporate governance-type costs that cannot be directly assigned are allocated based on a Modified Massachusetts Formula, which is a method that utilizes a combination of gross revenues, total assets and direct labor costs for the allocation base. The results of Exelon’s corporate operations are presented as “Other” within the consolidated financial statements and include intercompany eliminations unless otherwise disclosed. Exelon owns 100% of all of its significant consolidated subsidiaries, either directly or indirectly, except for ComEd, of which Exelon owns more than 99% , and BGE, of which Exelon owns 100% of the common stock but none of BGE’s preference stock. Exelon owned none of PECO’s preferred securities, which PECO redeemed in 2013. Exelon has reflected the third-party interests in ComEd, which totaled less than $1 million at December 31, 2015 and December 31, 2014 , as equity, PECO’s preferred securities as preferred securities of subsidiary through their redemption in 2013, and BGE’s preference stock as BGE preference stock not subject to mandatory redemption in its consolidated financial statements. BGE is subject to some ring-fencing measures established by order of the MDPSC. As part of this arrangement, BGE common stock is held directly by RF Holdco LLC, which is an indirect subsidiary of Exelon. GSS Holdings (BGE Utility), an unrelated party, holds a nominal non-economic interest in RF Holdco LLC with limited voting rights on specified matters. Generation owns 100% of all of its significant consolidated subsidiaries, either directly or indirectly, except for certain Exelon Wind projects, of which Generation holds a majority interest of 99% for certain periods of time, and CENG, of which Generation holds a 50.01% interest. The remaining interests are included in noncontrolling interest on Exelon’s and Generation’s Consolidated Balance Sheets. See Note 2 — Variable Interest Entities for further discussion of Exelon’s and Generation’s VIEs and the reversionary interests of the noncontrolling members for these certain subsidiaries. ComEd owns 100% of all of its significant consolidated subsidiaries, either directly or indirectly, except for RITELine Illinois, LLC, of which ComEd owns 75% and an additional 12.5% is indirectly owned by Exelon. Exelon and ComEd have reflected the third-party interests of 12.5% and 25% , respectively, in RITELine Illinois, LLC, which both totaled less than $1 million at December 31, 2015 and December 31, 2014 , as equity. Exelon consolidates the accounts of entities in which Exelon has a controlling financial interest, after the elimination of intercompany transactions. A controlling financial interest is evidenced by either a voting interest greater than 50% in which Exelon can exercise control over the operations and policies of the investee, or the results of a model that identifies Exelon or one of its subsidiaries as the primary beneficiary of a VIE. Where Exelon does not have a controlling financial interest in an entity, it applies proportionate consolidation, equity method accounting or cost method accounting. Exelon applies proportionate consolidation when it has an undivided interest in an asset and is proportionately liable for its share of each liability associated with the asset. Exelon proportionately consolidates its undivided ownership interests in jointly owned electric plants and transmission facilities, as well as its undivided ownership interests in Upstream natural gas exploration and production activities. Under proportionate consolidation, Exelon separately records its proportionate share of the assets, liabilities, revenues and expenses related to the undivided interest in the asset. Exelon applies equity method accounting when it has significant influence over an investee through an ownership in common stock, which generally approximates a 20% to 50% voting interest. Exelon applies equity method accounting to certain investments and joint ventures, including certain financing trusts of ComEd, PECO, and BGE. Under the equity method, Exelon reports its interest in the entity as an investment and Exelon’s percentage share of the earnings from the entity as single line items in its financial statements. Exelon uses the cost method if it holds less than 20% of the common stock of an entity. Under the cost method, Exelon reports its investment at cost and recognizes income only to the extent Exelon receives dividends or distributions. The accompanying consolidated financial statements have been prepared in accordance with GAAP for annual financial statements and in accordance with the instructions to Form 10-K and Regulation S-X promulgated by the SEC. Use of Estimates (Exelon, Generation, ComEd, PECO and BGE) The preparation of financial statements of each of the Registrants in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Areas in which significant estimates have been made include, but are not limited to, the accounting for nuclear decommissioning costs and other AROs, pension and other postretirement benefits, the application of purchase accounting, inventory reserves, allowance for uncollectible accounts, goodwill and asset impairments, derivative instruments, unamortized energy contracts, fixed asset depreciation, environmental costs and other loss contingencies, taxes and unbilled energy revenues. Actual results could differ from those estimates. Reclassifications (Exelon, Generation, ComEd, PECO and BGE) Certain prior year amounts in the registrants' Consolidated Statements of Operations and Comprehensive Income, Consolidated Balance Sheets and Consolidated Statements of Cash Flows have been reclassified between line items for comparative purposes. The reclassifications did not affect any of the Registrants’ net income, financial positions, or cash flows from operating activities. Exelon revised the presentation on the Statements of Operations and Comprehensive Income for PECO and BGE to reflect separately operating revenues from the sale of electricity and operating revenues from the sale of natural gas, as well as, purchased power expense and purchased fuel expense within the operating expenses section of the Statement of Operations and Comprehensive Income. Further, Exelon revised the presentation from total operating revenues to "Rate-regulated utility revenues" and "Competitive businesses revenues" on the face of Exelon’s consolidated Statement of Operations and Comprehensive Income for all periods presented. Similarly, Exelon will separately present rate-regulated purchased power and fuel expense and non-rate regulated purchased power and fuel expense on the face of Exelon’s consolidated Statement of Operations and Comprehensive Income for all periods presented. The reclassifications described herein were made for presentation purposes and did not affect any of the Registrants’ total revenues or net income. Accounting for the Effects of Regulation (Exelon, ComEd, PECO and BGE) Exelon, ComEd, PECO and BGE apply the authoritative guidance for accounting for certain types of regulation, which requires ComEd, PECO and BGE to record in their consolidated financial statements the effects of cost-based rate regulation for entities with regulated operations that meet the following criteria: 1) rates are established or approved by a third-party regulator; (2) rates are designed to recover the entities’ cost of providing services or products; and (3) there is a reasonable expectation that rates are set at levels that will recover the entities’ costs from customers. Exelon, ComEd, PECO and BGE account for their regulated operations in accordance with regulatory and legislative guidance from the regulatory authorities having jurisdiction, principally the ICC, the PAPUC, and the MDPSC, in the cases of ComEd, PECO and BGE, respectively, under state public utility laws and the FERC under various Federal laws. Regulatory assets and liabilities are amortized and the related expense or revenue is recognized in the Consolidated Statements of Operations consistent with the recovery or refund included in customer rates. Exelon believes that it is probable that its currently recorded regulatory assets and liabilities will be recovered and settled, respectively, in future rates. However, Exelon, ComEd, PECO and BGE continue to evaluate their respective abilities to apply the authoritative guidance for accounting for certain types of regulation, including consideration of current events in their respective regulatory and political environments. If a separable portion of ComEd’s, PECO’s or BGE’s business was no longer able to meet the criteria discussed above, the affected entities would be required to eliminate from their consolidated financial statements the effects of regulation for that portion, which could have a material impact on their results of operations and financial positions. See Note 3 — Regulatory Matters for additional information. The Registrants treat the impacts of a final rate order received after the balance sheet date but prior to the issuance of the financial statements as a non-recognized subsequent event, as the receipt of a final rate order is a separate and distinct event that has future impacts on the parties affected by the order. Revenues (Exelon, Generation, ComEd, PECO and BGE) Operating Revenues. Operating revenues are recorded as service is rendered or energy is delivered to customers. At the end of each month, the Registrants accrue an estimate for the unbilled amount of energy delivered or services provided to customers. ComEd records its best estimates of the distribution and transmission revenue impacts resulting from changes in rates that ComEd believes are probable of approval by the ICC and FERC in accordance with its formula rate mechanisms. BGE records its best estimate of the transmission revenue impact resulting from changes in rates that BGE believes are probable of approval by FERC in accordance with its formula rate mechanism. See Note 3 — Regulatory Matters and Note 6 — Accounts Receivable for further information. RTOs and ISOs. In RTO and ISO markets that facilitate the dispatch of energy and energy-related products, the Registrants generally report sales and purchases conducted on a net hourly basis in either revenues or purchased power on their Consolidated Statements of Operations and Comprehensive Income, the classification of which depends on the net hourly activity. In addition, capacity revenue and expense classification is based on the net sale or purchase position of the Company in the different RTOs and ISOs. Option Contracts, Swaps and Commodity Derivatives. Certain option contracts and swap arrangements that meet the definition of derivative instruments are recorded at fair value with subsequent changes in fair value recognized as revenue or expense. The classification of revenue or expense is based on the intent of the transaction. For example, gas transactions may be used to hedge the sale of power. This will result in the change in fair value recorded through revenue. As ComEd receives full cost recovery for energy procurement and related costs from retail customers, ComEd records the fair value of its energy swap contracts with unaffiliated suppliers as well as an offsetting regulatory asset or liability on its Consolidated Balance Sheets. Refer to Note 3 — Regulatory Matters and Note 13 — Derivative Financial Instruments for further information. Proprietary Trading Activities. Exelon and Generation account for Generation’s trading activities under the provisions of the authoritative guidance for accounting for contracts involved in energy trading and risk management activities, which require energy revenues and costs related to energy trading contracts to be presented on a net basis in the income statement. Commodity derivatives used for trading purposes are accounted for using the mark-to-market method with unrealized gains and losses recognized in operating revenues. Refer to Note 13 — Derivative Financial Instruments for further information. Income Taxes (Exelon, Generation, ComEd, PECO and BGE) Deferred Federal and state income taxes are provided on all significant temporary differences between the book basis and the tax basis of assets and liabilities and for tax benefits carried forward. Investment tax credits have been deferred on the Registrants’ Consolidated Balance Sheets and are recognized in book income over the life of the related property. In accordance with applicable authoritative guidance, the Registrants account for uncertain income tax positions using a benefit recognition model with a two-step approach; a more-likely-than-not recognition criterion; and a measurement approach that measures the position as the largest amount of tax benefit that is greater than 50% likely of being realized upon ultimate settlement. If it is not more-likely-than-not that the benefit of the tax position will be sustained on its technical merits, no benefit is recorded. Uncertain tax positions that relate only to timing of when an item is included on a tax return are considered to have met the recognition threshold. The Registrants recognize accrued interest related to unrecognized tax benefits in Interest expense or Other income and deductions (interest income) on their Consolidated Statements of Operations and Comprehensive Income. Pursuant to the IRC and relevant state taxing authorities, Exelon and its subsidiaries file consolidated or combined income tax returns for Federal and certain state jurisdictions where allowed or required. See Note 15 — Income Taxes for further information. Taxes Directly Imposed on Revenue-Producing Transactions (Exelon, Generation, ComEd, PECO and BGE) Exelon, Generation, ComEd, PECO and BGE collect certain taxes from customers such as sales and gross receipts taxes, along with other taxes, surcharges, and fees that are levied by state or local governments on the sale or distribution of gas and electricity. Some of these taxes are imposed on the customer, but paid by the Registrants, while others are imposed on the Registrants. Where these taxes are imposed on the customer, such as sales taxes, they are reported on a net basis with no impact to the Consolidated Statements of Operations and Comprehensive Income. However, where these taxes are imposed on the Registrants, such as gross receipts taxes or other surcharges or fees, they are reported on a gross basis. Accordingly, revenues are recognized for the taxes collected from customers along with an offsetting expense. See Note 24 — Supplemental Financial Information for Generation’s, ComEd’s, PECO’s and BGE’s utility taxes that are presented on a gross basis. Cash and Cash Equivalents (Exelon, Generation, ComEd, PECO and BGE) The Registrants consider investments purchased with an original maturity of three months or less to be cash equivalents. Restricted Cash and Cash Equivalents (Exelon, Generation, ComEd, PECO and BGE) Restricted cash and cash equivalents represent funds that are restricted to satisfy designated current liabilities. As of December 31, 2015 and 2014 , Exelon Corporate’s restricted cash and cash equivalents primarily represented restricted funds for payment of medical, dental, vision and long-term disability benefits. Additionally, as of December 31, 2015 and 2014 , Generation’s restricted cash and cash equivalents primarily included cash at Antelope Valley required for debt service and construction and cash at Continental Wind and ExGen Texas Power, which is required for debt service and financing of operation and maintenance of the underlying entities. As of December 31, 2015 and 2014 , ComEd’s restricted cash primarily represented cash collateral held from suppliers associated with ComEd’s energy and REC procurement contracts. As of December 31, 2015 and 2014 , PECO’s restricted cash primarily represented funds from the sales of assets that were subject to PECO’s mortgage indenture. As of December 31, 2015 and 2014 , BGE’s restricted cash primarily represented funds restricted at its consolidated variable interest entity for repayment of rate stabilization bonds and cash collateral held from suppliers. Restricted cash and cash equivalents not available to satisfy current liabilities are classified as noncurrent assets. As of December 31, 2015 and 2014 , Exelon’s and Generation’s NDT funds, which are designated to satisfy future decommissioning obligations, were classified as noncurrent assets. As of December 31, 2015 , Exelon, Generation, ComEd, PECO and BGE had investments in Rabbi trusts classified as noncurrent assets. Allowance for Uncollectible Accounts (Exelon, Generation, ComEd, PECO and BGE) The allowance for uncollectible accounts reflects the Registrants’ best estimates of losses on the accounts receivable balances. For Generation, the allowance is based on accounts receivable aging, historical experience and other currently available information. ComEd, PECO and BGE estimate the allowance for uncollectible accounts on customer receivables by applying loss rates developed specifically for each company to the outstanding receivable balance by customer risk segment. Risk segments represent a group of customers with similar credit quality indicators that are computed based on various attributes, including delinquency of their balances and payment history. Loss rates applied to the accounts receivable balances are based on historical average charge-offs as a percentage of accounts receivable in each risk segment. ComEd, PECO and BGE customers’ accounts are generally considered delinquent if the amount billed is not received by the time the next bill is issued, which normally occurs on a monthly basis. ComEd, PECO and BGE customer accounts are written off consistent with approved regulatory requirements. ComEd’s, PECO’s and BGE’s provisions for uncollectible accounts will continue to be affected by changes in volume, prices and economic conditions as well as changes in ICC, PAPUC and MDPSC regulations, respectively. See Note 3 — Regulatory Matters for additional information regarding the regulatory recovery of uncollectible accounts receivable at ComEd. Variable Interest Entities (Exelon, Generation, ComEd, PECO and BGE) Exelon accounts for its investments in and arrangements with VIEs based on the authoritative guidance which includes the following specific requirements: • requires an entity to qualitatively assess whether it should consolidate a VIE based on whether the entity (1) has the power to direct matters that most significantly impact the activities of the VIE, and (2) has the obligation to absorb losses or the right to receive benefits of the VIE that could potentially be significant to the VIE, • requires an ongoing reconsideration of this assessment instead of only upon certain triggering events, and • requires the entity that consolidates a VIE (the primary beneficiary) to disclose (1) the assets of the consolidated VIE, if they can be used to only settle specific obligations of the consolidated VIE, and (2) the liabilities of a consolidated VIE for which creditors do not have recourse to the general credit of the primary beneficiary. Based on the above accounting guidance, Exelon has adopted the following policies related to variable interest entities: • Exelon has disclosed, to the extent material, the assets of its consolidated VIEs that can only be used to settle specific obligations of the consolidated VIE, and the liabilities of Exelon’s consolidated VIEs for which creditors do not have recourse to Exelon’s general credit. • Exelon has qualitatively assessed whether the equity holders of the entity have the power to direct matters that most significantly impact the entity. See Note 2 — Variable Interest Entities for additional information. Inventories (Exelon, Generation, ComEd, PECO and BGE) Inventory is recorded at the lower of weighted average cost or market. Provisions are recorded for excess and obsolete inventory. Fossil Fuel. Fossil fuel inventory includes the weighted average costs of stored natural gas, propane and oil. The costs of natural gas, propane and oil are generally included in inventory when purchased and charged to fuel expense when used or sold. Materials and Supplies. Materials and supplies inventory generally includes the weighted average costs of transmission, distribution and generating plant materials. Materials are generally charged to inventory when purchased and expensed or capitalized to property, plant and equipment, as appropriate, when installed or used. Emission Allowances. Emission allowances are included in inventory (for emission allowances exercisable in the current year) and other deferred debits (for emission allowances that are exercisable beyond one year) and are carried at the lower of weighted average cost or market and charged to fuel expense as they are used in operations. Marketable Securities (Exelon, Generation, ComEd, PECO and BGE) All marketable securities are reported at fair value. Marketable securities held in the NDT funds are classified as trading securities and all other securities are classified as available-for-sale securities. Realized and unrealized gains and losses, net of tax, on Generation’s NDT funds associated with the Regulatory Agreement Units are included in regulatory liabilities at Exelon, ComEd and PECO and in noncurrent payables to affiliates at Generation and in noncurrent receivables from affiliates at ComEd and PECO. Realized and unrealized gains and losses, net of tax, on Generation’s NDT funds associated with the Non-Regulatory Agreement Units are included in earnings at Exelon and Generation. Unrealized gains and losses, net of tax, for Exelon's available-for-sale securities are reported in OCI. Any decline in the fair value of Exelon's available-for-sale securities below the cost basis is reviewed to determine if such decline is other-than-temporary. If the decline is determined to be other-than-temporary, the cost basis of the available-for-sale securities is written down to fair value as a new cost basis and the amount of the write-down is included in earnings. See Note 16 — Asset Retirement Obligations for information regarding marketable securities held by NDT funds and Note 24 — Supplemental Financial Information for additional information regarding ComEd’s and PECO’s regulatory assets and liabilities. Property, Plant and Equipment (Exelon, Generation, ComEd, PECO and BGE) Property, plant and equipment is recorded at original cost. Original cost includes construction-related direct labor and material costs. ComEd, PECO and BGE also include indirect construction costs including labor and related costs of departments associated with supporting construction activities. When appropriate, original cost also includes capitalized interest for Generation and Exelon Corporate and AFUDC for regulated property at ComEd, PECO and BGE. The cost of repairs and maintenance, including planned major maintenance activities and minor replacements of property, is charged to maintenance expense as incurred. Third parties reimburse ComEd, PECO and BGE for all or a portion of expenditures for certain capital projects. Such contributions in aid of construction costs (CIAC) are recorded as a reduction to Property, Plant and Equipment. DOE SGIG funds reimbursed to PECO and BGE have been accounted for as CIAC. For Generation, upon retirement, the cost of property is charged to accumulated depreciation in accordance with the composite method of depreciation. Upon replacement of an asset, the costs to remove the asset, net of salvage, are capitalized to gross plant when incurred as part of the cost of the newly-installed asset and recorded to depreciation expense over the life of the new asset. Removal costs, net of salvage, incurred for property that will not be replaced is charged to operating and maintenance expense as incurred. For ComEd, PECO and BGE, upon retirement, the cost of property, net of salvage, is charged to accumulated depreciation in accordance with the composite method of depreciation. ComEd’s and BGE’s depreciation expense includes the estimated cost of dismantling and removing plant from service upon retirement, which is consistent with each utility’s regulatory recovery method. ComEd’s and BGE’s actual incurred removal costs are applied against a related regulatory liability. PECO’s removal costs are capitalized to accumulated depreciation when incurred, and recorded to depreciation expense over the life of the new asset constructed consistent with PECO’s regulatory recovery method. Generation’s oil and gas exploration and production activities consist of working interests in gas producing fields. Generation accounts for these activities under the successful efforts method of accounting. Acquisition, development and exploration costs are capitalized. Costs of drilling exploratory wells are initially capitalized and later charged to expense if reserves are not discovered or deemed not to be commercially viable. Other exploratory costs are charged to expense when incurred. See Note 7 — Property, Plant and Equipment , Note 10 — Jointly Owned Electric Utility Plant and Note 24 — Supplemental Financial Information for additional information regarding property, plant and equipment. Nuclear Fuel (Exelon and Generation) The cost of nuclear fuel is capitalized within property, plant and equipment and charged to fuel expense using the unit-of-production method. Prior to May 16, 2014, the estimated disposal cost of SNF was established per the Standard Waste Contract with the DOE and was expensed through fuel expense at one mill ($0.001) per kWh of net nuclear generation. Effective May 16, 2014, the SNF disposal fee was set to zero by the DOE and Exelon and Generation are not accruing any further costs related to SNF disposal fees until a new fee structure goes into effect. On-site SNF storage costs are being reimbursed by the DOE since a DOE (or government-owned) long-term storage facility has not been completed. See Note 23 — Commitments and Contingencies for additional information regarding the SNF disposal fee. Nuclear Outage Costs (Exelon and Generation) Costs associated with nuclear outages, including planned major maintenance activities, are expensed to operating and maintenance expense or capitalized to property, plant and equipment (based on the nature of the activities) in the period incurred. New Site Development Costs (Exelon and Generation) New site development costs represent the costs incurred in the assessment and design of new power generating facilities. Such costs are capitalized when management considers project completion to be probable, primarily based on management’s determination that the project is economically and operationally feasible, management and/or the Exelon board of directors has approved the project and has committed to a plan to develop it, and Exelon and Generation have received the required regulatory approvals or management believes the receipt of required regulatory approvals is probable. Capitalized development costs are charged to Operating and maintenance expense when project completion is no longer probable. New site development costs incurred prior to a project’s completion being deemed probable are expensed as incurred. Approximately $22 million , $13 million and $10 million of costs were expensed by Exelon and Generation for the years ended December 31, 2015 , 2014 , and 2013 , respectively. These costs are related to the possible development of new power generating facilities. Capitalized Software Costs (Exelon, Generation, ComEd, PECO and BGE) Costs incurred during the application development stage of software projects that are internally developed or purchased for operational use are capitalized within property, plant, and equipment. Such capitalized amounts are amortized ratably over the expected lives of the projects when they become operational, generally not to exceed five years. Certain other capitalized software costs are being amortized over longer lives based on the expected life or pursuant to prescribed regulatory requirements. The following table presents net unamortized capitalized software costs and amortization of capitalized software costs by year: Net unamortized software costs Exelon Generation ComEd PECO BGE December 31, 2015 $ 633 $ 180 $ 172 $ 86 $ 178 December 31, 2014 596 193 133 84 163 Amortization of capitalized software costs Exelon Generation ComEd PECO BGE 2015 $ 208 $ 73 $ 47 $ 33 $ 46 2014 186 59 45 28 43 2013 198 67 52 33 36 Depreciation, Depletion and Amortization (Exelon, Generation, ComEd, PECO and BGE) Except for the amortization of nuclear fuel, depreciation is generally recorded over the estimated service lives of property, plant and equipment on a straight-line basis using the composite method. ComEd’s and BGE’s depreciation includes a provision for estimated removal costs as authorized by the respective regulators. The estimated service lives for ComEd, PECO and BGE are primarily based on the average service lives from the

Variable Interest Entities (Exe

Variable Interest Entities (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Variable Interest Entity [Abstract]
Variable Interest Entities (Exelon, Generation, ComEd, PECO and BGE)	Variable Interest Entities (Exelon, Generation, ComEd, PECO and BGE) A VIE is a legal entity that possesses any of the following characteristics: an insufficient amount of equity at risk to finance its activities, equity owners who do not have the power to direct the significant activities of the entity (or have voting rights that are disproportionate to their ownership interest), or equity owners who do not have the obligation to absorb expected losses or the right to receive the expected residual returns of the entity. Companies are required to consolidate a VIE if they are its primary beneficiary, which is the enterprise that has the power to direct the activities that most significantly affect the entity’s economic performance. At December 31, 2015 and 2014 , Exelon, Generation, and BGE collectively consolidated seven and six VIEs or VIE groups, respectively, for which the applicable Registrant was the primary beneficiary ( see Consolidated Variable Interest Entities below) . As of December 31, 2015 and 2014 , the Registrants had significant interests in eight and six other VIEs, respectively, for which the Registrants do not have the power to direct the entities’ activities and, accordingly, were not the primary beneficiary ( see Unconsolidated Variable Interest Entities below) . Consolidated Variable Interest Entities The carrying amounts and classification of the consolidated VIEs’ assets and liabilities included in the Registrants’ consolidated financial statements at December 31, 2015 and 2014 are as follows: December 31, 2015 December 31, 2014 (a) Exelon (b) Generation BGE Exelon (b) Generation BGE Current assets $ 909 $ 881 $ 23 $ 1,275 $ 1,247 $ 21 Noncurrent assets 8,009 8,004 3 7,573 7,560 3 Total assets $ 8,918 $ 8,885 $ 26 $ 8,848 $ 8,807 $ 24 Current liabilities $ 473 $ 387 $ 81 $ 611 $ 526 $ 77 Noncurrent liabilities 2,927 2,884 41 2,728 2,597 120 Total liabilities $ 3,400 $ 3,271 $ 122 $ 3,339 $ 3,123 $ 197 _______________________ (a) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to classification of deferred taxes and simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. (b) Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity. Except as specifically noted below, the assets in the table above are restricted for settlement of the VIE obligations and the liabilities in the table can only be settled using VIE resources. Exelon's, Generation's and BGE's consolidated VIEs consist of: RSB BondCo LLC. In 2007, BGE formed RSB BondCo LLC (BondCo), a special purpose bankruptcy remote limited liability company, to acquire and hold rate stabilization property and to issue and service bonds secured by the rate stabilization property. In June 2007, BondCo purchased rate stabilization property from BGE, including the right to assess, collect, and receive non-bypassable rate stabilization charges payable by all residential electric customers of BGE. These charges are being assessed in order to recover previously incurred power purchase costs that BGE deferred pursuant to Senate Bill 1. BGE has determined that BondCo is a VIE for which it is the primary beneficiary. As a result, BGE consolidates BondCo. BondCo’s assets are restricted and can only be used to settle the obligations of BondCo. Further, BGE is required to remit all payments it receives from customers for rate stabilization charges to BondCo. During 2015, 2014, and 2013, BGE remitted $86 million , $85 million , and $83 million , respectively, to BondCo. BGE did not provide any additional financial support to BondCo during 2015. Further, BGE does not have any contractual commitments or obligations to provide additional financial support to BondCo unless additional rate stabilization bonds are issued. The BondCo creditors do not have any recourse to the general credit of BGE in the event the rate stabilization charges are not sufficient to cover the bond principal and interest payments of BondCo. Retail Gas Group. During 2009, Constellation formed two new entities, which now are part of Generation, and combined them with its existing retail gas activities into a retail gas entity group for the purpose of entering into a collateralized gas supply agreement with a third-party gas supplier. While Generation owns 100% of these entities, it has been determined that the retail gas entity group is a VIE because there is not sufficient equity to fund the group’s activities without the additional credit support that is provided in the form of a parental guarantee. Generation is the primary beneficiary of the retail gas entity group; accordingly, Generation consolidates the retail gas entity group as a VIE. The third-party gas supply arrangement is collateralized as follows: • the assets of the retail gas entity group must be used to settle obligations under the third-party gas supply agreement before it can make any distributions to Generation, • the third-party gas supplier has a collateral interest in all of the assets and equity of the retail gas entity group, and • Generation provides a $75 million parental guarantee to the third-party gas supplier in support of the retail gas entity group. Other than credit support provided by the parental guarantee, Exelon or Generation do not have any contractual or other obligations to provide additional financial support under the collateralized third-party gas supply agreement. The third-party gas supply creditors do not have any recourse to Exelon’s or Generation’s general credit other than the parental guarantee. Solar Project Entity Group. In 2011, Generation acquired all of the equity interests in Antelope Valley Solar Ranch One (Antelope Valley) from First Solar, Inc., a 242 -MW solar PV project in northern Los Angeles County, California. In addition, Generation owns a number of limited liability companies that build, own, and operate solar power facilities. While Generation owns 100% of these entities, it has been determined that certain of the individual solar project entities are VIEs because the entities require additional subordinated financial support in the form of a parental guarantee of debt, loans from the customers in order to obtain the necessary funds for construction of the solar facilities, or the customers absorb price variability from the entities through the fixed price power and/or REC purchase agreements. Generation is the primary beneficiary of the solar project entities that qualify as VIEs because Generation controls the design, construction, and operation of the solar power facilities. Generation provides operating and capital funding to the solar entities for ongoing construction, operations and maintenance of the solar power facilities and provides limited recourse related to the Antelope Valley project. In addition, these solar VIE entities have an aggregate amount of outstanding debt with third parties of $655 million , as of December 31, 2015 , for which the creditors have no recourse to Generation. For additional information on these project-specific financing arrangements refer to Note 14 — Debt and Credit Agreements . Retail Power and Gas Companies. In March 2014, Generation began consolidating retail power and gas VIEs for which Generation is the primary beneficiary as a result of energy supply contracts that give Generation the power to direct the activities that most significantly affect the economic performance of the entities. Generation does not have an equity ownership interest in these entities, but provides approximately $12 million in credit support for the retail power and gas companies. These entities are included in Generation’s consolidated financial statements, and the consolidation of the VIEs do not have a material impact on Generation’s financial results or financial condition. Wind Project Entity Group . Generation owns and operates a number of wind project limited liability entities, the majority of which were acquired during 2010 with the acquisition of all of the equity interests of John Deere Renewables, LLC (now known as Exelon Wind). Generation has evaluated the significant agreements and ownership structures and the risks of each of its wind projects and underlying entities, and determined that certain of the entities are VIEs because either the projects have noncontrolling equity interest holders that absorb variability from the wind projects, or the customers absorb price variability from the entities through the fixed price power and/or REC purchase agreements. Generation is the primary beneficiary of the wind project entities that qualify as VIEs because Generation controls the design, construction, and operation of the wind generation facilities. While Generation owns 100% of the majority of the wind project entities, nine of the projects have noncontrolling equity interests of 1% held by third parties. Generation’s current economic interests in eight of these projects is significantly greater than its stated contractual governance rights and all of these projects have reversionary interest provisions that provide the noncontrolling interest holder with a purchase option, certain of which are considered bargain purchase prices, which, if exercised, transfers ownership of the projects to the noncontrolling interest holder upon either the passage of time or the achievement of targeted financial returns. The ownership agreements with the noncontrolling interests state that Generation is to provide financial support to the projects in proportion to its current 99% economic interests in the projects. However, no additional support to these projects beyond what was contractually required has been provided during 2015. As of December 31, 2015 , the carrying amount of the assets and liabilities that are consolidated as a result of Generation being the primary beneficiary of the wind VIE entities primarily relates to the wind generating assets, PPA intangible assets and working capital amounts. Other Generating Facilities. During the second quarter of 2015, Generation formed a limited liability company to build, own, and operate a backup generator. While Generation owns 100% of the backup generator company, it was determined that the entity is a VIE because the customer absorbs price variability from the entity through the fixed price backup generator agreement. Generation provides operating and capital funding to the backup generator company. Generation also owns 90% of a biomass fueled, combined heat and power company. In the second quarter of 2015, the entity was deemed to be a VIE because the entity requires additional subordinated financial support in the form of a parental guarantee provided by Generation for up to $ 275 million in support of the payment obligations related to the Engineering, Procurement and Construction contract for the facility (see Note 14 - Debt and Credit Agreements for additional details on Albany Green Energy, LLC). In addition to the parental guarantee, Generation provides operating and capital funding to the biomass fueled, combined heat and power company. Generation is the primary beneficiary of both entities since Generation has the power to direct the activities that most significantly affect the economic performance of the entities. CENG. Through March 31, 2014, CENG was operated as a joint venture with EDF and was governed by a board of ten directors, five of which were appointed by Generation and five by EDF. CENG was designed to operate under joint and equal control of Generation and EDF through the Board of Directors, subject to the Chairman of the Board’s final decision making authority on certain special matters; therefore, CENG was not subject to VIE guidance. Accordingly, Generation’s 50.01% interest in CENG was accounted for as an equity method investment. On April 1, 2014, Generation, CENG, and subsidiaries of CENG executed the Nuclear Operating Services Agreement (NOSA) pursuant to which Generation now conducts all activities associated with the operations of the CENG fleet and provides corporate and administrative services to CENG and the CENG fleet for the remaining life of the CENG nuclear plants as if they were a part of the Generation nuclear fleet, subject to the CENG member rights of EDF. As a result of executing the NOSA, CENG now qualifies as a VIE due to the disproportionate relationship between Generation’s 50.01% equity ownership interest and its role in conducting the operational activities of CENG and the CENG fleet conveyed through the NOSA. Further, since Generation is conducting the operational activities of CENG and the CENG fleet, Generation qualifies as the primary beneficiary of CENG and, therefore, is required to consolidate the financial position and results of operations of CENG. On April 1, 2014, Exelon and Generation derecognized Generation’s equity method investment in CENG and reflected all assets, liabilities, and the EDF noncontrolling interest in CENG at fair value on the consolidated balance sheets of Exelon and Generation, resulting in the recognition of a $261 million gain in their respective Consolidated Statements of Operations and Comprehensive Income for the year ended December 31, 2014 . For additional information on this transaction refer to Note 5 — Investment in Constellation Energy Nuclear Group, LLC . Generation and Exelon, where indicated, provide the following support to CENG (See Note 5 — Investment in Constellation Energy Nuclear Group, LLC and Note 26 — Related Party Transactions for additional information regarding Generation and Exelon’s transactions with CENG): • under the NOSA, Generation conducts all activities related to the operation of the CENG nuclear generation fleet owned by CENG subsidiaries (the CENG fleet) and provides corporate and administrative services for the remaining life and decommissioning of the CENG nuclear plants as if they were a part of the Generation nuclear fleet, subject to the CENG member rights of EDF, • under the Power Services Agency Agreement (PSAA), Generation provides scheduling, asset management, and billing services to the CENG fleet for the remaining operating life of the CENG nuclear plants, • under power purchase agreements with CENG, Generation purchased or will purchase 50.01% of the available output generated by the CENG nuclear plants not subject to other contractual agreements from January 2015 through the end of the operating life of each respective plant. However, pursuant to amendments dated March 31, 2015, the energy obligations under the Ginna Nuclear Power Plant (Ginna) PPAs have been suspended during the term of the expected Reliability Support Services Agreement (RSSA). (see Note 3 — Regulatory Matters for additional details), • Generation provided a $400 million loan to CENG. As of December 31, 2015 , the remaining obligation is $ 300 million including accrued interest, which reflects the principal payment made in January 2015 (see Note 5 — Investment in Constellation Energy Nuclear Group, LLC for more details), • Generation executed an Indemnity Agreement pursuant to which Generation agreed to indemnify EDF against third-party claims that may arise from any future nuclear incident (as defined in the Price Anderson Act) in connection with the CENG nuclear plants or their operations. Exelon guarantees Generation’s obligations under this Indemnity Agreement. (See Note 23 — Commitments and Contingencies for more details), • in connection with CENG’s severance obligations, Generation has agreed to reimburse CENG for a total of approximately $6 million of the severance benefits paid or to be paid in 2014 through 2016. As of December 31, 2015 , the remaining obligation is approximately $1 million , • Generation and EDF share in the $637 million of contingent payment obligations for the payment of contingent retrospective premium adjustments for the nuclear liability insurance (See Note 23 — Commitments and Contingencies for more details), • Generation provides a guarantee of approximately $7 million associated with hazardous waste management facilities and underground storage tanks. In addition, EDF executed a reimbursement agreement that provides reimbursement to Exelon for 49.99% of any amounts paid by Generation under this guarantee, • Generation and EDF are the members-insured with Nuclear Electric Insurance Limited and have assigned the loss benefits under the insurance and the NEIL premium costs to CENG and guarantee the obligations of CENG under these insurance programs in proportion to their respective member interests (see Note 23 — Commitments and Contingencies for more details), and • Exelon has executed an agreement to provide up to $245 million to support the operations of CENG as well as a $165 million guarantee of CENG’s cash pooling agreement with its subsidiaries. For each of the consolidated VIEs, except as otherwise noted: • the assets of the VIEs are restricted and can only be used to settle obligations of the respective VIE; • Exelon, Generation and BGE did not provide any additional material financial support to the VIEs; • Exelon, Generation and BGE did not have any material contractual commitments or obligations to provide financial support to the VIEs; and • the creditors of the VIEs did not have recourse to Exelon’s, Generation’s or BGE’s general credit. As of December 31, 2015 and 2014 , ComEd and PECO did not have any material consolidated VIEs. Assets and Liabilities of Consolidated VIEs Included within the balances above are assets and liabilities of certain consolidated VIEs for which the assets can only be used to settle obligations of those VIEs, and liabilities that creditors, or beneficiaries, do not have recourse to the general credit of the Registrants. As of December 31, 2015 and 2014 , these assets and liabilities primarily consisted of the following: December 31, 2015 December 31, 2014 (a) Exelon Generation BGE Exelon Generation BGE Cash and cash equivalents $ 164 $ 164 $ — $ 392 $ 392 $ — Restricted cash 100 77 23 117 96 21 Accounts receivable, net Customer 219 219 — 297 297 — Other 43 43 — 57 57 — Mark-to-market derivatives assets 140 140 — 171 171 — Inventory Materials and supplies 181 181 — 172 172 — Other current assets 35 30 — 37 30 — Total current assets 882 854 23 1,243 1,215 21 Property, plant and equipment, net 5,160 5,160 — 4,638 4,638 — Nuclear decommissioning trust funds 2,036 2,036 — 2,097 2,097 — Goodwill 47 47 — 47 47 — Mark-to-market derivatives assets 53 53 — 44 44 — Other noncurrent assets 90 85 3 90 77 3 Total noncurrent assets 7,386 7,381 3 6,916 6,903 3 Total assets $ 8,268 $ 8,235 $ 26 $ 8,159 $ 8,118 $ 24 Long-term debt due within one year $ 111 $ 27 $ 79 $ 87 $ 5 $ 75 Accounts payable 216 216 — 292 292 — Accrued expenses 115 113 2 111 108 2 Mark-to-market derivative liabilities 5 5 — 24 24 — Unamortized energy contract liabilities 12 12 — 22 22 — Other current liabilities 13 13 — 25 25 — Total current liabilities 472 386 81 561 476 77 Long-term debt 666 623 41 212 81 120 Asset retirement obligations 1,999 1,999 — 1,763 1,763 — Pension obligation (b) 9 9 — 9 9 — Unamortized energy contract liabilities 39 39 — 51 51 — Other noncurrent liabilities 79 79 — 132 132 — Noncurrent liabilities 2,792 2,749 41 2,167 2,036 120 Total liabilities $ 3,264 $ 3,135 $ 122 $ 2,728 $ 2,512 $ 197 ___________ (a) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to classification of deferred taxes and simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. (b) Includes the CNEG retail gas pension obligation, which is presented as a net asset balance within the Prepaid pension asset line item on Generation’s balance sheet. See Note 17 — Retirement Benefits for additional details. Unconsolidated Variable Interest Entities Exelon’s and Generation’s variable interests in unconsolidated VIEs generally include equity investments and energy purchase and sale contracts. For the equity investments, the carrying amount of the investments is reflected on Exelon’s and Generation’s Consolidated Balance Sheets in Investments. For the energy purchase and sale contracts (commercial agreements), the carrying amount of assets and liabilities in Exelon’s and Generation’s Consolidated Balance Sheets that relate to their involvement with the VIEs are predominately related to working capital accounts and generally represent the amounts owed by, or owed to, Exelon and Generation for the deliveries associated with the current billing cycles under the commercial agreements. Further, Exelon and Generation have not provided material debt or equity support, liquidity arrangements or performance guarantees associated with these commercial agreements. As of December 31, 2015 and 2014 , Exelon and Generation had significant unconsolidated variable interests in eight and six VIEs, respectively, for which Exelon or Generation, as applicable, was not the primary beneficiary; including certain equity method investments and certain commercial agreements. The increase in the number of unconsolidated VIEs is due to the execution of an energy purchase and sale agreement with a new unconsolidated VIE and an equity investment in a new unconsolidated VIE. The following tables present summary information about Exelon and Generation’s significant unconsolidated VIE entities: December 31, 2015 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 263 $ 164 $ 427 Total liabilities (a) 22 125 147 Exelon's ownership interest in VIE (a) — 11 11 Other ownership interests in VIE (a) 241 28 269 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 21 21 Contract intangible asset 9 — 9 Debt and payment guarantees — 3 3 Net assets pledged for Zion Station decommissioning (b) 17 — 17 December 31, 2014 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 114 $ 91 $ 205 Total liabilities (a) 3 49 52 Exelon's ownership interest in VIE (a) — 9 9 Other ownership interests in VIE (a) 111 33 144 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 13 13 Contract intangible asset 9 — 9 Debt and payment guarantees — 3 3 Net assets pledged for Zion Station decommissioning (b) 27 — 27 ___________________ (a) These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs. Exelon corrected an error in the December 31, 2014 balances within Commercial Agreement VIEs for an overstatement of Total assets, Total liabilities and Other ownership interests in VIE of $ 392 million , $ 234 million and $ 158 million , respectively. The error is not considered material to any prior period. (b) These items represent amounts on Exelon’s and Generation’s Consolidated Balance Sheets related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning includes gross pledged assets of $206 million and $319 million as of December 31, 2015 and December 31, 2014 , respectively; offset by payables to ZionSolutions LLC of $189 million and $292 million as of December 31, 2015 and December 31, 2014 , respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE. For each unconsolidated VIE, Exelon and Generation assessed the risk of a loss equal to their maximum exposure to be remote and, accordingly Exelon and Generation have not recognized a liability associated with any portion of the maximum exposure to loss. In addition, there are no agreements with, or commitments by, third parties that would materially affect the fair value or risk of their variable interests in these variable interest entities. Energy Purchase and Sale Agreements. Generation has several energy purchase and sale agreements with generating facilities. Generation has evaluated the significant agreements, ownership structures and risks of each entity, and determined that certain of the entities are VIEs because the entity absorbs risk through the sale of fixed price power and renewable energy credits. Generation has reviewed the entities and has determined that Generation is not the primary beneficiary of the VIEs because Generation does not have the power to direct the activities that most significantly impact the VIEs economic performance. ZionSolutions . Generation has an asset sale agreement with EnergySolutions, Inc. and certain of its subsidiaries, including ZionSolutions, LLC (ZionSolutions), which is further discussed in Note 16 — Asset Retirement Obligations . Under this agreement, ZionSolutions can put the assets and liabilities back to Generation when decommissioning activities under the asset sale agreement are complete. Generation has evaluated this agreement and determined that, through the put option, it has a variable interest in ZionSolutions but is not the primary beneficiary. As a result, Generation has concluded that consolidation is not required. Other than the asset sale agreement, Exelon and Generation do not have any contractual or other obligations to provide additional financial support and ZionSolutions’ creditors do not have any recourse to Exelon’s or Generation’s general credit. Investment in Energy Development Projects, Distributed Energy Companies, and Energy Generating Facilities. Generation has several equity investments in energy development projects and energy generating facilities. Generation has evaluated the significant agreements, ownership structures and risks of each of its equity investments, and determined that certain of the entities are VIEs because the entity has an insufficient amount of equity at risk to finance its activities, Generation guarantees the debt of the entity, provides equity support, or provides operating services to the entity. Generation has reviewed the entities and has determined that Generation is not the primary beneficiary of the entities that qualify as VIEs because Generation does not have the power to direct the activities that most significantly impact the VIEs economic performance. In July 2014, Generation entered into an arrangement to purchase a 90% equity interest and 90% of the tax attributes of a distributed energy company. Generation’s total equity commitment in this arrangement was $ 91 million and is paid incrementally over an approximate two year period (see Note 23 - Commitments and Contingencies for additional details). This arrangement did not meet the definition of a VIE and is recorded as an equity method investment. In June 2015, 2015 ESA Investco, LLC, then a wholly owned subsidiary of Generation, entered into an arrangement to purchase a 90% equity interest and 99% of the tax attributes of another distributed energy company. Separate from the equity investment, Generation provided $ 27 million in cash to the other (10%) equity holder in the distributed energy company in exchange for a convertible promissory note. In November 2015, Generation sold 69% of its equity interest in 2015 ESA Investco, LLC to a tax equity investor. Generation and the tax equity investor will contribute $ 250 million of equity incrementally through December 2016 in proportion to their ownership interests, which equates to approximately $ 172 million for the tax equity investor and $ 78 million for Generation (see Note 23 - Commitments and Contingencies for additional details). Generation and the tax equity investor provide a parental guarantee of up to $ 275 million in proportion to their ownership interests in support of 2015 ESA Investco, LLC's obligation to make equity contributions to the distributed energy company. The investment in the distributed energy company was evaluated and it was determined to be a VIE for which Generation is not the primary beneficiary. Generation continues to consolidate 2015 ESA Investco, LLC under the voting interest model. Both distributed energy companies from the 2014 and 2015 arrangements are considered related parties. ComEd, PECO and BGE The financing trust of ComEd, ComEd Financing III, the financing trusts of PECO, PECO Trust III and PECO Trust IV, and the financing trust of BGE, BGE Capital Trust II are not consolidated in Exelon’s, ComEd’s, PECO’s or BGE’s financial statements. These financing trusts were created to issue mandatorily redeemable trust preferred securities. ComEd, PECO, and BGE have concluded that they do not have a significant variable interest in ComEd Financing III, PECO Trust III, PECO Trust IV or BGE Capital Trust II as each Registrant financed its equity interest in the financing trusts through the issuance of subordinated debt and, therefore, has no equity at risk. See Note 14 — Debt and Credit Agreements for additional information.

Regulatory Matters (Exelon, Gen

Regulatory Matters (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Regulated Operations [Abstract]
Regulatory Matters (Exelon, Generation, ComEd, PECO and BGE)	(Exelon, Generation, ComEd, PECO and BGE) The following matters below discuss the current status of material regulatory and legislative proceedings of the Registrants. Illinois Regulatory Matters Energy Infrastructure Modernization Act (Exelon and ComEd). Background Since 2011, ComEd’s electric distribution rates are established through a performance-based rate formula, pursuant to EIMA. EIMA also provides a structure for substantial capital investment by utilities to modernize Illinois’ electric utility infrastructure. EIMA was scheduled to sunset, ending ComEd’s performance based rate formula and investment commitment, at December 31, 2017, unless approved to continue through 2022 by the Illinois General Assembly. On April 3, 2015, the Governor signed legislation extending the EIMA sunset from 2017 to 2019. Participating utilities are required to file an annual update to the performance-based formula rate tariff on or before May 1, with resulting rates effective in January of the following year. This annual formula rate update is based on prior year actual costs and current year projected capital additions (initial revenue requirement). The update also reconciles any differences between the revenue requirement in effect for the prior year and actual costs incurred for that year (annual reconciliation). See Annual Electric Distribution Filings below for further details. Throughout each year, ComEd records regulatory assets or regulatory liabilities and corresponding increases or decreases to Operating revenue for any differences between the revenue requirement in effect and ComEd’s best estimate of the revenue requirement expected to be approved by the ICC for that year’s reconciliation. As of December 31, 2015 , and December 31, 2014 , ComEd had a regulatory asset associated with the electric distribution formula rate of $ 189 million and $ 371 million , respectively. The regulatory asset associated with electric distribution true-up is amortized to Operating revenue in ComEd's Consolidated Statement of Operations and Comprehensive Income as the associated amounts are recovered through rates. Participating utilities are also required to file an annual update on their AMI implementation progress. On April 1, 2015, ComEd filed an annual progress report on its AMI Implementation Plan with the ICC, which allows for the installation of more than four million smart meters throughout ComEd's service territory by 2018. To date, approximately two million smart meters have been installed in the Chicago area. Pursuant to EIMA, ComEd annually contributes $ 4 million for customer education for as long as the AMI Deployment Plan remains in effect. Additionally, ComEd contributes $ 10 million annually through 2016 to fund customer assistance programs for low-income customers, which will not be recoverable through rates. Annual Electric Distribution Filings For each of the following years, the ICC approved the following total increases/(decreases) in ComEd's electric distributions formula rate filings: Annual Distribution Filings 2015 2014 2013 ComEd's requested total revenue requirement (decrease) increase $ (50 ) $ 269 $ 353 Final ICC Order Initial revenue requirement increase $ 85 $ 160 $ 160 Annual reconciliation (decrease) increase (152 ) 72 181 Total revenue requirement (decrease) increase $ (67 ) $ 232 $ 341 Allowed Return on Rate Base: Initial revenue requirement 7.05 % 7.06 % 6.94 % Annual reconciliation 7.02 % 7.04 % 6.94 % Allowed ROE: Initial revenue requirement 9.14 % (a) 9.25 % (a) 8.72 % Annual reconciliation 9.09 % (a) 9.20 % (a) 8.72 % Effective date of rates January 2016 January 2015 January 2014 __________________ (a) Includes a reduction of 5 basis points for a reliability performance metric penalty. Formula Rate Structure Investigation In October 2013, the ICC opened an investigation (the Investigation), in response to a complaint filed by the Illinois Attorney General, to change the formula rate structure by requesting three changes: the elimination of the income tax gross-up on the weighted average cost of capital used to calculate interest on the annual reconciliation balance, the netting of associated accumulated deferred income taxes against the annual reconciliation balance in calculating interest, and the use of average rather than year-end rate base for determining any ROE collar adjustment. On November 26, 2013, the ICC issued its final order in the Investigation, rejecting two of the proposed changes but accepting the proposed change to eliminate the income tax gross-up on the weighted average cost of capital used to calculate interest on the annual reconciliation balance. The accepted change became effective in January 2014, and reduced ComEd’s 2014 revenue by approximately $ 8 million . This change had no financial statement impact on ComEd in 2013. ComEd and intervenors requested rehearing, however all rehearing requests were denied by the ICC. ComEd and intervenors filed appeals with the Illinois Appellate Court. ComEd subsequently withdrew its appeal, but the Illinois Attorney General and the Citizens Utility Board continued to argue that the ICC had wrongly approved ComEd’s treatment of accumulated deferred income taxes (ADIT) relating to the annual reconciliation. On July 29, 2015, the Illinois Appellate Court rejected that appeal and affirmed the ICC's decision and its acceptance of ComEd’s treatment of ADIT. The period in which to file requests for further review has expired and that decision is final. Appeal of Initial Formula Rate Tariff On March 26, 2014, the Illinois Appellate Court issued an opinion with respect to ComEd’s appeal of the ICC’s order relating to ComEd’s initial formula rate tariff. The most significant financial issues under appeal related to ICC findings that were counter to the formula rate legislation and were clarified by subsequent legislation (Senate Bill 9). Therefore, only a subset of the issues originally appealed remained. The Court found against ComEd on each of the remaining issues: compensation related adjustments, billing determinants and the use of certain allocators. The Court’s opinion has no accounting impact as ComEd recorded the distribution formula regulatory asset consistent with the ICC’s final Order. On September 14, 2014, the Illinois Supreme Court declined to hear that appeal. ComEd elected not to seek review by the United States Supreme Court on the Federal law issues. Accordingly, the decision of the Illinois Appellate Court is considered final. Grand Prairie Gateway Transmission Line (ComEd). On December 2, 2013, ComEd filed a request to obtain the ICC’s approval to construct a 60 -mile overhead 345 kV transmission line that traverses Ogle, DeKalb, Kane and DuPage Counties in Northern Illinois. On May 28, 2014, in a separate proceeding, FERC issued an order granting ComEd’s request to include 100% of the capital costs recorded to construction work in progress during construction of the line in ComEd’s transmission rate base. If the project is cancelled or abandoned for reasons beyond ComEd’s control, FERC approved the ability for ComEd to recover 100% of its prudent costs incurred after May 21, 2014 and 50% of its costs incurred prior to May 21, 2014 in ComEd’s transmission rate base. The costs incurred for the project prior to May 21, 2014 were immaterial. ComEd has acquired numerous easements across the project route through voluntary transactions. ComEd will seek to acquire the property rights on the remaining 28 parcels through condemnation proceedings in the circuit courts. ComEd began construction of the line during the second quarter of 2015 with an in-service date expected in the second quarter of 2017. Illinois Procurement Proceedings (Exelon, Generation and ComEd). ComEd is permitted to recover its electricity procurement costs from retail customers without mark-up. Since June 2009, the IPA designs, and the ICC approves, an electricity supply portfolio for ComEd and the IPA administers a competitive process under which ComEd procures its electricity supply from various suppliers, including Generation. As of December 31, 2015, ComEd has completed the ICC-approved procurement process for a portion of its energy requirements through 2021. ComEd is required to purchase an increasing percentage of the electricity for customer deliveries from renewable energy resources. Purchases by customers of electricity from competitive electric generation suppliers, whether as a result of the customers’ own actions or as a result of municipal aggregation, are not included in this calculation and have the effect of reducing ComEd’s purchase obligation. ComEd entered into several 20 -year contracts with unaffiliated suppliers in December 2010 regarding the procurement of long-term renewable energy and associated RECs in order to meet its obligations under the Illinois' RPS. All associated costs are recoverable from customers. FutureGen Industrial Alliance, Inc (Exelon and ComEd). During 2013, the ICC approved, and directed ComEd and Ameren (the Utilities) to enter into 20 -year sourcing agreements with FutureGen Industrial Alliance, Inc (FutureGen), under which FutureGen will retrofit and repower an existing plant in Morgan County, Illinois to a 166 MW near zero emissions coal-fueled generation plant, with an assumed commercial operation date in 2017. The sourcing agreement provides that ComEd and Ameren will pay FutureGen’s contract prices, which are set annually pursuant to a formula rate. The contract prices are based on the difference between the costs of the facility and the revenues FutureGen receives from selling capacity and energy from the unit into the MISO or other markets, as well as any other revenue FutureGen receives from the operation of the facility. The order also directs ComEd and Ameren to recover these costs from their electric distribution customers through the use of a tariff, regardless of whether they purchase electricity from ComEd or Ameren, or from competitive electric generation suppliers. In February 2013, ComEd filed an appeal with the Illinois Appellate Court questioning the legality of requiring ComEd to procure power for retail customers purchasing electricity from competitive electric generation suppliers. On July 22, 2014, the Illinois Appellate Court issued its ruling re-affirming the ICC’s order requiring ComEd to enter into the sourcing agreement with FutureGen and allowing the use of a tariff to recover its costs. ComEd decided not to appeal the Illinois Appellate Court’s decision to the Illinois Supreme Court. However, the competitive electric generation suppliers and several large consumers petitioned for leave to appeal the Illinois Appellate Court’s decision. On November 26, 2014, the Illinois Supreme Court granted the petition. ComEd executed the sourcing agreement with FutureGen in accordance with the ICC’s order. In addition, ComEd filed a petition with the ICC seeking approval of the tariff allowing for the recovery of its costs associated with the FutureGen contract from all of its electric distribution customers, which was approved by the ICC on September 30, 2014. A significant portion of the cost of the development of FutureGen was being funded by the DOE under the American Recovery and Reinvestment Act of 2009. In early February 2015, the DOE suspended funding for the project until further clarity could be obtained on certain significant hurdles facing the project, including the outcome of the litigation described above. Whether or not the DOE funding will be reinstated at some later date is unknown at this time. On January 13, 2016, FutureGen informed the Illinois Supreme Court that it had ceased all development efforts on the FutureGen project and would soon be seeking to terminate the FutureGen supply agreements. Accordingly, FutureGen requested that the court dismiss the proceeding as moot. A decision from the Illinois Supreme Court dismissing the matter is expected in early 2016. In February 2016, FutureGen terminated its sourcing agreement with ComEd. As a result, ComEd is under no further obligation under this agreement. Energy Efficiency and Renewable Energy Resources (Exelon and ComEd). Electric utilities in Illinois are required to include cost-effective energy efficiency resources in their plans to meet an incremental annual program energy savings requirement of 2% of energy delivered in the year commencing June 1, 2015 and each year thereafter. Additionally, during the ten-year period that began June 1, 2008, electric utilities must implement cost-effective demand response measures to reduce peak demand by 0.1% over the prior year for eligible retail customers. The energy efficiency and demand response goals are subject to rate impact caps each year. Utilities are allowed recovery of costs for energy efficiency and demand response programs, subject to approval by the ICC. In January 2014, the ICC approved ComEd’s third three-year Energy Efficiency and Demand Response Plan covering the period June 2014 through May 2017. The plans are designed to meet Illinois' energy efficiency and demand response goals through May 2017, including reductions in delivered energy to all retail customers and in the peak demand of eligible retail customers. EIMA provides for additional energy efficiency in Illinois. Starting in the June 2013 through May 2014 period and occurring annually thereafter, as part of the IPA procurement plan, ComEd is to include cost-effective expansion of current energy efficiency programs, and additional new cost-effective and/or third-party energy efficiency programs that are identified through a request for proposal process. All cost-effective energy efficiency programs are included in the IPA procurement plan for consideration of implementation. While these programs are monitored separately from the Energy Efficiency Portfolio Standard (EEPS), funds for both the EEPS portfolio and IPA energy efficiency programs are collected under the same rider. Illinois utilities are required to procure cost-effective renewable energy resources in amounts that equal or exceed 2% of the total electricity that each electric utility supplies to its eligible retail customers. ComEd is also required to acquire amounts of renewable energy resources that will cumulatively increase this percentage to at least 10% by June 1, 2015, with an ultimate target of at least 25% by June 1, 2025. All goals are subject to rate impact criteria set forth by Illinois legislation. As of December 31, 2015 , ComEd had purchased sufficient renewable energy resources or equivalents, such as RECs, to comply with the Illinois legislation. ComEd currently retires all RECs upon transfer and acceptance. ComEd is permitted to recover procurement costs of RECs from retail customers without mark-up through rates. Pennsylvania Regulatory Matters 2015 Pennsylvania Electric Distribution Rate Case (Exelon and PECO). On March 27, 2015, PECO filed a petition with the PAPUC requesting an increase of $190 million to its annual service revenues for electric delivery, which requested an ROE of 10.95% . On September 10, 2015, PECO and interested parties filed with the PAPUC a petition for joint settlement for an increase of $127 million in annual distribution service revenue. No overall ROE was specified in the settlement. On December 17, 2015, the PAPUC approved the settlement of PECO’s electric distribution rate case. The approved electric delivery rates became effective on January 1, 2016. The settlement includes approval of the In-Program Arrearage Forgiveness (“IPAF”) Program, which provides for forgiveness of a portion of the eligible arrearage balance of its low-income Customer Assistance Program (CAP) accounts receivable that will be determined as of program inception in October 2016. The forgiveness will be granted to the extent CAP customers remain current with payments. The Settlement guarantees PECO’s recovery of two-thirds of the arrearage balance through a combination of customer payments and rate recovery, including through future rates cases if necessary. The remaining one-third of the arrearage balance will be absorbed by PECO, of which a portion has already been expensed as bad debt for CAP customer’s accounts receivable balances. Although the actual arrearage balance is not defined until program inception, PECO believes that it can reasonably estimate certain CAP customer accounts receivable balances as of December 31, 2015 that will remain outstanding at program inception. Management determined its best estimate based on historical collectability information. As a result, a regulatory asset of $7 million , representing the previously incurred bad debt expense associated with the estimated eligible accounts receivable balances, was recorded on Exelon’s and PECO’s Consolidated Balance Sheets as of December 31, 2015. This estimate will be revisited on a quarterly basis through program inception. 2010 Pennsylvania Electric and Natural Gas Distribution Rate Cases (Exelon and PECO). On December 16, 2010, the PAPUC approved the settlement of PECO’s electric and natural gas distribution rate cases, which were filed in March 2010, providing increases in annual service revenue of $225 million and $20 million , respectively. The settlements included a stipulation regarding how tax benefits related to the application of any new IRS guidance on repairs deduction methodology are to be handled from a rate-making perspective. The settlements required that the expected cash benefit from the application of any new guidance to tax years prior to 2011 be refunded to customers over a seven-year period. On August 19, 2011, the IRS issued Revenue Procedure 2011-43 providing a safe harbor method of tax accounting for electric transmission and distribution property. PECO adopted the safe harbor and elected a method change for the 2010 tax year. The total refund to customers for the tax cash benefit from the application of the safe harbor to costs incurred prior to 2010 was $ 171 million . On October 4, 2011, PECO filed a supplement to its electric distribution tariff to execute the refund to customers of the tax cash benefit related to the IRC Section 481(a) “catch-up” adjustment claimed on the 2010 income tax return, which is subject to adjustment based on the outcome of IRS examinations. Credits have been reflected in customer bills since January 1, 2012. In September 2012, PECO filed an application with the IRS to change its method of accounting for gas distribution repairs for the 2011 tax year. The expected total refund to customers for the tax cash benefit from the application of the new method to costs incurred prior to 2011 is $ 54 million . This amount is subject to adjustment based on the outcome of IRS examinations. Credits have been reflected in customer bills since January 1, 2013. PECO is awaiting IRS guidance that will provide a safe harbor method of accounting for gas transmission and distribution property. The prospective tax benefits claimed as a result of the new methodology will be reflected in tax expense in the year in which they are claimed on the tax return. As agreed to in the 2010 distribution rate case settlements, these benefits were reflected in the determination of revenue requirements in the 2015 electric distribution rate case discussed above and will be reflected in the next natural gas distribution rate case. See Note 15 — Income Taxes for additional information. The 2010 electric and natural gas distribution rate case settlements did not specify the rate of return upon which the settlement rates are based, but rather provided for an increase in annual revenue. PECO has not filed a transmission rate case since rates have been unbundled. Pennsylvania Procurement Proceedings (Exelon and PECO). Through PECO’s first two PAPUC approved DSP Programs, PECO procured electric supply for its default electric customers through PAPUC approved competitive procurements. DSP I and DSP II expired on May 31, 2013 and May 31, 2015, respectively. The second DSP Program included a number of retail market enhancements recommended by the PAPUC in its previously issued Retail Markets Intermediate Work Plan Order. PECO was also directed to submit a plan to allow its low-income CAP customers to purchase their generation supply from EGSs beginning in April 2014. In May 2013, PECO filed its CAP Shopping Plan with the PAPUC. By an Order entered on January 24, 2014, the PAPUC approved PECO’s plan, with modifications, to make CAP shopping available beginning April 15, 2014. On March 20, 2014, the Office of Consumer Advocate (OCA) and low-income advocacy groups filed an appeal and emergency request for a stay with the Pennsylvania Commonwealth Court, claiming that the PAPUC-ordered CAP Shopping plan does not contain sufficient protections for low-income customers. On July 14, 2015, the Court issued opinions on the OCA and low-income advocacy group appeal. Specifically, the Court remanded the issue to the PAPUC with instructions that it approve a rule revision to the PECO CAP Shopping Plan that would prohibit CAP customers from entering into contracts with an EGS that would impose early cancellation/termination fees. The PAPUC has appealed the Court's decision. PECO does not have information at this time as to what action it may be required to take following remand to the PAPUC. On December 4, 2014, the PAPUC approved PECO's third DSP Program. The program has a 24 -month term from June 1, 2015 through May 31, 2017, and complies with electric generation procurement guidelines set forth in Act 129. Under the program, PECO is procuring electric supply through four competitive procurements for fixed price full requirements contracts of two years or less for the residential classes and small and medium commercial classes and spot market price full requirement contracts for the large commercial and industrial class load. Beginning in June 2016, the medium commercial class (101-500 kW) will move to spot market pricing. As of December 31, 2015, PECO entered into contracts with PAPUC-approved bidders, including Generation, resulting from the first two of its four scheduled procurements. Charges incurred for electric supply procured through contracts with Generation are included in purchased power from affiliates on PECO's Consolidated Statement of Operations and Comprehensive Income. On March 12, 2015, PECO settled the CAP Design with the Office of Consumer Advocates (OCA) and Low Income Advocates, and filed the proposed plan with the PAPUC on March 20, 2015. The program design changes the rate structure of PECO's CAP to make the bills more affordable to customers enrolled in the assistance program. The CAP discounts continue to be recovered through PECO's universal service fund cost. On July 8, 2015, the CAP Design was approved by the PAPUC. PECO plans to implement the program changes in October 2016. Smart Meter and Smart Grid Investments (Exelon and PECO). In April 2010, pursuant to Act 129 and the follow-on Implementation Order of 2009, the PAPUC approved PECO’s Smart Meter Procurement and Installation Plan (SMPIP), under which PECO will install more than 1.6 million electric smart meters and an AMI communication network by 2020. PECO is currently in the second phase of the SMPIP and has deployed substantially all remaining smart meters as of December 31, 2015 , for a total of 1.7 million smart meters. In total, PECO currently expects to spend up to $ 589 million , excluding the cost of the original meters, on its smart meter infrastructure and approximately $ 155 million on smart grid investments through final deployment of which $ 200 million has been funded by SGIG. As of December 31, 2015 , PECO has spent $ 578 million and $ 155 million on smart meter and smart grid infrastructure, respectively, not including the DOE reimbursements received. Recovery of smart meter costs will be reflected in base rates effective January 1, 2016. Energy Efficiency Programs (Exelon and PECO). PECO’s PAPUC-approved Phase I EE&C Plan had a four-year term that began on June 1, 2009 and concluded on May 31, 2013. The Phase I plan set forth how PECO would meet the required reduction targets established by Act 129’s EE&C provisions. On November 15, 2013, PECO filed its final compliance report with the PAPUC communicating PECO had met all Phase I reduction targets. The PAPUC issued its Phase II EE&C implementation order on August 2, 2012, that provided energy consumption reduction requirements for the second phase of Act 129’s EE&C program, which went into effect on June 1, 2013. Pursuant to the Phase II implementation order, PECO filed its three-year EE&C Phase II Plan with the PAPUC on November 1, 2012. The plan set forth how PECO would reduce electric consumption by at least 1,125,852 MWh in its service territory for the period June 1, 2013 through May 31, 2016, adjusted for weather and extraordinary loads. The implementation order permitted PECO to apply any excess savings achieved during Phase I against its Phase II consumption reduction targets, with no reduction to its Phase II budget. In accordance with the Act 129 Phase II implementation order, at least 10% and 4.5% of the total consumption reductions had to be through programs directed toward PECO’s public and low income sectors, respectively. If PECO failed to achieve the required reductions in consumption, it would have been subject to civil penalties of up to $ 20 million , which would not be recoverable from ratepayers. Act 129 mandates that the total cost of the plan may not exceed 2% of the electric company’s total annual revenue as of December 31, 2006. On March 15, 2013 and February 28, 2014, PECO filed Petitions for Approval to amend its EE&C Phase II Plan to continue its DLC demand reduction program for mass market customers through May 31, 2014 and May 31, 2016, respectively. PECO proposed to fund the estimated $ 10 million annual costs of the plan by modifying incentive levels for other Phase II programs. The costs of the DLC program will be recovered through PECO’s Energy Efficiency Plan surcharge along with other Phase II Plan costs. The PAPUC granted PECO’s Petitions on May 5, 2013 and April 23, 2014, respectively. The PAPUC issued its Phase III EE&C implementation order on June 19, 2015, that provides energy consumption reduction requirements for the third phase of Act 129’s EE&C program with a five-year term from June 1, 2016 through May 31, 2021. The order tentatively established PECO’s five-year cumulative consumption reduction target at 2,080,553 MWh. Pursuant to the Phase III implementation order, PECO filed its five-year EE&C Phase III Plan with the PAPUC on November 30, 2015. The Plan sets forth how PECO will reduce electric consumption by at least 1,962,659 MWh, with a goal of 2,100,875 MWh in its service territory for the period June 1, 2016 through May 31, 2021. PECO expects a final decision from the PAPUC on PECO’s EE&C Phase III Plan during the first quarter of 2016. Alternative Energy Portfolio Standards (Exelon and PECO). In November 2004, Pennsylvania adopted the AEPS Act. The AEPS Act mandated that beginning in 2011, following the expiration of PECO’s rate cap transition period, certain percentages of electric energy sold to Pennsylvania retail electric customers shall be generated from certain alternative energy resources as measured in AECs. The requirement for electric energy that must come from Tier I alternative energy resources ranges from approximately 3.5% to 8% , and the requirement for Tier II alternative energy resources ranges from 6.2% to 10% . The required compliance percentages incrementally increase each annual compliance period, which is from June 1 through May 31, until May 31, 2021. These Tier I and Tier II alternative energy resources include acceptable energy sources as set forth in Act 129 and the AEPS Act. PECO continues to procure alternative energy credits through full requirements contracts and its existing long-term solar contracts to meet the annual AEPS compliance requirements. All AEPS compliance costs are being recovered on a full and current basis from default service customers through the GSA. Pennsylvania Retail Electricity and Gas Markets (Exelon and PECO). Beginning in 2011, the PAPUC issued an order outlining the next steps in its investigation into the status of competition in Pennsylvania’s retail electricity market. The PAPUC found that the existing default service model presents substantial impediments to the development of a vibrant retail market in Pennsylvania and directed its Office of Competitive Markets Oversight to evaluate potential intermediate and long-term structural changes to the default service model. Through various orders, the PAPUC issued default electric service pricing for customers in PECO’s service territory. See Pennsylvania procurement proceedings discussed above for additional details. In early 2014, the extreme weather in PECO's service territory resulted in increased electricity commodity costs causing certain shopping customers to receive unexpectedly high utility bills. In response to a significant number of customer complaints throughout Pennsylvania, on April 3, 2014, the PAPUC unanimously voted to adopt two rulemaking orders to address the issue. The first rulemaking order requires electric generation suppliers to provide more consumer education regarding their contract. The second rulemaking order requires electric distribution companies to enable customers to switch suppliers within three business days (known as accelerated switching). The improved customer education and accelerated switching were to be in place within 30 days and six months of approval of the orders, respectively. The orders became final on June 14, 2014. On December 4, 2014, the PAPUC approved PECO’s implementation plan (known as Bill on Supplier Switch), allowing PECO to implement accelerated switching by the December 15, 2014 deadline. On September 12, 2013, the PAPUC issued an Order that initiated an investigation into Pennsylvania’s natural gas retail market, including the role of the existing default service model and opportunities for market enhancements. On December 18, 2014, the PAPUC issued a Final Order directing the Office of Competitive Market Oversight (OCMO) to continue its investigation, confirming that natural gas distribution companies should remain with the default service model for the time being and directing establishment of a working group to examine other competitive issues. The OCMO has established a working group to review operation of the natural gas retail market and to consider potential recommendations on competitive issues. Pennsylvania Act 11 of 2012 (Exelon and PECO). In February 2012, Act 11 was signed into law, which provided the PAPUC authority to approve the implementation of a distribution system improvement charge (DSIC) in rates designed to recover capital project costs incurred to repair, improve or replace utilities’ aging electric and natural gas distribution systems in Pennsylvania. Prior to recovering costs pursuant to a DSIC, the PAPUC's implementation order requires a utility to have a Long Term Infrastructure Improvement Plan (LTIIP) approved by the Commission, which outlines how the utility is planning to increase its investment for repairing, improving or replacing aging infrastructure. On May 7, 2015, the PAPUC approved PECO's modified natural gas LTIIP. In accordance with the approved LTIIP, PECO plans to spend $534 million through 2022 to further accelerate the replacement of existing gas mains and to relocate meters from indoors to outside in accordance with recent PAPUC rulemaking. In addition, on March 20, 2015, PECO filed a petition with the PAPUC for approval of its gas DSIC mechanism for recovery of gas LTIIP expenditures. On September 11, 2015, the PAPUC entered its Opinion and Order approving PECO’s petition for a gas DSIC. On March 27, 2015, PECO filed a petition with the PAPUC for approval of its proposed electric DSIC and LTIIP. In accordance with the LTIIP (System 2020 plan), PECO plans to spend $275 million over the next five years to modernize and storm-harden its electric distribution system, making it more weather resistant and less vulnerable to damage. The DSIC will allow PECO the opportunity to recover the costs, subject to certain criteria, incurred to repair, improve or replace its electric distribution property between rate cases. On October 22, 2015, the PAPUC entered its Opinion and Order approving PECO’s proposed petition for its electric LTIIP and DSIC. Maryland Regulatory

Mergers, Acquisitions and Dispo

Mergers, Acquisitions and Dispositions (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
Mergers, Acquisitions and Dispositions	Proposed Merger with Pepco Holdings, Inc. (Exelon) Description of Transaction On April 29, 2014, Exelon and Pepco Holdings, Inc. (PHI) signed an agreement and plan of merger (as subsequently amended and restated as of July 18, 2014, the Merger Agreement) to combine the two companies in an all cash transaction. The resulting company will retain the Exelon name. Under the Merger Agreement, PHI’s shareholders will receive $27.25 of cash in exchange for each share of PHI common stock. Based on the outstanding shares of PHI’s common stock as of December 31, 2015 , PHI shareholders would receive $6.9 billion in total cash. In addition, in connection with the Merger Agreement, Exelon entered into a subscription agreement under which it has purchased $180 million of a class of nonvoting, nonconvertible and nontransferable preferred securities of PHI. The preferred securities are included in Other non-current assets on Exelon’s Consolidated Balance Sheet. PHI has the right to redeem the preferred securities at its option for the purchase price paid plus accrued dividends, if any. On November 2, 2015, Exelon and PHI each filed a new Notification and Report Form with the DOJ under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 (HSR Act) due to the expiration of the original filing. The HSR Act waiting period expired on December 2, 2015, and the HSR Act no longer precludes completion of the merger. To date, the PHI stockholders, the Virginia State Corporation Commission, the New Jersey Board of Public Utilities (NJBPU), the Delaware Public Service Commission (DPSC), the Maryland Public Service Commission (MDPSC) and the FERC have approved the merger of PHI and Exelon. The Federal Communications Commission has also approved the transfer of certain PHI communications licenses. On February 11, 2015, the NJBPU approved the proposed merger and the previously filed settlement signed and filed by Exelon, PHI, Atlantic City Electric (ACE), NJBPU staff, and the Independent Energy Coalition. The settlement provides a package of benefits to ACE customers and the state of New Jersey. This package of benefits includes the establishment of customer rate credit programs, with an aggregate value of $62 million for ACE customers and energy efficiency programs that will provide savings for ACE customers of $15 million . The March 6, 2015, order by the NJBPU approving the merger required that the consummation of the merger must take place no later than November 1, 2015 unless otherwise extended by the Board. On October 15, 2015, the NJBPU extended the November 1, 2015 date to June 30, 2016. On February 13, 2015, Exelon and PHI announced that they had reached a settlement agreement in the proceeding before the DPSC to review the proposed merger. The settlement, which was amended on April 7, 2015, was signed and filed by Exelon, PHI, Delmarva Power & Light Company (DPL), the DPSC Staff, the Delaware Public Advocate, the Delaware Department of Natural Resources and Environmental Control, the Delaware Sustainable Energy Utility, the Mid-Atlantic Renewable Energy Coalition and the Clean Air Council. As part of this settlement, Exelon and PHI proposed a package of benefits to DPL customers and the state of Delaware including the establishment of customer rate credits of $40 million for DPL customers in Delaware, $2 million of funding for energy efficiency programs for DPL low income customers, and $2 million of funding for workforce development. On June 2, 2015, the DPSC issued an order accepting the settlement and approving the merger between Exelon and PHI. On March 17, 2015, Exelon and PHI announced that they had reached settlements with multiple parties in the Maryland proceeding to review the proposed merger after filing a Request for Adoption of Settlements with the MDPSC. The settlements were signed and filed by Exelon, PHI, Montgomery County, Prince George’s County, the National Consumer Law Center, National Housing Trust, the Maryland Affordable Housing Coalition, the Housing Association of Nonprofit Developers, and a consortium of recreational trail advocacy organizations led by the Mid-Atlantic Off-Road Enthusiasts. Exelon and PHI also announced a settlement with The Alliance for Solar Choice. On May 15, 2015, the MDPSC approved the merger after modifying a number of the conditions in the settlements, resulting in total rate credits of $66 million , funding for energy efficiency programs of $43.2 million , a Green Sustainability Fund of $14.4 million , 20 MWs of renewable generation development and increased penalties related to reliability commitments. On May 18, 2015, Exelon and PHI accepted and committed to fulfill the conditions. On June 11, 2015, the Maryland Office of People’s Counsel (OPC), the Sierra Club, and the Chesapeake Climate Action Network filed Petitions for Judicial Review of the MDPSC’s approval of the merger with the Circuit Court for Queen Anne’s County. On June 23, 2015, Public Citizen, Inc. filed its Petition for Judicial Review with the Circuit Court for Queen Anne’s County. On July 10, 2015, Exelon and PHI filed a response in opposition to the Petitions for Review. On July 21, 2015, the OPC filed a motion to stay the MDPSC order approving the merger and to set a schedule for discovery and presentation of new evidence. On July 29, 2015, Public Citizen, Inc. filed a response supporting OPC’s motion to stay, and on July 31, 2015 the Sierra Club and the Chesapeake Climate Action Network filed a joint motion to stay. In July and August, Exelon, PHI, the MDPSC, Prince George’s County and Montgomery County filed responses opposing the motions to stay. The judge issued an order denying the motions for stay on August 12, 2015. On January 8, 2016, the Circuit Court judge affirmed the MDPSC’s order approving the merger and denied the petitions for judicial review filed by the OPC, the Sierra Club, the Chesapeake Climate Action Network (CCAN) and Public Citizen, Inc. On January 19, 2016, the OPC filed a notice of appeal to the Maryland Court of Special appeals, and on January 21, Sierra Club and CCAN filed a notice of appeal. In the ordinary course this appeal would be resolved no earlier than third quarter 2016. On August 27, 2015, the District of Columbia Public Service Commission (DCPSC) issued an Opinion and Order denying approval of the merger, concluding that the merger as presented was not in the public interest. Exelon and PHI filed an Application for Reconsideration with the DCPSC on September 28, 2015. On October 6, 2015, Exelon, PHI, the District of Columbia Government, the Office of Peoples Counsel, the District of Columbia Water and Sewer Authority, the National Consumer Law Center, National Housing Trust and National Housing Trust - Enterprise Preservation Corporation, and the Apartment and Office Building Association of Metropolitan Washington (collectively, Settling Parties) entered into a Nonunanimous Full Settlement Agreement and Stipulation (Settlement Agreement) with respect to the merger. Exelon and PHI subsequently filed a motion of joint applicants requesting the DCPSC to reopen the approval application to allow for consideration of the Settlement Agreement and granting additional requested relief. The new package of benefits totals $78 million and includes commitments to provide relief of residential customer base rate increases of $26 million , one-time direct bill credits of $14 million , low-income energy assistance of $16 million , improved reliability, a cleaner and greener D.C. through funding energy efficiency programs and development of renewable energy, and investment in local jobs and the local economy through workforce development of $5 million . It also guarantees charitable contributions totaling $19 million over 10 years. On October 28, 2015, the DCPSC agreed to reopen the approval application to allow for consideration of the Settlement Agreement. Since then, parties supporting and opposing the Settlement filed testimony, participated in formal hearings and, on December 23, 2015, submitted final briefs to the DCPSC. The parties now await a formal decision from the DCPSC. The Merger Agreement provides that either Exelon or PHI may terminate the Merger Agreement if the merger is not completed by October 28, 2015. Pursuant to a Letter Agreement related to the Settlement Agreement, Exelon and PHI have agreed, among other things, that they will not exercise their rights to terminate the Merger Agreement before March 4, 2016, except under limited circumstances. If the DCPSC does not approve the Settlement Agreement by March 4, 2016, either Exelon or PHI may terminate the Settlement Agreement. The settlements reached and commission orders received to date in Delaware, Maryland and New Jersey include a “most favored nation” provision which, generally speaking, requires allocation of merger benefits proportionately across all the jurisdictions. When applying the most favored nation provision to the settlement terms and other conditions established in the merger approvals received to date, and as proposed in the Settlement Agreement filed with the DCPSC, Exelon and PHI currently estimate direct benefits of $430 million or more on a net present value basis (excluding charitable contributions and renewable generation commitments) will be provided, including rate credits, funding for energy efficiency programs and other required commitments. Exelon and PHI anticipate substantially all of such amounts will be charged to earnings at the time of merger close and will be paid by the end of 2017. An additional $53 million will be charged to earnings at the time of the merger close for charitable contributions, which are then required to be paid over a period of 10 years. Commitments to develop renewable generation, which are expected to be primarily capital in nature, will be recognized as incurred. Upon completion of the merger, the actual nature, amount, timing and financial reporting treatment for these commitments may be materially different from the current projection. Exelon has been named in suits filed in the Delaware Chancery Court alleging that individual directors of PHI breached their fiduciary duties by entering into the proposed merger transaction and Exelon aided and abetted the individual directors’ breaches. The suits seek to enjoin PHI from completing the merger or seek rescission of the merger if completed. In addition, they also seek unspecified damages and costs. Exelon was also named in a federal court suit making similar claims. In September 2014, the parties reached a proposed settlement that would resolve all claims, which is subject to court approval. Final court approval of the proposed settlement is not anticipated until approximately 90 days after merger close. Exelon does not believe these suits will impact the completion of the transaction, and they are not expected to have a material impact on Exelon’s results of operations. Including 2014 and through December 31, 2015 , Exelon has incurred approximately $259 million of expense associated with the proposed merger. Of the total costs incurred, $121 million is primarily related to acquisition and integration costs and $138 million are for costs incurred to finance the transaction. The financing costs include $22 million of costs associated with the private exchange offer and redemption of certain Senior Unsecured Notes (see Note 14 — Debt and Credit Agreements for further information on the exchange), as well as, a net loss of $64 million related to the settlement of forward-starting interest-rate swaps. These swaps were terminated in connection with the $4.2 billion issuance of debt; refer to Note 13 — Derivative Financial Instruments for more information. The financing costs exclude costs to issue equity and the initial debt offering which we recorded to Exelon's Consolidated Balance Sheets. For the year ended, Acquisition, Integration and Financing Costs (a) 2015 2014 Exelon $ 80 $ 179 Generation 25 11 ComEd 10 4 PECO 5 2 BGE 5 2 ___________ (a) The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statement of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. Under certain circumstances, if the Merger Agreement is terminated, PHI may be required to pay Exelon a termination fee ranging from $259 million to $293 million plus certain expenses. If the Merger Agreement is terminated due to a failure to obtain a required regulatory approval, Exelon may be required to pay PHI a termination fee equal to $180 million through the redemption by PHI of the outstanding nonvoting preferred securities described above for no consideration other than the nominal par value of the stock, plus reimbursement of PHI's documented out-of-pocket expenses up to a maximum of $40 million . Merger Financing Exelon has raised cash to fund the all-cash purchase price, acquisition and integration related costs, and merger commitments, through the issuance of $4.2 billion of debt (of which $3.3 billion remains after execution of the exchange offer, see Note 14 — Debt and Credit Agreements for further information on the exchange), $1.15 billion of junior subordinated notes in the form of 23 million equity units, the issuance of $1.9 billion of common stock, cash proceeds of $1.8 billion from asset sales primarily at Generation (after-tax proceeds of approximately $1.4 billion ) and the remaining balance from cash on hand and/or short-term borrowings available to Exelon. Exelon will have sufficient cash to fund the all-cash purchase price, acquisition and integration related costs, and merger commitments. See Note 14 — Debt and Credit Agreements and Note 19 — Shareholder's Equity for further information on the debt and equity issuances. Acquisitions (Exelon and Generation) Acquisition of Integrys Energy Services, Inc. (Exelon and Generation) On November 1, 2014, Generation acquired the competitive retail electric and natural gas business activities of Integrys Energy Group, Inc. through the purchase of all of the stock of its wholly owned subsidiary, Integrys Energy Services, Inc. (IES) for a purchase price of $332 million , including net working capital. Generation has elected to account for the transaction as an asset acquisition for federal income tax purposes. The generation and solar asset businesses of Integrys are excluded from the transaction. The Purchase Agreement also includes various representations, warranties, covenants, indemnification and other provisions customary for a transaction of this nature. Consistent with the applicable accounting guidance, the fair value of the assets acquired and liabilities assumed was determined as of the acquisition date through the use of significant estimates and assumptions that are judgmental in nature. Some of the more significant estimates and assumptions used include: projected future cash flows (including the amount and timing); discount rates reflecting the risk inherent in the future cash flows; and future power and fuel market prices. The following table summarizes the acquisition-date fair value of the consideration transferred and the assets and liabilities assumed for the Integrys acquisition by Generation: Total consideration transferred $ 332 Identifiable assets acquired and liabilities assumed Working capital assets $ 390 Mark-to-market derivative assets 184 Unamortized energy contract assets 115 Customer relationships 50 Working capital liabilities (196 ) Mark-to-market derivative liabilities (57 ) Unamortized energy contract liabilities (110 ) Deferred tax liability (16 ) Total net identifiable assets, at fair value $ 360 Bargain purchase gain (after-tax) $ 28 The after-tax bargain purchase gain of $28 million is primarily the result of IES executing additional contract volumes between the date the acquisition agreement was signed and the closing of the transaction resulting in an increase in the fair value of the net assets acquired as of the acquisition date. The after-tax gain is included within Gain on consolidation and acquisition of businesses in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. IES's operating revenues and net loss included in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income for the period from November 1, 2014 to December 31, 2014 were $386 million and $(42) million , respectively. The net loss for the period from November 1, 2014 to December 31, 2014 includes pre-tax unrealized losses on derivative contracts of $108 million and the bargain purchase gain of $28 million . It is impracticable to determine the overall financial statement impact of IES for 2015 due to the integration of the business into ongoing operations. For the years ended December 31, 2015 and 2014 , Exelon and Generation incurred $5 million and $7 million , respectively, of merger and integration related costs which are included within Operating and maintenance expense in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. Asset Divestitures (Exelon and Generation) Including the Quail Run generating facility that was sold on January 21, 2015, Generation has sold certain generating assets with a total net book value of approximately $1.8 billion prior to consideration of asset impairments (See Note 8 — Impairment of Long-Lived Assets for further information), for total pre-tax proceeds of approximately $1.8 billion (after-tax proceeds of approximately $1.4 billion ) , which resulted in cumulative pre-tax gains on sale of approximately $412 million , which are included in Gain (loss) on sales of assets on Exelon's and Generation's Consolidated Statement of Operations and Comprehensive Income for the year ended December 31, 2014. The proceeds are expected to be used primarily to finance a portion of the merger with PHI. Station Net Generation Capacity Location Operating Segment Percent Owned Fore River 726 MW North Weymouth, MA New England 100 % West Valley 185 MW Salt Lake City, UT Other 100 % Keystone 714 MW Shelocta, PA Mid-Atlantic 41.98 % Conemaugh 532 MW New Florence, PA Mid-Atlantic 31.28 % Safe Harbor 278 MW Conestoga, PA Mid-Atlantic 66.7 % Quail Run 488 MW Odessa, TX ERCOT 100 % At December 31, 2014, the assets and liabilities of the Quail Run generating facility were reported as Assets held for sale and within Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets. The table below presents the major classes of assets and liabilities held for sale at December 31, 2014. Assets held for sale at December 31, 2015 are not material. December 31, 2014 Assets Property, plant and equipment, net (a) $ 143 Inventory 4 Total assets held for sale $ 147 Liabilities Accrued expenses $ 1 Asset retirement obligations 4 Total liabilities held for sale (b) $ 5 _____________ (a) The total aggregate book value of property, plant and equipment is net of a $50 million pre-tax impairment loss recorded within Operating and maintenance expense on Exelon’s and Generation’s Statements of Operations and Comprehensive Income for the year ended December 31, 2014. See Note 8 — Impairment of Long-Lived Assets for further information. (b) Included within Other current liabilities on Exelon's and Generation's Consolidated Balance Sheets.

Investment in Constellation Ene

Investment in Constellation Energy Nuclear Group, LLC (Exelon and Generation)	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
Investment in Constellation Energy Nuclear Group LLC (Exelon and Generation)	(Exelon and Generation) Generation owns a 50.01% interest in CENG, a nuclear generation business. Generation has historically had various agreements with CENG to purchase power and to provide certain services. For further information regarding these agreements, see Note 26 — Related Party Transactions . On April 1, 2014, Generation and subsidiaries of Generation and CENG entered into a Nuclear Operating Services Agreement (NOSA) pursuant to which Generation will operate the CENG nuclear generation fleet owned by CENG subsidiaries and provide corporate and administrative services for the remaining life of the CENG nuclear plants as if they were a part of the Generation nuclear fleet, subject to EDF’s rights as a member of CENG (the Integration Transaction). CENG will reimburse Generation for its direct and allocated costs for such services. As part of the arrangement, Nine Mile Point Nuclear Station, LLC, a subsidiary of CENG, also assigned to Generation its obligations as Operator of Nine Mile Point Unit 2 under an operating agreement with Long Island Power Authority, the Unit 2 co-owner. In addition, on April 1, 2014, the Power Services Agency Agreement (PSAA) was amended and extended until the permanent cessation of power generation by the CENG generation plants. In addition, on April 1, 2014, Generation made a $ 400 million loan to CENG, bearing interest at 5.25% per annum and payable out of specified available cash flows of CENG or payable upon the maturity date of April 1, 2034. Immediately following receipt of the proceeds of such loan, CENG made a $ 400 million special distribution to EDF. Unpaid principal and accrued interest on the loan was $300 million as of December 31, 2015 . Exelon, Generation, and subsidiaries of Generation, EDF and CENG also executed a Fourth Amended and Restated Operating Agreement for CENG on April 1, 2014, pursuant to which, among other things, CENG committed to make preferred distributions to Generation (after repayment of the $ 400 million loan and associated interest) quarterly out of specified available cash flows until Generation has received aggregate distributions of $ 400 million plus a return of 8.5% per annum from April 1, 2014 (Preferred Distribution Rights). Generation and EDF also entered into a Put Option Agreement on April 1, 2014, pursuant to which EDF has the option, exercisable beginning on January 1, 2016 and thereafter until June 30, 2022, to sell its 49.99% interest in CENG to Generation for a fair market value price determined by agreement of the parties, or absent agreement, a third-party arbitration process. The appraisers determining fair market value of EDF’s 49.99% interest in CENG under the Put Option Agreement are instructed to take into account all rights and obligations under the CENG Operating Agreement, including Generation’s rights with respect to any unpaid aggregate preferred distributions and the related return, and the value of Generation’s rights to other distributions. Under limited circumstances, the period for exercise of the put option may be extended for 18 months. In order to exercise its option, EDF must give 60 days advance written notice to Generation stating that it is exercising its option. As of the date these financial statements were issued, EDF has not given notice to Generation that it is exercising its option. On April 1, 2014, Generation also executed an Indemnity Agreement pursuant to which Generation indemnified EDF against third-party claims that may arise from any future nuclear incident (as defined in the Price Anderson Act) in connection with the CENG nuclear plants or their operations. Exelon guarantees Generation’s obligations under this indemnity. In addition, on April 1, 2014, Generation, EDF, CENG and Nine Mile Point Nuclear Station, LLC entered into an Employee Matters Agreement (EMA) that provides for the transfer of CENG employees to Exelon or one of its affiliates and Exelon's assumption of the sponsorship of the employee benefit plans (including certain incentive, health and welfare, and postemployment benefit plans, among others) and their related trusts by Exelon as the plan sponsor as of July 14, 2014. The EMA also generally requires CENG to fund the obligation related to pre-transfer service of employees, including the underfunded balance of the pension and other postretirement welfare benefit plans measured as of July 14, 2014 by making periodic payments to Generation. These payments will be made on an agreed payment schedule or upon the occurrence of certain specified events, such as EDF’s disposition of a majority of its interest in CENG. However, in the event that EDF exercises its rights under the Put Option, all payments not made as of the put closing date shall accelerate to be paid immediately prior to such closing date. As a condition to obtaining regulatory approval for the NOSA and related transactions from the NRC, Exelon executed a support agreement pursuant to which Exelon may be required under specified circumstances to provide up to $ 245 million of financial support to CENG (Exelon Support Agreement). The Exelon Support Agreement supersedes a previous support agreement under which Generation had agreed to provide up to $ 205 million of financial support for CENG. In addition, Exelon executed a Guarantee pursuant to which Exelon may be required under specified circumstances to provide up to $ 165 million in additional financial support for CENG. A previous support agreement executed by an affiliate of EDF remains in effect under which the EDF affiliate may be required to provide up to approximately $ 145 million of financial support for CENG under specified circumstances. The agreements were executed on April 1, 2014 when the NRC licenses were transferred to Generation. No liability has been recognized by Exelon for the guarantees. Prior to April 1, 2014, Exelon and Generation accounted for their investment in CENG under the equity method of accounting. From January 1, 2014, through March 31, 2014, Generation recorded $ 19 million of equity in losses of unconsolidated affiliates related to its investment in CENG and recorded $ 17 million of revenues from CENG. For the twelve months ended December 31, 2013, Generation recorded $ 9 million of equity in losses of unconsolidated affiliates related to its investment in CENG and $ 56 million of revenues from CENG. The book value of Generation’s investment in CENG prior to the consolidation was $ 1.9 billion , and the book value of the AOCI related to CENG prior to consolidation was $ 116 million , net of taxes of $ 77 million . As a result of the consolidation of CENG on April 1, 2014, there are several additional transactions included in Exelon’s and Generation’s Consolidated Financial Statements between CENG and Exelon's affiliates that are considered related party transactions to Generation. As further described in Note 26 — Related Party Transactions , EDF and Generation had a PPA with CENG under which they purchased 15% and 85% , respectively, of the nuclear output owned by CENG that was not sold to third parties under pre-existing PPAs through December 31, 2014. Beginning January 1, 2015 and continuing through the life of the respective plants, EDF and Generation purchase 49.99% and 50.01% , respectively, of the nuclear output owned by CENG not subject to other contractual agreements. Beginning April 1, 2014, CENG's sales to Generation have been eliminated in consolidation. For the years ended December 31, 2015 and 2014 , Generation had sales to EDF of $488 million and $137 million , respectively. See discussion above and Note 2 — Variable Interest Entities for additional information regarding other transactions between CENG and EDF included within Exelon and Generation’s consolidated financial statements and for additional information about the Registrants VIE's. Accounting for the Consolidation of CENG The transfer of the nuclear operating licenses and the execution of the NOSA on April 1, 2014, resulted in the derecognition of the equity method investment in CENG and the recording of all assets, liabilities and EDF’s noncontrolling interest in CENG at fair value on Exelon’s and Generation’s Consolidated Balance Sheets. As a result of the consolidation, Exelon and Generation recorded a net gain of $261 million within their respective Consolidated Statements of Operations and Comprehensive Income. This gain consists of approximately $136 million related to the step up to fair value basis of Generation's ownership interest in CENG, and approximately $132 million related to the settlement of pre-existing transactions between CENG and Generation. The net gain on the consolidation of CENG of $261 million is net of a $7 million payment to EDF. The fair value of CENG’s assets and liabilities recorded in consolidation was determined based on significant estimates and assumptions that are judgmental in nature, including projected future cash flows (including timing); discount rates reflecting risk inherent in the future cash flows; and future market prices. There were also judgments made to determine the expected useful lives assigned to each class of assets acquired and duration of liabilities assumed. The valuations necessary to assess the fair values of certain assets and liabilities were considered preliminary as a result of the short time period between the execution of the NOSA and the end of the second quarter of 2014. The estimates of the fair value of assets and liabilities could be modified for up to one year from April 1, 2014, as more information was obtained about the fair value of assets and liabilities. The principal items that have been revised include the asset retirement obligation liabilities and related asset retirement costs. These items have been updated with inputs from a third party engineering firm with corresponding adjustments recorded in 2014 and the first quarter of 2015. See Note 16 — Asset Retirement Obligations for discussion of the impacts of adjustments recorded during 2014 and 2015 related to updated estimates of the CENG asset retirement obligation liabilities. In the period of such revisions, these and any other material changes to the fair value assessments have resulted in adjustments to the amounts recorded upon consolidation. In addition, the asset or liability adjustments impacting depreciation and/or accretion expense recorded after the consolidation date have impacted Generation’s post-consolidation results of operations. Generation recorded the assets and liabilities of CENG at fair value as of April 1, 2014. The following assets and liabilities of CENG were recorded within Generation’s Consolidated Balance Sheets as of the date of integration, adjusted for the modifications discussed above: Fair Values Exelon and Generation Current assets $ 499 Nuclear decommissioning trust fund 1,955 Property, plant and equipment 3,073 Nuclear fuel 482 Other assets 10 Total assets 6,019 Current liabilities 237 Asset retirement obligation 1,816 Pension and other employee benefit obligations 281 Unamortized energy contract liabilities 171 Other liabilities 114 Total liabilities 2,619 Total net assets $ 3,400 Generation also recorded the fair value of the noncontrolling interest on its Consolidated Balance Sheets of approximately $ 1.5 billion , net of the fair value of $ 152 million for certain specified additional distribution rights under the Operating Agreement. In addition, the noncontrolling interest was further reduced by the $ 400 million special cash distribution to EDF. Due to the Preferred Distribution Rights that Generation has on CENG’s available cash, the earnings attributable to the noncontrolling interest on the Statements of Operations and Comprehensive Income as well as the corresponding adjustment to Noncontrolling interest on the Consolidated Balance Sheets will not be in proportion to Generation’s and EDF’s equity ownership interests. Rather, the attribution will consider Generation’s Preferred Distribution Rights and allocate net income based on each owner’s rights to CENG’s net assets. For the years ended December 31, 2015 and 2014 , Generation reduced by $18 million and $13 million , respectively, the amount of Net income attributable to noncontrolling interests on Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. As a result of the consolidation, Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income includes CENG’s incremental operating revenues of $509 million and $218 million and CENG’s net income (loss), prior to any intercompany eliminations and any adjustments for noncontrolling interest, of $(11) million and $407 million during the years ended December 31, 2015 and 2014 , respectively. Exelon and Generation incurred integration-related costs of $2 million and $26 million for the year ended December 31, 2015 and 2014 , respectively. The costs incurred are classified primarily within Operating and maintenance expense in Exelon’s and Generation’s respective Consolidated Statements of Operations and Comprehensive Income.

Accounts Receivable (Exelon, Ge

Accounts Receivable (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Receivables [Abstract]
Accounts Receivable (Exelon, Generation, ComEd, PECO and BGE)	(Exelon, Generation, ComEd, PECO and BGE) Accounts receivable at December 31, 2015 and 2014 included estimated unbilled revenues, representing an estimate for the unbilled amount of energy or services provided to customers, and is net of an allowance for uncollectible accounts as follows: 2015 Exelon Generation ComEd PECO BGE Unbilled customer revenues $ 1,203 $ 732 (a) $ 218 $ 105 $ 148 Allowance for uncollectible accounts (b) (284 ) (77 ) (75 ) (83 ) (c) (49 ) 2014 Exelon Generation ComEd PECO BGE Unbilled customer revenues $ 1,381 $ 823 (a) $ 204 $ 140 $ 214 Allowance for uncollectible accounts (b) (311 ) (60 ) (84 ) (100 ) (c) (67 ) (d) _________________________ (a) Represents unbilled portion of retail receivables estimated under Exelon’s unbilled critical accounting policy. (b) Includes the allowance for uncollectible accounts on customer and other accounts receivable. (c) Excludes the non-current allowance for uncollectible accounts of $8 million at both December 31, 2015 and 2014 , related to PECO’s current installment plan receivables described below. (d) At December 31, 2014 , as explained in Note 1 — Significant Accounting Policies , BGE estimated the allowance for uncollectible accounts on customer receivables by applying loss rates to the outstanding receivable balance by risk segment. The change in estimate resulted in a $19 million pre-tax charge to BGE's provision for uncollectible accounts expense for the year ended December 31, 2014 , which is included in Operating and maintenance expense on BGE's Consolidated Statements of Operations and Comprehensive Income. PECO Installment Plan Receivables (Exelon and PECO). PECO enters into payment agreements with certain delinquent customers, primarily residential, seeking to restore their service, as required by the PAPUC. Customers with past due balances that meet certain income criteria are provided the option to enter into an installment payment plan, some of which have terms greater than one year, to repay past due balances in addition to paying for their ongoing service on a current basis. The receivable balance for these payment agreement receivables is recorded in accounts receivable for the current portion and other deferred debits and other assets for the noncurrent portion. The net receivable balance for installment plans with terms greater than one year was $15 million at both December 31, 2015 and 2014 . The allowance for uncollectible accounts reserve methodology and assessment of the credit quality of the installment plan receivables are consistent with the customer accounts receivable methodology discussed in Note 1 — Significant Accounting Policies . The allowance for uncollectible accounts balance associated with these receivables at December 31, 2015 and December 31, 2014 of $15 million consists of $1 million , $3 million and $11 million for low risk, medium risk and high risk segments, respectively. The balance of the payment agreement is billed to the customer in equal monthly installments over the term of the agreement. Installment receivables outstanding as of December 31, 2015 and 2014 include balances not yet presented on the customer bill, accounts currently billed and an immaterial amount of past due receivables. When a customer defaults on its payment agreement, the terms of which are defined by plan type, the entire balance of the agreement becomes due and the balance is reclassified to current customer accounts receivable and reserved for in accordance with the methodology discussed in Note 1 — Significant Accounting Policies .

Property, Plant and Equipment (

Property, Plant and Equipment (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment (Exelon, Generation, ComEd, PECO and BGE)	Property, Plant and Equipment (Exelon, Generation, ComEd, PECO and BGE) Exelon The following table presents a summary of property, plant and equipment by asset category as of December 31, 2015 and 2014 : Average Service Life (years) 2015 2014 Asset Category Electric—transmission and distribution 5-90 $ 32,546 $ 30,157 Electric—generation 1-56 25,615 22,911 Gas—transportation and distribution 5-90 3,864 3,505 Common—electric and gas 5-50 1,149 1,169 Nuclear fuel (a) 1-8 6,384 5,947 Construction work in progress N/A 3,075 2,167 Other property, plant and equipment (b) 5-50 1,181 1,056 Total property, plant and equipment 73,814 66,912 Less: accumulated depreciation (c) 16,375 14,742 Property, plant and equipment, net $ 57,439 $ 52,170 _________________________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,266 million and $1,003 million at December 31, 2015 and 2014 , respectively. (b) Includes Generation’s buildings under capital lease with a net carrying value of $13 million and $15 million at December 31, 2015 and 2014 , respectively. The original cost basis of the buildings was $52 million , and total accumulated amortization was $39 million and $37 million , as of December 31, 2015 and 2014 , respectively. Also includes ComEd’s buildings under capital lease with a net carrying value at December 31, 2015 and 2014 , of $7 million and $8 million , respectively. The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million and $0.3 million as of December 31, 2015 and 2014 , respectively. Includes land held for future use and non utility property at ComEd, PECO, and BGE of $57 million , $21 million , and $32 million , respectively. These balances also include capitalized acquisition, development and exploration costs of $266 million and $242 million related to oil and gas production activities at Generation at December 31, 2015 and 2014 , respectively. Includes the original cost and progress payments associated with Generation’s turbine equipment held for future use with a carrying value of $146 million and $83 million at December 31, 2015 and 2014, respectively. (c) Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $2,861 million and $2,673 million as of December 31, 2015 and 2014 , respectively. The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2015 2014 2013 Electric—transmission and distribution 2.83 % 2.93 % 2.91 % Electric—generation 3.47 % 3.50 % 3.35 % Gas 2.17 % 2.13 % 2.06 % Common—electric and gas 7.79 % 7.32 % 7.53 % Generation The following table presents a summary of property, plant and equipment by asset category as of December 31, 2015 and 2014 : Average Service Life (years) 2015 2014 Asset Category Electric—generation 1-56 $ 25,615 19,004,000,000 $ 22,911 Nuclear fuel (a) 1-8 6,384 4,815,000,000 5,947 Construction work in progress N/A 2,017 1,352,000,000 1,404 Other property, plant and equipment (b) 5-31 466 374,000,000 378 Total property, plant and equipment 34,482 30,640 Less: accumulated depreciation (c) 8,639 7,612 Property, plant and equipment, net $ 25,843 $ 23,028 _________________________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,266 million and $1,003 million at December 31, 2015 and 2014 , respectively. (b) Includes buildings under capital lease with a net carrying value of $13 million and $15 million at December 31, 2015 and 2014 , respectively. The original cost basis of the buildings was $52 million , and total accumulated amortization was $39 million and $37 million , as of December 31, 2015 and 2014 , respectively. These balances also include capitalized acquisition, development and exploration costs of $266 million and $242 million related to oil and gas production activities at Generation at December 31, 2015 and 2014 , respectively. Includes the original cost and progress payments associated with Generation’s turbine equipment held for future use with a carrying value of $146 million and $83 million at December 31, 2015 and 2014, respectively. (c) Includes accumulated amortization of nuclear fuel in the reactor core of $2,861 million and $2,673 million as of December 31, 2015 and 2014 , respectively. The annual depreciation provisions as a percentage of average service life for electric generation assets were 3.47% , 3.50% and 3.35% for the years ended December 31, 2015 , 2014 and 2013 , respectively. License Renewals. Generation’s depreciation provisions are based on the estimated useful lives of its generating stations, which assume the renewal of the licenses for all nuclear generating stations (except for Oyster Creek) and the hydroelectric generating stations. As a result, the receipt of license renewals has no material impact on the Consolidated Statements of Operations and Comprehensive Income. See Note 3—Regulatory Matters for additional information regarding license renewals. ComEd The following table presents a summary of property, plant and equipment by asset category as of December 31, 2015 and 2014 : Average Service Life (years) 2015 2014 Asset Category Electric—transmission and distribution 5-80 $ 20,576 $ 18,884 Construction work in progress N/A 572 276 Other property, plant and equipment (a), (b) 38-50 64 65 Total property, plant and equipment 21,212 19,225 Less: accumulated depreciation 3,710 3,432 Property, plant and equipment, net $ 17,502 $ 15,793 _________________________ (a) Includes buildings under capital lease with a net carrying value at December 31, 2015 and 2014 of $7 million and $8 million , respectively. The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million and $0.3 million as of December 31, 2015 and 2014 , respectively. (b) Includes land held for future use and non-utility property. The annual depreciation provisions as a percentage of average service life for electric transmission and distribution assets were 3.03% , 3.05% and 2.97% for the years ended December 31, 2015 , 2014 and 2013 , respectively. PECO The following table presents a summary of property, plant and equipment by asset category as of December 31, 2015 and 2014 : Average Service Life (years) 2015 2014 Asset Category Electric—transmission and distribution 5-65 $ 7,230 $ 6,886 Gas—transportation and distribution 5-70 2,206 2,039 Common—electric and gas 5-50 631 618 Construction work in progress N/A 154 154 Other property, plant and equipment (a) 50 21 21 Total property, plant and equipment 10,242 9,718 Less: accumulated depreciation 3,101 2,917 Property, plant and equipment, net $ 7,141 $ 6,801 _________________________ (a) Represents land held for future use and non-utility property. The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2015 2014 2013 Electric—transmission and distribution 2.39 % 2.55 % 2.73 % Gas 1.87 % 1.84 % 1.79 % Common—electric and gas 5.16 % 5.16 % 6.65 % BGE The following table presents a summary of property, plant and equipment by asset category as of December 31, 2015 and 2014 : Average Service Life (years) 2015 2014 Asset Category Electric—transmission and distribution 5-90 $ 6,663 $ 6,339 Gas—distribution 5-90 1,951 1,761 Common—electric and gas 5-40 655 623 Construction work in progress N/A 312 317 Other property, plant and equipment (a) 20 32 32 Total property, plant and equipment 9,613 9,072 Less: accumulated depreciation 3,016 2,868 Property, plant and equipment, net $ 6,597 $ 6,204 _______________________ (a) Represents land held for future use and non-utility property. Average Service Life Percentage by Asset Category 2015 2014 2013 Electric—transmission and distribution 2.62 % 2.96 % 2.91 % Gas 2.50 % 2.47 % 2.36 % Common—electric and gas 10.35 % 9.49 % 8.45 % See Note 1 — Significant Accounting Policies for further information regarding property, plant and equipment policies and accounting for capitalized software costs for Exelon, Generation, ComEd, PECO and BGE. See Note 14 — Debt and Credit Agreements for further information regarding Exelon’s, ComEd’s, and PECO’s property, plant and equipment subject to mortgage liens.

Impairment of Long-lived Assets

Impairment of Long-lived Assets (Exelon and Generation)	12 Months Ended
	Dec. 31, 2015
Impairment or Disposal of Tangible Assets Disclosure [Abstract]
Impairment Of Long-Lived Assets (Exelon and Generation)	(Exelon and Generation) Long-Lived Assets (Exelon and Generation) Generation evaluates long-lived assets for recoverability whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. In the second quarter of each year, Generation updates the long-term fundamental energy prices, which includes a thorough evaluation of key assumptions including gas prices, load growth, environmental policy, plant retirements and renewable growth. In 2015, the year over year change in fundamentals did not indicate any impairments. In 2014, the year over year change in fundamentals suggested that the carrying value of certain merchant wind assets may be impaired. Generation concluded that the estimated undiscounted future cash flows and fair value of twelve wind projects, primarily located in West Texas, were less than their respective carrying values at May 31, 2014. As a result, long-lived assets held and used with a carrying amount of approximately $ 151 million were written down to their fair value of $ 65 million and a pre-tax impairment charge of $ 86 million was recorded within Operating and maintenance expense in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. In 2013, lower projected wind production and a decline in power prices suggested that the carrying value of certain wind projects with market price exposure for either all or a portion of the life of the asset may be impaired. Generation concluded that the estimated undiscounted future cash flows and fair value of eleven wind projects, primarily located in West Texas and Minnesota, were less than their respective carrying values at September 30, 2013. As a result, long-lived assets held and used with a carrying amount of approximately $ 75 million were written down to their fair value of $ 32 million and a pre-tax impairment charge of $ 43 million , net of the impairment amount attributable to noncontrolling interests for certain of the projects, was recorded within Operating and maintenance expense in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. During 2015 and 2014, significant declines in oil and gas prices suggested that the carrying value of certain Upstream assets may be impaired. Generation concluded that the estimated undiscounted future cash flows and fair value of various Upstream properties, primarily located in Oklahoma and Texas, were less than their respective carrying values at December 31, 2015 and 2014 . As a result, pre-tax impairment charges of $5 million and $124 million were recorded for the years ended December 31, 2015 and 2014 , respectively, within Operating and maintenance expense within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. After reflecting the impairment charges, Generation has $187 million of Upstream assets remaining on its Consolidated Balance Sheets at December 31, 2015 . Further declines in commodity prices could potentially result in future impairments of the Upstream assets. The fair value analysis used in the above impairments was primarily based on the income approach using significant unobservable inputs (Level 3) including revenue, generation and production forecasts, projected capital and maintenance expenditures and discount rates. Changes in the assumptions described above could potentially result in future impairments of Exelon’s long-lived assets, which could be material. In 2014, certain non-nuclear generating assets were identified as assets held for sale on Exelon's and Generation's Consolidated Balance Sheets. When long-lived assets are held for sale, an impairment loss is recognized to the extent that the asset's carrying value exceeds its estimated fair value less costs to sell. Long-lived assets with a carrying amount of approximately $1 billion were written down to their fair value of $556 million and a pre-tax impairment charge of $450 million was recorded within Operating and maintenance expense on Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. See Note 4 — Mergers, Acquisitions, and Dispositions for further informati on on asset sales. Nuclear Uprate Program (Exelon and Generation) Generation is engaged in individual projects as part of a planned power uprate program across its nuclear fleet. When economically viable, the projects take advantage of new production and measurement technologies, new materials and application of expertise gained from a half-century of nuclear power operations. Based on ongoing reviews, the nuclear uprate implementation plan was adjusted during 2013 to cancel certain projects. The Measurement Uncertainty Recapture (MUR) uprate projects at the Dresden and Quad Cities nuclear stations were cancelled as a result of the cost of additional plant modifications identified during final design work which, when combined with then current market conditions, made the projects not economically viable. Additionally, the market conditions prompted Generation to cancel the previously deferred extended power uprate projects at the LaSalle and Limerick nuclear stations. During 2013, Exelon and Generation recorded a pre-tax charge to Operating and maintenance expense and Interest expense within their Statements of Operations and Comprehensive Income of approximately $ 111 million and $ 8 million , respectively, to accrue remaining costs and reverse the previously capitalized costs. Like-Kind Exchange Transaction (Exelon) Prior to the PECO/Unicom Merger in October 2000, UII, LLC (formerly Unicom Investments, Inc.) (UII), a wholly owned subsidiary of Exelon, entered into a like-kind exchange transaction pursuant to which approximately $ 1.6 billion was invested in coal-fired generating station leases located in Georgia and Texas with two separate entities unrelated to Exelon. The generating stations were leased back to such entities as part of the transaction. See Note 15 — Income Taxes for further information. For financial accounting purposes, the investments are accounted for as direct financing lease investments. UII holds the leasehold interests in the generating stations in several separate bankruptcy remote, special purpose companies it directly or indirectly wholly owns. The lease agreements provide the lessees with fixed purchase options at the end of the lease terms. If the lessees do not exercise the fixed purchase options, Exelon has the ability to operate the stations and keep or market the power itself or require the lessees to arrange for a third-party to bid on a service contract for a period following the lease term. In any event, Exelon will be subject to residual value risk if the lessees do not exercise the fixed purchase options. This risk is partially mitigated by the fair value of the scheduled payments under the service contract. However, such payments are not guaranteed. Further, the term of the service contract is less than the expected remaining useful life of the plants and, therefore, Exelon’s exposure to residual value risk will not be mitigated by payments under the service contract in this remaining period. In 2000, under the terms of the lease agreements, UII received a prepayment of $ 1.2 billion for all rent, which reduced the investment in the leases. There are no minimum scheduled lease payments to be received over the remaining term of the leases. On February 26, 2014, UII and the City Public Service Board of San Antonio, Texas (CPS) finalized an agreement to terminate the leases on the generating station located in Texas, as described above, prior to its expiration dates. As a result of the lease termination, UII received a net early termination amount of $ 335 million from CPS and wrote down the net investment in the CPS long-term lease of $ 336 million in Investments in Exelon's Consolidated Balance Sheets in 2014; resulting in a pre-tax loss of $ 1 million being reflected in Operating and maintenance expense in the Consolidated Statements of Operations and Comprehensive Income in 2014. Pursuant to the applicable accounting guidance, Exelon is required to review the estimated residual values of its direct financing lease investments at least annually and record an impairment charge if the review indicates an other than temporary decline in the fair value of the residual values below their carrying values. Exelon estimates the fair value of the residual values of its direct financing lease investments under the income approach, which uses a discounted cash flow analysis, which takes into consideration significant unobservable inputs (Level 3) including the expected revenues to be generated and costs to be incurred to operate the plants over their remaining useful lives subsequent to the lease end dates. Significant assumptions used in estimating the fair value include fundamental energy and capacity prices, fixed and variable costs, capital expenditure requirements, discount rates, tax rates, and the estimated remaining useful lives of the plants. The estimated fair values also reflect the cash flows associated with the service contract option discussed above given that a market participant would take into consideration all of the terms and conditions contained in the lease agreements. Based on the annual reviews performed in the second quarters of 2015 and 2014 , the estimated residual value of Exelon’s direct financing leases for the Georgia generating stations experienced other than temporary declines given increases in estimated long-term operating and maintenance costs in the 2015 annual review and reduced long-term energy and capacity price expectations in the 2014 annual review. As a result, Exelon recorded $24 million pre-tax impairment charges in both 2015 and 2014 for these stations. These impairment charges were recorded within Investments and Operating and maintenance expense in Exelon’s Consolidated Balance Sheets and the Consolidated Statements of Operations and Comprehensive Income, respectively. Changes in the assumptions described above could potentially result in future impairments of Exelon’s direct financing lease investments, which could be material. Through December 31, 2015 , no events have occurred that would require Exelon to review the estimated residual values of its direct financing lease investments subsequent to the review performed in the second quarter of 2015 . At December 31, 2015 and 2014 , the components of the net investment in long-term leases were as follows: December 31, 2015 December 31, 2014 Estimated residual value of leased assets $ 639 $ 685 Less: unearned income 287 324 Net investment in long-term leases $ 352 $ 361

Jointly Owned Electric Utility

Jointly Owned Electric Utility Plant (Exelon, Generation, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Public Utilities, Property, Plant and Equipment [Abstract]
Jointly Owned Electric Utility Plant (Exelon, Generation, PECO and BGE)	(Exelon, Generation, PECO and BGE) Exelon, Generation, PECO and BGE’s undivided ownership interests in jointly owned electric plants and transmission facilities at December 31, 2015 and 2014 were as follows: Nuclear Generation Fossil Fuel Generation Transmission Other Quad Cities Peach Bottom Salem (a) Nine Mile Point Unit 2 (f) Wyman PA (b) DE/NJ (c) Other (d) Operator Generation Generation PSEG Nuclear Generation FP&L First Energy PSEG Ownership interest 75.00 % 50.00 % 42.59 % 82.00 % 5.89 % Various 42.55 % 44.24 % Exelon’s share at December 31, 2015: Plant (e) $ 1,035 $ 1,345 $ 566 $ 756 $ 3 $ 15 $ 65 $ 1 Accumulated depreciation (e) 309 368 167 42 3 7 35 1 Construction work in progress 11 18 40 56 — — — — Exelon’s share at December 31, 2014: Plant (e) $ 995 $ 1,095 $ 531 $ 676 $ 3 $ 14 $ 64 $ 2 Accumulated depreciation (e) 266 343 150 14 3 7 34 1 Construction work in progress 15 133 29 48 — — — — ________________________ (a) Generation also owns a proportionate share in the fossil fuel combustion turbine at Salem, which is fully depreciated. The gross book value was $3 million at December 31, 2015 and 2014 . (b) PECO and BGE own a 22% and 7% share, respectively, in 127 miles of 500 kV lines located in Pennsylvania; PECO and BGE also own a 20.7% and 10.56% share, respectively, of a 500 kV substation immediately outside of the Conemaugh fossil generating station which supplies power to the 500 kV lines including, but not limited to, the lines noted above. (c) PECO owns a 42.55% share in 131 miles of 500 kV lines located in Delaware and New Jersey as well as a 42.55% share in a 500 kV substation immediately outside of the Salem nuclear generating station in New Jersey which supplies power to the 500 kV lines including, but not limited to, the lines noted above. (d) Generation has a 44.24% ownership interest in assets located at Merrill Creek Reservoir located in New Jersey. (e) Excludes asset retirement costs. (f) On April 1, 2014, Generation assumed operational control of CENG's nuclear fleet, and as of that date, CENG’s operations are consolidated into Generation’s financial statements. As of December 31, 2013 , Generation’s ownership interest in CENG, including Nine Mile Point, was treated as an equity method investment, and thus did not represent an undivided Interest. See Note 5 - Investment in Constellation Energy Nuclear Group, LLC for additional information. Exelon’s, Generation’s, PECO’s and BGE’s undivided ownership interests are financed with their funds and all operations are accounted for as if such participating interests were wholly-owned facilities. Exelon’s, Generation’s, PECO’s and BGE’s share of direct expenses of the jointly owned plants are included in Purchased power and fuel and Operating and maintenance expenses on Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income and in Operating and maintenance expenses on PECO’s and BGE’s Consolidated Statements of Operations and Comprehensive Income.

Intangible Assets (Exelon, Gene

Intangible Assets (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets (Exelon, Generation, ComEd, PECO and BGE)	(Exelon, Generation, ComEd and PECO) Goodwill Exelon’s, Generation's and ComEd’s gross amount of goodwill, accumulated impairment losses and carrying amount of goodwill for the years ended December 31, 2015 and 2014 were as follows: ComEd Generation Exelon Gross (a) Accumulated Carrying Gross Carrying Gross Amount Accumulated Impairment Losses Carrying Amount Balance, January 1, 2014 $ 4,608 $ 1,983 $ 2,625 $ — $ — $ 4,608 $ 1,983 $ 2,625 Goodwill from business combination — — — 47 47 47 — 47 Balance, December 31, 2014 4,608 1,983 2,625 47 47 4,655 1,983 2,672 Impairment losses — — — — — — — — Balance, December 31, 2015 $ 4,608 $ 1,983 $ 2,625 $ 47 $ 47 $ 4,655 $ 1,983 $ 2,672 _______________________ (a) Reflects goodwill recorded in 2000 from the PECO/Unicom (predecessor parent company of ComEd) merger net of amortization, resolution of tax matters and other non-impairment-related changes as allowed under previous authoritative guidance. Goodwill is not amortized, but is subject to an assessment for impairment at least annually, or more frequently if events occur or circumstances change that would more likely than not reduce the fair value of the ComEd reporting unit below its carrying amount. Under the authoritative guidance for goodwill, a reporting unit is an operating segment or one level below an operating segment (known as a component) and is the level at which goodwill is tested for impairment. A component of an operating segment is a reporting unit if the component constitutes a business for which discrete financial information is available and its operating results are regularly reviewed by segment management. ComEd has a single operating segment for its combined business. There is no level below this operating segment for which operating results are regularly reviewed by segment management. Therefore, ComEd’s operating segment is considered its only reporting unit. Entities assessing goodwill for impairment have the option of first performing a qualitative assessment before calculating the fair value of the reporting unit (i.e., step one of the two-step fair value based impairment test). If an entity determines, on the basis of qualitative factors, that the fair value of the reporting unit is more likely than not less than the carrying amount, the two-step fair value based impairment test is required. Otherwise, no further testing is required. If an entity bypasses the qualitative assessment or performs the qualitative assessment, but determines that it is more likely than not that its fair value is less than its carrying amount, a quantitative two-step, fair value based test is performed. The first step compares the fair value of the reporting unit to its carrying amount, including goodwill. If the carrying amount of the reporting unit exceeds its fair value, the second step is performed. The second step requires an allocation of fair value to the individual assets and liabilities using purchase price allocation in order to determine the implied fair value of goodwill. If the implied fair value of goodwill is less than the carrying amount, an impairment loss is recorded as a reduction to goodwill and a charge to operating expense. Any goodwill impairment charge at ComEd will affect Exelon’s consolidated results of operations. ComEd’s valuation approach is based on a market participant view, pursuant to authoritative guidance for fair value measurement, and utilizes a weighted combination of a discounted cash flow analysis and a market multiples analysis. The discounted cash flow analysis relies on a single scenario reflecting “base case” or “best estimate” projected cash flows for ComEd’s business and includes an estimate of ComEd’s terminal value based on these expected cash flows using the generally accepted Gordon Dividend Growth formula, which derives a valuation using an assumed perpetual annuity based on the entity’s residual cash flows. The discount rate is based on the generally accepted Capital Asset Pricing Model and represents the weighted average cost of capital of comparable companies. The market multiples analysis utilizes multiples of business enterprise value to earnings, before interest, taxes, depreciation and amortization (EBITDA) of comparable companies in estimating fair value. Significant assumptions used in estimating the fair value include discount and growth rates, utility sector market performance and transactions, projected operating and capital cash flows from ComEd’s business and the fair value of debt. Management performs a reconciliation of the sum of the estimated fair value of all Exelon reporting units to Exelon’s enterprise value based on its trading price to corroborate the results of the discounted cash flow analysis and the market multiple analysis. 2015 and 2014 Goodwill Impairment Assessment. Pursuant to authoritative guidance, ComEd is required to test its goodwill for impairment annually and more frequently if an event occurs or circumstances change that suggest an impairment is more likely than not. ComEd performs its assessment as of November 1, of each year. For its 2015 and 2014 annual goodwill impairment assessments, ComEd qualitatively determined that its fair value was not more likely than not less than its carrying value. Therefore, ComEd did not perform quantitative assessments. As part of its qualitative assessments, ComEd evaluated, among other things, management’s best estimate of projected operating and capital cash flows for ComEd’s business, as well as, changes in certain market conditions, including the discount rate and regulated utility peer company EBITDA multiples, while also considering the passing margin from its last quantitative assessment performed as of November 1, 2013. Other Intangible Assets Exelon’s, Generation’s and ComEd’s other intangible assets and liabilities, included in Unamortized energy contract assets and liabilities and Other deferred debits and other assets in their Consolidated Balance Sheets, consisted of the following as of December 31, 2015 : Weighted Average Amortization Years (k) Estimated amortization expense Gross Accumulated Amortization Net 2016 2017 2018 2019 2020 Exelon Software License Agreement (a) 10.0 $ 95 $ (6 ) $ 89 $ 10 $ 10 $ 10 $ 10 $ 10 Generation Unamortized Energy Contracts (b) Exelon Wind (c) 18.0 224 (69 ) 155 14 14 14 14 10 Antelope Valley (d) 25.0 190 (20 ) 170 8 8 8 8 8 Constellation (e) 1.5 1,499 (1,473 ) 26 (33 ) (21 ) 11 8 10 CENG (f) 1.7 (97 ) 48 (49 ) (11 ) (15 ) (18 ) (15 ) (8 ) Integrys (g) 2.4 5 2 7 5 1 1 — — Customer Relationships (h) Constellation (e) 12.4 214 (76 ) 138 18 18 18 17 17 Integrys (g) 10.0 50 (6 ) 44 5 5 5 5 5 Trade Names Constellation (e) 10.0 243 (103 ) 140 23 23 23 23 23 ComEd Chicago settlement—1999 agreement (i) 21.8 100 (83 ) 17 3 3 3 4 4 Chicago settlement—2003 agreement (j) 17.9 62 (44 ) 18 4 4 4 3 3 Total intangible assets $ 2,585 $ (1,830 ) $ 755 $ 46 $ 50 $ 79 $ 77 $ 82 _________________________ (a) On May 31, 2015, Exelon entered into a long-term software license agreement. Exelon is required to make payments starting August 2015 through May 2024. The intangible asset recognized as a result of these payments is being amortized on a straight-line basis over the contract term. (b) Includes unamortized energy contract assets and liabilities on Exelon's and Generation's Consolidated Balance Sheets. Excludes $44 million of other miscellaneous unamortized energy contracts that have been acquired at various points in time. The estimated amortization for these miscellaneous unamortized energy contracts is $3 million , $0 million , $2 million , $3 million and $4 million for 2016 , 2017 , 2018 , 2019 and 2020 , respectively. (c) In December 2010, Generation acquired all of the equity interests of John Deere Renewables, LLC (later named Exelon Wind), adding 735 MWs of installed, operating wind capacity located in eight states. (d) In September 2011, Generation acquired all of the interest in Antelope Valley Solar Ranch One, a 242 MW solar project under development in northern Los Angeles County, CA from First Solar, Inc. (e) On March 12, 2012, Constellation merged into Exelon with Exelon continuing as the surviving corporation pursuant to the transactions contemplated by the Agreement and Plan of Merger. Since the merger transaction, Generation includes the former Constellation generation and customer supply operations. (f) See Note 5 — Investment in Constellation Energy Nuclear Group, LLC for additional information. (g) See Note 4 — Mergers, Acquisitions, and Dispositions for additional information. (h) Excludes $12 million of other miscellaneous customer relationships that have been acquired. The estimated amortization for these miscellaneous customer relationships is $1 million in each of the years from 2016 to 2020 . (i) In March 1999, ComEd entered into a settlement agreement with the City of Chicago associated with ComEd’s franchise agreement. Under the terms of the settlement, ComEd agreed to make payments to the City of Chicago each year from 1999 to 2002. The intangible asset recognized as a result of these payments is being amortized ratably over the remaining term of the franchise agreement, which ends in 2020. (j) In February 2003, ComEd entered into separate agreements with the City of Chicago and with Midwest Generation, LLC (Midwest Generation). Under the terms of the settlement agreement with the City of Chicago, ComEd agreed to pay the City of Chicago a total of $60 million over a ten -year period, beginning in 2003. The intangible asset recognized as a result of the settlement agreement is being amortized ratably over the remaining term of the City of Chicago franchise agreement, which ends in 2020. As required by the settlement, ComEd also made a payment of $2 million to a third-party on the City of Chicago’s behalf. Under the terms of the agreement with Midwest Generation, ComEd received payments of $32 million from Midwest Generation to relieve Midwest Generation’s obligation under the 1999 fossil sale agreement with ComEd to build the generation facility in the City of Chicago. The payments received by ComEd, which have been recorded in Other deferred credits and other liabilities, and other long-term liabilities on Exelon's and ComEd's Consolidated Balance Sheets are being recognized ratably (approximately $2 million annually) as an offset to amortization expense over the remaining term of the franchise agreement. (k) Weighted-average amortization period was calculated at the date of a) acquisition for acquired assets or b) settlement agreement. The following table summarizes the amortization expense related to intangible assets and liabilities for each of the years ended December 31, 2015 , 2014 and 2013 : For the Year Ended December 31, Exelon (a) Generation (a) ComEd 2015 $ 76 $ 69 $ 7 2014 179 179 7 2013 478 550 7 _________________________ (a) At Exelon, amortization of unamortized energy contracts totaling $22 million , $135 million and $430 million for the years ended December 31, 2015 , 2014 and 2013 , respectively, was recorded in Operating revenues or Purchase power and fuel expense within Exelon’s Consolidated Statement of Operations and Comprehensive Income. At Generation, amortization of unamortized energy contracts totaling $22 million , $135 million and $507 million for the years ended December 31, 2015 , 2014 and 2013 , respectively, was recorded in Operating revenues or Purchase power and fuel expense within Generation’s Consolidated Statement of Operations and Comprehensive Income Acquired Intangible Assets Accounting guidance for business combinations requires the acquirer to separately recognize identifiable intangible assets in the application of purchase accounting. Unamortized Energy Contracts. Unamortized energy contract assets and liabilities represent the remaining unamortized fair value of non-derivative energy contracts that Generation has acquired. The valuation of unamortized energy contracts was estimated by applying either the market approach or the income approach depending on the nature of the underlying contract. The market approach was utilized when prices and other relevant information generated by market transactions involving comparable transactions were available. Otherwise, the income approach, which is based upon discounted projected future cash flows associated with the underlying contracts, was utilized. The fair value is based upon certain unobservable inputs, which are considered Level 3 inputs, pursuant to applicable accounting guidance. Key estimates and inputs include forecasted power and fuel prices and the discount rate. The Exelon Wind unamortized energy contracts are amortized on a straight line basis over the period in which the associated contract revenues are recognized as a decrease in Operating revenue within Exelon’s and Generation’s Consolidated Statement of Operations and Comprehensive Income. In the case of Antelope Valley, Constellation, CENG and Integrys, the fair value amounts are amortized over the life of the contract in relation to the present value of the underlying cash flows as of the acquisition dates through either Operating revenues or Purchase power and fuel expense within Exelon’s and Generation’s Consolidated Statement of Operations and Comprehensive Income. Customer Relationships. The customer relationship intangible was determined based on a “multi-period excess method” of the income approach. Under this method, the intangible asset’s fair value is determined to be the estimated future cash flows that will be earned on the current customer base, taking into account expected contract renewals based on customer attrition rates and costs to retain those customers. The fair value is based upon certain unobservable inputs, which are considered Level 3 inputs, pursuant to applicable accounting guidance. Key assumptions include the customer attrition rate and the discount rate. The accounting guidance requires that customer-based intangibles be amortized over the period expected to be benefited using the pattern of economic benefit. The amortization of the customer relationships is recorded in Depreciation and amortization expense within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. Trade Name. The Constellation trade name intangible was determined based on the relief from royalty method of income approach whereby fair value is determined to be the present value of the license fees avoided by owning the assets. The fair value is based upon certain unobservable inputs, which are considered Level 3 inputs, pursuant to applicable accounting guidance. Key assumptions include the hypothetical royalty rate and the discount rate. The Constellation trade name intangible is amortized on a straight-line basis over a period of 10 years . The amortization of the trade name is recorded in Depreciation and amortization expense within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. Renewable Energy Credits and Alternative Energy Credits (Exelon, Generation, ComEd and PECO). Exelon’s, Generation’s, ComEd’s and PECO’s other intangible assets, included in Other current assets and Other deferred debits and other assets on the Consolidated Balance Sheets, include RECs (Exelon, Generation and ComEd) and AECs (Exelon and PECO). Purchased RECs are recorded at cost on the date they are purchased. The cost of RECs purchased on a stand-alone basis is based on the transaction price, while the cost of RECs acquired through PPAs represents the difference between the total contract price and the market price of energy at contract inception. Revenue for RECs that are part of a bundled power sale is recognized when the power is produced and delivered to the customer. As of December 31, 2015 , and 2014 , PECO had current AECs of $2 million and $13 million , respectively. PECO had no noncurrent AECs as of December 31, 2015 and 2014 . As of December 31, 2015 , and 2014 , Generation had current RECs of $251 million and $191 million , respectively, and $56 million and $44 million of noncurrent REC's, respectively. As of December 31, 2015 and 2014 , ComEd had current RECs of $5 million and $4 million , respectively. ComEd had no noncurrent RECs as of December 31, 2015 and 2014 . See Note 3 — Regulatory Matters and Note 23 — Commitments and Contingencies for additional information on RECs and AECs.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities (Exelon, Generation, ComEd, PECO and BGE)	(Exelon, Generation, ComEd, PECO and BGE) Fair Value of Financial Liabilities Recorded at the Carrying Amount The following tables present the carrying amounts and fair values of the Registrants’ short-term liabilities, long-term debt, SNF obligation, and trust preferred securities (long-term debt to financing trusts or junior subordinated debentures) as of December 31, 2015 and 2014 : Exelon December 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 536 $ 3 $ 533 $ — $ 536 $ 463 $ 463 Long-term debt (including amounts due within one year) (a) 25,145 931 23,644 1,349 25,924 21,014 22,936 Long-term debt to financing trusts (b) 641 — — 673 673 641 648 SNF obligation 1,021 — 818 — 818 1,021 833 Generation December 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 29 $ — $ 29 $ — $ 29 $ 36 $ 36 Long-term debt (including amounts due within one year) (a) 8,959 — 7,767 1,349 9,116 8,196 8,822 SNF obligation 1,021 — 818 — 818 1,021 833 ComEd December 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 294 $ — $ 294 $ — $ 294 $ 304 $ 304 Long-term debt (including amounts due within one year) (a) 6,509 — 7,069 — 7,069 5,925 6,788 Long-term debt to financing trusts (b) 205 — — 213 213 205 213 PECO December 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 2,580 $ — $ 2,786 $ — $ 2,786 $ 2,232 $ 2,537 Long-term debt to financing trusts 184 — — 195 195 184 199 BGE December 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 213 $ 3 $ 210 $ — $ 213 $ 123 $ 123 Long-term debt (including amounts due within one year) (a) 1,858 — 2,044 — 2,044 1,932 2,178 Long-term debt to financing trusts (b) 252 — — 264 264 252 236 _____________________ (a) Includes unamortized debt issuance costs of $180 million , $70 million , $38 million , $15 million and $9 million for Exelon, Generation, ComEd, PECO and BGE, respectively, at December 31, 2015 and $150 million , $70 million , $33 million , $14 million and $10 million at December 31, 2014. (b) Includes unamortized debt issuance costs of $7 million , $1 million and $6 million for Exelon, ComEd and BGE, respectively, at both December 31, 2015 and 2014. Short-Term Liabilities. The short-term liabilities included in the tables above are comprised of dividends payable (included in other current liabilities) (Level 1), short-term borrowings (Level 2) and third party financing (Level 3). The Registrants’ carrying amounts of the short-term liabilities are representative of fair value because of the short-term nature of these instruments. Long-Term Debt. The fair value amounts of Exelon’s taxable debt securities (Level 2) are determined by a valuation model that is based on a conventional discounted cash flow methodology and utilizes assumptions of current market pricing curves. In order to incorporate the credit risk of the Registrants into the discount rates, Exelon obtains pricing (i.e., U.S. Treasury rate plus credit spread) based on trades of existing Exelon debt securities as well as debt securities of other issuers in the electric utility sector with similar credit ratings in both the primary and secondary market, across the Registrants’ debt maturity spectrum. The credit spreads of various tenors obtained from this information are added to the appropriate benchmark U.S. Treasury rates in order to determine the current market yields for the various tenors. The yields are then converted into discount rates of various tenors that are used for discounting the respective cash flows of the same tenor for each bond or note. The fair value of Exelon's equity units (Level 1) are valued based on publicly traded securities issued by Exelon. The fair value of Generation’s non-government-backed fixed rate nonrecourse debt (Level 3) is based on market and quoted prices for its own and other nonrecourse debt with similar risk profiles. Given the low trading volume in the nonrecourse debt market, the price quotes used to determine fair value will reflect certain qualitative factors, such as market conditions, investor demand, new developments that might significantly impact the project cash flows or off-taker credit, and other circumstances related to the project (e.g., political and regulatory environment). The fair value of Generation’s government-backed fixed rate project financing debt (Level 3) is largely based on a discounted cash flow methodology that is similar to the taxable debt securities methodology described above. Due to the lack of market trading data on similar debt, the discount rates are derived based on the original loan interest rate spread to the applicable Treasury rate as well as a current market curve derived from government-backed securities. Variable rate project financing debt resets on a quarterly basis and the carrying value approximates fair value (Level 2). Generation also has tax-exempt debt (Level 2). Due to low trading volume in this market, qualitative factors, such as market conditions, investor demand, and circumstances related to the issuer (e.g., conduit issuer political and regulatory environment), may be incorporated into the credit spreads that are used to obtain the fair value as described above. SNF Obligation. The carrying amount of Generation’s SNF obligation (Level 2) is derived from a contract with the DOE to provide for disposal of SNF from Generation’s nuclear generating stations. When determining the fair value of the obligation, the future carrying amount of the SNF obligation estimated to be settled in 2025 is calculated by compounding the current book value of the SNF obligation at the 13-week Treasury rate. The compounded obligation amount is discounted back to present value using Generation’s discount rate, which is calculated using the same methodology as described above for the taxable debt securities, and an estimated maturity date of 2025. Long-Term Debt to Financing Trusts. Exelon’s long-term debt to financing trusts is valued based on publicly traded securities issued by the financing trusts. Due to low trading volume of these securities, qualitative factors, such as market conditions, investor demand, and circumstances related to each issue, this debt is classified as Level 3. Recurring Fair Value Measurements Exelon records the fair value of assets and liabilities in accordance with the hierarchy established by the authoritative guidance for fair value measurements. The hierarchy prioritizes the inputs to valuation techniques used to measure fair value into three levels as follows: • Level 1—quoted prices (unadjusted) in active markets for identical assets or liabilities that the Registrants have the ability to liquidate as of the reporting date. • Level 2—inputs other than quoted prices included within Level 1 that are directly observable for the asset or liability or indirectly observable through corroboration with observable market data. • Level 3—unobservable inputs, such as internally developed pricing models or third-party valuations for the asset or liability due to little or no market activity for the asset or liability. Transfers in and out of levels are recognized as of the end of the reporting period when the transfer occurred. Given derivatives categorized within Level 1 are valued using exchange-based quoted prices within observable periods, transfers between Level 2 and Level 1 were not material. Transfers into Level 2 from Level 3 generally occur when the contract tenure becomes more observable. Transfers into Level 3 from Level 2 generally occur due to changes in market liquidity or assumptions for certain commodity contracts. There were no transfers between Level 1 and Level 2 during the year ended December 31, 2015 for cash equivalents, nuclear decommissioning trust fund investments, pledged assets for Zion Station decommissioning, Rabbi trust investments, and deferred compensation obligations. Generation and Exelon The following tables present assets and liabilities measured and recorded at fair value on Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2015 and 2014 : Generation Exelon As of December 31, 2015 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 104 $ — $ — $ 104 $ 5,766 $ — $ — $ 5,766 Nuclear decommissioning trust fund investments Cash equivalents (b) 219 92 — 311 219 92 — 311 Generation Exelon As of December 31, 2015 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Equities 3,008 1,894 — 4,902 3,008 1,894 — 4,902 Fixed income Corporate debt — 1,824 242 2,066 — 1,824 242 2,066 U.S. Treasury and agencies 1,323 15 — 1,338 1,323 15 — 1,338 Foreign governments — 61 — 61 — 61 — 61 State and municipal debt — 326 — 326 — 326 — 326 Other (c) — 537 — 537 — — 537 — — — 537 Fixed income subtotal 1,323 2,763 242 4,328 1,323 2,763 242 4,328 Middle market lending — — 428 428 — — 428 428 Private equity — — 125 125 — — 125 125 Real estate — — 35 35 — — — — 35 35 Other — 216 — 216 — 216 — 216 Nuclear decommissioning trust fund investments subtotal (d) 4,550 4,965 830 10,345 4,550 4,965 830 10,345 Pledged assets for Zion Station decommissioning Cash equivalents — 17 — 17 — 17 — 17 Equities 1 5 — 6 1 5 — 6 Fixed income U.S. Treasury and agencies 6 2 — 8 6 2 — 8 Corporate debt — 46 — 46 — 46 — 46 Other — 1 — 1 — 1 — 1 Fixed income subtotal 6 49 — 55 6 49 — 55 Middle market lending — — 127 127 — — 127 127 Pledged assets for Zion Station decommissioning subtotal (e) 7 71 127 205 7 71 127 205 Rabbi trust investments in mutual funds (f) 17 — — — 17 48 — — 48 Commodity derivative assets Economic hedges 1,922 3,467 1,707 7,096 1,922 3,467 1,707 7,096 Proprietary trading 36 64 30 130 36 64 30 130 Effect of netting and allocation of collateral (g) (1,964 ) (2,629 ) (564 ) (5,157 ) (1,964 ) (2,629 ) (564 ) (5,157 ) Commodity derivative assets subtotal (6 ) 902 1,173 2,069 (6 ) 902 1,173 2,069 Interest rate and foreign currency derivative Derivatives designated as hedging instruments — — — — — 25 — 25 Economic hedges — 20 — 20 — 20 — 20 Proprietary trading 10 5 — 15 10 5 — 15 Effect of netting and allocation of collateral (3 ) (3 ) — (6 ) (3 ) (3 ) — (6 ) Interest rate and foreign currency derivative assets subtotal 7 22 — 29 7 47 — 54 Other investments — — 33 33 — — 33 33 Total assets 4,679 5,960 2,163 12,802 10,372 5,985 2,163 18,520 Liabilities Commodity derivative liabilities Economic hedges (2,382 ) (3,348 ) (850 ) (6,580 ) (2,382 ) (3,348 ) (1,097 ) (6,827 ) Proprietary trading (33 ) (57 ) (37 ) (127 ) (33 ) (57 ) (37 ) (127 ) Effect of netting and allocation of collateral (g) 2,440 3,186 765 6,391 2,440 3,186 765 6,391 Commodity derivative liabilities subtotal 25 (219 ) (122 ) (316 ) 25 (219 ) (369 ) (563 ) Interest rate and foreign currency derivative liabilities — — Derivatives designated as hedging instruments — (16 ) — (16 ) — (16 ) — (16 ) Economic hedges — (3 ) — (3 ) — (3 ) — (3 ) Proprietary trading (12 ) — — (12 ) (12 ) — — (12 ) Effect of netting and allocation of collateral 12 3 — 15 12 3 — 15 Generation Exelon As of December 31, 2015 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Interest rate and foreign currency derivative liabilities subtotal — (16 ) — (16 ) — (16 ) — (16 ) Deferred compensation obligation — (30 ) — (30 ) — (99 ) — (99 ) Total liabilities 25 (265 ) (122 ) (362 ) 25 (334 ) (369 ) (678 ) Total net assets $ 4,704 $ 5,695 $ 2,041 $ 12,440 $ 10,397 $ 5,651 $ 1,794 $ 17,842 Generation Exelon As of December 31, 2014 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 405 $ — $ — $ 405 $ 1,119 $ — $ — $ 1,119 Nuclear decommissioning trust fund investments Cash equivalents (b) 208 37 — 245 208 37 — 245 Equities 3,035 2,207 — 5,242 3,035 2,207 — 5,242 Fixed income Corporate debt — 2,023 239 2,262 — 2,023 239 2,262 U.S. Treasury and agencies 996 — — 996 996 — — 996 Foreign governments — 95 — 95 — 95 — 95 State and municipal debt — 438 — 438 — 438 — 438 Other — 511 — 511 — 511 — 511 Fixed income subtotal 996 3,067 239 4,302 996 3,067 239 4,302 Middle market lending — — 366 366 — — 366 366 Private equity — — 83 83 — — 83 83 Real estate — — 3 3 — — — — 3 3 Other (c) — 301 — 301 — 301 — 301 Nuclear decommissioning trust fund investments subtotal (d) 4,239 5,612 691 10,542 4,239 5,612 691 10,542 Pledged assets for Zion Station decommissioning Cash equivalents — 15 — 15 — 15 — 15 Equities 6 1 — 7 6 1 — 7 Fixed income U.S. Treasury and agencies 5 3 — 8 5 3 — 8 Corporate debt — 89 — 89 — 89 — 89 State and municipal debt — 10 — 10 — 10 — 10 Other — 3 — 3 — — 3 — — — 3 Fixed income subtotal 5 105 — 110 5 105 — 110 Middle market lending — — 184 184 — — 184 184 Pledged assets for Zion Station decommissioning subtotal (e) 11 121 184 316 11 121 184 316 Rabbi trust investments (f) Cash equivalents — — — — 1 — — 1 Mutual funds 16 — — 16 46 — — 46 Rabbi trust investments subtotal 16 — — 16 47 — — 47 Commodity derivative assets — — Economic hedges 1,667 3,465 1,681 6,813 1,667 3,465 1,681 6,813 Proprietary trading 201 284 27 512 201 284 27 512 Effect of netting and allocation of collateral (g) (1,982 ) (2,757 ) (557 ) (5,296 ) (1,982 ) (2,757 ) (557 ) (5,296 ) Commodity derivative assets subtotal (114 ) 992 1,151 2,029 (114 ) 992 1,151 2,029 Interest rate and foreign currency derivative assets — — Derivatives designated as hedging instruments — 8 — 8 — 31 — 31 Economic hedges — 12 — 12 — 13 — 13 Generation Exelon As of December 31, 2014 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Proprietary trading 18 9 — 27 18 9 — 27 Effect of netting and allocation of collateral (17 ) (12 ) — (29 ) (17 ) (31 ) — (48 ) Interest rate and foreign currency derivative assets subtotal 1 17 — 18 1 22 — 23 Other investments — — 3 3 2 — 3 5 Total assets 4,558 6,742 2,029 13,329 5,305 6,747 2,029 14,081 Liabilities Commodity derivative liabilities Economic hedges (2,241 ) (3,458 ) (788 ) (6,487 ) (2,241 ) (3,458 ) (995 ) (6,694 ) Proprietary trading (195 ) (295 ) (42 ) (532 ) (195 ) (295 ) (42 ) (532 ) Effect of netting and allocation of collateral (g) 2,416 3,557 729 6,702 2,416 3,557 729 6,702 Commodity derivative liabilities subtotal (20 ) (196 ) (101 ) (317 ) (20 ) (196 ) (308 ) (524 ) Interest rate and foreign currency derivative liabilities — — Derivatives designated as hedging instruments — (12 ) — (12 ) — (41 ) — (41 ) Economic hedges — (2 ) — (2 ) — (103 ) — (103 ) Proprietary trading (14 ) (9 ) — (23 ) (14 ) (9 ) — (23 ) Effect of netting and allocation of collateral 25 10 — 35 25 29 — 54 Interest rate and foreign currency derivative liabilities subtotal 11 (13 ) — (2 ) 11 (124 ) — (113 ) Deferred compensation obligation — (31 ) — (31 ) — (107 ) — (107 ) Total liabilities (9 ) (240 ) (101 ) (350 ) (9 ) (427 ) (308 ) (744 ) Total net assets $ 4,549 $ 6,502 $ 1,928 $ 12,979 $ 5,296 $ 6,320 $ 1,721 $ 13,337 _________________________ (a) Excludes certain cash equivalents considered to be held-to-maturity and not reported at fair value. (b) Includes $52 million and $43 million of cash received from outstanding repurchase agreements at December 31, 2015 and 2014 , respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below. (c) Includes derivative instruments of $(8) million and $(10) million , which have a total notional amount of $1,236 million and $794 million at December 31, 2015 and 2014 , respectively. The notional principal amounts for these instruments provide one measure of the transaction volume outstanding as of the fiscal years ended and do not represent the amount of the company's exposure to credit or market loss. (d) Excludes net liabilities of $(3) million and $(5) million at December 31, 2015 and 2014 , respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, repurchase agreement obligations, and payables related to pending securities purchases. The repurchase agreements are generally short-term in nature with durations generally of 30 days or less. (e) Excludes net assets of $1 million and $3 million at December 31, 2015 and 2014 , respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases. (f) Excludes $36 million and $35 million of cash surrender value of life insurance investment at December 31, 2015 and 2014 , respectively, at Exelon Consolidated. Excludes $13 million and $11 million of cash surrender value of life insurance investment at December 31, 2015 and 2014 , respectively, at Generation. (g) Collateral posted to/(received from) counterparties totaled $476 million , $557 million and $201 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2015 . Collateral posted to/(received from) counterparties totaled $434 million , $800 million and $172 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2014 . ComEd, PECO and BGE The following tables present assets and liabilities measured and recorded at fair value on the utility Registrants' Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2015 and 2014 : ComEd PECO BGE As of December 31, 2015 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents $ 29 $ — $ — $ 29 $ 271 $ — $ — $ 271 $ 25 $ — $ — $ 25 Rabbi trust investments in mutual funds (a) — — — — 8 — — 8 4 — — 4 Total assets 29 — — 29 279 — — 279 29 — — 29 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (12 ) — (12 ) — (4 ) — (4 ) Mark-to-market derivative liabilities (b) — — (247 ) (247 ) — — — — — — — — Total liabilities — (8 ) (247 ) (255 ) — (12 ) — (12 ) — (4 ) — (4 ) Total net assets (liabilities) $ 29 $ (8 ) $ (247 ) $ (226 ) $ 279 $ (12 ) $ — $ 267 $ 29 $ (4 ) $ — $ 25 ComEd PECO BGE As of December 31, 2014 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents $ 25 $ — $ — $ 25 $ 12 $ — $ — $ 12 $ 103 $ — $ — $ 103 Rabbi trust investments in mutual funds (a) — — — — 9 — — 9 5 — — 5 Total assets 25 — — 25 21 — — 21 108 — — 108 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (15 ) — (15 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (b) — — (207 ) (207 ) — — — — — — — — Total liabilities — (8 ) (207 ) (215 ) — (15 ) — (15 ) — (5 ) — (5 ) Total net assets (liabilities) $ 25 $ (8 ) $ (207 ) $ (190 ) $ 21 $ (15 ) $ — $ 6 $ 108 $ (5 ) $ — $ 103 _________________________ (a) At PECO, excludes $12 million and $14 million of the cash surrender value of life insurance investments at December 31, 2015 and 2014 , respectively. (b) The Level 3 balance includes the current and noncurrent liability of $23 million and $224 million , respectively, at December 31, 2015 , and $20 million and $187 million , respectively, at December 31, 2014 , related to floating-to-fixed energy swap contracts with unaffiliated suppliers. The following table presents the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis during the year ended December 31, 2015 and 2014 : Generation ComEd Exelon For The Year Ended December 31, 2015 Nuclear Pledged Assets Mark-to-Market Other Total Generation Mark-to-Market Derivatives (b) Eliminated in Consolidation Total Balance as of January 1, 2015 $ 691 $ 184 $ 1,050 $ 3 $ 1,928 $ (207 ) $ — $ 1,721 Total realized / unrealized gains (losses) Included in net income 4 — 22 (a) 1 27 — — 27 Included in noncurrent payables to affiliates 23 — — — 23 — (23 ) — Included in payable for Zion Station decommissioning — (2 ) — — (2 ) — — (2 ) Included in regulatory assets/liabilities — — — — — (40 ) 23 (17 ) Change in collateral — — 29 — 29 — — 29 Purchases, sales, issuances and settlements Purchases 226 20 144 30 420 — — 420 Sales (8 ) (75 ) (25 ) — (108 ) — — (108 ) Settlements (106 ) — — — (106 ) — — (106 ) Transfers into Level 3 4 — 80 — 84 — — 84 Transfers out of Level 3 (4 ) — (249 ) (1 ) (254 ) — — (254 ) Balance as of December 31, 2015 $ 830 $ 127 $ 1,051 $ 33 $ 2,041 $ (247 ) $ — $ 1,794 The amount of total gains included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of December 31, 2015 $ 4 $ — $ 856 $ — $ 860 $ — $ — $ 860 Generation ComEd Exelon For The Year Ended December 31, 2014 Nuclear Decommissioning Trust Fund Investments Pledged Assets for Zion Station Decommissioning Mark-to-Market Derivatives (d) Other Investments Total Generation Mark-to-Market Derivatives (b) Eliminated in Consolidation Total Balance as of January 1, 2014 $ 350 $ 112 $ 465 $ 15 $ 942 $ (193 ) $ — $ 749 Total realized / unrealized gains (losses) Included in net income 6 — 526 (a) — 532 — — 532 Included in other comprehensive income — — — — — — — — Included in noncurrent payables to affiliates 14 — — — 14 — (14 ) — Included in payable for Zion Station decommissioning — 2 — — 2 — — 2 Included in regulatory assets/liabilities — — — — — (14 ) 14 — Change in collateral — — 198 — 198 — — 198 Purchases, sales, issuances and settlements Purchases 400 120 76 (c) 2 598 — — 598 Sales (15 ) (50 ) (7 ) (8 ) (80 ) — — (80 ) Settlements (64 ) — — — (64 ) — — (64 ) Transfers into Level 3 — — (7 ) — (7 ) — — (7 ) Transfers out of Level 3 — — (201 ) (6 ) (207 ) — — (207 ) Balance as of December 31, 2014 $ 691 $ 184 $ 1,050 $ 3 $ 1,928 $ (207 ) $ — $ 1,721 The amount of total gains included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held as of December 31, 2014 $ 4 $ — $ 640 $ — $ 644 $ — $ — $ 644 _________________________ (a) Includes a reduction for the reclassification of $834 million and $114 million of realized gains due to the settlement of derivative contracts for the years ended December 31, 2015 and 2014 , respectively. (b) Includes $55 million of decreases in fair value and an increase for realized losses due to settlements of $(15) million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2015 . Includes $13 million of decreases in fair value and a reduction for realized gains due to settlements of $1 million for the year ended December 31, 2014 . (c) Includes $34 million of fair value from contracts acquired as a result of the Integrys acquisition. The following tables present the income statement classification of the total realized and unrealized gains (losses) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis during the years ended December 31, 2015 and 2014 : Generation Exelon Operating Revenues Purchased Power and Fuel Other, net (a) Operating Revenues Purchased Power and Fuel Other, net (a) Total gains (losses) included in net income for the year ended December 31, 2015 $ 67 $ (45 ) $ 4 $ 67 $ (45 ) $ 4 Change in the unrealized gains (losses) relating to assets and liabilities held for the year ended December 31, 2015 $ 858 $ (2 ) $ 4 $ 858 $ (2 ) $ 4 Generation Exelon Operating Revenues Purchased Power and Fuel Other, net (a) Operating Revenues Purchased Power and Fuel Other, net (a) Total gains (losses) included in net income for the year ended December 31, 2014 $ 614 $ (88 ) $ 6 $ 614 $ (88 ) $ 6 Change in the unrealized gains (losses) relating to assets and liabilities held for the year ended December 31, 2014 $ 663 $ (23 ) $ 4 $ 663 $ (23 ) $ 4 _________________________ (a) Other, net activity consists of realized and unrealized gains (losses) included in income for the NDT funds held by Generation. Valuation Techniques Used to Determine Fair Value The following describes the valuation techniques used to measure the fair value of the assets and liabilities shown in the tables above. Cash Equivalents (Exelon, Generation, ComEd, PECO and BGE). The Registrants’ cash equivalents include investments with maturities of three months or less when purchased. The cash equivalents shown in the fair value tables are comprised of investments in mutual and money market funds. The fair values of the shares of these funds are based on observable market prices and, therefore, have been categorized in Level 1 in the fair value hierarchy. Nuclear Decommissioning Trust Fund Investments and Pledged Assets for Zion Station Decommissioning (Exelon and Generation). The trust fund investments have been established to satisfy Generation’s and CENG's nuclear decommissioning obligations as required by the NRC. The NDT funds hold debt and equity securities directly and indirectly through commingled funds and mutual funds, which are included in Equities, Fixed Income and Other. Generation’s and CENG's NDT fund investments policies outline investment guidelines for the trusts and limit the trust funds’ exposures to investments in highly illiquid markets and other alternative investments. Investments with maturities of three months or less when purchased, including certain short-term fixed income securities are considered cash equivalents and included in the recurring fair value measurements hierarchy as Level 1 or Level 2. With respect to individually held equity securities, the trustees obtain prices from pricing services, whose prices are obtained from direct feeds from market exchanges, which Generation is able to independently corroborate. The fair values of equity securities held directly by the trust funds are based on quoted prices in active markets and are categorized in Level 1. Equity securities held individually are primarily traded on the New York Stock Exchange and NASDAQ-Global Select Market, which contain only actively traded securities due to the volume trading requirements imposed by these exchanges. For fixed income securities, multiple prices from pricing services are obtained whenever possible, which enables cross-provider validations in addition to checks for unusual daily movements. A primary price source is identified based on asset type, class or issue for each security. With respect to individually held fixed income securities, the trustees monitor prices supplied by pricing services and may use a supplemental price source or change the primary price source of a given security if the portfolio managers challenge an assigned price and the trustees determine that another price source is considered to be preferable. Generation has obtained an understanding of how these prices are derived, including the nature and observability of the inputs used in deriving such prices. Additionally, Generation selectively corroborates the fair values of securities by comparison to other market-based price sources. U.S. Treasury securities are categorized as Level 1 because they trade in a highly liquid and transparent market. The fair values of fixed income securities, excluding U.S. Treasury securities, are based on evaluated prices that reflect observable market information, such as actual trade information or similar securities, adjusted for observable differences and are categorized in Level 2. The fair values of private placement fixed income securities, which are included in Corporate debt, are determined using a third party valuation that contains significant unobservable inputs and are categorized in Level 3. Equity, balanced and fixed income commingled funds and mutual funds are maintained by investment companies and hold certain investments in accordance with a stated set of fund objectives such as holding short term fixed income securities or tracking the performance of certain equity indices by purchasing equity securities to replicate the capitalization and characteristics of the indices. The values of some of these funds are publicly quoted. For mutual funds which are publicly quoted, the funds are valued based on quoted prices in active markets and have been categorized as Level 1. For commingled funds and mutual funds, which are not publicly quoted, the fund administrators value the funds using NAV as a practical expedient for fair value, which is primarily derived from the quoted prices in active markets on the underlying securities. These investments typically can be redeemed monthly with 30 or less days of notice and without further restrictions, and, as a result are categorized as Level 2. Derivative instruments consisting primarily of interest rate swaps to manage risk are recorded at fair value. Derivative instruments are valued based on external price data of comparable securities and have been categorized as Level 2. Middle market lending are investments in loans or managed funds which lend to private companies. Generation elected the fair value option for its investments in certain limited partnerships that invest in middle market lending managed funds. The fair value of these loans is determined using a combination of valuation models including cost models, market models, and income models. Investments in middle market lending are categorized as Level 3 because the fair value of these securities is based largely on inputs that are unobservable and utilize complex valuation models. Investments in middle market lending typically cannot be redeemed until maturity of the term loan. Private equity and real estate investments include those in limited partnerships that invest in operating companies and real estate holding companies that are not publicly traded on a stock exchange, such as,leveraged buyouts, growth capital, venture capital, distressed investments, investments in natural resources, and direct investments in pools of real estate properties. The fair value of private equity and real estate investments is determined using NAV or its equivalent as a practical expedient. These investments typically cannot be redeemed and are generally liquidated over a period of 8 to 10 years from the initial investment date. Private equity and real estate valuations are reported by the fund manager and are based on the valuation of the underlying investments, which include inputs such as cost, operating results, discounted future cash flows, market based comparable data, and independent appraisals from sources with professional qualifications. Since these valuation inputs are not highly observable, private equity and real estate investments have been categorized as Level 3. As of December 31, 2015 , Generation has outstanding commitments to invest in middle market lending, corporate debt securities, private equity investments, and real estate investments of approximately $ 266 million . These commitments will be funded by Generation’s existing nuclear decommissioning trust funds. Concentrations of Credit Risk. Generation evaluated its NDT portfolios for the existence of significant concentrations of credit risk as of December 31, 2015 . Types of concentrations that were evaluated include, but are not limited to, investment concentrations in a single entity, type of industry, foreign country, and individual fund. As of December 31, 2015 , there were no significant concentrations (generally defined as greater than 10 percent) of risk in Generation's NDT assets. See Note 16 — Asset Retirement Obligations for further discussion on the NDT fund investments. Rabbi Trust Investments (Exelon, Generation, PECO and BGE). The Rabbi trusts were established to hold assets related to deferred compensation plans existing for certain active and retired members of Exelon’s executive management and directors. The Rabbi trusts assets are included in investments in the Registrants’ Consolidated Balance Sheets and consist primarily of mutual funds and life insurance policies. The mutual funds are maintained by investment companies and hold certain investments in accordance with a stated set of fund objectives, which are consistent with Exelon’s overall investment strategy. Mutual funds are publicly quoted and have been categorized as Level 1 given the clear observability of the prices. The life insurance policies are valued using the cash surrender value of the policies, which is provided by a third party. The cash surrender value inputs are not observable. Mark-to-Market Derivatives (Exelon, Gen

Derivative Financial Instrument

Derivative Financial Instruments (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments (Exelon, Generation, ComEd, PECO and BGE)	13 . Derivative Financial Instruments (Exelon, Generation, ComEd, PECO and BGE) The Registrants use derivative instruments to manage commodity price risk, foreign currency exchange rate risk, and interest rate risk related to ongoing business operations. Commodity Price Risk (Exelon, Generation, ComEd, PECO and BGE) To the extent the amount of energy Generation produces differs from the amount of energy it has contracted to sell, Exelon and Generation are exposed to market fluctuations in the prices of electricity, fossil fuels and other commodities. Each of the Registrants employ established policies and procedures to manage their risks associated with market fluctuations in commodity prices by entering into physical and financial derivative contracts, including swaps, futures, forwards, options and short-term and long-term commitments to purchase and sell energy and energy-related products. The Registrants believe these instruments, which are classified as either economic hedges or non-derivatives, mitigate exposure to fluctuations in commodity prices. Derivative accounting guidance requires that derivative instruments be recognized as either assets or liabilities at fair value, with changes in fair value of the derivative recognized in earnings each period. Other accounting treatments are available through special election and designation, provided they meet specific, restrictive criteria both at the time of designation and on an ongoing basis. These alternative permissible accounting treatments include normal purchase normal sale (NPNS), cash flow hedge, and fair value hedge. For commodity transactions, Generation no longer utilizes the special election provided for by the cash flow hedge designation and de-designated all of its existing cash flow hedges prior to the Constellation merger. Because the underlying forecasted transactions remained probable, the fair value of the effective portion of these cash flow hedges was frozen in Accumulated OCI and was reclassified to results of operations when the forecasted purchase or sale of the energy commodity occurred. The effect of this decision is that all derivative economic hedges related to commodities are recorded at fair value through earnings for the combined company, referred to as economic hedges in the following tables. The Registrants have applied the NPNS scope exception to certain derivative contracts for the forward sale of generation, power procurement agreements, and natural gas supply agreements. Non-derivative contracts for access to additional generation and certain sales to load-serving entities are accounted for primarily under the accrual method of accounting, which is further discussed in Note 23 — Commitments and Contingencies . Additionally, Generation is exposed to certain market risks through its proprietary trading activities. The proprietary trading activities are a complement to Generation’s energy marketing portfolio, but represent a small portion of Generation’s overall energy marketing activities. Economic Hedging. The Registrants are exposed to commodity price risk primarily relating to changes in the market price of electricity, fossil fuels, and other commodities associated with price movements resulting from changes in supply and demand, fuel costs, market liquidity, weather conditions, governmental regulatory and environmental policies, and other factors. Within Exelon, Generation has the most exposure to commodity price risk. As such, Generation uses a variety of derivative and non-derivative instruments to manage the commodity price risk of its electric generation facilities, including power and gas sales, fuel and energy purchases, natural gas transportation and pipeline capacity agreements and other energy-related products marketed and purchased. In order to manage these risks, Generation may enter into fixed-price derivative or non-derivative contracts to hedge the variability in future cash flows from forecasted sales of energy and gas and purchases of fuel and energy. The objectives for entering into such hedges include fixing the price for a portion of anticipated future electricity sales at a level that provides an acceptable return on electric generation operations, fixing the price of a portion of anticipated fuel purchases for the operation of power plants, and fixing the price for a portion of anticipated energy purchases to supply load-serving customers. The portion of forecasted transactions hedged may vary based upon management’s policies and hedging objectives, the market, weather conditions, operational and other factors. Generation is also exposed to differences between the locational settlement prices of certain economic hedges and the hedged generating units. This price difference is actively managed through other instruments which include derivative congestion products, whose changes in fair value are recognized in earnings each period, and auction revenue rights, which are accounted for on an accrual basis. In general, increases and decreases in forward market prices have a positive and negative impact, respectively, on Generation’s owned and contracted generation positions that have not been hedged. Generation hedges commodity price risk on a ratable basis over three-year periods. As of December 31, 2015 , the proportion of expected generation hedged for the major reportable segments was 90% - 93% , 60% - 63% and 28% - 31% for 2016 , 2017 , and 2018 , respectively. The percentage of expected generation hedged is the amount of equivalent sales divided by the expected generation. Expected generation is the volume of energy that best represents our commodity position in energy markets from owned or contracted for capacity based upon a simulated dispatch model that makes assumptions regarding future market conditions, which are calibrated to market quotes for power, fuel, load following products, and options. Equivalent sales represent all hedging products, which include economic hedges and certain non-derivative contracts, including Generation’s sales to ComEd, PECO and BGE to serve their retail load. On December 17, 2010, ComEd entered into several 20 -year floating-to-fixed energy swap contracts with unaffiliated suppliers for the procurement of long-term renewable energy and associated RECs. Delivery under the contracts began in June 2012. Pursuant to the ICC’s Order on December 19, 2012, ComEd’s commitments under the existing long-term contracts for energy and associated RECs were reduced for the June 2013 through May 2014 procurement period. In addition, the ICC's December 18, 2013 Order approved the reduction of ComEd's commitments under those contracts for the June 2014 through May 2015 procurement period, and the amount of the reductions was approved in March 2014. These contracts are designed to lock in a portion of the long-term commodity price risk resulting from the renewable energy resource procurement requirements in the Illinois Settlement Legislation. ComEd has not elected hedge accounting for these derivative financial instruments. ComEd records the fair value of the swap contracts on its balance sheet. Because ComEd receives full cost recovery for energy procurement and related costs from retail customers, the change in fair value each period is recorded by ComEd as a regulatory asset or liability. See Note 3 — Regulatory Matters for additional information. PECO has contracts to procure electric supply that were executed through the competitive procurement process outlined in its PAPUC-approved DSP Programs, which are further discussed in Note 3 — Regulatory Matters . Based on Pennsylvania legislation and the DSP Programs permitting PECO to recover its electric supply procurement costs from retail customers with no mark-up, PECO’s price risk related to electric supply procurement is limited. PECO locked in fixed prices for a significant portion of its commodity price risk through full requirements contracts and block contracts. PECO has certain full requirements contracts and block contracts that are considered derivatives and qualify for the NPNS scope exception under current derivative authoritative guidance. PECO’s natural gas procurement policy is designed to achieve a reasonable balance of long-term and short-term gas purchases under different pricing approaches in order to achieve system supply reliability at the least cost. PECO’s reliability strategy is two-fold. First, PECO must assure that there is sufficient transportation capacity to satisfy delivery requirements. Second, PECO must ensure that a firm source of supply exists to utilize the capacity resources. All of PECO’s natural gas supply and asset management agreements that are derivatives either qualify for the NPNS scope exception and have been designated as such, or have no mark-to-market balances because the derivatives are index priced. Additionally, in accordance with the 2015 PAPUC PGC settlement and to reduce the exposure of PECO and its customers to natural gas price volatility, PECO has continued its program to purchase natural gas for both winter and summer supplies using a layered approach of locking-in prices ahead of each season with long-term gas purchase agreements (those with primary terms of at least twelve months). Under the terms of the 2015 PGC settlement, PECO is required to lock in (i.e., economically hedge) the price of a minimum volume of its long-term gas commodity purchases. PECO’s gas-hedging program is designed to cover about 30% of planned natural gas purchases in support of projected firm sales. The hedging program for natural gas procurement has no direct impact on PECO’s financial position or results of operations as natural gas costs are fully recovered from customers under the PGC. BGE has contracts to procure SOS electric supply that are executed through a competitive procurement process approved by the MDPSC. The SOS rates charged recover BGE’s wholesale power supply costs and include an administrative fee. The administrative fee includes an incremental cost component and a shareholder return component for commercial and industrial rate classes. BGE’s price risk related to electric supply procurement is limited. BGE locks in fixed prices for all of its SOS requirements through full requirements contracts. Certain of BGE’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other BGE full requirements contracts are not derivatives. BGE provides natural gas to its customers under a MBR mechanism approved by the MDPSC. Under this mechanism, BGE’s actual cost of gas is compared to a market index (a measure of the market price of gas in a given period). The difference between BGE’s actual cost and the market index is shared equally between shareholders and customers. BGE must also secure fixed price contracts for at least 10% , but not more than 20% , of forecasted system supply requirements for flowing (i.e., non-storage) gas for the November through March period. These fixed-price contracts are not subject to sharing under the MBR mechanism. BGE also ensures it has sufficient pipeline transportation capacity to meet customer requirements. All of BGE’s natural gas supply and asset management agreements qualify for the NPNS scope exception and result in physical delivery. Proprietary Trading. Generation also enters into certain energy-related derivatives for proprietary trading purposes. Proprietary trading includes all contracts entered into with the intent of benefiting from shifts or changes in market prices as opposed to those entered into with the intent of hedging or managing risk. Proprietary trading activities are subject to limits established by Exelon’s RMC. The proprietary trading activities, which included settled physical sales volumes of 7,310 GWh, 10,571 GWh and 8,762 GWh for the years ended December 31, 2015 , 2014 and 2013 , are a complement to Generation’s energy marketing portfolio but represent a small portion of Generation’s revenue from energy marketing activities. ComEd, PECO and BGE do not enter into derivatives for proprietary trading purposes. Interest Rate and Foreign Exchange Risk (Exelon, Generation, ComEd, PECO and BGE) The Registrants use a combination of fixed-rate and variable-rate debt to manage interest rate exposure. The Registrants utilize fixed-to-floating interest rate swaps, which are typically designated as fair value hedges, as a means to manage their interest rate exposure. In addition, the Registrants may utilize interest rate derivatives to lock in rate levels in anticipation of future financings, which are typically designated as cash flow hedges. These strategies are employed to manage interest rate risks. At December 31, 2015 , Exelon had $800 million of notional amounts of fixed-to-floating hedges outstanding and Exelon and Generation had $738 million of notional amounts of floating-to-fixed hedges outstanding. Assuming the fair value and cash flow interest rate hedges are 100% effective, a hypothetical 50 bps increase in the interest rates associated with unhedged variable-rate debt (excluding Commercial Paper) and fixed-to-floating swaps would result in an approximately $6 million decrease in Exelon Consolidated pre-tax income for the year ended December 31, 2015 . To manage foreign exchange rate exposure associated with international energy purchases in currencies other than U.S. dollars, Generation utilizes foreign currency derivatives, which are typically designated as economic hedges. Below is a summary of the interest rate and foreign exchange hedge balances as of December 31, 2015 : Generation Other Exelon Description Derivatives Designated as Hedging Instruments Economic Hedges Proprietary (a) Collateral and Netting (b) Subtotal Derivatives Economic Hedges Collateral and Netting (b) Subtotal Total Mark-to-market $ — $ 10 $ 10 $ (5 ) $ 15 $ — $ — $ — $ — $ 15 Mark-to-market — 10 5 (1 ) 14 25 — — 25 39 Total mark-to-market — 20 15 (6 ) 29 25 — — 25 54 Mark-to-market (8 ) (2 ) (9 ) 11 (8 ) — — — — (8 ) Mark-to-market (8 ) (1 ) (3 ) 4 (8 ) — — — — (8 ) Total mark-to-market (16 ) (3 ) (12 ) 15 (16 ) — — — — (16 ) Total mark-to-market $ (16 ) $ 17 $ 3 $ 9 $ 13 $ 25 $ — $ — $ 25 $ 38 _________________________ (a) Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The characterization of the interest rate derivative contracts between the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure. Generation does not utilize proprietary trading interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates. (b) Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures subject to a master netting or similar agreement, such as accrued interest, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above. The following table provides a summary of the interest rate and foreign exchange hedge balances recorded by the Registrants as of December 31, 2014 : Generation Other Exelon Description Derivatives Designated as Hedging Instruments Economic Hedges Proprietary (a) Collateral and Netting (b) Subtotal Derivatives Economic Hedges Collateral and Netting (b) Subtotal Total Mark-to-market $ 7 $ 7 $ 20 $ (22 ) $ 12 $ 3 $ — $ — $ 3 $ 15 Mark-to-market 1 5 7 (7 ) 6 20 1 (19 ) $ 2 $ 8 Total mark-to-market 8 12 27 (29 ) 18 23 1 (19 ) 5 23 Mark-to-market (8 ) (2 ) (14 ) 25 1 — — — — 1 Mark-to-market (4 ) — (9 ) 10 (3 ) (29 ) (101 ) 19 (111 ) (114 ) Total mark-to-market (12 ) (2 ) (23 ) 35 (2 ) (29 ) (101 ) 19 (111 ) (113 ) Total mark-to-market $ (4 ) $ 10 $ 4 $ 6 $ 16 $ (6 ) $ (100 ) $ — $ (106 ) $ (90 ) _________________________ (a) Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The characterization of the interest rate derivative contracts between the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure. Generation does not utilize proprietary trading interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates. (b) Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures subject to a master netting or similar agreement, such as accrued interest, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above. Fair Value Hedges . For derivative instruments that are designated and qualify as fair value hedges, the gain or loss on the derivative as well as the offsetting loss or gain on the hedged item attributable to the hedged risk are recognized in current earnings. Exelon includes the gain or loss on the hedged items and the offsetting loss or gain on the related interest rate swaps in interest expense as follows: Year Ended December 31, Income Statement Location 2015 2014 2013 2015 2014 2013 Gain (Loss) on Swaps Gain (Loss) on Borrowings Generation Interest expense (a) $ (1 ) $ (16 ) $ (15 ) $ — $ 2 $ (6 ) Exelon Interest expense $ 2 $ 3 $ (24 ) $ (9 ) $ 15 $ (3 ) ______________________ (a) For the years ended December 31, 2015 and 2014 , the loss on Generation swaps included $(1) million and $(17) million realized in earnings, respectively, with an immaterial amount and $4 million excluded from hedge effectiveness testing, respectively. At December 31, 2015 , Exelon had total outstanding fixed-to-floating fair value hedges related to interest rate swaps of $800 million , with a derivative asset of $25 million . At December 31, 2014 , Exelon and Generation had outstanding fixed-to-floating fair value hedges related to interest rate swaps of $1,450 million and $550 million , with a derivative asset of $29 million and $7 million , respectively. During the years ended December 31, 2015 and 2014 , the impact on the results of operations, as a result of the ineffectiveness from fair value hedges, was a $17 million gain and $18 million gain, respectively. Cash Flow Hedges . During 2014, Exelon entered into $400 million of floating-to-fixed forward starting interest rate swaps to manage a portion of the interest rate exposure associated with the anticipated refinancing of existing debt. The swaps are designated as cash flow hedges. In January 2015, in connection with Generation's $750 million issuance of five-year Senior Unsecured Notes, Exelon terminated these swaps. As the original forecasted transactions were a series of future interest payments over a ten year period, a portion of the anticipated interest payments are probable not to occur. As a result, $26 million of anticipated payments were reclassified from Accumulated OCI to Other, net in Exelon's Consolidated Statement of Operations and Comprehensive Income. During the third quarter of 2014, ExGen Texas Power, LLC, a subsidiary of Generation, entered into a floating-to-fixed interest rate swap to manage a portion of its interest rate exposure in connection with the long-term borrowing. See Note 14 — Debt and Credit Agreements for additional information regarding the financing. The swaps have a notional amount of $500 million as of December 31, 2015 and expire in 2019. The swap was designated as a cash flow hedge in the fourth quarter of 2014. At December 31, 2015 , the subsidiary had a $12 million derivative liability related to the swap. During the first quarter of 2014, ExGen Renewables I, LLC, a subsidiary of Generation, entered into floating-to-fixed interest rate swaps to manage a portion of its interest rate exposure in connection with the long-term borrowings. See Note 14 — Debt and Credit Agreements for additional information regarding the financing. The swaps have a notional amount of $189 million as of December 31, 2015 and expire in 2020. The swaps are designated as cash flow hedges. At December 31, 2015 , the subsidiary had a $2 million derivative liability related to the swaps. During the years ended December 31, 2015 and 2014 , the impact on the results of operations as a result of ineffectiveness from cash flow hedges in continuing designated hedge relationships were immaterial . Economic Hedges. During the third quarter of 2011, Sacramento PV Energy, a subsidiary of Generation, entered into floating-to-fixed interest rate swaps to manage a portion of its interest rate exposure in connection with the long-term borrowings. See Note 14 — Debt and Credit Agreements for additional information regarding the financing. The swaps have a total notional amount of $25 million as of December 31, 2015 and expire in 2027. After the closing of the Constellation merger, the swaps were re-designated as cash flow hedges. During the first quarter of 2015, the swaps were de-designated as the forecasted transaction was no longer probable of occurring. All future changes in fair value are reflected in Interest expense. At December 31, 2015 , the subsidiary had a $2 million derivative liability related to these swaps, which included an immaterial amount that was amortized to Interest expense after de-designation. During the third quarter of 2012, Constellation Solar Horizons, a subsidiary of Generation, entered into a floating-to-fixed interest rate swap to manage a portion of its interest rate exposure in connection with the long-term borrowings. See Note 14 — Debt and Credit Agreements for additional information regarding the financing. The swap has a notional amount of $24 million as of December 31, 2015 , and expires in 2030. This swap was designated as a cash flow hedge. During the first quarter of 2015, the swaps were de-designated as the forecasted transaction was no longer probable of occurring. All future changes in fair value are reflected in Interest expense. At December 31, 2015 , the derivative asset related to the swap was immaterial . During the second quarter 2015, upon the issuance of debt, Exelon terminated $2,400 million of floating-to-fixed forward starting interest rate swaps. As a result of the termination of the swaps, Exelon realized a $64 million loss during the second quarter of 2015. At December 31, 2015 , Generation had immaterial notional amounts of interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions and $ 30 million in notional amounts of foreign currency exchange rate swaps that are marked-to-market to manage the exposure associated with international purchases of commodities in currencies other than U.S. dollars. Fair Value Measurement and Accounting for the Offsetting of Amounts Related to Certain Contracts (Exelon Generation, ComEd, PECO and BGE) Fair value accounting guidance and disclosures about offsetting assets and liabilities requires the fair value of derivative instruments to be shown in the Notes to the Consolidated Financial Statements on a gross basis, even when the derivative instruments are subject to legally enforceable master netting agreements and qualify for net presentation in the Consolidated Balance Sheet. A master netting agreement is an agreement between two counterparties that may have derivative and non-derivative contracts with each other providing for the net settlement of all referencing contracts via one payment stream, which takes place as the contracts deliver, when collateral is requested or in the event of default. Generation’s use of cash collateral is generally unrestricted unless Generation is downgraded below investment grade (i.e. to BB+ or Ba1). In the table below, Generation’s energy related economic hedges and proprietary trading derivatives are shown gross. The impact of the netting of fair value balances with the same counterparty that are subject to legally enforceable master netting agreements, as well as netting of cash collateral including initial margin on exchange positions, is aggregated in the collateral and netting column. As of December 31, 2015 and 2014 , $3 million and $8 million of cash collateral posted, respectively, was not offset against derivative positions because such collateral was not associated with any energy-related derivatives, were associated with accrual positions, or as of the balance sheet date there were no positions to offset. Excluded from the tables below are economic hedges that qualify for the NPNS scope exception and other non-derivative contracts that are accounted for under the accrual method of accounting. ComEd’s use of cash collateral is generally unrestricted unless ComEd is downgraded below investment grade (i.e. to BB+ or Ba1). Cash collateral held by PECO and BGE must be deposited in a non affiliate major U.S. commercial bank or foreign bank with a U.S. branch office that meet certain qualifications. The following table provides a summary of the derivative fair value balances recorded by the Registrants as of December 31, 2015 : Generation ComEd Exelon Derivatives Economic Hedges Proprietary Trading Collateral and Netting (a) Subtotal (b) Economic (c) Total Derivatives Mark-to-market derivative assets (current assets) $ 5,236 $ 108 $ (3,994 ) $ 1,350 $ — $ 1,350 Mark-to-market derivative assets (noncurrent assets) 1,860 22 (1,163 ) 719 — 719 Total mark-to-market derivative assets 7,096 130 (5,157 ) 2,069 — 2,069 Mark-to-market derivative liabilities (current liabilities) (4,907 ) (94 ) 4,827 (174 ) (23 ) (197 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,673 ) (33 ) 1,564 (142 ) (224 ) (366 ) Total mark-to-market derivative liabilities (6,580 ) (127 ) 6,391 (316 ) (247 ) (563 ) Total mark-to-market derivative net assets (liabilities) $ 516 $ 3 $ 1,234 $ 1,753 $ (247 ) $ 1,506 ______________________ (a) Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above. (b) Current and noncurrent assets are shown net of collateral of $352 million and $180 million , respectively, and current and noncurrent liabilities are shown net of collateral of $480 million and $222 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $1,234 million at December 31, 2015 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. The following table provides a summary of the derivative fair value balances recorded by the Registrants as of December 31, 2014 : Generation ComEd Exelon Derivatives Economic Proprietary Trading Collateral and (a) Subtotal (b) Economic (c) Total Derivatives Mark-to-market derivative assets (current assets) $ 4,992 $ 456 $ (4,184 ) $ 1,264 $ — $ 1,264 Mark-to-market derivative assets (noncurrent assets) 1,821 56 (1,112 ) 765 — 765 Total mark-to-market derivative assets 6,813 512 (5,296 ) 2,029 — 2,029 Mark-to-market derivative liabilities (current liabilities) (4,947 ) (468 ) 5,200 (215 ) (20 ) (235 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,540 ) (64 ) 1,502 (102 ) (187 ) (289 ) Total mark-to-market derivative liabilities (6,487 ) (532 ) 6,702 (317 ) (207 ) (524 ) Total mark-to-market derivative net assets (liabilities) $ 326 $ (20 ) $ 1,406 $ 1,712 $ (207 ) $ 1,505 ______________________ (a) Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above. (b) Current and noncurrent assets are shown net of collateral of $416 million and $171 million , respectively, and current and noncurrent liabilities are shown net of collateral of $599 million and $220 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $1,406 million at December 31, 2014 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. Cash Flow Hedges (Exelon, Generation and ComEd). As discussed previously, effective prior to the Constellation merger, Generation de-designated all of its cash flow hedges relating to commodity price risk. Because the underlying forecasted transactions remain at least reasonably probable, the fair value of the effective portion of these cash flow hedges was frozen in Accumulated OCI and is reclassified to results of operations when the forecasted purchase or sale of the energy commodity occurs, or becomes probable of not occurring. Generation began recording prospective changes in the fair value of these instruments through current earnings from the date of de-designation. As of December 31, 2015 , no unrealized balance remains in accumulated OCI to be reclassified by Generation. The tables below provide the activity of Accumulated OCI related to cash flow hedges for the years ended December 31, 2015 and 2014 , containing information about the changes in the fair value of cash flow hedges and the reclassification from Accumulated OCI into results of operations. The amounts reclassified from Accumulated OCI, when combined with the impacts of the hedged transactions, result in the ultimate recognition of net revenues or expenses at the contractual price. Income Statement Location Total Cash Flow Hedge OCI Activity, Net of Income Tax Generation Exelon Total Cash Flow Hedges Total Cash Flow Hedges Accumulated OCI derivative gain at January 1, 2014 $ 114 $ 120 Effective portion of changes in fair value (15 ) (31 ) Reclassifications from accumulated OCI to net income Operating revenues (117 ) (a) (117 ) (a) Accumulated OCI derivative gain at December 31, 2014 (18 ) (28 ) Effective portion of changes in fair value (8 ) (12 ) Reclassifications from accumulated OCI to net income Other, net — 16 (b) Reclassifications from accumulated OCI to net income Interest expense 7 (c) 7 (c) Reclassifications from accumulated OCI to net income Operating revenues (2 ) (2 ) Accumulated OCI derivative gain at December 31, 2015 $ (21 ) $ (19 ) _______________________ (a) Amount is net of related income tax expense of $78 million for the year ended December 31, 2014 . (b) Amount is net of related income tax benefit of $10 million for the year ended December 31, 2015 . (c) Amount is net of related income tax expense of $4 million for the year ended December 31, 2015 . During the years ended December 31, 2015 , 2014 , and 2013 , Generation’s former energy-related cash flow hedge activity impact to pre-tax earnings based on the reclassification adjustment from Accumulated OCI to earnings was a $2 million , $195 million and $683 million pre-tax gain, respectively. In addition, the effect of Exelon's former energy-related cash flow hedge activity impact on pre-tax earnings based on the reclassification adjustment from Accumulated OCI to earnings was a $2 million , $195 million an

Debt and Credit Agreements (Exe

Debt and Credit Agreements (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Debt and Credit Agreements (Exelon, Generation, ComEd, PECO and BGE)	(Exelon, Generation, ComEd, PECO and BGE) Short-Term Borrowings Exelon, ComEd and BGE meet their short-term liquidity requirements primarily through the issuance of commercial paper. Generation and PECO meet their short-term liquidity requirements primarily through the issuance of commercial paper and borrowings from the intercompany money pool. Exelon, Generation, ComEd, PECO and BGE had the following amounts of commercial paper borrowings at December 31, 2015 and 2014 : Maximum Program Size at December 31, Outstanding Commercial Paper at December 31, Average Interest Rate on Commercial Paper Borrowings for the Year Ended December 31, Commercial Paper Issuer 2015 (a)(b) 2014 (a)(b) 2015 2014 2015 2014 Exelon Corporate $ 500 $ 500 $ — $ — n.a. n.a. Generation 5,450 5,600 — — 0.49 % 0.32 % ComEd 1,000 1,000 294 304 0.53 % 0.33 % PECO 600 600 — — n.a. n.a. BGE 600 600 210 120 0.48 % 0.29 % Total $ 8,150 $ 8,300 $ 504 $ 424 _____________________ (a) Reflects aggregate bank commitments under the revolving and bilateral credit agreements (with the exception of $275 million and $200 million bilateral agreements for Generation as of December 31, 2015 and 2014 , respectively) that backstop the commercial paper program. See discussion and Credit Facilities table below for items affecting effective program size. (b) Excludes additional credit facilities for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million , $34 million , $34 million and $5 million , respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. The agreements for these facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of December 31, 2015 , letters of credit issued under these facilities totaled $7 million , $14 million , $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively. In order to maintain their respective commercial paper programs in the amounts indicated above, each Registrant must have revolving credit facilities in place, at least equal to the amount of its commercial paper program. While the amount of outstanding commercial paper does not reduce available capacity under a Registrant’s credit facility, a Registrant does not issue commercial paper in an aggregate amount exceeding the then available capacity under its credit facility. At December 31, 2015 , the Registrants had the following aggregate bank commitments, credit facility borrowings and available capacity under their respective credit facilities: Available Capacity at December 31, 2015 Borrower Aggregate Bank (a) Facility Draws Outstanding Letters of Credit (c) Actual To Support Additional Commercial (b) Exelon Corporate $ 500 $ — $ 26 $ 474 $ 474 Generation 5,725 — 1,449 4,276 4,174 ComEd 1,000 — 2 998 704 PECO 600 — 1 599 599 BGE 600 — — 600 390 Total $ 8,425 $ — $ 1,478 $ 6,947 $ 6,341 _______________________ (a) Excludes additional credit facilities for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million , $34 million , $34 million and $5 million , respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. The agreements for these facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of December 31, 2015 , letters of credit issued under these facilities totaled $7 million , $14 million , $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively. (b) Excludes $275 million bilateral credit facilities that do not back Generation’s commercial paper program. (c) Excludes nonrecourse debt letters of credit, see discussion below on Continental Wind. As of December 31, 2015 , there were no borrowings under the Registrants’ credit facilities. The following tables present the short-term borrowings activity for Exelon, Generation, ComEd, and BGE during 2015 , 2014 and 2013 . PECO did not have any short-term borrowings during 2015 , 2014 or 2013 . Exelon 2015 2014 2013 Average borrowings $ 499 $ 571 $ 254 Maximum borrowings outstanding 739 1,164 682 Average interest rates, computed on a daily basis 0.53 % 0.32 % 0.37 % Average interest rates, at December 31 0.88 % 0.53 % 0.35 % Generation 2015 2014 2013 Average borrowings $ 1 $ 93 $ 42 Maximum borrowings outstanding 50 552 291 Average interest rates, computed on a daily basis 0.49 % 0.32 % 0.32 % Average interest rates, at December 31 n.a. n.a. n.a. ComEd 2015 2014 2013 Average borrowings $ 461 $ 415 $ 203 Maximum borrowings outstanding 684 597 446 Average interest rates, computed on a daily basis 0.53 % 0.33 % 0.40 % Average interest rates, at December 31 0.89 % 0.50 % 0.37 % BGE 2015 2014 2013 Average borrowings $ 37 $ 64 $ 35 Maximum borrowings outstanding 210 180 135 Average interest rates, computed on a daily basis 0.48 % 0.29 % 0.31 % Average interest rates, computed at December 31 0.87 % 0.61 % 0.31 % Credit Agreements On October 23, 2015, the credit agreement for CENG's $100 million bilateral credit facility was amended and extended for an additional two years. This facility has been utilized by CENG to fund working capital and capital projects. This facility does not back Generation's commercial paper program. On January 5, 2016, Generation entered into a credit agreement establishing a $150 million bilateral credit facility, scheduled to mature in January of 2019. This facility does not back Generation's commercial paper program. Borrowings under Exelon Corporate’s, Generation’s, ComEd’s, PECO’s and BGE’s revolving credit facilities bear interest at a rate based upon either the prime rate or a LIBOR-based rate, plus an adder based upon the particular registrant’s credit rating. Exelon Corporate, Generation, ComEd, PECO and BGE have adders of 27.5 , 27.5 , 7.5 , 0.0 and 0.0 basis points for prime based borrowings and 127.5 , 127.5 , 107.5 , 90.0 and 100.0 basis points for LIBOR-based borrowings. The maximum adders for prime rate borrowings and LIBOR-based rate borrowings are 65 basis points and 165 basis points, respectively. The credit agreements also require the borrower to pay a facility fee based upon the aggregate commitments. The fee varies depending upon the respective credit ratings of the borrower. An event of default under any of the Registrants' credit agreements would not constitute an event of default under any of the other Registrants' credit agreements, except that a bankruptcy or other event of default in the payment of principal, premium or indebtedness in principal amount in excess of $100 million in the aggregate by Generation under its credit agreement would constitute an event of default under the Exelon Corporation credit agreement. Each credit agreement requires the affected borrower to maintain a minimum cash from operations to interest expense ratio for the twelve-month period ended on the last day of any quarter. The ratios exclude revenues and interest expenses attributable to securitization debt, certain changes in working capital, distributions on preferred securities of subsidiaries and, in the case of Exelon and Generation, interest on the debt of its project subsidiaries. The following table summarizes the minimum thresholds reflected in the credit agreements for the year ended December 31, 2015 : Exelon Generation ComEd PECO BGE Credit agreement threshold 2.50 to 1 3.00 to 1 2.00 to 1 2.00 to 1 2.00 to 1 At December 31, 2015 , the interest coverage ratios at the Registrants were as follows: Exelon Generation ComEd PECO BGE Interest coverage ratio 9.77 12.31 7.25 8.94 10.66 Long-Term Debt The following tables present the outstanding long-term debt at Exelon, Generation, ComEd, PECO and BGE as of December 31, 2015 and 2014 : Exelon Maturity Date December 31, Rates 2015 2014 Long-term debt Rate stabilization bonds 5.72 % - 5.82 % 2017 $ 120 $ 195 First mortgage bonds (a) 1.20 % - 6.45 % 2016 - 2045 9,019 8,079 Senior unsecured notes 1.55 % - 7.60 % 2017 - 2045 9,803 7,071 Unsecured bonds 2.80 % - 6.35 % 2016 - 2036 1,750 1,750 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 435 — Nuclear fuel procurement contracts 3.15 % - 3.35 % 2018 - 2020 127 70 Notes payable and other (b)(c) 1.43 % - 7.83 % 2016 - 2053 314 174 Junior subordinated notes 6.50 % 2024 1,150 1,150 Contract payment - junior subordinated notes 2.50 % 2017 64 108 Long-term software licensing agreement 3.95 % 2024 111 — Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,162 1,166 Variable rates 2.42 % - 5.00 % 2017 - 2030 1,058 1,101 Total long-term debt 25,113 20,864 Unamortized debt discount and premium, net (63 ) (37 ) Unamortized debt issuance costs (d) (180 ) (150 ) Fair value adjustment 275 333 Fair value hedge carrying value adjustment, net — 4 Long-term debt due within one year (1,500 ) (1,802 ) Long-term debt $ 23,645 $ 19,212 Long-term debt to financing trusts (e) Subordinated debentures to ComEd Financing III 6.35 % 2033 $ 206 $ 206 Subordinated debentures to PECO Trust III 7.38 % 2028 81 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Subordinated debentures to BGE Trust 6.20 % 2043 258 258 Total long-term debt to financing trusts 648 648 Unamortized debt issuance costs (d) (7 ) (7 ) Long-term debt to financing trusts $ 641 $ 641 ____________________ (a) Substantially all of ComEd’s assets other than expressly excepted property and substantially all of PECO’s assets are subject to the liens of their respective mortgage indentures. (b) Includes capital lease obligations of $29 million and $32 million at December 31, 2015 and 2014 , respectively. Lease payments of $4 million , $4 million , $4 million , $5 million , $4 million , and $8 million will be made in 2016 , 2017 , 2018 , 2019 , 2020 and thereafter, respectively. (c) Includes financing related to Albany Green Energy, LLC (AGE), which is a consolidated variable interest entity (see Note 2 - Variable Interest Entities for additional information). The agreement is scheduled to expire on November 17, 2017, at a variable rate equal to LIBOR plus 1.25%. As of December 31, 2015, $100 million was outstanding. (d) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. (e) Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets. Generation Maturity Date December 31, Rates 2015 2014 Long-term debt Senior unsecured notes 2.00 % - 7.60 % 2017 - 2042 $ 5,971 $ 5,771 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 435 — Nuclear fuel procurement contracts 3.15 % - 3.35 % 2018 - 2020 127 70 Notes payable and other (a)(b) 1.43 % 7.83 % 2016 - 2035 166 26 Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,162 1,166 Variable rates 2.42 % - 5.00 % 2017 - 2030 1,058 1,101 Total long-term debt 8,919 8,134 Fair value adjustment 127 146 Unamortized debt discount and premium, net (17 ) (14 ) Unamortized debt issuance costs (c) (70 ) (70 ) Long-term debt due within one year (90 ) (614 ) Long-term debt $ 8,869 $ 7,582 ______________________ (a) Includes Generation’s capital lease obligations of $21 million and $24 million at December 31, 2015 and 2014 , respectively. Generation will make lease payments of $4 million , $4 million , $4 million , $5 million and $4 million in 2016 , 2017 , 2018 , 2019 , 2020 , respectively. The capital lease matures in 2020. (b) Includes financing related to Albany Green Energy, LLC (AGE), which is a consolidated variable interest entity (see Note 2 - Variable Interest Entities for additional information). The agreement is scheduled to expire on November 17, 2017, at a variable rate equal to LIBOR plus 1.25%. As of December 31, 2015, $100 million was outstanding. (c) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. ComEd Maturity Date December 31, Rates 2015 2014 Long-term debt First mortgage bonds (a) 1.95 % - 6.45 % 2016 - 2045 $ 6,419 $ 5,829 Notes payable and other (b) 6.95 % - 7.49 % 2016 - 2053 148 148 Total long-term debt 6,567 5,977 Unamortized debt discount and premium, net (20 ) (19 ) Unamortized debt issuance costs (c) (38 ) (33 ) Long-term debt due within one year (665 ) (260 ) Long-term debt $ 5,844 $ 5,665 Long-term debt to financing trust (d) Subordinated debentures to ComEd Financing III 6.35 % 2033 $ 206 $ 206 Total long-term debt to financing trusts 206 206 Unamortized debt issuance costs (c) (1 ) (1 ) Long-term debt to financing trusts $ 205 $ 205 ______________________ (a) Substantially all of ComEd’s assets other than expressly excepted property are subject to the lien of its mortgage indenture. (b) Includes ComEd’s capital lease obligations of $8 million at both December 31, 2015 and 2014 , respectively. Lease payments of less than $1 million will be made from 2016 through expiration at 2053. (c) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. (d) Amount owed to this financing trust is recorded as Long-term debt to financing trust within ComEd’s Consolidated Balance Sheets. PECO Maturity Date December 31, Rates 2015 2014 Long-term debt First mortgage bonds (a) 1.20 % - 5.95 % 2016 - 2044 $ 2,600 $ 2,250 Total long-term debt 2,600 2,250 Unamortized debt discount and premium, net (5 ) (4 ) Unamortized debt issuance costs (b) (15 ) (14 ) Long-term debt due within one year (300 ) — Long-term debt $ 2,280 $ 2,232 Long-term debt to financing trusts (c) Subordinated debentures to PECO Trust III 7.38 % 2028 $ 81 $ 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Long-term debt to financing trusts $ 184 $ 184 _____________________ (a) Substantially all of PECO’s assets are subject to the lien of its mortgage indenture. (b) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. (c) Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets. BGE Maturity Date December 31, Rates 2015 2014 Long-term debt Rate stabilization bonds 5.72 % - 5.82 % 2017 $ 120 $ 195 Senior unsecured notes 2.80 % - 6.35 % 2016 - 2036 1,750 1,750 Total long-term debt 1,870 1,945 Unamortized debt discount and premium, net (3 ) (3 ) Unamortized debt issuance costs (a) (9 ) (10 ) Long-term debt due within one year (378 ) (75 ) Long-term debt $ 1,480 $ 1,857 Long-term debt to financing trusts (b) Subordinated debentures to BGE Capital Trust II 6.20 % 2043 $ 258 $ 258 Total long-term debt to financing trusts 258 258 Unamortized debt issuance costs (a) (6 ) (6 ) Long-term debt to financing trusts $ 252 $ 252 ___________________ (a) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. (b) Amount owed to this financing trust is recorded as Long-term debt to financing trust within BGE’s Consolidated Balance Sheets. Long-term debt maturities at Exelon, Generation, ComEd, PECO and BGE in the periods 2016 through 2020 and thereafter are as follows: Year Exelon Generation ComEd PECO BGE 2016 $ 1,487 $ 90 $ 665 $ 300 $ 378 2017 1,841 805 425 — 42 2018 1,393 53 840 500 — 2019 973 673 300 — — 2020 3,311 1,911 500 — — Thereafter 16,756 (a) 5,387 4,043 (b) 1,984 (c) 1,708 (d) Total $ 25,761 $ 8,919 $ 6,773 $ 2,784 $ 2,128 ____________________ (a) Includes $648 million due to ComEd, PECO and BGE financing trusts. (b) Includes $206 million due to ComEd financing trust. (c) Includes $184 million due to PECO financing trusts. (d) Includes $258 million due to BGE financing trust. PHI Merger Financing In May 2014, concurrently and in connection with entering into the agreement to acquire PHI, Exelon entered into a credit facility to which the lenders committed to provide Exelon a 364-day senior unsecured bridge credit facility of $7.2 billion to support the contemplated transaction and provide flexibility for timing of permanent financing. In June 2015, the remaining $3.2 billion bridge credit facility was terminated as a result of Exelon's issuance of $4.2 billion of long-term debt to fund a portion of the purchase price and related costs and expenses for the pending PHI merger and for general corporate purposes. In connection with the $4.2 billion issuance of Senior Unsecured Notes in 2015, the tranches due in 2025, 2035, and 2045 had to be redeemed at the principal amount plus a 1% premium of principal on December 31, 2015, if the PHI merger was not consummated or terminated prior to such date ("Special Mandatory Redemption"). Exelon also had the option to redeem those notes earlier at a 1% premium of principal, if Exelon determined that the merger would not be completed before December 31, 2015. On October 29, 2015, Exelon commenced a private exchange offer (Exchange Offer) to certain eligible holders whereby, for those that took part, the outstanding Senior Unsecured Notes in the 2025, 2035 and 2045 tranches were exchanged for new Senior Unsecured Notes. The new Senior Unsecured Notes have substantially the same terms as the outstanding Senior Unsecured Notes, except the outside date with regard to the special redemption provisions is June 30, 2016, (or the date the PHI merger is terminated if earlier), rather than December 31, 2015, and under certain circumstances, can be further extended to August 31, 2016. On December 2, 201 5, Exelon exchanged $1.9 billion of the Senior Unsecured Notes and paid a consent fee of approximately $5 million , which has been deferred on Exelon's Consolidated Balance Sheet and $4 million of third-party debt issuance costs, which were charged to earnings within Other, net on Exelon's Consolidated Statement of Operations and Comprehensive Income. On December 2, 2015, Exelon also redeemed $0.9 billion of Senior Unsecured Notes not exchanged in the Exchange Offer resulting in the payment of $9 million of redemption premium and the acceleration of the unamortized original issuance discount and deferred financing costs associated with the redeemed debt of $9 million , which were charged to earnings within Other, net on Exelon's Consolidated Statement of Operations and Comprehensive Income. Junior Subordinated Notes In June 2014, Exelon issued $1.15 billion of junior subordinated notes in the form of 23 million equity units at a stated amount of $50.00 per unit. Net proceeds from the issuance were $1.11 billion , net of a $35 million underwriter fee. The net proceeds are expected to be used to finance a portion of the merger and related costs and expenses for the pending PHI merger and for general corporate purposes. Each equity unit represents an undivided beneficial ownership interest in Exelon's 2.50% junior subordinated notes due in 2024 and a forward equity purchase contract which settles in 2017. The junior subordinated notes are expected to be remarketed in 2017. At the time of issuance, Exelon determined that the forward equity purchase contract had no value and therefore the entire $1.15 billion of junior subordinated notes were allocated to debt and recorded within Long-term debt on Exelon’s Consolidated Balance Sheet. Additionally, at the time of issuance, the present value of the contract payments of $131 million ("Contract Payment Obligation") were recorded to Long-term debt, representing the obligation to make contract payments, with an offsetting reduction to Common stock. The obligation for the contract payments is accreted to interest expense over the 3 year period ending in 2017 in Exelon’s Consolidated Statement of Operations and Comprehensive Income. During 2015, contract payments of $44 million related to the Contract Payment Obligation were included within Retirements of long-term debt in Exelon's Consolidated Statements of Cash Flows. During 2014, the Contract Payment Obligation was considered a non-cash financing transaction that was excluded from Exelon's Consolidated Statements of Cash Flows. Until settlement of the equity purchase contract, earnings per share dilution resulting from the equity unit issuance will be determined under the treasury stock method. Nonrecourse Debt Exelon and Generation have issued nonrecourse debt financing, in which approximately $2.4 billion of generating assets and $0.2 billion of Upstream gas properties have been pledged as collateral at December 31, 2015 . Borrowings under these agreements are secured by the assets and equity of each respective project. The lenders do not have recourse against Exelon or Generation in the event of a default. Denver Airport. In June 2011, Generation entered into a 20-year, $7 million solar loan agreement to finance a solar construction project in Denver, Colorado. The agreement is scheduled to mature on June 30, 2031. The agreement bears interest at a fixed rate of 5.50% annually with interest payable annually. As of December 31, 2015 , $ 7 million was outstanding. CEU Upstream. In July 2011, Generation entered into a 5-year asset-based lending agreement associated with certain Upstream gas properties that it owns. The borrowing base committed under the facility is $85 million as of December 31, 2015 . The commitment level can be decreased if the assets no longer support the current borrowing base, which would result in repayment of a portion or all of the outstanding balance. The commitment can be increased up to $500 million if the assets support a higher borrowing base and Generation is able to obtain additional commitments from lenders. Calculations of the borrowing base are impacted by projected production and commodity prices. The facility was amended and extended through January 2019. The agreement bears interest at a variable rate equal to LIBOR plus 2.50% and is payable monthly. As of December 31, 2015 , $68 million was outstanding under the facility. Sacramento PV Energy. In July 2011, a subsidiary of Generation entered into a 19-year, $41 million nonrecourse note to finance a 30 MW solar facility in Sacramento, California. The note is scheduled to mature on December 31, 2030. The note bears interest at a variable rate equal to LIBOR plus 2.25% and is payable quarterly. As of December 31, 2015 , $33 million was outstanding. The subsidiary also executed interest rate swaps with an initial notional value of $30 million at an interest rate of 3.57% in order to convert the variable interest payments to fixed payments on 75% of the $41 million facility amount, as required by the debt covenants. See Note 13 — Derivative Financial Instruments for additional information regarding interest rate swaps. Holyoke Solar Cooperative. In October 2011, Generation entered into a 20-year, $11 million solar loan agreement related to a solar construction project in Holyoke, Massachusetts. The agreement is scheduled to mature on December 2031. The agreement bears interest at a fixed rate of 5.25% annually with interest payable monthly. As of December 31, 2015 , $10 million was outstanding. Antelope Valley Solar Ranch One. In December 2011, the DOE Loan Programs Office issued a guarantee for up to $646 million for a nonrecourse loan from the Federal Financing Bank to support the financing of the construction of the Antelope Valley facility. The project became fully operational in the first half of 2014. The loan will mature on January 5, 2037. Interest rates on the loan were fixed upon each advance at a spread of 37.5 basis points above U.S. Treasuries of comparable maturity. The advances were completed as of December 31, 2015 and the outstanding loan balance will bear interest at an average blended interest rate of 2.82%. As of December 31, 2015 , $574 million was outstanding. In addition, Generation has issued letters of credit to support its equity investment in the project. As of December 31, 2015 , Generation had $69 million in letters of credit outstanding related to the project. Constellation Solar Horizons. In September 2012, a subsidiary of Generation entered into an 18-year $38 million nonrecourse note to recover capital used to build a 16 MW solar facility in Emmitsburg, Maryland. The note is scheduled to mature on September 7, 2030. The note bears interest at a variable rate equal to LIBOR plus 2.25% with interest payable quarterly. As of December 31, 2015 , $32 million was outstanding. The subsidiary also executed interest rate swaps for an initial notional amount of $29 million at an interest rate of 2.03% in order to convert the variable interest payments to fixed payments on 75% of the $38 million facility amount, as required by the debt covenants. See Note 13 — Derivative Financial Instruments for additional information regarding interest rate swaps. Continental Wind. In September 2013, Continental Wind, LLC (Continental Wind), an indirect subsidiary of Exelon and Generation, completed the issuance and sale of $613 million senior secured notes. Continental Wind owns and operates a portfolio of wind farms in Idaho, Kansas, Michigan, Oregon, New Mexico and Texas with a total net capacity of 667 MW. The net proceeds were distributed to Generation for its general business purposes. The notes are scheduled to mature on February 28, 2033. The notes bear interest at a fixed rate of 6.00% with interest payable semi-annually. As of December 31, 2015 , $572 million was outstanding. In addition, Continental Wind entered into a $131 million letter of credit facility and $10 million working capital revolver facility. Continental Wind has issued letters of credit to satisfy certain of its credit support and security obligations. As of December 31, 2015 , the Continental Wind letter of credit facility had $99 million in letters of credit outstanding related to the project. ExGen Renewables I. In February 2014, ExGen Renewables I, LLC (EGR), an indirect subsidiary of Exelon and Generation, borrowed $300 million aggregate principal amount pursuant to a nonrecourse senior secured loan. The proceeds were distributed to Generation for its general business purposes. The loan is scheduled to mature on February 6, 2021. The loan bears interest at a variable rate equal to LIBOR plus 4.25% , subject to a 1% LIBOR floor with interest payable quarterly. EGR indirectly owns Continental Wind. As of December 31, 2015 , $258 million was outstanding. In addition to the financing, EGR entered into interest rate swaps with an initial notional amount of $240 million at an interest rate of 2.03% to manage a portion of the interest rate exposure in connection with the financing. See Note 13 — Derivative Financial Instruments for additional information regarding interest rate swaps. ExGen Texas Power. In September 2014, ExGen Texas Power, LLC (EGTP), an indirect subsidiary of Exelon and Generation, issued $675 million aggregate principal amount of a nonrecourse senior secured term loan. The net proceeds were distributed to Generation for general business purposes. The loan is scheduled to mature on September 18, 2021. The term loan bears interest at a variable rate equal to LIBOR plus 4.75% , subject to a 1% LIBOR floor with interest payable quarterly. As of December 31, 2015 , $666 million was outstanding. As part of the agreement, a revolving credit facility was established for the amount of $20 million available through, and scheduled to mature on September 18, 2019. In addition to the financing, EGTP entered into interest rate swaps with an initial notional amount of approximately $505 million at an interest rate of 2.34% to hedge a portion of the interest rate exposure in connection with this financing, as required by the debt covenants. See Note 13 — Derivative Financial Instruments for additional information regarding interest rate swaps.

Income Taxes (Exelon, Generatio

Income Taxes (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes (Exelon, Generation, ComEd, PECO and BGE)	(Exelon, Generation, ComEd, PECO and BGE) Income tax expense (benefit) from continuing operations is comprised of the following components: For the Year Ended December 31, 2015 Exelon Generation ComEd PECO BGE Included in operations: Federal Current $ 407 $ 546 $ (80 ) $ 64 $ 25 Deferred 566 16 310 69 126 Investment tax credit amortization (22 ) (19 ) (2 ) — (1 ) State Current (86 ) (90 ) 7 (10 ) — Deferred 208 49 45 20 39 Total $ 1,073 $ 502 $ 280 $ 143 $ 189 For the Year Ended December 31, 2014 Exelon Generation ComEd PECO BGE Included in operations: Federal Current $ 121 $ 360 $ (171 ) $ 28 $ 24 Deferred 576 (35 ) 395 87 90 Investment tax credit amortization (20 ) (16 ) (2 ) — (1 ) State Current 42 35 7 (2 ) — Deferred (53 ) (137 ) 39 1 27 Total $ 666 $ 207 $ 268 $ 114 $ 140 For the Year Ended December 31, 2013 Exelon Generation ComEd PECO BGE Included in operations: Federal Current $ 744 $ 250 $ 160 $ 126 $ 9 Deferred 140 360 (27 ) 23 100 Investment tax credit amortization (15 ) (11 ) (2 ) (1 ) (1 ) State Current 181 50 50 16 — Deferred (6 ) (34 ) (29 ) (2 ) 26 Total $ 1,044 $ 615 $ 152 $ 162 $ 134 The effective income tax rate from continuing operations varies from the U.S. Federal statutory rate principally due to the following: For the Year Ended December 31, 2015 Exelon Generation ComEd PECO BGE U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 3.7 1.0 4.9 1.0 5.3 Qualified nuclear decommissioning trust fund loss (0.4 ) (0.8 ) — — — Domestic production activities deduction (0.7 ) (1.3 ) — — — Health care reform legislation — — — — 0.1 Amortization of investment tax credit, including deferred taxes on basis difference (0.9 ) (1.5 ) (0.3 ) (0.1 ) (0.1 ) Plant basis differences (1.5 ) — (0.1 ) (8.7 ) (0.7 ) Production tax credits and other credits (1.9 ) (3.4 ) — — — Non-controlling interest 0.3 0.5 — — — Statute of limitations expiration (1.4 ) (2.4 ) — — — Other — — 0.2 0.2 — Effective income tax rate 32.2 % 27.1 % 39.7 % 27.4 % 39.6 % For the Year Ended December 31, 2014 Exelon Generation ComEd PECO BGE U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 1.3 (1.9 ) 4.5 (0.1 ) 5.0 Qualified nuclear decommissioning trust fund income 2.4 4.8 — — — Domestic production activities deduction (2.0 ) (4.1 ) — — — Health care reform legislation 0.1 — 0.2 — 0.2 Amortization of investment tax credit, including deferred taxes on basis difference (1.1 ) (2.0 ) (0.3 ) (0.1 ) (0.3 ) Plant basis differences (1.9 ) — (0.1 ) (10.4 ) 0.2 Production tax credits and other credits (2.4 ) (4.8 ) — — — Non-controlling interest (1.8 ) (3.7 ) Statute of limitations expiration (2.6 ) (5.3 ) — — — Other (0.2 ) (1.1 ) 0.3 0.1 (0.2 ) Effective income tax rate 26.8 % 16.9 % 39.6 % 24.5 % 39.9 % For the Year Ended December 31, 2013 Exelon Generation ComEd PECO BGE U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 4.8 1.8 3.4 1.6 4.9 Qualified nuclear decommissioning trust fund income 3.7 6.1 — — — Domestic production activities deduction — — — — — Health care reform legislation 0.1 — 0.7 — 0.2 Amortization of investment tax credit, including deferred taxes on basis difference (1.9 ) (3.0 ) (0.6 ) (0.1 ) — Plant basis differences (1.6 ) — (0.8 ) (7.1 ) (0.2 ) Production tax credits and other credits (2.1 ) (3.4 ) (0.1 ) — — Statute of limitations expiration (0.1 ) (0.2 ) — — — Other (0.3 ) 0.4 0.3 (0.3 ) (0.9 ) Effective income tax rate 37.6 % 36.7 % 37.9 % 29.1 % 39.0 % The tax effects of temporary differences and carryforwards, which give rise to significant portions of the deferred tax assets (liabilities), as of December 31, 2015 and 2014 are presented below: For the Year Ended December 31, 2015 Exelon Generation ComEd PECO BGE Plant basis differences $ (13,393 ) $ (4,269 ) $ (4,424 ) $ (2,901 ) $ (1,821 ) Accrual based contracts (136 ) (136 ) — — — Derivatives and other financial instruments (203 ) (181 ) (4 ) — — Deferred pension and postretirement obligation 1,801 (371 ) (505 ) (9 ) (47 ) Nuclear decommissioning activities (592 ) (592 ) — — — Deferred debt refinancing costs 133 48 (15 ) (1 ) (4 ) Regulatory assets and liabilities (1,706 ) — (219 ) 16 (264 ) Tax loss carryforward 103 56 — — 33 Tax credit carryforward 327 374 — — — Investment in CENG (595 ) (595 ) — — — Other, net 1,112 425 270 105 27 Deferred income tax liabilities (net) $ (13,149 ) $ (5,241 ) $ (4,897 ) $ (2,790 ) $ (2,076 ) Unamortized investment tax credits (622 ) (598 ) (17 ) (2 ) (5 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (13,771 ) $ (5,839 ) $ (4,914 ) $ (2,792 ) $ (2,081 ) For the Year Ended December 31, 2014 Exelon Generation ComEd PECO BGE Plant basis differences $ (12,143 ) $ (3,834 ) $ (3,945 ) $ (2,749 ) $ (1,660 ) Accrual based contracts (178 ) (178 ) — — — Derivatives and other financial instruments (46 ) (79 ) (4 ) — — Deferred pension and postretirement obligation 1,914 (390 ) (543 ) 2 (53 ) Nuclear decommissioning activities (726 ) (726 ) — — — Deferred debt refinancing costs 112 57 (18 ) (2 ) (4 ) Regulatory assets and liabilities (1,824 ) — (286 ) 27 (258 ) Tax loss carryforward 111 48 — 11 39 Tax credit carryforward 97 143 — — — Investment in CENG (563 ) (563 ) — — — Other, net 1,029 346 255 111 30 Deferred income tax liabilities (net) $ (12,217 ) $ (5,176 ) $ (4,541 ) $ (2,600 ) $ (1,906 ) Unamortized investment tax credits (555 ) (528 ) (20 ) (2 ) (5 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (12,772 ) $ (5,704 ) $ (4,561 ) $ (2,602 ) $ (1,911 ) The following table provides the Registrants’ carryforwards and any corresponding valuation allowances as of December 31, 2015 . Exelon Generation ComEd PECO BGE Federal Federal general business credits carryforward 416 (a) 415 — — — State State net operating losses and other credit carryforwards 2,086 (b) 1,259 (b) — — 618 (c) Deferred taxes on state tax attributes (net) 117 66 — — 34 Valuation allowance on state tax attributes 13 11 — — 1 _____________________ (a) Exelon’s federal general business credit carryforwards will expire beginning in 2032. (b) Exelon’s and Generation's state net operating losses and other carryforwards, which are presented on a post-apportioned basis, will expire beginning in 2016. (c) BGE’s state net operating losses will expire beginning in 2026. Tabular reconciliation of unrecognized tax benefits The following table provides a reconciliation of the Registrants’ unrecognized tax benefits as of December 31, 2015 , 2014 and 2013 : Exelon Generation ComEd PECO BGE Unrecognized tax benefits at January 1, 2015 $ 1,829 $ 1,357 $ 149 $ 44 $ — Increases based on tax positions related to 2015 108 — — — 106 Change to positions that only affect timing (705 ) (659 ) (7 ) (44 ) — Increases based on tax positions prior to 2015 79 65 — — 14 Decreases based on tax positions prior to 2015 (116 ) (112 ) — — — Decrease from settlements with taxing authorities (31 ) (31 ) — — — Decreases from expiration of statute of limitations (86 ) (86 ) — — — Unrecognized tax benefits at December 31, 2015 $ 1,078 $ 534 $ 142 $ — $ 120 Exelon Generation ComEd PECO BGE Unrecognized tax benefits at January 1, 2014 $ 2,175 $ 1,415 $ 324 $ 44 $ — Increases based on tax positions related to 2014 15 15 — — — Change to positions that only affect timing (255 ) 33 (175 ) — — Increases based on tax positions prior to 2014 18 18 — — — Decreases based on tax positions prior to 2014 (1 ) (2 ) — — — Decrease from settlements with taxing authorities (35 ) (34 ) — — — Decreases from expiration of statute of limitations (88 ) (88 ) — — — Unrecognized tax benefits at December 31, 2014 $ 1,829 $ 1,357 $ 149 $ 44 $ — Exelon Generation ComEd PECO BGE Unrecognized tax benefits at January 1, 2013 $ 1,024 $ 876 $ 67 $ 44 $ — Increases based on tax positions related to 2013 19 19 — — — Change to positions that only affect timing 649 36 257 — — Increases based on tax positions prior to 2013 493 493 — — — Decreases based on tax positions prior to 2013 (6 ) (5 ) — — — Decreases from expiration of statute of limitations (4 ) (4 ) — — — Unrecognized tax benefits at December 31, 2013 $ 2,175 $ 1,415 $ 324 $ 44 $ — Included in Exelon’s unrecognized tax benefits balance at December 31, 2015 and 2014 are approximately $540 million and $1,129 million , respectively, of tax positions for which the ultimate tax benefit is highly certain, but for which there is uncertainty about the timing of such benefits. The disallowance of such positions would not materially affect the annual effective tax rate but would accelerate the payment of cash to, or defer the receipt of the cash tax benefit from, the taxing authority to an earlier or later period respectively. Nuclear Decommissioning Liabilities (Exelon and Generation) AmerGen filed income tax refund claims taking the position that nuclear decommissioning liabilities assumed as part of its acquisition of nuclear power plants are taken into account in determining the tax basis in the assets it acquired. The additional basis results primarily in reduced capital gains or increased capital losses on the sale of assets in nonqualified decommissioning funds and increased tax depreciation and amortization deductions. The IRS disagrees with this position and disallowed AmerGen's claims. In early 2009, Generation filed a complaint in the United States Court of Federal Claims to contest this determination. On September 17, 2013, the Court granted the government’s motion denying AmerGen’s claims for refund. In the first quarter of 2014, Exelon filed an appeal of the decision to the United States Court of Appeals for the Federal Circuit. On March 11, 2015, the Federal Circuit affirmed the lower court’s decision to deny AmerGen’s claims for refund. Exelon will not be pursuing further appeals with respect to this issue and, as a result, reduced Generation and PECO's unrecognized tax benefits by a total of $661 million and $43 million , respectively, in the first quarter of 2015. This change in unrecognized tax benefits had no impact on Exelon, Generation, or PECO's effective tax rate. Unrecognized tax benefits that if recognized would affect the effective tax rate Exelon and Generation have $538 million and $509 million , respectively, of unrecognized tax benefits at December 31, 2015 that, if recognized, would decrease the effective tax rate. BGE has $120 million of unrecognized tax benefits at December 31, 2015 that, if recognized, may be included in future base rates and that portion would have no impact to the effective tax rate. Exelon and Generation had $701 million and $672 million , respectively, of unrecognized tax benefits at December 31, 2014 that, if recognized, would decrease the effective tax rate. In 2015, the unrecognized tax benefits decreased at Exelon and Generation due to settlements with state tax authorities and the expiration of statues of limitations for certain state jurisdictions. Reasonably possible that total amount of unrecognized tax benefits could significantly increase or decrease within 12 months after the reporting date Like-Kind Exchange As of December 31, 2015 , Exelon and ComEd have approximately $397 million and $142 million of unrecognized tax benefits that could significantly decrease within the 12 months after the reporting date as a result of a decision in the like-kind exchange litigation described below. Exelon and ComEd have unrecognized tax benefits that, if recognized, would decrease Exelon's effective tax rate by $69 million and increase ComEd's effective tax rate by $11 million . Settlement of Income Tax Audits and Litigation As of December 31, 2015 , Exelon, Generation, and BGE have approximately $174 million , $54 million , and $120 million of unrecognized state tax benefits that could significantly decrease within the 12 months after the reporting date as a result of completing audits, potential settlements, and expected statute of limitation expirations. Of the above unrecognized tax benefits, Exelon and Generation have $54 million that, if recognized, would decrease the effective tax rate. The unrecognized tax benefit related to BGE, if recognized, may be included in future base rates and that portion would have no impact to the effective tax rate. Total amounts of interest and penalties recognized The following table represents the net interest receivable (payable), including interest related to tax positions reflected in the Registrants’ Consolidated Balance Sheets. Net interest receivable (payable) as of Exelon Generation ComEd PECO BGE December 31, 2015 $ (288 ) $ 80 $ (210 ) $ 3 $ (1 ) December 31, 2014 (310 ) 40 (203 ) 3 (1 ) The following table sets forth the net interest expense, including interest related to tax positions, recognized in interest expense (income) in other income and deductions in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. The Registrants have not accrued any material penalties with respect to uncertain tax positions. Net interest expense (income) for the years ended Exelon Generation ComEd PECO BGE December 31, 2015 $ (13 ) $ (31 ) $ 7 $ — $ — December 31, 2014 (36 ) (50 ) 6 — 1 December 31, 2013 391 17 281 (1 ) — Description of tax years that remain open to assessment by major jurisdiction Taxpayer Open Years Exelon (and predecessors) and subsidiaries consolidated Federal income tax returns 1999, 2001-2014 Exelon and subsidiaries Illinois unitary income tax returns 2007-2014 Constellation combined New York corporate income tax returns 2010-March 2012 Various separate company Pennsylvania corporate net income tax returns 2010-2014 BGE Maryland corporate net income tax returns 2011-2014 Various Exelon Maryland corporate net income tax returns 2012-2014 Various Constellation (Non-BGE) Maryland corporate net income tax returns 2011-2014 Other Tax Matters Like-Kind Exchange Exelon, through its ComEd subsidiary, took a position on its 1999 income tax return to defer approximately $1.2 billion of tax gain on the sale of ComEd’s fossil generating assets. The gain was deferred by reinvesting a portion of the proceeds from the sale in qualifying replacement property under the like-kind exchange provisions of the IRC. The like-kind exchange replacement property purchased by Exelon included interests in three municipal-owned electric generation facilities which were properly leased back to the municipalities. The IRS disagreed with this position and asserted that the entire gain of approximately $1.2 billion was taxable in 1999. Exelon has been unable to reach agreement with the IRS regarding the dispute over the like-kind exchange position. The IRS has asserted that Exelon's purchase and leaseback transaction is substantially similar to a leasing transaction, known as a SILO, which the IRS does not respect as the acquisition of an ownership interest in property. A SILO is a “listed transaction” that the IRS has identified as a potentially abusive tax shelter under guidance issued in 2005. Accordingly, the IRS has asserted that the sale of the fossil plants followed by the purchase and leaseback of the municipal owned generation facilities does not qualify as a like-kind exchange and the gain on the sale is fully subject to tax. The IRS has also asserted a penalty of approximately $ 90 million for a substantial understatement of tax. Exelon disagrees with the IRS and continues to believe that its like-kind exchange transaction is not the same as or substantially similar to a SILO. Although Exelon has been and remains willing to settle the disagreement on terms commensurate with the hazards of litigation, Exelon does not believe a settlement is possible. Because Exelon believed, as of December 31, 2012, that it was more-likely-than-not that Exelon would prevail in litigation, Exelon and ComEd had no liability for unrecognized tax benefits with respect to the like-kind exchange position. On January 9, 2013, the U.S. Court of Appeals for the Federal Circuit reversed the U.S. Court of Federal Claims and reached a decision for the government in Consolidated Edison v. United States. The Court disallowed Consolidated Edison’s deductions stemming from its participation in a LILO transaction that the IRS also has characterized as a tax shelter. In accordance with applicable accounting standards, Exelon is required to assess whether it is more-likely-than-not that it will prevail in litigation. Exelon continues to believe that its transaction is not a SILO and that it has a strong case on the merits. However, in light of the Consolidated Edison decision and Exelon’s current determination that settlement is unlikely, Exelon has concluded that subsequent to December 31, 2012, it is no longer more-likely-than-not that its position will be sustained. As a result, in the first quarter of 2013, Exelon recorded a non-cash charge to earnings of approximately $265 million , which represents the amount of interest expense (after-tax) and incremental state income tax expense for periods through March 31, 2013 that would be payable in the event that Exelon is unsuccessful in litigation. Of this amount, approximately $172 million was recorded at ComEd. Exelon intends to hold ComEd harmless from any unfavorable impacts of the after-tax interest amounts on ComEd’s equity. As such, ComEd recorded on its consolidated balance sheet as of March 31, 2013, a $172 million receivable and non-cash equity contributions from Exelon. Exelon and ComEd will continue to accrue interest on the unpaid tax liabilities related to the uncertain tax position, and the charges arising from future interest accruals are not expected to be material to the annual operating earnings of Exelon or ComEd. In addition, ComEd will continue to record non-cash equity contributions from Exelon in the amount of the net after-tax interest charges attributable to ComEd in connection with the like-kind exchange position. Exelon continues to believe that it is unlikely that the IRS’s assertion of penalties will ultimately be sustained and therefore no liability for the penalty has been recorded. On September 30, 2013, the IRS issued a notice of deficiency to Exelon for the like-kind exchange position. Exelon filed a petition on December 13, 2013 to initiate litigation in the United States Tax Court and the trial took place in August of 2015. Exelon was not required to remit any part of the asserted tax or penalty in order to litigate the issue. While the Tax Court could reach its decision as early as 2016, the litigation could take three to five years if an appeal is necessary. Decisions in the Tax Court are not controlled by the Federal Circuit’s decision in Consolidated Edison. In the first quarter of 2014, Exelon entered into an agreement to terminate its investment in one of the three municipal-owned electric generation properties in exchange for a net early termination amount of $335 million . In connection with the termination, Exelon deposited $65 million with the IRS, including $35 million by ComEd. The deposit can be redesignated to any tax year, if necessary, and may be used to satisfy any amounts owed as a result of the litigation. In the event of a fully successful IRS challenge to Exelon’s like-kind exchange position, the potential tax and after-tax interest, net of the deposit discussed above and exclusive of penalties, that could become currently payable as of December 31, 2015 may be as much as $760 million , of which approximately $280 million would be attributable to ComEd after consideration of Exelon’s agreement to hold ComEd harmless. Interest will continue to accrue until such time as payment is made. An appeal of an adverse decision in the Tax Court would necessitate either the posting of a bond or the payment of the tax and interest for the tax years before the court. A final appellate decision could take several years. Accounting for Generation Repairs (Exelon and Generation) On April 30, 2013, the IRS issued Revenue Procedure 2013-24 providing guidance for determining the appropriate tax treatment of costs incurred to repair electric generation assets. Generation changed its method of accounting for deducting repairs in accordance with this guidance beginning in the 2014 tax year. The adoption of the new method resulted in Generation recording a cash tax detriment of approximately $120 million in 2014 . Long-Term State Tax Apportionment (Exelon and Generation) The long-term state tax apportionment was revised in the fourth quarter of 2015 pursuant to Exelon's long-term state tax apportionment policy, resulting in the recording of a deferred state tax expense for Exelon and Generation of $ 41 million (net of Federal taxes) and $ 11 million (net of Federal taxes), respectively. In 2014, in accordance with the policy, Exelon and Generation recorded a deferred state tax benefit of $ 28 million (net of Federal taxes) and $ 40 million (net of Federal taxes), respectively. The amounts recorded for 2013 in accordance with the policy were immaterial. Allocation of Tax Benefits (Exelon, Generation, ComEd, PECO and BGE) Generation, ComEd, PECO and BGE are all party to an agreement with Exelon and other subsidiaries of Exelon that provides for the allocation of consolidated tax liabilities and benefits (Tax Sharing Agreement). The Tax Sharing Agreement provides that each party is allocated an amount of tax similar to that which would be owed had the party been separately subject to tax. In addition, any net benefit attributable to Exelon is reallocated to the other Registrants. That allocation is treated as a contribution to the capital of the party receiving the benefit. During 2015, Generation, PECO, and BGE recorded an allocation of Federal tax benefits from Exelon under the Tax Sharing Agreement of $ 57 million , $ 16 million , and $ 7 million respectively. ComEd did not record an allocation of Federal tax benefits from Exelon under the Tax Sharing Agreement as a result of a tax net operating loss. During 2014, Generation and PECO recorded an allocation of Federal tax benefits from Exelon under the Tax Sharing Agreement of $55 million and $25 million , respectively. ComEd and BGE did not record an allocation of Federal tax benefits from Exelon under the Tax Sharing Agreement as a result of tax net operating losses. During 2013, Generation and PECO recorded an allocation of Federal tax benefits from Exelon under the Tax Sharing Agreement of $26 million and $27 million , respectively. During 2013, ComEd and BGE did not record an allocation of Federal tax benefits from Exelon under the Tax Sharing Agreement as a result of ComEd’s and BGE’s tax net operating loss generated primarily by the bonus depreciation deduction allowed under the Tax Relief Act of 2010.

Asset Retirement Obligations (E

Asset Retirement Obligations (Exelon, Generation, ComEd and PECO)	12 Months Ended
	Dec. 31, 2015
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations (Exelon, Generation, ComEd and PECO)	(Exelon, Generation, ComEd, PECO and BGE) Nuclear Decommissioning Asset Retirement Obligations Generation has a legal obligation to decommission its nuclear power plants following the expiration of their operating licenses. To estimate its decommissioning obligation related to its nuclear generating stations for financial accounting and reporting purposes, Generation uses a probability-weighted, discounted cash flow model which, on a unit-by-unit basis, considers multiple outcome scenarios that include significant estimates and assumptions, and are based on decommissioning cost studies, cost escalation rates, probabilistic cash flow models and discount rates. Generation generally updates its ARO annually during the third quarter, unless circumstances warrant more frequent updates, based on its review of updated cost studies and its annual evaluation of cost escalation factors and probabilities assigned to various scenarios. The following table provides a rollforward of the nuclear decommissioning ARO reflected on Exelon’s and Generation’s Consolidated Balance Sheets, from January 1, 2014 to December 31, 2015 : Exelon and Generation Nuclear decommissioning ARO at January 1, 2014 $ 4,855 Consolidation of CENG (a) 1,760 Accretion expense 334 Net increase due to changes in, and timing of, estimated future cash flows 19 Costs incurred to decommission retired plants (7 ) Nuclear decommissioning ARO at December 31, 2014 (b) 6,961 Accretion expense 387 Net increase due to changes in, and timing of, estimated future cash flows 901 Costs incurred to decommission retired plants (3 ) Nuclear decommissioning ARO at December 31, 2015 (b) $ 8,246 _________________________ (a) Represents the fair value of the CENG ARO liability as of April 1, 2014, the date of consolidation. See Note 5 — Investment in Constellation Energy Nuclear Group, LLC for additional information. (b) Includes $ 7 million and $ 8 million as the current portion of the ARO at December 31, 2015 and 2014 , respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets. During 2015, Generation’s total nuclear ARO increased by approximately $1.3 billion , reflecting impacts of ARO updates completed during 2015 to reflect changes in amounts and timing of estimated decommissioning cash flows and impacts of year-to-date accretion of the ARO liability due to the passage of time. The increase in the ARO during 2015 was primarily driven by an increase of approximately $630 million for costs expected to be incurred for required site security during the decommissioning periods in which SNF remains on-site and until major reactor components and buildings have been dismantled and removed. This projected increase is based on emerging industry experience at nuclear sites in the planning or early stage of decommissioning indicating greater than originally expected numbers of security personnel required to be on site during these decommissioning periods. Generation will continue to monitor emerging security cost trends, including potential strategies to limit such costs by, for example, optimizing the transfer of SNF when DOE starts taking possession of SNF or increasing the use of dry SNF storage, and will adjust the ARO liability accordingly. The 2015 increase in the ARO includes an increase of approximately $285 million for the impacts of a change implemented in the 2015 annual assessment of Generation’s SNF storage and disposal cost estimation methodology to better align the projected timing of SNF transfers to the DOE with assumed plant shutdown dates as well as higher assumed probabilities of early retirements of certain economically challenged nuclear plants (See Note 9 - Implications of Potential Early Plant Retirements for additional information) and further accretion of the obligation. These increases were partially offset by reductions in estimated cost escalation rates, primarily for labor and energy costs. The financial statement impact related to the increase in the ARO due to the changes in, and timing of, estimated cash flows primarily resulted in a corresponding increase in Property, plant and equipment on Exelon’s and Generation’s Consolidated Balance Sheets. Approximately $8 million of the 2015 adjustment resulted in a credit to income, which is included in Operating and maintenance expense within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. During 2014 , Generation’s ARO increased by approximately $ 2.1 billion . The increase is largely driven by the recording of an ARO on Exelon’s and Generation’s Consolidated Balance Sheets at fair value, including subsequent purchase accounting adjustments, upon consolidation of CENG (see Note 5 — Investment in Constellation Energy Nuclear Group, LLC ). The change in the ARO was also driven by an increase for accretion of the obligation and an increase in the estimated costs to decommission Byron, Braidwood, and LaSalle nuclear units resulting from the completion of updated decommissioning costs studies received during 2014 as part of the annual assessment. These increases in the ARO were partially offset by decreases in the ARO due to a reduction in estimated escalation rates, primarily for labor and energy costs. The increase in the ARO due to the changes in, and timing of, estimated cash flows was offset within Property, plant and equipment on Exelon’s and Generation’s Consolidated Balance Sheets, aside from an approximate $ 16 million credit to income, which is included in Operating and maintenance expense within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. Nuclear Decommissioning Trust Fund Investments NDT funds have been established for each generating station unit to satisfy Generation’s nuclear decommissioning obligations. Generally, NDT funds established for a particular unit may not be used to fund the decommissioning obligations of any other unit. The NDT funds associated with Generation's nuclear units have been funded with amounts collected from the previous owners and their respective utility customers. PECO is authorized to collect funds, in revenues, for decommissioning the former PECO nuclear plants through regulated rates, and these collections are scheduled through the operating lives of the former PECO plants. The amounts collected from PECO customers are remitted to Generation and deposited into the NDT funds for the unit for which funds are collected. Every five years, PECO files a rate adjustment with the PAPUC that reflects PECO’s calculations of the estimated amount needed to decommission each of the former PECO units based on updated fund balances and estimated decommissioning costs. The rate adjustment is used to determine the amount collectible from PECO customers. The most recent rate adjustment occurred on January 1, 2013, and the effective rates currently yield annual collections of approximately $ 24 million . The next five-year adjustment is expected to be reflected in rates charged to PECO customers effective January 1, 2018. Aside from the former PECO units, Generation does not currently collect any amounts, nor is there any mechanism by which Generation can seek to collect additional amounts, from utility customers. Apart from the contributions made to the NDT funds from amounts previously collected from ComEd and currently collected from PECO customers, Generation has not made contributions to the NDT funds. Any shortfall of funds necessary for decommissioning, determined for each generating station unit, is ultimately required to be funded by Generation, with the exception of a shortfall for the current decommissioning activities at Zion Station, where certain decommissioning activities have been transferred to a third-party (see Zion Station Decommissioning below) and the CENG units, where any shortfall is required to be funded by both Generation and EDF. Generation, through PECO, has recourse to collect additional amounts from PECO customers related to a shortfall of NDT funds for the former PECO units, subject to certain limitations and thresholds, as prescribed by an order from the PAPUC. Generally, PECO, and likewise Generation will not be allowed to collect amounts associated with the first $ 50 million of any shortfall of trust funds compared to decommissioning costs, as well as 5% of any additional shortfalls, on an aggregate basis for all former PECO units. The initial $ 50 million and up to 5% of any additional shortfalls would be borne by Generation. No recourse exists to collect additional amounts from utility customers for any of Generation's other nuclear units. With respect to the former ComEd and PECO units, any funds remaining in the NDTs after all decommissioning has been completed are required to be refunded to ComEd’s or PECO’s customers, subject to certain limitations that allow sharing of excess funds with Generation related to the former PECO units. With respect to Generation's other nuclear units, Generation retains any funds remaining after decommissioning. However, in connection with CENG's acquisition of the Nine Mile Point and Ginna plants and settlements with certain regulatory agencies, CENG is subject to certain conditions pertaining to nuclear decommissioning trust funds that, if met, could possibly result in obligations to make payments to certain third parties (clawbacks). For Nine Mile Point and Ginna, the clawback provisions are triggered only in the event that the required decommissioning activities are discontinued or not started or completed in a timely manner. In the event that the clawback provisions are triggered for Nine Mile Point, then, depending upon the triggering event, an amount equal to 50% of the total amount withdrawn from the funds for non-decommissioning activities or 50% of any excess funds in the trust funds above the amounts required for decommissioning (including spent fuel management and decommissioning) is to be paid to the Nine Mile Point sellers. In the event that the clawback provisions are triggered for Ginna, then an amount equal to any estimated cost savings realized by not completing any of the required decommissioning activities is to be paid to the Ginna sellers. Generation expects to comply with applicable regulations and timely commence and complete all required decommissioning activities. At December 31, 2015 , and 2014 , Exelon and Generation had NDT fund investments totaling $ 10,342 million and $ 10,537 million , respectively. For additional information related to the NDT fund investments, refer to Note 12 — Fair Value of Financial Assets and Liabilities . The following table provides unrealized gains on NDT funds for 2015 , 2014 and 2013 : Exelon and Generation For the Years Ended December 31, 2015 2014 2013 Net unrealized gains (losses) on decommissioning trust funds—Regulatory Agreement Units (a) $ (282 ) $ 180 $ 406 Net unrealized gains (losses) on decommissioning trust funds—Non-Regulatory Agreement Units (b)(c) (197 ) 134 146 _______________________ (a) Net unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities on Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates on Generation’s Consolidated Balance Sheets. (b) Excludes $ 7 million , $ 29 million and $ 7 million of net unrealized gains related to the Zion Station pledged assets in 2015 , 2014 and 2013 , respectively. Net unrealized gains related to Zion Station pledged assets are included in the Payable for Zion Station decommissioning on Exelon’s and Generation’s Consolidated Balance Sheets. (c) Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included within Other, net in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. Interest and dividends on NDT fund investments are recognized when earned and are included in Other, net in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. Interest and dividends earned on the NDT fund investments for the Regulatory Agreement Units are eliminated within Other, net in Exelon’s and Generation’s Consolidated Statement of Operations and Comprehensive Income. Accounting Implications of the Regulatory Agreements with ComEd and PECO . Based on the regulatory agreement with the ICC that dictates Generation’s obligations related to the shortfall or excess of NDT funds necessary for decommissioning the former ComEd units on a unit-by-unit basis, as long as funds held in the NDT funds are expected to exceed the total estimated decommissioning obligation, decommissioning-related activities, including realized and unrealized gains and losses on the NDT funds and accretion of the decommissioning obligation, are generally offset within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. The offset of decommissioning-related activities within the Consolidated Statement of Operations and Comprehensive Income results in an equal adjustment to the noncurrent payables to affiliates at Generation and an adjustment to the regulatory liabilities at Exelon. Likewise, ComEd has recorded an equal noncurrent affiliate receivable from Generation and corresponding regulatory liability. Should the expected value of the NDT fund for any former ComEd unit fall below the amount of the expected decommissioning obligation for that unit, the accounting to offset decommissioning-related activities in the Consolidated Statement of Operations and Comprehensive Income for that unit would be discontinued, the decommissioning-related activities would be recognized in the Consolidated Statements of Operations and Comprehensive Income and the adverse impact to Exelon’s and Generation’s results of operations and financial position could be material. As of December 31, 2015 , the NDT funds of each of the former ComEd units, except for Zion (see Zion Station Decommissioning below), are expected to exceed the related decommissioning obligation for each of the units. For the purposes of making this determination, the decommissioning obligation referred to is different, as described below, from the calculation used in the NRC minimum funding obligation filings based on NRC guidelines. Based on the regulatory agreement supported by the PAPUC that dictates Generation’s rights and obligations related to the shortfall or excess of trust funds necessary for decommissioning the former PECO units, regardless of whether the funds held in the NDT funds are expected to exceed or fall short of the total estimated decommissioning obligation, decommissioning-related activities are generally offset within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. The offset of decommissioning-related activities within the Consolidated Statement of Operations and Comprehensive Income results in an equal adjustment to the noncurrent payables to affiliates at Generation and an adjustment to the regulatory liabilities at Exelon. Likewise, PECO has recorded an equal noncurrent affiliate receivable from Generation and a corresponding regulatory liability. Any changes to the PECO regulatory agreements could impact Exelon’s and Generation’s ability to offset decommissioning-related activities within the Consolidated Statement of Operations and Comprehensive Income, and the impact to Exelon’s and Generation’s results of operations and financial position could be material. The decommissioning-related activities related to the Non-Regulatory Agreement Units are reflected in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. Refer to Note 3 — Regulatory Matters and Note 26 — Related Party Transactions for information regarding regulatory liabilities at ComEd and PECO and intercompany balances between Generation, ComEd and PECO reflecting the obligation to refund to customers any decommissioning-related assets in excess of the related decommissioning obligations. Zion Station Decommissioning On September 1, 2010, Generation completed an Asset Sale Agreement (ASA) with EnergySolutions Inc. and its wholly owned subsidiaries, EnergySolutions, LLC (EnergySolutions) and ZionSolutions under which ZionSolutions has assumed responsibility for decommissioning Zion Station, which is located in Zion, Illinois and ceased operation in 1998. Specifically, Generation transferred to ZionSolutions substantially all of the assets (other than land) associated with Zion Station, including assets held in related NDT funds. In consideration for Generation’s transfer of those assets, ZionSolutions assumed decommissioning and other liabilities, excluding the obligation to dispose of SNF and decommission the SNF dry storage facility, associated with Zion Station. Pursuant to the ASA, ZionSolutions will periodically request reimbursement from the Zion Station-related NDT funds for costs incurred related to its decommissioning efforts at Zion Station. During 2013, EnergySolutions entered a definitive acquisition agreement and was acquired by another Company. Generation reviewed the acquisition as it relates to the ASA to decommission Zion Station. Based on that review, Generation determined that the acquisition will not adversely impact decommissioning activities under the ASA. ZionSolutions is subject to certain restrictions on its ability to request reimbursements from the Zion Station NDT funds as defined within the ASA. Therefore, the transfer of the Zion Station assets did not qualify for asset sale accounting treatment and, as a result, the related NDT funds were reclassified to Pledged assets for Zion Station decommissioning within Generation’s and Exelon’s Consolidated Balance Sheets and will continue to be measured in the same manner as prior to the completion of the transaction. Additionally, the transferred ARO for decommissioning was replaced with a Payable for Zion Station decommissioning in Generation’s and Exelon’s Consolidated Balance Sheets. Changes in the value of the Zion Station NDT assets, net of applicable taxes, will be recorded as a change in the Payable to ZionSolutions. At no point will the payable to ZionSolutions exceed the project budget of the costs remaining to decommission Zion Station. Generation has retained its obligation for the SNF. Following ZionSolutions' completion of its contractual obligations and transfer of the NRC license to Generation, Generation will store the SNF at Zion Station until it is transferred to the DOE for ultimate disposal, and will complete all remaining decommissioning activities associated with the SNF dry storage facility. Generation has a liability of approximately $ 84 million , which is included within the nuclear decommissioning ARO at December 31, 2015 . Generation also has retained NDT assets to fund its obligation to maintain the SNF at Zion Station until transfer to the DOE and to complete all remaining decommissioning activities for the SNF storage facility. Any shortage of funds necessary to maintain the SNF and decommission the SNF storage facility is ultimately required to be funded by Generation. Any Zion Station NDT funds remaining after the completion of all decommissioning activities will be returned to ComEd customers in accordance with the applicable orders. The following table provides the pledged assets and payables to ZionSolutions, and withdrawals by ZionSolutions at December 31, 2015 and 2014 : Exelon and Generation 2015 2014 Carrying value of Zion Station pledged assets $ 206 $ 319 Payable to Zion Solutions (a) 189 292 Current portion of payable to Zion Solutions (b) 99 137 Cumulative withdrawals by Zion Solutions to pay decommissioning costs (c) 786 666 ___________________ (a) Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT Funds. The NDT Funds will be utilized to satisfy the tax obligations as gains and losses are realized. (b) Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets. (c) Includes project expenses to decommission Zion Station and estimated tax payments on Zion Station NDT fund earnings. ZionSolutions leased the land associated with Zion Station from Generation pursuant to a Lease Agreement. Under the Lease Agreement, ZionSolutions has committed to complete the required decommissioning work according to an established schedule and constructed a dry cask storage facility on the land and has loaded the SNF from the SNF pools onto the dry cask storage facility at Zion Station. Rent payable under the Lease Agreement is $ 1.00 per year, although the Lease Agreement requires ZionSolutions to pay property taxes associated with Zion Station and penalty rents may accrue if there are unexcused delays in the progress of decommissioning work at Zion Station or the construction of the dry cask SNF storage facility. To reduce the risk of default by ZionSolutions, EnergySolutions provided a $ 200 million letter of credit to be used to fund decommissioning costs in the event the NDT assets are insufficient. EnergySolutions and its parent company have also provided a performance guarantee and EnergySolutions has entered into other agreements that will provide rights and remedies for Generation and the NRC in the case of other specified events of default, including a special purpose easement for disposal capacity at the EnergySolutions site in Clive, Utah, for all LLRW volume of Zion Station. NRC Minimum Funding Requirements NRC regulations require that licensees of nuclear generating facilities demonstrate reasonable assurance that funds will be available in specified minimum amounts to decommission the facility at the end of its life. The estimated decommissioning obligations as calculated using the NRC methodology differ from the ARO recorded on Generation’s and Exelon’s Consolidated Balance Sheets primarily due to differences in the type of costs included in the estimates, the basis for estimating such costs, and assumptions regarding the decommissioning alternatives to be used, potential license renewals, decommissioning cost escalation, and the growth rate in the NDT funds. Under NRC regulations, if the minimum funding requirements calculated under the NRC methodology are less than the future value of the NDT funds, also calculated under the NRC methodology, then the NRC requires either further funding or other financial guarantees. Key assumptions used in the minimum funding calculation using the NRC methodology at December 31, 2015 include: (1) consideration of costs only for the removal of radiological contamination at each unit; (2) the option on a unit-by-unit basis to use generic, non-site specific cost estimates; (3) consideration of only one decommissioning scenario for each unit; (4) the plants cease operation at the end of their current license lives (with no assumed license renewals for those units that have not already received renewals and with an assumed end-of-operations date of 2019 for Oyster Creek); (5) the assumption of current nominal dollar cost estimates that are neither escalated through the anticipated period of decommissioning, nor discounted using the CARFR; and (6) assumed annual after-tax returns on the NDT funds of 2% ( 3% for the former PECO units, as specified by the PAPUC). In contrast, the key criteria and assumptions used by Generation to determine the ARO and to forecast the target growth in the NDT funds at December 31, 2015 include: (1) the use of site specific cost estimates that are updated at least once every five years; (2) the inclusion in the ARO estimate of all legally unavoidable costs required to decommission the unit (e.g., radiological decommissioning and full site restoration for certain units, on-site spent fuel maintenance and storage subsequent to ceasing operations and until DOE acceptance, and disposal of certain low-level radioactive waste); (3) the consideration of multiple scenarios where decommissioning activities are completed under three possible scenarios ranging from 10 to 70 years after the cessation of plant operations; (4) the assumption plants cease operating at the end of an extended license life (assuming 20 -year license renewal extensions, except Oyster Creek with an assumed end-of-operations date of 2019); (5) the measurement of the obligation at the present value of the future estimated costs and an annual average accretion of the ARO of approximately 5% through a period of approximately 30 years after the end of the extended lives of the units; and (6) an estimated targeted annual pre-tax return on the NDT funds of 6.1% to 6.3% (as compared to a historical 5-year annual average pre-tax return of approximately 7% ). Generation is required to provide to the NRC a biennial report by unit (annually for units that have been retired or are within five years of the current approved license life), based on values as of December 31, addressing Generation’s ability to meet the NRC minimum funding levels. Depending on the value of the trust funds, Generation may be required to take steps, such as providing financial guarantees through letters of credit or parent company guarantees or making additional contributions to the trusts, which could be significant, to ensure that the trusts are adequately funded and that NRC minimum funding requirements are met. As a result, Exelon’s and Generation’s cash flows and financial position may be significantly adversely affected. On March 31, 2014, Generation submitted its NRC required annual decommissioning funding report as of December 31, 2013 for reactors that have been shut down except for Zion Station which is included on a separate report to the NRC submitted by EnergySolutions (see Zion Station Decommissioning above). This submittal also included the required updated financial tests for the Limerick Unit 1 parent guarantee that had been established in 2013. There was no change to the amount of the parent guarantee, or the funding status of these reactors. Adequate decommissioning funding assurance was in place for all reactors owned by Generation. During 2014, the operating license for Limerick Unit 1 was extended by 20 years. As a result of this extension, and the subsequent funding assurance calculation performed by the NRC, it was found that the parent company guarantee was no longer required and thus the parent guarantee for Limerick Unit 1 has been cancelled effective March 13, 2015. See Note 3 — Regulatory Matters for additional information regarding the operating license extension for Limerick Unit 1. Generation filed its biennial decommissioning funding status report with the NRC on March 31, 2015. This report reflects the status of decommissioning funding assurance as of December 31, 2014. Due to increased cost estimates received in the second half of 2014, Braidwood Unit 1, Braidwood Unit 2, and Byron Unit 2 did not meet the NRC's minimum funding assurance criteria as of December 31, 2014. NRC guidance provides licensees with two years or by the time of submitting the next biennial report (on or before March 31, 2017) to resolve funding assurance shortfalls. During this period, Generation will monitor funding assurance and new developments, including the impact of a 20-year license renewal for Braidwood and Byron, to assess the status of funding assurance and to take steps, if necessary, to address any funding shortfall on these funds on or before March 31, 2017. On February 4, 2016, Generation submitted an updated decommissioning funding status report with the NRC for Braidwood Units 1 and 2, and Byron Unit 2. This report reflected the recently approved license renewals for these units, and showed that they have adequate decommissioning funding assurance, and that the shortfall identified in the March 31, 2015 report has now been resolved. The increased security costs discussed above will be taken into consideration, as appropriate and in accordance with the regulatory requirements, in Generation's future decommissioning funding status reports submitted to the NRC. Generation does not expect the increased costs to change Generation's NRC minimum funding assurance status. As the future values of trust funds change due to market conditions, the NRC minimum funding status of Generation’s units will change. In addition, if changes occur to the regulatory agreement with the PAPUC that currently allows amounts to be collected from PECO customers for decommissioning the former PECO units, the NRC minimum funding status of those plants could change at subsequent NRC filing dates. Non-Nuclear Asset Retirement Obligations (Exelon, Generation, ComEd, PECO and BGE) Generation has AROs for plant closure costs associated with its fossil and renewable generating facilities, including asbestos abatement, removal of certain storage tanks, restoring leased land to the condition it was in prior to construction of renewable generating stations and other decommissioning-related activities. ComEd, PECO and BGE have AROs primarily associated with the abatement and disposal of equipment and buildings contaminated with asbestos and PCBs. See Note 1 — Significant Accounting Policies for additional information on the Registrants’ accounting policy for AROs. The following table provides a rollforward of the non-nuclear AROs reflected on the Registrants’ Consolidated Balance Sheets from January 1, 2014 to December 31, 2015 : Exelon Generation ComEd PECO BGE Non-nuclear AROs at January 1, 2014 $ 351 $ 201 $ 101 $ 30 $ 19 Net increase (decrease) due to changes in, and timing of, estimated future cash flows (a) (1 ) (2 ) 2 — (1 ) Development projects (b) 11 11 — — — Accretion expense (c) 15 11 3 1 — Liabilities held for sale (d) (4 ) (4 ) — — — Sale of generating assets (e) (20 ) (20 ) — — — Payments (6 ) (3 ) (2 ) (1 ) — Non-nuclear AROs at December 31, 2014 (f) 346 194 104 30 18 Net increase (decrease) due to changes in, and timing of, estimated future cash flows (a) (10 ) (12 ) 6 (4 ) — Development projects (b) 10 10 — — — Accretion expense (c) 16 10 5 1 — Sale of generating assets (e) (2 ) (2 ) — — — Payments (5 ) (3 ) (2 ) — — Non-nuclear AROs at December 31, 2015 (f) $ 355 $ 197 $ 113 $ 27 $ 18 ________________________ (a) During the year ended December 31, 2015 , Generation recorded a decrease of $(2) million in Operating and maintenance expense. ComEd, PECO, and BGE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2015 . During the year ended December 31, 2014 , Generation recorded a decrease of $(2) million and ComEd recorded an increase of $1 million in Operating and maintenance expense. PECO and BGE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2014 . (b) Relates to new AROs recorded due to the construction of solar, wind and other non-nuclear generating sites. (c) For ComEd, PECO, and BGE, the majority of the accretion is recorded as an increase to a regulatory asset due to the associated regulatory treatment. (d) Represents AROs related to generating stations classified as held for sale. See Note 4 — Mergers, Acquisitions, and Dispositions for further information. (e) Reflects a reduction to the ARO resulting primarily from the sales of Schuylkill generating station in 2015 and Keystone and Conemaugh generating stations in 2014. See Note 4 — Mergers, Acquisitions, and Dispositions for further information. (f) Excludes $5 million , $2 million , $0 million and $1 million as the current portion of the ARO at December 31, 2015 for Generation, ComEd, PECO and BGE, respectively. Excludes $1 million , $1 million , $1 million and $1 million as the current portion of the ARO at December 31, 2014 for Generation, ComEd, PECO and BGE, respectively. This is included in Other current liabilities on the Registrants' respective Consolidated Balance Sheets.

Implications of Potential Early

Implications of Potential Early Plant Retirements Implications of Potential Early Plant Retirements (Exelon, Generation)	12 Months Ended
	Dec. 31, 2015
Implications of Potential Early Plant Retirements [Abstract]
Implications Of Potential Early Retirement Disclosure [Text Block]	9 . Implications of Potential Early Plant Retirements (Exelon and Generation) Exelon and Generation continue to evaluate the current and expected economic value of each of Generation’s nuclear plants. Factors that will continue to affect the economic value of Generation’s nuclear plants include, but are not limited to: market power prices, results of capacity auctions, potential legislative solutions in New York and Illinois such as the proposed Low Carbon Portfolio Standard (LCPS) legislation, the impact of final rules from the EPA requiring reduction of carbon and other emissions and the efforts of the states to implement those final rules, and the outcome of the Ginna RSSA hearing and settlement procedures and the resulting contractual terms and conditions. On September 10, 2015, after considering the results of the recent PJM capacity auctions, Exelon and Generation decided to defer decisions about the future operations of its Quad Cities and Byron nuclear plants and will offer both plants in the 2019/2020 auction in May 2016. As a result of clearing the other PJM capacity auction in September 2015 for the 2017/2018 transitional capacity auction, Exelon and Generation will continue to operate its Quad Cities nuclear power plant through at least May 2018. The Byron plant is already obligated to operate through May 2019. On October 29, 2015, Exelon and Generation announced the deferral of any decision about the future operations of its Clinton nuclear plant and plans to bid the plant into the MISO capacity auction for the 2016-2017 planning year in April 2016. This decision was driven by MISO’s acknowledgment of the need for market design changes to ensure long-term power system reliability in southern Illinois, the desire to provide Illinois policy makers with additional time to consider needed reforms as well as the potential long-term impact of EPA’s Clean Power Plan. Exelon and Generation previously committed to cease operation of the Oyster Creek nuclear plant by the end of 2019. Exelon and Generation have not made any decisions regarding potential nuclear plant closures at other sites at this time. As a result of a decision to early retire one or more other nuclear plants, certain changes in accounting treatment would be triggered and Exelon’s and Generation’s results of operations and cash flows could be materially affected by a number of items including, among other items: accelerated depreciation expense, impairment charges related to inventory that cannot be used at other nuclear units and cancellation of in-flight capital projects, accelerated amortization of plant specific nuclear fuel costs, employee-related costs (i.e. severance, relocation, retention, etc.), accelerated asset retirement obligation expense related to future decommissioning activities, and additional funding of nuclear decommissioning trust funds. In addition, any early plant retirement would also result in reduced operating costs, lower fuel expense, and lower capital expenditures in the periods beyond shutdown. While there are a number of Generation’s nuclear plants that are at risk of early retirement, the following table provides the balance sheet amounts as of December 31, 2015 for significant assets and liabilities associated with the three nuclear plants currently considered by management to be at the greatest risk of early retirement due to their current economic valuations and other factors: (in millions) Quad Cities Clinton Ginna Total Asset Balances Materials and supplies inventory $ 50 $ 57 $ 29 $ 136 Nuclear fuel inventory, net 218 107 60 385 Completed plant, net 1,030 579 127 1,736 Construction work in progress 11 9 11 31 Liability Balances Asset retirement obligation (698 ) (401 ) (644 ) (1,743 ) NRC License Renewal Term 2032 2046 (a) 2029 ________ (a) Assumes Clinton seeks and receives a 20-year operating license renewal extension. In the event a decision is made to retire early one or more nuclear plants, the precise timing of the retirement date, and resulting financial statement impact, is uncertain and would be influenced by a number of factors such as the results of any transmission system reliability study assessments, the nature of any co-owner requirements and stipulations, and decommissioning trust fund requirements, among other factors. However, the earliest retirement date for any plant would usually be the first year in which the unit does not have capacity obligations and just prior to its next scheduled nuclear refueling outage date in that year.

Retirement Benefits (Exelon, Ge

Retirement Benefits (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Retirement Benefits (Exelon, Generation, ComEd, PECO and BGE)	(Exelon, Generation, ComEd, PECO and BGE) As of December 31, 2015 , Exelon sponsored defined benefit pension plans and other postretirement benefit plans for essentially all Generation, ComEd, PECO, BGE and BSC employees. The table below shows the pension and other postretirement benefit plans in which employees of each operating company participated at December 31, 2015 . Operating Company (d) Name of Plan: Generation ComEd PECO BGE BSC Qualified Pension Plans: Exelon Corporation Retirement Program (a) X X X X X Exelon Corporation Cash Balance Pension Plan (a) X X X X X Exelon Corporation Pension Plan for Bargaining Unit Employees (a) X X X Exelon New England Union Employees Pension Plan (a) X Exelon Employee Pension Plan for Clinton, TMI and Oyster Creek (a) X X X X Pension Plan of Constellation Energy Group, Inc. (b) X X X X X Pension Plan of Constellation Energy Nuclear Group, LLC (c) X X X Nine Mile Point Pension Plan (c) X X Constellation Mystic Power, LLC Union Employees Pension Plan Including Plan A and Plan B (b) X Non-Qualified Pension Plans: Exelon Corporation Supplemental Pension Benefit Plan and 2000 Excess Benefit Plan (a) X X X X Exelon Corporation Supplemental Management Retirement Plan (a) X X X X X Constellation Energy Group, Inc. Senior Executive Supplemental Plan (b) X X X Constellation Energy Group, Inc. Supplemental Pension Plan (b) X X X Constellation Energy Group, Inc. Benefits Restoration Plan (b) X X X X Constellation Nuclear Plan, LLC Executive Retirement Plan (c) X X Constellation Energy Nuclear Plan, LLC Benefits Restoration Plan (c) X X Baltimore Gas & Electric Company Executive Benefit Plan (b) X X X Baltimore Gas & Electric Company Manager Benefit Plan (b) X X X X Operating Company (d) Name of Plan: Generation ComEd PECO BGE BSC Other Postretirement Benefit Plans: PECO Energy Company Retiree Medical Plan (a) X X X X X Exelon Corporation Health Care Program (a) X X X X X Exelon Corporation Employees’ Life Insurance Plan (a) X X X X X Constellation Energy Group, Inc. Retiree Medical Plan (b) X X X X X Constellation Energy Group, Inc. Retiree Dental Plan (b) X X X Constellation Energy Group, Inc. Employee Life Insurance Plan and Family Life Insurance Plan (b) X X X X X Constellation Mystic Power, LLC Post-Employment Medical Account Savings Plan (b) X Exelon New England Union Post-Employment Medical Savings Account Plan (a) X Retiree Medical Plan of Constellation Energy Nuclear Group LLC (c) X X X Retiree Dental Plan of Constellation Energy Nuclear Group LLC (c) X X X Nine Mile Point Nuclear Station, LLC Medical Care and Prescription Drug Plan for Retired Employees (c) X X ______________________ (a) These plans are collectively referred to as the Legacy Exelon plans. (b) These plans are collectively referred to as the Legacy Constellation Energy Group (CEG) Plans. (c) These plans are collectively referred to as the Legacy CENG plans. (d) Employees generally remain in their legacy benefit plans when transferring between operating companies. Exelon’s traditional and cash balance pension plans are intended to be tax-qualified defined benefit plans. Substantially all non-union employees and electing union employees hired on or after January 1, 2001 participate in cash balance pension plans. Effective January 1, 2009, substantially all newly-hired union-represented employees participate in cash balance pension plans. Exelon has elected that the trusts underlying these plans be treated under the IRC as qualified trusts. If certain conditions are met, Exelon can deduct payments made to the qualified trusts, subject to certain IRC limitations. Benefit Obligations, Plan Assets and Funded Status Exelon recognizes the overfunded or underfunded status of defined benefit pension and OPEB plans as an asset or liability on its balance sheet, with offsetting entries to Accumulated OCI and regulatory assets (liabilities), in accordance with the applicable authoritative guidance. The measurement date for the plans is December 31. During the first quarter of 2015 , Exelon received an updated valuation of its pension and other postretirement benefit obligations to reflect actual census data as of January 1, 2015 . This valuation resulted in an increase to the pension obligation of $45 million and an increase to the other postretirement benefit obligation of $57 million . Additionally, Accumulated other comprehensive loss (AOCL) increased by approximately $27 million (after tax), regulatory assets increased by approximately $48 million , and regulatory liabilities decreased by approximately $11 million . The following table provides a rollforward of the changes in the benefit obligations and plan assets for the most recent two years for all plans combined: Pension Benefits Other Postretirement Benefits 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at beginning of year $ 18,256 $ 15,459 $ 4,197 $ 4,451 Service cost 326 293 119 117 Interest cost 710 749 167 186 Plan participants’ contributions — — 42 42 Actuarial (gain) loss (582 ) 2,095 (341 ) 502 Plan amendments — — (23 ) (1,012 ) Acquisitions/divestitures (a) — 594 — 142 Curtailments — (8 ) — — Settlements (34 ) (30 ) — — Gross benefits paid (923 ) (896 ) (223 ) (231 ) Net benefit obligation at end of year $ 17,753 $ 18,256 $ 3,938 $ 4,197 Pension Benefits Other Postretirement Benefits 2015 2014 2015 2014 Change in plan assets: Fair value of net plan assets at beginning of year $ 14,874 $ 13,571 $ 2,430 $ 2,238 Actual return on plan assets (32 ) 1,443 4 90 Employer contributions 462 332 40 291 Plan participants’ contributions — — 42 42 Gross benefits paid (923 ) (896 ) (223 ) (231 ) Acquisitions/divestitures (a) — 454 — — Settlements (34 ) (30 ) — — Fair value of net plan assets at end of year $ 14,347 $ 14,874 $ 2,293 $ 2,430 _______________________ (a) On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, Exelon became a sponsor of CENG’s pension and OPEB plans effective July 14, 2014. See Note 5 - Investment in Constellation Energy Nuclear Group, LLC for further information. Exelon presents its benefit obligations and plan assets net on its balance sheet within the following line items: Pension Benefits Other Postretirement Benefits 2015 2014 2015 2014 Other current liabilities $ 21 $ 16 $ 27 $ 25 Pension obligations 3,385 3,366 — — Non-pension postretirement benefit obligations — — 1,618 1,742 Unfunded status (net benefit obligation less net plan assets) $ 3,406 $ 3,382 $ 1,645 $ 1,767 The funded status of the pension and other postretirement benefit obligations refers to the difference between plan assets and estimated obligations of the plan. The funded status changes over time due to several factors, including contribution levels, assumed discount rates and actual returns on plan assets. The following tables provide the projected benefit obligations (PBO), accumulated benefit obligation (ABO), and fair value of plan assets for all pension plans with a PBO or ABO in excess of plan assets. PBO in excess of plan assets 2015 2014 Projected benefit obligation $ 17,753 $ 18,256 Fair value of net plan assets 14,347 14,874 ABO in excess of plan assets 2015 2014 Projected benefit obligation $ 17,753 $ 18,256 Accumulated benefit obligation 16,792 17,191 Fair value of net plan assets 14,347 14,874 On a PBO basis, the plans were funded at 81% at December 31, 2015 compared to 81% at December 31, 2014 . On an ABO basis, the plans were funded at 85% at December 31, 2015 compared to 87% at December 31, 2014 . The ABO differs from the PBO in that the ABO includes no assumption about future compensation levels. Components of Net Periodic Benefit Costs The majority of the 2015 pension benefit cost for Exelon-sponsored plans is calculated using an expected long-term rate of return on plan assets of 7.00% and a discount rate of 3.94% . The majority of the 2015 other postretirement benefit cost is calculated using an expected long-term rate of return on plan assets of 6.46% for funded plans and a discount rate of 3.92% . A portion of the net periodic benefit cost for all pension and OPEB plans are capitalized within each of the Registrant's Consolidated Balance Sheets. The following table presents the components of Exelon’s net periodic benefit costs, prior to any capitalization, for the years ended December 31, 2015 , 2014 and 2013 . Pension Benefits Other Postretirement Benefits 2015 2014 2013 2015 2014 2013 Components of net periodic benefit cost: Service cost $ 326 $ 293 $ 317 $ 119 $ 117 $ 162 Interest cost 710 749 650 167 186 194 Expected return on assets (1,026 ) (994 ) (1,015 ) (151 ) (154 ) (132 ) Amortization of: Prior service cost (credit) 13 14 14 (174 ) (122 ) (19 ) Actuarial loss 571 420 562 80 50 83 Settlement charges 2 2 9 — — — Net periodic benefit cost $ 596 $ 484 $ 537 $ 41 $ 77 $ 288 Components of AOCI and Regulatory Assets Under the authoritative guidance for regulatory accounting, a portion of current year actuarial gains and losses and prior service costs (credits) is capitalized within Exelon’s Consolidated Balance Sheets to reflect the expected regulatory recovery of these amounts, which would otherwise be recorded to AOCI. The following tables provide the components of AOCI and regulatory assets (liabilities) for the years ended December 31, 2015 , 2014 and 2013 for all plans combined. Pension Benefits Other Postretirement Benefits 2015 2014 2013 2015 2014 2013 Changes in plan assets and benefit obligations recognized in AOCI and regulatory assets (liabilities): Current year actuarial loss (gain) $ 476 $ 1,639 $ (1,169 ) $ (194 ) $ 561 $ (628 ) Amortization of actuarial loss (571 ) (420 ) (562 ) (80 ) (50 ) (83 ) Current year prior service (credit) cost — — — (23 ) (1,012 ) 15 Amortization of prior service (cost) credit (13 ) (14 ) (14 ) 174 122 19 Settlements (2 ) (2 ) (8 ) — — — Total recognized in AOCI and regulatory assets (liabilities) (a) $ (110 ) $ 1,203 $ (1,753 ) $ (123 ) $ (379 ) $ (677 ) ______________________ (a) Of the $110 million gain related to pension benefits, $64 million and $46 million were recognized in AOCI and regulatory assets, respectively, during 2015 . Of the $123 million gain related to other postretirement benefits, $63 million and $60 million were recognized in AOCI and regulatory assets (liabilities), respectively, during 2015 . Of the $1,203 million loss related to pension benefits, $788 million and $415 million were recognized in AOCI and regulatory assets, respectively, during 2014 . Of the $379 million gain related to other postretirement benefits, $162 million and $217 million were recognized in AOCI and regulatory assets (liabilities), respectively, during 2014 . Of the $1,753 million gain related to pension benefits, $1,071 million and $682 million were recognized in AOCI and regulatory assets, respectively, during 2013 . Of the $677 million gain related to other postretirement benefits, $352 million and $325 million were recognized in AOCI and regulatory assets, respectively, during 2013 . The following table provides the components of Exelon’s gross accumulated other comprehensive loss and regulatory assets (liabilities) that have not been recognized as components of periodic benefit cost at December 31, 2015 and 2014 , respectively, for all plans combined: Pension Benefits Other Postretirement Benefits 2015 2014 2015 2014 Prior service cost (credit) $ 36 $ 49 $ (812 ) $ (963 ) Actuarial loss 7,310 7,407 711 985 Total (a) $ 7,346 $ 7,456 $ (101 ) $ 22 _______________________ (a) Of the $7,346 million related to pension benefits, $4,246 million and $3,100 million are included in AOCI and regulatory assets, respectively, at December 31, 2015 . Of the $(101) million related to other postretirement benefits, $(63) million and $(38) million are included in AOCI and regulatory assets (liabilities), respectively, at December 31, 2015 . Of the $7,456 million related to pension benefits, $4,310 million and $3,146 million are included in AOCI and regulatory assets, respectively, at December 31, 2014 . The $22 million related to other postretirement benefits is included in regulatory assets (liabilities) at December 31, 2014 . The following table provides the components of Exelon’s AOCI and regulatory assets(liabilities) at December 31, 2015 (included in the table above) that are expected to be amortized as components of periodic benefit cost in 2016 . These estimates are subject to the completion of an actuarial valuation of Exelon’s pension and other postretirement benefit obligations, which will reflect actual census data as of January 1, 2016 and actual claims activity as of December 31, 2015 . The valuation is expected to be completed in the first quarter of 2016 for the majority of the benefit plans. Pension Benefits Other Postretirement Benefits Prior service cost (credit) $ 13 $ (175 ) Actuarial loss 501 50 Total (a) $ 514 $ (125 ) ___________________ (a) Of the $514 million related to pension benefits at December 31, 2015 , $290 million and $224 million are expected to be amortized from AOCI and regulatory assets in 2016 , respectively. Of the $(125) million related to other postretirement benefits at December 31, 2015 , $(64) million and $(61) million are expected to be amortized from AOCI and regulatory assets (liabilities) in 2016 , respectively. Assumptions The measurement of the plan obligations and costs of providing benefits under Exelon’s defined benefit and other postretirement plans involves various factors, including the development of valuation assumptions and accounting policy elections. When developing the required assumptions, Exelon considers historical information as well as future expectations. The measurement of benefit obligations and costs is impacted by several assumptions including the discount rate applied to benefit obligations, the long-term EROA, Exelon’s expected level of contributions to the plans, the long-term expected investment rate credited to employees participating in cash balance plans and the anticipated rate of increase of health care costs. Additionally, assumptions related to plan participants include the incidence of mortality, the expected remaining service period, the level of compensation and rate of compensation increases, employee age and length of service, among other factors. Expected Rate of Return. In selecting the EROA, Exelon considers historical economic indicators (including inflation and GDP growth) that impact asset returns, as well as expectations regarding future long-term capital market performance, weighted by Exelon’s target asset class allocations. Mortality. For the December 31, 2014 actuarial valuation, Exelon changed its assumption of mortality to reflect more recent expectations of future improvements in life expectancy. The change was supported through completion of an experience study and supplemental analyses performed by its actuaries. The change in assumption resulted in increases of $361 million and $117 million in the pension and other postretirement benefits obligations as of December 31, 2014, respectively. There were no changes to the mortality assumption in 2015 . The following assumptions were used to determine the benefit obligations for the plans at December 31, 2015 , 2014 and 2013 . Assumptions used to determine year-end benefit obligations are the assumptions used to estimate the subsequent year’s net periodic benefit costs. Pension Benefits Other Postretirement Benefits 2015 2014 2013 2015 2014 2013 Discount rate 4.29 % 3.94 % 4.80 % 4.29 % 3.92 % 4.90 % Rate of compensation increase (a) (a) (b) (a) (a) (b) Mortality table RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table with Scale AA improvements RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table with Scale AA improvements Health care cost trend on covered charges N/A N/A N/A 5.50% decreasing to ultimate trend of 5.00% in 2017 6.00% 6.00% decreasing to ultimate trend of 5.00% in 2017 _____________________________ (a) 3.25% through 2019 and 3.75% thereafter. (b) 3.25% through 2018 and 3.75% thereafter. The following assumptions were used to determine the net periodic benefit costs for all the plans for the years ended December 31, 2015 , 2014 and 2013 : Pension Benefits Other Postretirement Benefits 2015 2014 2013 2015 2014 2013 Discount rate 3.94 % (a) 4.80 % (b) 3.92 % (c) 3.92 % (a) 4.90 % (b) 4.00 % (c) Expected return on plan assets 7.00 % (d) 7.00 % (d) 7.50 % (d) 6.50 % (d) 6.59 % (d) 6.45 % (d) Rate of compensation increase (e) (f) (g) (e) (f) (g) Mortality table RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table with Scale AA improvements RP-2000 table with Scale AA improvements RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table with Scale AA improvements RP-2000 table with Scale AA improvements Health care cost trend on covered charges N/A N/A N/A 6.00% decreasing to ultimate trend of 5.00% in 2017 6.00% 6.50% decreasing to ultimate trend of 5.00% in 2017 ___________________________ (a) The discount rates above represent the initial discount rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2015 . Discount rates for CENG's legacy pension and OPEB plans ranged from 3.68% - 4.14% and 4.32% - 4.43% , respectively. (b) The discount rates above represent the initial discount rates used to establish the majority of Exelon's pension and other postretirement benefits costs for the year ended December 31, 2014 . Certain of the other postretirement benefit plans were remeasured as of April 30, 2014 using an expected long-term rate of return on plan assets of 6.59% and a discount rate of 4.30% . Costs of the year ended December 31, 2014 reflect the impact of this remeasurement. On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, Exelon became the sponsor of CENG’s legacy pension and OPEB plans effective July 14, 2014; discount rates for those plans, impacting 2014 costs, ranged from 3.60% - 4.30% and 4.09% - 4.55% , respectively. See Note 5 - Investment in Constellation Energy Nuclear Group, LLC for further information. (c) The discount rates above represent the initial discounts rates used to establish Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2013 . Certain of the benefit plans were remeasured during the year using discount rates of 4.21% and 4.66% for pension and other postretirement benefits, respectively. Costs for the year ended December 31, 2013 reflect the impact of these remeasurements. (d) Not applicable to pension and other postretirement benefit plans that do not have plan assets. (e) 3.25% through 2019 and 3.75% thereafter. (f) 3.25% through 2018 and 3.75% thereafter. (g) 3.25% through 2017 and 3.75% thereafter. Assumed health care cost trend rates impact the other postretirement benefit plan costs reported for Exelon's participant populations with plan designs that do not have a cap on cost growth. A one percentage point change in assumed health care cost trend rates would have the following effects: Effect of a one percentage point increase in assumed health care cost trend: on 2015 total service and interest cost components $ 12 on postretirement benefit obligation at December 31, 2015 100 Effect of a one percentage point decrease in assumed health care cost trend: on 2015 total service and interest cost components (9 ) on postretirement benefit obligation at December 31, 2015 (89 ) Health Care Reform Legislation In March 2010, the Health Care Reform Acts were signed into law, which contain a number of provisions that impact retiree health care plans provided by employers, including a provision that imposes an excise tax on certain high-cost plans whereby premiums paid over a prescribed threshold will be taxed at a 40% rate. Additional legislation was passed in December 2015 that made some changes to the law, including moving the implementation date of the excise tax from 2018 to 2020. Although the excise tax does not go into effect until 2020, accounting guidance requires Exelon to incorporate the estimated impact of the excise tax in its annual actuarial valuation. The application of the legislation is still unclear and Exelon continues to monitor the Department of Labor and IRS for additional guidance. Certain key assumptions are required to estimate the impact of the excise tax on Exelon’s other postretirement benefit obligation, including projected inflation rates (based on the CPI). Exelon reflected its best estimate of the expected impact in its annual actuarial valuation. Contributions The following table provides contributions made by Generation, ComEd, PECO, BGE and BSC to the pension and other postretirement benefit plans: Pension Benefits Other Postretirement Benefits 2015 (a) 2014 (a) 2013 2015 2014 2013 Generation $ 231 $ 173 $ 119 $ 14 $ 124 $ 30 ComEd 143 122 118 7 125 4 PECO 40 11 11 — 5 20 BGE 1 — — 16 17 24 BSC (b) 47 26 91 3 20 5 Exelon $ 462 $ 332 $ 339 $ 40 $ 291 $ 83 _________________________ (a) Exelon's and Generation's pension contributions include $36 million and $43 million related to the legacy CENG plans that was funded by CENG as provided in an Employee Matters Agreement (EMA) between Exelon and CENG for the years ended December 31, 2015 and 2014 , respectively. (b) Includes $5 million , $9 million , and $72 million of pension contributions funded by Exelon Corporate, for the years ended December 31, 2015 , 2014 , and 2013 , respectively. Management considers various factors when making pension funding decisions, including actuarially determined minimum contribution requirements under ERISA, contributions required to avoid benefit restrictions and at-risk status as defined by the Pension Protection Act of 2006 (the Act), management of the pension obligation and regulatory implications. The Act requires the attainment of certain funding levels to avoid benefit restrictions (such as an inability to pay lump sums or to accrue benefits prospectively), and at-risk status (which triggers higher minimum contribution requirements and participant notification). Additionally, the projected contribution reflects a funding strategy of contributing the greater of $250 million until the qualified plans are fully funded on an ABO basis, and the minimum amounts under ERISA to avoid benefit restrictions and at-risk status. This level funding strategy helps minimize volatility of future period required pension contributions. Exelon plans to contribute $250 million to its qualified pension plans in 2016 , of which Generation, ComEd, PECO, and BGE will contribute $134 million , $30 million , $28 million , and $31 million , respectively. Exelon's and Generation's expected qualified pension plan contributions above include $25 million related to the legacy CENG plans that will be funded by CENG as provided in an EMA between Exelon and CENG. Unlike the qualified pension plans, Exelon’s non-qualified pension plans are not funded. Exelon plans to make non-qualified pension plan benefit payments of $21 million in 2016 , of which Generation, ComEd, PECO, and BGE will make payments of $9 million , $2 million , $1 million and $1 million , respectively. Unlike the qualified pension plans, other postretirement plans are not subject to statutory minimum contribution requirements. Exelon’s management has historically considered several factors in determining the level of contributions to its other postretirement benefit plans, including levels of benefit claims paid and regulatory implications (amounts deemed prudent to meet regulatory expectations and best assure continued rate recovery). In 2016 , Exelon anticipates funding its other postretirement benefit plans based on the funding considerations discussed above, with the exception of those plans which remain unfunded. Exelon expects to make other postretirement benefit plan contributions, including benefit payments related to unfunded plans, of approximately $35 million in 2016 , of which Generation, ComEd, PECO, and BGE expect to contribute $13 million , $3 million , $1 million , and $18 million , respectively. Estimated Future Benefit Payments Estimated future benefit payments to participants in all of the pension plans and postretirement benefit plans at December 31, 2015 were: Pension Benefits Other Postretirement Benefits 2016 $ 1,153 $ 217 2017 997 223 2018 1,009 228 2019 1,036 235 2020 1,071 244 2021 through 2025 5,923 1,341 Total estimated future benefit payments through 2025 $ 11,189 $ 2,488 Allocation to Exelon Subsidiaries Generation, ComEd, PECO, and BGE account for their participation in Exelon’s pension and other postretirement benefit plans by applying multi-employer accounting. Employee-related assets and liabilities, including both pension and postretirement liabilities, for the legacy Exelon plans were allocated by Exelon to its subsidiaries based on the number of active employees as of January 1, 2001 as part of Exelon’s corporate restructuring. The obligation for Generation, ComEd and PECO reflects the initial allocation and the cumulative costs incurred and contributions made since January 1, 2001. Historically, Exelon has allocated the components of pension and other postretirement costs to the subsidiaries in the legacy Exelon plans based upon several factors, including the measures of active employee participation in each participating unit. Pension and other postretirement benefit contributions were allocated to legacy Exelon subsidiaries in proportion to active service costs recognized and total costs recognized, respectively. Beginning in 2015, Exelon began allocating costs related to its legacy Exelon pension and other postretirement benefit plans to its subsidiaries based on both active and retired employee participation and contributions are allocated based on accounting cost. The impact of this allocation methodology change is not material to any Registrant. For legacy CEG and legacy CENG plans, components of pension and other postretirement benefit costs and contributions have been, and will continue to be, allocated to the subsidiaries based on employee participation (both active and retired). The amounts below were included in capital expenditures and Operating and maintenance expense for the years ended December 31, 2015 , 2014 and 2013 , respectively, for Generation’s, ComEd’s, PECO’s, BSC’s and BGE’s allocated portion of the pension and other postretirement benefit plan costs. These amounts include the recognized contractual termination benefit charges, curtailment gains, and settlement charges: For the Year Ended December 31, Generation ComEd PECO BSC (a) BGE Exelon 2015 $ 269 $ 206 $ 39 $ 57 $ 66 637 2014 250 162 36 46 67 561 2013 347 309 43 71 55 825 _____________________ (a) These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO or BGE amounts above. Plan Assets Investment Strategy. On a regular basis, Exelon evaluates its investment strategy to ensure that plan assets will be sufficient to pay plan benefits when due. As part of this ongoing evaluation, Exelon may make changes to its targeted asset allocation and investment strategy. Exelon has developed and implemented a liability hedging investment strategy for its qualified pension plans that has reduced the volatility of its pension assets relative to its pension liabilities. Exelon is likely to continue to gradually increase the liability hedging portfolio as the funded status of its plans improves. The overall objective is to achieve attractive risk-adjusted returns that will balance the liquidity requirements of the plans’ liabilities while striving to minimize the risk of significant losses. Trust assets for Exelon’s other postretirement plans are managed in a diversified investment strategy that prioritizes maximizing liquidity and returns while minimizing asset volatility. Exelon used an EROA of 7.00% and 6.71% to estimate its 2016 pension and other postretirement benefit costs, respectively. Exelon’s pension and other postretirement benefit plan target asset allocations at December 31, 2015 and 2014 asset allocations were as follows: Pension Plans Percentage of Plan Assets at December 31, Asset Category Target Allocation 2015 2014 Equity securities 32 % 35 % 33 % Fixed income securities 37 % 34 37 Alternative investments (a) 31 % 31 30 Total 100 % 100 % Other Postretirement Benefit Plans Percentage of Plan Assets at December 31, Asset Category Target Allocation 2015 2014 Equity securities 39 % 43 % 42 % Fixed income securities 26 % 27 34 Alternative investments (a) 35 % 30 24 Total 100 % 100 % ___________________ (a) Alternative investments include private equity, hedge funds, real estate, and private credit. Concentrations of Credit Risk. Exelon evaluated its pension and other postretirement benefit plans’ asset portfolios for the existence of significant concentrations of credit risk as of December 31, 2015 . Types of concentrations that were evaluated include, but are not limited to, investment concentrations in a single entity, type of industry, foreign country, and individual fund. As of December 31, 2015 , there were no significant concentrations (defined as greater than 10% of plan assets) of risk in Exelon’s pension and other postretirement benefit plan assets. Fair Value Measurements The following table presents Exelon’s pension and other postretirement benefit plan assets measured and recorded at fair value on Exelon’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy at December 31, 2015 and 2014 : At December 31, 2015 (a) Level 1 Level 2 Level 3 Total Pension plan assets Cash equivalents $ 210 $ — $ — $ 210 Equities (b) 3,571 1,462 2 5,035 Fixed income: U.S. Treasury and agencies 1,001 79 — 1,080 State and municipal debt — 61 — 61 Corporate debt — 2,901 165 3,066 Other (b) — 395 203 598 Fixed income subtotal 1,001 3,436 368 4,805 Private equity — — 924 924 Hedge funds — 1,129 795 1,924 Real estate — — 725 725 Private credit — — 699 699 Pension plan assets subtotal 4,782 6,027 3,513 14,322 At December 31, 2015 (a) Level 1 Level 2 Level 3 Total Other postretirement benefit plan assets Cash equivalents 15 — — 15 Equities 510 482 — 992 Fixed income: U.S. Treasury and agencies 11 53 — 64 State and municipal debt — 131 — 131 Corporate debt — 44 — 44 Other 155 205 — 360 Fixed income subtotal 166 433 — 599 Hedge funds — 312 139 451 Real estate — — 131 131 Private credit — — 103 103 Other postretirement benefit plan assets subtotal 691 1,227 373 2,291 Total pension and other postretirement benefit plan assets (c) $ 5,473 $ 7,254 $ 3,886 $ 16,613 At December 31, 2014 (a) Level 1 Level 2 Level 3 Total Pension plan assets Cash equivalents $ 1 $ — $ — $ 1 Equities (b) 3,261 1,449 2 4,712 Fixed income: U.S. Treasury and agencies 1,051 88 — 1,139 State and municipal debt — 80 — 80 Corporate debt — 3,125 120 3,245 Other (b) — 930 152 1,082 Fixed income subtotal 1,051 4,223 272 5,546 Private equity — — 900 900 Hedge funds — 1,355 785 2,140 Real estate 243 — 685 928 Private credit — — 607 607 Pension plan assets subtotal 4,556 7,027 3,251 14,834 At December 31, 2014 (a) Level 1 Level 2 Level 3 Total Other postretirement benefit plan assets Cash equivalents 11 — — 11 Equities 480 525 — 1,005 Fixed income: U.S. Treasury and agencies 15 59 — 74 State and municipal debt — 197 — 197 Corporate debt — 42 — 42 Other 253 272 — 525 Fixed income subtotal 268 570 — 838 Hedge funds — 339 — 339 Real estate 8 — 116 124 Private credit — — 110 110 Other postretirement benefit plan assets subtotal 767 1,434 226 2,427 Total pension and other postretirement benefit plan assets (c) $ 5,323 $ 8,461 $ 3,477 $ 17,261 __________________________ (a) See Note 12 — Fair Value of Financial Assets and Liabilities for a description of levels within the fair value hierarchy. (b) Includes derivative instruments of $5 million and $(3) million , which have a total notional amount of $1,774 million and $1,491 million at December 31, 2015 and 2014 , respectively. The notional principal amounts for these instruments provide one m

Severance (Exelon, Generation,

Severance (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Restructuring and Related Activities [Abstract]
Severance (Exelon, Generation, ComEd and PECO)	(Exelon, Generation, ComEd, PECO and BGE) The Registrants have an ongoing severance plan under which, in general, the longer an employee worked prior to termination the greater the amount of severance benefits. The Registrants record a liability and expense or regulatory asset for severance once terminations are probable of occurrence and the related severance benefits can be reasonably estimated. For severance benefits that are incremental to its ongoing severance plan (“one-time termination benefits”), the Registrants measure the obligation and record the expense at fair value at the communication date if there are no future service requirements, or, if future service is required to receive the termination benefit, ratably over the required service period. Ongoing Severance Plans The Registrants provide severance, health and welfare benefits under Exelon’s ongoing severance benefit plans to terminated employees in the normal course of business. These benefits are accrued for when the benefits are considered probable and can be reasonably estimated. For the years ended December 31, 2015 , 2014 , and 2013 , the Registrants recorded the following severance costs associated with these ongoing severance benefits within Operating and maintenance expense in their Consolidated Statements of Operations and Comprehensive Income: Severance Benefits (a) Severance Charges-2015 Severance Charges-2014 Severance Charges-2013 ________________________ (a) The amounts above for Generation include $ 1 million , $ 1 million , and $ 2 million for amounts billed by BSC through intercompany allocations for the years ended December 31, 2015 , December 31, 2014 , and December 31, 2013 , respectively. Amounts billed by BSC to ComEd, PECO and BGE were not material. The severance liability balances associated with these ongoing severance benefits as of December 31, 2015 and 2014 are not material.

Shareholder Equity (Exelon, Com

Shareholder Equity (Exelon, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Stockholders' Equity Note Disclosure [Text Block]	19 . Shareholder's Equity (Exelon, ComEd, PECO and BGE) The following table presents common stock authorized and outstanding as of December 31, 2015 and 2014 : December 31, 2015 2014 Par Value Shares Authorized Shares Outstanding Common Stock Exelon no par value 2,000,000,000 919,924,742 859,833,343 ComEd $ 12.50 250,000,000 127,016,973 127,016,947 PECO no par value 500,000,000 170,478,507 170,478,507 BGE no par value 175,000,000 1,000 1,000 ComEd had 73,434 and 73,533 warrants outstanding to purchase ComEd common stock at December 31, 2015 and 2014 , respectively. The warrants entitle the holders to convert such warrants into common stock of ComEd at a conversion rate of one share of common stock for three warrants. At December 31, 2015 and 2014 , 24,478 and 24,511 shares of common stock, respectively, were reserved for the conversion of warrants. Equity Securities Offering In June 2014, Exelon marketed an equity offering of 57.5 million shares of its common stock at a public offering price of $ 35 per share. In connection with such offering, Exelon entered into forward sale agreements with two counterparties. In July 2015, Exelon settled the forward sale agreement by the issuance of 57.5 million shares of Exelon common stock. Exelon received net cash proceeds of $1.87 billion , which was calculated based on a forward price of $32.48 per share as specified in the forward sale agreements. Use of net proceeds will be to fund the pending merger with PHI and related costs and expenses, and for general corporate purposes. The forward sale agreements are classified as equity transactions. As a result, no amounts were recorded in the consolidated financial statements until the July 2015 settlement of the forward sale agreements. However, prior to the July 2015 settlement, incremental shares, if any, were included within the calculation of diluted EPS using the treasury stock method. Concurrent with the forward equity transaction, Exelon also issued $1.15 billion of junior subordinated notes in the form of 23 million equity units. See Note 14 — Debt and Credit Agreements for further information on the equity units. Share Repurchases Share Repurchase Programs . There currently is no Exelon Board of Director authority to repurchase shares. Any previous shares repurchased are held as treasury shares, at cost, unless cancelled or reissued at the discretion of Exelon’s management. Under the previous share repurchase programs, 35 million shares of common stock are held as treasury stock with a cost of $2.3 billion at December 31, 2015 . During 2015 , 2014 and 2013 , Exelon had no common stock repurchases. Preferred and Preference Securities of Subsidiaries At December 31, 2015 and 2014 , Exelon was authorized to issue up to 100,000,000 shares of preferred securities, none of which were outstanding. At December 31, 2015 and 2014 , ComEd prior preferred securities and ComEd cumulative preference securities consisted of 850,000 shares and 6,810,451 shares authorized, respectively, none of which were outstanding. At December 31, 2015 and 2014 , BGE cumulative preference stock, $100 par value, consisted of 6,500,000 shares authorized of which 1,900,000 are outstanding as set forth in the table below. Shares of BGE preference stock have no voting power except for the following: • The preference stock has one vote per share on any charter amendment that i) with regards to either dividends or distribution of assets, would create or authorize any shares of stock ranking prior to or on a parity with the preference stock or ii) substantially adversely affect the contract rights, as expressly set forth in BGE’s charter, of the preference stock. Each such amendment would require the affirmative vote of two-thirds of all the shares of preference stock outstanding; and • Whenever BGE fails to pay full dividends on the preference stock and such failure continues for one year, the preference stock shall have one vote per share on all matters, until and unless such dividends shall have been paid in full. Upon liquidation, the holders of the preference stock of each series outstanding are entitled to receive the par amount of their shares and an amount equal to the unpaid accrued dividends. December 31, Redemption (a) 2015 2014 2015 2014 Shares Outstanding Dollar Amount Series (without mandatory redemption) 7.125%, 1993 Series $ 100.00 400,000 400,000 $ 40 $ 40 6.97%, 1993 Series 100.00 500,000 500,000 50 50 6.70%, 1993 Series 100.00 400,000 400,000 40 40 6.99%, 1995 Series 100.00 600,000 600,000 60 60 Total preference stock 1,900,000 1,900,000 $ 190 $ 190 ______________________ (a) Redeemable, at the option of BGE, at the indicated dollar amounts per share, plus accrued and unpaid dividends.

Stock-Based Compensation Plans

Stock-Based Compensation Plans (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Common Stock [Abstract]
Stock-Based Compensation Plans	(Exelon, Generation, ComEd, PECO and BGE) Stock-Based Compensation Plans Exelon grants stock-based awards through its LTIP, which primarily includes stock options, restricted stock units and performance share awards. At December 31, 2015 , there were approximately 16 million shares authorized for issuance under the LTIP. For the years ended December 31, 2015 , 2014 and 2013 , exercised and distributed stock-based awards were primarily issued from authorized but unissued common stock shares. The Compensation Committee of Exelon’s Board of Directors changed the mix of awards granted under the LTIP in 2013 by eliminating stock options in favor of the use of full value shares, consisting of 67% performance shares and 33% restricted stock units. The performance share awards granted in 2013 will cliff vest at the end of a three -year performance period. The performance share awards granted in 2012 and earlier had a one -year performance period and vested ratably over three years . To address the reduction in annual award opportunity resulting from the transition to a three -year cliff vesting performance period, the Compensation Committee also approved a one-time grant of performance share transition awards in 2013, which vested one-third after one year , with the remaining balance vesting over a two -year performance period. These one-time 2013 performance share transition awards will be settled 50% in common stock and 50% in cash, except for awards granted to executive vice presidents and higher officers that may be settled 100% in cash if certain Exelon stock ownership requirements are satisfied. In addition to this change, in 2013 ComEd and in 2014 PECO and BGE transitioned from Exelon stock-based awards to cash award programs with payouts based on the performance of each respective utility. The following tables do not include expense related to these plans as they are not considered stock-based compensation plans under the applicable accounting guidance . The following table presents the stock-based compensation expense included in Exelon’s Consolidated Statements of Operations and Comprehensive Income for the years ended December 31, 2015 , 2014 and 2013 : Year Ended December 31, Components of Stock-Based Compensation Expense 2015 2014 2013 Performance share awards $ 41 $ 59 $ 48 Restricted stock units 71 61 61 Stock options 1 2 3 Other stock-based awards 6 5 6 Total stock-based compensation expense included in operating and maintenance expense 119 127 118 Income tax benefit (46 ) (47 ) (44 ) Total after-tax stock-based compensation expense $ 73 $ 80 $ 74 The following table presents stock-based compensation expense (pre-tax) for the years ended December 31, 2015 , 2014 and 2013 : Year Ended December 31, Subsidiaries 2015 2014 2013 Generation $ 64 $ 52 $ 48 ComEd 6 7 9 PECO 3 3 5 BGE 3 5 6 BSC (a) 43 60 50 Total $ 119 $ 127 $ 118 ________________________ (a) These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO and BGE amounts above. There were no significant stock-based compensation costs capitalized during the years ended December 31, 2015 , 2014 and 2013 . Exelon receives a tax deduction based on the intrinsic value of the award on the exercise date for stock options and the distribution date for performance share awards and restricted stock units. For each award, throughout the requisite service period, Exelon recognizes the tax benefit related to compensation costs. The following table presents information regarding Exelon’s tax benefits for the years ended December 31, 2015 , 2014 and 2013 : Year Ended December 31, 2015 2014 2013 Realized tax benefit when exercised/distributed: Restricted stock units $ 30 $ 17 $ 11 Performance share awards 18 11 11 Stock deferral plan — — 1 Stock Options Non-qualified stock options to purchase shares of Exelon’s common stock were granted under the LTIP through 2012. Due to changes in the LTIP, there were no stock options granted in 2013, 2014 or 2015. For all stock options granted through 2012, the exercise price of the stock options is equal to the fair market value of the underlying stock on the date of option grant. The vesting period of stock options is generally four years. All stock options expire ten years from the date of grant. The value of stock options at the date of grant is expensed over the requisite service period using the straight-line method. The requisite service period for stock options is generally four years . However, certain stock options become fully vested upon the employee reaching retirement-eligibility. The value of the stock options granted to retirement-eligible employees is either recognized immediately upon the date of grant or through the date at which the employee reaches retirement eligibility. The fair value of each option is estimated on the date of grant using the Black-Scholes-Merton option-pricing model. The following table presents the weighted average assumptions used in the pricing model for grants and the resulting weighted average grant date fair value of stock options granted for the year ended 2012: Year ended December 31, 2012 Dividend yield 5.28 % Expected volatility 23.20 % Risk-free interest rate 1.30 % Expected life (years) 6.25 Weighted average grant date fair value (per share) 4.18 The assumptions above relate to Exelon stock options granted in 2012 and therefore do not include stock options that were converted in connection with the merger with Constellation during the year ended 2012. The dividend yield is based on several factors, including Exelon’s most recent dividend payment at the grant date and the average stock price over the previous year. Expected volatility is based on implied volatilities of traded stock options in Exelon’s common stock and historical volatility over the estimated expected life of the stock options. The risk-free interest rate for a security with a term equal to the expected life is based on a yield curve constructed from U.S. Treasury strips at the time of grant. For each year presented, the expected life represents the period of time the stock options are expected to be outstanding and is based on the simplified method. Exelon believes that the simplified method is appropriate due to several factors that result in historical exercise data not being sufficient to determine a reasonable estimate of expected term. Exelon uses historical data to estimate employee forfeitures, which are compared to actual forfeitures on a quarterly basis and adjusted as necessary. The following table presents information with respect to stock option activity for the year ended December 31, 2015 : Shares Weighted Average Exercise Price (per share) Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value Balance of shares outstanding at December 31, 2014 18,830,967 $ 46.85 Options exercised (7,133 ) 21.25 Options forfeited (5,250 ) 39.81 Options expired (3,245,827 ) 47.75 Balance of shares outstanding at December 31, 2015 15,572,757 $ 46.68 3.85 $ 9 Exercisable at December 31, 2015 (a) 15,490,507 $ 46.72 3.84 $ 9 ____________________ (a) Includes stock options issued to retirement eligible employees. The following table summarizes additional information regarding stock options exercised for the years ended December 31, 2015 , 2014 and 2013 : Year Ended December 31, 2015 2014 2013 Intrinsic value (a) $ — $ 3 $ 4 Cash received for exercise price — 7 19 ______________________ (a) The difference between the market value on the date of exercise and the option exercise price. The following table summarizes Exelon’s nonvested stock option activity for the year ended December 31, 2015 : Shares Weighted Average Exercise Price (per share) Nonvested at December 31, 2014 (a) 432,035 $ 39.91 Vested (344,535 ) 39.93 Forfeited (5,250 ) 39.81 Nonvested at December 31, 2015 (a) 82,250 $ 39.81 _____________________ (a) Excludes 279,000 and 746,140 of stock options issued to retirement-eligible employees as of December 31, 2015 and 2014 , respectively, as they are fully vested. At December 31, 2015 , $0.1 million of total unrecognized compensation costs related to nonvested stock options are expected to be recognized over the remaining weighted-average period of less than a year. Restricted Stock Units Restricted stock units are granted under the LTIP with the majority being settled in a specific number of shares of common stock after the service condition has been met. The corresponding cost of services is measured based on the grant date fair value of the restricted stock unit issued. The value of the restricted stock units is expensed over the requisite service period using the straight-line method. The requisite service period for restricted stock units is generally three to five years . However, certain restricted stock unit awards become fully vested upon the employee reaching retirement-eligibility. The value of the restricted stock units granted to retirement-eligible employees is either recognized immediately upon the date of grant or through the date at which the employee reaches retirement eligibility. Exelon uses historical data to estimate employee forfeitures, which are compared to actual forfeitures on a quarterly basis and adjusted as necessary. The following table summarizes Exelon’s nonvested restricted stock unit activity for the year ended December 31, 2015 : Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2014 (a) 3,758,218 $ 31.27 Granted 2,132,856 36.55 Vested (1,597,255 ) 32.88 Forfeited (76,232 ) 33.06 Undistributed vested awards (b) (654,333 ) 35.35 Nonvested at December 31, 2015 (a) 3,563,254 $ 32.92 _______________________ (a) Excludes 1,097,630 and 975,116 of restricted stock units issued to retirement-eligible employees as of December 31, 2015 and 2014 , respectively, as they are fully vested. (b) Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2015 . The weighted average grant date fair value (per share) of restricted stock units granted for the years ended December 31, 2015 , 2014 and 2013 was $36.55 , $28.71 and $31.06 , respectively. At December 31, 2015 and 2014 , Exelon had obligations related to outstanding restricted stock units not yet settled of $97 million and $85 million , respectively, which are included in common stock in Exelon’s Consolidated Balance Sheets. For the years ended December 31, 2015 , 2014 and 2013 , Exelon settled restricted stock units with fair value totaling $75 million , $43 million and $28 million , respectively. At December 31, 2015 , $56 million of total unrecognized compensation costs related to nonvested restricted stock units are expected to be recognized over the remaining weighted-average period of 2 years. Performance Share Awards Performance share awards are granted under the LTIP. The 2015 and 2014 performance share awards are being settled 50% in common stock and 50% in cash at the end of the three-year performance period except for awards granted to executive vice presidents and higher officers that may be settled 100% in cash if certain ownership requirements are satisfied. The performance shares granted prior to 2012 generally vest and settle over a three-year period with the holders receiving shares of common stock and/or cash annually during the vesting period. The common stock portion of the performance share and one-time 2013 performance share transition awards is considered an equity award and is valued based on Exelon's stock price on the grant date. The cash portion of the awards is considered a liability award which is remeasured each reporting period based on Exelon’s current stock price. As the value of the common stock and cash portions of the awards are based on Exelon’s stock price during the performance period, coupled with changes in the total shareholder return modifier and expected payout of the award, the compensation costs are subject to volatility until payout is established. For nonretirement-eligible employees, stock-based compensation costs are recognized over the vesting period of three years using the graded-vesting method. For performance share and one-time performance share transition awards granted to retirement-eligible employees, the value of the performance shares is recognized ratably over the vesting period, which is the year of grant. The following table summarizes Exelon’s nonvested performance share awards activity for the year ended December 31, 2015 : Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2014 (a) 2,696,097 $ 30.62 Granted 1,556,273 35.88 Change in performance (118,398 ) 35.88 Vested (704,141 ) 32.80 Forfeited (52,167 ) 32.25 Undistributed vested awards (b) (820,505 ) 33.95 Nonvested at December 31, 2015 (a) 2,557,159 $ 31.88 _______________________ (a) Excludes 1,817,883 and 1,535,791 of performance share awards issued to retirement-eligible employees as of December 31, 2015 and 2014 , respectively, as they are fully vested. (b) Represents performance share awards that vested but were not distributed to retirement-eligible employees during 2015 . The weighted average grant date fair value (per share) of performance share awards granted during the years ended December 31, 2015 , 2014 and 2013 was $35.88 , $28.75 , and $31.55 , respectively. During the years ended December 31, 2015 , 2014 and 2013 , Exelon settled performance shares with a fair value totaling $46 million , $27 million and $26 million , respectively, of which $29 million , $13 million and $12 million was paid in cash, respectively. As of December 31, 2015 , $27 million of total unrecognized compensation costs related to nonvested performance shares are expected to be recognized over the remaining weighted-average period of 1.4 years . The following table presents the balance sheet classification of obligations related to outstanding performance share awards not yet settled: December 31, 2015 2014 Current liabilities (a) $ 28 $ 28 Deferred credits and other liabilities (b) 32 36 Common stock 35 33 Total $ 95 $ 97 __________________________ (a) Represents the current liability related to performance share awards expected to be settled in cash. (b) Represents the long-term liability related to performance share awards expected to be settled in cash.

Earnings Per Share and Equity (

Earnings Per Share and Equity (Exelon)	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Earnings Per Share and Equity (Exelon)	(Exelon) Diluted earnings per share is calculated by dividing Net income attributable to common shareholders by the weighted average number of shares of common stock outstanding, including shares to be issued upon exercise of stock options, performance share awards and restricted stock outstanding under Exelon’s LTIPs considered to be common stock equivalents. The following table sets forth the components of basic and diluted earnings per share and shows the effect of the stock options, performance share awards and restricted stock on the weighted average number of shares outstanding used in calculating diluted earnings per share: Year Ended December 31, 2015 2014 2013 Net income attributable to common shareholders $ 2,269 $ 1,623 $ 1,719 Weighted average common shares outstanding—basic 890 860 856 Assumed exercise and/or distributions of stock-based awards 3 4 4 Weighted average common shares outstanding—diluted 893 864 860 The number of stock options not included in the calculation of diluted common shares outstanding due to their antidilutive effect was approximately 16 million in 2015 , 17 million in 2014 , and 20 million in 2013 . The number of equity units related to the PHI merger not included in the calculation of diluted common shares outstanding due to their antidilutive effect was 3 million for the year ended December 2015 and less than 1 million for the year ended December 31, 2014. Additionally, there were no forward units related to the PHI merger not included in the calculation of diluted common shares outstanding due to their antidilutive effect for the years ended December 31, 2015 and 2014. Refer to Note 19 — Shareholder's Equity for further information regarding the equity units and equity forward units. Under share repurchase programs, 35 million shares of common stock are held as treasury stock with a cost of $ 2.3 billion as of December 31, 2015 . In 2008, Exelon management decided to defer indefinitely any share repurchases.

Changes in Accumulated Other Co

Changes in Accumulated Other Comprehensive Income (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Changes in Accumulated Other Comprehensive Income (Exelon, Generation, PECO)	Changes in Accumulated Other Comprehensive Income (Exelon, Generation, and PECO) The following tables present changes in accumulated other comprehensive income (loss) (AOCI) by component for the years ended December 31, 2015 and 2014 : For the Year Ended December 31, 2015 Gains and (Losses) on Cash Flow Hedges Unrealized Gains and (Losses) on Marketable Securities Pension and Foreign Currency Items AOCI of Equity Investments Total Exelon (a) Beginning balance $ (28 ) $ 3 $ (2,640 ) $ (19 ) $ — $ (2,684 ) OCI before reclassifications (12 ) — (100 ) (21 ) (3 ) (136 ) Amounts reclassified from AOCI (b) 21 — 175 — — 196 Net current-period OCI 9 — 75 (21 ) (3 ) 60 Ending balance $ (19 ) $ 3 $ (2,565 ) $ (40 ) $ (3 ) $ (2,624 ) Generation (a) Beginning balance $ (18 ) $ 1 $ — $ (19 ) $ — $ (36 ) OCI before reclassifications (8 ) — — (21 ) (3 ) (32 ) Amounts reclassified from AOCI (b) 5 — — — — 5 Net current-period OCI (3 ) — — (21 ) (3 ) (27 ) Ending balance $ (21 ) $ 1 $ — $ (40 ) $ (3 ) $ (63 ) PECO (a) Beginning balance $ — $ 1 $ — $ — $ — $ 1 OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI — — — — — — Ending balance $ — $ 1 $ — $ — $ — $ 1 For the Year Ended December 31, 2014 Gains and Unrealized Pension and Foreign AOCI of Total Exelon (a) Beginning balance $ 120 $ 2 $ (2,260 ) $ (10 ) $ 108 $ (2,040 ) OCI before reclassifications (31 ) (1 ) (498 ) (9 ) 11 (528 ) Amounts reclassified from AOCI (b) (117 ) 2 118 — (119 ) (116 ) Net current-period OCI (148 ) 1 (380 ) (9 ) (108 ) (644 ) Ending balance $ (28 ) $ 3 $ (2,640 ) $ (19 ) $ — $ (2,684 ) Generation (a) Beginning balance $ 114 $ 2 $ — $ (10 ) $ 108 214 OCI before reclassifications (15 ) (1 ) — (9 ) 11 (14 ) Amounts reclassified from AOCI (b) (117 ) — — — (119 ) (236 ) Net current-period OCI (132 ) (1 ) — (9 ) (108 ) (250 ) Ending balance $ (18 ) $ 1 $ — $ (19 ) $ — $ (36 ) PECO (a) Beginning balance $ — $ 1 $ — $ — $ — $ 1 OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI — — — — — — Ending balance $ — $ 1 $ — $ — $ — $ 1 _______________________ (a) All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income. (b) See next tables for details about these reclassifications. ComEd, PECO, and BGE did not have any reclassifications out of AOCI to Net income during the years ended December 31, 2015 and 2014 . The following tables present amounts reclassified out of AOCI to Net income for Exelon and Generation during the years ended December 31, 2015 and 2014 : For the Year Ended December 31, 2015 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statements of Operations and Comprehensive Income Exelon Generation Gains and (losses) on cash flow hedges Terminated interest rate swaps $ (26 ) $ — Other, net Energy related hedges 2 2 Operating revenues Other cash flow hedges (11 ) (11 ) Interest expense Total before tax (35 ) (9 ) Tax benefit 14 4 Net of tax $ (21 ) $ (5 ) Comprehensive income Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 74 $ — Actuarial losses (b) (361 ) — Total before tax (287 ) — Tax benefit 112 — Net of tax $ (175 ) $ — Total Reclassifications $ (196 ) $ (5 ) Comprehensive income For the Year Ended December 31, 2014 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statements of Operations and Comprehensive Income Exelon Generation Gains and (losses) on cash flow hedges Energy related hedges $ 195 $ 195 Operating revenues Total before tax 195 195 Tax expense (78 ) (78 ) Net of tax $ 117 $ 117 Comprehensive income Gains and (losses) on available for sale securities Other available securities for sale $ (2 ) $ — Other Income and Deductions Total before tax (2 ) — Net of tax $ (2 ) $ — Comprehensive income Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 46 $ — Actuarial losses (b) (239 ) — Total before tax (193 ) — Tax benefit 75 — Net of tax $ (118 ) $ — Comprehensive income Equity investments Sale of equity method investment $ 5 $ 5 Equity in losses of unconsolidated affiliates Reversal of CENG equity method AOCI 193 193 Gain on Consolidation of CENG Total before tax 198 198 Tax expense (79 ) (79 ) Net of tax $ 119 $ 119 Total Reclassifications $ 116 $ 236 Comprehensive income _____________________ (a) Amounts in parenthesis represent a decrease in net income. (b) This accumulated other comprehensive income component is included in the computation of net periodic pension and OPEB cost (see Note 17 — Retirement Benefits for additional details). (c) Amortization of the deferred compensation unit plan is allocated to capital and operating and maintenance expense. The following table presents income tax expense (benefit) allocated to each component of other comprehensive income (loss) during the years ended December 31, 2015 and 2014 : For the Years Ended December 31, 2015 2014 2013 Exelon Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 30 $ 19 $ — Actuarial loss reclassified to periodic cost (140 ) (93 ) (133 ) Pension and non-pension postretirement benefit plan valuation adjustment 62 317 (430 ) Change in unrealized (gain) loss on cash flow hedges (6 ) 96 166 Change in unrealized (gain) loss on equity investments 1 73 (71 ) Total $ (53 ) $ 412 $ (468 ) Generation Change in unrealized loss on cash flow hedges $ 2 $ 84 $ 262 Change in unrealized (gain) loss on equity investments 1 73 (72 ) Total $ 3 $ 157 $ 190

Commitments and Contingencies (

Commitments and Contingencies (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies (Exelon, Generation, ComEd, PECO and BGE)	(Exelon, Generation, ComEd, PECO and BGE) Commitments Constellation Merger Commitments In February 2012, the MDPSC issued an Order approving the Exelon and Constellation merger. As part of the MDPSC Order, Exelon agreed to provide a package of benefits to BGE customers, the City of Baltimore and the State of Maryland, resulting in an estimated direct investment in the State of Maryland of approximately $1 billion. The direct investment estimate includes $95 million to $120 million relating to the construction of a headquarters building in Baltimore for Generation’s competitive energy businesses. The direct investment commitment also includes $500 million to $600 million relating to Exelon and Generation’s development or assistance in the development of 275 - 300 MWs of new generation in Maryland, which is expected to be completed within a period of 10 years. Exelon and Generation have incurred $393 million towards satisfying the commitment for new generation development in the state of Maryland, with approximately 220 MW of the new generation commencing with commercial operations to date. The MDPSC order contemplates various options for complying with the new generation development commitments, including building or acquiring generating assets, making subsidy or compliance payments, or in circumstances in which the generation build is delayed or certain specified provisions are elected, making liquidated damages payments. Exelon and Generation expect that the majority of these commitments will be satisfied by building or acquiring generating assets and, therefore, will be primarily capital in nature and recognized as incurred. However, during the third quarter of 2014, the conditions associated with one of the generation development commitments changed such that Exelon and Generation now believe that the most likely outcome will involve making subsidy payments and/or liquidated damages payments rather than constructing the specified generating plant. As a result, Exelon and Generation recorded a pre-tax $44 million loss contingency related to this generation development commitment which is included in Operating and maintenance expense in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income for the year ended December 31, 2014. While this $44 million loss contingency represents Generation’s best estimate of the future obligation, it is reasonably possible that Exelon and Generation could ultimately be required to make cumulative subsidy payments of up to a maximum of approximately $105 million over a 20-year period dependent on actual generating output from a successfully constructed generating plant. Equity Investment Commitments As part of Generation's recent investments in technology development, Generation enters into equity purchase agreements that include commitments to invest additional equity through incremental payments to fund the anticipated needs of the planned operations of the associated companies. The commitment includes approximately $ 20 million of in-kind services and 100% of 2015 ESA Investco, LLC’s equity commitment since 2015 ESA Investco, LLC is consolidated by Generation (see Note 2 - Variable Interest Entities for additional details). As of December 31, 2015 , Generation’s estimated commitment relating to its equity purchase agreements, including in-kind services contributions, is anticipated to be as follows: Total 2016 (a) $ 299 2017 21 2018 7 2019 — Total $ 327 ___________________________ (a) The noncontrolling interest holder of 2015 ESA Investco, LLC will contribute up to $172 million in support of a portion of this equity commitment. Commercial Commitments Exelon’s commercial commitments as of December 31, 2015 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2016 2017 2018 2019 2020 2021 Letters of credit (non-debt) (a) $ 1,583 $ 1,565 $ 5 $ — $ — $ 13 $ — Surety bonds (b) 809 733 49 3 2 16 6 Financing trust guarantees (c) 628 — — — — — 628 Energy marketing contract guarantees (d) 3,126 3,126 — — — — — Nuclear insurance premiums (e) 3,060 — — — — — 3,060 Total commercial commitments $ 9,206 $ 5,424 $ 54 $ 3 $ 2 $ 29 $ 3,694 ___________________________ (a) Letters of credit (non-debt)—Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (c) Includes $ 200 million of Trust Preferred Securities of ComEd Financing III, $ 178 million of Trust Preferred Securities of PECO Trust III and IV and $ 250 million of Trust Preferred Securities of BGE Capital Trust II. (d) Energy marketing contract guarantees—Guarantees issued to ensure performance under energy commodity contracts. Amount includes approximately $ 3.1 billion of guarantees issued by Exelon and Generation on behalf of its Constellation businesses to allow it the flexibility needed to conduct business with counterparties without having to post other forms of collateral. The majority of these guarantees contain evergreen provisions that require the guarantee to remain in effect until cancelled. Exelon’s estimated net exposure for obligations under commercial transactions covered by these guarantees is approximately $ 0.5 billion at December 31, 2015 , which represents the total amount Exelon could be required to fund based on December 31, 2015 market prices. (e) Nuclear insurance premiums—Represents the maximum amount that Generation would be required to pay for retrospective premiums in the event of nuclear disaster at any domestic site under the Secondary Financial Protection pool as required under the Price-Anderson Act as well as the current aggregate annual retrospective premium obligation that could be imposed by NEIL. See the Nuclear Insurance section within this note for additional details on Generation’s nuclear insurance premiums. Generation’s commercial commitments as of December 31, 2015 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2016 2017 2018 2019 2020 2021 Letters of credit (non-debt) (a) $ 1,503 $ 1,485 $ 5 $ — $ — $ 13 $ — Surety bonds 737 692 45 — — — — Energy marketing contract guarantees (b) 1,532 1,532 — — — — — Nuclear insurance premiums (c) 3,060 — — — — — 3,060 Total commercial commitments $ 6,832 $ 3,709 $ 50 $ — $ — $ 13 $ 3,060 ________________________ (a) Letters of credit (non-debt)—Non-debt letters of credit maintained to provide credit support for certain transactions as requested by third parties. (b) Energy marketing contract guarantees—Guarantees issued to ensure performance under energy commodity contracts. Amount includes approximately $ 1.5 billion of guarantees issued by Generation on behalf of its Constellation businesses to allow it the flexibility needed to conduct business with counterparties without having to post other forms of collateral. The majority of these guarantees contain evergreen provisions that require the guarantee to remain in effect until cancelled. Generation’s estimated net exposure for obligations under commercial transactions covered by these guarantees is approximately $ 0.3 billion at December 31, 2015 , which represents the total amount Generation could be required to fund based on December 31, 2015 market prices. (c) Nuclear insurance premiums — Represents the maximum amount that Generation would be required to pay for retrospective premiums in the event of nuclear disaster at any domestic site, including CENG sites, under the Secondary Financial Protection pool as required under the Price-Anderson Act as well as the current aggregate annual retrospective premium obligation that could be imposed by NEIL. See the Nuclear Insurance section within this note for additional details on Generation’s nuclear insurance premiums. ComEd’s commercial commitments as of December 31, 2015 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2016 2017 2018 2019 2020 2021 Letters of credit (non-debt) (a) $ 16 $ 16 $ — $ — $ — $ — $ — Surety bonds (b) 8 6 — 2 — — — Financing trust guarantees (c) 200 — — — — — 200 Total commercial commitments $ 224 $ 22 $ — $ 2 $ — $ — $ 200 _________________________ (a) Letters of credit (non-debt)—ComEd maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (c) Performance guarantees—Reflects full and unconditional guarantee of Trust Preferred Securities of ComEd Financing III which is a 100% owned finance subsidiary of ComEd. PECO’s commercial commitments as of December 31, 2015 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2016 2017 2018 2019 2020 2021 Letters of credit (non-debt) (a) $ 22 $ 22 $ — $ — $ — $ — $ — Surety bonds (b) 9 9 — — — — — Financing trust guarantees (c) 178 — — — — — 178 Total commercial commitments $ 209 $ 31 $ — $ — $ — $ — $ 178 ________________________ (a) Letters of credit (non-debt)—PECO maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (c) Performance guarantees—Reflects full and unconditional guarantee of Trust Preferred Securities of PECO Trust III and IV, which are 100% owned finance subsidiaries of PECO. BGE’s commercial commitments as of December 31, 2015 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2016 2017 2018 2019 2020 2021 Letters of credit (non-debt) (a) $ 2 $ 2 $ — $ — $ — $ — $ — Surety bonds (b) 10 10 — — — — — Financing trust guarantees (c) 250 — — — — — 250 Total commercial commitments $ 262 $ 12 $ — $ — $ — $ — $ 250 ________________________ (a) Letters of credit (non-debt)—BGE maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (c) Performance guarantee—Reflects full and unconditional guarantee of Trust Preferred Securities of BGE Capital Trust which is an unconsolidated VIE of BGE. Leases Minimum future operating lease payments, including lease payments for contracted generation, vehicles, real estate, computers, rail cars, operating equipment and office equipment, as of December 31, 2015 were: Exelon (a) Generation (a)(b) ComEd (c) PECO (c) BGE (c)(d) 2016 $ 133 $ 86 $ 14 $ 3 $ 12 2017 109 69 9 3 10 2018 86 57 5 2 9 2019 74 45 5 2 8 2020 70 44 3 2 7 Remaining years 702 655 1 — 19 Total minimum future lease payments $ 1,174 $ 956 $ 37 $ 12 $ 65 ______________________ (a) Excludes Generation’s contingent operating lease payments associated with contracted generation agreements. (b) The Generation column above includes minimum future lease payments associated with a 20 -year lease agreement for the Baltimore headquarters that became effective during the second quarter of 2015. Generation’s total commitments under the lease agreement are $ 4 million , $ 10 million , $ 11 million , $ 13 million , $ 14 million , and $ 271 million related to years 2016, 2017, 2018, 2019, 2020 and thereafter, respectively. (c) Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO and BGE have excluded these payments from the remaining years, as such amounts would not be meaningful. ComEd’s, PECO’s, and BGE’s annual obligation for these arrangements, included in each of the years 2016—2020, was $ 2 million , $ 3 million , and $ 1 million respectively. (d) Includes all future lease payments on a 99 year real estate lease that expires in 2106 . The following table presents the Registrants’ rental expense under operating leases for the years ended December 31, 2015, 2014 and 2013: For the Year Ended December 31, Exelon Generation (a) ComEd PECO BGE 2015 $ 922 $ 851 $ 12 $ 9 $ 32 2014 865 806 15 14 12 2013 806 744 15 21 11 __________________________ (a) Includes contingent operating lease payments associated with contracted generation agreements that are not included in the minimum future operating lease payments table above. Payments made under Generation’s contracted generation lease agreements totaled $ 798 million , $ 755 million and $ 694 million during 2015, 2014 and 2013, respectively. Excludes contract amortization associated with purchase accounting and contract acquisitions. For information regarding capital lease obligations, see Note 14 —Debt and Credit Agreements. Nuclear Insurance Generation is subject to liability, property damage and other risks associated with major incidents at any of its nuclear stations, including the CENG nuclear stations. Generation has mitigated its financial exposure to these risks through insurance and other industry risk-sharing provisions. The Price-Anderson Act was enacted to ensure the availability of funds for public liability claims arising from an incident at any of the U.S. licensed nuclear facilities and also to limit the liability of nuclear reactor owners for such claims from any single incident. As of December 31, 2015 , the current liability limit per incident is $13.5 billion and is subject to change to account for the effects of inflation and changes in the number of licensed reactors. An inflation adjustment must be made at least once every 5 years and the last inflation adjustment was made effective September 10, 2013. In accordance with the Price-Anderson Act, Generation maintains financial protection at levels equal to the amount of liability insurance available from private sources through the purchase of private nuclear energy liability insurance for public liability claims that could arise in the event of an incident. As of December 31, 2015 , the amount of nuclear energy liability insurance purchased is $ 375 million for each operating site. Additionally, the Price-Anderson Act requires a second layer of protection through the mandatory participation in a retrospective rating plan for power reactors (currently 103 reactors) resulting in an additional $ 13.1 billion in funds available for public liability claims. Participation in this secondary financial protection pool requires the operator of each reactor to fund its proportionate share of costs for any single incident that exceeds the primary layer of financial protection. Under the Price-Anderson Act, the maximum assessment in the event of an incident for each nuclear operator, per reactor, per incident (including a 5% surcharge), is $ 127.3 million , payable at no more than $ 19 million per reactor per incident per year. Exelon’s maximum liability per incident is approximately $ 2.7 billion , including CENG's related liability. In addition, the U.S. Congress could impose revenue-raising measures on the nuclear industry to pay public liability claims exceeding the $ 13.5 billion limit for a single incident. As part of the execution of the NOSA on April 1, 2014, Generation executed an Indemnity Agreement pursuant to which Generation agreed to indemnify EDF and its affiliates against third-party claims that may arise from any future nuclear incident (as defined in the Price-Anderson Act) in connection with the CENG nuclear plants or their operations. Exelon guarantees Generation’s obligations under this indemnity. See Note 5 - Investment in Constellation Energy Nuclear Group, LLC for additional information on Generation’s operations relating to CENG. Generation is required each year to report to the NRC the current levels and sources of property insurance that demonstrates Generation possesses sufficient financial resources to stabilize and decontaminate a reactor and reactor station site in the event of an accident. The property insurance maintained for each facility is currently provided through insurance policies purchased from NEIL, an industry mutual insurance company of which Generation is a member. NEIL may declare distributions to its members as a result of favorable operating experience. In recent years NEIL has made distributions to its members, but Generation cannot predict the level of future distributions or if they will continue at all. Generation's portion of the distribution declared by NEIL is estimated to be $20.7 million for 2015, and was $18.3 million for 2014 and $18.5 million for 2013. The distributions were recorded as a reduction to Operating and maintenance expense within Exelon and Generation’s Consolidated Statements of Operations and Comprehensive Income. Premiums paid to NEIL by its members are subject to assessment for adverse loss experience (the retrospective premium obligation). NEIL has never exercised this assessment since its formation in 1973, and while Generation cannot predict the level of future assessments, or if they will be imposed at all, as of December 31, 2015 , the current maximum aggregate annual retrospective premium obligation for Generation is approximately $365 million . NEIL requires its members to maintain an investment grade credit rating or to ensure collectability of their annual retrospective premium obligation by providing a financial guarantee, letter of credit, deposit premium, or some other means of assurance. NEIL provides “all risk” property damage, decontamination and premature decommissioning insurance for each station for losses resulting from damage to its nuclear plants, either due to accidents or acts of terrorism. If the decision is made to decommission the facility, a portion of the insurance proceeds will be allocated to a fund, which Generation is required by the NRC to maintain, to provide for decommissioning the facility. In the event of an insured loss, Generation is unable to predict the timing of the availability of insurance proceeds to Generation and the amount of such proceeds that would be available. In the event that one or more acts of terrorism cause accidental property damage within a twelve-month period from the first accidental property damage under one or more policies for all insured plants, the maximum recovery for all losses by all insureds will be an aggregate of $ 3.2 billion plus such additional amounts as the insurer may recover for all such losses from reinsurance, indemnity and any other source, applicable to such losses. For its insured losses, Generation is self-insured to the extent that losses are within the policy deductible or exceed the amount of insurance maintained. Uninsured losses and other expenses, to the extent not recoverable from insurers or the nuclear industry, could also be borne by Generation. Any such losses could have a material adverse effect on Exelon’s and Generation’s financial condition, results of operations and liquidity. Spent Nuclear Fuel Obligation Under the NWPA, the DOE is responsible for the development of a geologic repository for and the disposal of SNF and high-level radioactive waste. As required by the NWPA, Generation is a party to contracts with the DOE (Standard Contracts) to provide for disposal of SNF from Generation’s nuclear generating stations. In accordance with the NWPA and the Standard Contracts, Generation historically had paid the DOE one mill ( $0.001 ) per kWh of net nuclear generation for the cost of SNF disposal. On November 19, 2013, the D.C. Circuit Court ordered the DOE to submit to Congress a proposal to reduce the current SNF disposal fee to zero, unless and until there is a viable disposal program. On May 9, 2014, the DOE notified Generation that the SNF disposal fee remained in effect through May 15, 2014, after which time the fee was set to zero. As a result, for the year ended December 31, 2015, Generation did not incur any expense in SNF disposal fees. For the year ended December 31, 2014 and 2013, Generation incurred expense of $49 million and $136 million , respectively, in SNF disposal fees recorded in Purchased power and fuel expense within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income, including Exelon’s share of Salem and net of co-owner reimbursements (not including such fees incurred by CENG). Until such time as a new fee structure is in effect, Exelon and Generation will not accrue any further costs related to SNF disposal fees. This fee may be adjusted prospectively in order to ensure full cost recovery. The NWPA and the Standard Contracts required the DOE to begin taking possession of SNF generated by nuclear generating units by no later than January 31, 1998. The DOE, however, failed to meet that deadline and its performance has been, and is expected to be, delayed significantly. The 2010 Federal budget (which became effective October 1, 2009) eliminated almost all funding for the creation of the Yucca Mountain repository while the Obama administration devised a new strategy for long-term SNF management. A Blue Ribbon Commission (BRC) on America’s Nuclear Future, appointed by the U.S. Energy Secretary, released a report on January 26, 2012, detailing comprehensive recommendations for creating a safe, long-term solution for managing and disposing of the nation’s spent nuclear fuel and high-level radioactive waste. In early 2013, the DOE issued an updated “Strategy for the Management and Disposal of Used Nuclear Fuel and High-Level Radioactive Waste” in response to the BRC recommendations. This strategy included a consolidated interim storage facility that is planned to be operational in 2025. Generation uses the 2025 date as the assumed date for when the DOE will begin accepting SNF for purposes of determining nuclear decommissioning asset retirement obligations. In August 2004, Generation and the DOJ, in close consultation with the DOE, reached a settlement under which the government agreed to reimburse Generation, subject to certain damage limitations based on the extent of the government’s breach, for costs associated with storage of SNF at Generation’s nuclear stations pending the DOE’s fulfillment of its obligations. Settlement agreements pertaining to Calvert Cliffs and Ginna were executed during 2011, and Nine Mile Point during 2012, (the “DOE Settlement Agreements”), as amended in 2014 for Calvert Cliffs and Nine Mile Point, under which the government has agreed to reimburse the costs associated with SNF storage expended or to be expended through 2016 as a result of the DOE delays . The DOE Settlement Agreement is expected to be amended for Ginna in a similar manner as needed. Generation, including CENG, submits annual reimbursement requests to the DOE for costs associated with the storage of SNF. In all cases, reimbursement requests are made only after costs are incurred and only for costs resulting from DOE delays in accepting the SNF. Under the settlement agreement, Generation has received cumulative cash reimbursements for costs incurred as follows: Total Net (a) Cumulative cash reimbursements (b) $ 945 $ 804 _____________________________ (a) Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Creek. (b) Includes $53 million and $49 million , respectively, for amounts received since April 1, 2014, for costs incurred under the CENG DOE Settlement Agreements prior to the consolidation of CENG. As of December 31, 2015, and 2014, the amount of SNF storage costs for which reimbursement has been or will be requested from the DOE under the DOE settlement agreements is as follows: December 31, 2015 December 31, 2014 DOE receivable - current (a) $ 76 $ 82 DOE receivable - noncurrent (b) 14 7 Amounts owed to co-owners (a)(c) (5 ) (5 ) _____________________________ (a) Recorded in Accounts receivable, other. (b) Recorded in Deferred debits and other assets, other (c) Non-CENG amounts owed to co-owners are recorded in Accounts receivable, other. CENG amounts owed to co-owners are recorded in Accounts payable. Represents amounts owed to the co-owners of Peach Bottom, Quad Cities, and Nine Mile Point Unit 2 generating facilities. The Standard Contracts with the DOE also required the payment to the DOE of a one-time fee applicable to nuclear generation through April 6, 1983. The fee related to the former PECO units has been paid. Pursuant to the Standard Contracts, ComEd previously elected to defer payment of the one-time fee of $277 million for its units (which are now part of Generation), with interest to the date of payment, until just prior to the first delivery of SNF to the DOE. As of December 31, 2015 , the unfunded SNF liability for the one-time fee with interest was $1,021 million . Interest accrues at the 13 -week Treasury Rate. The 13 -week Treasury Rate in effect, for calculation of the interest accrual at December 31, 2015 , was 0.112% . The liabilities for SNF disposal costs, including the one-time fee, were transferred to Generation as part of Exelon’s 2001 corporate restructuring. The outstanding one-time fee obligations for the Nine Mile Point, Ginna, Oyster Creek and TMI units remain with the former owners. The Clinton and Calvert Cliffs units have no outstanding obligation. See Note 12 — Fair Value of Financial Assets and Liabilities for additional information. Environmental Matters General. The Registrants’ operations have in the past, and may in the future, require substantial expenditures in order to comply with environmental laws. Additionally, under Federal and state environmental laws, the Registrants are generally liable for the costs of remediating environmental contamination of property now or formerly owned by them and of property contaminated by hazardous substances generated by them. The Registrants own or lease a number of real estate parcels, including parcels on which their operations or the operations of others may have resulted in contamination by substances that are considered hazardous under environmental laws. In addition, the Registrants are currently involved in a number of proceedings relating to sites where hazardous substances have been deposited and may be subject to additional proceedings in the future. ComEd, PECO and BGE have identified sites where former MGP activities have or may have resulted in actual site contamination. For almost all of these sites, there are additional PRPs that may share responsibility for the ultimate remediation of each location. • ComEd has identified 42 sites, 17 of which have been remediated and approved by the Illinois EPA or the U.S. EPA and 25 that are currently under some degree of active study and/or remediation. ComEd expects the majority of the remediation at these sites to continue through at least 2020. • PECO has identified 26 sites, 16 of which have been remediated in accordance with applicable PA DEP regulatory requirements. The remaining 10 sites are currently under some degree of active study and/or remediation. PECO expects the majority of the remediation at these sites to continue through at least 2021. • BGE has identified 13 former gas manufacturing or purification sites that it currently owns or owned at one time through a predecessor’s acquisition. Two gas manufacturing sites require some level of remediation and ongoing monitoring under the direction of the MDE. The required costs at these Two sites are not considered material. An investigation of an additional gas purification site was completed during the first quarter of 2015 at the direction of the MDE. For more information, see the discussion of the Riverside site below. ComEd, pursuant to an ICC order, and PECO, pursuant to settlements of natural gas distribution rate cases with the PAPUC, are currently recovering environmental remediation costs of former MGP facility sites through customer rates. See Note 3 — Regulatory Matters for additional information regarding the associated regulatory assets. BGE is authorized to recover, and is currently recovering, environmental costs for the remediation of the former MGP facility sites from customers; however, while BGE does not have a rider for MGP clean-up costs, BGE has historically received recovery of actual clean-up costs in distribution rates. ComEd, PECO and BGE have recorded regulatory assets for the recovery of these costs. As of December 31, 2015 and 2014, the Registrants had accrued the following undiscounted amounts for environmental liabilities in Other current liabilities and Other deferred credits and other liabilities within their respective Consolidated Balance Sheets: December 31, 2015 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation (a) Exelon $ 369 $ 301 Generation 63 — ComEd 266 264 PECO 37 35 BGE (a) 3 2 December 31, 2014 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 347 $ 277 Generation 63 — ComEd 238 235 PECO 45 42 BGE 1 — _____________________________ (a) For BGE, includes reserve for Riverside, a gas purification site. See discussion below for additional information. The historical nature of the MGP sites and the fact that many of the sites have been buried and built over, impacts the ability to determine a precise estimate of the ultimate costs prior to initial sampling and determination of the exact scope and method of remedial activity. Management determines its best estimate of remediation costs using all available information at the time of each study, including probabilistic and deterministic modeling for ComEd and PECO, and the remediation standards currently required by the applicable state environmental agency. Prior to completion of any significant clean up, each site remediation plan is approved by the appropriate state environmental agency. During the third quarter of 2015, ComEd and PECO completed an annual study of their future estimated MGP remediation requirements. For ComEd, the results of the study resulted in a $50 million increase to ComEd's environmental liabilities and related regulatory assets. The increase at ComEd was primarily driven by refined assumptions and scopes based on further experience and analysis, including one site where a new option is being considered for a facility under which contamination exists and certain sites where another PRP leads the remediation efforts and ComEd shares responsibility. For PECO, the results of the study resulted in a $1 million decrease to PECO's environmental liabilities and related regulatory assets. The Registrants cannot reasonably estimate whether they will incur other significant liabilities for additional investigation and remediation costs at these or additional sites identified by the Registrants, environmental agencies or others, or whether such costs will be recoverable from third parties, including customers. Water Quality Groundwater Contamination. In October 2007, a subsidiary of Constellation entered into a consent decree with the MDE relating to groundwater contamination at a third-party facility that was licensed to accept fly ash, a byproduct generated by coal-fired plants. The consent decree required the payment of a $ 1 million penalty, remediation of groundwater contamination resulting from the ash placement operations at the site, replacement of drinking water supplies in the vicinity of the site, and monitoring of groundwater conditions. As of December 31, 2015 and 2014, Generation’s remaining groundwater contamination reserve was $ 12 million and $ 13 million respectively. Air Quality Notices and Finding of Violations and Midwest Generation Bankruptcy. In December 1999, ComEd sold several generating stations to Midwest Generation, LLC (Midwest Generation), a subsidiary of Edison Mission Energy (EME). Under the terms of the sale agreement, Midwest Generation and EME assumed responsibility for environmental liabilities associated with the ownership, occupancy, use and operation of the stations, including responsibility for compliance by the stations with environmental laws before their purchase by Midwest Generation. Midwest Generation and EME additionally agreed to indemnify and hold ComEd and its affiliates harmless from claims, fines, penalties, liabilities and expenses arising from third party claims against ComEd resulting from or arising out of the environmental liabilities assumed by Midwest Generation and EME under the terms of the agreement governing the sale. In connection wi

Supplemental Financial Informat

Supplemental Financial Information (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Supplemental Financial Information [Abstract]
Supplemental Financial Information (Exelon, Generation, ComEd, PECO and BGE)	24 . Supplemental Financial Information (Exelon, Generation, ComEd, PECO and BGE) Supplemental Statement of Operations Information The following tables provide additional information about the Registrants’ Consolidated Statements of Operations and Comprehensive Income for the years ended December 31, 2015 , 2014 and 2013 . For the year ended December 31, 2015 Exelon Generation ComEd PECO BGE Taxes other than income Utility (a) $ 474 $ 105 $ 236 $ 133 $ 85 Property 407 250 27 11 119 Payroll 201 118 28 14 16 Other 118 16 5 2 4 Total taxes other than income $ 1,200 $ 489 296 $ 160 $ 224 For the year ended December 31, 2014 Exelon Generation ComEd PECO BGE Taxes other than income Utility (a) $ 456 $ 89 $ 238 $ 128 $ 86 Property 396 240 25 15 114 Payroll 200 118 28 14 18 Other 102 18 2 2 3 Total taxes other than income $ 1,154 $ 465 $ 293 $ 159 $ 221 For the year ended December 31, 2013 Exelon Generation ComEd PECO BGE Taxes other than income Utility (a) $ 449 $ 79 $ 241 $ 129 $ 82 Property 302 205 24 14 112 Payroll 159 89 27 13 15 Other 185 16 7 2 4 Total taxes other than income $ 1,095 $ 389 $ 299 $ 158 $ 213 _____________________ (a) Generation’s utility tax represents gross receipts tax related to its retail operations and ComEd’s, PECO’s and BGE’s utility taxes represent municipal and state utility taxes and gross receipts taxes related to their operating revenues. The offsetting collection of utility taxes from customers is recorded in revenues on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. For the year ended December 31, 2015 Exelon Generation ComEd PECO BGE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) — Regulatory agreement units $ 232 $ 232 $ — $ — $ — Non-regulatory agreement units 156 156 — — — Net unrealized losses on decommissioning trust funds— Regulatory agreement units (282 ) (282 ) — — — Non-regulatory agreement units (197 ) (197 ) — — — Net unrealized gains on pledged assets— Zion Station decommissioning 7 7 — — — Regulatory offset to decommissioning trust fund-related activities (b) 21 21 — — — Total decommissioning-related activities (63 ) (63 ) — — — Investment income (loss) 8 3 — (2 ) 4 (c) Long-term lease income 15 — — — — Interest income related to uncertain income tax positions 1 1 — — — AFUDC—Equity 24 — 5 5 14 Terminated interest rate swaps (d) (26 ) — — — — PHI merger related debt exchange (e) (22 ) — — — — Other 17 (1 ) 16 2 — Other, net $ (46 ) $ (60 ) $ 21 $ 5 $ 18 For the year ended December 31, 2014 Exelon Generation ComEd PECO BGE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) — Regulatory agreement units $ 216 $ 216 $ — $ — $ — Non-regulatory agreement units 159 159 — — — Net unrealized gains on decommissioning trust funds— Regulatory agreement units 180 180 — — — Non-regulatory agreement units 134 134 — — — Net unrealized gains on pledged assets— Zion Station decommissioning 29 29 — — — Regulatory offset to decommissioning trust fund-related activities (b) (358 ) (358 ) — Total decommissioning-related activities 360 360 — — — Investment income 1 1 — (1 ) 7 (c) Long-term lease income 24 — — — — Interest income related to uncertain income tax positions 40 54 — — — AFUDC—Equity 21 — 3 6 12 Other 9 (9 ) 14 2 (1 ) Other, net $ 455 $ 406 $ 17 $ 7 $ 18 For the year ended December 31, 2013 Exelon Generation ComEd PECO BGE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) — Regulatory agreement units $ 256 $ 256 $ — $ — $ — Non-regulatory agreement units 77 77 — — — Net unrealized gains on decommissioning trust funds— Regulatory agreement units 406 406 — — — Non-regulatory agreement units 146 146 — — — Net unrealized gains on pledged assets— Zion Station decommissioning 7 7 — — — Regulatory offset to decommissioning trust fund-related activities (b) (546 ) (546 ) — — Total decommissioning-related activities 346 346 — — — Investment income 8 (1 ) — (1 ) 9 (c) Long-term lease income 28 — — — — Interest income related to uncertain income tax positions 24 4 — — — AFUDC—Equity 22 — 11 4 7 Other 32 6 15 3 1 Other, net $ 460 $ 355 $ 26 $ 6 $ 17 _________________________ (a) Includes investment income and realized gains and losses on sales of investments within the nuclear decommissioning trust funds. (b) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 16 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (c) Relates to the cash return on BGE’s rate stabilization deferral. See Note 3 — Regulatory Matters for additional information regarding the rate stabilization deferral. (d) In January 2015, in connection with Generation's $750 million issuance of five-year Senior Unsecured Notes, Exelon terminated certain floating-to-fixed interest rate swaps. As the original forecasted transactions were a series of future interest payments over a ten year period, a portion of the anticipated interest payments are probable not to occur. As a result, $26 million of anticipated payments were reclassified from Accumulated OCI to Other, net in Exelon's Consolidated Statement of Operations and Comprehensive Income. (e) See Note 14 — Debt and Credit Agreements and 4 — Mergers, Acquisitions, and Dispositions for additional information on the PHI merger related debt exchange. Supplemental Cash Flow Information The following tables provide additional information regarding the Registrants’ Consolidated Statements of Cash Flows for the years ended December 31, 2015 , 2014 and 2013 . For the year ended December 31, 2015 Exelon Generation ComEd PECO BGE Depreciation, amortization, accretion and depletion Property, plant and equipment $ 2,227 $ 1,007 $ 635 $ 240 $ 289 Regulatory assets 170 — 72 20 77 Amortization of intangible assets, net 54 47 — — — Amortization of energy contract assets and liabilities (a) 22 22 — — — Nuclear fuel (b) 1,116 1,116 — — — ARO accretion (c) 398 397 — — — Total depreciation, amortization, accretion and depletion $ 3,987 $ 2,589 $ 707 $ 260 $ 366 For the year ended December 31, 2014 Exelon Generation ComEd PECO BGE Depreciation, amortization, accretion and depletion Property, plant and equipment $ 2,080 $ 922 $ 588 $ 227 $ 288 Regulatory assets 191 — 99 9 83 Amortization of intangible assets, net 44 44 — — — Amortization of energy contract assets and liabilities (a) 135 135 — — — Nuclear fuel (b) 1,073 1,073 — — — ARO accretion (c) 345 345 — — — Total depreciation, amortization, accretion and depletion $ 3,868 $ 2,519 $ 687 $ 236 $ 371 For the year ended December 31, 2013 Exelon Generation ComEd PECO BGE Depreciation, amortization, accretion and depletion Property, plant and equipment $ 1,893 $ 813 $ 545 $ 219 $ 264 Regulatory assets 212 — 119 9 84 Amortization of intangible assets, net 48 43 5 — — Amortization of energy contract assets and liabilities (a) 430 507 — — — Nuclear fuel (b) 921 921 — — — ARO accretion (c) 275 275 — — — Total depreciation, amortization and accretion $ 3,779 $ 2,559 $ 669 $ 228 $ 348 ________________________ (a) Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (b) Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (c) Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. For the year ended December 31, 2015 Exelon Generation ComEd PECO BGE Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 930 $ 348 $ 308 $ 94 $ 120 Income taxes (net of refunds) 342 476 (265 ) 64 73 Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 637 $ 269 $ 206 $ 39 $ 65 Loss from equity method investments 7 8 — — — Provision for uncollectible accounts 120 22 53 30 15 Provision for excess and obsolete inventory 10 9 1 — — Stock-based compensation costs 97 — — — — Other decommissioning-related activity (a) (82 ) (82 ) — — — Energy-related options (b) 21 21 — — — Amortization of regulatory asset related to debt costs 7 — 5 2 — Amortization of rate stabilization deferral 73 — — — 73 Amortization of debt fair value adjustment (17 ) (17 ) — — — Amortization of debt costs 58 15 4 2 2 Discrete impacts from EIMA (c) 144 — 144 — — Lower of cost or market inventory adjustment 23 23 — — — Other 11 — 3 (3 ) (18 ) Total other non-cash operating activities $ 1,109 $ 268 $ 416 $ 70 $ 137 Non-cash investing and financing activities: Change in PPE related to ARO update $ 885 $ 885 $ — $ — $ — Change in capital expenditures not paid 96 82 34 (13 ) (9 ) Non-cash financing of capital projects 77 77 — — — Nuclear fuel procurement (d) 57 57 — — — Indemnification of like-kind exchange position (e) — — 7 — — Long-term software licensing agreement (f) 95 — — — — ____________________________ (a) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 16 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate tariff. See Note 3 — Regulatory Matters for more information. (d) Relates to the nuclear fuel procurement contract for the purchase of fixed quantities of converted uranium, which was delivered to Generation in 2015. Generation is required to make payments starting September 28, 2018, with the final payment being due no later than September 30, 2020. (e) See Note 15 — Income Taxes for discussion of the like-kind exchange tax position. (f) Relates to a long-term software license agreement entered into on May 30, 2015. Exelon is required to make payments starting August of 2015 through May of 2024. See Note 14 — Debt and Credit Agreements for additional information. For the year ended December 31, 2014 Exelon Generation ComEd PECO BGE Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 940 $ 322 $ 292 $ 94 $ 111 Income taxes (net of refunds) 314 227 (6 ) 85 (21 ) Pension and non-pension postretirement benefit costs $ 560 $ 249 $ 162 $ 36 $ 64 Loss from equity method investments 22 20 — — — Provision for uncollectible accounts 156 14 26 52 64 Provision for excess and obsolete inventory 5 5 — — — Stock-based compensation costs 91 — — — — Other decommissioning-related activity (a) (132 ) (132 ) — — — Energy-related options (b) 122 122 — — — Amortization of regulatory asset related to debt costs 11 — 8 3 — Amortization of rate stabilization deferral 65 — — — 65 Amortization of debt fair value adjustment (23 ) (23 ) — — — Merger-related commitments 44 44 — — — Amortization of debt costs 53 12 4 2 2 Discrete impacts from EIMA (c) 53 — 53 — — Lower of cost or market inventory adjustment 29 29 — — — Other (2 ) 6 2 (1 ) (15 ) Total other non-cash operating activities $ 1,054 $ 346 $ 255 $ 92 $ 180 Non-cash investing and financing activities: Change in PPE related to ARO update $ 72 $ 72 $ — $ — $ — Change in capital expenditures not paid 220 (61 ) (d) 78 — 25 Fair value of net assets recorded upon CENG consolidation (e) 3,400 3,400 — — — Issuance of equity units (f) 131 — — — — Nuclear fuel procurement (g) 70 70 — — — Indemnification of like-kind exchange position (h) — — 5 — — ______________________ (a) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 16 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate tariff. See Note 3 — Regulatory Matters for more information. (d) Includes $170 million of changes in capital expenditures not paid between December 31, 2014 and 2013 related to Antelope Valley. (e) See Note 5 — Investment in Constellation Energy Nuclear Group, LLC for additional information. (f) Relates to the present value of the contract payments for the equity units issued by Exelon. See Note 20 — Stock-Based Compensation Plans for additional information. (g) Relates to the nuclear fuel procurement contracts for the purchase of fixed quantities of uranium, which was delivered to Generation in 2014. Generation is required to make payments starting June 30, 2016, with the final payment being due no later than June 30, 2018. (h) See Note 15 — Income Taxes for discussion of the like-kind exchange tax position. For the year ended December 31, 2013 Exelon Generation ComEd PECO BGE Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 866 $ 291 $ 283 $ 95 $ 130 Income taxes (net of refunds) 112 (18 ) 33 70 42 Pension and non-pension postretirement benefit costs $ 825 $ 345 $ 308 $ 43 $ 56 Gain from equity method investments (10 ) (10 ) — — — Provision for uncollectible accounts 101 10 (15 ) 61 44 Provision for excess and obsolete inventory 9 9 — — — Stock-based compensation costs 120 — — — — Other decommissioning-related activity (a) (169 ) (169 ) — — — Energy-related options (b) 104 104 — — — Amortization of regulatory asset related to debt costs 12 — 9 3 — Amortization of rate stabilization deferral 66 — — — 66 Amortization of debt fair value adjustment (34 ) (34 ) — — — Discrete impacts from EIMA (c) (271 ) — (271 ) — — Amortization of debt costs 18 10 1 2 2 Other (53 ) 5 (4 ) (1 ) (15 ) Total other non-cash operating activities $ 718 $ 270 $ 28 $ 108 $ 153 Non-cash investing and financing activities: Change in PPE related to ARO update $ (128 ) $ (128 ) $ — $ — $ 4 Change in capital expenditures not paid (38 ) (107 ) (d) (8 ) 13 (48 ) Consolidated VIE dividend to noncontrolling interest 63 63 — — — Indemnification of like-kind exchange position (e) — — 176 — — _________________________ (a) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 16 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through pre-established performance-based formula rate tariff. See Note 3 — Regulatory Matters . (d) Includes $55 million of changes in capital expenditures not paid between December 31, 2013 and 2012 related to Antelope Valley. (e) See Note 15 — Income Taxes for discussion of the like-kind exchanged tax position. DOE Smart Grid Investment Grant (Exelon, PECO and BGE). For the year ended December 31, 2014 , PECO has included in the capital expenditures line item under investing activities of the cash flow statement capital expenditures of $ 2 million and reimbursements of $ 5 million related to PECO’s DOE SGIG programs. For the year ended December 31, 2015 , PECO had no capital expenditures or reimbursements, as the DOE SGIG program was completed during 2014. For the year ended December 31, 2013 , Exelon, PECO and BGE have included in the capital expenditures line item under investing activities of the cash flow statement capital expenditures of $ 74 million , $ 27 million and $ 47 million , and reimbursements of $ 95 million , $ 37 million and $ 58 million , related to PECO’s and BGE’s DOE SGIG programs. See Note 3 — Regulatory Matters for additional information regarding the DOE SGIG. Supplemental Balance Sheet Information The following tables provide additional information about assets and liabilities of the Registrants at December 31, 2015 and 2014 . December 31, 2015 Exelon Generation ComEd PECO BGE Investments Equity method investments: Financing trusts (a) $ 22 $ — $ 6 $ 8 $ 8 Bloom 63 63 — — — Net Power 23 23 — — — Other equity method investments 4 3 — — — Total equity method investments 112 89 6 8 8 Other investments: Net investment in leases (b) 358 6 — — — Employee benefit trusts and investments (c) 85 31 — 20 4 Other cost method investments 55 55 — — — Other available for sale investments 29 29 — — — Total investments $ 639 $ 210 $ 6 $ 28 $ 12 December 31, 2014 Exelon Generation ComEd PECO BGE Investments Equity method investments: Financing trusts (a) $ 22 $ — $ 6 $ 8 $ 8 Bloom 13 13 — — — Net Power 9 9 — — — Sunnyside 5 5 — — — Other equity method investments 1 1 — — — Total equity method investments 50 28 6 8 8 Other investments: Net investment in leases (b) 367 7 — — — Employee benefit trusts and investments (c) 85 27 — 23 4 Other cost method investments 37 37 — — — Other available for sale investments 5 5 — — — Total investments $ 544 $ 104 $ 6 $ 31 $ 12 _________________________ (a) Includes investments in affiliated financing trusts, which were not consolidated within the financial statements of Exelon and are shown as investments on the Consolidated Balance Sheets. See Note 1 — Significant Accounting Policies for additional information. (b) Represents direct financing lease investments. See Note 8 — Impairment of Long-Lived Assets for additional information. (c) The Registrants’ investments in these marketable securities are recorded at fair market value. The following tables provide additional information about liabilities of the Registrants at December 31, 2015 and 2014 . December 31, 2015 Exelon Generation ComEd PECO BGE Accrued expenses Compensation-related accruals (a) $ 1,014 $ 547 $ 183 $ 66 $ 57 Taxes accrued 293 186 63 4 23 Interest accrued 915 77 443 35 27 Severance accrued 21 11 3 — 1 Other accrued expenses 133 114 14 4 2 Total accrued expenses $ 2,376 $ 935 $ 706 $ 109 $ 110 December 31, 2014 Exelon Generation ComEd PECO BGE Accrued expenses Compensation-related accruals (a) $ 832 $ 447 $ 153 $ 50 $ 58 Taxes accrued 305 248 59 3 42 Interest accrued 240 66 102 33 29 Severance accrued 49 33 2 1 2 Other accrued expenses 113 (b) 92 (b) 15 4 — Total accrued expenses $ 1,539 $ 886 $ 331 $ 91 $ 131 _______________________ (a) Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits. (b) Includes $19 million for amounts accrued related to Antelope Valley as of December 31, 2014 .

Segment Information (Exelon, Ge

Segment Information (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
Segment Information (Exelon, Generation, ComEd, PECO and BGE)	Segment Information (Exelon, Generation, ComEd, PECO and BGE) Operating segments for each of the Registrants are determined based on information used by the chief operating decision maker(s) (CODM) in deciding how to evaluate performance and allocate resources at each of the Registrants. Exelon has nine reportable segments, which include ComEd, PECO, BGE and Generation’s six power marketing reportable segments, consisting of the Mid-Atlantic, Midwest, New England, New York, ERCOT and all other power regions referred to collectively as “Other Power Regions”, which includes activities in the South, West and Canada. ComEd, PECO and BGE each represent a single reportable segment, and as such, no separate segment information is provided for these Registrants. Exelon, ComEd, PECO and BGE's CODMs evaluate the performance of and allocate resources to ComEd, PECO and BGE based on net income and return on equity. The basis for Generation's reportable segments is the integrated management of its electricity business that is located in different geographic regions, and largely representative of the footprints of ISO/RTO and/or NERC regions, which utilize multiple supply sources to provide electricity through various distribution channels (wholesale and retail). Generation's hedging strategies and risk metrics are also aligned to these same geographic regions. Descriptions of each of Generation’s six reportable segments are as follows: • Mid-Atlantic represents operations in the eastern half of PJM, which includes New Jersey, Maryland, Virginia, West Virginia, Delaware, the District of Columbia and parts of Pennsylvania and North Carolina. • Midwest represents operations in the western half of PJM, which includes portions of Illinois, Pennsylvania, Indiana, Ohio, Michigan, Kentucky and Tennessee, and the United States footprint of MISO, excluding MISO’s Southern Region, which covers all or most of North Dakota, South Dakota, Nebraska, Minnesota, Iowa, Wisconsin, the remaining parts of Illinois, Indiana, Michigan and Ohio not covered by PJM, and parts of Montana, Missouri and Kentucky. • New England represents the operations within ISO-NE covering the states of Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont. • New York represents operations within ISO-NY, which covers the state of New York in its entirety. • ERCOT represents operations within Electric Reliability Council of Texas, covering most of the state of Texas. • Other Power Regions : • South represents operations in the FRCC, MISO’s Southern Region, and the remaining portions of the SERC not included within MISO or PJM, which includes all or most of Florida, Arkansas, Louisiana, Mississippi, Alabama, Georgia, Tennessee, North Carolina, South Carolina and parts of Missouri, Kentucky and Texas. Generation’s South region also includes operations in the SPP, covering Kansas, Oklahoma, most of Nebraska and parts of New Mexico, Texas, Louisiana, Missouri, Mississippi and Arkansas. • West represents operations in the WECC, which includes California ISO, and covers the states of California, Oregon, Washington, Arizona, Nevada, Utah, Idaho, Colorado, and parts of New Mexico, Wyoming and South Dakota. • Canada represents operations across the entire country of Canada and includes AESO, OIESO and the Canadian portion of MISO. The CODMs for Exelon and Generation evaluate the performance of Generation’s power marketing activities and allocate resources based on revenue net of purchased power and fuel expense (RNF). Generation believes that RNF is a useful measurement of operational performance. RNF is not a presentation defined under GAAP and may not be comparable to other companies’ presentations or deemed more useful than the GAAP information provided elsewhere in this report. Generation’s operating revenues include all sales to third parties and affiliated sales to ComEd, PECO, and BGE. Purchased power costs include all costs associated with the procurement and supply of electricity including capacity, energy and ancillary services. Fuel expense includes the fuel costs for Generation’s owned generation and fuel costs associated with tolling agreements. The results of Generation's other business activities are not regularly reviewed by the CODM and are therefore not classified as operating segments or included in the regional reportable segment amounts. These activities include natural gas, as well as other miscellaneous business activities that are not significant to Generation's overall operating revenues or results of operations. Further, Generation’s unrealized mark-to-market gains and losses on economic hedging activities and its amortization of certain intangible assets and liabilities relating to commodity contracts recorded at fair value from mergers and acquisitions are also not included in the regional reportable segment amounts. Exelon and Generation do not use a measure of total assets in making decisions regarding allocating resources to or assessing the performance of these reportable segments. An analysis and reconciliation of the Registrants’ reportable segment information to the respective information in the consolidated financial statements for the years ended December 31, 2015 , 2014 , and 2013 is as follows: Generation (a) ComEd PECO BGE Other (b) Intersegment Eliminations Exelon Operating revenues (c) : 2015 Competitive businesses electric revenues $ 15,944 $ — $ — $ — $ — $ (744 ) $ 15,200 Competitive businesses natural gas revenues 2,433 — — — — — 2,433 Competitive businesses other revenues 758 — — — — (1 ) 757 Rate-regulated electric revenues — 4,905 2,486 2,490 — (5 ) 9,876 Rate-regulated natural gas revenues — — 546 645 — (15 ) 1,176 Shared service and other revenues — — — — 1,372 (1,367 ) 5 2014 Competitive businesses electric revenues $ 14,533 $ — $ — $ — $ — $ (760 ) $ 13,773 Generation (a) ComEd PECO BGE Other (b) Intersegment Eliminations Exelon Competitive businesses natural gas revenues 2,705 — — — — (1 ) 2,704 Competitive businesses other revenues 155 — — — — (1 ) 154 Rate-regulated electric revenues — 4,564 2,448 2,460 — (5 ) 9,467 Rate-regulated natural gas revenues — — 646 705 — (26 ) 1,325 Shared service and other revenues — — — — 1,285 (1,279 ) 6 2013 Competitive businesses electric revenues $ 13,862 $ — $ — $ — $ — $ (1,366 ) $ 12,496 Competitive businesses natural gas revenues 1,721 — — — — — 1,721 Competitive businesses other revenues 47 — — — — (1 ) 46 Rate-regulated electric revenues — 4,464 2,500 2,405 — (4 ) 9,365 Rate-regulated natural gas revenues — — 600 660 — (14 ) 1,246 Shared service and other revenues — — — — 1,241 (1,227 ) 14 Intersegment revenues (d) : 2015 $ 745 $ 4 $ 2 $ 14 $ 1,367 $ (2,127 ) $ 5 2014 762 4 2 25 1,280 (2,067 ) 6 2013 1,367 3 1 13 1,237 (2,607 ) 14 Depreciation and amortization 2015 $ 1,054 $ 707 $ 260 $ 366 $ 63 $ — $ 2,450 2014 967 687 236 371 53 — 2,314 2013 856 669 228 348 52 — 2,153 Operating expenses (c) : 2015 $ 16,872 $ 3,889 $ 2,404 $ 2,578 $ 1,444 $ (2,131 ) $ 25,056 2014 16,923 3,586 2,522 2,726 1,353 (2,071 ) 25,039 2013 13,976 3,510 2,434 2,616 1,324 (2,618 ) 21,242 Equity in earnings (losses) of unconsolidated affiliates 2015 $ (8 ) $ — $ — $ — $ 1 $ — $ (7 ) 2014 (20 ) — — — — — (20 ) 2013 10 — — — — — 10 Interest expense, net: 2015 $ 365 $ 332 $ 114 $ 99 $ 123 $ — $ 1,033 2014 356 321 113 106 169 — 1,065 2013 357 579 115 122 183 — 1,356 Income (loss) before income taxes: 2015 $ 1,850 $ 706 $ 521 $ 477 $ (219 ) $ (5 ) $ 3,330 2014 1,226 676 466 351 (227 ) (6 ) 2,486 2013 1,675 401 557 344 (191 ) (13 ) 2,773 Income taxes: 2015 $ 502 $ 280 $ 143 $ 189 $ (41 ) $ — $ 1,073 Generation (a) ComEd PECO BGE Other (b) Intersegment Eliminations Exelon 2014 207 268 114 140 (63 ) — 666 2013 615 152 162 134 (20 ) 1 1,044 Net income (loss): 2015 $ 1,340 $ 426 $ 378 $ 288 $ (177 ) $ (5 ) $ 2,250 2014 1,019 408 352 211 (164 ) (6 ) 1,820 2013 1,060 249 395 210 (171 ) (14 ) 1,729 Capital expenditures: 2015 $ 3,841 $ 2,398 $ 601 $ 719 $ 65 $ — 7,624 2014 3,012 1,689 661 620 95 — 6,077 2013 2,752 1,433 537 587 86 — 5,395 Total assets: 2015 $ 46,529 $ 26,532 $ 10,367 $ 8,295 $ 15,389 $ (11,728 ) $ 95,384 2014 44,951 25,358 9,860 8,056 9,711 (11,520 ) 86,416 __________________________ (a) Generation includes the six power marketing reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. For the year ended December 31, 2015 , intersegment revenues for Generation include revenue from sales to PECO of $ 224 million and sales to BGE of $ 502 million in the Mid-Atlantic region, and sales to ComEd of $ 18 million in the Midwest region, which eliminate upon consolidation. For the year ended December 31, 2014 , intersegment revenues for Generation include revenue from sales to PECO of $ 198 million and sales to BGE of $ 387 million in the Mid-Atlantic region, and sales to ComEd of $ 176 million in the Midwest region, which eliminate upon consolidation. For the year ended December 31, 2013 , intersegment revenues for Generation include revenue from sales to PECO of $ 405 million and sales to BGE of $ 455 million in the Mid-Atlantic region, and sales to ComEd of $ 506 million in the Midwest region, net of $ 7 million related to the unrealized mark-to-market losses related to the ComEd swap, which eliminate upon consolidation. (b) Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities. (c) For the years ended December 31, 2015 , 2014 and 2013 , utility taxes of $105 million , $89 million and $79 million , respectively, are included in revenues and expenses for Generation. For the years ended December 31, 2015 , 2014 and 2013 , utility taxes of $236 million , $238 million and $241 million , respectively, are included in revenues and expenses for ComEd. For the years ended December 31, 2015 , 2014 and 2013 , utility taxes of $133 million , $128 million and $129 million , respectively, are included in revenues and expenses for PECO. For the years ended December 31, 2015 , 2014 and 2013 , utility taxes of $85 million , $86 million and $82 million are included in revenues and expenses for BGE, respectively. (d) Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations and Comprehensive Income. Generation total revenues: 2015 2014 2013 Revenues from external customers (b) Intersegment revenues Total revenues Revenues from external customers (b)(d) Intersegment revenues (d) Total revenues Revenues from external customers (b)(d) Intersegment revenues (d) Total revenues Mid-Atlantic (a) $ 5,974 $ (74 ) $ 5,900 $ 5,414 $ (155 ) $ 5,259 $ 5,261 $ (57 ) $ 5,204 Midwest 4,712 (2 ) 4,710 4,488 (13 ) 4,475 4,298 (28 ) 4,270 New England 2,217 (5 ) 2,212 1,468 (46 ) 1,422 1,279 (42 ) 1,237 New York 996 (11 ) 985 846 (3 ) 843 717 (3 ) 714 ERCOT 863 (6 ) 857 938 (3 ) 935 1,223 (7 ) 1,216 Other Power Regions 1,182 (80 ) 1,102 1,379 (70 ) 1,309 1,084 (116 ) 968 Total Revenues for Reportable Segments $ 15,944 $ (178 ) $ 15,766 $ 14,533 $ (290 ) $ 14,243 $ 13,862 $ (253 ) $ 13,609 Other (c) 3,191 178 3,369 2,860 290 3,150 1,768 253 2,021 Total Generation Consolidated Operating Revenues $ 19,135 $ — $ 19,135 $ 17,393 $ — $ 17,393 $ 15,630 $ — $ 15,630 _______________________ (a) On April 1, 2014, Generation assumed operational control of CENG's nuclear fleet. As a result, beginning on April 1, 2014, CENG's revenues are included on a fully consolidated basis. (b) Includes all wholesale and retail electric sales to third parties and affiliated sales to ComEd, PECO and BGE. (c) Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $7 million increase to revenues, a $ 289 million decrease to revenues, and a $ 767 million decrease to revenues for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2015 , 2014 , and 2013 , respectively, unrealized mark-to-market gains of $203 million , losses of $174 million , and gains of $220 million for the years ended December 31, 2015 , 2014 , and 2013 , respectively, and elimination of intersegment revenues. (d) Exelon corrected an error in the December 31, 2014 and December 31, 2013 balances within Intersegment revenues and Revenues from external customers for an overstatement of Intersegment revenues for Reportable Segments of $284 million and $252 million for the years ended December 31, 2014 and 2013 , respectively, an understatement of Revenues from external customers for Reportable Segments of $284 million and $252 million for the years ended December 31, 2014 and 2013 , respectively, an understatement of Intersegment revenues for Other of $284 million and $252 million for the years ended December 31, 2014 and 2013 , respectively, and an overstatement of Revenues from external customers for Other of $284 million and $252 million for the years ended December 31, 2014 and 2013 , respectively. The error is not considered material to any prior period, and there is no net impact to Total Revenues. Generation total revenues net of purchased power and fuel expense: 2015 2014 2013 RNF from external (b) Intersegment Total RNF RNF from external (b)(d) Intersegment RNF d) Total RNF RNF from external (b)(d) Intersegment (d) Total RNF Mid-Atlantic (a) $ 3,556 $ 15 $ 3,571 $ 3,544 $ (113 ) $ 3,431 $ 3,287 $ (17 ) $ 3,270 Midwest 2,912 (20 ) 2,892 2,607 (8 ) 2,599 2,606 (20 ) 2,586 New England 519 (58 ) 461 450 (99 ) 351 299 (114 ) 185 New York 584 50 634 439 44 483 (55 ) 51 (4 ) ERCOT 425 (132 ) 293 573 (256 ) 317 627 (191 ) 436 Other Power Regions 440 (190 ) 250 517 (190 ) 327 397 (196 ) 201 Total Revenues net of purchased power and fuel expense for Reportable Segments $ 8,436 $ (335 ) $ 8,101 $ 8,130 $ (622 ) $ 7,508 $ 7,161 $ (487 ) $ 6,674 Other (c) 678 335 1,013 (662 ) 622 (40 ) 272 487 759 Total Generation Revenues net of purchased power and fuel expense $ 9,114 $ — $ 9,114 $ 7,468 $ — $ 7,468 $ 7,433 $ — $ 7,433 ____________________________ (a) On April 1, 2014, Generation assumed operational control of CENG's nuclear fleet. As a result, beginning on April 1, 2014, CENG's revenue net of purchased power and fuel expense are included on a fully consolidated basis. (b) Includes purchases and sales from third parties and affiliated sales to ComEd, PECO and BGE. (c) Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $8 million increase in RNF, a $ 124 million decrease in RNF, and a $ 488 million decrease in RNF for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2015 , 2014 , and 2013 , respectively, unrealized mark-to-market gains of $257 million , losses of $591 million , and gains of $504 million for the years ended December 31, 2015 , 2014 , and 2013 , respectively, and the elimination of intersegment revenue net of purchased power and fuel expense. (d) Exelon corrected an error in the December 31, 2014 and December 31, 2013 balances within Intersegment RNF and RNF from external customers for an understatement of $8 million and an overstatement of $134 million of Intersegment RNF for Reportable Segments for the years ended December 31, 2014 and 2013 , respectively, an understatement of RNF from external customers for Reportable Segments of $11 million and $134 million for the years ended December 31, 2014 and 2013 , respectively, an overstatement of $8 million and an understatement $134 million of Intersegment RNF for Other for the years ended December 31, 2014 and 2013 , respectively, and an overstatement of RNF from external customers for Other of $11 million and $134 million for the years ended December 31, 2014 and 2013 , respectively. This also included an understatement of total RNF for Reportable Segments and an overstatement of total RNF for Other of $19 million for the year ended December 31, 2014 . The error is not considered material to any prior period, and there is no net impact to Generation Total RNF for 2013 or 2014.

Related Party Transactions (Exe

Related Party Transactions (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Related Party Transactions [Abstract]
Related-Party Transactions (Exelon, Generation, ComEd, PECO and BGE)	(Exelon, Generation, ComEd, PECO and BGE) Exelon The financial statements of Exelon include related party transactions as presented in the tables below: For the Years Ended December 31, 2015 2014 2013 Operating revenues from affiliates: PECO (a) $ 1 $ 1 $ 10 CENG (b) — 17 56 BGE (a) 4 5 4 Other 4 — — Total operating revenues from affiliates $ 9 $ 23 $ 70 Purchase power and fuel from affiliates: CENG (c) $ — $ 282 $ 992 Keystone Fuels, LLC (d) — 138 144 Conemaugh Fuels, LLC (d) — 99 98 Safe Harbor Water Power Corp (d) — 12 22 Total purchase power and fuel from affiliates $ — $ 531 $ 1,256 Interest expense to affiliates, net: ComEd Financing III $ 13 $ 13 $ 13 PECO Trust III 6 6 6 PECO Trust IV 6 6 6 BGE Capital Trust II 16 16 16 Total interest expense to affiliates, net $ 41 $ 41 $ 41 Earnings (losses) in equity method investments: CENG (e) $ — $ (19 ) $ 9 Qualifying facilities and domestic power projects (8 ) (1 ) 1 Other $ 1 $ — $ — Total earnings (losses) in equity method investments $ (7 ) $ (20 ) $ 10 December 31, 2015 2014 Payables to affiliates (current): ComEd Financing III $ 4 $ 4 PECO Trust III 1 1 BGE Capital Trust II 3 3 Total payables to affiliates (current) $ 8 $ 8 Long-term debt due to financing trusts: ComEd Financing III $ 205 $ 205 PECO Trust III 81 81 PECO Trust IV 103 103 BGE Capital Trust II 252 252 Total long-term debt due to financing trusts $ 641 $ 641 ____________________________ (a) The intersegment profit associated with the sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statement of Operations. See Note 3 — Regulatory Matters for additional information. (b) Beginning in 2012, Generation entered into a power services agency agreement (PSAA) with the CENG plants, which as of April 1, 2014, was amended and extended until the permanent cessation of power generation by the CENG generation plants. The PSAA is an agreement under which Generation provides scheduling, asset management and billing services to the CENG plants for a specified monthly fee. The charges for services reflect the cost of the services. On April 1, 2014, Generation and CENG entered into a Nuclear Operating Services Agreement (NOSA) pursuant to which Generation will operate the CENG nuclear generation fleet owned by CENG subsidiaries and provide corporate and administrative services for the remaining life of the CENG nuclear plants as if they were part of the Generation nuclear fleet. For further information regarding the Investment in CENG, see Note 5 — Investment in Constellation Energy Nuclear Group, LLC . (c) CENG owns 100% of four nuclear units in Maryland and New York and 82% of Nine Mile Point Unit 2 in New York. Beginning in 2012, Generation had a PPA under which it purchased 85% of the nuclear plant output owned by CENG that was not sold to third parties under pre-existing unit-contingent PPAs through 2014. Beginning on January 1, 2015 and continuing to the end of the life of the respective plants, Generation will purchase on a unit-contingent basis 50.01% of the nuclear plant output owned by CENG and a subsidiary of EDF will purchase on a unit-contingent basis 49.99% of the nuclear plant output owned by CENG (EDF PPA) not sold to third parties. Beginning April 1, 2014, sales to Generation are eliminated in consolidation. For further information regarding the Investment in CENG, see Note 5 — Investment in Constellation Energy Nuclear Group, LLC . (d) During 2014, Generation closed the sale of Safe Harbor Water Power Corporation, Keystone Fuels, LLC, and Conemaugh Fuels LLC. Generation recorded purchase power and fuel costs from affiliates related to these generating assets during the time these assets were still partially owned by Generation. See Note 4 — Mergers, Acquisitions, and Dispositions for more information. (e) Prior to April 1, 2014, Generation’s total gain (loss) in equity method investments includes equity investment income (loss) and amortization of the basis difference established as a result of purchase accounting applied upon Constellation merger in 2012. CENG was fully consolidated on April 1, 2014. For further information regarding the Investment in CENG, see Note 5 — Investment in Constellation Energy Nuclear Group, LLC . Transactions involving Generation, ComEd, PECO and BGE are further described in the tables below. Generation The financial statements of Generation include related party transactions as presented in the tables below: For the Years Ended December 31, 2015 2014 2013 Operating revenues from affiliates: ComEd (a) $ 18 $ 176 $ 506 PECO (b) 224 198 405 BGE (c) 502 387 455 CENG (d) — 17 56 BSC 1 1 1 Other 4 — — Total operating revenues from affiliates $ 749 $ 779 $ 1,423 Purchase power and fuel from affiliates: ComEd $ — $ 1 $ 1 BGE 14 25 13 CENG (e) — 282 992 Keystone Fuels, LLC (i) — 138 144 Conemaugh Fuels, LLC (i) — 99 98 Safe Harbor Water Power Corporation (i) — 12 22 Total purchase power and fuel from affiliates $ 14 $ 557 $ 1,270 Operating and maintenance from affiliates: ComEd (f) $ 4 $ 3 $ 2 PECO (f) 2 2 1 BSC (g) 614 618 571 Total operating and maintenance from affiliates $ 620 $ 623 $ 574 Interest expense to affiliates, net: Exelon Corporate (j) $ 43 $ 53 $ 59 Earnings (losses) in equity method investments CENG (h) $ — $ (19 ) $ 9 Qualifying facilities and domestic power projects (8 ) (1 ) 1 Total earnings (losses) in equity method investments $ (8 ) $ (20 ) $ 10 Capitalized costs BSC (g) $ 76 $ 91 $ 93 Cash distribution paid to member $ 2,474 $ 645 $ 625 Contribution from member $ 47 $ 53 $ 26 December 31, 2015 2014 Receivables from affiliates (current): ComEd (a) $ 15 $ 43 PECO (b) 36 29 BGE (c) 31 40 Other 1 1 Total receivables from affiliates (current) $ 83 $ 113 Intercompany money pool (current): Exelon Corporate $ 1,252 $ — Long-term debt due to affiliates (current): Exelon Corporate (l) $ — $ 556 Payables to affiliates (current): Exelon Corporate (j) $ 16 $ 12 BSC (g) 78 83 ComEd 9 12 Other 1 — Total payables to affiliates (current) $ 104 $ 107 Long-term debt due to affiliates (noncurrent): Exelon Corporate (l) $ 933 $ 943 Payables to affiliates (noncurrent): BSC (g) $ — $ 1 ComEd (k) 2,172 2,389 PECO (k) 405 490 Total payables to affiliates (noncurrent) $ 2,577 $ 2,880 _______________________ (a) Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3 — Regulatory Matters for additional information. (b) Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has five-year and ten-year agreements with PECO to sell non-solar and solar AECs, respectively. See Note 3 — Regulatory Matters for additional information. (c) Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3 — Regulatory Matters for additional information. (d) Beginning in 2012, Generation entered into a power services agency agreement (PSAA) with the CENG plants, which as of April 1, 2014, was amended and extended until the permanent cessation of power generation by the CENG generation plants. The PSAA is an agreement under which Generation provides scheduling, asset management and billing services to the CENG plants for a specified monthly fee. The charges for services reflect the cost of the services. On April 1, 2014, Generation and CENG entered into a Nuclear Operating Services Agreement (NOSA) pursuant to which Generation will operate the CENG nuclear generation fleet owned by CENG subsidiaries and provide corporate and administrative services for the remaining life of the CENG nuclear plants as if they were part of the Generation nuclear fleet. For further information regarding the Investment in CENG, see Note 5 — Investment in Constellation Energy Nuclear Group, LLC . (e) CENG owns 100% of four nuclear units in Maryland and New York and 82% of Nine Mile Point Unit 2 in New York. Beginning in 2012, Generation had a PPA under which it purchased 85% of the nuclear plant output owned by CENG that was not sold to third parties under pre-existing unit-contingent PPAs through 2014. Beginning on January 1, 2015 and continuing to the end of the life of the respective plants, Generation will purchase on a unit-contingent basis 50.01% of the nuclear plant output owned by CENG and a subsidiary of EDF will purchase on a unit-contingent basis 49.99% of the nuclear plant output owned by CENG (EDF PPA) not sold to third parties. Beginning April 1, 2014, sales to Generation are eliminated in consolidation. For further information regarding the Investment in CENG, see Note 5 — Investment in Constellation Energy Nuclear Group, LLC . (f) Generation requires electricity for its own use at its generating stations. Generation purchases electricity and distribution and transmission services from PECO and only distribution and transmission services from ComEd for the delivery of electricity to its generating stations. (g) Generation receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (h) Prior to April 1, 2014, Generation’s total gain (loss) in equity method investments includes equity income (loss) and amortization of the basis difference established as a result of purchase accounting applied upon Constellation merger in 2012. CENG was fully consolidated on April 1, 2014. For further information regarding the Investment in CENG, see Note 5 — Investment in Constellation Energy Nuclear Group, LLC . (i) During 2014, Generation closed the sale of Safe Harbor Water Power Corporation, Keystone Fuels, LLC, and Conemaugh Fuels LLC. Generation recorded purchase power and fuel costs from affiliates related to these generating assets during the time these assets were still partially owned by Generation. See Note 4 — Mergers, Acquisitions, and Dispositions for more information. (j) The balance consists of interest owed to Exelon Corporation related to the senior unsecured notes, as well as, expense related to certain invoices Exelon Corporation processed on behalf of Generation. (k) Generation has long-term payables to ComEd and PECO as a result of the nuclear decommissioning contractual construct whereby, to the extent NDT funds are greater than the underlying ARO at the end of decommissioning, such amounts are due back to ComEd and PECO, as applicable, for payment to their respective customers. See Note 16 — Asset Retirement Obligations . (l) In connection with the debt obligations assumed by Exelon as part of the Constellation merger, Exelon and subsidiaries of Generation (former Constellation subsidiaries) assumed intercompany loan agreements that mirror the terms and amounts of the third-party debt obligations of Exelon, resulting in intercompany notes payable included in Long-term Debt to affiliate on Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation on Exelon’s Consolidated Balance Sheets. ComEd The financial statements of ComEd include related party transactions as presented in the tables below: For the Years Ended December 31, 2015 2014 2013 Operating revenues from affiliates Generation $ 4 $ 4 $ 3 Purchased power from affiliate Generation (a) $ 18 $ 176 $ 512 Operating and maintenance from affiliate BSC (b) $ 195 $ 166 $ 157 Interest expense to affiliates, net: ComEd Financing III $ 13 $ 13 $ 13 Capitalized costs BSC (b) $ 103 $ 77 $ 69 Cash dividends paid to parent $ 299 $ 307 $ 220 Contribution from parent $ 202 $ 273 $ — December 31, 2015 2014 Prepaid voluntary employee beneficiary association trust (c) $ 11 $ 13 Receivable from affiliates (current): Voluntary employee beneficiary association trust $ 2 $ 2 Generation 9 12 Exelon Corporate (e) 188 — Total receivable from affiliates (current) $ 199 $ 14 Receivable from affiliates (noncurrent): Generation (d) $ 2,172 $ 2,389 Exelon Corporate (e) — 182 Total receivable from affiliates (noncurrent) $ 2,172 $ 2,571 Payables to affiliates (current): Generation (a) $ 15 $ 43 BSC (b) 39 32 ComEd Financing III 4 4 PECO 2 2 Exelon Corporate 2 3 Total payables to affiliates (current) $ 62 $ 84 Long-term debt to ComEd financing trust ComEd Financing III $ 205 $ 205 _______________________ (a) ComEd procures a portion of its electricity supply requirements from Generation under an ICC-approved RFP contract. ComEd also purchases RECs from Generation. In addition, purchased power expense includes the settled portion of the financial swap contract with Generation, which expired in 2013. See Note 3 — Regulatory Matters and Note 13 — Derivative Financial Instruments for additional information. (b) ComEd receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (c) The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for ComEd’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets. (d) ComEd has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct for generating facilities previously owned by ComEd. To the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to ComEd for payment to ComEd’s customers. (e) Represents indemnification from Exelon Corporate related to the like-kind exchange transaction. PECO The financial statements of PECO include related party transactions as presented in the tables below: For the Years Ended December 31, 2015 2014 2013 Operating revenues from affiliates: Generation (a) $ 2 $ 2 $ 1 Purchased power from affiliate Generation (b) $ 220 $ 194 $ 392 Operating and maintenance from affiliates: BSC (c) $ 107 $ 96 $ 98 Generation 3 3 3 Total operating and maintenance from affiliates $ 110 $ 99 $ 101 Interest expense to affiliates, net: PECO Trust III $ 6 $ 6 $ 6 PECO Trust IV 6 6 6 Total interest expense to affiliates, net $ 12 $ 12 $ 12 Capitalized costs BSC (c) $ 40 $ 39 $ 46 Cash dividends paid to parent $ 279 $ 320 $ 332 Contribution from parent $ 16 $ 24 $ 27 December 31, 2015 2014 Prepaid voluntary employee beneficiary association trust (d) $ 2 $ 3 Receivable from affiliate (current): ComEd $ 2 $ 2 BGE — 1 Total receivable from affiliates (current) $ 2 $ 3 Receivable from affiliate (noncurrent): Generation (e) $ 405 $ 490 Payables to affiliates (current): Generation (b) $ 36 $ 29 BSC (c) 17 20 Exelon Corporate 1 2 PECO Trust III 1 1 Total payables to affiliates (current) $ 55 $ 52 Long-term debt to financing trusts: PECO Trust III $ 81 $ 81 PECO Trust IV 103 103 Total long-term debt to financing trusts $ 184 $ 184 ________________________ (a) PECO provides energy to Generation for Generation’s own use. (b) PECO purchases electric supply from Generation under contracts executed through its competitive procurement process. In addition, PECO has five-year and ten-year agreements with Generation to purchase non-solar and solar AECs, respectively. See Note 3 — Regulatory Matters for additional information on AECs. (c) PECO receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (d) The voluntary employee beneficiary association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for PECO’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. (e) PECO has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct, whereby, to the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to PECO for payment to PECO’s customers. BGE The financial statements of BGE include related party transactions as presented in the tables below: For the Years Ended December 31, 2015 2014 2013 Operating revenues from affiliates: Generation (a) $ 14 $ 25 $ 13 Purchased power from affiliate Generation (b) $ 498 $ 382 $ 452 Operating and maintenance from affiliates: BSC (c) $ 118 $ 103 $ 83 Interest expense to affiliates, net: BGE Capital Trust II $ 16 $ 16 $ 16 Capitalized costs BSC (c) $ 28 $ 19 $ 15 Cash dividends paid to parent $ 158 $ — $ — Contribution from parent $ 7 $ — $ — December 31, 2015 2014 Prepaid voluntary employee beneficiary association trust (d) $ — $ 1 Payables to affiliates (current): Generation (b) $ 31 $ 40 BSC (c) 17 17 Exelon Corporate 1 5 PECO — 1 BGE Capital Trust II 3 3 Total payables to affiliates (current) $ 52 $ 66 Long-term debt to BGE financing trust BGE Capital Trust II $ 252 $ 252 ______________________ (a) BGE provides energy to Generation for Generation’s own use. (b) BGE procures a portion of its electricity and gas supply requirements from Generation under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3 — Regulatory Matters for additional information. (c) BGE receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (d) The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for BGE’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets.

Quarterly Data (Unaudited) (Exe

Quarterly Data (Unaudited) (Exelon, Generation, ComEd, PECO and BGE)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Quarterly Data (Unaudited) (Exelon, Generation, ComEd, PECO and BGE)	(Unaudited) (Exelon, Generation, ComEd, PECO and BGE) Exelon The data shown below, which may not equal the total for the year due to the effects of rounding and dilution, includes all adjustments that Exelon considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2015 2014 2015 2014 2015 2014 Quarter ended: March 31 $ 8,830 $ 7,237 $ 1,366 (a) $ 168 (b) $ 693 $ 90 June 30 6,514 6,024 1,134 (a) 842 (b) 638 522 September 30 7,401 6,912 1,200 (a) 1,738 (b) 629 993 December 31 6,702 7,255 707 348 309 18 (c) ____________________________ (a) In the first, second, and third quarter of 2015, Exelon reclassified $(1) million , $7 million , and $2 million , respectively, to Operating income for presentation purposes in Exelon's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect Exelon's Net (Loss) Income on Common Stock. (b) In the first, second, and third quarter of 2014, Exelon reclassified $5 million , $13 million , and $339 million , respectively, to Operating income for presentation purposes in Exelon's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect Exelon's Net (Loss) Income on Common Stock. (c) Includes charges to earnings related to the impairments of certain generating assets which were held for sale and certain Upstream exploration assets. See Note 8 — Impairment of Long-Lived Assets of the Combined Notes to Consolidated Financial Statements for additional information. Average Basic Shares Outstanding (in millions) Net Income 2015 2014 2015 2014 Quarter ended: March 31 862 858 $ 0.80 $ 0.10 June 30 863 860 0.74 0.61 September 30 913 861 0.69 1.15 December 31 921 861 0.34 0.02 Average Diluted Shares Outstanding (in millions) Net Income 2015 2014 2015 2014 Quarter ended: March 31 867 861 $ 0.80 $ 0.10 June 30 866 864 0.74 0.60 September 30 915 863 0.69 1.15 December 31 924 868 0.33 0.02 The following table presents the New York Stock Exchange—Composite Common Stock Prices and dividends by quarter on a per share basis: 2015 2014 Fourth Quarter Third Quarter Second Quarter First Quarter Fourth Quarter Third Quarter Second Quarter First Quarter High price $ 31.37 $ 34.44 $ 34.98 $ 38.25 $ 38.93 $ 36.26 $ 37.73 $ 33.94 Low price 25.09 28.41 31.28 31.71 33.07 30.66 33.11 26.45 Close 27.77 29.70 31.42 33.61 37.08 34.09 36.48 33.56 Dividends 0.310 0.310 0.310 0.310 0.310 0.310 0.310 0.310 Generation The data shown below includes all adjustments that Generation considers necessary for a fair presentation of such amounts: Operating Revenues Operating (Loss) Income Net (Loss) Income on Membership Interest 2015 2014 2015 (a) 2014 2015 2014 Quarter ended: March 31 $ 5,840 $ 4,390 $ 719 (a) $ (384 ) (b) $ 443 $ (185 ) June 30 4,232 3,789 703 (a) 441 (b) 398 340 September 30 4,768 4,412 622 (a) 1,225 (b) 377 771 December 31 4,294 4,802 230 (105 ) 154 (91 ) ____________________________ (a) In the first, second, and third quarter of 2015, Generation reclassified $(1) million , $7 million , and $1 million , respectively, to Operating (loss) income for presentation purposes in Generation's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect Generation's Net (Loss) Income on Membership Interest. (b) In the first, second, and third quarter of 2014, Generation reclassified $5 million , $12 million , and $338 million , respectively, to Operating (loss) income for presentation purposes in Generation's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect Generation's Net (Loss) Income on Membership Interest. ComEd The data shown below includes all adjustments that ComEd considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2015 2014 2015 2014 2015 2014 Quarter ended: March 31 $ 1,185 $ 1,134 $ 230 $ 238 $ 90 $ 98 June 30 1,148 1,128 243 258 (a) 99 111 September 30 1,376 1,222 327 287 (a) 149 126 December 31 1,196 1,079 217 196 87 73 ____________________________ (a) In both the second and third quarter of 2014, ComEd reclassified $1 million to Operating income for presentation purposes in ComEd's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect ComEd's Net (Loss) Income. PECO The data shown below includes all adjustments that PECO considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income on Common Stock 2015 2014 2015 2014 2015 2014 Quarter ended: March 31 $ 985 $ 993 $ 223 $ 149 $ 139 $ 89 June 30 661 656 124 134 70 84 September 30 740 693 154 133 90 81 December 31 645 750 128 156 79 98 BGE The data shown below includes all adjustments that BGE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income attributable to Common Shareholders 2015 2014 2015 2014 2015 2014 Quarter ended: March 31 $ 1,036 $ 1,054 $ 204 $ 169 $ 106 $ 85 June 30 628 653 99 55 44 16 September 30 725 697 110 102 51 46 December 31 746 761 144 113 74 52

Schedule I - Condensed Financia

Schedule I - Condensed Financial Information of Parent (Exelon Corporate)	12 Months Ended
	Dec. 31, 2015
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Schedule I - Condensed Financial Information of Parent (Exelon Corporate)	Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Statements of Operations and Other Comprehensive Income For the Years Ended December 31, (In millions) 2015 2014 2013 Operating expenses Operating and maintenance $ — $ 9 $ 9 Operating and maintenance from affiliates 43 38 34 Other 4 3 12 Total operating expenses 47 50 55 Operating loss (47 ) (50 ) (55 ) Other income and (deductions) Interest expense, net (168 ) (237 ) (116 ) Equity in earnings of investments 2,461 1,779 1,903 Interest income from affiliates, net 43 53 36 Other, net (43 ) (2 ) (78 ) Total other income 2,293 1,593 1,745 Income before income taxes 2,246 1,543 1,690 Income taxes (23 ) (80 ) (29 ) Net income $ 2,269 $ 1,623 $ 1,719 Other comprehensive income (loss) Pension and non-pension postretirement benefit plans: Prior service cost (benefit) reclassified to periodic costs $ (46 ) $ (30 ) $ — Actuarial loss reclassified to periodic cost 220 147 208 Transition obligation reclassified to periodic cost — — — Pension and non-pension postretirement benefit plan valuation adjustment (99 ) (497 ) 669 Unrealized loss on cash flow hedges 9 (148 ) (248 ) Unrealized gain on marketable securities — 1 2 Unrealized gain on equity investments (3 ) 8 106 Unrealized loss on foreign currency translation (21 ) (9 ) (10 ) Reversal of CENG equity method AOCI — (116 ) — Other comprehensive income (loss) 60 (644 ) 727 Comprehensive income $ 2,329 $ 979 $ 2,446 See Notes to Financial Statements Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Statements of Cash Flows For the Years Ended December 31, (In millions) 2015 2014 2013 Net cash flows provided by operating activities $ 3,071 $ 806 $ 1,053 Cash flows from investing activities Return on investment of direct financing lease termination — 335 — Changes in Exelon intercompany money pool (1,217 ) (83 ) (60 ) Note receivable from affiliates 550 — 484 Capital expenditures — 1 — Change in restricted cash — — 38 Investment in affiliates (212 ) (70 ) (38 ) Other investing activities (55 ) (126 ) 15 Net cash flows provided by (used in) investing activities (934 ) 57 439 Cash flows from financing activities Changes in short-term borrowings — — 10 Issuance of long-term debt 4,200 1,150 — Retirement of long-term debt (2,263 ) (23 ) (450 ) Issuance of common stock 1,868 — — Dividends paid on common stock (1,105 ) (1,065 ) (1,249 ) Proceeds from employee stock plans 32 35 47 Other financing activities (58 ) (84 ) (6 ) Net cash flows provided by (used in) financing activities 2,674 13 (1,648 ) Increase (decrease) in cash and cash equivalents 4,811 876 (156 ) Cash and cash equivalents at beginning of period 879 3 159 Cash and cash equivalents at end of period $ 5,690 $ 879 $ 3 See Notes to Financial Statements Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Balance Sheets December 31, (In millions) 2015 2014 ASSETS Current assets Cash and cash equivalents $ 5,690 $ 879 Accounts receivable, net Other accounts receivable 272 209 Accounts receivable from affiliates 20 24 Notes receivable from affiliates 1,478 818 Regulatory assets 241 254 Other 5 22 Total current assets 7,706 2,206 Property, plant and equipment, net 53 54 Deferred debits and other assets Regulatory assets 3,072 3,186 Investments in affiliates 26,119 26,670 Deferred income taxes 2,036 2,147 Non-pension postretirement benefit asset 108 — Notes receivable from affiliates 933 943 Other 404 149 Total deferred debits and other assets 32,672 33,095 Total assets $ 40,431 $ 35,355 See Notes to Financial Statements Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Balance Sheets December 31, (In millions) 2015 2014 LIABILITIES AND SHAREHOLDERS’ EQUITY Current liabilities Short-term borrowings $ 188 $ — Long-term debt due within one year 60 1,409 Accounts payable 5 2 Accrued expenses 440 25 Regulatory liabilities 63 51 Pension obligations 52 45 Other 1 30 Total current liabilities 809 1,562 Long-term debt 6,017 2,818 Long-term debt to affiliate — 182 Deferred credits and other liabilities Regulatory liabilities 31 37 Pension obligations 7,520 7,638 Non-pension postretirement benefit obligations — 16 Deferred income taxes 134 93 Other 122 398 Total deferred credits and other liabilities 7,807 8,182 Total liabilities 14,633 12,744 Commitments and contingencies Shareholders’ equity Common stock (No par value, 2000 shares authorized, 920 shares and 860 shares outstanding at December 31, 2015 and 2014, respectively) 18,678 16,709 Treasury stock, at cost (35 shares at December 31, 2015 and 2014, respectively) (2,327 ) (2,327 ) Retained earnings 12,068 10,910 Accumulated other comprehensive loss, net (2,624 ) (2,684 ) Total shareholders’ equity 25,795 22,608 BGE preference stock not subject to mandatory redemption 3 3 Total liabilities and shareholders’ equity $ 40,431 $ 35,355 See Notes to Financial Statements Basis of Presentation Exelon Corporate is a holding company that conducts substantially all of its business operations through its subsidiaries. These condensed financial statements and related footnotes have been prepared in accordance with Rule 12-04, Schedule I of Regulation S-X. These statements should be read in conjunction with the consolidated financial statements and notes thereto of Exelon Corporation. Exelon Corporate owns 100% of all of its significant subsidiaries, either directly or indirectly, except for Commonwealth Edison Company (ComEd), of which Exelon Corporate owns more than 99% , and BGE, of which Exelon owns 100% of the common stock but none of BGE’s preferred stock. Exelon owned none of PECO’s preference securities, which PECO redeemed in 2013. Mergers On April 29, 2014, Exelon and Pepco Holdings, Inc. (PHI) signed an agreement and plan of merger (as subsequently amended and restated as of July 18, 2014, the Merger Agreement) to combine the two companies in an all cash transaction. The resulting company will retain the Exelon name. See Note 4 — Mergers, Acquisitions, and Dispositions of the Combined Notes to Consolidated Financial Statements for additional information on the Merger Agreement with PHI. For BGE’s debt, the difference between fair value and book value of BGE’s assets acquired and liabilities assumed is recorded as a regulatory asset at Exelon Corporate as Exelon did not apply push-down accounting to BGE as part of the 2012 Constellation Merger. See Note 3 — Regulatory Matters of the Combined Notes to Consolidated Financial Statements for additional information on the fair value of BGE long-term debt regulatory asset. Debt and Credit Agreements Short-Term Borrowings Exelon Corporate meets its short-term liquidity requirements primarily through the issuance of commercial paper. Exelon Corporate had no commercial paper borrowings at both December 31, 2015 and December 31, 2014 . Credit Agreements On May 30, 2014, Exelon Corporate amended and extended its unsecured syndicated revolving credit facility with aggregate bank commitments of $500 million through May 2019. As of December 31, 2015 , Exelon Corporation had available capacity under those commitments of $474 million . See Note 14 — Debt and Credit Agreements of the Combined Notes to Consolidated Financial Statements for further information regarding Exelon Corporation’s credit agreement. Long-Term Debt The following tables present the outstanding long-term debt for Exelon Corporate as of December 31, 2015 and December 31, 2014 : Maturity Date December 31, Rates 2015 2014 Long-term debt Junior subordinated notes 6.5 % 2024 $ 1,150 $ 1,150 Contract payment - junior subordinated notes 2.5 % 2017 64 108 Senior unsecured notes (a) 1.6 % - 7.6 % 2017 - 2045 4,639 2,658 Total long-term debt 5,853 3,916 Unamortized debt discount and premium, net (4 ) 1 Unamortized debt issuance costs (47 ) (23 ) Fair value adjustment of consolidated subsidiary 275 333 Long-term debt due within one year (60 ) (1,409 ) Long-term debt $ 6,017 $ 2,818 ___________ (a) Senior unsecured notes include mirror debt that is held on both Generation and Exelon Corporation's balance sheets. The debt maturities for Exelon Corporate for the periods 2016 , 2017 , 2018 , 2019 , 2020 and thereafter are as follows: 2016 $ 45 2017 569 2018 — 2019 — 2020 1,450 Remaining years 3,789 Total long-term debt $ 5,853 Commitments and Contingencies See Note 23 — Commitments and Contingencies of the Combined Notes to Consolidated Financial Statements for Exelon Corporate’s commitments and contingencies related to environmental matters and fund transfer restrictions. Related Party Transactions The financial statements of Exelon Corporate include related party transactions as presented in the tables below: For the Years Ended December 31, (In millions) 2015 2014 2013 Operating and maintenance from affiliates: BSC (a) $ 43 $ 38 $ 34 Interest income from affiliates, net: Generation $ 43 $ 53 $ 36 Equity in earnings of investments: Exelon Energy Delivery Company, LLC (b) $ 1,079 $ 958 $ 834 Exelon Ventures Company, LLC (c) — 926 1,076 UII, LLC 20 (6 ) (2 ) Exelon Transmission Company, LLC (8 ) (7 ) (5 ) Exelon Enterprise (1 ) (1 ) — Generation 1,371 (91 ) — Total equity in earnings of investments $ 2,461 $ 1,779 $ 1,903 Cash contributions received from affiliates $ 3,209 $ 1,370 $ 1,175 December 31, (in millions) 2015 2014 Accounts receivable from affiliates (current): BSC (a) $ — $ 2 Generation 16 12 ComEd 2 3 PECO 1 2 BGE 1 5 Total accounts receivable from affiliates (current) $ 20 $ 24 Notes receivable from affiliates (current): BSC (a) $ 226 $ 262 Generation (d) 1,252 556 Total receivable from affiliates (current): $ 1,478 $ 818 Investments in affiliates: BSC (a) $ 191 $ 193 Exelon Energy Delivery Company, LLC (b) 14,163 13,590 UII, LLC 102 130 Exelon Transmission Company, LLC 3 1 Voluntary Employee Beneficiary Association trust 7 9 Exelon Enterprises 22 23 Generation 11,637 12,720 Other (6 ) 4 Total investments in affiliates $ 26,119 $ 26,670 Notes receivable from affiliates (non-current): Generation (d) $ 933 $ 943 Notes payable to affiliates (current): ComEd $ 188 $ — Long-term debt to affiliates (non-current): ComEd $ — $ 182 _____________________ (a) Exelon Corporate receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. (b) Exelon Energy Delivery Company, LLC consists of ComEd, PECO and BGE. (c) Exelon Ventures Company, LLC primarily consisted of Generation and was fully dissolved as of December 31, 2014. Exelon Enterprises, Exelon Generation Company, LLC, and Exelon Consolidations are now directly owned Exelon Corporate investments as of December 31, 2014. (d) In connection with the debt obligations assumed by Exelon as part of the Constellation merger, Exelon and subsidiaries of Generation (former Constellation subsidiaries) assumed intercompany loan agreements that mirror the terms and amounts of the third-party debt obligations of Exelon, resulting in intercompany notes payable included in Long-Term Debt to affiliate on Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation on Exelon’s Consolidated Balance Sheets.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2015
Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	Exelon Corporation and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2015 Allowance for uncollectible accounts (a) $ 311 $ 113 $ 27 (b) $ 167 (c) $ 284 Deferred tax valuation allowance 50 — (27 ) 10 13 Reserve for obsolete materials 95 10 2 2 105 For the year ended December 31, 2014 Allowance for uncollectible accounts (a) $ 272 $ 175 $ 69 (b) $ 205 (c) $ 311 Deferred tax valuation allowance 13 — 37 — 50 Reserve for obsolete materials 58 5 34 2 95 For the year ended December 31, 2013 Allowance for uncollectible accounts (a) $ 293 $ 121 $ 37 (b) $ 179 (c) $ 272 Deferred tax valuation allowance 36 1 — 24 13 Reserve for obsolete materials 53 17 — 12 58 ___________________ (a) Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $ 8 million, $ 8 million, and $ 9 million for the years ended December 31, 2015 , 2014 , and 2013 , respectively. (b) Includes charges for late payments and non-service receivables. (c) Write-off of individual accounts receivable. Exelon Generation Company, LLC and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Generation 1. Financial Statements: Report of Independent Registered Public Accounting Firm dated February 10, 2016 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2015, 2014 and 2013 Consolidated Statements of Cash Flows for the Years Ended December 31, 2015, 2014 and 2013 Consolidated Balance Sheets at December 31, 2015 and 2014 Consolidated Statements of Changes in Member’s Equity for the Years Ended December 31, 2015, 2014 and 2013 Notes to Consolidated Financial Statements 2. Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Exelon Generation Company, LLC and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2015 Allowance for uncollectible accounts $ 60 $ 22 $ — $ 5 $ 77 Deferred tax valuation allowance 48 — (27 ) 10 11 Reserve for obsolete materials 93 9 — — 102 For the year ended December 31, 2014 Allowance for uncollectible accounts $ 57 $ 14 $ 8 $ 19 $ 60 Deferred tax valuation allowance 11 — 37 — 48 Reserve for obsolete materials 55 5 32 (1 ) 93 For the year ended December 31, 2013 Allowance for uncollectible accounts $ 84 $ (16 ) $ — $ 11 $ 57 Deferred tax valuation allowance 35 1 — 25 11 Reserve for obsolete materials 50 16 — 11 55 Commonwealth Edison Company and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts ComEd 1. Financial Statements: Report of Independent Registered Public Accounting Firm dated February 10, 2016 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2015, 2014 and 2013 Consolidated Statements of Cash Flows for the Years Ended December 31, 2015, 2014 and 2013 Consolidated Balance Sheets at December 31, 2015 and 2014 Consolidated Statements of Changes in Shareholders’ Equity for the Years Ended December 31, 2015, 2014 and 2013 Notes to Consolidated Financial Statements 2. Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Commonwealth Edison Company and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2015 Allowance for uncollectible accounts $ 84 $ 39 $ 18 (a) $ 66 (b) $ 75 Reserve for obsolete materials 2 1 2 2 3 For the year ended December 31, 2014 Allowance for uncollectible accounts $ 62 $ 45 $ 33 (a) $ 56 (b) $ 84 Reserve for obsolete materials 2 — 2 2 2 For the year ended December 31, 2013 Allowance for uncollectible accounts $ 70 $ 33 $ 29 (a) $ 70 (b) $ 62 Reserve for obsolete materials 2 1 — 1 2 _____________________ (a) Primarily charges for late payments and non-service receivables. (b) Write-off of individual accounts receivable. PECO Energy Company and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts PECO 1. Financial Statements: Report of Independent Registered Public Accounting Firm dated February 10, 2016 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2015, 2014 and 2013 Consolidated Statements of Cash Flows for the Years Ended December 31, 2015, 2014 and 2013 Consolidated Balance Sheets at December 31, 2015 and 2014 Consolidated Statements of Changes in Shareholders’ Equity for the Years Ended December 31, 2015, 2014 and 2013 Notes to Consolidated Financial Statements 2. Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto PECO Energy Company and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2015 Allowance for uncollectible accounts (a) $ 100 $ 37 $ 9 (b) $ 63 (c) $ 83 Reserve for obsolete materials 1 — — — 1 For the year ended December 31, 2014 Allowance for uncollectible accounts (a) $ 107 $ 52 $ 11 (b) $ 70 (c) $ 100 Reserve for obsolete materials 1 — — — 1 For the year ended December 31, 2013 Allowance for uncollectible accounts (a) $ 99 $ 61 $ 7 (b) $ 60 (c) $ 107 Reserve for obsolete materials 1 — — — 1 _____________________ (a) Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $ 8 million, $ 8 million, and $ 9 million for the years ended December 31, 2015 , 2014 , and 2013 , respectively. (b) Primarily charges for late payments. (c) Write-off of individual accounts receivable. Baltimore Gas and Electric Company and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts BGE 1. Financial Statements: Report of Independent Registered Public Accounting Firm dated February 10, 2016 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2015, 2014 and 2013 Consolidated Statements of Cash Flows for the Years Ended December 31, 2015, 2014 and 2013 Consolidated Balance Sheets at December 31, 2015 and 2014 Consolidated Statements of Changes in Shareholders’ Equity for the Years Ended December 31, 2015, 2014 and 2013 Notes to Consolidated Financial Statements 2. Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Baltimore Gas and Electric Company and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2015 Allowance for uncollectible accounts $ 67 $ 15 $ — (b) $ 33 (a) $ 49 Deferred tax valuation allowance 1 — — — 1 Reserve for obsolete materials — — — — — For the year ended December 31, 2014 Allowance for uncollectible accounts $ 46 $ 64 $ 17 (b) $ 60 (a) $ 67 Deferred tax valuation allowance 1 — — — 1 Reserve for obsolete materials 1 — — 1 — For the year ended December 31, 2013 Allowance for uncollectible accounts $ 40 $ 43 $ 1 $ 38 (a) $ 46 Deferred tax valuation allowance 1 — — — 1 Reserve for obsolete materials 1 — — — 1 _____________________ (a) Write-off of individual accounts receivable. (b) Primarily charges for late payments.

Significant Accounting Polici38

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Description of Business (Exelon, Generation, ComEd, PECO and BGE)	Description of Business (Exelon, Generation, ComEd, PECO and BGE) Exelon is a utility services holding company engaged through its principal subsidiaries in the energy generation and energy delivery businesses. On April 1, 2014, Generation assumed the operating licenses and corresponding operational control of CENG’s nuclear fleet. As a result, Exelon and Generation consolidated CENG’s financial position and results of operations into their businesses. Prior to April 1, 2014, Exelon and Generation accounted for CENG as an equity method investment. Refer to Note 5 — Investment in Constellation Energy Nuclear Group, LLC for further information regarding the integration transaction. The energy generation business includes: • Generation : Physical delivery and marketing of owned and contracted electric generation capacity and provision of renewable and other energy-related products and services, and natural gas exploration and production activities. Generation has six reportable segments consisting of the Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. The energy delivery businesses include: • ComEd : Purchase and regulated retail sale of electricity and the provision of distribution and transmission services in northern Illinois, including the City of Chicago. • PECO : Purchase and regulated retail sale of electricity and the provision of distribution and transmission services in southeastern Pennsylvania, including the City of Philadelphia, and the purchase and regulated retail sale of natural gas and the provision of distribution services in the Pennsylvania counties surrounding the City of Philadelphia. • BGE : Purchase and regulated retail sale of electricity and the provision of distribution and transmission services in central Maryland, including the City of Baltimore, and the purchase and regulated retail sale of natural gas and the provision of distribution services in central Maryland, including the City of Baltimore. Basis of Presentation (Exelon, Generation, ComEd, PECO and BGE) This is a combined annual report of Exelon, Generation, ComEd, PECO and BGE. The Notes to the Consolidated Financial Statements apply to Exelon, Generation, ComEd, PECO and BGE as indicated above in the Index to Combined Notes to Consolidated Financial Statements and parenthetically next to each corresponding disclosure. When appropriate, Exelon, Generation, ComEd, PECO and BGE are named specifically for their related activities and disclosures. Each of the Registrant’s Consolidated Financial Statements includes the accounts of its subsidiaries. All intercompany transactions have been eliminated. As a result of the Registrants' 2014 divestiture of certain unconsolidated affiliates considered integral to their operations and the consolidation of CENG during 2014, all Equity in earnings (losses) from unconsolidated affiliates have been presented below Income taxes in the Registrants' Consolidated Statements of Operations and Comprehensive Income starting in the first quarter of 2015. Through its business services subsidiary, BSC, Exelon provides its subsidiaries with a variety of support services at cost, including legal, human resources, financial, information technology and supply management services. The costs of BSC, including support services, are directly charged or allocated to the applicable subsidiaries using a cost-causative allocation method. Corporate governance-type costs that cannot be directly assigned are allocated based on a Modified Massachusetts Formula, which is a method that utilizes a combination of gross revenues, total assets and direct labor costs for the allocation base. The results of Exelon’s corporate operations are presented as “Other” within the consolidated financial statements and include intercompany eliminations unless otherwise disclosed. Exelon owns 100% of all of its significant consolidated subsidiaries, either directly or indirectly, except for ComEd, of which Exelon owns more than 99% , and BGE, of which Exelon owns 100% of the common stock but none of BGE’s preference stock. Exelon owned none of PECO’s preferred securities, which PECO redeemed in 2013. Exelon has reflected the third-party interests in ComEd, which totaled less than $1 million at December 31, 2015 and December 31, 2014 , as equity, PECO’s preferred securities as preferred securities of subsidiary through their redemption in 2013, and BGE’s preference stock as BGE preference stock not subject to mandatory redemption in its consolidated financial statements. BGE is subject to some ring-fencing measures established by order of the MDPSC. As part of this arrangement, BGE common stock is held directly by RF Holdco LLC, which is an indirect subsidiary of Exelon. GSS Holdings (BGE Utility), an unrelated party, holds a nominal non-economic interest in RF Holdco LLC with limited voting rights on specified matters. Generation owns 100% of all of its significant consolidated subsidiaries, either directly or indirectly, except for certain Exelon Wind projects, of which Generation holds a majority interest of 99% for certain periods of time, and CENG, of which Generation holds a 50.01% interest. The remaining interests are included in noncontrolling interest on Exelon’s and Generation’s Consolidated Balance Sheets. See Note 2 — Variable Interest Entities for further discussion of Exelon’s and Generation’s VIEs and the reversionary interests of the noncontrolling members for these certain subsidiaries. ComEd owns 100% of all of its significant consolidated subsidiaries, either directly or indirectly, except for RITELine Illinois, LLC, of which ComEd owns 75% and an additional 12.5% is indirectly owned by Exelon. Exelon and ComEd have reflected the third-party interests of 12.5% and 25% , respectively, in RITELine Illinois, LLC, which both totaled less than $1 million at December 31, 2015 and December 31, 2014 , as equity. Exelon consolidates the accounts of entities in which Exelon has a controlling financial interest, after the elimination of intercompany transactions. A controlling financial interest is evidenced by either a voting interest greater than 50% in which Exelon can exercise control over the operations and policies of the investee, or the results of a model that identifies Exelon or one of its subsidiaries as the primary beneficiary of a VIE. Where Exelon does not have a controlling financial interest in an entity, it applies proportionate consolidation, equity method accounting or cost method accounting. Exelon applies proportionate consolidation when it has an undivided interest in an asset and is proportionately liable for its share of each liability associated with the asset. Exelon proportionately consolidates its undivided ownership interests in jointly owned electric plants and transmission facilities, as well as its undivided ownership interests in Upstream natural gas exploration and production activities. Under proportionate consolidation, Exelon separately records its proportionate share of the assets, liabilities, revenues and expenses related to the undivided interest in the asset. Exelon applies equity method accounting when it has significant influence over an investee through an ownership in common stock, which generally approximates a 20% to 50% voting interest. Exelon applies equity method accounting to certain investments and joint ventures, including certain financing trusts of ComEd, PECO, and BGE. Under the equity method, Exelon reports its interest in the entity as an investment and Exelon’s percentage share of the earnings from the entity as single line items in its financial statements. Exelon uses the cost method if it holds less than 20% of the common stock of an entity. Under the cost method, Exelon reports its investment at cost and recognizes income only to the extent Exelon receives dividends or distributions. The accompanying consolidated financial statements have been prepared in accordance with GAAP for annual financial statements and in accordance with the instructions to Form 10-K and Regulation S-X promulgated by the SEC.
Use Of Estimates (Exelon, Generation, ComEd, PECO and BGE)	Use of Estimates (Exelon, Generation, ComEd, PECO and BGE) The preparation of financial statements of each of the Registrants in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Areas in which significant estimates have been made include, but are not limited to, the accounting for nuclear decommissioning costs and other AROs, pension and other postretirement benefits, the application of purchase accounting, inventory reserves, allowance for uncollectible accounts, goodwill and asset impairments, derivative instruments, unamortized energy contracts, fixed asset depreciation, environmental costs and other loss contingencies, taxes and unbilled energy revenues. Actual results could differ from those estimates.
Reclassifications (Exelon, ComEd, and BGE)	Reclassifications (Exelon, Generation, ComEd, PECO and BGE) Certain prior year amounts in the registrants' Consolidated Statements of Operations and Comprehensive Income, Consolidated Balance Sheets and Consolidated Statements of Cash Flows have been reclassified between line items for comparative purposes. The reclassifications did not affect any of the Registrants’ net income, financial positions, or cash flows from operating activities. Exelon revised the presentation on the Statements of Operations and Comprehensive Income for PECO and BGE to reflect separately operating revenues from the sale of electricity and operating revenues from the sale of natural gas, as well as, purchased power expense and purchased fuel expense within the operating expenses section of the Statement of Operations and Comprehensive Income. Further, Exelon revised the presentation from total operating revenues to "Rate-regulated utility revenues" and "Competitive businesses revenues" on the face of Exelon’s consolidated Statement of Operations and Comprehensive Income for all periods presented. Similarly, Exelon will separately present rate-regulated purchased power and fuel expense and non-rate regulated purchased power and fuel expense on the face of Exelon’s consolidated Statement of Operations and Comprehensive Income for all periods presented. The reclassifications described herein were made for presentation purposes and did not affect any of the Registrants’ total revenues or net income.
Accounting for the Effects of Regulation (Exelon, ComEd, PECO and BGE)	Accounting for the Effects of Regulation (Exelon, ComEd, PECO and BGE) Exelon, ComEd, PECO and BGE apply the authoritative guidance for accounting for certain types of regulation, which requires ComEd, PECO and BGE to record in their consolidated financial statements the effects of cost-based rate regulation for entities with regulated operations that meet the following criteria: 1) rates are established or approved by a third-party regulator; (2) rates are designed to recover the entities’ cost of providing services or products; and (3) there is a reasonable expectation that rates are set at levels that will recover the entities’ costs from customers. Exelon, ComEd, PECO and BGE account for their regulated operations in accordance with regulatory and legislative guidance from the regulatory authorities having jurisdiction, principally the ICC, the PAPUC, and the MDPSC, in the cases of ComEd, PECO and BGE, respectively, under state public utility laws and the FERC under various Federal laws. Regulatory assets and liabilities are amortized and the related expense or revenue is recognized in the Consolidated Statements of Operations consistent with the recovery or refund included in customer rates. Exelon believes that it is probable that its currently recorded regulatory assets and liabilities will be recovered and settled, respectively, in future rates. However, Exelon, ComEd, PECO and BGE continue to evaluate their respective abilities to apply the authoritative guidance for accounting for certain types of regulation, including consideration of current events in their respective regulatory and political environments. If a separable portion of ComEd’s, PECO’s or BGE’s business was no longer able to meet the criteria discussed above, the affected entities would be required to eliminate from their consolidated financial statements the effects of regulation for that portion, which could have a material impact on their results of operations and financial positions. See Note 3 — Regulatory Matters for additional information. The Registrants treat the impacts of a final rate order received after the balance sheet date but prior to the issuance of the financial statements as a non-recognized subsequent event, as the receipt of a final rate order is a separate and distinct event that has future impacts on the parties affected by the order.
Revenues (Exelon, Generation, ComEd, PECO and BGE)	Revenues (Exelon, Generation, ComEd, PECO and BGE) Operating Revenues. Operating revenues are recorded as service is rendered or energy is delivered to customers. At the end of each month, the Registrants accrue an estimate for the unbilled amount of energy delivered or services provided to customers. ComEd records its best estimates of the distribution and transmission revenue impacts resulting from changes in rates that ComEd believes are probable of approval by the ICC and FERC in accordance with its formula rate mechanisms. BGE records its best estimate of the transmission revenue impact resulting from changes in rates that BGE believes are probable of approval by FERC in accordance with its formula rate mechanism. See Note 3 — Regulatory Matters and Note 6 — Accounts Receivable for further information. RTOs and ISOs. In RTO and ISO markets that facilitate the dispatch of energy and energy-related products, the Registrants generally report sales and purchases conducted on a net hourly basis in either revenues or purchased power on their Consolidated Statements of Operations and Comprehensive Income, the classification of which depends on the net hourly activity. In addition, capacity revenue and expense classification is based on the net sale or purchase position of the Company in the different RTOs and ISOs. Option Contracts, Swaps and Commodity Derivatives. Certain option contracts and swap arrangements that meet the definition of derivative instruments are recorded at fair value with subsequent changes in fair value recognized as revenue or expense. The classification of revenue or expense is based on the intent of the transaction. For example, gas transactions may be used to hedge the sale of power. This will result in the change in fair value recorded through revenue. As ComEd receives full cost recovery for energy procurement and related costs from retail customers, ComEd records the fair value of its energy swap contracts with unaffiliated suppliers as well as an offsetting regulatory asset or liability on its Consolidated Balance Sheets. Refer to Note 3 — Regulatory Matters and Note 13 — Derivative Financial Instruments for further information. Proprietary Trading Activities. Exelon and Generation account for Generation’s trading activities under the provisions of the authoritative guidance for accounting for contracts involved in energy trading and risk management activities, which require energy revenues and costs related to energy trading contracts to be presented on a net basis in the income statement. Commodity derivatives used for trading purposes are accounted for using the mark-to-market method with unrealized gains and losses recognized in operating revenues. Refer to Note 13 — Derivative Financial Instruments for further information.
Income Taxes (Exelon, Generation, ComEd, PECO and BGE)	Income Taxes (Exelon, Generation, ComEd, PECO and BGE) Deferred Federal and state income taxes are provided on all significant temporary differences between the book basis and the tax basis of assets and liabilities and for tax benefits carried forward. Investment tax credits have been deferred on the Registrants’ Consolidated Balance Sheets and are recognized in book income over the life of the related property. In accordance with applicable authoritative guidance, the Registrants account for uncertain income tax positions using a benefit recognition model with a two-step approach; a more-likely-than-not recognition criterion; and a measurement approach that measures the position as the largest amount of tax benefit that is greater than 50% likely of being realized upon ultimate settlement. If it is not more-likely-than-not that the benefit of the tax position will be sustained on its technical merits, no benefit is recorded. Uncertain tax positions that relate only to timing of when an item is included on a tax return are considered to have met the recognition threshold. The Registrants recognize accrued interest related to unrecognized tax benefits in Interest expense or Other income and deductions (interest income) on their Consolidated Statements of Operations and Comprehensive Income. Pursuant to the IRC and relevant state taxing authorities, Exelon and its subsidiaries file consolidated or combined income tax returns for Federal and certain state jurisdictions where allowed or required. See Note 15 — Income Taxes for further information. Taxes Directly Imposed on Revenue-Producing Transactions (Exelon, Generation, ComEd, PECO and BGE) Exelon, Generation, ComEd, PECO and BGE collect certain taxes from customers such as sales and gross receipts taxes, along with other taxes, surcharges, and fees that are levied by state or local governments on the sale or distribution of gas and electricity. Some of these taxes are imposed on the customer, but paid by the Registrants, while others are imposed on the Registrants. Where these taxes are imposed on the customer, such as sales taxes, they are reported on a net basis with no impact to the Consolidated Statements of Operations and Comprehensive Income. However, where these taxes are imposed on the Registrants, such as gross receipts taxes or other surcharges or fees, they are reported on a gross basis. Accordingly, revenues are recognized for the taxes collected from customers along with an offsetting expense. See Note 24 — Supplemental Financial Information for Generation’s, ComEd’s, PECO’s and BGE’s utility taxes that are presented on a gross basis.
Cash and Cash Equivalents (Exelon, Generation, ComEd, PECO and BGE)	Cash and Cash Equivalents (Exelon, Generation, ComEd, PECO and BGE) The Registrants consider investments purchased with an original maturity of three months or less to be cash equivalents. Restricted Cash and Cash Equivalents (Exelon, Generation, ComEd, PECO and BGE) Restricted cash and cash equivalents represent funds that are restricted to satisfy designated current liabilities. As of December 31, 2015 and 2014 , Exelon Corporate’s restricted cash and cash equivalents primarily represented restricted funds for payment of medical, dental, vision and long-term disability benefits. Additionally, as of December 31, 2015 and 2014 , Generation’s restricted cash and cash equivalents primarily included cash at Antelope Valley required for debt service and construction and cash at Continental Wind and ExGen Texas Power, which is required for debt service and financing of operation and maintenance of the underlying entities. As of December 31, 2015 and 2014 , ComEd’s restricted cash primarily represented cash collateral held from suppliers associated with ComEd’s energy and REC procurement contracts. As of December 31, 2015 and 2014 , PECO’s restricted cash primarily represented funds from the sales of assets that were subject to PECO’s mortgage indenture. As of December 31, 2015 and 2014 , BGE’s restricted cash primarily represented funds restricted at its consolidated variable interest entity for repayment of rate stabilization bonds and cash collateral held from suppliers. Restricted cash and cash equivalents not available to satisfy current liabilities are classified as noncurrent assets. As of December 31, 2015 and 2014 , Exelon’s and Generation’s NDT funds, which are designated to satisfy future decommissioning obligations, were classified as noncurrent assets. As of December 31, 2015 , Exelon, Generation, ComEd, PECO and BGE had investments in Rabbi trusts classified as noncurrent assets.
Allowance for Uncollectible Accounts (Exelon, Generation, ComEd, PECO and BGE)	Allowance for Uncollectible Accounts (Exelon, Generation, ComEd, PECO and BGE) The allowance for uncollectible accounts reflects the Registrants’ best estimates of losses on the accounts receivable balances. For Generation, the allowance is based on accounts receivable aging, historical experience and other currently available information. ComEd, PECO and BGE estimate the allowance for uncollectible accounts on customer receivables by applying loss rates developed specifically for each company to the outstanding receivable balance by customer risk segment. Risk segments represent a group of customers with similar credit quality indicators that are computed based on various attributes, including delinquency of their balances and payment history. Loss rates applied to the accounts receivable balances are based on historical average charge-offs as a percentage of accounts receivable in each risk segment. ComEd, PECO and BGE customers’ accounts are generally considered delinquent if the amount billed is not received by the time the next bill is issued, which normally occurs on a monthly basis. ComEd, PECO and BGE customer accounts are written off consistent with approved regulatory requirements. ComEd’s, PECO’s and BGE’s provisions for uncollectible accounts will continue to be affected by changes in volume, prices and economic conditions as well as changes in ICC, PAPUC and MDPSC regulations, respectively. See Note 3 — Regulatory Matters for additional information regarding the regulatory recovery of uncollectible accounts receivable at ComEd.
Variable Interest Entities (Exelon, Generation, ComEd, PECO and BGE)	Variable Interest Entities (Exelon, Generation, ComEd, PECO and BGE) Exelon accounts for its investments in and arrangements with VIEs based on the authoritative guidance which includes the following specific requirements: • requires an entity to qualitatively assess whether it should consolidate a VIE based on whether the entity (1) has the power to direct matters that most significantly impact the activities of the VIE, and (2) has the obligation to absorb losses or the right to receive benefits of the VIE that could potentially be significant to the VIE, • requires an ongoing reconsideration of this assessment instead of only upon certain triggering events, and • requires the entity that consolidates a VIE (the primary beneficiary) to disclose (1) the assets of the consolidated VIE, if they can be used to only settle specific obligations of the consolidated VIE, and (2) the liabilities of a consolidated VIE for which creditors do not have recourse to the general credit of the primary beneficiary. Based on the above accounting guidance, Exelon has adopted the following policies related to variable interest entities: • Exelon has disclosed, to the extent material, the assets of its consolidated VIEs that can only be used to settle specific obligations of the consolidated VIE, and the liabilities of Exelon’s consolidated VIEs for which creditors do not have recourse to Exelon’s general credit. • Exelon has qualitatively assessed whether the equity holders of the entity have the power to direct matters that most significantly impact the entity. See Note 2 — Variable Interest Entities for additional information.
Inventories (Exelon, Generation, ComEd, PECO and BGE)	Inventories (Exelon, Generation, ComEd, PECO and BGE) Inventory is recorded at the lower of weighted average cost or market. Provisions are recorded for excess and obsolete inventory. Fossil Fuel. Fossil fuel inventory includes the weighted average costs of stored natural gas, propane and oil. The costs of natural gas, propane and oil are generally included in inventory when purchased and charged to fuel expense when used or sold. Materials and Supplies. Materials and supplies inventory generally includes the weighted average costs of transmission, distribution and generating plant materials. Materials are generally charged to inventory when purchased and expensed or capitalized to property, plant and equipment, as appropriate, when installed or used. Emission Allowances. Emission allowances are included in inventory (for emission allowances exercisable in the current year) and other deferred debits (for emission allowances that are exercisable beyond one year) and are carried at the lower of weighted average cost or market and charged to fuel expense as they are used in operations.
Marketable Securities (Exelon, Generation, ComEd, PECO and BGE)	Marketable Securities (Exelon, Generation, ComEd, PECO and BGE) All marketable securities are reported at fair value. Marketable securities held in the NDT funds are classified as trading securities and all other securities are classified as available-for-sale securities. Realized and unrealized gains and losses, net of tax, on Generation’s NDT funds associated with the Regulatory Agreement Units are included in regulatory liabilities at Exelon, ComEd and PECO and in noncurrent payables to affiliates at Generation and in noncurrent receivables from affiliates at ComEd and PECO. Realized and unrealized gains and losses, net of tax, on Generation’s NDT funds associated with the Non-Regulatory Agreement Units are included in earnings at Exelon and Generation. Unrealized gains and losses, net of tax, for Exelon's available-for-sale securities are reported in OCI. Any decline in the fair value of Exelon's available-for-sale securities below the cost basis is reviewed to determine if such decline is other-than-temporary. If the decline is determined to be other-than-temporary, the cost basis of the available-for-sale securities is written down to fair value as a new cost basis and the amount of the write-down is included in earnings. See Note 16 — Asset Retirement Obligations for information regarding marketable securities held by NDT funds and Note 24 — Supplemental Financial Information for additional information regarding ComEd’s and PECO’s regulatory assets and liabilities.
Property Plant And Equipment (Exelon, Generation, ComEd, PECO and BGE)	Property, Plant and Equipment (Exelon, Generation, ComEd, PECO and BGE) Property, plant and equipment is recorded at original cost. Original cost includes construction-related direct labor and material costs. ComEd, PECO and BGE also include indirect construction costs including labor and related costs of departments associated with supporting construction activities. When appropriate, original cost also includes capitalized interest for Generation and Exelon Corporate and AFUDC for regulated property at ComEd, PECO and BGE. The cost of repairs and maintenance, including planned major maintenance activities and minor replacements of property, is charged to maintenance expense as incurred. Third parties reimburse ComEd, PECO and BGE for all or a portion of expenditures for certain capital projects. Such contributions in aid of construction costs (CIAC) are recorded as a reduction to Property, Plant and Equipment. DOE SGIG funds reimbursed to PECO and BGE have been accounted for as CIAC. For Generation, upon retirement, the cost of property is charged to accumulated depreciation in accordance with the composite method of depreciation. Upon replacement of an asset, the costs to remove the asset, net of salvage, are capitalized to gross plant when incurred as part of the cost of the newly-installed asset and recorded to depreciation expense over the life of the new asset. Removal costs, net of salvage, incurred for property that will not be replaced is charged to operating and maintenance expense as incurred. For ComEd, PECO and BGE, upon retirement, the cost of property, net of salvage, is charged to accumulated depreciation in accordance with the composite method of depreciation. ComEd’s and BGE’s depreciation expense includes the estimated cost of dismantling and removing plant from service upon retirement, which is consistent with each utility’s regulatory recovery method. ComEd’s and BGE’s actual incurred removal costs are applied against a related regulatory liability. PECO’s removal costs are capitalized to accumulated depreciation when incurred, and recorded to depreciation expense over the life of the new asset constructed consistent with PECO’s regulatory recovery method. Generation’s oil and gas exploration and production activities consist of working interests in gas producing fields. Generation accounts for these activities under the successful efforts method of accounting. Acquisition, development and exploration costs are capitalized. Costs of drilling exploratory wells are initially capitalized and later charged to expense if reserves are not discovered or deemed not to be commercially viable. Other exploratory costs are charged to expense when incurred. See Note 7 — Property, Plant and Equipment , Note 10 — Jointly Owned Electric Utility Plant and Note 24 — Supplemental Financial Information for additional information regarding property, plant and equipment.
Nuclear Fuel (Exelon and Generation)	Nuclear Fuel (Exelon and Generation) The cost of nuclear fuel is capitalized within property, plant and equipment and charged to fuel expense using the unit-of-production method. Prior to May 16, 2014, the estimated disposal cost of SNF was established per the Standard Waste Contract with the DOE and was expensed through fuel expense at one mill ($0.001) per kWh of net nuclear generation. Effective May 16, 2014, the SNF disposal fee was set to zero by the DOE and Exelon and Generation are not accruing any further costs related to SNF disposal fees until a new fee structure goes into effect. On-site SNF storage costs are being reimbursed by the DOE since a DOE (or government-owned) long-term storage facility has not been completed. See Note 23 — Commitments and Contingencies for additional information regarding the SNF disposal fee.
Nuclear Outage Costs (Exelon and Generation)	Nuclear Outage Costs (Exelon and Generation) Costs associated with nuclear outages, including planned major maintenance activities, are expensed to operating and maintenance expense or capitalized to property, plant and equipment (based on the nature of the activities) in the period incurred.
New Site Development Costs (Exelon and Generation)	New Site Development Costs (Exelon and Generation) New site development costs represent the costs incurred in the assessment and design of new power generating facilities. Such costs are capitalized when management considers project completion to be probable, primarily based on management’s determination that the project is economically and operationally feasible, management and/or the Exelon board of directors has approved the project and has committed to a plan to develop it, and Exelon and Generation have received the required regulatory approvals or management believes the receipt of required regulatory approvals is probable. Capitalized development costs are charged to Operating and maintenance expense when project completion is no longer probable. New site development costs incurred prior to a project’s completion being deemed probable are expensed as incurred. Approximately $22 million , $13 million and $10 million of costs were expensed by Exelon and Generation for the years ended December 31, 2015 , 2014 , and 2013 , respectively. These costs are related to the possible development of new power generating facilities.
Capitalized Software Costs (Exelon, Generation, ComEd, PECO and BGE)	Capitalized Software Costs (Exelon, Generation, ComEd, PECO and BGE) Costs incurred during the application development stage of software projects that are internally developed or purchased for operational use are capitalized within property, plant, and equipment. Such capitalized amounts are amortized ratably over the expected lives of the projects when they become operational, generally not to exceed five years. Certain other capitalized software costs are being amortized over longer lives based on the expected life or pursuant to prescribed regulatory requirements
Depreciation, Depletion, and Amortization (Exelon, Generation, ComEd, PECO and BGE)	Depreciation, Depletion and Amortization (Exelon, Generation, ComEd, PECO and BGE) Except for the amortization of nuclear fuel, depreciation is generally recorded over the estimated service lives of property, plant and equipment on a straight-line basis using the composite method. ComEd’s and BGE’s depreciation includes a provision for estimated removal costs as authorized by the respective regulators. The estimated service lives for ComEd, PECO and BGE are primarily based on the average service lives from the most recent depreciation study for each respective company. The estimated service lives of the nuclear-fuel generating facilities are based on the remaining useful lives of the stations, which assume a 20 -year license renewal extension of the operating licenses (to the extent that such renewal has not yet been granted) for all of Generation’s operating nuclear generating stations except for Oyster Creek. The estimated service lives of the hydroelectric generating facilities are based on the remaining useful lives of the stations, which assume a license renewal extension of the operating licenses. The estimated service lives of the fossil fuel and other renewable generating facilities are based on the remaining useful lives of the stations, which Generation periodically evaluates based on feasibility assessments taking into account economic and capital requirement considerations. See Note 7 — Property, Plant and Equipment for further information regarding depreciation. Depletion of oil and gas exploration and production activities is recorded using the units-of-production method over the remaining life of the estimated proved reserves at the field level for acquisition costs and over the remaining life of proved developed reserves at the field level for development costs. The estimates for oil and gas reserves are based on internal calculations. Amortization of regulatory assets and liabilities are recorded over the recovery or refund period specified in the related legislation or regulatory agreement. When the recovery or refund period is less than one year, amortization is recorded to the line item in which the deferred cost or income would have originally been recorded in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Amortization of ComEd’s distribution formula rate regulatory asset and ComEd’s and BGE’s transmission formula rate regulatory assets is recorded to Operating revenues. Amortization of income tax related regulatory assets and liabilities is generally recorded to Income tax expense. With the exception of the regulatory assets and liabilities discussed above, when the recovery period is more than one year, the amortization is generally recorded to Depreciation and amortization in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 3 — Regulatory Matters and Note 24 — Supplemental Financial Information for additional information regarding Generation’s nuclear fuel, Generation’s ARC and the amortization of ComEd’s, PECO’s and BGE’s regulatory assets.
Asset Retirement Obligations (Exelon, Generation, ComEd, PECO and BGE)	Asset Retirement Obligations (Exelon, Generation, ComEd, PECO and BGE) The authoritative guidance for accounting for AROs requires the recognition of a liability for a legal obligation to perform an asset retirement activity even though the timing and/or method of settlement may be conditional on a future event. To estimate its decommissioning obligation related to its nuclear generating stations, Generation uses a probability-weighted, discounted cash flow model which, on a unit-by-unit basis, considers multiple outcome scenarios that include significant estimates and assumptions, and are based on decommissioning cost studies, cost escalation rates, probabilistic cash flow models and discount rates. Generation generally updates its ARO annually during the third quarter, unless circumstances warrant more frequent updates, based on its review of updated cost studies and its annual evaluation of cost escalation factors and probabilities assigned to various scenarios. Decommissioning cost studies are updated, on a rotational basis, for each of Generation’s nuclear units at least every five years unless circumstances warrant more frequent updates (such as a change in assumed operating life for a nuclear plant). As part of the annual cost study update process, Generation evaluates newly assumed costs or substantive changes in previously assumed costs to determine if the cost estimate impacts are sufficiently material to warrant application of the updated estimates to the AROs across the nuclear fleet outside of the normal five-year rotating cost study update cycle. The liabilities associated with Exelon’s non-nuclear AROs are adjusted on an ongoing rotational basis, at least once every five years. Changes to the recorded value of an ARO result from the passage of new laws and regulations, revisions to either the timing or amount of estimates of undiscounted cash flows, and estimates of cost escalation factors. AROs are accreted throughout each year to reflect the time value of money for these present value obligations through a charge to Operating and maintenance expense in the Consolidated Statements of Operations and Comprehensive Income or, in the case of the majority of ComEd’s, PECO’s, and BGE’s accretion, through an increase to regulatory assets. See Note 16 — Asset Retirement Obligations for additional information.
Capitalized Interest (Exelon, Generation, ComEd, PECO and BGE)	Capitalized Interest and AFUDC (Exelon, Generation, ComEd, PECO and BGE) During construction, Exelon and Generation capitalize the costs of debt funds used to finance non-regulated construction projects. Capitalization of debt funds is recorded as a charge to construction work in progress and as a non-cash credit to interest expense.
Allowance For Funds Used During Construction (Exelon, Generation, ComEd, PECO and BGE)	Exelon, ComEd, PECO and BGE apply the authoritative guidance for accounting for certain types of regulation to calculate AFUDC, which is the cost, during the period of construction, of debt and equity funds used to finance construction projects for regulated operations. AFUDC is recorded to construction work in progress and as a non-cash credit to AFUDC that is included in interest expense for debt-related funds and other income and deductions for equity-related funds. The rates used for capitalizing AFUDC are computed under a method prescribed by regulatory authorities.
Guarantees (Exelon, Generation, ComEd, PECO and BGE)	Guarantees (Exelon, Generation, ComEd, PECO and BGE) The Registrants recognize, at the inception of a guarantee, a liability for the fair market value of the obligations they have undertaken by issuing the guarantee, including the ongoing obligation to perform over the term of the guarantee in the event that the specified triggering events or conditions occur. The liability that is initially recognized at the inception of the guarantee is reduced as the Registrants are released from risk under the guarantee. Depending on the nature of the guarantee, the release from risk of the Registrant may be recognized only upon the expiration or settlement of the guarantee or by a systematic and rational amortization method over the term of the guarantee. See Note 23 — Commitments and Contingencies for additional information.
Long-lived Assets (Exelon, Generation, ComEd, PECO and BGE)	Long-Lived Assets. The Registrants evaluate the carrying value of their long-lived assets or asset groups, excluding goodwill, when circumstances indicate the carrying value of those assets may not be recoverable. Indicators of impairment may include a deteriorating business climate, including, but not limited to, declines in energy prices, condition of the asset, specific regulatory disallowance, or plans to dispose of a long-lived asset significantly before the end of its useful life. The Registrants determine if long-lived assets and asset groups are impaired by comparing the undiscounted expected future cash flows to the carrying value. When the undiscounted cash flow analysis indicates a long-lived asset or asset group is not recoverable, the amount of the impairment loss is determined by measuring the excess of the carrying amount of the long-lived asset or asset group over its fair value less costs to sell. Cash flows for long-lived assets and asset groups are determined at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities. The cash flows from the generating units are generally evaluated at a regional portfolio level along with cash flows generated from the customer supply and risk management activities, including cash flows from related intangible assets and liabilities on the balance sheet. In certain cases, generating assets may be evaluated on an individual basis where those assets are contracted on a long-term basis with a third party and operations are independent of other generation assets (typically contracted renewables). See Note 8 — Impairment of Long-Lived Assets for additional information.
Goodwill (Exelon, Generation, ComEd, PECO and BGE)	Goodwill. Goodwill represents the excess of the purchase price paid over the estimated fair value of the assets acquired and liabilities assumed in the acquisition of a business. Goodwill is not amortized, but is tested for impairment at least annually or on an interim basis if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying value. See Note 11 — Intangible Assets for additional information regarding Exelon’s, Generation's and ComEd’s goodwill.
Equity Method Investments (Exelon, Generation, ComEd, PECO and BGE)	Equity Method Investments. Exelon and Generation regularly monitor and evaluate equity method investments to determine whether they are impaired. An impairment is recorded when the investment has experienced a decline in value that is other-than-temporary in nature. Additionally, if the project in which Generation holds an investment recognizes an impairment loss, Exelon and Generation would record their proportionate share of that impairment loss and evaluate the investment for an other-than-temporary decline in value. Equity Investment Earnings (Losses) of Unconsolidated Affiliates (Exelon and Generation) Exelon and Generation include equity in earnings from equity method investments in qualifying facilities, power projects and joint ventures, in equity in earnings (losses) of unconsolidated affiliates within their Consolidated Statements of Operations and Comprehensive Income. Equity in earnings (losses) of unconsolidated affiliates also includes any adjustments to amortize the difference, if any, except for goodwill and land, between their cost in an equity method investment and the underlying equity in net assets of the investee at the date of investment. Exelon and Generation continuously monitor for issues that potentially could impact future profitability of these equity method investments and which could result in the recognition of an impairment loss if such investment experiences an other-than-temporary decline in value.
Direct Financing Lease Investments (Exelon, Generation, ComEd, PECO and BGE)	Direct Financing Lease Investments. Direct financing lease investments represent the estimated residual values of leased coal-fired plants in Georgia. Exelon reviews the estimated residual values of its direct financing lease investments and records an impairment charge if the review indicates an other-than-temporary decline in the fair value of the residual values below their carrying values. See Note 8 — Impairment of Long-Lived Assets for additional information.
Derivatives Financial Instruments (Exelon, Generation, ComEd, PECO and BGE)	Derivative Financial Instruments (Exelon, Generation, ComEd, PECO and BGE) All derivatives are recognized on the balance sheet at their fair value unless they qualify for certain exceptions, including the normal purchases and normal sales exception. Additionally, derivatives that qualify and are designated for hedge accounting are classified as either hedges of the fair value of a recognized asset or liability or of an unrecognized firm commitment (fair value hedge) or hedges of a forecasted transaction or the variability of cash flows to be received or paid related to a recognized asset or liability (cash flow hedge). For fair value hedges, changes in fair values for both the derivative and the underlying hedged exposure are recognized in earnings each period. For cash flow hedges, the portion of the derivative gain or loss that is effective in offsetting the change in the cost or value of the underlying exposure is deferred in accumulated OCI and later reclassified into earnings when the underlying transaction occurs. Gains and losses from the ineffective portion of any hedge are recognized in earnings immediately. For derivative contracts intended to serve as economic hedges and that are not designated or do not qualify for hedge accounting or the normal purchases and normal sales exception, changes in the fair value of the derivatives are recognized in earnings each period. Amounts classified in earnings are included in revenue, purchased power and fuel, interest expense or other, net on the Consolidated Statement of Operations based on the activity the transaction is economically hedging. For energy-related derivatives entered into for proprietary trading purposes, which are subject to Exelon’s Risk Management Policy, changes in the fair value of the derivatives are recognized in earnings each period. All amounts classified in earnings related to proprietary trading are included in revenue on the Consolidated Statement of Operations. Cash inflows and outflows related to derivative instruments are included as a component of operating, investing or financing cash flows in the Consolidated Statements of Cash Flows, depending on the nature of each transaction. For commodity derivative contracts Generation no longer utilizes the election provided for by the cash flow hedge designation and de-designated all of its existing cash flow hedges prior to the Constellation merger. Because the underlying forecasted transactions remained probable, the fair value of the effective portion of these cash flow hedges was frozen in accumulated OCI and was reclassified to results of operations when the forecasted purchase or sale of the energy commodity occurred through March 31, 2015. The effect of this decision is that all derivatives executed to hedge economic risk related to commodities are recorded at fair value with changes in fair value recognized through earnings for the combined company. As part of Generation’s energy marketing business, Generation enters into contracts to buy and sell energy to meet the requirements of its customers. These contracts include short-term and long-term commitments to purchase and sell energy and energy-related products in the energy markets with the intent and ability to deliver or take delivery of the underlying physical commodity. Normal purchases and normal sales are contracts where physical delivery is probable, quantities are expected to be used or sold in the normal course of business over a reasonable period of time and will not be financially settled. Revenues and expenses on derivative contracts that qualify, and are designated, as normal purchases and normal sales are recognized when the underlying physical transaction is completed. While these contracts are considered derivative financial instruments, they are not required to be recorded at fair value, but rather are recorded on an accrual basis of accounting. See Note 13 — Derivative Financial Instruments for additional information.
Retirement Benefits (Exelon, Generation, ComEd, PECO and BGE)	Retirement Benefits (Exelon, Generation, ComEd, PECO and BGE) Exelon sponsors defined benefit pension plans and other postretirement benefit plans for essentially all Generation, ComEd, PECO, BGE and BSC employees. The measurement of the plan obligations and costs of providing benefits under these plans involve various factors, including numerous assumptions and accounting elections. The assumptions are reviewed annually and at any interim remeasurement of the plan obligations. The impact of assumption changes or experience different from that assumed on pension and other postretirement benefit obligations is recognized over time rather than immediately recognized in the income statement. Gains or losses in excess of the greater of ten percent of the projected benefit obligation or the MRV of plan assets are amortized over the expected average remaining service period of plan participants. See Note 17 — Retirement Benefits for additional discussion of Exelon’s accounting for retirement benefits.
Investment, Policy [Policy Text Block]	Debt and Equity Security Investments. Exelon and Generation regularly monitor and evaluate debt and equity investments to determine whether they are impaired. An impairment is recorded when the investment has experienced a decline in value that is other-than-temporary in nature. Equity Investment Earnings (Losses) of Unconsolidated Affiliates (Exelon and Generation) Exelon and Generation include equity in earnings from equity method investments in qualifying facilities, power projects and joint ventures, in equity in earnings (losses) of unconsolidated affiliates within their Consolidated Statements of Operations and Comprehensive Income. Equity in earnings (losses) of unconsolidated affiliates also includes any adjustments to amortize the difference, if any, except for goodwill and land, between their cost in an equity method investment and the underlying equity in net assets of the investee at the date of investment. Exelon and Generation continuously monitor for issues that potentially could impact future profitability of these equity method investments and which could result in the recognition of an impairment loss if such investment experiences an other-than-temporary decline in value.
New Accounting Pronouncements (Exelon, Generation, ComEd, PECO and BGE)	New Accounting Pronouncements (Exelon, Generation, ComEd, PECO and BGE) Exelon has identified the following new accounting standards that have been recently adopted that management believes may significantly affect the Registrants. Balance Sheet Classification of Deferred Taxes In November 2015, the FASB issued authoritative guidance that requires deferred tax assets and deferred tax liabilities to be classified as noncurrent in a classified statement of financial position. The guidance is effective for periods beginning after December 15, 2016, with early adoption permitted. The guidance can be applied either prospectively or retrospectively. The Registrants early adopted the standard retrospectively in the fourth quarter of 2015, resulting in the following impacts as of December 31, 2014 in the Consolidated Balance Sheets of the Registrants: For the year ended December 31, 2014 Exelon Generation ComEd PECO BGE Increase (Decrease) Current assets - Deferred income taxes $ (244 ) $ (327 ) $ — $ (69 ) $ (6 ) Deferred debits and other assets - Other 3 — — — — Current liabilities - Deferred income taxes — — (63 ) — (52 ) Deferred credits and other liabilities - Deferred income taxes (241 ) (327 ) 63 (69 ) 46 The adoption of this guidance had no impact on the Registrants’ Consolidated Statements of Operations and Comprehensive Income and Consolidated Statements of Cash Flows. Simplifying the Accounting for Measurement-Period Adjustments In September 2015, the FASB issued authoritative guidance that requires an acquirer in a business combination to recognize adjustments to provisional amounts that are identified during the measurement period in the reporting period in which the adjustment amounts are determined and to record, in the same period’s financial statements, the effect on earnings of changes in depreciation, amortization, or other income effects, if any, as a result of the change to the provisional amounts, calculated as if the accounting had been completed at the acquisition date. Under current guidance, such effects would be retrospectively recorded in prior periods. The guidance is effective for periods beginning after December 15, 2015. The guidance is required to be applied prospectively to adjustments to provisional amounts that occur after the effective date with earlier application permitted for financial statements that have not been issued. The Registrants early adopted the standard in the fourth quarter of 2015. The adoption of this guidance had no impact on the Registrants’ Consolidated Balance Sheets, Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows and disclosures. Application of Normal Purchases Normal Sales Exception to Power Contracts in Nodal Energy Markets In August 2015, the FASB issued authoritative guidance addressing the ability of entities to elect the normal purchase normal sales (NPNS) scope exception when the contract for the purchase or sale of electricity on a forward basis is delivered to a nodal energy market or transmitted through a nodal energy market. The NPNS scope exception allows entities to treat certain contracts that qualify as derivatives as contracts that do not require recognition at fair value. The guidance specifies that the use of locational marginal pricing by an independent system operator in such transactions does not constitute net settlement of a contract for the purchase or sale of electricity, even in scenarios in which legal title to the associated electricity is conveyed to the independent system operator during transmission. Consequently, the use of locational marginal pricing by the independent system operator does not cause that contract to fail to meet the physical delivery criterion of the NPNS scope exception. Consistent with the Registrants' current practice, if the physical delivery criterion is met, along with all of the other criteria of the NPNS scope exception, an entity may elect to designate that contract as NPNS. The guidance is effective upon issuance and should be applied prospectively. The adoption of this guidance had no impact on the Registrants’ Consolidated Balance Sheets, Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows and disclosures. Simplifying the Presentation of Debt Issuance Costs In April 2015, the FASB issued authoritative guidance that changes the presentation of debt issuance costs in financial statements. The new guidance requires entities to present such costs in the balance sheet as a direct reduction to the related debt liability rather than as a deferred cost (i.e., an asset) as required by current guidance. The new guidance does not change the recognition or measurement of debt issuance costs. The guidance is effective for the Registrants for fiscal years beginning after December 15, 2015. Early adoption is permitted for financial statements that have not been previously issued. The guidance is required to be applied retrospectively to all prior periods presented. The Registrants early adopted the standard retrospectively in the fourth quarter of 2015. The adoption of this guidance resulted in a reclassification of $157 million , $70 million , $34 million , $14 million , and $16 million as of December 31, 2014, from Other long-term assets to Long-term debt, including Long-term debt to financing trusts, in the Consolidated Balance Sheets of Exelon, Generation, ComEd, PECO and BGE, respectively. The standard did not impact the Consolidated Statements of Operations and Comprehensive Income and Consolidated Statements of Cash Flows of the Registrants. In August 2015, the FASB issued clarifying authoritative guidance for debt issuance costs incurred in connection with line-of-credit arrangements. The guidance states that an entity should defer and present debt issuance costs as an asset and subsequently amortize the deferred debt issuance costs ratably over the term of the line-of-credit arrangement. The adoption of this guidance had no impact on the Registrants’ Consolidated Balance Sheets, Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows and disclosures. The following recently issued accounting standards are not yet required to be reflected in the combined financial statements of the Registrants. Recognition and Measurement of Financial Assets and Financial Liabilities In January 2016, the FASB issued authoritative guidance which (i) requires all investments in equity securities, including other ownership interests such as partnerships, unincorporated joint ventures and limited liability companies, to be carried at fair value through net income, (ii) requires an incremental recognition and disclosure requirement related to the presentation of fair value changes of financial liabilities for which the fair value option has been elected, (iii) amends several disclosure requirements, including the methods and significant assumptions used to estimate fair value or a description of the changes in the methods and assumptions used to estimate fair value, and (iv) requires disclosure of the fair value of financial assets and liabilities measured at amortized cost at the amount that would be received to sell the asset or paid to transfer the liability. The standard is effective for fiscal years beginning after December 15, 2017 with early adoption permitted. The guidance is required to be applied retrospectively with a cumulative effect adjustment to retained earnings for initial application of the guidance at the date of adoption (modified retrospective method). The Registrants are currently assessing the impacts this guidance may have on their Consolidated Balance Sheets, Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows and disclosures as well as the potential to early adopt the guidance. Simplifying the Measurement of Inventory In July 2015, the FASB issued authoritative guidance that requires inventory to be measured at the lower of cost or net realizable value. The new guidance defines net realizable value as the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. This definition is consistent with existing authoritative guidance. Current guidance requires inventory to be measured at the lower of cost or market where market could be replacement cost, net realizable value or net realizable value less an approximately normal profit margin. The guidance is effective for periods beginning after December 15, 2016 with early adoption permitted. The guidance is required to be applied prospectively. The Registrants do not expect that this guidance will have a significant impact on their Consolidated Balance Sheets, Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows and disclosures. The Registrants are currently assessing the potential to early adopt the guidance. Disclosures for Investments in Certain Entities that Calculate Net Asset Value per Share In May 2015, FASB issued authoritative guidance that removes the requirement to categorize within the fair value hierarchy all investments for which fair value is measured using the net asset value per share practical expedient. Investments measured at net asset value per share using the practical expedient will be presented as a reconciling item between the fair value hierarchy disclosure and the investment line item on the statement of financial position. The guidance also removes the requirement to make certain disclosures for all investments that are eligible to be measured at fair value using the net asset value per share practical expedient. Rather, those disclosures are limited to investments for which the entity has elected to measure the fair value using the practical expedient. The guidance is effective for the Registrants for fiscal years beginning after December 15, 2015 with early adoption permitted. The guidance is required to be applied retrospectively to all prior periods presented. The Registrants are currently assessing the impacts this guidance may have on their disclosures. There will be no impact to the Registrants' Consolidated Balance Sheets, Consolidated Statements of Operations and Comprehensive Income and Consolidated Statements of Cash Flows. Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement In April 2015, the FASB issued authoritative guidance that clarifies the circumstances under which a cloud computing customer would account for the arrangement as a license of internal-use software. A cloud computing arrangement would include a software license if (1) the customer has a contractual right to take possession of the software at any time during the hosting period without significant penalty and (2) it is feasible for the customer to either run the software on its own hardware or contract with another party unrelated to the vendor to host the software. If the arrangement does not contain a software license, it would be accounted for as a service contract. Beginning January 1, 2016, the Registrants will apply the standard prospectively and do not expect that this guidance will have a significant impact on their Consolidated Balance Sheets, Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows and disclosures. Amendments to the Consolidation Analysis In February 2015, the FASB issued authoritative guidance that amends the consolidation analysis for variable interest entities (VIEs) as well as voting interest entities. The new guidance primarily (1) changes the assessment of limited partnerships as VIEs, (2) amends the effect that fees paid to a decision maker or service provider have on the VIE analysis, (3) amends how variable interests held by a reporting entity’s related parties and de facto agents impact its consolidation conclusion, (4) clarifies how to determine whether equity holders (as a group) have power over an entity, and (5) provides a scope exception for registered and similar unregistered money market funds. The guidance is effective for the Registrants for the first interim period beginning on or after December 15, 2015. The guidance can be applied retrospectively to each prior reporting period presented (full retrospective method) or retrospectively with a cumulative effect adjustment to retained earnings for initial application of the guidance at the date of adoption (modified retrospective method). The Registrants are in the process of evaluating the standard and have not identified any changes to consolidation conclusions as a result of the new guidance and therefore have not elected an adoption method. Based on the analysis completed to date, a limited number of additional entities will be considered variable interest entities when the guidance is adopted, and required disclosures will be included in the Variable Interest Entities footnote. Revenue from Contracts with Customers In May 2014, the FASB issued authoritative guidance that changes the criteria for recognizing revenue from a contract with a customer. The new standard replaces existing guidance on revenue recognition, including most industry specific guidance, with a five step model for recognizing and measuring revenue from contracts with customers. The objective of the new standard is to provide a single, comprehensive revenue recognition model for all contracts with customers to improve comparability within industries, across industries and across capital markets. The underlying principle is that an entity will recognize revenue to depict the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. The guidance also requires a number of disclosures regarding the nature, amount, timing and uncertainty of revenue and the related cash flows. The guidance can be applied retrospectively to each prior reporting period presented (full retrospective method) or retrospectively with a cumulative effect adjustment to retained earnings for initial application of the guidance at the date of initial adoption (modified retrospective method). The Registrants are currently assessing the impacts this guidance may have on their Consolidated Balance Sheets, Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows and disclosures as well as the transition method that they will use to adopt the guidance. Exelon is considering the impacts of the new guidance on our ability to recognize revenue for certain contracts where collectability is in question, our accounting for contributions in aid of construction, bundled sales contracts and contracts with pricing provisions that may require us to recognize revenue at prices other than the contract price (e.g., straight line or forward curve). In addition, the Registrants will be required to capitalize costs to acquire new contracts, whereas Exelon currently expenses those costs as incurred. In August 2015, the FASB issued an amendment to provide a one year deferral of the effective date to annual reporting periods beginning on or after December 15, 2017, as well as an option to early adopt the standard for annual periods beginning on or after December 15, 2016. The Registrants do not plan to early adopt the standard.

Significant Accounting Polici39

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Schedule Of Capitalized Software	The following table presents net unamortized capitalized software costs and amortization of capitalized software costs by year: Net unamortized software costs Exelon Generation ComEd PECO BGE December 31, 2015 $ 633 $ 180 $ 172 $ 86 $ 178 December 31, 2014 596 193 133 84 163 Amortization of capitalized software costs Exelon Generation ComEd PECO BGE 2015 $ 208 $ 73 $ 47 $ 33 $ 46 2014 186 59 45 28 43 2013 198 67 52 33 36
Schedule Of Capitalized Interest And AFUDC	The following table summarizes total incurred interest, capitalized interest and credits to AFUDC by year: Exelon (a) Generation (a) ComEd PECO BGE 2015 Total incurred interest (b) $ 1,170 $ 445 $ 336 $ 116 $ 113 Capitalized interest 79 79 — — — Credits to AFUDC debt and equity 44 — 9 7 28 2014 Total incurred interest (b) $ 1,144 $ 419 $ 323 $ 115 $ 118 Capitalized interest 63 63 — — — Credits to AFUDC debt and equity 37 — 5 8 24 2013 Total incurred interest (b) $ 1,423 $ 411 $ 584 $ 117 $ 129 Capitalized interest 54 54 — — — Credits to AFUDC debt and equity 35 — 16 6 13 _______________________ (a) On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, the 2014 financial results include CENG’s financial position and results of operations beginning April 1, 2014. (b) Includes interest expense to affiliates.
New Accounting Pronouncement, Early Adoption [Table Text Block]	The Registrants early adopted the standard retrospectively in the fourth quarter of 2015, resulting in the following impacts as of December 31, 2014 in the Consolidated Balance Sheets of the Registrants: For the year ended December 31, 2014 Exelon Generation ComEd PECO BGE Increase (Decrease) Current assets - Deferred income taxes $ (244 ) $ (327 ) $ — $ (69 ) $ (6 ) Deferred debits and other assets - Other 3 — — — — Current liabilities - Deferred income taxes — — (63 ) — (52 ) Deferred credits and other liabilities - Deferred income taxes (241 ) (327 ) 63 (69 ) 46

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	12 Months Ended
	Dec. 31, 2015
Variable Interest Entity [Abstract]
Schedule of Variable Interest Entities	As of December 31, 2015 and 2014 , these assets and liabilities primarily consisted of the following: December 31, 2015 December 31, 2014 (a) Exelon Generation BGE Exelon Generation BGE Cash and cash equivalents $ 164 $ 164 $ — $ 392 $ 392 $ — Restricted cash 100 77 23 117 96 21 Accounts receivable, net Customer 219 219 — 297 297 — Other 43 43 — 57 57 — Mark-to-market derivatives assets 140 140 — 171 171 — Inventory Materials and supplies 181 181 — 172 172 — Other current assets 35 30 — 37 30 — Total current assets 882 854 23 1,243 1,215 21 Property, plant and equipment, net 5,160 5,160 — 4,638 4,638 — Nuclear decommissioning trust funds 2,036 2,036 — 2,097 2,097 — Goodwill 47 47 — 47 47 — Mark-to-market derivatives assets 53 53 — 44 44 — Other noncurrent assets 90 85 3 90 77 3 Total noncurrent assets 7,386 7,381 3 6,916 6,903 3 Total assets $ 8,268 $ 8,235 $ 26 $ 8,159 $ 8,118 $ 24 Long-term debt due within one year $ 111 $ 27 $ 79 $ 87 $ 5 $ 75 Accounts payable 216 216 — 292 292 — Accrued expenses 115 113 2 111 108 2 Mark-to-market derivative liabilities 5 5 — 24 24 — Unamortized energy contract liabilities 12 12 — 22 22 — Other current liabilities 13 13 — 25 25 — Total current liabilities 472 386 81 561 476 77 Long-term debt 666 623 41 212 81 120 Asset retirement obligations 1,999 1,999 — 1,763 1,763 — Pension obligation (b) 9 9 — 9 9 — Unamortized energy contract liabilities 39 39 — 51 51 — Other noncurrent liabilities 79 79 — 132 132 — Noncurrent liabilities 2,792 2,749 41 2,167 2,036 120 Total liabilities $ 3,264 $ 3,135 $ 122 $ 2,728 $ 2,512 $ 197 ___________ (a) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to classification of deferred taxes and simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. (b) Includes the CNEG retail gas pension obligation, which is presented as a net asset balance within the Prepaid pension asset line item on Generation’s balance sheet. See Note 17 — Retirement Benefits for additional details. The following tables present summary information about Exelon and Generation’s significant unconsolidated VIE entities: December 31, 2015 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 263 $ 164 $ 427 Total liabilities (a) 22 125 147 Exelon's ownership interest in VIE (a) — 11 11 Other ownership interests in VIE (a) 241 28 269 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 21 21 Contract intangible asset 9 — 9 Debt and payment guarantees — 3 3 Net assets pledged for Zion Station decommissioning (b) 17 — 17 December 31, 2014 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 114 $ 91 $ 205 Total liabilities (a) 3 49 52 Exelon's ownership interest in VIE (a) — 9 9 Other ownership interests in VIE (a) 111 33 144 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 13 13 Contract intangible asset 9 — 9 Debt and payment guarantees — 3 3 Net assets pledged for Zion Station decommissioning (b) 27 — 27 ___________________ (a) These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs. Exelon corrected an error in the December 31, 2014 balances within Commercial Agreement VIEs for an overstatement of Total assets, Total liabilities and Other ownership interests in VIE of $ 392 million , $ 234 million and $ 158 million , respectively. The error is not considered material to any prior period. (b) These items represent amounts on Exelon’s and Generation’s Consolidated Balance Sheets related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning includes gross pledged assets of $206 million and $319 million as of December 31, 2015 and December 31, 2014 , respectively; offset by payables to ZionSolutions LLC of $189 million and $292 million as of December 31, 2015 and December 31, 2014 , respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE. The carrying amounts and classification of the consolidated VIEs’ assets and liabilities included in the Registrants’ consolidated financial statements at December 31, 2015 and 2014 are as follows: December 31, 2015 December 31, 2014 (a) Exelon (b) Generation BGE Exelon (b) Generation BGE Current assets $ 909 $ 881 $ 23 $ 1,275 $ 1,247 $ 21 Noncurrent assets 8,009 8,004 3 7,573 7,560 3 Total assets $ 8,918 $ 8,885 $ 26 $ 8,848 $ 8,807 $ 24 Current liabilities $ 473 $ 387 $ 81 $ 611 $ 526 $ 77 Noncurrent liabilities 2,927 2,884 41 2,728 2,597 120 Total liabilities $ 3,400 $ 3,271 $ 122 $ 3,339 $ 3,123 $ 197 _______________________ (a) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to classification of deferred taxes and simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. (b) Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2015
Regulated Operations [Abstract]
Public Utilities General Disclosures [Table Text Block]	For each of the following years, the ICC approved the following total increases/(decreases) in ComEd's electric distributions formula rate filings: Annual Distribution Filings 2015 2014 2013 ComEd's requested total revenue requirement (decrease) increase $ (50 ) $ 269 $ 353 Final ICC Order Initial revenue requirement increase $ 85 $ 160 $ 160 Annual reconciliation (decrease) increase (152 ) 72 181 Total revenue requirement (decrease) increase $ (67 ) $ 232 $ 341 Allowed Return on Rate Base: Initial revenue requirement 7.05 % 7.06 % 6.94 % Annual reconciliation 7.02 % 7.04 % 6.94 % Allowed ROE: Initial revenue requirement 9.14 % (a) 9.25 % (a) 8.72 % Annual reconciliation 9.09 % (a) 9.20 % (a) 8.72 % Effective date of rates January 2016 January 2015 January 2014 __________________ (a) Includes a reduction of 5 basis points for a reliability performance metric penalty. For each of the following years, the following total increases/(decreases) were included in ComEd's and BGE's electric transmission formula rate filings: ComEd BGE Annual Transmission Filings 2015 2014 2013 2015 2014 2013 Initial revenue requirement increase (a) $ 68 $ 36 $ 38 $ — $ 9 $ 2 Annual reconciliation (decrease) increase 18 (14 ) 30 (3 ) 5 (3 ) Total revenue requirement increase $ 86 $ 22 $ 68 $ (3 ) $ 14 $ (1 ) Allowed return on rate base (b) 8.61 % 8.62 % 8.7 % 8.46 % 8.53 % 8.35 % Allowed ROE 11.5 % 11.5 % 11.5 % 11.3 % 11.3 % 11.3 % Effective date of rates (c) June 2015 June 2014 June 2013 June 2015 June 2014 June 2013 _____________ (a) For BGE, this excludes the increase in revenue requirement associated with dedicated facilities charges. The increases for dedicated facilities were $13 million and $3 million for 2015 and 2014, respectively. There were no dedicated facilities charges in 2013 for BGE. (b) Refers to the weighted average debt and equity return on transmission rate bases for ComEd and BGE. As part of the FERC-approved settlement of ComEd’s 2007 transmission rate case, the rate of return on common equity is 11.50% and the common equity component of the ratio used to calculate the weighted average debt and equity return for the transmission formula rate is currently capped at 55%. As part of the FERC-approved settlement of BGE's 2005 transmission rate case, the rate of return on common equity is 11.30%, inclusive of a 50 basis point incentive for participating in PJM. (c) The time period for any challenges to the annual transmission formula rate update filings expired with no challenges submitted.
Regulatory Construction Commitment	ComEd, PECO and BGE will work with PJM to continue to evaluate the scope and timing of any required construction projects. ComEd, PECO and BGE’s estimated commitments are as follows: Total 2016 2017 2018 2019 2020 ComEd $ 297 $ 204 $ 61 $ 26 $ 6 $ — PECO 67 31 24 8 4 — BGE 373 140 112 62 46 13
Schedule of Regulatory Assets	December 31, 2015 Exelon ComEd PECO BGE Regulatory assets Pension and other postretirement benefits $ 3,156 $ — $ — $ — Deferred income taxes 1,616 64 1,473 79 AMI programs 399 140 63 196 Under-recovered distribution service costs 189 189 — — Debt costs 47 46 1 8 Fair value of BGE long-term debt 162 — — — Severance 9 — — 9 Asset retirement obligations 108 67 22 19 MGP remediation costs 286 255 30 1 Under-recovered uncollectible accounts 52 52 — — Renewable energy 247 247 — — Energy and transmission programs 84 43 1 40 Deferred storm costs 2 — — 2 Electric generation-related regulatory asset 20 — — 20 Rate stabilization deferral 87 — — 87 Energy efficiency and demand response programs 279 — 1 278 Merger integration costs 6 — — 6 Conservation voltage reduction 3 — — 3 Under-recovered revenue decoupling 30 — — 30 CAP arrearage 7 — 7 — Other 35 10 19 3 Total regulatory assets 6,824 1,113 1,617 781 Less: current portion 759 218 34 267 Total noncurrent regulatory assets $ 6,065 $ 895 $ 1,583 $ 514 The following tables provide information about the regulatory assets and liabilities of Exelon, ComEd, PECO and BGE as of December 31, 2015 and 2014. December 31, 2015 Exelon ComEd PECO BGE Regulatory assets Pension and other postretirement benefits $ 3,156 $ — $ — $ — Deferred income taxes 1,616 64 1,473 79 AMI programs 399 140 63 196 Under-recovered distribution service costs 189 189 — — Debt costs 47 46 1 8 Fair value of BGE long-term debt 162 — — — Severance 9 — — 9 Asset retirement obligations 108 67 22 19 MGP remediation costs 286 255 30 1 Under-recovered uncollectible accounts 52 52 — — Renewable energy 247 247 — — Energy and transmission programs 84 43 1 40 Deferred storm costs 2 — — 2 Electric generation-related regulatory asset 20 — — 20 Rate stabilization deferral 87 — — 87 Energy efficiency and demand response programs 279 — 1 278 Merger integration costs 6 — — 6 Conservation voltage reduction 3 — — 3 Under-recovered revenue decoupling 30 — — 30 CAP arrearage 7 — 7 — Other 35 10 19 3 Total regulatory assets 6,824 1,113 1,617 781 Less: current portion 759 218 34 267 Total noncurrent regulatory assets $ 6,065 $ 895 $ 1,583 $ 514
Schedule of Regulatory Liabilities	December 31, 2015 Exelon ComEd PECO BGE Regulatory liabilities Other postretirement benefits $ 94 $ — $ — $ — Nuclear decommissioning 2,577 2,172 405 — Removal costs 1,527 1,332 — 195 Energy efficiency and demand response programs 92 52 40 — DLC program costs 9 — 9 — Electric distribution tax repairs 95 — 95 — Gas distribution tax repairs 28 — 28 — Energy and transmission programs 131 53 60 18 Over-recovered revenue decoupling 1 — — 1 Other 16 5 2 8 Total regulatory liabilities 4,570 3,614 639 222 Less: current portion 369 155 112 38 Total noncurrent regulatory liabilities $ 4,201 $ 3,459 $ 527 $ 184
Purchase Of Receivables	The following tables provide information about the purchased receivables of the Registrants as of December 31, 2015 and 2014 . As of December 31, 2015 Exelon ComEd PECO BGE Purchased receivables (a) $ 229 $ 103 $ 67 $ 59 Allowance for uncollectible accounts (b) (31 ) (16 ) (7 ) (8 ) Purchased receivables, net $ 198 $ 87 $ 60 $ 51 As of December 31, 2014 Exelon ComEd PECO BGE Purchased receivables (a) $ 290 $ 139 $ 76 $ 75 Allowance for uncollectible accounts (b) (42 ) (21 ) (8 ) (13 ) Purchased receivables, net $ 248 $ 118 $ 68 $ 62 _________________________ (a) PECO’s gas POR program became effective on January 1, 2012 and includes a 1% discount on purchased receivables in order to recover the implementation costs of the program. The implementation costs were fully recovered and the 1% discount was reset to 0%, effective July 2015. (b) For ComEd and BGE, reflects the incremental allowance for uncollectible accounts recorded, which is in addition to the purchase discount. For ComEd, the incremental uncollectible accounts expense is recovered through its Purchase of Receivables with Consolidated Billing (PORCB) tariff.
Schedule of Public Utilities Genera Disclosures [Table Text Block]	ComEd BGE Annual Transmission Filings 2015 2014 2013 2015 2014 2013 Initial revenue requirement increase (a) $ 68 $ 36 $ 38 $ — $ 9 $ 2 Annual reconciliation (decrease) increase 18 (14 ) 30 (3 ) 5 (3 ) Total revenue requirement increase $ 86 $ 22 $ 68 $ (3 ) $ 14 $ (1 ) Allowed return on rate base (b) 8.61 % 8.62 % 8.7 % 8.46 % 8.53 % 8.35 % Allowed ROE 11.5 % 11.5 % 11.5 % 11.3 % 11.3 % 11.3 % Effective date of rates (c) June 2015 June 2014 June 2013 June 2015 June 2014 June 2013

Mergers, Acquisitions and Dis42

Mergers, Acquisitions and Dispositions (Tables)	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition	The following table summarizes the acquisition-date fair value of the consideration transferred and the assets and liabilities assumed for the Integrys acquisition by Generation: Total consideration transferred $ 332 Identifiable assets acquired and liabilities assumed Working capital assets $ 390 Mark-to-market derivative assets 184 Unamortized energy contract assets 115 Customer relationships 50 Working capital liabilities (196 ) Mark-to-market derivative liabilities (57 ) Unamortized energy contract liabilities (110 ) Deferred tax liability (16 ) Total net identifiable assets, at fair value $ 360 Bargain purchase gain (after-tax) $ 28
Summary of Asset Divestitures	The table below presents the major classes of assets and liabilities held for sale at December 31, 2014. Assets held for sale at December 31, 2015 are not material. December 31, 2014 Assets Property, plant and equipment, net (a) $ 143 Inventory 4 Total assets held for sale $ 147 Liabilities Accrued expenses $ 1 Asset retirement obligations 4 Total liabilities held for sale (b) $ 5 _____________ (a) The total aggregate book value of property, plant and equipment is net of a $50 million pre-tax impairment loss recorded within Operating and maintenance expense on Exelon’s and Generation’s Statements of Operations and Comprehensive Income for the year ended December 31, 2014. See Note 8 — Impairment of Long-Lived Assets for further information. (b) Included within Other current liabilities on Exelon's and Generation's Consolidated Balance Sheets. Station Net Generation Capacity Location Operating Segment Percent Owned Fore River 726 MW North Weymouth, MA New England 100 % West Valley 185 MW Salt Lake City, UT Other 100 % Keystone 714 MW Shelocta, PA Mid-Atlantic 41.98 % Conemaugh 532 MW New Florence, PA Mid-Atlantic 31.28 % Safe Harbor 278 MW Conestoga, PA Mid-Atlantic 66.7 % Quail Run 488 MW Odessa, TX ERCOT 100 %
Restructuring and Related Costs [Table Text Block]	For the year ended, Acquisition, Integration and Financing Costs (a) 2015 2014 Exelon $ 80 $ 179 Generation 25 11 ComEd 10 4 PECO 5 2 BGE 5 2 ___________ (a) The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statement of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. .

Investment in Constellation E43

Investment in Constellation Energy Nuclear Group, LLC (Tables)	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
Schedule of total equity in earnings of investment in CENG	The following assets and liabilities of CENG were recorded within Generation’s Consolidated Balance Sheets as of the date of integration, adjusted for the modifications discussed above: Fair Values Exelon and Generation Current assets $ 499 Nuclear decommissioning trust fund 1,955 Property, plant and equipment 3,073 Nuclear fuel 482 Other assets 10 Total assets 6,019 Current liabilities 237 Asset retirement obligation 1,816 Pension and other employee benefit obligations 281 Unamortized energy contract liabilities 171 Other liabilities 114 Total liabilities 2,619 Total net assets $ 3,400

Accounts Receivable (Tables)

Accounts Receivable (Tables)	12 Months Ended
	Dec. 31, 2015
Receivables [Abstract]
Schedule Of Accounts Notes Loans And Financing Receivable	Accounts receivable at December 31, 2015 and 2014 included estimated unbilled revenues, representing an estimate for the unbilled amount of energy or services provided to customers, and is net of an allowance for uncollectible accounts as follows: 2015 Exelon Generation ComEd PECO BGE Unbilled customer revenues $ 1,203 $ 732 (a) $ 218 $ 105 $ 148 Allowance for uncollectible accounts (b) (284 ) (77 ) (75 ) (83 ) (c) (49 ) 2014 Exelon Generation ComEd PECO BGE Unbilled customer revenues $ 1,381 $ 823 (a) $ 204 $ 140 $ 214 Allowance for uncollectible accounts (b) (311 ) (60 ) (84 ) (100 ) (c) (67 ) (d) _________________________ (a) Represents unbilled portion of retail receivables estimated under Exelon’s unbilled critical accounting policy. (b) Includes the allowance for uncollectible accounts on customer and other accounts receivable. (c) Excludes the non-current allowance for uncollectible accounts of $8 million at both December 31, 2015 and 2014 , related to PECO’s current installment plan receivables described below. (d) At December 31, 2014 , as explained in Note 1 — Significant Accounting Policies , BGE estimated the allowance for uncollectible accounts on customer receivables by applying loss rates to the outstanding receivable balance by risk segment. The change in estimate resulted in a $19 million pre-tax charge to BGE's provision for uncollectible accounts expense for the year ended December 31, 2014 , which is included in Operating and maintenance expense on BGE's Consolidated Statements of Operations and Comprehensive Income.

Property, Plant, and Equipment

Property, Plant, and Equipment (Tables)	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The following table presents a summary of property, plant and equipment by asset category as of December 31, 2015 and 2014 : Average Service Life (years) 2015 2014 Asset Category Electric—generation 1-56 $ 25,615 19,004,000,000 $ 22,911 Nuclear fuel (a) 1-8 6,384 4,815,000,000 5,947 Construction work in progress N/A 2,017 1,352,000,000 1,404 Other property, plant and equipment (b) 5-31 466 374,000,000 378 Total property, plant and equipment 34,482 30,640 Less: accumulated depreciation (c) 8,639 7,612 Property, plant and equipment, net $ 25,843 $ 23,028 _________________________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,266 million and $1,003 million at December 31, 2015 and 2014 , respectively. (b) Includes buildings under capital lease with a net carrying value of $13 million and $15 million at December 31, 2015 and 2014 , respectively. The original cost basis of the buildings was $52 million , and total accumulated amortization was $39 million and $37 million , as of December 31, 2015 and 2014 , respectively. These balances also include capitalized acquisition, development and exploration costs of $266 million and $242 million related to oil and gas production activities at Generation at December 31, 2015 and 2014 , respectively. Includes the original cost and progress payments associated with Generation’s turbine equipment held for future use with a carrying value of $146 million and $83 million at December 31, 2015 and 2014, respectively. (c) Includes accumulated amortization of nuclear fuel in the reactor core of $2,861 million and $2,673 million as of December 31, 2015 and 2014 , respectively The following table presents a summary of property, plant and equipment by asset category as of December 31, 2015 and 2014 : Average Service Life (years) 2015 2014 Asset Category Electric—transmission and distribution 5-90 $ 32,546 $ 30,157 Electric—generation 1-56 25,615 22,911 Gas—transportation and distribution 5-90 3,864 3,505 Common—electric and gas 5-50 1,149 1,169 Nuclear fuel (a) 1-8 6,384 5,947 Construction work in progress N/A 3,075 2,167 Other property, plant and equipment (b) 5-50 1,181 1,056 Total property, plant and equipment 73,814 66,912 Less: accumulated depreciation (c) 16,375 14,742 Property, plant and equipment, net $ 57,439 $ 52,170 _________________________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,266 million and $1,003 million at December 31, 2015 and 2014 , respectively. (b) Includes Generation’s buildings under capital lease with a net carrying value of $13 million and $15 million at December 31, 2015 and 2014 , respectively. The original cost basis of the buildings was $52 million , and total accumulated amortization was $39 million and $37 million , as of December 31, 2015 and 2014 , respectively. Also includes ComEd’s buildings under capital lease with a net carrying value at December 31, 2015 and 2014 , of $7 million and $8 million , respectively. The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million and $0.3 million as of December 31, 2015 and 2014 , respectively. Includes land held for future use and non utility property at ComEd, PECO, and BGE of $57 million , $21 million , and $32 million , respectively. These balances also include capitalized acquisition, development and exploration costs of $266 million and $242 million related to oil and gas production activities at Generation at December 31, 2015 and 2014 , respectively. Includes the original cost and progress payments associated with Generation’s turbine equipment held for future use with a carrying value of $146 million and $83 million at December 31, 2015 and 2014, respectively. (c) Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $2,861 million and $2,673 million as of December 31, 2015 and 2014 , respectively The following table presents a summary of property, plant and equipment by asset category as of December 31, 2015 and 2014 : Average Service Life (years) 2015 2014 Asset Category Electric—transmission and distribution 5-80 $ 20,576 $ 18,884 Construction work in progress N/A 572 276 Other property, plant and equipment (a), (b) 38-50 64 65 Total property, plant and equipment 21,212 19,225 Less: accumulated depreciation 3,710 3,432 Property, plant and equipment, net $ 17,502 $ 15,793 _________________________ (a) Includes buildings under capital lease with a net carrying value at December 31, 2015 and 2014 of $7 million and $8 million , respectively. The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million and $0.3 million as of December 31, 2015 and 2014 , respectively. (b) Includes land held for future use and non-utility property. The following table presents a summary of property, plant and equipment by asset category as of December 31, 2015 and 2014 : Average Service Life (years) 2015 2014 Asset Category Electric—transmission and distribution 5-90 $ 6,663 $ 6,339 Gas—distribution 5-90 1,951 1,761 Common—electric and gas 5-40 655 623 Construction work in progress N/A 312 317 Other property, plant and equipment (a) 20 32 32 Total property, plant and equipment 9,613 9,072 Less: accumulated depreciation 3,016 2,868 Property, plant and equipment, net $ 6,597 $ 6,204 _______________________ (a) Represents land held for future use and non-utility property The following table presents a summary of property, plant and equipment by asset category as of December 31, 2015 and 2014 : Average Service Life (years) 2015 2014 Asset Category Electric—transmission and distribution 5-65 $ 7,230 $ 6,886 Gas—transportation and distribution 5-70 2,206 2,039 Common—electric and gas 5-50 631 618 Construction work in progress N/A 154 154 Other property, plant and equipment (a) 50 21 21 Total property, plant and equipment 10,242 9,718 Less: accumulated depreciation 3,101 2,917 Property, plant and equipment, net $ 7,141 $ 6,801 _________________________ (a) Represents land held for future use and non-utility property
Property Plant And Equipment Average Service Life Percentage By Asset Category Table	The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2015 2014 2013 Electric—transmission and distribution 2.83 % 2.93 % 2.91 % Electric—generation 3.47 % 3.50 % 3.35 % Gas 2.17 % 2.13 % 2.06 % Common—electric and gas 7.79 % 7.32 % 7.53 % The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2015 2014 2013 Electric—transmission and distribution 2.39 % 2.55 % 2.73 % Gas 1.87 % 1.84 % 1.79 % Common—electric and gas 5.16 % 5.16 % 6.65 % Average Service Life Percentage by Asset Category 2015 2014 2013 Electric—transmission and distribution 2.62 % 2.96 % 2.91 % Gas 2.50 % 2.47 % 2.36 % Common—electric and gas 10.35 % 9.49 % 8.45 %

Impairment of Long-Lived asse46

Impairment of Long-Lived assets (Tables)	12 Months Ended
	Dec. 31, 2015
Impairment or Disposal of Tangible Assets Disclosure [Abstract]
Schedule of Capital Leased Assets	At December 31, 2015 and 2014 , the components of the net investment in long-term leases were as follows: December 31, 2015 December 31, 2014 Estimated residual value of leased assets $ 639 $ 685 Less: unearned income 287 324 Net investment in long-term leases $ 352 $ 361

Jointly Owned Electric Utilit47

Jointly Owned Electric Utility Plant (Tables)	12 Months Ended
	Dec. 31, 2015
Public Utilities, Property, Plant and Equipment [Abstract]
Schedule of Jointly Owned Utility Plants	Exelon, Generation, PECO and BGE’s undivided ownership interests in jointly owned electric plants and transmission facilities at December 31, 2015 and 2014 were as follows: Nuclear Generation Fossil Fuel Generation Transmission Other Quad Cities Peach Bottom Salem (a) Nine Mile Point Unit 2 (f) Wyman PA (b) DE/NJ (c) Other (d) Operator Generation Generation PSEG Nuclear Generation FP&L First Energy PSEG Ownership interest 75.00 % 50.00 % 42.59 % 82.00 % 5.89 % Various 42.55 % 44.24 % Exelon’s share at December 31, 2015: Plant (e) $ 1,035 $ 1,345 $ 566 $ 756 $ 3 $ 15 $ 65 $ 1 Accumulated depreciation (e) 309 368 167 42 3 7 35 1 Construction work in progress 11 18 40 56 — — — — Exelon’s share at December 31, 2014: Plant (e) $ 995 $ 1,095 $ 531 $ 676 $ 3 $ 14 $ 64 $ 2 Accumulated depreciation (e) 266 343 150 14 3 7 34 1 Construction work in progress 15 133 29 48 — — — — ________________________ (a) Generation also owns a proportionate share in the fossil fuel combustion turbine at Salem, which is fully depreciated. The gross book value was $3 million at December 31, 2015 and 2014 . (b) PECO and BGE own a 22% and 7% share, respectively, in 127 miles of 500 kV lines located in Pennsylvania; PECO and BGE also own a 20.7% and 10.56% share, respectively, of a 500 kV substation immediately outside of the Conemaugh fossil generating station which supplies power to the 500 kV lines including, but not limited to, the lines noted above. (c) PECO owns a 42.55% share in 131 miles of 500 kV lines located in Delaware and New Jersey as well as a 42.55% share in a 500 kV substation immediately outside of the Salem nuclear generating station in New Jersey which supplies power to the 500 kV lines including, but not limited to, the lines noted above. (d) Generation has a 44.24% ownership interest in assets located at Merrill Creek Reservoir located in New Jersey. (e) Excludes asset retirement costs.

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule Of Goodwill	Exelon’s, Generation's and ComEd’s gross amount of goodwill, accumulated impairment losses and carrying amount of goodwill for the years ended December 31, 2015 and 2014 were as follows: ComEd Generation Exelon Gross (a) Accumulated Carrying Gross Carrying Gross Amount Accumulated Impairment Losses Carrying Amount Balance, January 1, 2014 $ 4,608 $ 1,983 $ 2,625 $ — $ — $ 4,608 $ 1,983 $ 2,625 Goodwill from business combination — — — 47 47 47 — 47 Balance, December 31, 2014 4,608 1,983 2,625 47 47 4,655 1,983 2,672 Impairment losses — — — — — — — — Balance, December 31, 2015 $ 4,608 $ 1,983 $ 2,625 $ 47 $ 47 $ 4,655 $ 1,983 $ 2,672 _______________________ (a) Reflects goodwill recorded in 2000 from the PECO/Unicom (predecessor parent company of ComEd) merger net of amortization, resolution of tax matters and other non-impairment-related changes as allowed under previous authoritative guidance.
Schedule of Finite-Lived Intangible Assets	Exelon’s, Generation’s and ComEd’s other intangible assets and liabilities, included in Unamortized energy contract assets and liabilities and Other deferred debits and other assets in their Consolidated Balance Sheets, consisted of the following as of December 31, 2015 : Weighted Average Amortization Years (k) Estimated amortization expense Gross Accumulated Amortization Net 2016 2017 2018 2019 2020 Exelon Software License Agreement (a) 10.0 $ 95 $ (6 ) $ 89 $ 10 $ 10 $ 10 $ 10 $ 10 Generation Unamortized Energy Contracts (b) Exelon Wind (c) 18.0 224 (69 ) 155 14 14 14 14 10 Antelope Valley (d) 25.0 190 (20 ) 170 8 8 8 8 8 Constellation (e) 1.5 1,499 (1,473 ) 26 (33 ) (21 ) 11 8 10 CENG (f) 1.7 (97 ) 48 (49 ) (11 ) (15 ) (18 ) (15 ) (8 ) Integrys (g) 2.4 5 2 7 5 1 1 — — Customer Relationships (h) Constellation (e) 12.4 214 (76 ) 138 18 18 18 17 17 Integrys (g) 10.0 50 (6 ) 44 5 5 5 5 5 Trade Names Constellation (e) 10.0 243 (103 ) 140 23 23 23 23 23 ComEd Chicago settlement—1999 agreement (i) 21.8 100 (83 ) 17 3 3 3 4 4 Chicago settlement—2003 agreement (j) 17.9 62 (44 ) 18 4 4 4 3 3 Total intangible assets $ 2,585 $ (1,830 ) $ 755 $ 46 $ 50 $ 79 $ 77 $ 82 _________________________ (a) On May 31, 2015, Exelon entered into a long-term software license agreement. Exelon is required to make payments starting August 2015 through May 2024. The intangible asset recognized as a result of these payments is being amortized on a straight-line basis over the contract term. (b) Includes unamortized energy contract assets and liabilities on Exelon's and Generation's Consolidated Balance Sheets. Excludes $44 million of other miscellaneous unamortized energy contracts that have been acquired at various points in time. The estimated amortization for these miscellaneous unamortized energy contracts is $3 million , $0 million , $2 million , $3 million and $4 million for 2016 , 2017 , 2018 , 2019 and 2020 , respectively. (c) In December 2010, Generation acquired all of the equity interests of John Deere Renewables, LLC (later named Exelon Wind), adding 735 MWs of installed, operating wind capacity located in eight states. (d) In September 2011, Generation acquired all of the interest in Antelope Valley Solar Ranch One, a 242 MW solar project under development in northern Los Angeles County, CA from First Solar, Inc. (e) On March 12, 2012, Constellation merged into Exelon with Exelon continuing as the surviving corporation pursuant to the transactions contemplated by the Agreement and Plan of Merger. Since the merger transaction, Generation includes the former Constellation generation and customer supply operations. (f) See Note 5 — Investment in Constellation Energy Nuclear Group, LLC for additional information. (g) See Note 4 — Mergers, Acquisitions, and Dispositions for additional information. (h) Excludes $12 million of other miscellaneous customer relationships that have been acquired. The estimated amortization for these miscellaneous customer relationships is $1 million in each of the years from 2016 to 2020 . (i) In March 1999, ComEd entered into a settlement agreement with the City of Chicago associated with ComEd’s franchise agreement. Under the terms of the settlement, ComEd agreed to make payments to the City of Chicago each year from 1999 to 2002. The intangible asset recognized as a result of these payments is being amortized ratably over the remaining term of the franchise agreement, which ends in 2020. (j) In February 2003, ComEd entered into separate agreements with the City of Chicago and with Midwest Generation, LLC (Midwest Generation). Under the terms of the settlement agreement with the City of Chicago, ComEd agreed to pay the City of Chicago a total of $60 million over a ten -year period, beginning in 2003. The intangible asset recognized as a result of the settlement agreement is being amortized ratably over the remaining term of the City of Chicago franchise agreement, which ends in 2020. As required by the settlement, ComEd also made a payment of $2 million to a third-party on the City of Chicago’s behalf. Under the terms of the agreement with Midwest Generation, ComEd received payments of $32 million from Midwest Generation to relieve Midwest Generation’s obligation under the 1999 fossil sale agreement with ComEd to build the generation facility in the City of Chicago. The payments received by ComEd, which have been recorded in Other deferred credits and other liabilities, and other long-term liabilities on Exelon's and ComEd's Consolidated Balance Sheets are being recognized ratably (approximately $2 million annually) as an offset to amortization expense over the remaining term of the franchise agreement. (k) Weighted-average amortization period was calculated at the date of a) acquisition for acquired assets or b) settlement agreement.
Schedule Of Finite-Lived Intangible Assets Amortization Expense	The following table summarizes the amortization expense related to intangible assets and liabilities for each of the years ended December 31, 2015 , 2014 and 2013 : For the Year Ended December 31, Exelon (a) Generation (a) ComEd 2015 $ 76 $ 69 $ 7 2014 179 179 7 2013 478 550 7 _________________________ (a) At Exelon, amortization of unamortized energy contracts totaling $22 million , $135 million and $430 million for the years ended December 31, 2015 , 2014 and 2013 , respectively, was recorded in Operating revenues or Purchase power and fuel expense within Exelon’s Consolidated Statement of Operations and Comprehensive Income. At Generation, amortization of unamortized energy contracts totaling $22 million , $135 million and $507 million for the years ended December 31, 2015 , 2014 and 2013 , respectively, was recorded in Operating revenues or Purchase power and fuel expense within Generation’s Consolidated Statement of Operations and Comprehensive Income

Fair Value of Financial Asset49

Fair Value of Financial Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis	The following tables present assets and liabilities measured and recorded at fair value on the utility Registrants' Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2015 and 2014 : ComEd PECO BGE As of December 31, 2015 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents $ 29 $ — $ — $ 29 $ 271 $ — $ — $ 271 $ 25 $ — $ — $ 25 Rabbi trust investments in mutual funds (a) — — — — 8 — — 8 4 — — 4 Total assets 29 — — 29 279 — — 279 29 — — 29 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (12 ) — (12 ) — (4 ) — (4 ) Mark-to-market derivative liabilities (b) — — (247 ) (247 ) — — — — — — — — Total liabilities — (8 ) (247 ) (255 ) — (12 ) — (12 ) — (4 ) — (4 ) Total net assets (liabilities) $ 29 $ (8 ) $ (247 ) $ (226 ) $ 279 $ (12 ) $ — $ 267 $ 29 $ (4 ) $ — $ 25 ComEd PECO BGE As of December 31, 2014 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents $ 25 $ — $ — $ 25 $ 12 $ — $ — $ 12 $ 103 $ — $ — $ 103 Rabbi trust investments in mutual funds (a) — — — — 9 — — 9 5 — — 5 Total assets 25 — — 25 21 — — 21 108 — — 108 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (15 ) — (15 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (b) — — (207 ) (207 ) — — — — — — — — Total liabilities — (8 ) (207 ) (215 ) — (15 ) — (15 ) — (5 ) — (5 ) Total net assets (liabilities) $ 25 $ (8 ) $ (207 ) $ (190 ) $ 21 $ (15 ) $ — $ 6 $ 108 $ (5 ) $ — $ 103 _________________________ (a) At PECO, excludes $12 million and $14 million of the cash surrender value of life insurance investments at December 31, 2015 and 2014 , respectively. (b) The Level 3 balance includes the current and noncurrent liability of $23 million and $224 million , respectively, at December 31, 2015 , and $20 million and $187 million , respectively, at December 31, 2014 , related to floating-to-fixed energy swap contracts with unaffiliated suppliers. The following tables present the carrying amounts and fair values of the Registrants’ short-term liabilities, long-term debt, SNF obligation, and trust preferred securities (long-term debt to financing trusts or junior subordinated debentures) as of December 31, 2015 and 2014 : Exelon December 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 536 $ 3 $ 533 $ — $ 536 $ 463 $ 463 Long-term debt (including amounts due within one year) (a) 25,145 931 23,644 1,349 25,924 21,014 22,936 Long-term debt to financing trusts (b) 641 — — 673 673 641 648 SNF obligation 1,021 — 818 — 818 1,021 833 Generation December 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 29 $ — $ 29 $ — $ 29 $ 36 $ 36 Long-term debt (including amounts due within one year) (a) 8,959 — 7,767 1,349 9,116 8,196 8,822 SNF obligation 1,021 — 818 — 818 1,021 833 ComEd December 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 294 $ — $ 294 $ — $ 294 $ 304 $ 304 Long-term debt (including amounts due within one year) (a) 6,509 — 7,069 — 7,069 5,925 6,788 Long-term debt to financing trusts (b) 205 — — 213 213 205 213 PECO December 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 2,580 $ — $ 2,786 $ — $ 2,786 $ 2,232 $ 2,537 Long-term debt to financing trusts 184 — — 195 195 184 199 BGE December 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 213 $ 3 $ 210 $ — $ 213 $ 123 $ 123 Long-term debt (including amounts due within one year) (a) 1,858 — 2,044 — 2,044 1,932 2,178 Long-term debt to financing trusts (b) 252 — — 264 264 252 236
Fair value of financial liabilities recorded at the carrying amount	The following tables present assets and liabilities measured and recorded at fair value on Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2015 and 2014 : Generation Exelon As of December 31, 2015 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 104 $ — $ — $ 104 $ 5,766 $ — $ — $ 5,766 Nuclear decommissioning trust fund investments Cash equivalents (b) 219 92 — 311 219 92 — 311 Generation Exelon As of December 31, 2015 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Equities 3,008 1,894 — 4,902 3,008 1,894 — 4,902 Fixed income Corporate debt — 1,824 242 2,066 — 1,824 242 2,066 U.S. Treasury and agencies 1,323 15 — 1,338 1,323 15 — 1,338 Foreign governments — 61 — 61 — 61 — 61 State and municipal debt — 326 — 326 — 326 — 326 Other (c) — 537 — 537 — — 537 — — — 537 Fixed income subtotal 1,323 2,763 242 4,328 1,323 2,763 242 4,328 Middle market lending — — 428 428 — — 428 428 Private equity — — 125 125 — — 125 125 Real estate — — 35 35 — — — — 35 35 Other — 216 — 216 — 216 — 216 Nuclear decommissioning trust fund investments subtotal (d) 4,550 4,965 830 10,345 4,550 4,965 830 10,345 Pledged assets for Zion Station decommissioning Cash equivalents — 17 — 17 — 17 — 17 Equities 1 5 — 6 1 5 — 6 Fixed income U.S. Treasury and agencies 6 2 — 8 6 2 — 8 Corporate debt — 46 — 46 — 46 — 46 Other — 1 — 1 — 1 — 1 Fixed income subtotal 6 49 — 55 6 49 — 55 Middle market lending — — 127 127 — — 127 127 Pledged assets for Zion Station decommissioning subtotal (e) 7 71 127 205 7 71 127 205 Rabbi trust investments in mutual funds (f) 17 — — — 17 48 — — 48 Commodity derivative assets Economic hedges 1,922 3,467 1,707 7,096 1,922 3,467 1,707 7,096 Proprietary trading 36 64 30 130 36 64 30 130 Effect of netting and allocation of collateral (g) (1,964 ) (2,629 ) (564 ) (5,157 ) (1,964 ) (2,629 ) (564 ) (5,157 ) Commodity derivative assets subtotal (6 ) 902 1,173 2,069 (6 ) 902 1,173 2,069 Interest rate and foreign currency derivative Derivatives designated as hedging instruments — — — — — 25 — 25 Economic hedges — 20 — 20 — 20 — 20 Proprietary trading 10 5 — 15 10 5 — 15 Effect of netting and allocation of collateral (3 ) (3 ) — (6 ) (3 ) (3 ) — (6 ) Interest rate and foreign currency derivative assets subtotal 7 22 — 29 7 47 — 54 Other investments — — 33 33 — — 33 33 Total assets 4,679 5,960 2,163 12,802 10,372 5,985 2,163 18,520 Liabilities Commodity derivative liabilities Economic hedges (2,382 ) (3,348 ) (850 ) (6,580 ) (2,382 ) (3,348 ) (1,097 ) (6,827 ) Proprietary trading (33 ) (57 ) (37 ) (127 ) (33 ) (57 ) (37 ) (127 ) Effect of netting and allocation of collateral (g) 2,440 3,186 765 6,391 2,440 3,186 765 6,391 Commodity derivative liabilities subtotal 25 (219 ) (122 ) (316 ) 25 (219 ) (369 ) (563 ) Interest rate and foreign currency derivative liabilities — — Derivatives designated as hedging instruments — (16 ) — (16 ) — (16 ) — (16 ) Economic hedges — (3 ) — (3 ) — (3 ) — (3 ) Proprietary trading (12 ) — — (12 ) (12 ) — — (12 ) Effect of netting and allocation of collateral 12 3 — 15 12 3 — 15 Generation Exelon As of December 31, 2015 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Interest rate and foreign currency derivative liabilities subtotal — (16 ) — (16 ) — (16 ) — (16 ) Deferred compensation obligation — (30 ) — (30 ) — (99 ) — (99 ) Total liabilities 25 (265 ) (122 ) (362 ) 25 (334 ) (369 ) (678 ) Total net assets $ 4,704 $ 5,695 $ 2,041 $ 12,440 $ 10,397 $ 5,651 $ 1,794 $ 17,842
Assets and liabilities measured and recorded at fair value on recurring basis	Generation Exelon As of December 31, 2014 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 405 $ — $ — $ 405 $ 1,119 $ — $ — $ 1,119 Nuclear decommissioning trust fund investments Cash equivalents (b) 208 37 — 245 208 37 — 245 Equities 3,035 2,207 — 5,242 3,035 2,207 — 5,242 Fixed income Corporate debt — 2,023 239 2,262 — 2,023 239 2,262 U.S. Treasury and agencies 996 — — 996 996 — — 996 Foreign governments — 95 — 95 — 95 — 95 State and municipal debt — 438 — 438 — 438 — 438 Other — 511 — 511 — 511 — 511 Fixed income subtotal 996 3,067 239 4,302 996 3,067 239 4,302 Middle market lending — — 366 366 — — 366 366 Private equity — — 83 83 — — 83 83 Real estate — — 3 3 — — — — 3 3 Other (c) — 301 — 301 — 301 — 301 Nuclear decommissioning trust fund investments subtotal (d) 4,239 5,612 691 10,542 4,239 5,612 691 10,542 Pledged assets for Zion Station decommissioning Cash equivalents — 15 — 15 — 15 — 15 Equities 6 1 — 7 6 1 — 7 Fixed income U.S. Treasury and agencies 5 3 — 8 5 3 — 8 Corporate debt — 89 — 89 — 89 — 89 State and municipal debt — 10 — 10 — 10 — 10 Other — 3 — 3 — — 3 — — — 3 Fixed income subtotal 5 105 — 110 5 105 — 110 Middle market lending — — 184 184 — — 184 184 Pledged assets for Zion Station decommissioning subtotal (e) 11 121 184 316 11 121 184 316 Rabbi trust investments (f) Cash equivalents — — — — 1 — — 1 Mutual funds 16 — — 16 46 — — 46 Rabbi trust investments subtotal 16 — — 16 47 — — 47 Commodity derivative assets — — Economic hedges 1,667 3,465 1,681 6,813 1,667 3,465 1,681 6,813 Proprietary trading 201 284 27 512 201 284 27 512 Effect of netting and allocation of collateral (g) (1,982 ) (2,757 ) (557 ) (5,296 ) (1,982 ) (2,757 ) (557 ) (5,296 ) Commodity derivative assets subtotal (114 ) 992 1,151 2,029 (114 ) 992 1,151 2,029 Interest rate and foreign currency derivative assets — — Derivatives designated as hedging instruments — 8 — 8 — 31 — 31 Economic hedges — 12 — 12 — 13 — 13 Generation Exelon As of December 31, 2014 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Proprietary trading 18 9 — 27 18 9 — 27 Effect of netting and allocation of collateral (17 ) (12 ) — (29 ) (17 ) (31 ) — (48 ) Interest rate and foreign currency derivative assets subtotal 1 17 — 18 1 22 — 23 Other investments — — 3 3 2 — 3 5 Total assets 4,558 6,742 2,029 13,329 5,305 6,747 2,029 14,081 Liabilities Commodity derivative liabilities Economic hedges (2,241 ) (3,458 ) (788 ) (6,487 ) (2,241 ) (3,458 ) (995 ) (6,694 ) Proprietary trading (195 ) (295 ) (42 ) (532 ) (195 ) (295 ) (42 ) (532 ) Effect of netting and allocation of collateral (g) 2,416 3,557 729 6,702 2,416 3,557 729 6,702 Commodity derivative liabilities subtotal (20 ) (196 ) (101 ) (317 ) (20 ) (196 ) (308 ) (524 ) Interest rate and foreign currency derivative liabilities — — Derivatives designated as hedging instruments — (12 ) — (12 ) — (41 ) — (41 ) Economic hedges — (2 ) — (2 ) — (103 ) — (103 ) Proprietary trading (14 ) (9 ) — (23 ) (14 ) (9 ) — (23 ) Effect of netting and allocation of collateral 25 10 — 35 25 29 — 54 Interest rate and foreign currency derivative liabilities subtotal 11 (13 ) — (2 ) 11 (124 ) — (113 ) Deferred compensation obligation — (31 ) — (31 ) — (107 ) — (107 ) Total liabilities (9 ) (240 ) (101 ) (350 ) (9 ) (427 ) (308 ) (744 ) Total net assets $ 4,549 $ 6,502 $ 1,928 $ 12,979 $ 5,296 $ 6,320 $ 1,721 $ 13,337 _________________________ (a) Excludes certain cash equivalents considered to be held-to-maturity and not reported at fair value. (b) Includes $52 million and $43 million of cash received from outstanding repurchase agreements at December 31, 2015 and 2014 , respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below. (c) Includes derivative instruments of $(8) million and $(10) million , which have a total notional amount of $1,236 million and $794 million at December 31, 2015 and 2014 , respectively. The notional principal amounts for these instruments provide one measure of the transaction volume outstanding as of the fiscal years ended and do not represent the amount of the company's exposure to credit or market loss. (d) Excludes net liabilities of $(3) million and $(5) million at December 31, 2015 and 2014 , respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, repurchase agreement obligations, and payables related to pending securities purchases. The repurchase agreements are generally short-term in nature with durations generally of 30 days or less. (e) Excludes net assets of $1 million and $3 million at December 31, 2015 and 2014 , respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases. (f) Excludes $36 million and $35 million of cash surrender value of life insurance investment at December 31, 2015 and 2014 , respectively, at Exelon Consolidated. Excludes $13 million and $11 million of cash surrender value of life insurance investment at December 31, 2015 and 2014 , respectively, at Generation. (g) Collateral posted to/(received from) counterparties totaled $476 million , $557 million and $201 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2015 . Collateral posted to/(received from) counterparties totaled $434 million , $800 million and $172 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2014 .
Total realized and unrealized gains (losses) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis	The following table presents the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis during the year ended December 31, 2015 and 2014 : Generation ComEd Exelon For The Year Ended December 31, 2015 Nuclear Pledged Assets Mark-to-Market Other Total Generation Mark-to-Market Derivatives (b) Eliminated in Consolidation Total Balance as of January 1, 2015 $ 691 $ 184 $ 1,050 $ 3 $ 1,928 $ (207 ) $ — $ 1,721 Total realized / unrealized gains (losses) Included in net income 4 — 22 (a) 1 27 — — 27 Included in noncurrent payables to affiliates 23 — — — 23 — (23 ) — Included in payable for Zion Station decommissioning — (2 ) — — (2 ) — — (2 ) Included in regulatory assets/liabilities — — — — — (40 ) 23 (17 ) Change in collateral — — 29 — 29 — — 29 Purchases, sales, issuances and settlements Purchases 226 20 144 30 420 — — 420 Sales (8 ) (75 ) (25 ) — (108 ) — — (108 ) Settlements (106 ) — — — (106 ) — — (106 ) Transfers into Level 3 4 — 80 — 84 — — 84 Transfers out of Level 3 (4 ) — (249 ) (1 ) (254 ) — — (254 ) Balance as of December 31, 2015 $ 830 $ 127 $ 1,051 $ 33 $ 2,041 $ (247 ) $ — $ 1,794 The amount of total gains included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of December 31, 2015 $ 4 $ — $ 856 $ — $ 860 $ — $ — $ 860 Generation Exelon Operating Revenues Purchased Power and Fuel Other, net (a) Operating Revenues Purchased Power and Fuel Other, net (a) Total gains (losses) included in net income for the year ended December 31, 2014 $ 614 $ (88 ) $ 6 $ 614 $ (88 ) $ 6 Change in the unrealized gains (losses) relating to assets and liabilities held for the year ended December 31, 2014 $ 663 $ (23 ) $ 4 $ 663 $ (23 ) $ 4 _________________________ (a) Other, net activity consists of realized and unrealized gains (losses) included in income for the NDT funds held by Generation. The following tables present the income statement classification of the total realized and unrealized gains (losses) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis during the years ended December 31, 2015 and 2014 : Generation Exelon Operating Revenues Purchased Power and Fuel Other, net (a) Operating Revenues Purchased Power and Fuel Other, net (a) Total gains (losses) included in net income for the year ended December 31, 2015 $ 67 $ (45 ) $ 4 $ 67 $ (45 ) $ 4 Change in the unrealized gains (losses) relating to assets and liabilities held for the year ended December 31, 2015 $ 858 $ (2 ) $ 4 $ 858 $ (2 ) $ 4 Generation ComEd Exelon For The Year Ended December 31, 2014 Nuclear Decommissioning Trust Fund Investments Pledged Assets for Zion Station Decommissioning Mark-to-Market Derivatives (d) Other Investments Total Generation Mark-to-Market Derivatives (b) Eliminated in Consolidation Total Balance as of January 1, 2014 $ 350 $ 112 $ 465 $ 15 $ 942 $ (193 ) $ — $ 749 Total realized / unrealized gains (losses) Included in net income 6 — 526 (a) — 532 — — 532 Included in other comprehensive income — — — — — — — — Included in noncurrent payables to affiliates 14 — — — 14 — (14 ) — Included in payable for Zion Station decommissioning — 2 — — 2 — — 2 Included in regulatory assets/liabilities — — — — — (14 ) 14 — Change in collateral — — 198 — 198 — — 198 Purchases, sales, issuances and settlements Purchases 400 120 76 (c) 2 598 — — 598 Sales (15 ) (50 ) (7 ) (8 ) (80 ) — — (80 ) Settlements (64 ) — — — (64 ) — — (64 ) Transfers into Level 3 — — (7 ) — (7 ) — — (7 ) Transfers out of Level 3 — — (201 ) (6 ) (207 ) — — (207 ) Balance as of December 31, 2014 $ 691 $ 184 $ 1,050 $ 3 $ 1,928 $ (207 ) $ — $ 1,721 The amount of total gains included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held as of December 31, 2014 $ 4 $ — $ 640 $ — $ 644 $ — $ — $ 644 _________________________ (a) Includes a reduction for the reclassification of $834 million and $114 million of realized gains due to the settlement of derivative contracts for the years ended December 31, 2015 and 2014 , respectively. (b) Includes $55 million of decreases in fair value and an increase for realized losses due to settlements of $(15) million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2015 . Includes $13 million of decreases in fair value and a reduction for realized gains due to settlements of $1 million for the year ended December 31, 2014 . (c) Includes $34 million of fair value from contracts acquired as a result of the Integrys acquisition.
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis, valuation technique	The table below discloses the significant inputs to the forward curve used to value these positions. Type of trade Fair Value at December 31,2015 Valuation Technique Unobservable Input Range Mark-to-market derivatives—Economic hedges (Generation) (a)(c) $ 857 Discounted Cash Flow Forward power price $11 - $88 (d) Forward gas price $1.18 - $8.95 (d) Option Model Volatility percentage 5% - 152% Mark-to-market derivatives—Proprietary trading (Generation) (a)(c) $ (7 ) Discounted Cash Flow Forward power price $13 - $78 (d) Mark-to-market derivatives (ComEd) $ (247 ) Discounted Cash Flow Forward heat rate (b) 9x - 10x Marketability reserve 3.5% - 7% Renewable factor 87% - 128% _________________________ (a) The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions. (b) Quoted forward natural gas rates are utilized to project the forward power curve for the delivery of energy at specified future dates. The natural gas curve is extrapolated beyond its observable period to the end of the contract’s delivery. (c) The fair values do not include cash collateral posted on level three positions of $201 million as of December 31, 2015 . (d) Unlike the previous year, the New England region was not a significant driver for the upper end of the ranges for power and gas as of December 31, 2015 . Type of trade Fair Value at December 31, 2014 Valuation Technique Unobservable Input Range Mark-to-market derivatives—Economic hedges (Generation) (a)(c) $ 893 Discounted Cash Flow Forward power price $15 - $120 (d) Forward gas price $1.52 - $14.02 (d) Option Model Volatility percentage 8% - 257% Mark-to-market derivatives— Proprietary trading (Generation) (a)(c) $ (15 ) Discounted Cash Flow Forward power price $15 - $117 (d) Mark-to-market derivatives (ComEd) $ (207 ) Discounted Cash Flow Forward heat rate (b) 8x - 9x Marketability reserve 3.5% - 8% Renewable factor 86% - 126% __________________________ (a) The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions. (b) Quoted forward natural gas rates are utilized to project the forward power curve for the delivery of energy at specified future dates. The natural gas curve is extrapolated beyond its observable period to the end of the contract’s delivery. (c) The fair values do not include cash collateral posted on level three positions of $172 million as of December 31, 2014 (d) The upper ends of the ranges are driven by the winter power and gas prices in the New England region. Without the New England region, the upper ends of the ranges for power and gas would be approximately $97 and $8.14 , respectively and would be approximately $76 for power proprietary trading.

Derivative Financial Instrume50

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of the derivative fair value	Below is a summary of the interest rate and foreign exchange hedge balances as of December 31, 2015 : Generation Other Exelon Description Derivatives Designated as Hedging Instruments Economic Hedges Proprietary (a) Collateral and Netting (b) Subtotal Derivatives Economic Hedges Collateral and Netting (b) Subtotal Total Mark-to-market $ — $ 10 $ 10 $ (5 ) $ 15 $ — $ — $ — $ — $ 15 Mark-to-market — 10 5 (1 ) 14 25 — — 25 39 Total mark-to-market — 20 15 (6 ) 29 25 — — 25 54 Mark-to-market (8 ) (2 ) (9 ) 11 (8 ) — — — — (8 ) Mark-to-market (8 ) (1 ) (3 ) 4 (8 ) — — — — (8 ) Total mark-to-market (16 ) (3 ) (12 ) 15 (16 ) — — — — (16 ) Total mark-to-market $ (16 ) $ 17 $ 3 $ 9 $ 13 $ 25 $ — $ — $ 25 $ 38 _________________________ (a) Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The characterization of the interest rate derivative contracts between the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure. Generation does not utilize proprietary trading interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates. (b) Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures subject to a master netting or similar agreement, such as accrued interest, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above. The following table provides a summary of the interest rate and foreign exchange hedge balances recorded by the Registrants as of December 31, 2014 : Generation Other Exelon Description Derivatives Designated as Hedging Instruments Economic Hedges Proprietary (a) Collateral and Netting (b) Subtotal Derivatives Economic Hedges Collateral and Netting (b) Subtotal Total Mark-to-market $ 7 $ 7 $ 20 $ (22 ) $ 12 $ 3 $ — $ — $ 3 $ 15 Mark-to-market 1 5 7 (7 ) 6 20 1 (19 ) $ 2 $ 8 Total mark-to-market 8 12 27 (29 ) 18 23 1 (19 ) 5 23 Mark-to-market (8 ) (2 ) (14 ) 25 1 — — — — 1 Mark-to-market (4 ) — (9 ) 10 (3 ) (29 ) (101 ) 19 (111 ) (114 ) Total mark-to-market (12 ) (2 ) (23 ) 35 (2 ) (29 ) (101 ) 19 (111 ) (113 ) Total mark-to-market $ (4 ) $ 10 $ 4 $ 6 $ 16 $ (6 ) $ (100 ) $ — $ (106 ) $ (90 ) _________________________ (a) Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The characterization of the interest rate derivative contracts between the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure. Generation does not utilize proprietary trading interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates. (b) Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures subject to a master netting or similar agreement, such as accrued interest, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above. The following table provides a summary of the derivative fair value balances recorded by the Registrants as of December 31, 2015 : Generation ComEd Exelon Derivatives Economic Hedges Proprietary Trading Collateral and Netting (a) Subtotal (b) Economic (c) Total Derivatives Mark-to-market derivative assets (current assets) $ 5,236 $ 108 $ (3,994 ) $ 1,350 $ — $ 1,350 Mark-to-market derivative assets (noncurrent assets) 1,860 22 (1,163 ) 719 — 719 Total mark-to-market derivative assets 7,096 130 (5,157 ) 2,069 — 2,069 Mark-to-market derivative liabilities (current liabilities) (4,907 ) (94 ) 4,827 (174 ) (23 ) (197 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,673 ) (33 ) 1,564 (142 ) (224 ) (366 ) Total mark-to-market derivative liabilities (6,580 ) (127 ) 6,391 (316 ) (247 ) (563 ) Total mark-to-market derivative net assets (liabilities) $ 516 $ 3 $ 1,234 $ 1,753 $ (247 ) $ 1,506 ______________________ (a) Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above. (b) Current and noncurrent assets are shown net of collateral of $352 million and $180 million , respectively, and current and noncurrent liabilities are shown net of collateral of $480 million and $222 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $1,234 million at December 31, 2015 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. The following table provides a summary of the derivative fair value balances recorded by the Registrants as of December 31, 2014 : Generation ComEd Exelon Derivatives Economic Proprietary Trading Collateral and (a) Subtotal (b) Economic (c) Total Derivatives Mark-to-market derivative assets (current assets) $ 4,992 $ 456 $ (4,184 ) $ 1,264 $ — $ 1,264 Mark-to-market derivative assets (noncurrent assets) 1,821 56 (1,112 ) 765 — 765 Total mark-to-market derivative assets 6,813 512 (5,296 ) 2,029 — 2,029 Mark-to-market derivative liabilities (current liabilities) (4,947 ) (468 ) 5,200 (215 ) (20 ) (235 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,540 ) (64 ) 1,502 (102 ) (187 ) (289 ) Total mark-to-market derivative liabilities (6,487 ) (532 ) 6,702 (317 ) (207 ) (524 ) Total mark-to-market derivative net assets (liabilities) $ 326 $ (20 ) $ 1,406 $ 1,712 $ (207 ) $ 1,505 ______________________ (a) Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above. (b) Current and noncurrent assets are shown net of collateral of $416 million and $171 million , respectively, and current and noncurrent liabilities are shown net of collateral of $599 million and $220 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $1,406 million at December 31, 2014 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.
Gain or loss on the hedged items and the offsetting loss or gain on the related interest rate swaps in interest expense	Exelon includes the gain or loss on the hedged items and the offsetting loss or gain on the related interest rate swaps in interest expense as follows: Year Ended December 31, Income Statement Location 2015 2014 2013 2015 2014 2013 Gain (Loss) on Swaps Gain (Loss) on Borrowings Generation Interest expense (a) $ (1 ) $ (16 ) $ (15 ) $ — $ 2 $ (6 ) Exelon Interest expense $ 2 $ 3 $ (24 ) $ (9 ) $ 15 $ (3 ) ______________________ (a) For the years ended December 31, 2015 and 2014 , the loss on Generation swaps included $(1) million and $(17) million realized in earnings, respectively, with an immaterial amount and $4 million excluded from hedge effectiveness testing, respectively.
The activity of accumulated OCI related to cash flow hedges	The tables below provide the activity of Accumulated OCI related to cash flow hedges for the years ended December 31, 2015 and 2014 , containing information about the changes in the fair value of cash flow hedges and the reclassification from Accumulated OCI into results of operations. The amounts reclassified from Accumulated OCI, when combined with the impacts of the hedged transactions, result in the ultimate recognition of net revenues or expenses at the contractual price. Income Statement Location Total Cash Flow Hedge OCI Activity, Net of Income Tax Generation Exelon Total Cash Flow Hedges Total Cash Flow Hedges Accumulated OCI derivative gain at January 1, 2014 $ 114 $ 120 Effective portion of changes in fair value (15 ) (31 ) Reclassifications from accumulated OCI to net income Operating revenues (117 ) (a) (117 ) (a) Accumulated OCI derivative gain at December 31, 2014 (18 ) (28 ) Effective portion of changes in fair value (8 ) (12 ) Reclassifications from accumulated OCI to net income Other, net — 16 (b) Reclassifications from accumulated OCI to net income Interest expense 7 (c) 7 (c) Reclassifications from accumulated OCI to net income Operating revenues (2 ) (2 ) Accumulated OCI derivative gain at December 31, 2015 $ (21 ) $ (19 ) _______________________ (a) Amount is net of related income tax expense of $78 million for the year ended December 31, 2014 . (b) Amount is net of related income tax benefit of $10 million for the year ended December 31, 2015 . (c) Amount is net of related income tax expense of $4 million for the year ended December 31, 2015 .
Change in fair value and reclassification of derivative contracts	In the tables below, “Change in fair value” represents the change in fair value of the derivative contracts held at the reporting date. The “Reclassification to realized at settlement” represents the recognized change in fair value that was reclassified to realized due to settlement of the derivative during the period. Location on Income Statement For the Years Ended December 31, 2015 2014 2013 Change in fair value of commodity positions Operating Revenues $ 8 $ (1 ) $ (22 ) Reclassification to realized at settlement of commodity positions Operating Revenues (14 ) (29 ) (15 ) Net commodity mark-to-market gains (losses) Operating Revenues (6 ) (30 ) (37 ) Change in fair value of treasury positions Operating Revenues 8 1 1 Reclassification to realized at settlement of treasury positions Operating Revenues (10 ) 3 (3 ) Net treasury mark-to market gains (losses) Operating Revenues (2 ) 4 (2 ) Net mark-to market gains (losses) Operating Revenues $ (8 ) $ (26 ) $ (39 ) In the tables below, “Change in fair value” represents the change in fair value of the derivative contracts held at the reporting date. The “Reclassification to realized at settlement” represents the recognized change in fair value that was reclassified to realized due to settlement of the derivative during the period. Generation Intercompany Eliminations Exelon Corporate Exelon Year Ended December 31, 2015 Operating Revenues Purchased Power and Fuel Interest Expense Total Operating (a) Interest Expense Total Change in fair value of commodity positions $ 759 $ (355 ) $ — $ 404 $ — $ — $ 404 Reclassification to realized at settlement of commodity positions (563 ) 409 — (154 ) — — (154 ) Net commodity mark-to-market gains (losses) 196 54 — 250 — — 250 Change in fair value of treasury positions 13 — — 13 — 36 49 Reclassification to realized at settlement of treasury positions (6 ) — — (6 ) — 64 58 Net treasury mark-to market gains (losses) 7 — — 7 — 100 107 Net mark-to market gains (losses) $ 203 $ 54 $ — $ 257 $ — $ 100 $ 357 Generation Intercompany Eliminations Exelon Corporate Exelon Year Ended December 31, 2014 Operating Revenues Purchased Power and Fuel Interest Expense Total Operating Interest Expense Total Change in fair value of commodity positions $ (413 ) $ (194 ) $ — $ (607 ) $ — $ — $ (607 ) Reclassification to realized at settlement of commodity positions 231 (223 ) — 8 — — 8 Net commodity mark-to-market gains (losses) (182 ) (417 ) — (599 ) — — (599 ) Change in fair value of treasury positions 10 — (2 ) 8 — (100 ) (92 ) Reclassification to realized at settlement of treasury positions (2 ) — — (2 ) — — (2 ) Net treasury mark-to market gains (losses) 8 — (2 ) 6 — (100 ) (94 ) Net mark-to market gains (losses) $ (174 ) $ (417 ) $ (2 ) $ (593 ) $ — $ (100 ) $ (693 ) Generation Intercompany Exelon Corporate Exelon Year Ended December 31, 2013 Operating Purchased Interest Expense Total Operating (a) Interest Expense Total Change in fair value of commodity positions $ 286 $ 180 $ — $ 466 $ (6 ) $ — $ 460 Reclassification to realized at settlement of commodity positions (64 ) 104 — 40 13 — 53 Net commodity mark-to-market gains (losses) 222 284 — 506 7 — 513 Change in fair value of treasury positions (1 ) — (4 ) (5 ) — — (5 ) Reclassification to realized at settlement of treasury positions (1 ) — — (1 ) — — (1 ) Net treasury mark-to market gains (losses) (2 ) — (4 ) (6 ) — — (6 ) Net mark-to market gains (losses) $ 220 $ 284 $ (4 ) $ 500 $ 7 $ — $ 507 ________________________ (a) Prior to the Constellation merger, the five-year financial swap contract between Generation and ComEd was de-designated. As a result, all prospective changes in fair value were recorded to operating revenues and eliminated in consolidation.
Information on Generation's credit exposure for all derivative instruments, normal purchase normal sales, and applicable payables and receivables, net of collateral and instruments that are subject to master netting agreements	The figures in the tables below exclude credit risk exposure from individual retail counterparties, Nuclear fuel procurement contracts and exposure through RTOs, ISOs, NYMEX, ICE and Nodal commodity exchanges, further discussed in ITEM 7A. — QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK . Additionally, the figures in the tables below exclude exposures with affiliates, including net receivables with ComEd, PECO and BGE of $15 million , $36 million and $31 million , respectively. Rating as of December 31, 2015 Total Exposure Before Credit Collateral Credit Collateral (a) Net Exposure Number of Counterparties Greater than 10% of Net Exposure Net Exposure of Counterparties Greater than 10% of Net Exposure Investment grade $ 1,397 $ 50 $ 1,347 1 $ 432 Non-investment grade 67 25 42 — — No external ratings Internally rated—investment grade 521 — 521 — — Internally rated—non-investment grade 77 7 70 — — Total $ 2,062 $ 82 $ 1,980 1 $ 432 Net Credit Exposure by Type of Counterparty December 31, 2015 Financial institutions $ 187 Investor-owned utilities, marketers, power producers 886 Energy cooperatives and municipalities 872 Other 35 Total $ 1,980 ______________________ (a) As of December 31, 2015 , credit collateral held from counterparties where Generation had credit exposure included $13 million of cash and $69 million of letters of credit. The aggregate fair value of all derivative instruments with credit-risk-related contingent features in a liability position that are not fully collateralized (excluding transactions on the exchanges that are fully collateralized) is detailed in the table below: For the Years Ended December 31, Credit-Risk Related Contingent Feature 2015 2014 Gross Fair Value of Derivative Contracts Containing this Feature (a) $ (932 ) $ (1,433 ) Offsetting Fair Value of In-the-Money Contracts Under Master Netting Arrangements (b) 684 1,140 Net Fair Value of Derivative Contracts Containing This Feature (c) $ (248 ) $ (293 ) __________________________ (a) Amount represents the gross fair value of out-of-the-money derivative contracts containing credit-risk-related contingent features ignoring the effects of master netting agreements. (b) Amount represents the offsetting fair value of in-the-money derivative contracts under legally enforceable master netting agreements with the same counterparty, which reduces the amount of any liability for which a Registrant could potentially be required to post collateral. (c) Amount represents the net fair value of out-of-the-money derivative contracts containing credit-risk related contingent features after considering the mitigating effects of offsetting positions under master netting arrangements and reflects the actual net liability upon which any potential contingent collateral obligations would be based.

Debt and Credit Agreements (Tab

Debt and Credit Agreements (Tables)	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Schedule of Short-term Debt	Exelon, Generation, ComEd, PECO and BGE had the following amounts of commercial paper borrowings at December 31, 2015 and 2014 : Maximum Program Size at December 31, Outstanding Commercial Paper at December 31, Average Interest Rate on Commercial Paper Borrowings for the Year Ended December 31, Commercial Paper Issuer 2015 (a)(b) 2014 (a)(b) 2015 2014 2015 2014 Exelon Corporate $ 500 $ 500 $ — $ — n.a. n.a. Generation 5,450 5,600 — — 0.49 % 0.32 % ComEd 1,000 1,000 294 304 0.53 % 0.33 % PECO 600 600 — — n.a. n.a. BGE 600 600 210 120 0.48 % 0.29 % Total $ 8,150 $ 8,300 $ 504 $ 424 _____________________ (a) Reflects aggregate bank commitments under the revolving and bilateral credit agreements (with the exception of $275 million and $200 million bilateral agreements for Generation as of December 31, 2015 and 2014 , respectively) that backstop the commercial paper program. See discussion and Credit Facilities table below for items affecting effective program size. (b) Excludes additional credit facilities for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million , $34 million , $34 million and $5 million , respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. The agreements for these facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of December 31, 2015 , letters of credit issued under these facilities totaled $7 million , $14 million , $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively. The following tables present the short-term borrowings activity for Exelon, Generation, ComEd, and BGE during 2015 , 2014 and 2013 . PECO did not have any short-term borrowings during 2015 , 2014 or 2013 . Exelon 2015 2014 2013 Average borrowings $ 499 $ 571 $ 254 Maximum borrowings outstanding 739 1,164 682 Average interest rates, computed on a daily basis 0.53 % 0.32 % 0.37 % Average interest rates, at December 31 0.88 % 0.53 % 0.35 % Generation 2015 2014 2013 Average borrowings $ 1 $ 93 $ 42 Maximum borrowings outstanding 50 552 291 Average interest rates, computed on a daily basis 0.49 % 0.32 % 0.32 % Average interest rates, at December 31 n.a. n.a. n.a. ComEd 2015 2014 2013 Average borrowings $ 461 $ 415 $ 203 Maximum borrowings outstanding 684 597 446 Average interest rates, computed on a daily basis 0.53 % 0.33 % 0.40 % Average interest rates, at December 31 0.89 % 0.50 % 0.37 % BGE 2015 2014 2013 Average borrowings $ 37 $ 64 $ 35 Maximum borrowings outstanding 210 180 135 Average interest rates, computed on a daily basis 0.48 % 0.29 % 0.31 % Average interest rates, computed at December 31 0.87 % 0.61 % 0.31 %
Schedule of Line of Credit Facilities	At December 31, 2015 , the Registrants had the following aggregate bank commitments, credit facility borrowings and available capacity under their respective credit facilities: Available Capacity at December 31, 2015 Borrower Aggregate Bank (a) Facility Draws Outstanding Letters of Credit (c) Actual To Support Additional Commercial (b) Exelon Corporate $ 500 $ — $ 26 $ 474 $ 474 Generation 5,725 — 1,449 4,276 4,174 ComEd 1,000 — 2 998 704 PECO 600 — 1 599 599 BGE 600 — — 600 390 Total $ 8,425 $ — $ 1,478 $ 6,947 $ 6,341 _______________________ (a) Excludes additional credit facilities for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million , $34 million , $34 million and $5 million , respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. The agreements for these facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of December 31, 2015 , letters of credit issued under these facilities totaled $7 million , $14 million , $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively. (b) Excludes $275 million bilateral credit facilities that do not back Generation’s commercial paper program. (c) Excludes nonrecourse debt letters of credit, see discussion below on Continental Wind.
Schedule Of Credit Agreement Covenants	The following table summarizes the minimum thresholds reflected in the credit agreements for the year ended December 31, 2015 : Exelon Generation ComEd PECO BGE Credit agreement threshold 2.50 to 1 3.00 to 1 2.00 to 1 2.00 to 1 2.00 to 1 At December 31, 2015 , the interest coverage ratios at the Registrants were as follows: Exelon Generation ComEd PECO BGE Interest coverage ratio 9.77 12.31 7.25 8.94 10.66
Schedule of Long-term Debt Instruments	PECO Maturity Date December 31, Rates 2015 2014 Long-term debt First mortgage bonds (a) 1.20 % - 5.95 % 2016 - 2044 $ 2,600 $ 2,250 Total long-term debt 2,600 2,250 Unamortized debt discount and premium, net (5 ) (4 ) Unamortized debt issuance costs (b) (15 ) (14 ) Long-term debt due within one year (300 ) — Long-term debt $ 2,280 $ 2,232 Long-term debt to financing trusts (c) Subordinated debentures to PECO Trust III 7.38 % 2028 $ 81 $ 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Long-term debt to financing trusts $ 184 $ 184 _____________________ (a) Substantially all of PECO’s assets are subject to the lien of its mortgage indenture. (b) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. (c) Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets. Generation Maturity Date December 31, Rates 2015 2014 Long-term debt Senior unsecured notes 2.00 % - 7.60 % 2017 - 2042 $ 5,971 $ 5,771 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 435 — Nuclear fuel procurement contracts 3.15 % - 3.35 % 2018 - 2020 127 70 Notes payable and other (a)(b) 1.43 % 7.83 % 2016 - 2035 166 26 Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,162 1,166 Variable rates 2.42 % - 5.00 % 2017 - 2030 1,058 1,101 Total long-term debt 8,919 8,134 Fair value adjustment 127 146 Unamortized debt discount and premium, net (17 ) (14 ) Unamortized debt issuance costs (c) (70 ) (70 ) Long-term debt due within one year (90 ) (614 ) Long-term debt $ 8,869 $ 7,582 ______________________ (a) Includes Generation’s capital lease obligations of $21 million and $24 million at December 31, 2015 and 2014 , respectively. Generation will make lease payments of $4 million , $4 million , $4 million , $5 million and $4 million in 2016 , 2017 , 2018 , 2019 , 2020 , respectively. The following tables present the outstanding long-term debt at Exelon, Generation, ComEd, PECO and BGE as of December 31, 2015 and 2014 : Exelon Maturity Date December 31, Rates 2015 2014 Long-term debt Rate stabilization bonds 5.72 % - 5.82 % 2017 $ 120 $ 195 First mortgage bonds (a) 1.20 % - 6.45 % 2016 - 2045 9,019 8,079 Senior unsecured notes 1.55 % - 7.60 % 2017 - 2045 9,803 7,071 Unsecured bonds 2.80 % - 6.35 % 2016 - 2036 1,750 1,750 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 435 — Nuclear fuel procurement contracts 3.15 % - 3.35 % 2018 - 2020 127 70 Notes payable and other (b)(c) 1.43 % - 7.83 % 2016 - 2053 314 174 Junior subordinated notes 6.50 % 2024 1,150 1,150 Contract payment - junior subordinated notes 2.50 % 2017 64 108 Long-term software licensing agreement 3.95 % 2024 111 — Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,162 1,166 Variable rates 2.42 % - 5.00 % 2017 - 2030 1,058 1,101 Total long-term debt 25,113 20,864 Unamortized debt discount and premium, net (63 ) (37 ) Unamortized debt issuance costs (d) (180 ) (150 ) Fair value adjustment 275 333 Fair value hedge carrying value adjustment, net — 4 Long-term debt due within one year (1,500 ) (1,802 ) Long-term debt $ 23,645 $ 19,212 Long-term debt to financing trusts (e) Subordinated debentures to ComEd Financing III 6.35 % 2033 $ 206 $ 206 Subordinated debentures to PECO Trust III 7.38 % 2028 81 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Subordinated debentures to BGE Trust 6.20 % 2043 258 258 Total long-term debt to financing trusts 648 648 Unamortized debt issuance costs (d) (7 ) (7 ) Long-term debt to financing trusts $ 641 $ 641 ____________________ (a) Substantially all of ComEd’s assets other than expressly excepted property and substantially all of PECO’s assets are subject to the liens of their respective mortgage indentures. (b) Includes capital lease obligations of $29 million and $32 million at December 31, 2015 and 2014 , respectively. Lease payments of $4 million , $4 million , $4 million , $5 million , $4 million , and $8 million will be made in 2016 , 2017 , 2018 , 2019 , 2020 and thereafter, respectively. (c) Includes financing related to Albany Green Energy, LLC (AGE), which is a consolidated variable interest entity (see Note 2 - Variable Interest Entities for additional information). The agreement is scheduled to expire on November 17, 2017, at a variable rate equal to LIBOR plus 1.25%. As of December 31, 2015, $100 million was outstanding. (d) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. (e) Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets. ComEd Maturity Date December 31, Rates 2015 2014 Long-term debt First mortgage bonds (a) 1.95 % - 6.45 % 2016 - 2045 $ 6,419 $ 5,829 Notes payable and other (b) 6.95 % - 7.49 % 2016 - 2053 148 148 Total long-term debt 6,567 5,977 Unamortized debt discount and premium, net (20 ) (19 ) Unamortized debt issuance costs (c) (38 ) (33 ) Long-term debt due within one year (665 ) (260 ) Long-term debt $ 5,844 $ 5,665 Long-term debt to financing trust (d) Subordinated debentures to ComEd Financing III 6.35 % 2033 $ 206 $ 206 Total long-term debt to financing trusts 206 206 Unamortized debt issuance costs (c) (1 ) (1 ) Long-term debt to financing trusts $ 205 $ 205 ______________________ (a) Substantially all of ComEd’s assets other than expressly excepted property are subject to the lien of its mortgage indenture. (b) Includes ComEd’s capital lease obligations of $8 million at both December 31, 2015 and 2014 , respectively. Lease payments of less than $1 million will be made from 2016 through expiration at 2053. (c) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. (d) Amount owed to this financing trust is recorded as Long-term debt to financing trust within ComEd’s Consolidated Balance Sheets. BGE Maturity Date December 31, Rates 2015 2014 Long-term debt Rate stabilization bonds 5.72 % - 5.82 % 2017 $ 120 $ 195 Senior unsecured notes 2.80 % - 6.35 % 2016 - 2036 1,750 1,750 Total long-term debt 1,870 1,945 Unamortized debt discount and premium, net (3 ) (3 ) Unamortized debt issuance costs (a) (9 ) (10 ) Long-term debt due within one year (378 ) (75 ) Long-term debt $ 1,480 $ 1,857 Long-term debt to financing trusts (b) Subordinated debentures to BGE Capital Trust II 6.20 % 2043 $ 258 $ 258 Total long-term debt to financing trusts 258 258 Unamortized debt issuance costs (a) (6 ) (6 ) Long-term debt to financing trusts $ 252 $ 252 ___________________ (a) Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information. (b) Amount owed to this financing trust is recorded as Long-term debt to financing trust within BGE’s Consolidated Balance Sheets.
Schedule of Maturities of Long-term Debt	Long-term debt maturities at Exelon, Generation, ComEd, PECO and BGE in the periods 2016 through 2020 and thereafter are as follows: Year Exelon Generation ComEd PECO BGE 2016 $ 1,487 $ 90 $ 665 $ 300 $ 378 2017 1,841 805 425 — 42 2018 1,393 53 840 500 — 2019 973 673 300 — — 2020 3,311 1,911 500 — — Thereafter 16,756 (a) 5,387 4,043 (b) 1,984 (c) 1,708 (d) Total $ 25,761 $ 8,919 $ 6,773 $ 2,784 $ 2,128 ____________________ (a) Includes $648 million due to ComEd, PECO and BGE financing trusts. (b) Includes $206 million due to ComEd financing trust. (c) Includes $184 million due to PECO financing trusts. (d) Includes $258 million due to BGE financing trust.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The following table represents the net interest receivable (payable), including interest related to tax positions reflected in the Registrants’ Consolidated Balance Sheets. Net interest receivable (payable) as of Exelon Generation ComEd PECO BGE December 31, 2015 $ (288 ) $ 80 $ (210 ) $ 3 $ (1 ) December 31, 2014 (310 ) 40 (203 ) 3 (1 ) Income tax expense (benefit) from continuing operations is comprised of the following components: For the Year Ended December 31, 2015 Exelon Generation ComEd PECO BGE Included in operations: Federal Current $ 407 $ 546 $ (80 ) $ 64 $ 25 Deferred 566 16 310 69 126 Investment tax credit amortization (22 ) (19 ) (2 ) — (1 ) State Current (86 ) (90 ) 7 (10 ) — Deferred 208 49 45 20 39 Total $ 1,073 $ 502 $ 280 $ 143 $ 189 For the Year Ended December 31, 2014 Exelon Generation ComEd PECO BGE Included in operations: Federal Current $ 121 $ 360 $ (171 ) $ 28 $ 24 Deferred 576 (35 ) 395 87 90 Investment tax credit amortization (20 ) (16 ) (2 ) — (1 ) State Current 42 35 7 (2 ) — Deferred (53 ) (137 ) 39 1 27 Total $ 666 $ 207 $ 268 $ 114 $ 140 For the Year Ended December 31, 2013 Exelon Generation ComEd PECO BGE Included in operations: Federal Current $ 744 $ 250 $ 160 $ 126 $ 9 Deferred 140 360 (27 ) 23 100 Investment tax credit amortization (15 ) (11 ) (2 ) (1 ) (1 ) State Current 181 50 50 16 — Deferred (6 ) (34 ) (29 ) (2 ) 26 Total $ 1,044 $ 615 $ 152 $ 162 $ 134
Interest Income and Interest Expense Disclosure [Table Text Block]	The following table sets forth the net interest expense, including interest related to tax positions, recognized in interest expense (income) in other income and deductions in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. The Registrants have not accrued any material penalties with respect to uncertain tax positions. Net interest expense (income) for the years ended Exelon Generation ComEd PECO BGE December 31, 2015 $ (13 ) $ (31 ) $ 7 $ — $ — December 31, 2014 (36 ) (50 ) 6 — 1 December 31, 2013 391 17 281 (1 ) —
Effective Income Tax Rate Reconciliation	The effective income tax rate from continuing operations varies from the U.S. Federal statutory rate principally due to the following: For the Year Ended December 31, 2015 Exelon Generation ComEd PECO BGE U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 3.7 1.0 4.9 1.0 5.3 Qualified nuclear decommissioning trust fund loss (0.4 ) (0.8 ) — — — Domestic production activities deduction (0.7 ) (1.3 ) — — — Health care reform legislation — — — — 0.1 Amortization of investment tax credit, including deferred taxes on basis difference (0.9 ) (1.5 ) (0.3 ) (0.1 ) (0.1 ) Plant basis differences (1.5 ) — (0.1 ) (8.7 ) (0.7 ) Production tax credits and other credits (1.9 ) (3.4 ) — — — Non-controlling interest 0.3 0.5 — — — Statute of limitations expiration (1.4 ) (2.4 ) — — — Other — — 0.2 0.2 — Effective income tax rate 32.2 % 27.1 % 39.7 % 27.4 % 39.6 % For the Year Ended December 31, 2014 Exelon Generation ComEd PECO BGE U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 1.3 (1.9 ) 4.5 (0.1 ) 5.0 Qualified nuclear decommissioning trust fund income 2.4 4.8 — — — Domestic production activities deduction (2.0 ) (4.1 ) — — — Health care reform legislation 0.1 — 0.2 — 0.2 Amortization of investment tax credit, including deferred taxes on basis difference (1.1 ) (2.0 ) (0.3 ) (0.1 ) (0.3 ) Plant basis differences (1.9 ) — (0.1 ) (10.4 ) 0.2 Production tax credits and other credits (2.4 ) (4.8 ) — — — Non-controlling interest (1.8 ) (3.7 ) Statute of limitations expiration (2.6 ) (5.3 ) — — — Other (0.2 ) (1.1 ) 0.3 0.1 (0.2 ) Effective income tax rate 26.8 % 16.9 % 39.6 % 24.5 % 39.9 % For the Year Ended December 31, 2013 Exelon Generation ComEd PECO BGE U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 4.8 1.8 3.4 1.6 4.9 Qualified nuclear decommissioning trust fund income 3.7 6.1 — — — Domestic production activities deduction — — — — — Health care reform legislation 0.1 — 0.7 — 0.2 Amortization of investment tax credit, including deferred taxes on basis difference (1.9 ) (3.0 ) (0.6 ) (0.1 ) — Plant basis differences (1.6 ) — (0.8 ) (7.1 ) (0.2 ) Production tax credits and other credits (2.1 ) (3.4 ) (0.1 ) — — Statute of limitations expiration (0.1 ) (0.2 ) — — — Other (0.3 ) 0.4 0.3 (0.3 ) (0.9 ) Effective income tax rate 37.6 % 36.7 % 37.9 % 29.1 % 39.0 %
Tax Effects of Temporary Differences	The tax effects of temporary differences and carryforwards, which give rise to significant portions of the deferred tax assets (liabilities), as of December 31, 2015 and 2014 are presented below: For the Year Ended December 31, 2015 Exelon Generation ComEd PECO BGE Plant basis differences $ (13,393 ) $ (4,269 ) $ (4,424 ) $ (2,901 ) $ (1,821 ) Accrual based contracts (136 ) (136 ) — — — Derivatives and other financial instruments (203 ) (181 ) (4 ) — — Deferred pension and postretirement obligation 1,801 (371 ) (505 ) (9 ) (47 ) Nuclear decommissioning activities (592 ) (592 ) — — — Deferred debt refinancing costs 133 48 (15 ) (1 ) (4 ) Regulatory assets and liabilities (1,706 ) — (219 ) 16 (264 ) Tax loss carryforward 103 56 — — 33 Tax credit carryforward 327 374 — — — Investment in CENG (595 ) (595 ) — — — Other, net 1,112 425 270 105 27 Deferred income tax liabilities (net) $ (13,149 ) $ (5,241 ) $ (4,897 ) $ (2,790 ) $ (2,076 ) Unamortized investment tax credits (622 ) (598 ) (17 ) (2 ) (5 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (13,771 ) $ (5,839 ) $ (4,914 ) $ (2,792 ) $ (2,081 ) For the Year Ended December 31, 2014 Exelon Generation ComEd PECO BGE Plant basis differences $ (12,143 ) $ (3,834 ) $ (3,945 ) $ (2,749 ) $ (1,660 ) Accrual based contracts (178 ) (178 ) — — — Derivatives and other financial instruments (46 ) (79 ) (4 ) — — Deferred pension and postretirement obligation 1,914 (390 ) (543 ) 2 (53 ) Nuclear decommissioning activities (726 ) (726 ) — — — Deferred debt refinancing costs 112 57 (18 ) (2 ) (4 ) Regulatory assets and liabilities (1,824 ) — (286 ) 27 (258 ) Tax loss carryforward 111 48 — 11 39 Tax credit carryforward 97 143 — — — Investment in CENG (563 ) (563 ) — — — Other, net 1,029 346 255 111 30 Deferred income tax liabilities (net) $ (12,217 ) $ (5,176 ) $ (4,541 ) $ (2,600 ) $ (1,906 ) Unamortized investment tax credits (555 ) (528 ) (20 ) (2 ) (5 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (12,772 ) $ (5,704 ) $ (4,561 ) $ (2,602 ) $ (1,911 )
Summary of Loss Carryforwards	The following table provides the Registrants’ carryforwards and any corresponding valuation allowances as of December 31, 2015 . Exelon Generation ComEd PECO BGE Federal Federal general business credits carryforward 416 (a) 415 — — — State State net operating losses and other credit carryforwards 2,086 (b) 1,259 (b) — — 618 (c) Deferred taxes on state tax attributes (net) 117 66 — — 34 Valuation allowance on state tax attributes 13 11 — — 1 _____________________ (a) Exelon’s federal general business credit carryforwards will expire beginning in 2032. (b) Exelon’s and Generation's state net operating losses and other carryforwards, which are presented on a post-apportioned basis, will expire beginning in 2016. (c) BGE’s state net operating losses will expire beginning in 2026
Reconciliation of Unrecognized Tax Benefits Excluding Amounts Pertaining to Examined Tax Returns Foll Forward	The following table provides a reconciliation of the Registrants’ unrecognized tax benefits as of December 31, 2015 , 2014 and 2013 : Exelon Generation ComEd PECO BGE Unrecognized tax benefits at January 1, 2015 $ 1,829 $ 1,357 $ 149 $ 44 $ — Increases based on tax positions related to 2015 108 — — — 106 Change to positions that only affect timing (705 ) (659 ) (7 ) (44 ) — Increases based on tax positions prior to 2015 79 65 — — 14 Decreases based on tax positions prior to 2015 (116 ) (112 ) — — — Decrease from settlements with taxing authorities (31 ) (31 ) — — — Decreases from expiration of statute of limitations (86 ) (86 ) — — — Unrecognized tax benefits at December 31, 2015 $ 1,078 $ 534 $ 142 $ — $ 120 Exelon Generation ComEd PECO BGE Unrecognized tax benefits at January 1, 2014 $ 2,175 $ 1,415 $ 324 $ 44 $ — Increases based on tax positions related to 2014 15 15 — — — Change to positions that only affect timing (255 ) 33 (175 ) — — Increases based on tax positions prior to 2014 18 18 — — — Decreases based on tax positions prior to 2014 (1 ) (2 ) — — — Decrease from settlements with taxing authorities (35 ) (34 ) — — — Decreases from expiration of statute of limitations (88 ) (88 ) — — — Unrecognized tax benefits at December 31, 2014 $ 1,829 $ 1,357 $ 149 $ 44 $ — Exelon Generation ComEd PECO BGE Unrecognized tax benefits at January 1, 2013 $ 1,024 $ 876 $ 67 $ 44 $ — Increases based on tax positions related to 2013 19 19 — — — Change to positions that only affect timing 649 36 257 — — Increases based on tax positions prior to 2013 493 493 — — — Decreases based on tax positions prior to 2013 (6 ) (5 ) — — — Decreases from expiration of statute of limitations (4 ) (4 ) — — — Unrecognized tax benefits at December 31, 2013 $ 2,175 $ 1,415 $ 324 $ 44 $ —
Summary of Open Tax Years by Jurisdiction	Description of tax years that remain open to assessment by major jurisdiction Taxpayer Open Years Exelon (and predecessors) and subsidiaries consolidated Federal income tax returns 1999, 2001-2014 Exelon and subsidiaries Illinois unitary income tax returns 2007-2014 Constellation combined New York corporate income tax returns 2010-March 2012 Various separate company Pennsylvania corporate net income tax returns 2010-2014 BGE Maryland corporate net income tax returns 2011-2014 Various Exelon Maryland corporate net income tax returns 2012-2014 Various Constellation (Non-BGE) Maryland corporate net income tax returns 2011-2014

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2015
Asset Retirement Obligation Disclosure [Abstract]
Nuclear Decommissioning Asset Retirement Obligation Rollforward	The following table provides a rollforward of the nuclear decommissioning ARO reflected on Exelon’s and Generation’s Consolidated Balance Sheets, from January 1, 2014 to December 31, 2015 : Exelon and Generation Nuclear decommissioning ARO at January 1, 2014 $ 4,855 Consolidation of CENG (a) 1,760 Accretion expense 334 Net increase due to changes in, and timing of, estimated future cash flows 19 Costs incurred to decommission retired plants (7 ) Nuclear decommissioning ARO at December 31, 2014 (b) 6,961 Accretion expense 387 Net increase due to changes in, and timing of, estimated future cash flows 901 Costs incurred to decommission retired plants (3 ) Nuclear decommissioning ARO at December 31, 2015 (b) $ 8,246 _________________________ (a) Represents the fair value of the CENG ARO liability as of April 1, 2014, the date of consolidation. See Note 5 — Investment in Constellation Energy Nuclear Group, LLC for additional information. (b) Includes $ 7 million and $ 8 million as the current portion of the ARO at December 31, 2015 and 2014 , respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.
Unrealized Gains Losses On Nuclear Decommissioning Trust Funds	The following table provides unrealized gains on NDT funds for 2015 , 2014 and 2013 : Exelon and Generation For the Years Ended December 31, 2015 2014 2013 Net unrealized gains (losses) on decommissioning trust funds—Regulatory Agreement Units (a) $ (282 ) $ 180 $ 406 Net unrealized gains (losses) on decommissioning trust funds—Non-Regulatory Agreement Units (b)(c) (197 ) 134 146 _______________________ (a) Net unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities on Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates on Generation’s Consolidated Balance Sheets. (b) Excludes $ 7 million , $ 29 million and $ 7 million of net unrealized gains related to the Zion Station pledged assets in 2015 , 2014 and 2013 , respectively. Net unrealized gains related to Zion Station pledged assets are included in the Payable for Zion Station decommissioning on Exelon’s and Generation’s Consolidated Balance Sheets. (c) Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included within Other, net in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.
Nuclear Decommissioning Pledged Assets	The following table provides the pledged assets and payables to ZionSolutions, and withdrawals by ZionSolutions at December 31, 2015 and 2014 : Exelon and Generation 2015 2014 Carrying value of Zion Station pledged assets $ 206 $ 319 Payable to Zion Solutions (a) 189 292 Current portion of payable to Zion Solutions (b) 99 137 Cumulative withdrawals by Zion Solutions to pay decommissioning costs (c) 786 666 ___________________ (a) Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT Funds. The NDT Funds will be utilized to satisfy the tax obligations as gains and losses are realized. (b) Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets. (c) Includes project expenses to decommission Zion Station and estimated tax payments on Zion Station NDT fund earnings.
Non Nuclear Decommissioning Asset Retirement Obligation Rollforward	The following table provides a rollforward of the non-nuclear AROs reflected on the Registrants’ Consolidated Balance Sheets from January 1, 2014 to December 31, 2015 : Exelon Generation ComEd PECO BGE Non-nuclear AROs at January 1, 2014 $ 351 $ 201 $ 101 $ 30 $ 19 Net increase (decrease) due to changes in, and timing of, estimated future cash flows (a) (1 ) (2 ) 2 — (1 ) Development projects (b) 11 11 — — — Accretion expense (c) 15 11 3 1 — Liabilities held for sale (d) (4 ) (4 ) — — — Sale of generating assets (e) (20 ) (20 ) — — — Payments (6 ) (3 ) (2 ) (1 ) — Non-nuclear AROs at December 31, 2014 (f) 346 194 104 30 18 Net increase (decrease) due to changes in, and timing of, estimated future cash flows (a) (10 ) (12 ) 6 (4 ) — Development projects (b) 10 10 — — — Accretion expense (c) 16 10 5 1 — Sale of generating assets (e) (2 ) (2 ) — — — Payments (5 ) (3 ) (2 ) — — Non-nuclear AROs at December 31, 2015 (f) $ 355 $ 197 $ 113 $ 27 $ 18 ________________________ (a) During the year ended December 31, 2015 , Generation recorded a decrease of $(2) million in Operating and maintenance expense. ComEd, PECO, and BGE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2015 . During the year ended December 31, 2014 , Generation recorded a decrease of $(2) million and ComEd recorded an increase of $1 million in Operating and maintenance expense. PECO and BGE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2014 . (b) Relates to new AROs recorded due to the construction of solar, wind and other non-nuclear generating sites. (c) For ComEd, PECO, and BGE, the majority of the accretion is recorded as an increase to a regulatory asset due to the associated regulatory treatment. (d) Represents AROs related to generating stations classified as held for sale. See Note 4 — Mergers, Acquisitions, and Dispositions for further information. (e) Reflects a reduction to the ARO resulting primarily from the sales of Schuylkill generating station in 2015 and Keystone and Conemaugh generating stations in 2014. See Note 4 — Mergers, Acquisitions, and Dispositions for further information. (f) Excludes $5 million , $2 million , $0 million and $1 million as the current portion of the ARO at December 31, 2015 for Generation, ComEd, PECO and BGE, respectively. Excludes $1 million , $1 million , $1 million and $1 million as the current portion of the ARO at December 31, 2014 for Generation, ComEd, PECO and BGE, respectively. This is included in Other current liabilities on the Registrants' respective Consolidated Balance Sheets.

Implications of Potential Ear54

Implications of Potential Early Plant Retirements Implications of Potential Early Plant Retirements (Tables)	12 Months Ended
	Dec. 31, 2015
Implications of Potential Early Plant Retirements [Abstract]
Implications of Potential Early Plant Retirement [Table Text Block] [Table Text Block]	(in millions) Quad Cities Clinton Ginna Total Asset Balances Materials and supplies inventory $ 50 $ 57 $ 29 $ 136 Nuclear fuel inventory, net 218 107 60 385 Completed plant, net 1,030 579 127 1,736 Construction work in progress 11 9 11 31 Liability Balances Asset retirement obligation (698 ) (401 ) (644 ) (1,743 ) NRC License Renewal Term 2032 2046 (a) 2029

Retirement Benefits (Tables)

Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Schedule Of Pension And Other Postretirement Participation	Operating Company (d) Name of Plan: Generation ComEd PECO BGE BSC Qualified Pension Plans: Exelon Corporation Retirement Program (a) X X X X X Exelon Corporation Cash Balance Pension Plan (a) X X X X X Exelon Corporation Pension Plan for Bargaining Unit Employees (a) X X X Exelon New England Union Employees Pension Plan (a) X Exelon Employee Pension Plan for Clinton, TMI and Oyster Creek (a) X X X X Pension Plan of Constellation Energy Group, Inc. (b) X X X X X Pension Plan of Constellation Energy Nuclear Group, LLC (c) X X X Nine Mile Point Pension Plan (c) X X Constellation Mystic Power, LLC Union Employees Pension Plan Including Plan A and Plan B (b) X Non-Qualified Pension Plans: Exelon Corporation Supplemental Pension Benefit Plan and 2000 Excess Benefit Plan (a) X X X X Exelon Corporation Supplemental Management Retirement Plan (a) X X X X X Constellation Energy Group, Inc. Senior Executive Supplemental Plan (b) X X X Constellation Energy Group, Inc. Supplemental Pension Plan (b) X X X Constellation Energy Group, Inc. Benefits Restoration Plan (b) X X X X Constellation Nuclear Plan, LLC Executive Retirement Plan (c) X X Constellation Energy Nuclear Plan, LLC Benefits Restoration Plan (c) X X Baltimore Gas & Electric Company Executive Benefit Plan (b) X X X Baltimore Gas & Electric Company Manager Benefit Plan (b) X X X X Operating Company (d) Name of Plan: Generation ComEd PECO BGE BSC Other Postretirement Benefit Plans: PECO Energy Company Retiree Medical Plan (a) X X X X X Exelon Corporation Health Care Program (a) X X X X X Exelon Corporation Employees’ Life Insurance Plan (a) X X X X X Constellation Energy Group, Inc. Retiree Medical Plan (b) X X X X X Constellation Energy Group, Inc. Retiree Dental Plan (b) X X X Constellation Energy Group, Inc. Employee Life Insurance Plan and Family Life Insurance Plan (b) X X X X X Constellation Mystic Power, LLC Post-Employment Medical Account Savings Plan (b) X Exelon New England Union Post-Employment Medical Savings Account Plan (a) X Retiree Medical Plan of Constellation Energy Nuclear Group LLC (c) X X X Retiree Dental Plan of Constellation Energy Nuclear Group LLC (c) X X X Nine Mile Point Nuclear Station, LLC Medical Care and Prescription Drug Plan for Retired Employees (c) X X ______________________ (a) These plans are collectively referred to as the Legacy Exelon plans. (b) These plans are collectively referred to as the Legacy Constellation Energy Group (CEG) Plans. (c) These plans are collectively referred to as the Legacy CENG plans. (d) Employees generally remain in their legacy benefit plans when transferring between operating companies.
Defined Benefit Plan Change In Benefit Obligation RollForward	The following table provides a rollforward of the changes in the benefit obligations and plan assets for the most recent two years for all plans combined: Pension Benefits Other Postretirement Benefits 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at beginning of year $ 18,256 $ 15,459 $ 4,197 $ 4,451 Service cost 326 293 119 117 Interest cost 710 749 167 186 Plan participants’ contributions — — 42 42 Actuarial (gain) loss (582 ) 2,095 (341 ) 502 Plan amendments — — (23 ) (1,012 ) Acquisitions/divestitures (a) — 594 — 142 Curtailments — (8 ) — — Settlements (34 ) (30 ) — — Gross benefits paid (923 ) (896 ) (223 ) (231 ) Net benefit obligation at end of year $ 17,753 $ 18,256 $ 3,938 $ 4,197 Pension Benefits Other Postretirement Benefits 2015 2014 2015 2014 Change in plan assets: Fair value of net plan assets at beginning of year $ 14,874 $ 13,571 $ 2,430 $ 2,238 Actual return on plan assets (32 ) 1,443 4 90 Employer contributions 462 332 40 291 Plan participants’ contributions — — 42 42 Gross benefits paid (923 ) (896 ) (223 ) (231 ) Acquisitions/divestitures (a) — 454 — — Settlements (34 ) (30 ) — — Fair value of net plan assets at end of year $ 14,347 $ 14,874 $ 2,293 $ 2,430 _______________________ (a) On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, Exelon became a sponsor of CENG’s pension and OPEB plans effective July 14, 2014. See Note 5 - Investment in Constellation Energy Nuclear Group, LLC for further information.
Schedule of Amounts Recognized in Balance Sheet	Exelon presents its benefit obligations and plan assets net on its balance sheet within the following line items: Pension Benefits Other Postretirement Benefits 2015 2014 2015 2014 Other current liabilities $ 21 $ 16 $ 27 $ 25 Pension obligations 3,385 3,366 — — Non-pension postretirement benefit obligations — — 1,618 1,742 Unfunded status (net benefit obligation less net plan assets) $ 3,406 $ 3,382 $ 1,645 $ 1,767
Defined Benefit Plan Pension Plans With Projected Benefit Obligations And Accumulated Benefit Obligations In Excess Of Plan Assets	The following tables provide the projected benefit obligations (PBO), accumulated benefit obligation (ABO), and fair value of plan assets for all pension plans with a PBO or ABO in excess of plan assets. PBO in excess of plan assets 2015 2014 Projected benefit obligation $ 17,753 $ 18,256 Fair value of net plan assets 14,347 14,874 ABO in excess of plan assets 2015 2014 Projected benefit obligation $ 17,753 $ 18,256 Accumulated benefit obligation 16,792 17,191 Fair value of net plan assets 14,347 14,874
Schedule of Defined Benefit Plans Disclosures	A portion of the net periodic benefit cost for all pension and OPEB plans are capitalized within each of the Registrant's Consolidated Balance Sheets. The following table presents the components of Exelon’s net periodic benefit costs, prior to any capitalization, for the years ended December 31, 2015 , 2014 and 2013 . Pension Benefits Other Postretirement Benefits 2015 2014 2013 2015 2014 2013 Components of net periodic benefit cost: Service cost $ 326 $ 293 $ 317 $ 119 $ 117 $ 162 Interest cost 710 749 650 167 186 194 Expected return on assets (1,026 ) (994 ) (1,015 ) (151 ) (154 ) (132 ) Amortization of: Prior service cost (credit) 13 14 14 (174 ) (122 ) (19 ) Actuarial loss 571 420 562 80 50 83 Settlement charges 2 2 9 — — — Net periodic benefit cost $ 596 $ 484 $ 537 $ 41 $ 77 $ 288
Changes In Plan Assets And Benefit Obligations Recognized In OCI And Regulatory Assets	The following tables provide the components of AOCI and regulatory assets (liabilities) for the years ended December 31, 2015 , 2014 and 2013 for all plans combined. Pension Benefits Other Postretirement Benefits 2015 2014 2013 2015 2014 2013 Changes in plan assets and benefit obligations recognized in AOCI and regulatory assets (liabilities): Current year actuarial loss (gain) $ 476 $ 1,639 $ (1,169 ) $ (194 ) $ 561 $ (628 ) Amortization of actuarial loss (571 ) (420 ) (562 ) (80 ) (50 ) (83 ) Current year prior service (credit) cost — — — (23 ) (1,012 ) 15 Amortization of prior service (cost) credit (13 ) (14 ) (14 ) 174 122 19 Settlements (2 ) (2 ) (8 ) — — — Total recognized in AOCI and regulatory assets (liabilities) (a) $ (110 ) $ 1,203 $ (1,753 ) $ (123 ) $ (379 ) $ (677 ) ______________________ (a) Of the $110 million gain related to pension benefits, $64 million and $46 million were recognized in AOCI and regulatory assets, respectively, during 2015 . Of the $123 million gain related to other postretirement benefits, $63 million and $60 million were recognized in AOCI and regulatory assets (liabilities), respectively, during 2015 . Of the $1,203 million loss related to pension benefits, $788 million and $415 million were recognized in AOCI and regulatory assets, respectively, during 2014 . Of the $379 million gain related to other postretirement benefits, $162 million and $217 million were recognized in AOCI and regulatory assets (liabilities), respectively, during 2014 . Of the $1,753 million gain related to pension benefits, $1,071 million and $682 million were recognized in AOCI and regulatory assets, respectively, during 2013 . Of the $677 million gain related to other postretirement benefits, $352 million and $325 million were recognized in AOCI and regulatory assets, respectively, during 2013 .
Changes In Plan Assets And Benefit Obligations Not Recognized In OCI And Regulatory Assets	The following table provides the components of Exelon’s gross accumulated other comprehensive loss and regulatory assets (liabilities) that have not been recognized as components of periodic benefit cost at December 31, 2015 and 2014 , respectively, for all plans combined: Pension Benefits Other Postretirement Benefits 2015 2014 2015 2014 Prior service cost (credit) $ 36 $ 49 $ (812 ) $ (963 ) Actuarial loss 7,310 7,407 711 985 Total (a) $ 7,346 $ 7,456 $ (101 ) $ 22 _______________________ (a) Of the $7,346 million related to pension benefits, $4,246 million and $3,100 million are included in AOCI and regulatory assets, respectively, at December 31, 2015 . Of the $(101) million related to other postretirement benefits, $(63) million and $(38) million are included in AOCI and regulatory assets (liabilities), respectively, at December 31, 2015 . Of the $7,456 million related to pension benefits, $4,310 million and $3,146 million are included in AOCI and regulatory assets, respectively, at December 31, 2014 . The $22 million related to other postretirement benefits is included in regulatory assets (liabilities) at December 31, 2014 .
Defined Benefit Plan Amounts That Will Be Amortized From Accumulated Other Comprehensive Income Loss And Regulatory Assets In Next Fiscal Year	The valuation is expected to be completed in the first quarter of 2016 for the majority of the benefit plans. Pension Benefits Other Postretirement Benefits Prior service cost (credit) $ 13 $ (175 ) Actuarial loss 501 50 Total (a) $ 514 $ (125 ) ___________________ (a) Of the $514 million related to pension benefits at December 31, 2015 , $290 million and $224 million are expected to be amortized from AOCI and regulatory assets in 2016 , respectively. Of the $(125) million related to other postretirement benefits at December 31, 2015 , $(64) million and $(61) million are expected to be amortized from AOCI and regulatory assets (liabilities) in 2016 , respectively.
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Benefit Obligation	The following assumptions were used to determine the benefit obligations for the plans at December 31, 2015 , 2014 and 2013 . Assumptions used to determine year-end benefit obligations are the assumptions used to estimate the subsequent year’s net periodic benefit costs. Pension Benefits Other Postretirement Benefits 2015 2014 2013 2015 2014 2013 Discount rate 4.29 % 3.94 % 4.80 % 4.29 % 3.92 % 4.90 % Rate of compensation increase (a) (a) (b) (a) (a) (b) Mortality table RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table with Scale AA improvements RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table with Scale AA improvements Health care cost trend on covered charges N/A N/A N/A 5.50% decreasing to ultimate trend of 5.00% in 2017 6.00% 6.00% decreasing to ultimate trend of 5.00% in 2017 _____________________________ (a) 3.25% through 2019 and 3.75% thereafter. (b) 3.25% through 2018 and 3.75% thereafter.
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Net Periodic Benefit Cost	The following assumptions were used to determine the net periodic benefit costs for all the plans for the years ended December 31, 2015 , 2014 and 2013 : Pension Benefits Other Postretirement Benefits 2015 2014 2013 2015 2014 2013 Discount rate 3.94 % (a) 4.80 % (b) 3.92 % (c) 3.92 % (a) 4.90 % (b) 4.00 % (c) Expected return on plan assets 7.00 % (d) 7.00 % (d) 7.50 % (d) 6.50 % (d) 6.59 % (d) 6.45 % (d) Rate of compensation increase (e) (f) (g) (e) (f) (g) Mortality table RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table with Scale AA improvements RP-2000 table with Scale AA improvements RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table with Scale AA improvements RP-2000 table with Scale AA improvements Health care cost trend on covered charges N/A N/A N/A 6.00% decreasing to ultimate trend of 5.00% in 2017 6.00% 6.50% decreasing to ultimate trend of 5.00% in 2017 ___________________________ (a) The discount rates above represent the initial discount rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2015 . Discount rates for CENG's legacy pension and OPEB plans ranged from 3.68% - 4.14% and 4.32% - 4.43% , respectively. (b) The discount rates above represent the initial discount rates used to establish the majority of Exelon's pension and other postretirement benefits costs for the year ended December 31, 2014 . Certain of the other postretirement benefit plans were remeasured as of April 30, 2014 using an expected long-term rate of return on plan assets of 6.59% and a discount rate of 4.30% . Costs of the year ended December 31, 2014 reflect the impact of this remeasurement. On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, Exelon became the sponsor of CENG’s legacy pension and OPEB plans effective July 14, 2014; discount rates for those plans, impacting 2014 costs, ranged from 3.60% - 4.30% and 4.09% - 4.55% , respectively. See Note 5 - Investment in Constellation Energy Nuclear Group, LLC for further information. (c) The discount rates above represent the initial discounts rates used to establish Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2013 . Certain of the benefit plans were remeasured during the year using discount rates of 4.21% and 4.66% for pension and other postretirement benefits, respectively. Costs for the year ended December 31, 2013 reflect the impact of these remeasurements. (d) Not applicable to pension and other postretirement benefit plans that do not have plan assets. (e) 3.25% through 2019 and 3.75% thereafter. (f) 3.25% through 2018 and 3.75% thereafter. (g) 3.25% through 2017 and 3.75% thereafter.
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates	A one percentage point change in assumed health care cost trend rates would have the following effects: Effect of a one percentage point increase in assumed health care cost trend: on 2015 total service and interest cost components $ 12 on postretirement benefit obligation at December 31, 2015 100 Effect of a one percentage point decrease in assumed health care cost trend: on 2015 total service and interest cost components (9 ) on postretirement benefit obligation at December 31, 2015 (89 )
Pension And Other Postretirement Benefit Contributions	The following table provides contributions made by Generation, ComEd, PECO, BGE and BSC to the pension and other postretirement benefit plans: Pension Benefits Other Postretirement Benefits 2015 (a) 2014 (a) 2013 2015 2014 2013 Generation $ 231 $ 173 $ 119 $ 14 $ 124 $ 30 ComEd 143 122 118 7 125 4 PECO 40 11 11 — 5 20 BGE 1 — — 16 17 24 BSC (b) 47 26 91 3 20 5 Exelon $ 462 $ 332 $ 339 $ 40 $ 291 $ 83 _________________________ (a) Exelon's and Generation's pension contributions include $36 million and $43 million related to the legacy CENG plans that was funded by CENG as provided in an Employee Matters Agreement (EMA) between Exelon and CENG for the years ended December 31, 2015 and 2014 , respectively. (b) Includes $5 million , $9 million , and $72 million of pension contributions funded by Exelon Corporate, for the years ended December 31, 2015 , 2014 , and 2013 , respectively.
Defined Benefit Plan Estimated Future Benefit Payments	Estimated future benefit payments to participants in all of the pension plans and postretirement benefit plans at December 31, 2015 were: Pension Benefits Other Postretirement Benefits 2016 $ 1,153 $ 217 2017 997 223 2018 1,009 228 2019 1,036 235 2020 1,071 244 2021 through 2025 5,923 1,341 Total estimated future benefit payments through 2025 $ 11,189 $ 2,488
Schedule Of Pension And Other Postretirement Benefit Costs	. These amounts include the recognized contractual termination benefit charges, curtailment gains, and settlement charges: For the Year Ended December 31, Generation ComEd PECO BSC (a) BGE Exelon 2015 $ 269 $ 206 $ 39 $ 57 $ 66 637 2014 250 162 36 46 67 561 2013 347 309 43 71 55 825 _____________________ (a) These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO or BGE amounts above.
Defined Benefit Plan Weighted Average Asset Allocations And Target Allocations	Exelon’s pension and other postretirement benefit plan target asset allocations at December 31, 2015 and 2014 asset allocations were as follows: Pension Plans Percentage of Plan Assets at December 31, Asset Category Target Allocation 2015 2014 Equity securities 32 % 35 % 33 % Fixed income securities 37 % 34 37 Alternative investments (a) 31 % 31 30 Total 100 % 100 % Other Postretirement Benefit Plans Percentage of Plan Assets at December 31, Asset Category Target Allocation 2015 2014 Equity securities 39 % 43 % 42 % Fixed income securities 26 % 27 34 Alternative investments (a) 35 % 30 24 Total 100 % 100 % ___________________ (a) Alternative investments include private equity, hedge funds, real estate, and private credit.
Defined Benefit Plan Fair Value Of Plan Assets	The following table presents Exelon’s pension and other postretirement benefit plan assets measured and recorded at fair value on Exelon’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy at December 31, 2015 and 2014 : At December 31, 2015 (a) Level 1 Level 2 Level 3 Total Pension plan assets Cash equivalents $ 210 $ — $ — $ 210 Equities (b) 3,571 1,462 2 5,035 Fixed income: U.S. Treasury and agencies 1,001 79 — 1,080 State and municipal debt — 61 — 61 Corporate debt — 2,901 165 3,066 Other (b) — 395 203 598 Fixed income subtotal 1,001 3,436 368 4,805 Private equity — — 924 924 Hedge funds — 1,129 795 1,924 Real estate — — 725 725 Private credit — — 699 699 Pension plan assets subtotal 4,782 6,027 3,513 14,322 At December 31, 2015 (a) Level 1 Level 2 Level 3 Total Other postretirement benefit plan assets Cash equivalents 15 — — 15 Equities 510 482 — 992 Fixed income: U.S. Treasury and agencies 11 53 — 64 State and municipal debt — 131 — 131 Corporate debt — 44 — 44 Other 155 205 — 360 Fixed income subtotal 166 433 — 599 Hedge funds — 312 139 451 Real estate — — 131 131 Private credit — — 103 103 Other postretirement benefit plan assets subtotal 691 1,227 373 2,291 Total pension and other postretirement benefit plan assets (c) $ 5,473 $ 7,254 $ 3,886 $ 16,613 At December 31, 2014 (a) Level 1 Level 2 Level 3 Total Pension plan assets Cash equivalents $ 1 $ — $ — $ 1 Equities (b) 3,261 1,449 2 4,712 Fixed income: U.S. Treasury and agencies 1,051 88 — 1,139 State and municipal debt — 80 — 80 Corporate debt — 3,125 120 3,245 Other (b) — 930 152 1,082 Fixed income subtotal 1,051 4,223 272 5,546 Private equity — — 900 900 Hedge funds — 1,355 785 2,140 Real estate 243 — 685 928 Private credit — — 607 607 Pension plan assets subtotal 4,556 7,027 3,251 14,834 At December 31, 2014 (a) Level 1 Level 2 Level 3 Total Other postretirement benefit plan assets Cash equivalents 11 — — 11 Equities 480 525 — 1,005 Fixed income: U.S. Treasury and agencies 15 59 — 74 State and municipal debt — 197 — 197 Corporate debt — 42 — 42 Other 253 272 — 525 Fixed income subtotal 268 570 — 838 Hedge funds — 339 — 339 Real estate 8 — 116 124 Private credit — — 110 110 Other postretirement benefit plan assets subtotal 767 1,434 226 2,427 Total pension and other postretirement benefit plan assets (c) $ 5,323 $ 8,461 $ 3,477 $ 17,261 __________________________ (a) See Note 12 — Fair Value of Financial Assets and Liabilities for a description of levels within the fair value hierarchy. (b) Includes derivative instruments of $5 million and $(3) million , which have a total notional amount of $1,774 million and $1,491 million at December 31, 2015 and 2014 , respectively. The notional principal amounts for these instruments provide one measure of the transaction volume outstanding as of the fiscal years ended and do not represent the amount of the company’s exposure to credit or market loss. (c) Excludes net assets of $27 million and $42 million at December 31, 2015 and 2014 , respectively, which are required to reconcile to the fair value of net plan assets. These items consist primarily of receivables related to pending securities sales, interest and dividends receivable, and payables related to pending securities purchases.
Defined Benefit Plan Fair Value Of Plan Assets Unobservable Input Reconciliation	The following table presents the reconciliation of Level 3 assets and liabilities measured at fair value for pension and other postretirement benefit plans for the years ended December 31, 2015 and 2014 : Hedge funds Private equity Real estate Fixed income Equities Private Credit Total Pension Assets Balance as of January 1, 2015 $ 785 $ 900 $ 685 $ 272 $ 2 $ 607 $ 3,251 Actual return on plan assets: Relating to assets still held at the reporting date (39 ) 60 76 (14 ) — (19 ) 64 Relating to assets sold during the period 4 — 9 — — — 13 Purchases, sales and settlements: Purchases 104 186 116 125 — 200 731 Sales (57 ) — (54 ) (7 ) — (5 ) (123 ) Settlements (a) (2 ) (222 ) (107 ) (8 ) — (84 ) (423 ) Balance as of December 31, 2015 $ 795 $ 924 $ 725 $ 368 $ 2 $ 699 $ 3,513 Other Postretirement Benefits Balance as of January 1, 2015 $ — $ — $ 116 $ — $ — $ 110 $ 226 Actual return on plan assets: Relating to assets still held at the reporting date 1 — 15 — — (7 ) 9 Purchases, sales and settlements: Purchases 138 — 62 — — — 200 Settlements (a) — — (62 ) — — — (62 ) Balance as of December 31, 2015 $ 139 $ — $ 131 $ — $ — $ 103 $ 373 Hedge funds Private equity Real estate Fixed income Equities Private credit Total Pension Assets Balance as of January 1, 2014 $ 706 $ 806 $ 544 $ 41 $ 2 $ 371 $ 2,470 Actual return on plan assets: Relating to assets still held at the reporting date 59 112 81 7 — 20 279 Relating to assets sold during the period 2 — — — — 1 3 Purchases, sales and settlements: Purchases 74 169 112 227 — 265 847 Sales (25 ) — (19 ) (3 ) — (13 ) (60 ) Settlements (a) (1 ) (203 ) (60 ) — — (37 ) (301 ) Transfers into (out of) Level 3 (b)(c) (30 ) 16 27 — — — 13 Balance as of December 31, 2014 $ 785 $ 900 $ 685 $ 272 $ 2 $ 607 $ 3,251 Other Postretirement Benefits Balance as of January 1, 2014 $ — $ 2 $ 109 $ — $ — $ 4 $ 115 Actual return on plan assets: Relating to assets still held at the reporting date — — 13 — — 1 14 Purchases, sales and settlements: Purchases — 1 1 — — 109 111 Sales — (2 ) (7 ) — — (4 ) (13 ) Settlements (a) — (1 ) — — — — (1 ) Balance as of December 31, 2014 $ — $ — $ 116 $ — $ — $ 110 $ 226 ________________________ (a) Represents cash settlements only. (b) In connection with the Employee Matters Agreement between EDF and Exelon, Exelon assumed the pension plan assets of Nine Mile Point Nuclear Station, LLC and Constellation Energy Nuclear Group, LLC resulting in transfers into Level 3 of $56 million . (c) As of January 1, 2015 and January 1, 2014, hedge fund investments that contained redemption restrictions limiting Exelon’s ability to redeem the investments within a reasonable period of time were classified as Level 3 investments. As of December 31, 2014, restrictions for certain investments no longer applied, therefore allowing redemption within a reasonable period of time from the measurement date at NAV. As such, these hedge fund investments are reflected as transfers out of Level 3 to Level 2 of $43 million in 2014 .
Schedule Of Defined Contributions	. The following table presents matching contributions to the savings plan for the years ended December 31, 2015 , 2014 and 2013 : For the Year Ended December 31, Exelon (a) Generation (a) ComEd PECO BGE BSC (b) 2015 $ 148 $ 80 $ 32 $ 11 $ 14 $ 11 2014 103 51 26 8 8 10 2013 85 40 22 8 8 7 _________________________ (a) Includes $9 million and $5 million related to CENG for the year ended December 31, 2015, and for the period from April 1, 2014 to December 31, 2014, respectively. (b) These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These costs are not included in the Generation, ComEd, PECO, or BGE amounts above.

Severance (Tables)

Severance (Tables)	12 Months Ended
	Dec. 31, 2015
Restructuring and Related Activities [Abstract]
Business Acquisition, Integration, Restructuring and Other Related Costs [Text Block]	.
Schedule of Restructuring and Related Costs	For the year ended, Acquisition, Integration and Financing Costs (a) 2015 2014 Exelon $ 80 $ 179 Generation 25 11 ComEd 10 4 PECO 5 2 BGE 5 2 ___________ (a) The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statement of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. .
Schedule of Corporate Restructuring Severance Obligations	.
Schedule Of Severance Costs	For the years ended December 31, 2015 , 2014 , and 2013 , the Registrants recorded the following severance costs associated with these ongoing severance benefits within Operating and maintenance expense in their Consolidated Statements of Operations and Comprehensive Income: Severance Benefits (a) Severance Charges-2015 Severance Charges-2014 Severance Charges-2013 ________________________ (a) The amounts above for Generation include $ 1 million , $ 1 million , and $ 2 million for amounts billed by BSC through intercompany allocations for the years ended December 31, 2015 , December 31, 2014 , and December 31, 2013 , respectively. Amounts billed by BSC to ComEd, PECO and BGE were not material.

Contingently Redeemable Noncont

Contingently Redeemable Noncontrolling Interest Contingently Redeemable Noncontrolling Interest (Table)	12 Months Ended
	Dec. 31, 2015
Noncontrolling Interest Disclosure [Abstract]
Redeemable Noncontrolling Interest [Table Text Block]	The following table summarizes the changes in the contingently redeemable noncontrolling interest for the year ended December 31, 2015: Year Ended December 31, 2015 Beginning Balance $ — Cash received from noncontrolling interest 32 Release of contingency (4 ) Ending Balance $ 28 18 . Contingently Redeemable Noncontrolling Interest (Exelon, Generation) In November 2015, 2015 ESA Investco, LLC, a wholly owned subsidiary of Generation, entered into an arrangement to sell a portion of its equity to a tax equity investor. Pursuant to the operating agreement, in certain situations the equity contributions made by the noncontrolling interest holder could be contingently redeemable. These situations are outside of the control of Generation and the noncontrolling interest holder resulting in a portion of the noncontrolling interest being considered contingently redeemable and thus presented in mezzanine equity in the consolidated balance sheet. The following table summarizes the changes in the contingently redeemable noncontrolling interest for the year ended December 31, 2015: Year Ended December 31, 2015 Beginning Balance $ — Cash received from noncontrolling interest 32 Release of contingency (4 ) Ending Balance $ 28

Shareholder Equity Shareholder

Shareholder Equity Shareholder Equity (Tables)	12 Months Ended
	Dec. 31, 2015
Shareholder [Abstract]
Schedule of Common Stock Outstanding Roll Forward [Table Text Block]	The following table presents common stock authorized and outstanding as of December 31, 2015 and 2014 : December 31, 2015 2014 Par Value Shares Authorized Shares Outstanding Common Stock Exelon no par value 2,000,000,000 919,924,742 859,833,343 ComEd $ 12.50 250,000,000 127,016,973 127,016,947 PECO no par value 500,000,000 170,478,507 170,478,507 BGE no par value 175,000,000 1,000 1,000
Schedule of Auction Market Preferred Securities by Stock Series [Table Text Block]	December 31, Redemption (a) 2015 2014 2015 2014 Shares Outstanding Dollar Amount Series (without mandatory redemption) 7.125%, 1993 Series $ 100.00 400,000 400,000 $ 40 $ 40 6.97%, 1993 Series 100.00 500,000 500,000 50 50 6.70%, 1993 Series 100.00 400,000 400,000 40 40 6.99%, 1995 Series 100.00 600,000 600,000 60 60 Total preference stock 1,900,000 1,900,000 $ 190 $ 190 ______________________ (a) Redeemable, at the option of BGE, at the indicated dollar amounts per share, plus accrued and unpaid dividends.
Schedule of Stock by Class

Stock-Based Compensation Plan59

Stock-Based Compensation Plans (Exelon, Generation, ComEd, PECO and BGE) (Tables)	12 Months Ended
	Dec. 31, 2015
Common Stock [Abstract]
Schedule of Stock by Class
Stock Based Compensation Tax Benefit	The following table presents information regarding Exelon’s tax benefits for the years ended December 31, 2015 , 2014 and 2013 : Year Ended December 31, 2015 2014 2013 Realized tax benefit when exercised/distributed: Restricted stock units $ 30 $ 17 $ 11 Performance share awards 18 11 11 Stock deferral plan — — 1
Schedule of Assumptions Used	The following table presents the weighted average assumptions used in the pricing model for grants and the resulting weighted average grant date fair value of stock options granted for the year ended 2012: Year ended December 31, 2012 Dividend yield 5.28 % Expected volatility 23.20 % Risk-free interest rate 1.30 % Expected life (years) 6.25 Weighted average grant date fair value (per share) 4.18
Schedule of Share-based Compensation, Stock Options, Activity	The following table presents information with respect to stock option activity for the year ended December 31, 2015 : Shares Weighted Average Exercise Price (per share) Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value Balance of shares outstanding at December 31, 2014 18,830,967 $ 46.85 Options exercised (7,133 ) 21.25 Options forfeited (5,250 ) 39.81 Options expired (3,245,827 ) 47.75 Balance of shares outstanding at December 31, 2015 15,572,757 $ 46.68 3.85 $ 9 Exercisable at December 31, 2015 (a) 15,490,507 $ 46.72 3.84 $ 9 ____________________ (a) Includes stock options issued to retirement eligible employees.
Stock Options Exercised	The following table summarizes additional information regarding stock options exercised for the years ended December 31, 2015 , 2014 and 2013 : Year Ended December 31, 2015 2014 2013 Intrinsic value (a) $ — $ 3 $ 4 Cash received for exercise price — 7 19 ______________________ (a) The difference between the market value on the date of exercise and the option exercise price.
Schedule of Nonvested Share Activity	The following table summarizes Exelon’s nonvested stock option activity for the year ended December 31, 2015 : Shares Weighted Average Exercise Price (per share) Nonvested at December 31, 2014 (a) 432,035 $ 39.91 Vested (344,535 ) 39.93 Forfeited (5,250 ) 39.81 Nonvested at December 31, 2015 (a) 82,250 $ 39.81 _____________________ (a) Excludes 279,000 and 746,140 of stock options issued to retirement-eligible employees as of December 31, 2015 and 2014 , respectively, as they are fully vested.
Schedule of Nonvested Restricted Stock Units Activity	The following table summarizes Exelon’s nonvested restricted stock unit activity for the year ended December 31, 2015 : Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2014 (a) 3,758,218 $ 31.27 Granted 2,132,856 36.55 Vested (1,597,255 ) 32.88 Forfeited (76,232 ) 33.06 Undistributed vested awards (b) (654,333 ) 35.35 Nonvested at December 31, 2015 (a) 3,563,254 $ 32.92 _______________________ (a) Excludes 1,097,630 and 975,116 of restricted stock units issued to retirement-eligible employees as of December 31, 2015 and 2014 , respectively, as they are fully vested. (b) Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2015 .
Schedule of Nonvested Performance-based Units Activity	The following table summarizes Exelon’s nonvested performance share awards activity for the year ended December 31, 2015 : Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2014 (a) 2,696,097 $ 30.62 Granted 1,556,273 35.88 Change in performance (118,398 ) 35.88 Vested (704,141 ) 32.80 Forfeited (52,167 ) 32.25 Undistributed vested awards (b) (820,505 ) 33.95 Nonvested at December 31, 2015 (a) 2,557,159 $ 31.88 _______________________ (a) Excludes 1,817,883 and 1,535,791 of performance share awards issued to retirement-eligible employees as of December 31, 2015 and 2014 , respectively, as they are fully vested. (b) Represents performance share awards that vested but were not distributed to retirement-eligible employees during 2015 .
Not Settled Performance Share Awards Balance Sheet Presentation	The following table presents the balance sheet classification of obligations related to outstanding performance share awards not yet settled: December 31, 2015 2014 Current liabilities (a) $ 28 $ 28 Deferred credits and other liabilities (b) 32 36 Common stock 35 33 Total $ 95 $ 97 __________________________ (a) Represents the current liability related to performance share awards expected to be settled in cash. (b) Represents the long-term liability related to performance share awards expected to be settled in cash.
Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]	The following table presents the stock-based compensation expense included in Exelon’s Consolidated Statements of Operations and Comprehensive Income for the years ended December 31, 2015 , 2014 and 2013 : Year Ended December 31, Components of Stock-Based Compensation Expense 2015 2014 2013 Performance share awards $ 41 $ 59 $ 48 Restricted stock units 71 61 61 Stock options 1 2 3 Other stock-based awards 6 5 6 Total stock-based compensation expense included in operating and maintenance expense 119 127 118 Income tax benefit (46 ) (47 ) (44 ) Total after-tax stock-based compensation expense $ 73 $ 80 $ 74
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]	The following table presents stock-based compensation expense (pre-tax) for the years ended December 31, 2015 , 2014 and 2013 : Year Ended December 31, Subsidiaries 2015 2014 2013 Generation $ 64 $ 52 $ 48 ComEd 6 7 9 PECO 3 3 5 BGE 3 5 6 BSC (a) 43 60 50 Total $ 119 $ 127 $ 118 ________________________ (a) These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO and BGE amounts above.

Earnings Per Share and Equity60

Earnings Per Share and Equity (Tables)	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Reconciliation of basic and diluted earnings per share	The following table sets forth the components of basic and diluted earnings per share and shows the effect of the stock options, performance share awards and restricted stock on the weighted average number of shares outstanding used in calculating diluted earnings per share: Year Ended December 31, 2015 2014 2013 Net income attributable to common shareholders $ 2,269 $ 1,623 $ 1,719 Weighted average common shares outstanding—basic 890 860 856 Assumed exercise and/or distributions of stock-based awards 3 4 4 Weighted average common shares outstanding—diluted 893 864 860

Changes in Accumulated Other 61

Changes in Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Schedule Of Accumulated Other Comprehensive Income (Loss)	The following tables present changes in accumulated other comprehensive income (loss) (AOCI) by component for the years ended December 31, 2015 and 2014 : For the Year Ended December 31, 2015 Gains and (Losses) on Cash Flow Hedges Unrealized Gains and (Losses) on Marketable Securities Pension and Foreign Currency Items AOCI of Equity Investments Total Exelon (a) Beginning balance $ (28 ) $ 3 $ (2,640 ) $ (19 ) $ — $ (2,684 ) OCI before reclassifications (12 ) — (100 ) (21 ) (3 ) (136 ) Amounts reclassified from AOCI (b) 21 — 175 — — 196 Net current-period OCI 9 — 75 (21 ) (3 ) 60 Ending balance $ (19 ) $ 3 $ (2,565 ) $ (40 ) $ (3 ) $ (2,624 ) Generation (a) Beginning balance $ (18 ) $ 1 $ — $ (19 ) $ — $ (36 ) OCI before reclassifications (8 ) — — (21 ) (3 ) (32 ) Amounts reclassified from AOCI (b) 5 — — — — 5 Net current-period OCI (3 ) — — (21 ) (3 ) (27 ) Ending balance $ (21 ) $ 1 $ — $ (40 ) $ (3 ) $ (63 ) PECO (a) Beginning balance $ — $ 1 $ — $ — $ — $ 1 OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI — — — — — — Ending balance $ — $ 1 $ — $ — $ — $ 1 For the Year Ended December 31, 2014 Gains and Unrealized Pension and Foreign AOCI of Total Exelon (a) Beginning balance $ 120 $ 2 $ (2,260 ) $ (10 ) $ 108 $ (2,040 ) OCI before reclassifications (31 ) (1 ) (498 ) (9 ) 11 (528 ) Amounts reclassified from AOCI (b) (117 ) 2 118 — (119 ) (116 ) Net current-period OCI (148 ) 1 (380 ) (9 ) (108 ) (644 ) Ending balance $ (28 ) $ 3 $ (2,640 ) $ (19 ) $ — $ (2,684 ) Generation (a) Beginning balance $ 114 $ 2 $ — $ (10 ) $ 108 214 OCI before reclassifications (15 ) (1 ) — (9 ) 11 (14 ) Amounts reclassified from AOCI (b) (117 ) — — — (119 ) (236 ) Net current-period OCI (132 ) (1 ) — (9 ) (108 ) (250 ) Ending balance $ (18 ) $ 1 $ — $ (19 ) $ — $ (36 ) PECO (a) Beginning balance $ — $ 1 $ — $ — $ — $ 1 OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI — — — — — — Ending balance $ — $ 1 $ — $ — $ — $ 1 _______________________ (a) All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income. (b) See next tables for details about these reclassifications.
Reclassification Out Of Accumulated Other Comprehensive Income	The following tables present amounts reclassified out of AOCI to Net income for Exelon and Generation during the years ended December 31, 2015 and 2014 : For the Year Ended December 31, 2015 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statements of Operations and Comprehensive Income Exelon Generation Gains and (losses) on cash flow hedges Terminated interest rate swaps $ (26 ) $ — Other, net Energy related hedges 2 2 Operating revenues Other cash flow hedges (11 ) (11 ) Interest expense Total before tax (35 ) (9 ) Tax benefit 14 4 Net of tax $ (21 ) $ (5 ) Comprehensive income Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 74 $ — Actuarial losses (b) (361 ) — Total before tax (287 ) — Tax benefit 112 — Net of tax $ (175 ) $ — Total Reclassifications $ (196 ) $ (5 ) Comprehensive income For the Year Ended December 31, 2014 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statements of Operations and Comprehensive Income Exelon Generation Gains and (losses) on cash flow hedges Energy related hedges $ 195 $ 195 Operating revenues Total before tax 195 195 Tax expense (78 ) (78 ) Net of tax $ 117 $ 117 Comprehensive income Gains and (losses) on available for sale securities Other available securities for sale $ (2 ) $ — Other Income and Deductions Total before tax (2 ) — Net of tax $ (2 ) $ — Comprehensive income Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 46 $ — Actuarial losses (b) (239 ) — Total before tax (193 ) — Tax benefit 75 — Net of tax $ (118 ) $ — Comprehensive income Equity investments Sale of equity method investment $ 5 $ 5 Equity in losses of unconsolidated affiliates Reversal of CENG equity method AOCI 193 193 Gain on Consolidation of CENG Total before tax 198 198 Tax expense (79 ) (79 ) Net of tax $ 119 $ 119 Total Reclassifications $ 116 $ 236 Comprehensive income _____________________ (a) Amounts in parenthesis represent a decrease in net income. (b) This accumulated other comprehensive income component is included in the computation of net periodic pension and OPEB cost (see Note 17 — Retirement Benefits for additional details). (c) Amortization of the deferred compensation unit plan is allocated to capital and operating and maintenance expense.
Schedule of Components of Income Tax Expense (Benefit)	The following table presents income tax expense (benefit) allocated to each component of other comprehensive income (loss) during the years ended December 31, 2015 and 2014 : For the Years Ended December 31, 2015 2014 2013 Exelon Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 30 $ 19 $ — Actuarial loss reclassified to periodic cost (140 ) (93 ) (133 ) Pension and non-pension postretirement benefit plan valuation adjustment 62 317 (430 ) Change in unrealized (gain) loss on cash flow hedges (6 ) 96 166 Change in unrealized (gain) loss on equity investments 1 73 (71 ) Total $ (53 ) $ 412 $ (468 ) Generation Change in unrealized loss on cash flow hedges $ 2 $ 84 $ 262 Change in unrealized (gain) loss on equity investments 1 73 (72 ) Total $ 3 $ 157 $ 190

Commitments and Contingencies62

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Environmental Loss Contingency Tables [Abstract]
Schedule of Government Settlement Agreements
Energy Commitments
Utility Energy Purchase Commitments
Other Purchase Obligation
Fuel Purchase Commitments
Commercial Commitments	PECO’s commercial commitments as of December 31, 2015 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2016 2017 2018 2019 2020 2021 Letters of credit (non-debt) (a) $ 22 $ 22 $ — $ — $ — $ — $ — Surety bonds (b) 9 9 — — — — — Financing trust guarantees (c) 178 — — — — — 178 Total commercial commitments $ 209 $ 31 $ — $ — $ — $ — $ 178 ________________________ (a) Letters of credit (non-debt)—PECO maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (c) Performance guarantees—Reflects full and unconditional guarantee of Trust Preferred Securities of PECO Trust III and IV, which are 100% owned finance subsidiaries of PECO. ComEd’s commercial commitments as of December 31, 2015 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2016 2017 2018 2019 2020 2021 Letters of credit (non-debt) (a) $ 16 $ 16 $ — $ — $ — $ — $ — Surety bonds (b) 8 6 — 2 — — — Financing trust guarantees (c) 200 — — — — — 200 Total commercial commitments $ 224 $ 22 $ — $ 2 $ — $ — $ 200 _________________________ (a) Letters of credit (non-debt)—ComEd maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (c) Performance guarantees—Reflects full and unconditional guarantee of Trust Preferred Securities of ComEd Financing III which is a 100% owned finance subsidiary of ComEd. Exelon’s commercial commitments as of December 31, 2015 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2016 2017 2018 2019 2020 2021 Letters of credit (non-debt) (a) $ 1,583 $ 1,565 $ 5 $ — $ — $ 13 $ — Surety bonds (b) 809 733 49 3 2 16 6 Financing trust guarantees (c) 628 — — — — — 628 Energy marketing contract guarantees (d) 3,126 3,126 — — — — — Nuclear insurance premiums (e) 3,060 — — — — — 3,060 Total commercial commitments $ 9,206 $ 5,424 $ 54 $ 3 $ 2 $ 29 $ 3,694 ___________________________ (a) Letters of credit (non-debt)—Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (c) Includes $ 200 million of Trust Preferred Securities of ComEd Financing III, $ 178 million of Trust Preferred Securities of PECO Trust III and IV and $ 250 million of Trust Preferred Securities of BGE Capital Trust II. (d) Energy marketing contract guarantees—Guarantees issued to ensure performance under energy commodity contracts. Amount includes approximately $ 3.1 billion of guarantees issued by Exelon and Generation on behalf of its Constellation businesses to allow it the flexibility needed to conduct business with counterparties without having to post other forms of collateral. The majority of these guarantees contain evergreen provisions that require the guarantee to remain in effect until cancelled. Exelon’s estimated net exposure for obligations under commercial transactions covered by these guarantees is approximately $ 0.5 billion at December 31, 2015 , which represents the total amount Exelon could be required to fund based on December 31, 2015 market prices. (e) Nuclear insurance premiums—Represents the maximum amount that Generation would be required to pay for retrospective premiums in the event of nuclear disaster at any domestic site under the Secondary Financial Protection pool as required under the Price-Anderson Act as well as the current aggregate annual retrospective premium obligation that could be imposed by NEIL. See the Nuclear Insurance section within this note for additional details on Generation’s nuclear insurance premiums. BGE’s commercial commitments as of December 31, 2015 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2016 2017 2018 2019 2020 2021 Letters of credit (non-debt) (a) $ 2 $ 2 $ — $ — $ — $ — $ — Surety bonds (b) 10 10 — — — — — Financing trust guarantees (c) 250 — — — — — 250 Total commercial commitments $ 262 $ 12 $ — $ — $ — $ — $ 250 ________________________ (a) Letters of credit (non-debt)—BGE maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (c) Performance guarantee—Reflects full and unconditional guarantee of Trust Preferred Securities of BGE Capital Trust which is an unconsolidated VIE of BGE. Generation’s commercial commitments as of December 31, 2015 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2016 2017 2018 2019 2020 2021 Letters of credit (non-debt) (a) $ 1,503 $ 1,485 $ 5 $ — $ — $ 13 $ — Surety bonds 737 692 45 — — — — Energy marketing contract guarantees (b) 1,532 1,532 — — — — — Nuclear insurance premiums (c) 3,060 — — — — — 3,060 Total commercial commitments $ 6,832 $ 3,709 $ 50 $ — $ — $ 13 $ 3,060 ________________________ (a) Letters of credit (non-debt)—Non-debt letters of credit maintained to provide credit support for certain transactions as requested by third parties. (b) Energy marketing contract guarantees—Guarantees issued to ensure performance under energy commodity contracts. Amount includes approximately $ 1.5 billion of guarantees issued by Generation on behalf of its Constellation businesses to allow it the flexibility needed to conduct business with counterparties without having to post other forms of collateral. The majority of these guarantees contain evergreen provisions that require the guarantee to remain in effect until cancelled. Generation’s estimated net exposure for obligations under commercial transactions covered by these guarantees is approximately $ 0.3 billion at December 31, 2015 , which represents the total amount Generation could be required to fund based on December 31, 2015 market prices. (c) Nuclear insurance premiums — Represents the maximum amount that Generation would be required to pay for retrospective premiums in the event of nuclear disaster at any domestic site, including CENG sites, under the Secondary Financial Protection pool as required under the Price-Anderson Act as well as the current aggregate annual retrospective premium obligation that could be imposed by NEIL. See the Nuclear Insurance section within this note for additional details on Generation’s nuclear insurance premiums.
Other Commitments
Operating Leases Of Lessee Disclosure	Minimum future operating lease payments, including lease payments for contracted generation, vehicles, real estate, computers, rail cars, operating equipment and office equipment, as of December 31, 2015 were: Exelon (a) Generation (a)(b) ComEd (c) PECO (c) BGE (c)(d) 2016 $ 133 $ 86 $ 14 $ 3 $ 12 2017 109 69 9 3 10 2018 86 57 5 2 9 2019 74 45 5 2 8 2020 70 44 3 2 7 Remaining years 702 655 1 — 19 Total minimum future lease payments $ 1,174 $ 956 $ 37 $ 12 $ 65 ______________________ (a) Excludes Generation’s contingent operating lease payments associated with contracted generation agreements. (b) The Generation column above includes minimum future lease payments associated with a 20 -year lease agreement for the Baltimore headquarters that became effective during the second quarter of 2015. Generation’s total commitments under the lease agreement are $ 4 million , $ 10 million , $ 11 million , $ 13 million , $ 14 million , and $ 271 million related to years 2016, 2017, 2018, 2019, 2020 and thereafter, respectively. (c) Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO and BGE have excluded these payments from the remaining years, as such amounts would not be meaningful. ComEd’s, PECO’s, and BGE’s annual obligation for these arrangements, included in each of the years 2016—2020, was $ 2 million , $ 3 million , and $ 1 million respectively. (d) Includes all future lease payments on a 99 year real estate lease that expires in 2106 .
Operating Leases Rent Expense	The following table presents the Registrants’ rental expense under operating leases for the years ended December 31, 2015, 2014 and 2013: For the Year Ended December 31, Exelon Generation (a) ComEd PECO BGE 2015 $ 922 $ 851 $ 12 $ 9 $ 32 2014 865 806 15 14 12 2013 806 744 15 21 11 __________________________ (a) Includes contingent operating lease payments associated with contracted generation agreements that are not included in the minimum future operating lease payments table above. Payments made under Generation’s contracted generation lease agreements totaled $ 798 million , $ 755 million and $ 694 million during 2015, 2014 and 2013, respectively.
Accrued environmental liabilities	As of December 31, 2015 and 2014, the Registrants had accrued the following undiscounted amounts for environmental liabilities in Other current liabilities and Other deferred credits and other liabilities within their respective Consolidated Balance Sheets: December 31, 2015 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation (a) Exelon $ 369 $ 301 Generation 63 — ComEd 266 264 PECO 37 35 BGE (a) 3 2 December 31, 2014 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 347 $ 277 Generation 63 — ComEd 238 235 PECO 45 42 BGE 1 —

Supplemental Financial Inform63

Supplemental Financial Information (Tables)	12 Months Ended
	Dec. 31, 2015
Supplemental Financial Information [Abstract]
Components of taxes other than income	The following tables provide additional information about the Registrants’ Consolidated Statements of Operations and Comprehensive Income for the years ended December 31, 2015 , 2014 and 2013 . For the year ended December 31, 2015 Exelon Generation ComEd PECO BGE Taxes other than income Utility (a) $ 474 $ 105 $ 236 $ 133 $ 85 Property 407 250 27 11 119 Payroll 201 118 28 14 16 Other 118 16 5 2 4 Total taxes other than income $ 1,200 $ 489 296 $ 160 $ 224 For the year ended December 31, 2014 Exelon Generation ComEd PECO BGE Taxes other than income Utility (a) $ 456 $ 89 $ 238 $ 128 $ 86 Property 396 240 25 15 114 Payroll 200 118 28 14 18 Other 102 18 2 2 3 Total taxes other than income $ 1,154 $ 465 $ 293 $ 159 $ 221 For the year ended December 31, 2013 Exelon Generation ComEd PECO BGE Taxes other than income Utility (a) $ 449 $ 79 $ 241 $ 129 $ 82 Property 302 205 24 14 112 Payroll 159 89 27 13 15 Other 185 16 7 2 4 Total taxes other than income $ 1,095 $ 389 $ 299 $ 158 $ 213 _____________________ (a) Generation’s utility tax represents gross receipts tax related to its retail operations and ComEd’s, PECO’s and BGE’s utility taxes represent municipal and state utility taxes and gross receipts taxes related to their operating revenues. The offsetting collection of utility taxes from customers is recorded in revenues on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
Components of non-operating income and expenses	For the year ended December 31, 2015 Exelon Generation ComEd PECO BGE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) — Regulatory agreement units $ 232 $ 232 $ — $ — $ — Non-regulatory agreement units 156 156 — — — Net unrealized losses on decommissioning trust funds— Regulatory agreement units (282 ) (282 ) — — — Non-regulatory agreement units (197 ) (197 ) — — — Net unrealized gains on pledged assets— Zion Station decommissioning 7 7 — — — Regulatory offset to decommissioning trust fund-related activities (b) 21 21 — — — Total decommissioning-related activities (63 ) (63 ) — — — Investment income (loss) 8 3 — (2 ) 4 (c) Long-term lease income 15 — — — — Interest income related to uncertain income tax positions 1 1 — — — AFUDC—Equity 24 — 5 5 14 Terminated interest rate swaps (d) (26 ) — — — — PHI merger related debt exchange (e) (22 ) — — — — Other 17 (1 ) 16 2 — Other, net $ (46 ) $ (60 ) $ 21 $ 5 $ 18 For the year ended December 31, 2014 Exelon Generation ComEd PECO BGE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) — Regulatory agreement units $ 216 $ 216 $ — $ — $ — Non-regulatory agreement units 159 159 — — — Net unrealized gains on decommissioning trust funds— Regulatory agreement units 180 180 — — — Non-regulatory agreement units 134 134 — — — Net unrealized gains on pledged assets— Zion Station decommissioning 29 29 — — — Regulatory offset to decommissioning trust fund-related activities (b) (358 ) (358 ) — Total decommissioning-related activities 360 360 — — — Investment income 1 1 — (1 ) 7 (c) Long-term lease income 24 — — — — Interest income related to uncertain income tax positions 40 54 — — — AFUDC—Equity 21 — 3 6 12 Other 9 (9 ) 14 2 (1 ) Other, net $ 455 $ 406 $ 17 $ 7 $ 18 For the year ended December 31, 2013 Exelon Generation ComEd PECO BGE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) — Regulatory agreement units $ 256 $ 256 $ — $ — $ — Non-regulatory agreement units 77 77 — — — Net unrealized gains on decommissioning trust funds— Regulatory agreement units 406 406 — — — Non-regulatory agreement units 146 146 — — — Net unrealized gains on pledged assets— Zion Station decommissioning 7 7 — — — Regulatory offset to decommissioning trust fund-related activities (b) (546 ) (546 ) — — Total decommissioning-related activities 346 346 — — — Investment income 8 (1 ) — (1 ) 9 (c) Long-term lease income 28 — — — — Interest income related to uncertain income tax positions 24 4 — — — AFUDC—Equity 22 — 11 4 7 Other 32 6 15 3 1 Other, net $ 460 $ 355 $ 26 $ 6 $ 17 _________________________ (a) Includes investment income and realized gains and losses on sales of investments within the nuclear decommissioning trust funds. (b) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 16 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (c) Relates to the cash return on BGE’s rate stabilization deferral. See Note 3 — Regulatory Matters for additional information regarding the rate stabilization deferral. (d) In January 2015, in connection with Generation's $750 million issuance of five-year Senior Unsecured Notes, Exelon terminated certain floating-to-fixed interest rate swaps. As the original forecasted transactions were a series of future interest payments over a ten year period, a portion of the anticipated interest payments are probable not to occur. As a result, $26 million of anticipated payments were reclassified from Accumulated OCI to Other, net in Exelon's Consolidated Statement of Operations and Comprehensive Income. (e) See Note 14 — Debt and Credit Agreements and 4 — Mergers, Acquisitions, and Dispositions for additional information on the PHI merger related debt exchange.
Components of depreciation, amortization and accretion, and other, net	The following tables provide additional information regarding the Registrants’ Consolidated Statements of Cash Flows for the years ended December 31, 2015 , 2014 and 2013 . For the year ended December 31, 2015 Exelon Generation ComEd PECO BGE Depreciation, amortization, accretion and depletion Property, plant and equipment $ 2,227 $ 1,007 $ 635 $ 240 $ 289 Regulatory assets 170 — 72 20 77 Amortization of intangible assets, net 54 47 — — — Amortization of energy contract assets and liabilities (a) 22 22 — — — Nuclear fuel (b) 1,116 1,116 — — — ARO accretion (c) 398 397 — — — Total depreciation, amortization, accretion and depletion $ 3,987 $ 2,589 $ 707 $ 260 $ 366 For the year ended December 31, 2014 Exelon Generation ComEd PECO BGE Depreciation, amortization, accretion and depletion Property, plant and equipment $ 2,080 $ 922 $ 588 $ 227 $ 288 Regulatory assets 191 — 99 9 83 Amortization of intangible assets, net 44 44 — — — Amortization of energy contract assets and liabilities (a) 135 135 — — — Nuclear fuel (b) 1,073 1,073 — — — ARO accretion (c) 345 345 — — — Total depreciation, amortization, accretion and depletion $ 3,868 $ 2,519 $ 687 $ 236 $ 371 For the year ended December 31, 2013 Exelon Generation ComEd PECO BGE Depreciation, amortization, accretion and depletion Property, plant and equipment $ 1,893 $ 813 $ 545 $ 219 $ 264 Regulatory assets 212 — 119 9 84 Amortization of intangible assets, net 48 43 5 — — Amortization of energy contract assets and liabilities (a) 430 507 — — — Nuclear fuel (b) 921 921 — — — ARO accretion (c) 275 275 — — — Total depreciation, amortization and accretion $ 3,779 $ 2,559 $ 669 $ 228 $ 348 ________________________ (a) Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (b) Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (c) Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
Schedule of Cash Flow, Supplemental Disclosure	For the year ended December 31, 2015 Exelon Generation ComEd PECO BGE Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 930 $ 348 $ 308 $ 94 $ 120 Income taxes (net of refunds) 342 476 (265 ) 64 73 Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 637 $ 269 $ 206 $ 39 $ 65 Loss from equity method investments 7 8 — — — Provision for uncollectible accounts 120 22 53 30 15 Provision for excess and obsolete inventory 10 9 1 — — Stock-based compensation costs 97 — — — — Other decommissioning-related activity (a) (82 ) (82 ) — — — Energy-related options (b) 21 21 — — — Amortization of regulatory asset related to debt costs 7 — 5 2 — Amortization of rate stabilization deferral 73 — — — 73 Amortization of debt fair value adjustment (17 ) (17 ) — — — Amortization of debt costs 58 15 4 2 2 Discrete impacts from EIMA (c) 144 — 144 — — Lower of cost or market inventory adjustment 23 23 — — — Other 11 — 3 (3 ) (18 ) Total other non-cash operating activities $ 1,109 $ 268 $ 416 $ 70 $ 137 Non-cash investing and financing activities: Change in PPE related to ARO update $ 885 $ 885 $ — $ — $ — Change in capital expenditures not paid 96 82 34 (13 ) (9 ) Non-cash financing of capital projects 77 77 — — — Nuclear fuel procurement (d) 57 57 — — — Indemnification of like-kind exchange position (e) — — 7 — — Long-term software licensing agreement (f) 95 — — — — ____________________________ (a) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 16 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate tariff. See Note 3 — Regulatory Matters for more information. (d) Relates to the nuclear fuel procurement contract for the purchase of fixed quantities of converted uranium, which was delivered to Generation in 2015. Generation is required to make payments starting September 28, 2018, with the final payment being due no later than September 30, 2020. (e) See Note 15 — Income Taxes for discussion of the like-kind exchange tax position. (f) Relates to a long-term software license agreement entered into on May 30, 2015. Exelon is required to make payments starting August of 2015 through May of 2024. See Note 14 — Debt and Credit Agreements for additional information. For the year ended December 31, 2014 Exelon Generation ComEd PECO BGE Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 940 $ 322 $ 292 $ 94 $ 111 Income taxes (net of refunds) 314 227 (6 ) 85 (21 ) Pension and non-pension postretirement benefit costs $ 560 $ 249 $ 162 $ 36 $ 64 Loss from equity method investments 22 20 — — — Provision for uncollectible accounts 156 14 26 52 64 Provision for excess and obsolete inventory 5 5 — — — Stock-based compensation costs 91 — — — — Other decommissioning-related activity (a) (132 ) (132 ) — — — Energy-related options (b) 122 122 — — — Amortization of regulatory asset related to debt costs 11 — 8 3 — Amortization of rate stabilization deferral 65 — — — 65 Amortization of debt fair value adjustment (23 ) (23 ) — — — Merger-related commitments 44 44 — — — Amortization of debt costs 53 12 4 2 2 Discrete impacts from EIMA (c) 53 — 53 — — Lower of cost or market inventory adjustment 29 29 — — — Other (2 ) 6 2 (1 ) (15 ) Total other non-cash operating activities $ 1,054 $ 346 $ 255 $ 92 $ 180 Non-cash investing and financing activities: Change in PPE related to ARO update $ 72 $ 72 $ — $ — $ — Change in capital expenditures not paid 220 (61 ) (d) 78 — 25 Fair value of net assets recorded upon CENG consolidation (e) 3,400 3,400 — — — Issuance of equity units (f) 131 — — — — Nuclear fuel procurement (g) 70 70 — — — Indemnification of like-kind exchange position (h) — — 5 — — ______________________ (a) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 16 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate tariff. See Note 3 — Regulatory Matters for more information. (d) Includes $170 million of changes in capital expenditures not paid between December 31, 2014 and 2013 related to Antelope Valley. (e) See Note 5 — Investment in Constellation Energy Nuclear Group, LLC for additional information. (f) Relates to the present value of the contract payments for the equity units issued by Exelon. See Note 20 — Stock-Based Compensation Plans for additional information. (g) Relates to the nuclear fuel procurement contracts for the purchase of fixed quantities of uranium, which was delivered to Generation in 2014. Generation is required to make payments starting June 30, 2016, with the final payment being due no later than June 30, 2018. (h) See Note 15 — Income Taxes for discussion of the like-kind exchange tax position. For the year ended December 31, 2013 Exelon Generation ComEd PECO BGE Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 866 $ 291 $ 283 $ 95 $ 130 Income taxes (net of refunds) 112 (18 ) 33 70 42 Pension and non-pension postretirement benefit costs $ 825 $ 345 $ 308 $ 43 $ 56 Gain from equity method investments (10 ) (10 ) — — — Provision for uncollectible accounts 101 10 (15 ) 61 44 Provision for excess and obsolete inventory 9 9 — — — Stock-based compensation costs 120 — — — — Other decommissioning-related activity (a) (169 ) (169 ) — — — Energy-related options (b) 104 104 — — — Amortization of regulatory asset related to debt costs 12 — 9 3 — Amortization of rate stabilization deferral 66 — — — 66 Amortization of debt fair value adjustment (34 ) (34 ) — — — Discrete impacts from EIMA (c) (271 ) — (271 ) — — Amortization of debt costs 18 10 1 2 2 Other (53 ) 5 (4 ) (1 ) (15 ) Total other non-cash operating activities $ 718 $ 270 $ 28 $ 108 $ 153 Non-cash investing and financing activities: Change in PPE related to ARO update $ (128 ) $ (128 ) $ — $ — $ 4 Change in capital expenditures not paid (38 ) (107 ) (d) (8 ) 13 (48 ) Consolidated VIE dividend to noncontrolling interest 63 63 — — — Indemnification of like-kind exchange position (e) — — 176 — — _________________________ (a) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 16 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through pre-established performance-based formula rate tariff. See Note 3 — Regulatory Matters . (d) Includes $55 million of changes in capital expenditures not paid between December 31, 2013 and 2012 related to Antelope Valley. (e) See Note 15 — Income Taxes for discussion of the like-kind exchanged tax position.
Investments	The following tables provide additional information about assets and liabilities of the Registrants at December 31, 2015 and 2014 . December 31, 2015 Exelon Generation ComEd PECO BGE Investments Equity method investments: Financing trusts (a) $ 22 $ — $ 6 $ 8 $ 8 Bloom 63 63 — — — Net Power 23 23 — — — Other equity method investments 4 3 — — — Total equity method investments 112 89 6 8 8 Other investments: Net investment in leases (b) 358 6 — — — Employee benefit trusts and investments (c) 85 31 — 20 4 Other cost method investments 55 55 — — — Other available for sale investments 29 29 — — — Total investments $ 639 $ 210 $ 6 $ 28 $ 12 December 31, 2014 Exelon Generation ComEd PECO BGE Investments Equity method investments: Financing trusts (a) $ 22 $ — $ 6 $ 8 $ 8 Bloom 13 13 — — — Net Power 9 9 — — — Sunnyside 5 5 — — — Other equity method investments 1 1 — — — Total equity method investments 50 28 6 8 8 Other investments: Net investment in leases (b) 367 7 — — — Employee benefit trusts and investments (c) 85 27 — 23 4 Other cost method investments 37 37 — — — Other available for sale investments 5 5 — — — Total investments $ 544 $ 104 $ 6 $ 31 $ 12 _________________________ (a) Includes investments in affiliated financing trusts, which were not consolidated within the financial statements of Exelon and are shown as investments on the Consolidated Balance Sheets. See Note 1 — Significant Accounting Policies for additional information. (b) Represents direct financing lease investments. See Note 8 — Impairment of Long-Lived Assets for additional information. (c) The Registrants’ investments in these marketable securities are recorded at fair market value.
Accrued Liabilities Current	The following tables provide additional information about liabilities of the Registrants at December 31, 2015 and 2014 . December 31, 2015 Exelon Generation ComEd PECO BGE Accrued expenses Compensation-related accruals (a) $ 1,014 $ 547 $ 183 $ 66 $ 57 Taxes accrued 293 186 63 4 23 Interest accrued 915 77 443 35 27 Severance accrued 21 11 3 — 1 Other accrued expenses 133 114 14 4 2 Total accrued expenses $ 2,376 $ 935 $ 706 $ 109 $ 110 December 31, 2014 Exelon Generation ComEd PECO BGE Accrued expenses Compensation-related accruals (a) $ 832 $ 447 $ 153 $ 50 $ 58 Taxes accrued 305 248 59 3 42 Interest accrued 240 66 102 33 29 Severance accrued 49 33 2 1 2 Other accrued expenses 113 (b) 92 (b) 15 4 — Total accrued expenses $ 1,539 $ 886 $ 331 $ 91 $ 131 _______________________ (a) Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits. (b) Includes $19 million for amounts accrued related to Antelope Valley as of December 31, 2014 .

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
Analysis and reconciliation of reportable segment information	An analysis and reconciliation of the Registrants’ reportable segment information to the respective information in the consolidated financial statements for the years ended December 31, 2015 , 2014 , and 2013 is as follows: Generation (a) ComEd PECO BGE Other (b) Intersegment Eliminations Exelon Operating revenues (c) : 2015 Competitive businesses electric revenues $ 15,944 $ — $ — $ — $ — $ (744 ) $ 15,200 Competitive businesses natural gas revenues 2,433 — — — — — 2,433 Competitive businesses other revenues 758 — — — — (1 ) 757 Rate-regulated electric revenues — 4,905 2,486 2,490 — (5 ) 9,876 Rate-regulated natural gas revenues — — 546 645 — (15 ) 1,176 Shared service and other revenues — — — — 1,372 (1,367 ) 5 2014 Competitive businesses electric revenues $ 14,533 $ — $ — $ — $ — $ (760 ) $ 13,773 Generation (a) ComEd PECO BGE Other (b) Intersegment Eliminations Exelon Competitive businesses natural gas revenues 2,705 — — — — (1 ) 2,704 Competitive businesses other revenues 155 — — — — (1 ) 154 Rate-regulated electric revenues — 4,564 2,448 2,460 — (5 ) 9,467 Rate-regulated natural gas revenues — — 646 705 — (26 ) 1,325 Shared service and other revenues — — — — 1,285 (1,279 ) 6 2013 Competitive businesses electric revenues $ 13,862 $ — $ — $ — $ — $ (1,366 ) $ 12,496 Competitive businesses natural gas revenues 1,721 — — — — — 1,721 Competitive businesses other revenues 47 — — — — (1 ) 46 Rate-regulated electric revenues — 4,464 2,500 2,405 — (4 ) 9,365 Rate-regulated natural gas revenues — — 600 660 — (14 ) 1,246 Shared service and other revenues — — — — 1,241 (1,227 ) 14 Intersegment revenues (d) : 2015 $ 745 $ 4 $ 2 $ 14 $ 1,367 $ (2,127 ) $ 5 2014 762 4 2 25 1,280 (2,067 ) 6 2013 1,367 3 1 13 1,237 (2,607 ) 14 Depreciation and amortization 2015 $ 1,054 $ 707 $ 260 $ 366 $ 63 $ — $ 2,450 2014 967 687 236 371 53 — 2,314 2013 856 669 228 348 52 — 2,153 Operating expenses (c) : 2015 $ 16,872 $ 3,889 $ 2,404 $ 2,578 $ 1,444 $ (2,131 ) $ 25,056 2014 16,923 3,586 2,522 2,726 1,353 (2,071 ) 25,039 2013 13,976 3,510 2,434 2,616 1,324 (2,618 ) 21,242 Equity in earnings (losses) of unconsolidated affiliates 2015 $ (8 ) $ — $ — $ — $ 1 $ — $ (7 ) 2014 (20 ) — — — — — (20 ) 2013 10 — — — — — 10 Interest expense, net: 2015 $ 365 $ 332 $ 114 $ 99 $ 123 $ — $ 1,033 2014 356 321 113 106 169 — 1,065 2013 357 579 115 122 183 — 1,356 Income (loss) before income taxes: 2015 $ 1,850 $ 706 $ 521 $ 477 $ (219 ) $ (5 ) $ 3,330 2014 1,226 676 466 351 (227 ) (6 ) 2,486 2013 1,675 401 557 344 (191 ) (13 ) 2,773 Income taxes: 2015 $ 502 $ 280 $ 143 $ 189 $ (41 ) $ — $ 1,073 Generation (a) ComEd PECO BGE Other (b) Intersegment Eliminations Exelon 2014 207 268 114 140 (63 ) — 666 2013 615 152 162 134 (20 ) 1 1,044 Net income (loss): 2015 $ 1,340 $ 426 $ 378 $ 288 $ (177 ) $ (5 ) $ 2,250 2014 1,019 408 352 211 (164 ) (6 ) 1,820 2013 1,060 249 395 210 (171 ) (14 ) 1,729 Capital expenditures: 2015 $ 3,841 $ 2,398 $ 601 $ 719 $ 65 $ — 7,624 2014 3,012 1,689 661 620 95 — 6,077 2013 2,752 1,433 537 587 86 — 5,395 Total assets: 2015 $ 46,529 $ 26,532 $ 10,367 $ 8,295 $ 15,389 $ (11,728 ) $ 95,384 2014 44,951 25,358 9,860 8,056 9,711 (11,520 ) 86,416 __________________________ (a) Generation includes the six power marketing reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. For the year ended December 31, 2015 , intersegment revenues for Generation include revenue from sales to PECO of $ 224 million and sales to BGE of $ 502 million in the Mid-Atlantic region, and sales to ComEd of $ 18 million in the Midwest region, which eliminate upon consolidation. For the year ended December 31, 2014 , intersegment revenues for Generation include revenue from sales to PECO of $ 198 million and sales to BGE of $ 387 million in the Mid-Atlantic region, and sales to ComEd of $ 176 million in the Midwest region, which eliminate upon consolidation. For the year ended December 31, 2013 , intersegment revenues for Generation include revenue from sales to PECO of $ 405 million and sales to BGE of $ 455 million in the Mid-Atlantic region, and sales to ComEd of $ 506 million in the Midwest region, net of $ 7 million related to the unrealized mark-to-market losses related to the ComEd swap, which eliminate upon consolidation. (b) Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities. (c) For the years ended December 31, 2015 , 2014 and 2013 , utility taxes of $105 million , $89 million and $79 million , respectively, are included in revenues and expenses for Generation. For the years ended December 31, 2015 , 2014 and 2013 , utility taxes of $236 million , $238 million and $241 million , respectively, are included in revenues and expenses for ComEd. For the years ended December 31, 2015 , 2014 and 2013 , utility taxes of $133 million , $128 million and $129 million , respectively, are included in revenues and expenses for PECO. For the years ended December 31, 2015 , 2014 and 2013 , utility taxes of $85 million , $86 million and $82 million are included in revenues and expenses for BGE, respectively. (d) Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations and Comprehensive Income.
Analysis and reconciliation of reportable segment revenues for Generation	2015 2014 2013 Revenues from external customers (b) Intersegment revenues Total revenues Revenues from external customers (b)(d) Intersegment revenues (d) Total revenues Revenues from external customers (b)(d) Intersegment revenues (d) Total revenues Mid-Atlantic (a) $ 5,974 $ (74 ) $ 5,900 $ 5,414 $ (155 ) $ 5,259 $ 5,261 $ (57 ) $ 5,204 Midwest 4,712 (2 ) 4,710 4,488 (13 ) 4,475 4,298 (28 ) 4,270 New England 2,217 (5 ) 2,212 1,468 (46 ) 1,422 1,279 (42 ) 1,237 New York 996 (11 ) 985 846 (3 ) 843 717 (3 ) 714 ERCOT 863 (6 ) 857 938 (3 ) 935 1,223 (7 ) 1,216 Other Power Regions 1,182 (80 ) 1,102 1,379 (70 ) 1,309 1,084 (116 ) 968 Total Revenues for Reportable Segments $ 15,944 $ (178 ) $ 15,766 $ 14,533 $ (290 ) $ 14,243 $ 13,862 $ (253 ) $ 13,609 Other (c) 3,191 178 3,369 2,860 290 3,150 1,768 253 2,021 Total Generation Consolidated Operating Revenues $ 19,135 $ — $ 19,135 $ 17,393 $ — $ 17,393 $ 15,630 $ — $ 15,630 _______________________ (a) On April 1, 2014, Generation assumed operational control of CENG's nuclear fleet. As a result, beginning on April 1, 2014, CENG's revenues are included on a fully consolidated basis. (b) Includes all wholesale and retail electric sales to third parties and affiliated sales to ComEd, PECO and BGE. (c) Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $7 million increase to revenues, a $ 289 million decrease to revenues, and a $ 767 million decrease to revenues for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2015 , 2014 , and 2013 , respectively, unrealized mark-to-market gains of $203 million , losses of $174 million , and gains of $220 million for the years ended December 31, 2015 , 2014 , and 2013 , respectively, and elimination of intersegment revenues. (d) Exelon corrected an error in the December 31, 2014 and December 31, 2013 balances within Intersegment revenues and Revenues from external customers for an overstatement of Intersegment revenues for Reportable Segments of $284 million and $252 million for the years ended December 31, 2014 and 2013 , respectively, an understatement of Revenues from external customers for Reportable Segments of $284 million and $252 million for the years ended December 31, 2014 and 2013 , respectively, an understatement of Intersegment revenues for Other of $284 million and $252 million for the years ended December 31, 2014 and 2013 , respectively, and an overstatement of Revenues from external customers for Other of $284 million and $252 million for the years ended December 31, 2014 and 2013 , respectively. The error is not considered material to any prior period, and there is no net impact to Total Revenues.
Reconciliation of revenues from segments to consolidated	Generation total revenues net of purchased power and fuel expense: 2015 2014 2013 RNF from external (b) Intersegment Total RNF RNF from external (b)(d) Intersegment RNF d) Total RNF RNF from external (b)(d) Intersegment (d) Total RNF Mid-Atlantic (a) $ 3,556 $ 15 $ 3,571 $ 3,544 $ (113 ) $ 3,431 $ 3,287 $ (17 ) $ 3,270 Midwest 2,912 (20 ) 2,892 2,607 (8 ) 2,599 2,606 (20 ) 2,586 New England 519 (58 ) 461 450 (99 ) 351 299 (114 ) 185 New York 584 50 634 439 44 483 (55 ) 51 (4 ) ERCOT 425 (132 ) 293 573 (256 ) 317 627 (191 ) 436 Other Power Regions 440 (190 ) 250 517 (190 ) 327 397 (196 ) 201 Total Revenues net of purchased power and fuel expense for Reportable Segments $ 8,436 $ (335 ) $ 8,101 $ 8,130 $ (622 ) $ 7,508 $ 7,161 $ (487 ) $ 6,674 Other (c) 678 335 1,013 (662 ) 622 (40 ) 272 487 759 Total Generation Revenues net of purchased power and fuel expense $ 9,114 $ — $ 9,114 $ 7,468 $ — $ 7,468 $ 7,433 $ — $ 7,433 ____________________________ (a) On April 1, 2014, Generation assumed operational control of CENG's nuclear fleet. As a result, beginning on April 1, 2014, CENG's revenue net of purchased power and fuel expense are included on a fully consolidated basis. (b) Includes purchases and sales from third parties and affiliated sales to ComEd, PECO and BGE. (c) Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $8 million increase in RNF, a $ 124 million decrease in RNF, and a $ 488 million decrease in RNF for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2015 , 2014 , and 2013 , respectively, unrealized mark-to-market gains of $257 million , losses of $591 million , and gains of $504 million for the years ended December 31, 2015 , 2014 , and 2013 , respectively, and the elimination of intersegment revenue net of purchased power and fuel expense. (d) Exelon corrected an error in the December 31, 2014 and December 31, 2013 balances within Intersegment RNF and RNF from external customers for an understatement of $8 million and an overstatement of $134 million of Intersegment RNF for Reportable Segments for the years ended December 31, 2014 and 2013 , respectively, an understatement of RNF from external customers for Reportable Segments of $11 million and $134 million for the years ended December 31, 2014 and 2013 , respectively, an overstatement of $8 million and an understatement $134 million of Intersegment RNF for Other for the years ended December 31, 2014 and 2013 , respectively, and an overstatement of RNF from external customers for Other of $11 million and $134 million for the years ended December 31, 2014 and 2013 , respectively. This also included an understatement of total RNF for Reportable Segments and an overstatement of total RNF for Other of $19 million for the year ended December 31, 2014 . The error is not considered material to any prior period, and there is no net impact to Generation Total RNF for 2013 or 2014.

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2015
Related Party Transactions [Abstract]
Related Party Transactions Income Statement Disclosure	The financial statements of PECO include related party transactions as presented in the tables below: For the Years Ended December 31, 2015 2014 2013 Operating revenues from affiliates: Generation (a) $ 2 $ 2 $ 1 Purchased power from affiliate Generation (b) $ 220 $ 194 $ 392 Operating and maintenance from affiliates: BSC (c) $ 107 $ 96 $ 98 Generation 3 3 3 Total operating and maintenance from affiliates $ 110 $ 99 $ 101 Interest expense to affiliates, net: PECO Trust III $ 6 $ 6 $ 6 PECO Trust IV 6 6 6 Total interest expense to affiliates, net $ 12 $ 12 $ 12 Capitalized costs BSC (c) $ 40 $ 39 $ 46 Cash dividends paid to parent $ 279 $ 320 $ 332 Contribution from parent $ 16 $ 24 $ 27 The financial statements of BGE include related party transactions as presented in the tables below: For the Years Ended December 31, 2015 2014 2013 Operating revenues from affiliates: Generation (a) $ 14 $ 25 $ 13 Purchased power from affiliate Generation (b) $ 498 $ 382 $ 452 Operating and maintenance from affiliates: BSC (c) $ 118 $ 103 $ 83 Interest expense to affiliates, net: BGE Capital Trust II $ 16 $ 16 $ 16 Capitalized costs BSC (c) $ 28 $ 19 $ 15 Cash dividends paid to parent $ 158 $ — $ — Contribution from parent $ 7 $ — $ — The financial statements of Exelon include related party transactions as presented in the tables below: For the Years Ended December 31, 2015 2014 2013 Operating revenues from affiliates: PECO (a) $ 1 $ 1 $ 10 CENG (b) — 17 56 BGE (a) 4 5 4 Other 4 — — Total operating revenues from affiliates $ 9 $ 23 $ 70 Purchase power and fuel from affiliates: CENG (c) $ — $ 282 $ 992 Keystone Fuels, LLC (d) — 138 144 Conemaugh Fuels, LLC (d) — 99 98 Safe Harbor Water Power Corp (d) — 12 22 Total purchase power and fuel from affiliates $ — $ 531 $ 1,256 Interest expense to affiliates, net: ComEd Financing III $ 13 $ 13 $ 13 PECO Trust III 6 6 6 PECO Trust IV 6 6 6 BGE Capital Trust II 16 16 16 Total interest expense to affiliates, net $ 41 $ 41 $ 41 Earnings (losses) in equity method investments: CENG (e) $ — $ (19 ) $ 9 Qualifying facilities and domestic power projects (8 ) (1 ) 1 Other $ 1 $ — $ — Total earnings (losses) in equity method investments $ (7 ) $ (20 ) $ 10 The financial statements of Generation include related party transactions as presented in the tables below: For the Years Ended December 31, 2015 2014 2013 Operating revenues from affiliates: ComEd (a) $ 18 $ 176 $ 506 PECO (b) 224 198 405 BGE (c) 502 387 455 CENG (d) — 17 56 BSC 1 1 1 Other 4 — — Total operating revenues from affiliates $ 749 $ 779 $ 1,423 Purchase power and fuel from affiliates: ComEd $ — $ 1 $ 1 BGE 14 25 13 CENG (e) — 282 992 Keystone Fuels, LLC (i) — 138 144 Conemaugh Fuels, LLC (i) — 99 98 Safe Harbor Water Power Corporation (i) — 12 22 Total purchase power and fuel from affiliates $ 14 $ 557 $ 1,270 Operating and maintenance from affiliates: ComEd (f) $ 4 $ 3 $ 2 PECO (f) 2 2 1 BSC (g) 614 618 571 Total operating and maintenance from affiliates $ 620 $ 623 $ 574 Interest expense to affiliates, net: Exelon Corporate (j) $ 43 $ 53 $ 59 Earnings (losses) in equity method investments CENG (h) $ — $ (19 ) $ 9 Qualifying facilities and domestic power projects (8 ) (1 ) 1 Total earnings (losses) in equity method investments $ (8 ) $ (20 ) $ 10 Capitalized costs BSC (g) $ 76 $ 91 $ 93 Cash distribution paid to member $ 2,474 $ 645 $ 625 Contribution from member $ 47 $ 53 $ 26 The financial statements of ComEd include related party transactions as presented in the tables below: For the Years Ended December 31, 2015 2014 2013 Operating revenues from affiliates Generation $ 4 $ 4 $ 3 Purchased power from affiliate Generation (a) $ 18 $ 176 $ 512 Operating and maintenance from affiliate BSC (b) $ 195 $ 166 $ 157 Interest expense to affiliates, net: ComEd Financing III $ 13 $ 13 $ 13 Capitalized costs BSC (b) $ 103 $ 77 $ 69 Cash dividends paid to parent $ 299 $ 307 $ 220 Contribution from parent $ 202 $ 273 $ —
Related Party Transactions Balance Sheet Disclosure	December 31, 2015 2014 Prepaid voluntary employee beneficiary association trust (d) $ — $ 1 Payables to affiliates (current): Generation (b) $ 31 $ 40 BSC (c) 17 17 Exelon Corporate 1 5 PECO — 1 BGE Capital Trust II 3 3 Total payables to affiliates (current) $ 52 $ 66 Long-term debt to BGE financing trust BGE Capital Trust II $ 252 $ 252 ______________________ (a) BGE provides energy to Generation for Generation’s own use. (b) BGE procures a portion of its electricity and gas supply requirements from Generation under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3 — Regulatory Matters for additional information. (c) BGE receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (d) The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for BGE’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets. December 31, 2015 2014 Receivables from affiliates (current): ComEd (a) $ 15 $ 43 PECO (b) 36 29 BGE (c) 31 40 Other 1 1 Total receivables from affiliates (current) $ 83 $ 113 Intercompany money pool (current): Exelon Corporate $ 1,252 $ — Long-term debt due to affiliates (current): Exelon Corporate (l) $ — $ 556 Payables to affiliates (current): Exelon Corporate (j) $ 16 $ 12 BSC (g) 78 83 ComEd 9 12 Other 1 — Total payables to affiliates (current) $ 104 $ 107 Long-term debt due to affiliates (noncurrent): Exelon Corporate (l) $ 933 $ 943 Payables to affiliates (noncurrent): BSC (g) $ — $ 1 ComEd (k) 2,172 2,389 PECO (k) 405 490 Total payables to affiliates (noncurrent) $ 2,577 $ 2,880 _______________________ (a) Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3 — Regulatory Matters for additional information. (b) Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has five-year and ten-year agreements with PECO to sell non-solar and solar AECs, respectively. See Note 3 — Regulatory Matters for additional information. (c) Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3 — Regulatory Matters for additional information. (d) Beginning in 2012, Generation entered into a power services agency agreement (PSAA) with the CENG plants, which as of April 1, 2014, was amended and extended until the permanent cessation of power generation by the CENG generation plants. The PSAA is an agreement under which Generation provides scheduling, asset management and billing services to the CENG plants for a specified monthly fee. The charges for services reflect the cost of the services. On April 1, 2014, Generation and CENG entered into a Nuclear Operating Services Agreement (NOSA) pursuant to which Generation will operate the CENG nuclear generation fleet owned by CENG subsidiaries and provide corporate and administrative services for the remaining life of the CENG nuclear plants as if they were part of the Generation nuclear fleet. For further information regarding the Investment in CENG, see Note 5 — Investment in Constellation Energy Nuclear Group, LLC . (e) CENG owns 100% of four nuclear units in Maryland and New York and 82% of Nine Mile Point Unit 2 in New York. Beginning in 2012, Generation had a PPA under which it purchased 85% of the nuclear plant output owned by CENG that was not sold to third parties under pre-existing unit-contingent PPAs through 2014. Beginning on January 1, 2015 and continuing to the end of the life of the respective plants, Generation will purchase on a unit-contingent basis 50.01% of the nuclear plant output owned by CENG and a subsidiary of EDF will purchase on a unit-contingent basis 49.99% of the nuclear plant output owned by CENG (EDF PPA) not sold to third parties. Beginning April 1, 2014, sales to Generation are eliminated in consolidation. For further information regarding the Investment in CENG, see Note 5 — Investment in Constellation Energy Nuclear Group, LLC . (f) Generation requires electricity for its own use at its generating stations. Generation purchases electricity and distribution and transmission services from PECO and only distribution and transmission services from ComEd for the delivery of electricity to its generating stations. (g) Generation receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (h) Prior to April 1, 2014, Generation’s total gain (loss) in equity method investments includes equity income (loss) and amortization of the basis difference established as a result of purchase accounting applied upon Constellation merger in 2012. CENG was fully consolidated on April 1, 2014. For further information regarding the Investment in CENG, see Note 5 — Investment in Constellation Energy Nuclear Group, LLC . (i) During 2014, Generation closed the sale of Safe Harbor Water Power Corporation, Keystone Fuels, LLC, and Conemaugh Fuels LLC. Generation recorded purchase power and fuel costs from affiliates related to these generating assets during the time these assets were still partially owned by Generation. See Note 4 — Mergers, Acquisitions, and Dispositions for more information. (j) The balance consists of interest owed to Exelon Corporation related to the senior unsecured notes, as well as, expense related to certain invoices Exelon Corporation processed on behalf of Generation. (k) Generation has long-term payables to ComEd and PECO as a result of the nuclear decommissioning contractual construct whereby, to the extent NDT funds are greater than the underlying ARO at the end of decommissioning, such amounts are due back to ComEd and PECO, as applicable, for payment to their respective customers. See Note 16 — Asset Retirement Obligations . (l) In connection with the debt obligations assumed by Exelon as part of the Constellation merger, Exelon and subsidiaries of Generation (former Constellation subsidiaries) assumed intercompany loan agreements that mirror the terms and amounts of the third-party debt obligations of Exelon, resulting in intercompany notes payable included in Long-term Debt to affiliate on Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation on Exelon’s Consolidated Balance Sheets. December 31, 2015 2014 Payables to affiliates (current): ComEd Financing III $ 4 $ 4 PECO Trust III 1 1 BGE Capital Trust II 3 3 Total payables to affiliates (current) $ 8 $ 8 Long-term debt due to financing trusts: ComEd Financing III $ 205 $ 205 PECO Trust III 81 81 PECO Trust IV 103 103 BGE Capital Trust II 252 252 Total long-term debt due to financing trusts $ 641 $ 641 ____________________________ (a) The intersegment profit associated with the sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statement of Operations. See Note 3 — Regulatory Matters for additional information. (b) Beginning in 2012, Generation entered into a power services agency agreement (PSAA) with the CENG plants, which as of April 1, 2014, was amended and extended until the permanent cessation of power generation by the CENG generation plants. The PSAA is an agreement under which Generation provides scheduling, asset management and billing services to the CENG plants for a specified monthly fee. The charges for services reflect the cost of the services. On April 1, 2014, Generation and CENG entered into a Nuclear Operating Services Agreement (NOSA) pursuant to which Generation will operate the CENG nuclear generation fleet owned by CENG subsidiaries and provide corporate and administrative services for the remaining life of the CENG nuclear plants as if they were part of the Generation nuclear fleet. For further information regarding the Investment in CENG, see Note 5 — Investment in Constellation Energy Nuclear Group, LLC . (c) CENG owns 100% of four nuclear units in Maryland and New York and 82% of Nine Mile Point Unit 2 in New York. Beginning in 2012, Generation had a PPA under which it purchased 85% of the nuclear plant output owned by CENG that was not sold to third parties under pre-existing unit-contingent PPAs through 2014. Beginning on January 1, 2015 and continuing to the end of the life of the respective plants, Generation will purchase on a unit-contingent basis 50.01% of the nuclear plant output owned by CENG and a subsidiary of EDF will purchase on a unit-contingent basis 49.99% of the nuclear plant output owned by CENG (EDF PPA) not sold to third parties. Beginning April 1, 2014, sales to Generation are eliminated in consolidation. For further information regarding the Investment in CENG, see Note 5 — Investment in Constellation Energy Nuclear Group, LLC . (d) During 2014, Generation closed the sale of Safe Harbor Water Power Corporation, Keystone Fuels, LLC, and Conemaugh Fuels LLC. Generation recorded purchase power and fuel costs from affiliates related to these generating assets during the time these assets were still partially owned by Generation. See Note 4 — Mergers, Acquisitions, and Dispositions for more information. (e) Prior to April 1, 2014, Generation’s total gain (loss) in equity method investments includes equity investment income (loss) and amortization of the basis difference established as a result of purchase accounting applied upon Constellation merger in 2012. CENG was fully consolidated on April 1, 2014. For further information regarding the Investment in CENG, see Note 5 — Investment in Constellation Energy Nuclear Group, LLC . December 31, 2015 2014 Prepaid voluntary employee beneficiary association trust (d) $ 2 $ 3 Receivable from affiliate (current): ComEd $ 2 $ 2 BGE — 1 Total receivable from affiliates (current) $ 2 $ 3 Receivable from affiliate (noncurrent): Generation (e) $ 405 $ 490 Payables to affiliates (current): Generation (b) $ 36 $ 29 BSC (c) 17 20 Exelon Corporate 1 2 PECO Trust III 1 1 Total payables to affiliates (current) $ 55 $ 52 Long-term debt to financing trusts: PECO Trust III $ 81 $ 81 PECO Trust IV 103 103 Total long-term debt to financing trusts $ 184 $ 184 ________________________ (a) PECO provides energy to Generation for Generation’s own use. (b) PECO purchases electric supply from Generation under contracts executed through its competitive procurement process. In addition, PECO has five-year and ten-year agreements with Generation to purchase non-solar and solar AECs, respectively. See Note 3 — Regulatory Matters for additional information on AECs. (c) PECO receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (d) The voluntary employee beneficiary association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for PECO’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. (e) PECO has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct, whereby, to the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to PECO for payment to PECO’s customers. December 31, 2015 2014 Prepaid voluntary employee beneficiary association trust (c) $ 11 $ 13 Receivable from affiliates (current): Voluntary employee beneficiary association trust $ 2 $ 2 Generation 9 12 Exelon Corporate (e) 188 — Total receivable from affiliates (current) $ 199 $ 14 Receivable from affiliates (noncurrent): Generation (d) $ 2,172 $ 2,389 Exelon Corporate (e) — 182 Total receivable from affiliates (noncurrent) $ 2,172 $ 2,571 Payables to affiliates (current): Generation (a) $ 15 $ 43 BSC (b) 39 32 ComEd Financing III 4 4 PECO 2 2 Exelon Corporate 2 3 Total payables to affiliates (current) $ 62 $ 84 Long-term debt to ComEd financing trust ComEd Financing III $ 205 $ 205 _______________________ (a) ComEd procures a portion of its electricity supply requirements from Generation under an ICC-approved RFP contract. ComEd also purchases RECs from Generation. In addition, purchased power expense includes the settled portion of the financial swap contract with Generation, which expired in 2013. See Note 3 — Regulatory Matters and Note 13 — Derivative Financial Instruments for additional information. (b) ComEd receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (c) The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for ComEd’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets. (d) ComEd has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct for generating facilities previously owned by ComEd. To the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to ComEd for payment to ComEd’s customers. (e) Represents indemnification from Exelon Corporate related to the like-kind exchange transaction.

Quarterly Data (Unaudited) (Tab

Quarterly Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Data [Line Items]
Quarterly Financial Information	The data shown below, which may not equal the total for the year due to the effects of rounding and dilution, includes all adjustments that Exelon considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2015 2014 2015 2014 2015 2014 Quarter ended: March 31 $ 8,830 $ 7,237 $ 1,366 (a) $ 168 (b) $ 693 $ 90 June 30 6,514 6,024 1,134 (a) 842 (b) 638 522 September 30 7,401 6,912 1,200 (a) 1,738 (b) 629 993 December 31 6,702 7,255 707 348 309 18 (c) ____________________________ (a) In the first, second, and third quarter of 2015, Exelon reclassified $(1) million , $7 million , and $2 million , respectively, to Operating income for presentation purposes in Exelon's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect Exelon's Net (Loss) Income on Common Stock. (b) In the first, second, and third quarter of 2014, Exelon reclassified $5 million , $13 million , and $339 million , respectively, to Operating income for presentation purposes in Exelon's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect Exelon's Net (Loss) Income on Common Stock. (c) Includes charges to earnings related to the impairments of certain generating assets which were held for sale and certain Upstream exploration assets. See Note 8 — Impairment of Long-Lived Assets of the Combined Notes to Consolidated Financial Statements for additional information.
Average Basic And Diluted Shares And Net Income Per Basic And Diluted Share	Average Basic Shares Outstanding (in millions) Net Income 2015 2014 2015 2014 Quarter ended: March 31 862 858 $ 0.80 $ 0.10 June 30 863 860 0.74 0.61 September 30 913 861 0.69 1.15 December 31 921 861 0.34 0.02 Average Diluted Shares Outstanding (in millions) Net Income 2015 2014 2015 2014 Quarter ended: March 31 867 861 $ 0.80 $ 0.10 June 30 866 864 0.74 0.60 September 30 915 863 0.69 1.15 December 31 924 868 0.33 0.02
Per Share Information	The following table presents the New York Stock Exchange—Composite Common Stock Prices and dividends by quarter on a per share basis: 2015 2014 Fourth Quarter Third Quarter Second Quarter First Quarter Fourth Quarter Third Quarter Second Quarter First Quarter High price $ 31.37 $ 34.44 $ 34.98 $ 38.25 $ 38.93 $ 36.26 $ 37.73 $ 33.94 Low price 25.09 28.41 31.28 31.71 33.07 30.66 33.11 26.45 Close 27.77 29.70 31.42 33.61 37.08 34.09 36.48 33.56 Dividends 0.310 0.310 0.310 0.310 0.310 0.310 0.310 0.310
Exelon Generation Co L L C [Member]
Quarterly Financial Data [Line Items]
Quarterly Financial Information	The data shown below includes all adjustments that Generation considers necessary for a fair presentation of such amounts: Operating Revenues Operating (Loss) Income Net (Loss) Income on Membership Interest 2015 2014 2015 (a) 2014 2015 2014 Quarter ended: March 31 $ 5,840 $ 4,390 $ 719 (a) $ (384 ) (b) $ 443 $ (185 ) June 30 4,232 3,789 703 (a) 441 (b) 398 340 September 30 4,768 4,412 622 (a) 1,225 (b) 377 771 December 31 4,294 4,802 230 (105 ) 154 (91 ) ____________________________ (a) In the first, second, and third quarter of 2015, Generation reclassified $(1) million , $7 million , and $1 million , respectively, to Operating (loss) income for presentation purposes in Generation's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect Generation's Net (Loss) Income on Membership Interest. (b) In the first, second, and third quarter of 2014, Generation reclassified $5 million , $12 million , and $338 million , respectively, to Operating (loss) income for presentation purposes in Generation's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect Generation's Net (Loss) Income on Membership Interest.
Commonwealth Edison Co [Member]
Quarterly Financial Data [Line Items]
Quarterly Financial Information	The data shown below includes all adjustments that ComEd considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2015 2014 2015 2014 2015 2014 Quarter ended: March 31 $ 1,185 $ 1,134 $ 230 $ 238 $ 90 $ 98 June 30 1,148 1,128 243 258 (a) 99 111 September 30 1,376 1,222 327 287 (a) 149 126 December 31 1,196 1,079 217 196 87 73 ____________________________ (a) In both the second and third quarter of 2014, ComEd reclassified $1 million to Operating income for presentation purposes in ComEd's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect ComEd's Net (Loss) Income.
PECO Energy Co [Member]
Quarterly Financial Data [Line Items]
Quarterly Financial Information	The data shown below includes all adjustments that PECO considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income on Common Stock 2015 2014 2015 2014 2015 2014 Quarter ended: March 31 $ 985 $ 993 $ 223 $ 149 $ 139 $ 89 June 30 661 656 124 134 70 84 September 30 740 693 154 133 90 81 December 31 645 750 128 156 79 98
Baltimore Gas and Electric Company [Member]
Quarterly Financial Data [Line Items]
Quarterly Financial Information	The data shown below includes all adjustments that BGE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income attributable to Common Shareholders 2015 2014 2015 2014 2015 2014 Quarter ended: March 31 $ 1,036 $ 1,054 $ 204 $ 169 $ 106 $ 85 June 30 628 653 99 55 44 16 September 30 725 697 110 102 51 46 December 31 746 761 144 113 74 52

Significant Accounting Polici67

Significant Accounting Policies - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt	$ 23,645,000,000	$ 19,212,000,000
Percentage ownership of consolidated subsidiaries	100.00%
Percentage ownership of common stock	100.00%
Third Party interest in ComEd (less than $1 million)	$ 1,308,000,000	1,332,000,000
Minimum expectation of tax position to be realized	50.00%
New Accounting Pronouncement, Early Adoption, Effect [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt		157,000,000
Commonwealth Edison Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	99.00%
Third Party interest in ComEd (less than $1 million)	$ 1,000,000	1,000,000
CENG [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	50.01%
RITELine Illinois LLC [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Third Party interest in ComEd (less than $1 million)	$ 1,000,000	1,000,000
Minority interest ownership percentage by parent	12.50%
Exelon Generation Co L L C [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt	$ 7,936,000,000	6,639,000,000
Third Party interest in ComEd (less than $1 million)	$ 1,307,000,000	1,333,000,000
Ownership interest upper bound	99.00%
Ownership interest	50.01%
Cost of spent nuclear fuel disposal per kWh of net nuclear generation	$ (0.001)
Development costs expensed	22,000,000	13,000,000	$ 10,000,000
Exelon Generation Co L L C [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt		70,000,000
Commonwealth Edison Co [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt	$ 5,844,000,000	5,665,000,000
Percentage ownership of consolidated subsidiaries	100.00%
Commonwealth Edison Co [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt		34,000,000
Commonwealth Edison Co [Member] | RITELine Illinois LLC [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	75.00%
Third-party percentage interest in subsidiaries	25.00%
PECO Energy Co [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt	$ 2,280,000,000	2,232,000,000
PECO Energy Co [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt		14,000,000
Baltimore Gas and Electric Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt	$ 1,480,000,000	1,857,000,000
Baltimore Gas and Electric Company [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Long-term debt		$ 16,000,000
Minimum [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	20.00%
Maximum [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	50.00%
Nuclear-Fuel Generating Facilities License Extension [Member] | Exelon Generation Co L L C [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Useful life	20 years

Significant Accounting Polici68

Significant Accounting Policies - Summary of Capitalized Software Costs (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Capitalized Software [Line Items]
Net unamortized software costs	[1]	$ 633	$ 596
Amortization of capitalized software costs	[1],[2]	208	186	$ 198
Exelon Generation Co L L C [Member]
Capitalized Software [Line Items]
Net unamortized software costs	[1]	180	193
Amortization of capitalized software costs	[1],[2]	73	59	67
Commonwealth Edison Co [Member]
Capitalized Software [Line Items]
Net unamortized software costs		172	133
Amortization of capitalized software costs		47	45	52
PECO Energy Co [Member]
Capitalized Software [Line Items]
Net unamortized software costs		86	84
Amortization of capitalized software costs		33	28	33
Baltimore Gas and Electric Company [Member]
Capitalized Software [Line Items]
Net unamortized software costs		178	163
Amortization of capitalized software costs	[2]	$ 46	$ 43	$ 36
[1]	Net unamortized software costsExelon Generation ComEd PECO BGEDecember 31, 2015$633 $180 $172 $86 $178December 31, 2014596 193 133 84 163 Amortization of capitalized software costsExelon Generation ComEd PECO BGE 2015$208 $73 $47 $33 $462014186 59 45 28 432013198 67 52 33 36
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246QjdBNkMxMjBFNTNGRENEMjMyODQxMjI1RThCMzdCRjEM}

Significant Accounting Polici69

Significant Accounting Policies - Summary of Total Interest Incurred, Capitalized and Credits to AFUDC (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1],[2],[3]	$ 1,170	$ 1,144	$ 1,423
Capitalized interest	[1],[3]	79	63	54
Credits to AFUDC debt and equity	[1],[3]	44	37	35
Exelon Generation Co L L C [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1],[2],[3]	445	419	411
Capitalized interest	[1],[3]	79	63	54
Credits to AFUDC debt and equity	[1],[3]	0	0	0
Commonwealth Edison Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[2]	336	323	584
Capitalized interest		0	0	0
Credits to AFUDC debt and equity		9	5	16
PECO Energy Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[2]	116	115	117
Capitalized interest		0	0	0
Credits to AFUDC debt and equity		7	8	6
Baltimore Gas and Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1],[2]	113	118	129
Capitalized interest	[1]	0	0	0
Credits to AFUDC debt and equity	[1]	$ 28	$ 24	$ 13
[1]	.
[2]	Includes interest expense to affiliates.
[3]	On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, the 2014 financial results include CENG’s financial position and results of operations beginning April 1, 2014.

Significant Accounting Polici70

Significant Accounting Policies Balance Sheet Classification of Deferred Taxes (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Other noncurrent assets	$ 1,445,000,000	$ 923,000,000
Other noncurrent liabilities	1,491,000,000	2,147,000,000
New Accounting Pronouncement, Early Adoption, Effect [Member]
Deferred Income Taxes and Other Assets, Current	(244)
Other noncurrent assets	3
Deferred Tax Liabilities, Gross, Current	0
Other noncurrent liabilities	(241)
Commonwealth Edison Co [Member]
Other noncurrent assets	324,000,000	237,000,000
Other noncurrent liabilities	507,000,000	889,000,000
Commonwealth Edison Co [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Deferred Income Taxes and Other Assets, Current	0
Other noncurrent assets	0
Deferred Tax Liabilities, Gross, Current	(63)
Other noncurrent liabilities	63
Exelon Generation Co L L C [Member]
Other noncurrent assets	627,000,000	578,000,000
Other noncurrent liabilities	602,000,000	719,000,000
Exelon Generation Co L L C [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Deferred Income Taxes and Other Assets, Current	(327)
Other noncurrent assets	0
Deferred Tax Liabilities, Gross, Current	0
Other noncurrent liabilities	(327)
PECO Energy Co [Member]
Other noncurrent assets	21,000,000	20,000,000
Other noncurrent liabilities	90,000,000	95,000,000
PECO Energy Co [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Deferred Income Taxes and Other Assets, Current	(69)
Other noncurrent assets	0
Deferred Tax Liabilities, Gross, Current	0
Other noncurrent liabilities	(69)
Baltimore Gas and Electric Company [Member]
Other noncurrent assets	8,000,000	9,000,000
Other noncurrent liabilities	61,000,000	$ 60,000,000
Baltimore Gas and Electric Company [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Deferred Income Taxes and Other Assets, Current	(6)
Other noncurrent assets	0
Deferred Tax Liabilities, Gross, Current	(52)
Other noncurrent liabilities	$ 46

Variable Interest Entities - Na

Variable Interest Entities - Narrative (Details) $ in Millions	Apr. 01, 2014USD ($)	Sep. 30, 2015USD ($)	Dec. 31, 2015USD ($)VIEprojectMW	Dec. 31, 2014USD ($)VIE	Dec. 31, 2013USD ($)	Jun. 09, 2015USD ($)	Jul. 18, 2014USD ($)
Variable Interest Entity [Line Items]
Note Receivable		$ 27
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Number of variable interest entities not consolidated by equity holders | VIE			8	6
Number of variable interest entities consolidated | VIE			7	6
Consolidated Variable Interest Entity [Abstract]
Parental guarantee provided			$ 75
Required purchases of power from CENG's nuclear plants not sold to third parties			85.00%
Purchase of nuclear output by EDF			49.99%
Guarantee obligations maximum exposure			$ 9,206
Other Severance Charges [Member]
Consolidated Variable Interest Entity [Abstract]
Severance charges recorded			6
Constellation Energy Nuclear Group [Member] | Financial Guarantee [Member]
Consolidated Variable Interest Entity [Abstract]
Guarantee obligations maximum exposure	$ 165
Constellation Energy Nuclear Group [Member] | Payment Guarantee [Member]
Consolidated Variable Interest Entity [Abstract]
Due to affiliate	$ 245
Distributed Energy Company [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests			250				$ 91
Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests			172
Exelon Generation Co L L C [Member]
Consolidated Variable Interest Entity [Abstract]
Parental guarantee provided			$ 12
Ownership Percentage Of Consolidated Variable Interest Entities			100.00%
Debt and Capital Lease Obligations			$ 8,869	$ 7,582
Wind project entities with noncontrolling equity interests | project			9
Noncontrolling equity interest ownership percentage held by third parties			1.00%
Number of projects with significant economic power | project			8
Ownership interests in project entities			99.00%
Ownership interest			50.01%
Required purchases of power from CENG's nuclear plants not sold to third parties	85.00%
Severance charges recorded			$ 1
Purchase of nuclear output by EDF	49.99%
Guarantee obligations maximum exposure			6,832
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Consolidated Variable Interest Entity [Abstract]
Due from affiliates	$ 400		300
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member] | Payment Guarantee [Member]
Consolidated Variable Interest Entity [Abstract]
Due to affiliate	205
Exelon Generation Co L L C [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests			78
Consolidated Variable Interest Entity [Abstract]
Parental guarantee provided			$ 275
Exelon Generation Co L L C [Member] | Solar Project Limited Liability Companies [Member]
Consolidated Variable Interest Entity [Abstract]
Business Acquisitions, Megawatts Acquired | MW			242
Ownership Percentage Of Consolidated Variable Interest Entities			100.00%
Debt and Capital Lease Obligations			$ 655
Exelon Generation Co L L C [Member] | AGE Biomass project [Member]
Consolidated Variable Interest Entity [Abstract]
Ownership Percentage Of Consolidated Variable Interest Entities			100.00%
Ownership interests in project entities			90.00%
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Consolidated Variable Interest Entity [Abstract]
Parental guarantee provided	7		$ 7			$ 275
Remeasurement gain from derecognition of equity method investment	$ 261
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Equity Method Investment Variable Interest Entities [Member]
Consolidated Variable Interest Entity [Abstract]
Parental guarantee provided			637
Baltimore Gas and Electric Company [Member]
Consolidated Variable Interest Entity [Abstract]
Guarantee obligations maximum exposure			262
Baltimore Gas and Electric Company [Member] | RSB Bond Co LLC [Member]
Consolidated Variable Interest Entity [Abstract]
Remittance of payments received from customers for rate stabilization to BondCo.			$ 86	$ 85	$ 83

Variable Interest Entities - Ca

Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Dec. 31, 2015		Dec. 31, 2014
Variable Interest Entity [Line Items]
Current assets	[1]	$ 909	[2]	$ 1,275
Noncurrent assets	[1]	8,009	[2]	7,573
Total assets	[1]	8,918	[2]	8,848
Current liabilities	[1]	473	[2]	611
Noncurrent liabilities	[1]	2,927	[2]	2,728
Total liabilities	[1]	3,400	[2]	3,339
Assets	[3]	95,384		86,416
Liabilities	[3]	68,062		62,283
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		881	[2]	1,247
Noncurrent assets		8,004	[2]	7,560
Total assets		8,885	[2]	8,807
Current liabilities		387	[2]	526
Noncurrent liabilities		2,884	[2]	2,597
Total liabilities		3,271	[2]	3,123
Assets	[4]	46,529		44,951
Liabilities	[4]	33,559		30,900
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		23		21
Noncurrent assets		3		3
Total assets		26		24
Current liabilities		81		77
Noncurrent liabilities		41		120
Total liabilities		122		197
Assets	[5]	8,295		8,056
Liabilities	[5]	$ 5,418		$ 5,303
[1]	Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246MjU1NjY5QzIzOUJDQTEyODQyNjUxMjI1RThCM0I0ODAM}
[3]	Exelon’s consolidated assets include $8,268 million and $8,159 million at December 31, 2015 and December 31, 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,264 million and $2,728 million at December 31, 2015 and December 31, 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.
[4]	Generation’s consolidated assets include $8,235 million and $8,118 million at December 31, 2015 and 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,135 million and $2,512 million at December 31, 2015 and 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities.
[5]	BGE’s consolidated assets include $26 million and $24 million at December 31, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE that can only be used to settle the liabilities of the VIE. BGE’s consolidated liabilities include $122 million and $197 million at December 31, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. See Note 2 - Variable Interest Entities.

Variable Interest Entities - As

Variable Interest Entities - Assets and Liabilities of VIEs which Creditors or Beneficiaries have No Recourse (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 6,502	$ 1,878	$ 1,609	$ 1,486
Customer		3,187	3,482
Other		912	1,227
Mark-to-market derivative assets		1,365	1,279
Materials and supplies		1,104	1,024
Other current assets		748	865
Total current assets		15,334	11,853
Property, plant and equipment, net		57,439	52,170
Nuclear decommissioning trust funds		10,342	10,537
Goodwill		2,672	2,672	2,625
Mark-to-market derivative assets		758	773
Other noncurrent assets		1,445	923
Total deferred debits and other assets		22,611	22,393
Total assets	[1]	95,384	86,416
Long-term debt due within one year		1,500	1,802
Accounts payable		2,883	3,048
Accrued expenses		2,376	1,539
Mark-to-market derivative liabilities		205	234
Energy Marketing Contract Liabilities, Current		100	238
Other current liabilities		842	931
Total current liabilities		9,118	8,762
Long-term debt		23,645	19,212
Asset retirement obligations		8,585	7,295
Pension obligations		3,385	3,366
Energy Marketing Contract Liabilities, Noncurrent		117	211
Other noncurrent liabilities		1,491	2,147
Total deferred credits and other liabilities		34,658	33,668
Total liabilities	[1]	68,062	62,283
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		164	392
Restricted cash		100	117
Customer		219	297
Other		43	57
Mark-to-market derivative assets		140	171
Materials and supplies		181	172
Other current assets		35	37
Total current assets		882	1,243
Property, plant and equipment, net		5,160	4,638
Nuclear decommissioning trust funds		2,036	2,097
Goodwill		47	47
Mark-to-market derivative assets		53	44
Other noncurrent assets		90	90
Total deferred debits and other assets		7,386	6,916
Total assets		8,268	8,159
Long-term debt due within one year		111	87
Accounts payable		216	292
Accrued expenses		115	111
Mark-to-market derivative liabilities		5	24
Energy Marketing Contract Liabilities, Current		12	22
Other current liabilities		13	25
Total current liabilities		472	561
Long-term debt		666	212
Asset retirement obligations		1,999	1,763
Pension obligations	[2]	9	9
Energy Marketing Contract Liabilities, Noncurrent		39	51
Other noncurrent liabilities		79	132
Total deferred credits and other liabilities		2,792	2,167
Total liabilities		3,264	2,728
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		431	780	1,258	671
Restricted cash		123	158
Customer		2,095	2,295
Other		360	318
Mark-to-market derivative assets		1,365	1,276
Materials and supplies		880	847
Other current assets		531	658
Total current assets		6,342	7,311
Property, plant and equipment, net		25,843	23,028
Nuclear decommissioning trust funds		10,342	10,537
Goodwill		47	47	0
Mark-to-market derivative assets		733	771
Other noncurrent assets		627	578
Total deferred debits and other assets		14,344	14,612
Total assets	[3]	46,529	44,951
Long-term debt due within one year		90	58
Accounts payable		1,583	1,759
Accrued expenses		935	886
Mark-to-market derivative liabilities		182	214
Energy Marketing Contract Liabilities, Current		100	238
Other current liabilities		356	413
Total current liabilities		4,933	4,459
Long-term debt		7,936	6,639
Asset retirement obligations		8,431	7,146
Energy Marketing Contract Liabilities, Noncurrent		117	211
Other noncurrent liabilities		602	719
Total deferred credits and other liabilities		19,757	18,859
Total liabilities	[3]	33,559	30,900
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		164	392
Restricted cash		77	96
Customer		219	297
Other		43	57
Mark-to-market derivative assets		140	171
Materials and supplies		181	172
Other current assets		30	30
Total current assets		854	1,215
Property, plant and equipment, net		5,160	4,638
Nuclear decommissioning trust funds		2,036	2,097
Goodwill		47	47
Mark-to-market derivative assets		53	44
Other noncurrent assets		85	77
Total deferred debits and other assets		7,381	6,903
Total assets		8,235	8,118
Long-term debt due within one year		27	5
Accounts payable		216	292
Accrued expenses		113	108
Mark-to-market derivative liabilities		5	24
Energy Marketing Contract Liabilities, Current		12	22
Other current liabilities		13	25
Total current liabilities		386	476
Long-term debt		623	81
Asset retirement obligations		1,999	1,763
Pension obligations	[2]	9	9
Energy Marketing Contract Liabilities, Noncurrent		39	51
Other noncurrent liabilities		79	132
Total deferred credits and other liabilities		2,749	2,036
Total liabilities		3,135	2,512
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		9	64	$ 31	$ 89
Customer		300	390
Other		112	82
Materials and supplies		33	30
Other current assets		3	5
Total current assets		845	951
Property, plant and equipment, net		6,597	6,204
Other noncurrent assets		8	9
Total deferred debits and other assets		853	901
Total assets	[4]	8,295	8,056
Long-term debt due within one year		378	75
Accounts payable		209	215
Accrued expenses		110	131
Other current liabilities		35	51
Total current liabilities		1,134	794
Long-term debt		1,480	1,857
Asset retirement obligations		17	17
Other noncurrent liabilities		61	60
Total deferred credits and other liabilities		2,552	2,400
Total liabilities	[4]	5,418	5,303
Baltimore Gas and Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0	0
Restricted cash		23	21
Customer		0	0
Other		0	0
Mark-to-market derivative assets		0	0
Materials and supplies		0	0
Other current assets		0	0
Total current assets		23	21
Property, plant and equipment, net		0	0
Nuclear decommissioning trust funds		0	0
Goodwill		0	0
Mark-to-market derivative assets		0	0
Other noncurrent assets		3	3
Total deferred debits and other assets		3	3
Total assets		26	24
Long-term debt due within one year		79	75
Accounts payable		0	0
Accrued expenses		2	2
Mark-to-market derivative liabilities		0	0
Energy Marketing Contract Liabilities, Current		0	0
Other current liabilities		0	0
Total current liabilities		81	77
Long-term debt		41	120
Asset retirement obligations		0	0
Pension obligations	[2]	0	0
Energy Marketing Contract Liabilities, Noncurrent		0	0
Other noncurrent liabilities		0	0
Total deferred credits and other liabilities		41	120
Total liabilities		$ 122	$ 197
[1]	Exelon’s consolidated assets include $8,268 million and $8,159 million at December 31, 2015 and December 31, 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,264 million and $2,728 million at December 31, 2015 and December 31, 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.
[2]	Includes the CNEG retail gas pension obligation, which is presented as a net asset balance within the Prepaid pension asset line item on Generation’s balance sheet. See Note 17—Retirement Benefits for additional details
[3]	Generation’s consolidated assets include $8,235 million and $8,118 million at December 31, 2015 and 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,135 million and $2,512 million at December 31, 2015 and 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities.
[4]	BGE’s consolidated assets include $26 million and $24 million at December 31, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE that can only be used to settle the liabilities of the VIE. BGE’s consolidated liabilities include $122 million and $197 million at December 31, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. See Note 2 - Variable Interest Entities.

Variable Interest Entities - Su

Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Total assets	[1]	$ 427	$ 205
Total liabilities	[1]	147	52
Our ownership interest	[1]	11	9
Other ownership interests	[1]	269	144
Pledged assets for Zion Station decommissioning		206	319
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Pledged assets for Zion Station decommissioning		206	319
Payable To Thirdparty To Decommission Nuclear Plant Funded By Pledged Assets	[2]	189	292
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	[1]	263	114
Total liabilities	[1]	22	3
Our ownership interest	[1]	0	0
Other ownership interests	[1]	241	111
Commercial Agreement Variable Interest Entities [Member] | Scenario, Adjustment [Member]
Variable Interest Entity [Line Items]
Total assets			392
Total liabilities			234
Other ownership interests			158
Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	[1]	164	91
Total liabilities	[1]	125	49
Our ownership interest	[1]	11	9
Other ownership interests	[1]	28	33
Investments [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss		21	13
Investments [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss		0	0
Investments [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss		21	13
Contract Intangible Asset [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss		9	9
Contract Intangible Asset [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss		9	9
Contract Intangible Asset [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss		0	0
Payment Guarantee [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss		3	3
Payment Guarantee [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss		0	0
Payment Guarantee [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss		3	3
Asset Held In Trust Noncurrent [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	[3]	17	27
Asset Held In Trust Noncurrent [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	[3]	17	27
Asset Held In Trust Noncurrent [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	[3]	$ 0	$ 0
[1]	These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs.
[2]	Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT Funds. The NDT Funds will be utilized to satisfy the tax obligations as gains and losses are realized.
[3]	These items represent amounts on Exelon’s and Generation’s Consolidated Balance Sheets related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning includes gross pledged assets of $206 million and $319 million as of December 31, 2015 and December 31, 2014, respectively; offset by payables to ZionSolutions LLC of $189 million and $292 million as of December 31, 2015 and December 31, 2014, respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE.

Regulatory Matters - Narrative

Regulatory Matters - Narrative (Details)	Dec. 17, 2015USD ($)	Nov. 30, 2015MWh	Nov. 06, 2015USD ($)	Oct. 20, 2015	Sep. 10, 2015USD ($)	Jun. 19, 2015MWh	May. 27, 2015USD ($)	May. 07, 2015USD ($)	Mar. 27, 2015USD ($)	Dec. 08, 2014	Sep. 15, 2014USD ($)	Aug. 21, 2014USD ($)	Dec. 13, 2013	Dec. 02, 2013Vmi	Aug. 23, 2013USD ($)	Mar. 15, 2013USD ($)	Feb. 27, 2013	Dec. 05, 2012USD ($)	Nov. 01, 2012MWh	Jul. 31, 2012USD ($)	Apr. 12, 2012MW	Aug. 09, 2011USD ($)	Jan. 31, 2014USD ($)	Sep. 30, 2012USD ($)	Aug. 31, 2010USD ($)smart_meter	Dec. 31, 2015USD ($)Vsmart_meter	Dec. 31, 2014USD ($)MW	Dec. 31, 2013USD ($)	Dec. 31, 2012	Dec. 31, 2007USD ($)	Dec. 31, 2015USD ($)smart_meter	Nov. 30, 2010USD ($)	Nov. 30, 2005USD ($)	Nov. 05, 2015USD ($)	Oct. 30, 2015USD ($)	Jun. 03, 2014USD ($)	Mar. 31, 2014USD ($)	Feb. 26, 2014USD ($)	Mar. 31, 2012USD ($)	Dec. 16, 2010USD ($)
Regulatory Matters Additional Narrative Information [Line Items]
Revenue reduction																							$ 8,000,000
Substation kilovolt | V																										500,000
Near zero emissions coal fueled generation plant | MW																											166
Parent company pension OPEB regulatory assets noncurrent																										$ 3,156,000,000					$ 3,156,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount																										$ (50,000,000)	$ 269,000,000	$ 353,000,000
Public Utilities, Approved Equity Capital Structure, Annual Reconciliation, Percentage																										7.02%	7.04%	6.94%
Regulatory Assets																										$ 6,824,000,000	$ 6,923,000,000				6,824,000,000
Noncurrent regulatory assets																										6,065,000,000	6,076,000,000				6,065,000,000
Regulatory liabilities																										369,000,000	310,000,000				369,000,000
Business Combination, Integration Related Costs																										80,000,000	179,000,000				121,000,000
Regulatory Liabilities																										4,570,000,000	4,860,000,000				4,570,000,000
Public Utilities, Approved Rate Increase (Decrease), Annual Reconciliation, Amount																										(152,000,000)	72,000,000	$ 181,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount																										$ (67,000,000)	$ 232,000,000	$ 341,000,000
Public Utilities, Approved Equity Capital Structure, Initial Revenue Requirement, Percentage																										7.05%	7.06%	6.94%
Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										$ 92,000,000	$ 59,000,000				92,000,000
Over Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										131,000,000	84,000,000				$ 131,000,000
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Additional revenue requirement allowed by updated government order																										$ 137,000,000	$ 88,000,000
Weighted average debt and equity return																										8.61%	8.62%	8.70%			8.61%
Rate of return on common equity																										11.50%	11.50%	11.50%
Subsequent contribution to technology innovation trust																				$ 4,000,000
Utility annual customer assistance																				$ 10,000,000
Term of contract																										20 years
Demand response peak demand reduction																										2.00%					2.00%
Low income sector consumption reduction targets Act 129 Phase II																										0.10%
Renewable energy procurement																										2.00%					2.00%
Regulatory Assets																										$ 1,113,000,000	$ 1,201,000,000				$ 1,113,000,000
Noncurrent regulatory assets																										895,000,000	852,000,000				895,000,000
Gross transmission revenue requirement																										68,000,000	36,000,000	$ 38,000,000
Transmission revenue true up																										18,000,000	(14,000,000)	30,000,000
Net transmission revenue requirement																										86,000,000	22,000,000	$ 68,000,000
Regulatory liabilities																										155,000,000	125,000,000				155,000,000
Business Combination, Integration Related Costs																										10,000,000	4,000,000
Regulatory Liabilities																										3,614,000,000	3,780,000,000				3,614,000,000
Customer refundable fees																										$ 0	3,000,000				0
Customer refundable fees, interest																											1,000,000
Commonwealth Edison Co [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Renewable energy resources cumulatively increase																										10.00%
Commonwealth Edison Co [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Renewable energy resources cumulatively increase																										25.00%
Commonwealth Edison Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										$ 52,000,000	25,000,000				52,000,000
Commonwealth Edison Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										53,000,000	19,000,000				$ 53,000,000
Over Recovered electric Supply Costs																										29,000,000	3,000,000
Renewable Energy Requirement Revenue																										$ 24,000,000	$ 16,000,000
Commonwealth Edison Co [Member] | Energy Related Derivative [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Term of contract																										20 years
Commonwealth Edison Co [Member] | FutureGen Industry Alliance [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Term of contract																											20 years
Commonwealth Edison Co [Member] | Northern Illinois Project [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Length of transmission line | mi														60
Substation kilovolt | V														345,000
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Low income sector consumption reduction targets Act 129 Phase II																		4.50%
Electric distribution tax repairs																						$ 171,000,000
Gas distribution tax repairs refund																								$ 54,000,000
Smart meters initial phase deployment | smart_meter																										1,600,000					1,600,000
Estimated number of smart meters to be installed | smart_meter																										1,700,000					1,700,000
Projected investment in smart meters																										$ 589,000,000					$ 589,000,000
Projected investment in smart grid infrastructure																										155,000,000					155,000,000
Total smart grid smart meter investment grant awarded																										200,000,000					200,000,000
Total smart meter spend on investment																										578,000,000					578,000,000
Total smart grid spend on investment																										155,000,000					155,000,000
Smart grid investment grant awarded							$ 275,000,000	$ 534,000,000
Cumulative consumption reduction targets | MWh						2,080,553													1,125,852
Public sector maximum consumption reduction targets Act 129 Phase II																		10.00%
Proposed funding Of direct load control program costs																$ 10,000,000
Requested increase in electric revenues																																								$ 225,000,000
Requested increase in gas revenues																																								$ 20,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 127,000,000				$ 190,000,000
Public Utilities, Requested Rate Increase (Decrease), Percentage									10.95%
Regulatory Assets																										1,617,000,000	$ 1,558,000,000				1,617,000,000
Noncurrent regulatory assets																										1,583,000,000	1,529,000,000				1,583,000,000
Regulatory liabilities																										112,000,000	90,000,000				112,000,000
Cost recovery for significant one-time events	$ 7,000,000
Business Combination, Integration Related Costs																										5,000,000	2,000,000
Regulatory Liabilities																										639,000,000	747,000,000				639,000,000
PECO Energy Co [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Percentage Tier I alternative energy resources																													3.50%
Percentage Tier II alternative energy resources																													6.20%
PECO Energy Co [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Low income sector consumption reduction targets Act 129 Phase II																		2.00%
Cumulative consumption reduction targets | MWh		2,100,875
Percentage Tier I alternative energy resources																													8.00%
Percentage Tier II alternative energy resources																													10.00%
PECO Energy Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Maximum civil penalty under Act 129																		$ 20,000,000
PECO Energy Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										40,000,000	34,000,000				40,000,000
PECO Energy Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										60,000,000	$ 58,000,000				$ 60,000,000
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Current year revenue adjustment																										$ 200,000,000
Weighted average debt and equity return																										8.46%	8.53%	8.35%			8.46%
Rate of return on common equity																										11.30%	11.30%	11.30%
Increase in electric delivery service revenue resulting from rate case settlement or order.																											$ 22,000,000	$ 34,000,000
Increase in gas delivery service revenue resulting from rate case settlement or order.																											38,000,000	12,000,000
Estimated number of smart meters to be installed | smart_meter																									2,000,000
Projected investment in smart meters			$ 103,000,000																							$ 37,000,000					$ 37,000,000
Total smart meter spend on investment			140,000,000
Vendor refund			30,000,000
Annual depreciation expense decrease regulated property												$ 20,000,000
Adjustment to electric revenues increase requested			$ 121,000,000								$ 99,000,000				$ 83,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount											$ 68,000,000				$ 24,000,000											79,000,000
Requested rate of return on common equity			10.60%										9.75%
Rate Of Return Common Equity Gas Distribution			10.50%										9.60%
Regulatory Assets																										781,000,000	724,000,000				781,000,000
Total projected smart meter smart grid spend																									$ 480,000,000
Reimbursements received from the DOE																									$ 200,000,000
Noncurrent regulatory assets																										514,000,000	510,000,000				514,000,000
Upfront fee																																						$ 75
Recurring fee																																		$ 5.5				$ 11
Gross transmission revenue requirement																										0	9,000,000	2,000,000
Transmission revenue true up																										(3,000,000)	5,000,000	(3,000,000)
Net transmission revenue requirement																										(3,000,000)	14,000,000	$ (1,000,000)
Rate of return on common equity in federal energy regulatory committee complaint										8.80%							8.70%
Regulatory liabilities																										38,000,000	44,000,000				38,000,000
Smart grid incremental cost																										11,000,000
Business Combination, Integration Related Costs																										5,000,000	2,000,000
Site contingency, recovery from third party of environmental remediation cost																																$ 1,000,000	$ 5,000,000
Regulatory Liabilities																										$ 222,000,000	244,000,000				222,000,000
Deferred costs, noncurrent																																					$ 8,000,000		$ 16,000,000
Rate cap imposed on public utility subsidiary																										15.00%
Deferred purchased power costs																														$ 306,000,000
Environmental costs recognized, recovery credited to expense																										$ 73,000,000	65,000,000
Baltimore Gas and Electric Company [Member] | FERC Transmission Complaint [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Return on Equity, Percentage				10.00%													10.80%
Customer refund liability																																			$ 14,000,000
Baltimore Gas and Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										0	0				0
Baltimore Gas and Electric Company [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																										19,000,000	28,000,000				19,000,000
Regulatory Liabilities																										18,000,000	7,000,000				18,000,000
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Gas Revenue [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										1,000,000	12,000,000				1,000,000
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Electric Revenue [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											7,000,000
Baltimore Gas and Electric Company [Member] | Under-Recovered Electric Revenue Decoupling [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																										30,000,000					30,000,000
Baltimore Gas and Electric Company [Member] | Waldorf Project [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Capacity of natural gas fired combined cycle generation plant (in MW) | MW																					700
Initial term of proposed contract																					20 years
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Minimum purchase obligation																																				$ 25,000,000
Maximum purchase obligation																																				$ 35,000,000
Business Combination, Integration Related Costs																										25,000,000	11,000,000
Exelon Generation Co L L C [Member] | Conowingo [Member]
Regulatory Matters Additional Narrative Information [Line Items]
License costs																										23,000,000
Exelon Generation Co L L C [Member] | Muddy Run [Member]
Regulatory Matters Additional Narrative Information [Line Items]
License costs																										22,000,000
Commonwealth Edison and Baltimore Gas and Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities																										94,000,000					94,000,000
Energy Efficiency And Demand Response Programs [Member] | PECO Energy Co [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Cumulative consumption reduction targets | MWh		1,962,659
Over-Recovered Electric Transmission Cost [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										3,000,000	3,000,000				3,000,000
Over Recovered Electric Energy And Transmission Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										14,000,000					14,000,000
DSP Program costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										35,000,000	39,000,000				35,000,000
OverRecoveredNaturalGasSupply [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										22,000,000	16,000,000				22,000,000
OverRecoveredNaturalGasSupply [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										5,000,000	$ 7,000,000				5,000,000
Stride Program [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Captial and OM estimates current year																										113,000,000					113,000,000
Regulatory liabilities																										$ 1,000,000					$ 1,000,000

Regulatory Matters - Estimated

Regulatory Matters - Estimated Commitments related to PJM Agreements (Details) $ in Millions	Dec. 31, 2015USD ($)
Other Commitments [Line Items]
Total	$ 3.5
Construction Expansion Plans [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Total	297
2,015	204
2,016	61
2,017	26
2,018	6
2,019	0
Construction Expansion Plans [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Total	67
2,015	31
2,016	24
2,017	8
2,018	4
2,019	0
Construction Expansion Plans [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Total	373
2,015	140
2,016	112
2,017	62
2,018	46
2,019	$ 13

Regulatory Matters - Schedule o

Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 17, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015
Regulatory Assets [Line Items]
Current regulatory assets		$ 759	$ 847	$ 759
Noncurrent regulatory assets		6,065	6,076	6,065
Regulatory Assets		6,824	6,923	6,824
Business Combination, Integration Related Costs		80	179	121
Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3,156	3,256	3,156
Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1,616	1,542	1,616
AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		399	296	399
Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		189	371	189
Debt Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		47	57	47
Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		162	190	162
Severance [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9	12	9
Asset Retirement Obligations [Member]
Regulatory Assets [Line Items]
Regulatory Assets		108	116	108
Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		286	257	286
Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		52	67	52
Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		247	207	247
Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		84	48	84
Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2	3	2
Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets		20	30	20
Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Regulatory Assets		87	160	87
Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		$ 279	248	279
Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		5 years
Regulatory Assets		$ 6	8	6
ConservativeVoltageReductionProgram [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3	2	3
Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		30	7	30
Other Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets			46
Regulatory Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets		35		35
CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		7		7
Commonwealth Edison Co [Member]
Regulatory Assets [Line Items]
Current regulatory assets		218	349	218
Noncurrent regulatory assets		895	852	895
Regulatory Assets		1,113	1,201	1,113
Business Combination, Integration Related Costs		10	4
Commonwealth Edison Co [Member] | Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Commonwealth Edison Co [Member] | Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Regulatory Assets		64	64	64
Commonwealth Edison Co [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		140	91	140
Commonwealth Edison Co [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		189	371	189
Under over recovered distribution service costs		142	286
Cost recovery for significant one-time events		47	85
Regulatory assets due to deferred storm costs		36	66
Business Combination, Integration Related Costs		11	19
Commonwealth Edison Co [Member] | Debt Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		46	53	46
Commonwealth Edison Co [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Commonwealth Edison Co [Member] | Severance [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Commonwealth Edison Co [Member] | Asset Retirement Obligations [Member]
Regulatory Assets [Line Items]
Regulatory Assets		67	74	67
Commonwealth Edison Co [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		255	219	255
Commonwealth Edison Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		52	67	52
Commonwealth Edison Co [Member] | Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		247	207	247
Commonwealth Edison Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		43	33	43
Electric Transmission Costs Under-Recovery		31	22
Business Combination, Integration Related Costs		7	7
Underrecovered Electric Supply cost			4
Commonwealth Edison Co [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Commonwealth Edison Co [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Commonwealth Edison Co [Member] | Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Commonwealth Edison Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Commonwealth Edison Co [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Commonwealth Edison Co [Member] | ConservativeVoltageReductionProgram [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		0
Commonwealth Edison Co [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Commonwealth Edison Co [Member] | Regulatory Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets		10		10
Commonwealth Edison Company [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets			33
Commonwealth Edison Company [Member] | Under-Recovered Electric Supply Costs [Member]
Regulatory Assets [Line Items]
Electric Transmission Costs Under-Recovery		5
Commonwealth Edison Company [Member] | Conservation Voltage Reductio [Member]
Regulatory Assets [Line Items]
Regulatory Assets			0
Commonwealth Edison Company [Member] | Other Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets			22
PECO Energy Co [Member]
Regulatory Assets [Line Items]
Current regulatory assets		34	29	34
Noncurrent regulatory assets		1,583	1,529	1,583
Regulatory Assets		1,617	1,558	1,617
Cost recovery for significant one-time events	$ 7
Business Combination, Integration Related Costs		5	2
PECO Energy Co [Member] | Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
PECO Energy Co [Member] | Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Regulatory Assets		$ 1,473	1,400	1,473
PECO Energy Co [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		10 years
Regulatory Assets		$ 63	77	63
PECO Energy Co [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
PECO Energy Co [Member] | Debt Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1	4	1
PECO Energy Co [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
PECO Energy Co [Member] | Severance [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
PECO Energy Co [Member] | Asset Retirement Obligations [Member]
Regulatory Assets [Line Items]
Regulatory Assets		22	26	22
PECO Energy Co [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		30	37	30
PECO Energy Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
PECO Energy Co [Member] | Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
PECO Energy Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1	0	1
PECO Energy Co [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
PECO Energy Co [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
PECO Energy Co [Member] | Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
PECO Energy Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1	0	1
PECO Energy Co [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
PECO Energy Co [Member] | ConservativeVoltageReductionProgram [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0		0
PECO Energy Co [Member] | Conservation Voltage Reductio [Member]
Regulatory Assets [Line Items]
Regulatory Assets			0
PECO Energy Co [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
PECO Energy Co [Member] | Other Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets			14
PECO Energy Co [Member] | Regulatory Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets		19		19
PECO Energy Co [Member] | CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		7		7
Baltimore Gas and Electric Company [Member]
Regulatory Assets [Line Items]
Current regulatory assets		267	214	267
Noncurrent regulatory assets		514	510	514
Regulatory Assets		781	724	781
Business Combination, Integration Related Costs		5	2
Baltimore Gas and Electric Company [Member] | Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Baltimore Gas and Electric Company [Member] | Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Regulatory Assets		$ 79	78	79
Baltimore Gas and Electric Company [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		10 years
Noncurrent regulatory assets		$ 196	128	196
Regulatory Assets		196	128	196
Baltimore Gas and Electric Company [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Baltimore Gas and Electric Company [Member] | Debt Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		8	9	8
Baltimore Gas and Electric Company [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Baltimore Gas and Electric Company [Member] | Severance [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9	12	9
Baltimore Gas and Electric Company [Member] | Asset Retirement Obligations [Member]
Regulatory Assets [Line Items]
Regulatory Assets		19	16	19
Baltimore Gas and Electric Company [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1	1	1
Baltimore Gas and Electric Company [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Baltimore Gas and Electric Company [Member] | Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0	0
Baltimore Gas and Electric Company [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		40	15	40
Business Combination, Integration Related Costs			4
Baltimore Gas and Electric Company [Member] | Under Recovered Electric Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		28	10	28
Baltimore Gas and Electric Company [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2	3	2
Baltimore Gas and Electric Company [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets		20	30	20
Baltimore Gas and Electric Company [Member] | Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Regulatory Assets		87	160	87
Baltimore Gas and Electric Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		278	248	278
Baltimore Gas and Electric Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		6	8	6
Baltimore Gas and Electric Company [Member] | ConservativeVoltageReductionProgram [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3		3
Baltimore Gas and Electric Company [Member] | Conservation Voltage Reductio [Member]
Regulatory Assets [Line Items]
Regulatory Assets			2
Baltimore Gas and Electric Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		30	7	30
Baltimore Gas and Electric Company [Member] | Other Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets			7
Baltimore Gas and Electric Company [Member] | Regulatory Assets [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3		3
Over Recovered Energy And Transmission Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Assets [Line Items]
Over Recovered electric Supply Costs		29	3
Over Recovered Energy And Transmission Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		$ 19	$ 28	$ 19

Regulatory Matters - Schedule78

Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 4,570	$ 4,860
Regulatory liabilities	369	310
Noncurrent regulatory liabilities	4,201	4,550
Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	94	88
Asset Retirement Obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,577	2,879
Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,527	1,566
Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	92	59
Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	9	10
Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	95	102
Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	28	49
Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	131	84
Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		3
Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1	12
Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	16	8
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3,614	3,780
Regulatory liabilities	155	125
Noncurrent regulatory liabilities	3,459	3,655
Commonwealth Edison Co [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Asset Retirement Obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,172	2,389
Commonwealth Edison Co [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,332	1,343
Commonwealth Edison Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	52	25
Commonwealth Edison Co [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Renewable Energy Requirement Revenue	24	16
Regulatory Liabilities	53	19
Commonwealth Edison Co [Member] | Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		3
Commonwealth Edison Co [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	5	1
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	639	747
Regulatory liabilities	112	90
Noncurrent regulatory liabilities	527	657
PECO Energy Co [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Asset Retirement Obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	405	490
PECO Energy Co [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	40	34
PECO Energy Co [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	9	10
PECO Energy Co [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	95	102
PECO Energy Co [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	28	49
PECO Energy Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	60	58
PECO Energy Co [Member] | Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
PECO Energy Co [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2	4
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	222	244
Regulatory liabilities	38	44
Noncurrent regulatory liabilities	184	200
Baltimore Gas and Electric Company [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Asset Retirement Obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	195	223
Baltimore Gas and Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	18	7
Baltimore Gas and Electric Company [Member] | Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1	12
Baltimore Gas and Electric Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 8	2
Over Recovered Electric Energy And Transmission Costs [Member] | Commonwealth Edison Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		$ 19

Regulatory Matters - Purchase o

Regulatory Matters - Purchase of Receivables Programs (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Purchase Of Receivables [Line Items]
Purchased receivables	[1]	$ 229	$ 290
Allowance for uncollectible accounts	[2]	(31)	(42)
Purchased receivables, net		198	248
Commonwealth Edison Co [Member]
Purchase Of Receivables [Line Items]
Purchased receivables	[1]	103	139
Allowance for uncollectible accounts	[2]	(16)	(21)
Purchased receivables, net		$ 87	118
PECO Energy Co [Member]
Purchase Of Receivables [Line Items]
Purchase of Receivables, Discount Rate related to Implementation Costs		1.00%
Purchased receivables	[1]	$ 67	76
Allowance for uncollectible accounts	[2]	(7)	(8)
Purchased receivables, net		60	68
Baltimore Gas and Electric Company [Member]
Purchase Of Receivables [Line Items]
Purchased receivables	[1]	59	75
Allowance for uncollectible accounts	[2]	(8)	(13)
Purchased receivables, net		$ 51	$ 62
[1]	(a) PECO’s gas POR program became effective on January 1, 2012 and includes a 1% discount on purchased receivables in order to recover the implementation costs of the program. The implementation costs were fully recovered and the 1% discount was reset to 0%, effective July 2015.
[2]	(b) For ComEd and BGE, reflects the incremental allowance for uncollectible accounts recorded, which is in addition to the purchase discount. For ComEd, the incremental uncollectible accounts expense is recovered through its Purchase of Receivables with Consolidated Billing (PORCB) tariff.

Regulatory Matters Annual Elect

Regulatory Matters Annual Electric Distribution Filings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ (50)		$ 269		$ 353
Public Utilities, Approved Rate Increase (Decrease), Amount	67		(232)		(341)
Public Utilities, Approved Rate Increase (Decrease), Initial Revenue Requirement, Amount	85		160		160
Public Utilities, Approved Rate Increase (Decrease), Annual Reconciliation, Amount	$ (152)		$ 72		$ 181
Public Utilities, Approved Equity Capital Structure, Annual Reconciliation, Percentage	7.02%		7.04%		6.94%
Public Utilities, Approved Equity Capital Structure, Initial Revenue Requirement, Percentage	7.05%		7.06%		6.94%
Public Utilities, Approved Return on Equity, Initial Revenue Requirement, Percentage	9.14%	[1]	9.25%	[1]	8.72%
Public Utilities, Approved Return on Equity, Annual Reconciliation, Percentage	9.09%	[1]	9.20%	[1]	8.72%
[1]	(a) Includes a reduction of 5 basis points for a reliability performance metric penalty.

Mergers, Acquisitions and Dis81

Mergers, Acquisitions and Dispositions - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions		Nov. 01, 2014	Dec. 31, 2014	Dec. 31, 2015		Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014		Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	May. 31, 2014	May. 30, 2012
Business Acquisition [Line Items]
Junior Subordinated Notes, Noncurrent							$ 1,150,000,000							$ 1,150,000,000
Forward Contract Indexed to Issuer's Equity, Indexed Shares							23							23
Other noncurrent assets			$ 923,000,000	$ 1,445,000,000					$ 923,000,000						$ 1,445,000,000	$ 923,000,000		$ 1,445,000,000
Total acquisition costs															40,000,000	386,000,000	$ 0
Business Acquisition, Transaction Costs				259,000,000											259,000,000			259,000,000
Business Combination, Integration Related Costs															80,000,000	179,000,000		121,000,000
Bridge loan							$ 3,200,000,000							$ 3,200,000,000					$ 7,200,000,000
Revenues				6,702,000,000		$ 7,401,000,000	6,514,000,000	$ 8,830,000,000	7,255,000,000	$ 6,912,000,000	$ 6,024,000,000	$ 7,237,000,000			29,447,000,000	27,429,000,000	24,888,000,000
Comprehensive Income (Loss), Net of Tax, Attributable to Parent															2,310,000,000	1,176,000,000	2,456,000,000
Net income				309,000,000	[1]	629,000,000	638,000,000	693,000,000	18,000,000	993,000,000	522,000,000	90,000,000	[2]		2,250,000,000	1,820,000,000	1,729,000,000
Derivative, Loss on Derivative														$ 64,000,000
Merger and integration related costs																44,000,000
Change in capital expenditures not paid															96,000,000	220,000,000	(38,000,000)
Net present value of settlement amount															430,000,000
Cost of Reimbursable Expense															40,000,000
Payments of Merger Related Costs, Financing Activities															138,000,000
Payments of Debt Restructuring Costs	[3]														22,000,000
New Jersey Board Of Public Utilities [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				62,000,000											62,000,000			62,000,000
Delaware Public Service Commission [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				40,000,000											40,000,000			40,000,000
Maryland Public Service Commission [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				66,000,000											66,000,000			66,000,000
District of Columbia Public Service Commission [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				78,000,000											78,000,000			78,000,000
Energy Efficiency Program [Member] | New Jersey Board Of Public Utilities [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				15,000,000											15,000,000			15,000,000
Energy Efficiency Program [Member] | Delaware Public Service Commission [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				2,000,000											2,000,000			2,000,000
Energy Efficiency Program [Member] | Maryland Public Service Commission [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				43,000,000											43,000,000			43,000,000
Workforce Development [Member] | Delaware Public Service Commission [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				2,000,000											2,000,000			2,000,000
Workforce Development [Member] | District of Columbia Public Service Commission [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				5,000,000											5,000,000			5,000,000
Green Sustainability Fund [Member] | Maryland Public Service Commission [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				14,000,000											14,000,000			14,000,000
Rate Bill Credits [Member] | District of Columbia Public Service Commission [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				26,000,000											26,000,000			26,000,000
OneTimeBillCredit [Member] | District of Columbia Public Service Commission [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				14,000,000											14,000,000			14,000,000
LowIncomeAssistance [Member] | District of Columbia Public Service Commission [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				16,000,000											16,000,000			16,000,000
Charitable Contributions [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				53,000,000											53,000,000			53,000,000
Charitable Contributions [Member] | District of Columbia Public Service Commission [Member]
Business Acquisition [Line Items]
Business Acquisition, Preacquisition Contingency, Amount of Settlement				19,000,000											19,000,000			19,000,000
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Other noncurrent assets			578,000,000	627,000,000					578,000,000						627,000,000	578,000,000		627,000,000
Total acquisition costs															40,000,000	386,000,000	0
Business Combination, Integration Related Costs															25,000,000	11,000,000
Revenues			386,000,000	4,294,000,000		4,768,000,000	4,232,000,000	5,840,000,000	4,802,000,000	4,412,000,000	3,789,000,000	4,390,000,000			19,135,000,000	17,393,000,000	15,630,000,000
Comprehensive Income (Loss), Net of Tax, Attributable to Parent															1,313,000,000	769,000,000	761,000,000
Net income			(42,000,000)	154,000,000		377,000,000	398,000,000	443,000,000	(91,000,000)	771,000,000	340,000,000	(185,000,000)			1,340,000,000	1,019,000,000	1,060,000,000
Merger and integration related costs																44,000,000
Expected pre-tax proceeds																1,800,000,000
Expected after-tax proceeds																1,400,000,000
Change in capital expenditures not paid															82,000,000	(61,000,000)	(107,000,000)
Development costs expensed															22,000,000	13,000,000	10,000,000
Baltimore Gas and Electric Company [Member]
Business Acquisition [Line Items]
Other noncurrent assets			9,000,000	8,000,000					9,000,000						8,000,000	9,000,000		8,000,000
Business Combination, Integration Related Costs															5,000,000	2,000,000
Revenues				746,000,000		725,000,000	628,000,000	1,036,000,000	761,000,000	697,000,000	653,000,000	1,054,000,000			3,135,000,000	3,165,000,000	3,065,000,000
Comprehensive Income (Loss), Net of Tax, Attributable to Parent															288,000,000	211,000,000	210,000,000
Net income				74,000,000		51,000,000	44,000,000	106,000,000	52,000,000	46,000,000	16,000,000	85,000,000			288,000,000	211,000,000	210,000,000
Merger and integration related costs																0
Maximum loss contingency																				$ 1,700,000
Change in capital expenditures not paid															(9,000,000)	25,000,000	48,000,000
Commonwealth Edison Co [Member]
Business Acquisition [Line Items]
Other noncurrent assets			237,000,000	324,000,000					237,000,000						324,000,000	237,000,000		324,000,000
Business Combination, Integration Related Costs															10,000,000	4,000,000
Revenues				1,196,000,000		1,376,000,000	1,148,000,000	1,185,000,000	1,079,000,000	1,222,000,000	1,128,000,000	1,134,000,000			4,905,000,000	4,564,000,000	4,464,000,000
Comprehensive Income (Loss), Net of Tax, Attributable to Parent															426,000,000	408,000,000	249,000,000
Net income				87,000,000		149,000,000	99,000,000	90,000,000	73,000,000	126,000,000	111,000,000	98,000,000			426,000,000	408,000,000	249,000,000
Merger and integration related costs																0
Change in capital expenditures not paid															34,000,000	78,000,000	(8,000,000)
PECO Energy Co [Member]
Business Acquisition [Line Items]
Other noncurrent assets			20,000,000	21,000,000					20,000,000						21,000,000	20,000,000		$ 21,000,000
Business Combination, Integration Related Costs															5,000,000	2,000,000
Revenues				645,000,000		740,000,000	661,000,000	985,000,000	750,000,000	693,000,000	656,000,000	993,000,000			3,032,000,000	3,094,000,000	3,100,000,000
Comprehensive Income (Loss), Net of Tax, Attributable to Parent															378,000,000	352,000,000	395,000,000
Net income				$ 79,000,000		$ 90,000,000	$ 70,000,000	$ 139,000,000	$ 98,000,000	$ 81,000,000	$ 84,000,000	$ 89,000,000			378,000,000	352,000,000	395,000,000
Merger and integration related costs																0
Change in capital expenditures not paid															$ (13,000,000)	$ 0	$ 13,000,000
Pepco Holdings [Member]
Business Acquisition [Line Items]
Share price				$ 27.25											$ 27.25			$ 27.25
Payments to acquire businesses															$ 6,900,000,000
Pepco Holdings [Member] | Minimum [Member]
Business Acquisition [Line Items]
Business exit costs															259,000,000
Pepco Holdings [Member] | Maximum [Member]
Business Acquisition [Line Items]
Other long-term investments				$ 180,000,000											180,000,000			$ 180,000,000
Business exit costs															293,000,000
Intergrys Energy Group Inc [Member] | Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Total consideration transferred		$ 332,000,000
Bargain purchase gain (after-tax)		28,000,000
Derivative, Loss on Derivative		$ 108,000,000
Merger and integration related costs			$ 7,000,000												$ 5,000,000
[1]	Includes charges to earnings related to the impairments of certain generating assets which were held for sale and certain Upstream exploration assets. See Note 8—Impairment of Long-Lived Assets of the Combined Notes to Consolidated Financial Statements for additional information.
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246NEExNTZFREE4NkYwMUZCQUZDQTExMjI1RThCRDM3QzcM}
[3]	(e)See Note 14—Debt and Credit Agreements and 4—Mergers, Acquisitions, and Dispositions for additional information on the PHI merger related debt exchange.

Mergers, Acquisitions and Dis82

Mergers, Acquisitions and Dispositions - Summary of Integrys Energy Group Acquisition (Details) - Exelon Generation Co L L C [Member] - Intergrys Energy Group Inc [Member] $ in Millions	Nov. 01, 2014USD ($)
Business Acquisition [Line Items]
Total consideration transferred	$ 332
Working capital assets	390
Mark-to-market derivative assets	184
Unamortized energy contracts	115
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	50
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities	(196)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Derivative Liabilities	(57)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities	(110)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent	(16)
Total net assets	360
Bargain purchase gain (after-tax)	$ 28

Mergers, Acquisitions and Dis83

Mergers, Acquisitions and Dispositions - Costs Recognized after Closing of Merger (Details) $ in Millions	12 Months Ended
	Dec. 31, 2013USD ($)$ / Customer
Business Acquisition [Line Items]
Rate credit per residential customer (in usd per customer) | $ / Customer	100
Charitable contributions, per year | $	$ 7
Period for charitable contributions	10 years
Baltimore Gas and Electric Company [Member]
Business Acquisition [Line Items]
Rate credit per residential customer (in usd per customer) | $ / Customer	100
Charitable contributions, per year | $	$ 7
Period for charitable contributions	10 years
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Rate credit per residential customer (in usd per customer) | $ / Customer	100
Charitable contributions, per year | $	$ 7
Period for charitable contributions	10 years

Mergers, Acquisitions and Dis84

Mergers, Acquisitions and Dispositions - Summary of Asset Divestitures (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)MW	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Long Lived Assets Held-for-sale [Line Items]
Gain (Loss) on Sale of Assets and Asset Impairment Charges | $	$ 18	$ 437	$ 13
Fore River [Member]
Long Lived Assets Held-for-sale [Line Items]
Percent Owned	100.00%
Net Generation Capacity	726,000,000
West Valley [Member]
Long Lived Assets Held-for-sale [Line Items]
Percent Owned	100.00%
Net Generation Capacity	185,000,000
Keystone [Member]
Long Lived Assets Held-for-sale [Line Items]
Percent Owned	41.98%
Net Generation Capacity	714,000,000
Conemaugh [Member]
Long Lived Assets Held-for-sale [Line Items]
Percent Owned	31.28%
Net Generation Capacity	532,000,000
Safe Harbor [Member]
Long Lived Assets Held-for-sale [Line Items]
Percent Owned	66.70%
Net Generation Capacity	278,000,000
Quail Run [Member]
Long Lived Assets Held-for-sale [Line Items]
Percent Owned	100.00%
Net Generation Capacity	488,000,000
Exelon Generation Co L L C [Member]
Long Lived Assets Held-for-sale [Line Items]
Gain (Loss) on Sale of Assets and Asset Impairment Charges | $	$ 12	437	$ 13
Gain on Sale of Investments | $		$ 412

Mergers, Acquisitions and Dis85

Mergers, Acquisitions and Dispositions - Summary of Major Classes of Assets and Liabilities Held for Sale (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2014	Dec. 31, 2015
Significant Acquisitions and Disposals [Line Items]
Total assets held for sale		$ 147	$ 4
Accrued expenses		1,539	2,376
Other current liabilities		931	842
Electricity Generation Plant, Non-Nuclear [Member]
Significant Acquisitions and Disposals [Line Items]
Property, plant and equipment, net	[1]	143
Inventory		4
Total assets held for sale		147
Accrued expenses			1
Other current liabilities			$ 4
Total liabilities held for sale	[2]	5
Asset impairment charges		$ 50
[1]	The total aggregate book value of property, plant and equipment is net of a $50 million pre-tax impairment loss recorded within Operating and maintenance expense on Exelon’s and Generation’s Statements of Operations and Comprehensive Income for the year ended December 31, 2014. See Note 8 — Impairment of Long-Lived Assets for further information.
[2]	Included within Other current liabilities on Exelon's and Generation's Consolidated Balance Sheets.

Investment in Constellation E86

Investment in Constellation Energy Nuclear Group, LLC - Narrative (Details) - USD ($) $ in Millions	Apr. 01, 2014	Dec. 31, 2014		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2015	Jun. 09, 2015
Schedule of Equity Method Investments [Line Items]
Purchase of nuclear output by EDF													49.99%
Guarantee obligations maximum exposure				$ 9,206									$ 9,206					$ 9,206
Revenues				6,702	$ 7,401	$ 6,514	$ 8,830	$ 7,255		$ 6,912	$ 6,024	$ 7,237	29,447	$ 27,429		$ 24,888
Accumulated other comprehensive loss, net		$ (2,684)	[1]	(2,624)				(2,684)	[1]				$ (2,624)	(2,684)	[1]	(2,040)	[1]	(2,624)
Required purchases of power from CENG's nuclear plants not sold to third parties													85.00%
Operating revenues from affiliates													$ 9	23		70
Parental guarantee provided				$ 75									75					75
Business Combination, Integration Related Costs													$ 80	179				$ 121
Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Accumulated other comprehensive loss, net	$ 1,500
Constellation Energy Nuclear Group [Member] | Payment Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Due to affiliate	245
Constellation Energy Nuclear Group [Member] | Financial Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Guarantee obligations maximum exposure	$ 165
Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest				50.01%									50.01%					50.01%
Cash distribution paid to member													$ 2,474	645		625
Purchase of nuclear output by EDF	49.99%
Guarantee obligations maximum exposure				$ 6,832									6,832					$ 6,832
Total equity investment earnings (losses) - CENG												19				9
Revenues		386		4,294	$ 4,768	$ 4,232	$ 5,840	4,802		$ 4,412	$ 3,789	4,390	19,135	17,393		15,630
Accumulated other comprehensive loss, net		(36)	[1]	(63)				(36)	[1]				$ (63)	(36)	[1]	214	[1]	(63)
Allocation of federal tax benefit under tax sharing agreement		$ 55						$ 55				77		55
Required purchases of power from CENG's nuclear plants not sold to third parties	85.00%
Subsequent purchases of power from CENG's nuclear plants not sold to third parties													50.01%
Operating revenues from affiliates													$ 749	779		1,423
Parental guarantee provided				12									12					12
Business Combination, Integration Related Costs													25	11
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Schedule of Equity Method Investments [Line Items]
Remeasurement gain from derecognition of equity method investment	$ 261
Business combination, step acquisition, equity interest in acquiree, fair value	136
Business acquisition, preexisting relationship, gain (loss) recognized	132
Parental guarantee provided	7			7									7					7	$ 275
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Revenues												17	509	218		$ 56
Investment in CENG												1,900
Accumulated other comprehensive loss, net												$ 116
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Due from affiliates	$ 400			$ 300									300					$ 300
Interest rate on loan to CENG	5.25%
Allocation of federal tax benefit under tax sharing agreement	$ 152
Reduction to net income attributable to noncontrolling interest													18	13
Net Income (Loss) Attributable to Parent													(11)	407
Business Combination, Integration Related Costs													2	26
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member] | Payment Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Due to affiliate	$ 205
Exelon Generation Co L L C [Member] | EDFI [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Operating revenues from affiliates													$ 488	$ 137
Electricite De France LLC [Member]
Schedule of Equity Method Investments [Line Items]
Required purchases of power from CENG's nuclear plants not sold to third parties	15.00%
Subsequent purchases of power from CENG's nuclear plants not sold to third parties													49.99%
Electricite De France LLC [Member] | Constellation Energy Nuclear Group [Member] | Financial Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Guarantee obligations maximum exposure	$ 145
Constellation Energy Group LLC [Member]
Schedule of Equity Method Investments [Line Items]
Interest rate on distribution	8.50%
Constellation Energy Group LLC [Member] | EDFI [Member]
Schedule of Equity Method Investments [Line Items]
Cash distribution paid to member	$ 400
[1]	All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.

Investment in Constellation E87

Investment in Constellation Energy Nuclear Group, LLC - Schedule of Assets and Liabilities of CENG (Details) - Exelon Generation Co L L C [Member] - Constellation Energy Nuclear Group [Member] $ in Millions	Apr. 01, 2014USD ($)
Business Acquisition [Line Items]
Current assets	$ 499
Nuclear decommissioning trust fund	1,955
Property, plant and equipment	3,073
Nuclear fuel	482
Other assets	10
Total assets	6,019
Current liabilities	237
Asset retirement obligation	1,816
Pension and other employee benefit obligations	281
Unamortized energy contract liabilities	171
Other liabilities	114
Total liabilities	2,619
Total net assets	$ 3,400

Accounts Receivable - Schedule

Accounts Receivable - Schedule of Estimated Unbilled Revenues (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		$ 1,203	$ 1,381
Allowance for uncollectible accounts	[1]	(284)	(311)
Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues	[2]	732	823
Allowance for uncollectible accounts	[1]	(77)	(60)
Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		218	204
Allowance for uncollectible accounts	[1]	(75)	(84)
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		105	140
Allowance for uncollectible accounts	[1],[3]	(83)	(100)
Current financing receivable allowance for credit losses		8
Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		148	214
Allowance for uncollectible accounts	[1],[4]	(49)	$ (67)
Charged to Costs and Expenses		$ 19
[1]	Includes the allowance for uncollectible accounts on customer and other accounts receivable.
[2]	Represents unbilled portion of retail receivables estimated under Exelon’s unbilled critical accounting policy.
[3]	the non-current allowance for uncollectible accounts of $8 million at both December 31, 2015 and 2014, related to PECO’s current installment plan receivables described below.
[4]	At December 31, 2014, as explained in Note 1—Significant Accounting Policies, BGE estimated the allowance for uncollectible accounts on customer receivables by applying loss rates to the outstanding receivable balance by risk segment. The change in estimate resulted in a $19 million pre-tax charge to BGE's provision for uncollectible accounts expense for the year ended December 31, 2014, which is included in Operating and maintenance expense on BGE's Consolidated Statements of Operations and Comprehensive Income.

Accounts Receivable - Narrative

Accounts Receivable - Narrative (Details) $ in Millions	Dec. 31, 2015USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Installment plan receivables	$ 15
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Installment plan receivables uncollectible accounts reserve	15
Risk Level, Low [Member] | PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Installment plan receivables uncollectible accounts reserve	1
Risk Level, Medium [Member] | PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Installment plan receivables	3
Risk Level, High [Member] | PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Installment plan receivables	$ 11

Property, Plant and Equipment -

Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 73,814	$ 66,912
Less: accumulated depreciation	[1]	16,375	14,742
Property, plant and equipment, net		57,439	52,170
Nuclear fuel - work in progress		1,266	1,003
Buildings under capital lease		13	15
Original cost basis for buildings		52
Plant Held for Future Use Amount		57
Accumulated depreciation for buildings		39	37
Accumulated amortization of nuclear fuel		2,861	2,673
Electric Transmission and Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 32,546	30,157
Electric Transmission and Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		90 years
Electric Transmission and Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		5 years
Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 25,615	22,911
Electric Generation Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		56 years
Electric Generation Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		1 year
Gas Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 3,864	3,505
Gas Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		90 years
Gas Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		5 years
Common Electric And Gas T And D Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 1,149	1,169
Common Electric And Gas T And D Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		50 years
Common Electric And Gas T And D Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		5 years
Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[2]	$ 6,384	5,947
Nuclear Fuel [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	[2]	8 years
Nuclear Fuel [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	[2]	1 year
Public Utilities Property Plant And Equipment Construction Work In Progress [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 3,075	2,167
Other Capitalized Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[3]	$ 1,181	1,056
Other Capitalized Property Plant and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	[3]	50 years
Other Capitalized Property Plant and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	[3]	5 years
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 34,482	30,640
Less: accumulated depreciation	[4]	8,639	7,612
Property, plant and equipment, net		25,843	23,028
Exelon Generation Co L L C [Member] | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 25,615	22,911
Exelon Generation Co L L C [Member] | Electric Generation Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		56 years
Exelon Generation Co L L C [Member] | Electric Generation Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		1 year
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[5]	$ 6,384	5,947
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	[5]	8 years
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	[5]	1 year
Exelon Generation Co L L C [Member] | Public Utilities Property Plant And Equipment Construction Work In Progress [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 2,017	1,404
Exelon Generation Co L L C [Member] | Other Capitalized Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[6]	$ 466	378
Exelon Generation Co L L C [Member] | Other Capitalized Property Plant and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	[6]	31 years
Exelon Generation Co L L C [Member] | Other Capitalized Property Plant and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	[6]	6 years
Commonwealth Edison Co [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 21,212	19,225
Less: accumulated depreciation		3,710	3,432
Property, plant and equipment, net		17,502	15,793
Buildings under capital lease			8
Original cost basis for buildings		8
Commonwealth Edison Co [Member] | Electric Transmission and Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 20,576	18,884
Commonwealth Edison Co [Member] | Electric Transmission and Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		80 years
Commonwealth Edison Co [Member] | Electric Transmission and Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		5 years
Commonwealth Edison Co [Member] | Public Utilities Property Plant And Equipment Construction Work In Progress [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 572	276
Commonwealth Edison Co [Member] | Other Capitalized Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[7]	$ 64	65
Commonwealth Edison Co [Member] | Other Capitalized Property Plant and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	[7]	50 years
Commonwealth Edison Co [Member] | Other Capitalized Property Plant and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	[7]	39 years
PECO Energy Co [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 10,242	9,718
Less: accumulated depreciation		3,101	2,917
Property, plant and equipment, net		7,141	6,801
PECO Energy Co [Member] | Electric Transmission and Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 7,230	6,886
PECO Energy Co [Member] | Electric Transmission and Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		65 years
PECO Energy Co [Member] | Electric Transmission and Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		5 years
PECO Energy Co [Member] | Gas Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 2,206	2,039
PECO Energy Co [Member] | Gas Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		70 years
PECO Energy Co [Member] | Gas Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		5 years
PECO Energy Co [Member] | Common Electric And Gas T And D Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 631	618
PECO Energy Co [Member] | Common Electric And Gas T And D Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		50 years
PECO Energy Co [Member] | Common Electric And Gas T And D Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		5 years
PECO Energy Co [Member] | Public Utilities Property Plant And Equipment Construction Work In Progress [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 154	154
PECO Energy Co [Member] | Other Capitalized Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	[8]	50 years
Total property, plant and equipment	[8]	$ 21	21
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		9,613	9,072
Less: accumulated depreciation		3,016	2,868
Property, plant and equipment, net		6,597	6,204
Baltimore Gas and Electric Company [Member] | Electric Transmission and Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 6,663	6,339
Baltimore Gas and Electric Company [Member] | Electric Transmission and Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		90 years
Baltimore Gas and Electric Company [Member] | Electric Transmission and Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		5 years
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 1,951	1,761
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		90 years
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		5 years
Baltimore Gas and Electric Company [Member] | Common Electric And Gas T And D Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 655	623
Baltimore Gas and Electric Company [Member] | Common Electric And Gas T And D Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		40 years
Baltimore Gas and Electric Company [Member] | Common Electric And Gas T And D Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		5 years
Baltimore Gas and Electric Company [Member] | Public Utilities Property Plant And Equipment Construction Work In Progress [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 312	317
Baltimore Gas and Electric Company [Member] | Other Capitalized Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	[9]	20 years
Total property, plant and equipment	[9]	$ 32	$ 32
[1]	Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $2,861 million and $2,673 million as of December 31, 2015 and 2014, respectively
[2]	Includes nuclear fuel that is in the fabrication and installation phase of $1,266 million and $1,003 million at December 31, 2015 and 2014, respectively.
[3]	Includes Generation’s buildings under capital lease with a net carrying value of $13 million and $15 million at December 31, 2015 and 2014, respectively. The original cost basis of the buildings was $52 million, and total accumulated amortization was $39 million and $37 million, as of December 31, 2015 and 2014, respectively. Also includes ComEd’s buildings under capital lease with a net carrying value at December 31, 2015 and 2014, of $7 million and $8 million, respectively. The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million and $0.3 million as of December 31, 2015 and 2014, respectively. Includes land held for future use and non utility property at ComEd, PECO, and BGE of $57 million, $21 million, and $32 million, respectively. These balances also include capitalized acquisition, development and exploration costs of $266 million and $242 million related to oil and gas production activities at Generation
[4]	Includes accumulated amortization of nuclear fuel in the reactor core of $2,861 million and $2,673 million as of December 31, 2015 and 2014, respectively
[5]	Includes nuclear fuel that is in the fabrication and installation phase of $1,266 million and $1,003 million at December 31, 2015 and 2014, respectively
[6]	Includes buildings under capital lease with a net carrying value of $13 million and $15 million at December 31, 2015 and 2014, respectively. The original cost basis of the buildings was $52 million, and total accumulated amortization was $39 million and $37 million, as of December 31, 2015 and 2014, respectively. These balances also include capitalized acquisition, development and exploration costs of $266 million and $242 million related to oil and gas production activities at Generation at December 31, 2015 and 2014, respectively.
[7]	Includes buildings under capital lease with a net carrying value at December 31, 2015 and 2014 of $7 million and $8 million, respectively. The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million and $0.3 million as of December 31, 2015 and 2014, respectively
[8]	Represents land held for future use and non-utility property
[9]	Represents land held for future use and non-utility property

Property, Plant and Equipment91

Property, Plant and Equipment - Annual Depreciation Provisions as Percentage of Average Service Life (Details)	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Electric Transmission and Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.83%	2.93%	2.91%
Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	3.47%	3.50%	3.35%
Gas Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.17%	2.13%	2.06%
Common Electric And Gas T And D Equipment [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	7.79%	7.32%	7.53%
PECO Energy Co [Member] | Electric Transmission and Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.39%	2.55%	2.73%
PECO Energy Co [Member] | Gas Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.87%	1.84%	1.79%
PECO Energy Co [Member] | Common Electric And Gas T And D Equipment [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	5.16%	5.16%	6.65%
Baltimore Gas and Electric Company [Member] | Electric Transmission and Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.62%	2.96%	2.91%
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.50%	2.47%	2.36%
Baltimore Gas and Electric Company [Member] | Common Electric And Gas T And D Equipment [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	10.35%	9.49%	8.45%

Property, Plant and Equipment92

Property, Plant and Equipment - Narrative (Details)	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	3.47%	3.50%	3.35%
Exelon Generation Co L L C [Member] | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	3.50%	3.50%	3.35%
Commonwealth Edison Co [Member]
Property, Plant and Equipment [Line Items]
Annual depreciation rate	3.03%	3.05%	2.97%

Impairment of Long-lived Asse93

Impairment of Long-lived Assets - Narrative (Details) - USD ($)		May. 31, 2014	Feb. 26, 2014	Sep. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2000	Oct. 31, 2000
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Impairment charges					$ 24,000,000
Interest costs incurred	[1],[2],[3]				1,170,000,000	$ 1,144,000,000	$ 1,423,000,000
Estimated residual value of leased assets					639,000,000	685,000,000			$ 1,600,000,000
Capital lease net investment in direct financing leases prepayments received								$ 1,200,000,000
Proceeds from termination of direct financing lease investment			$ 335,000,000		0	335,000,000	0
Capital leases net investment in direct financing leases writeoff			$ 336,000,000
Pre Tax Loss						1,000,000
Exelon Generation Co L L C [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Carrying amount of long lived assets to be written down		$ 151,000,000		$ 75,000,000		1,000,000,000
Fair value of impaired assets		65,000,000		32,000,000		556,000,000
Impairment charges		$ 86,000,000		$ 43,000,000		450,000,000
Utilities Operating Expense, Impairments							111,000,000
Interest costs incurred	[1],[2],[3]				445,000,000	419,000,000	411,000,000
Exelon Generation Co L L C [Member] | Interest Expense [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Interest costs incurred							8,000,000
Baltimore Gas and Electric Company [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Interest costs incurred	[1],[2]				113,000,000	118,000,000	$ 129,000,000
Constellation Energy Group LLC [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Impairment charges					$ 5,000,000	$ 124,000,000
[1]	.
[2]	Includes interest expense to affiliates.
[3]	On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, the 2014 financial results include CENG’s financial position and results of operations beginning April 1, 2014.

Impairment of Long-lived Asse94

Impairment of Long-lived Assets - Components of Net Investment in Long-term Leases (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Oct. 31, 2000
Impairment or Disposal of Tangible Assets Disclosure [Abstract]
Estimated residual value of leased assets	$ 639	$ 685	$ 1,600
Less: unearned income	287	324
Net investment in long-term leases	$ 352	$ 361

Jointly Owned Electric Utilit95

Jointly Owned Electric Utility Plant - Ownership Interests in Jointly Owned Electric Plants and Transmission Facilities (Details) $ in Millions		12 Months Ended
		Dec. 31, 2015USD ($)Vmi		Dec. 31, 2014USD ($)
Jointly Owned Utility Plant Footnote [Abstract]
Substation capacity | V		500,000
Salem [Member]
Jointly Owned Utility Plant Footnote [Abstract]
Substation capacity | V		500,000
Conemaugh [Member]
Jointly Owned Utility Plant Footnote [Abstract]
Substation capacity | V		500,000
Pennsylvania [Member]
Jointly Owned Utility Plant Footnote [Abstract]
Miles of transmission voltage lines | mi		127
Transmission line capacity | V		500,000
Delaware And New Jersey [Member]
Jointly Owned Utility Plant Footnote [Abstract]
Miles of transmission voltage lines | mi		131
Substation capacity | V		500,000
Exelon Generation Co L L C [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		44.24%
Exelon Generation Co L L C [Member] | Nuclear Generation [Member] | Quad Cities [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator		Generation
Ownership interest		75.00%
Plant		$ 1,035	[1]	$ 995	[2]
Accumulated depreciation		309	[1]	266	[2]
Construction work in progress		11		15
Jointly Owned Utility Plant Footnote [Abstract]
Plant		$ 1,035	[1]	995	[2]
Exelon Generation Co L L C [Member] | Nuclear Generation [Member] | Peach Bottom [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator		Generation
Ownership interest		50.00%
Plant		$ 1,345	[1]	1,095	[2]
Accumulated depreciation		368	[1]	343	[2]
Construction work in progress		18		133
Jointly Owned Utility Plant Footnote [Abstract]
Plant		$ 1,345	[1]	1,095	[2]
Exelon Generation Co L L C [Member] | Nuclear Generation [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	[3]	PSEG Nuclear
Ownership interest	[3]	42.59%
Plant	[2],[3]	$ 566		531
Accumulated depreciation	[2],[3]	167		150
Construction work in progress	[3]	40		29
Jointly Owned Utility Plant Footnote [Abstract]
Plant	[2],[3]	566		531
Exelon Generation Co L L C [Member] | Fossil Fuel Generation [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant		3		3
Jointly Owned Utility Plant Footnote [Abstract]
Plant		$ 3		3
Exelon Generation Co L L C [Member] | Fossil Fuel Generation [Member] | Wyman [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator		FP&L
Ownership interest		5.89%
Plant	[1],[2]	$ 3		3
Accumulated depreciation	[1],[2]	3		3
Construction work in progress		0		0
Jointly Owned Utility Plant Footnote [Abstract]
Plant	[1],[2]	$ 3		3
Exelon Generation Co L L C [Member] | Other Service [Member] | Other Locations [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	[1]
Ownership interest	[1]	44.24%
Plant	[1],[2]	$ 1		2
Accumulated depreciation	[1],[2]	1		1
Construction work in progress	[1]	0		0
Jointly Owned Utility Plant Footnote [Abstract]
Plant	[1],[2]	$ 1		2
PECO Energy Co [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		42.55%
PECO Energy Co [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		20.70%
PECO Energy Co [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		22.00%
PECO Energy Co [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		42.55%
PECO Energy Co [Member] | Electric Transmission [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	[4]	First Energy
Plant	[2],[4]	$ 15		14
Accumulated depreciation	[2],[4]	7		7
Construction work in progress	[4]	0		0
Jointly Owned Utility Plant Footnote [Abstract]
Plant	[2],[4]	$ 15		14
PECO Energy Co [Member] | Electric Transmission [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	[5]	PSEG
Ownership interest	[5]	42.55%
Plant	[2],[5]	$ 65		64
Accumulated depreciation	[2],[5]	35		34
Construction work in progress	[5]	0		0
Jointly Owned Utility Plant Footnote [Abstract]
Plant	[2],[5]	$ 65		$ 64
Baltimore Gas and Electric Company [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		10.56%
Baltimore Gas and Electric Company [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		7.00%
[1]	Excludes asset retirement costs.
[2]	.
[3]	Generation also owns a proportionate share in the fossil fuel combustion turbine at Salem, which is fully depreciated. The gross book value was $3 million at December 31, 2015 and 2014.
[4]	PECO owns a 42.55% share in 131 miles of 500kV lines located in Delaware and New Jersey as well as a 42.55% share in a 500kV substation immediately outside of the Salem nuclear generating station in New Jersey which supplies power to the 500kV lines including, but not limited to, the lines noted above.
[5]	Generation has a 44.24% ownership interest in assets located at Merrill Creek Reservoir located in New Jersey.

Intangible Assets - Schedule of

Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Line Items]
Goodwill, Impairment Loss		$ 0
Goodwill [Roll Forward]
Goodwill, Gross		4,655	$ 4,655	$ 4,608
Goodwill, Impaired, Accumulated Impairment Loss		1,983	1,983	1,983
Goodwill, beginning balance		2,672	2,625
Goodwill, ending balance		2,672	2,672
Commonwealth Edison Co [Member]
Goodwill [Line Items]
Goodwill, Impairment Loss	[1]	0
Goodwill [Roll Forward]
Goodwill, Gross	[1]	4,608	4,608	4,608
Goodwill, Impaired, Accumulated Impairment Loss		1,983	1,983	1,983
Goodwill, beginning balance		2,625	2,625
Goodwill, ending balance		2,625	2,625
Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Goodwill, Impairment Loss		0
Goodwill [Roll Forward]
Goodwill, Gross		47	47	$ 0
Goodwill, beginning balance		47	0
Goodwill from business combination			47
Goodwill, ending balance		$ 47	$ 47
[1]	Reflects goodwill recorded in 2000 from the PECO/Unicom (predecessor parent company of ComEd) merger net of amortization, resolution of tax matters and other non-impairment-related changes as allowed under previous authoritative guidance.

Intangible Assets - Narrative (

Intangible Assets - Narrative (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Line Items]
Finite lived intangible assets gross		$ 2,585
Commonwealth Edison Co [Member]
Goodwill [Line Items]
Amortization of Intangible Assets		7	$ 7	$ 7
Current alternative or renewable energy credits		5	4
Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Current alternative or renewable energy credits		251	191
Alternative Or Renewable Energy Credits Noncurrent		56	44
PECO Energy Co [Member]
Goodwill [Line Items]
Current alternative or renewable energy credits		2	13
Unamortized Energy Contracts [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]	22	135	430
Unamortized Energy Contracts [Member] | Commonwealth Edison Co [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]		0	0
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]	22	135	507
Unamortized Energy Contracts [Member] | PECO Energy Co [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]	0	$ 0	$ 0
Constellation Energy Group LLC [Member] | Unamortized Energy Contracts [Member]
Goodwill [Line Items]
Finite lived intangible assets gross	[2],[3]	$ 1,499
Constellation Energy Group LLC [Member] | Trade Names [Member]
Goodwill [Line Items]
Useful life		10 years
Finite lived intangible assets gross	[3]	$ 243
[1]	Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[2]	Includes unamortized energy contract assets and liabilities on Exelon's and Generation's Consolidated Balance Sheets. Excludes $44 million of other miscellaneous unamortized energy contracts that have been acquired at various points in time. The estimated amortization for these miscellaneous unamortized energy contracts is $3 million, $0 million, $2 million, $3 million and $4 million for 2016, 2017, 2018, 2019 and 2020, respectively.
[3]	On March 12, 2012, Constellation merged into Exelon with Exelon continuing as the surviving corporation pursuant to the transactions contemplated by the Agreement and Plan of Merger. Since the merger transaction, Generation includes the former Constellation generation and customer supply operations.

Intangible Assets - Schedule 98

Intangible Assets - Schedule of Other Intangible Assets (Details) $ in Millions		1 Months Ended			12 Months Ended
		Sep. 30, 2011MW	Dec. 31, 2010MW	Feb. 28, 2003USD ($)	Dec. 31, 2015USD ($)
Finite-Lived Intangible Assets [Line Items]
Gross					$ 2,585
Accumulated Amortization					(1,830)
Net					755
2,015					(46)
Finite-Lived Intangible Assets, Amortization Expense, Year Two					(50)
2,017					(79)
2,018					(77)
2,019					(82)
Other miscellaneous unamortized energy contracts					$ 44
Licensing Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[1],[2]				10 years
Gross	[1]				$ 95
Accumulated Amortization	[1]				(6)
Net	[1]				89
2,015	[1]				(10)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	[1]				(10)
2,017	[1]				(10)
2,018	[1]				(10)
2,019	[1]				$ (10)
Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
Chicago payment made to city				$ 60
Period for payment				10 years
City of Chicago payment made to 3rd party				$ (2)
City of Chicago payment received				32
Reduction of amortization expense				$ (2)
Commonwealth Edison Co [Member] | Intangible Asset Nineteen Ninety Nine Chicago Settlement Agreement [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[3]				21 years 9 months 18 days
Gross	[3]				$ 100
Accumulated Amortization	[3]				(83)
Net	[3]				17
2,015	[3]				(3)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	[3]				(3)
2,017	[3]				(3)
2,018	[3]				(4)
2,019	[3]				$ (4)
Commonwealth Edison Co [Member] | Intangible Asset Two Thousand Three Chicago Settlement Agreement [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[4]				17 years 10 months 24 days
Gross	[4]				$ 62
Accumulated Amortization	[4]				(44)
Net	[4]				18
2,015	[4]				(4)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	[4]				(4)
2,017	[4]				(4)
2,018	[4]				(3)
2,019	[4]				(3)
Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
2,015					(3)
Finite-Lived Intangible Assets, Amortization Expense, Year Two					0
2,017					(2)
2,018					(3)
2,019					$ (4)
Exelon Wind Acquisition [Member] | Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Wind turbine supply megawatt | MW			735
Exelon Wind Acquisition [Member] | Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[5],[6]				18 years
Gross	[5],[6]				$ 224
Accumulated Amortization	[5],[6]				(69)
Net	[5],[6]				155
2,015	[5],[6]				(14)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	[5],[6]				(14)
2,017	[5],[6]				(14)
2,018	[5],[6]				(14)
2,019	[5],[6]				$ (10)
Antelope Valley Acquisition [Member] | Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Wind turbine supply megawatt | MW		242
Antelope Valley Acquisition [Member] | Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[6],[7]				25 years
Gross	[6],[7]				$ 190
Accumulated Amortization	[6],[7]				(20)
Net	[6],[7]				170
2,015	[6],[7]				(8)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	[6],[7]				(8)
2,017	[6],[7]				(8)
2,018	[6],[7]				(8)
2,019	[6],[7]				$ (8)
Constellation Energy Group LLC [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[6],[8]				1 year 6 months
Gross	[6],[8]				$ 1,499
Accumulated Amortization	[6],[8]				(1,473)
Net	[6],[8]				26
2,015	[6],[8]				(33)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	[6],[8]				(21)
2,017	[6],[8]				(11)
2,018	[6],[8]				(8)
2,019	[6],[8]				$ (10)
Constellation Energy Group LLC [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[8]				10 years
Gross	[8]				$ 243
Accumulated Amortization	[8]				(103)
Net	[8]				140
2,015	[8]				(23)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	[8]				(23)
2,017	[8]				(23)
2,018	[8]				(23)
2,019	[8]				$ (23)
Constellation Energy Group LLC [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[8],[9]				12 years 4 months 24 days
Gross	[8],[9]				$ 214
Accumulated Amortization	[8],[9]				(76)
Net	[8],[9]				138
2,015	[8],[9]				(18)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	[8],[9]				(18)
2,017	[8],[9]				(18)
2,018	[8],[9]				(17)
2,019	[8],[9]				$ (17)
CENG [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[6],[10]				1 year 8 months 12 days
Gross	[6],[10]				$ (97)
Accumulated Amortization	[6],[10]				48
Net	[6],[10]				(49)
2,015	[6],[10]				(11)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	[6],[10]				(15)
2,017	[6],[10]				(18)
2,018	[6],[10]				(15)
2,019	[6],[10]				$ (8)
Integrys [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[6],[10]				2 years 4 months 24 days
Gross	[6],[11]				$ 5
Accumulated Amortization	[6],[11]				2
Net	[6],[11]				7
2,015	[6],[11]				(5)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	[6],[11]				(1)
2,017	[6],[11]				(1)
2,018	[6],[11]				0
2,019	[6],[11]				$ 0
Integrys [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[9],[11]				10 years
Gross	[9],[11]				$ 50
Accumulated Amortization	[9],[11]				(6)
Net	[9],[11]				44
2,015	[9],[11]				(5)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	[9],[11]				(5)
2,017	[9],[11]				(5)
2,018	[9],[11]				(5)
2,019	[9],[11]				(5)
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
2,015					(1)
Other Intangible Assets [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Net	[8],[9]				$ 12
[1]	(a)On May 31, 2015, Exelon entered into a long-term software license agreement. Exelon is required to make payments starting August 2015 through May 2024. The intangible asset recognized as a result of these payments is being amortized on a straight-line basis over the contract term.
[2]	Weighted-average amortization period was calculated at the date of a) acquisition for acquired assets or b) settlement agreement.
[3]	In March 1999, ComEd entered into a settlement agreement with the City of Chicago associated with ComEd’s franchise agreement. Under the terms of the settlement, ComEd agreed to make payments to the City of Chicago each year from 1999 to 2002. The intangible asset recognized as a result of these payments is being amortized ratably over the remaining term of the franchise agreement, which ends in 2020.
[4]	In February 2003, ComEd entered into separate agreements with the City of Chicago and with Midwest Generation, LLC (Midwest Generation). Under the terms of the settlement agreement with the City of Chicago, ComEd agreed to pay the City of Chicago a total of $60 million over a ten-year period, beginning in 2003. The intangible asset recognized as a result of the settlement agreement is being amortized ratably over the remaining term of the City of Chicago franchise agreement, which ends in 2020. As required by the settlement, ComEd also made a payment of $2 million to a third-party on the City of Chicago’s behalf. Under the terms of the agreement with Midwest Generation, ComEd received payments of $32 million from Midwest Generation to relieve Midwest Generation’s obligation under the 1999 fossil sale agreement with ComEd to build the generation facility in the City of Chicago. The payments received by ComEd, which have been recorded in Other deferred credits and other liabilities, and other long-term liabilities on Exelon's and ComEd's Consolidated Balance Sheets are being recognized ratably (approximately $2 million annually) as an offset to amortization expense over the remaining term of the franchise agreement.
[5]	In December 2010, Generation acquired all of the equity interests of John Deere Renewables, LLC (later named Exelon Wind), adding 735MWs of installed, operating wind capacity located in eight states.
[6]	Includes unamortized energy contract assets and liabilities on Exelon's and Generation's Consolidated Balance Sheets. Excludes $44 million of other miscellaneous unamortized energy contracts that have been acquired at various points in time. The estimated amortization for these miscellaneous unamortized energy contracts is $3 million, $0 million, $2 million, $3 million and $4 million for 2016, 2017, 2018, 2019 and 2020, respectively.
[7]	In September 2011, Generation acquired all of the interest in Antelope Valley Solar Ranch One, a 242 MW solar project under development in northern Los Angeles County, CA from First Solar, Inc.
[8]	On March 12, 2012, Constellation merged into Exelon with Exelon continuing as the surviving corporation pursuant to the transactions contemplated by the Agreement and Plan of Merger. Since the merger transaction, Generation includes the former Constellation generation and customer supply operations.
[9]	(h)Excludes $12 million of other miscellaneous customer relationships that have been acquired. The estimated amortization for these miscellaneous customer relationships is $1 million in each of the years from 2016 to 2020.
[10]	See Note 5—Investment in Constellation Energy Nuclear Group, LLC for additional information.
[11]	See Note 4—Mergers, Acquisitions, and Dispositions for additional information.

Intangible Assets - Summary of

Intangible Assets - Summary of Amortization Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense		$ 7	$ 7	$ 7
Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	[1]	22	135	430
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	[1]	$ 22	135	507
Unamortized Energy Contracts [Member] | Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	[1]		$ 0	$ 0
[1]	Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

Fair Value of Financial Asse100

Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		$ 533	$ 460
Long-term debt (including amounts due within one year) (a)		275	333
Due to Related Parties, Noncurrent	[1]	641	641
Spent Nuclear Fuel Obligation, Noncurrent		1,021	1,021
Debt Issuance Cost		180	150
Financing Trust Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Cost		7
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		536	463
Long-term debt (including amounts due within one year) (a)		25,145	21,014
Due to Related Parties, Noncurrent		641	641
Spent Nuclear Fuel Obligation, Noncurrent		1,021	1,021
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		536	463
Long-term debt (including amounts due within one year) (a)		25,924	22,936
Due to Related Parties, Noncurrent		673	648
SNF obligation		818	833
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		3
Long-term debt (including amounts due within one year) (a)		931
Due to Related Parties, Noncurrent		0
SNF obligation		0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		533
Long-term debt (including amounts due within one year) (a)		23,644
Due to Related Parties, Noncurrent		0
SNF obligation		818
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		0
Long-term debt (including amounts due within one year) (a)		1,349
Due to Related Parties, Noncurrent		673
SNF obligation		0
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		29	36
Long-term debt (including amounts due within one year) (a)		127	146
Due to Related Parties, Noncurrent		933	943
Spent Nuclear Fuel Obligation, Noncurrent		1,021	1,021
Debt Issuance Cost		70	70
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		29	36
Long-term debt (including amounts due within one year) (a)		8,959	8,196
Spent Nuclear Fuel Obligation, Noncurrent		1,021	1,021
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		29	36
Long-term debt (including amounts due within one year) (a)		9,116	8,822
SNF obligation		818	833
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		0
Long-term debt (including amounts due within one year) (a)		0
SNF obligation		0
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		29
Long-term debt (including amounts due within one year) (a)		7,767
SNF obligation		818
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		0
Long-term debt (including amounts due within one year) (a)		1,349
SNF obligation		0
Commonwealth Edison Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		294	304
Due to Related Parties, Noncurrent		205	205
Debt Issuance Cost		38	33
Commonwealth Edison Co [Member] | Financing Trust Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Cost		1
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		294	304
Long-term debt (including amounts due within one year) (a)		6,509	5,925
Due to Related Parties, Noncurrent		205	205
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		294	304
Long-term debt (including amounts due within one year) (a)		7,069	6,788
Due to Related Parties, Noncurrent		213	213
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		0
Long-term debt (including amounts due within one year) (a)		0
Due to Related Parties, Noncurrent		0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		294
Long-term debt (including amounts due within one year) (a)		7,069
Due to Related Parties, Noncurrent		0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		0
Long-term debt (including amounts due within one year) (a)		0
Due to Related Parties, Noncurrent		213
PECO Energy Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to Related Parties, Noncurrent		184	184
Debt Issuance Cost		15	14
PECO Energy Co [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year) (a)		2,580	2,232
Due to Related Parties, Noncurrent		184	184
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year) (a)		2,786	2,537
Due to Related Parties, Noncurrent		195	199
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year) (a)		0
Due to Related Parties, Noncurrent		0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year) (a)		2,786
Due to Related Parties, Noncurrent		0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year) (a)		0
Due to Related Parties, Noncurrent		195
Baltimore Gas and Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		210	120
Long-term debt (including amounts due within one year) (a)			1,932
Due to Related Parties, Noncurrent		252	252
Debt Issuance Cost		9	10
Baltimore Gas and Electric Company [Member] | Financing Trust Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Cost		6
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		213	123
Long-term debt (including amounts due within one year) (a)		1,858
Due to Related Parties, Noncurrent		252
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		213	123
Long-term debt (including amounts due within one year) (a)		2,044	2,178
Due to Related Parties, Noncurrent		264	$ 236
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		3
Long-term debt (including amounts due within one year) (a)		0
Due to Related Parties, Noncurrent		0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		210
Long-term debt (including amounts due within one year) (a)		2,044
Due to Related Parties, Noncurrent		0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		0
Long-term debt (including amounts due within one year) (a)		0
Due to Related Parties, Noncurrent		$ 264
[1]	Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets.

Fair Value of Financial Asse101

Fair Value of Financial Assets and Liabilities - Fair Value Measurement of Assets and Liabilities, Recurring and Nonrecurring (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	$ 5,766	$ 1,119
Derivative Liability, Noncurrent		374	403
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash Surrender Value of Life Insurance		36	35
Derivative Liability, Noncurrent		374	403
Derivative Liability, Current		205	234
Cash and Cash Equivalents, Fair Value Disclosure	[1]	5,766	1,119
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value		(8)	(10)
Derivative Asset, Notional Amount		1,236	794
Derivative, collateral, right to reclaim cash		52	43
Nuclear Decommissioning Trust Fund Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair Value Net Assets Liabilities Excluded From Nuclear Decommissioning Trust Fund Investments		(3)	(5)
Pledged Assets For Zion Station Decommissioning [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair Value Net Assets Liabilities Excluded From Nuclear Decommissioning Trust Fund Investments		1	3
Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		17,842	13,337
FinancialAssetsFairValueDisclosure1		18,520	14,081
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Deferred Compensation Liability, Current and Noncurrent		99	107
Financial Liabilities Fair Value Disclosure		678	744
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure		678	744
Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		563	524
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		563	524
Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		6,391	6,702
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		6,391	6,702
Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	113
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	113
Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		6,827	6,694
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		6,827	6,694
Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12	23
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12	23
Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		15	54
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		15	54
Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	41
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	41
Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3	103
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3	103
Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		326	438
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		326	438
Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		10,345	10,542
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		10,345	10,542
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,066	2,262
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,066	2,262
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,338	996
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,338	996
Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		61	95
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		61	95
Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		537	511
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		537	511
Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		428	366
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		428	366
Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		35	3
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		35	3
Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		216	301
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		216	301
Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		17	15
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		17	15
Fair Value, Measurements, Recurring [Member] | Private Equity Funds, Domestic [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,902	5,242
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,902	5,242
Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,328	4,302
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,328	4,302
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		311	245
Investments, Fair Value Disclosure			1
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		311	245
Investments, Fair Value Disclosure			1
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		125	83
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		125	83
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	5,766	1,119
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Fair Value, Amount Offset Against Collateral, Net		476	434
Cash and Cash Equivalents, Fair Value Disclosure	[1]	5,766	1,119
Fair Value, Inputs, Level 1 [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		10,397	5,296
FinancialAssetsFairValueDisclosure1		10,372	5,305
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		(25)	9
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure		(25)	9
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		25	(20)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		25	(20)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		33	195
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		33	195
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		2,440	2,416
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		2,440	2,416
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	(11)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	(11)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		2,382	2,241
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		2,382	2,241
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12	14
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12	14
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12	25
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12	25
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,550	4,239
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,550	4,239
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | CorporateDebtSecuritiesZoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,323	996
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,323	996
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	5
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	5
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | State and Municipal Debt Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure			0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed income Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	5
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	5
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		7	11
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		7	11
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds, Domestic [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		3,008	3,035
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		3,008	3,035
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	6
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	6
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,323	996
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,323	996
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		48	46
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		48	46
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		219	208
Investments, Fair Value Disclosure			1
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		219	208
Investments, Fair Value Disclosure			1
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		6	114
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,922	1,667
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		36	201
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(1,964)	(1,982)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		10	18
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(3)	(17)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		7	1
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	2
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	2
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Fair Value, Amount Offset Against Collateral, Net		557	800
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
Fair Value, Inputs, Level 2 [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		127	532
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		127	532
Fair Value, Inputs, Level 2 [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		20	13
Fair Value, Inputs, Level 2 [Member] | CorporateDebtSecuritiesZoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		46	89
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		46	89
Fair Value, Inputs, Level 2 [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		8	8
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		8	8
Fair Value, Inputs, Level 2 [Member] | State and Municipal Debt Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			10
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure			10
Fair Value, Inputs, Level 2 [Member] | Other Fixed income Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	3
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	3
Fair Value, Inputs, Level 2 [Member] | Fixed Income Securities Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		55	110
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		55	110
Fair Value, Inputs, Level 2 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		205	316
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		205	316
Fair Value, Inputs, Level 2 [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	7
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	7
Fair Value, Inputs, Level 2 [Member] | MiddleMarketLending Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		127	184
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		127	184
Fair Value, Inputs, Level 2 [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		48	46
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		48	46
Fair Value, Inputs, Level 2 [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		2,069	2,029
Fair Value, Inputs, Level 2 [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		7,096	6,813
Fair Value, Inputs, Level 2 [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		130	512
Fair Value, Inputs, Level 2 [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(5,157)	(5,296)
Fair Value, Inputs, Level 2 [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		15	27
Fair Value, Inputs, Level 2 [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(6)	(48)
Fair Value, Inputs, Level 2 [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		25	31
Fair Value, Inputs, Level 2 [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		54	23
Fair Value, Inputs, Level 2 [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		33	5
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		33	5
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		5,651	6,320
FinancialAssetsFairValueDisclosure1		5,985	6,747
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Deferred Compensation Liability, Current and Noncurrent		99	107
Financial Liabilities Fair Value Disclosure		334	427
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure		334	427
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		219	196
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		219	196
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		57	295
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		57	295
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3,186	3,557
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3,186	3,557
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	124
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	124
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3,348	3,458
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3,348	3,458
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	9
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	9
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3	29
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3	29
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	41
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	41
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3	103
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3	103
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		326	438
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		326	438
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,965	5,612
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,965	5,612
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,824	2,023
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,824	2,023
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | CorporateDebtSecuritiesZoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		46	89
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		46	89
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		15	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		15	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2	3
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2	3
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		61	95
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		61	95
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | State and Municipal Debt Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			10
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure			10
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		537	511
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		537	511
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed income Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	3
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	3
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		49	105
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		49	105
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		216	301
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		216	301
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		71	121
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		71	121
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		17	15
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		17	15
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds, Domestic [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,894	2,207
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,894	2,207
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		5	1
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		5	1
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,763	3,067
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,763	3,067
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		92	37
Investments, Fair Value Disclosure			0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		92	37
Investments, Fair Value Disclosure			0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		902	992
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		3,467	3,465
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		64	284
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(2,629)	(2,757)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		5	9
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(3)	(31)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		25	31
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		47	22
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
Derivative Liability, Noncurrent			187
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Fair Value, Amount Offset Against Collateral, Net		201	172
Derivative Liability, Noncurrent			187
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
Fair Value, Inputs, Level 3 [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		1,794	1,721
FinancialAssetsFairValueDisclosure1		2,163	2,029
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		369	308
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure		369	308
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		369	308
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		369	308
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		37	42
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		37	42
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		765	729
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		765	729
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		1,097	995
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		1,097	995
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		830	691
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		830	691
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		242	239
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		242	239
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | CorporateDebtSecuritiesZoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | State and Municipal Debt Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure			0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed income Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		428	366
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		428	366
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		35	3
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		35	3
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		127	184
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		127	184
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds, Domestic [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		242	239
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		242	239
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		127	184
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		127	184
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Investments, Fair Value Disclosure			0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Investments, Fair Value Disclosure			0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		125	83
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		125	83
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,173	1,151
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,707	1,681
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		30	27
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(564)	(557)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		33	3
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		33	3
Exelon Generation Co L L C [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	104	405
Derivative Liability, Noncurrent		150	105
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash Surrender Value of Life Insurance		13	11
Derivative Liability, Noncurrent		150	105
Derivative Liability, Current		182	214
Cash and Cash Equivalents, Fair Value Disclosure	[1]	104	405
Derivative, collateral, right to reclaim cash		3	8
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		12,440	12,979
FinancialAssetsFairValueDisclosure1		12,802	13,329
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Deferred Compensation Liability, Current and Noncurrent		30	31
Financial Liabilities Fair Value Disclosure		362	350
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure		362	350
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		316	317
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		316	317
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		6,391	6,702
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		6,391	6,702
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	2
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	2
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		6,580	6,487
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		6,580	6,487
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12	23
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12	23
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		15	35
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		15	35
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	12
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	12
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3	2
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3	2
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		326	438
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		326	438
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		10,345	10,542
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		10,345	10,542
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,066	2,262
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,066	2,262
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,338	996
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,338	996
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		61	95
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		61	95
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		537	511
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		537	511
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		428	366
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		428	366
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		35	3
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		35	3
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		216	301
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		216	301
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		17	15
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		17	15
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds, Domestic [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,902	5,242
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,902	5,242
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,328	4,302
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,328	4,302
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		311	245
Investments, Fair Value Disclosure			0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		311	245
Investments, Fair Value Disclosure			0
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		125	83
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		125	83
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	104	405
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	104	405
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		4,704	4,549
FinancialAssetsFairValueDisclosure1		4,679	4,558
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		(25)	9
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure		(25)	9
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		25	(20)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		25	(20)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		33	195
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		33	195
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		2,440	2,416
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		2,440	2,416
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	(11)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	(11)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		2,382	2,241
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		2,382	2,241
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12	14
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12	14
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12	25
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12	25
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,550	4,239
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,550	4,239
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | CorporateDebtSecuritiesZoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,323	996
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,323	996
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	5
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	5
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | State and Municipal Debt Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure			0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed income Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	5
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	5
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		7	11
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		7	11
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds, Domestic [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		3,008	3,035
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		3,008	3,035
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	6
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	6
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,323	996
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,323	996
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		17	16
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		17	16
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		219	208
Investments, Fair Value Disclosure			0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		219	208
Investments, Fair Value Disclosure			0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		6	114
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,922	1,667
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		36	201
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(1,964)	(1,982)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		10	18
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(3)	(17)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		7	1
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		127	532
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		127	532
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		20	12
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		17	16
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		17	16
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		2,069	2,029
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		7,096	6,813
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		130	512
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(5,157)	(5,296)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		15	27
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(6)	(29)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	8
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		29	18
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		33	3
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		33	3
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		5,695	6,502
FinancialAssetsFairValueDisclosure1		5,960	6,742
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Deferred Compensation Liability, Current and Noncurrent		30	31
Financial Liabilities Fair Value Disclosure		265	240
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure		265	240
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		219	196
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		219	196
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		57	295
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		57	295
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3,186	3,557
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3,186	3,557
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	13
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	13
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3,348	3,458
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3,348	3,458
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	9
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	9
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3	10
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3	10
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	12
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		16	12
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3	2
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		3	2
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		326	438
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		326	438
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,965	5,612
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,965	5,612
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,824	2,023
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,824	2,023
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | CorporateDebtSecuritiesZoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		46	89
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		46	89
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		15	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		15	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2	3
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2	3
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		61	95
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		61	95
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | State and Municipal Debt Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			10
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure			10
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		537	511
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		537	511
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed income Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	3
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	3
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		49	105
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		49	105
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		216	301
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		216	301
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		71	121
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		71	121
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		17	15
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		17	15
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds, Domestic [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,894	2,207
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,894	2,207
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		5	1
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		5	1
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,763	3,067
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,763	3,067
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		92	37
Investments, Fair Value Disclosure			0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		92	37
Investments, Fair Value Disclosure			0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		902	992
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		3,467	3,465
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		64	284
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(2,629)	(2,757)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		5	9
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(3)	(12)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	8
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		22	17
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		2,041	1,928
FinancialAssetsFairValueDisclosure1		2,163	2,029
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		122	101
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure		122	101
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		122	101
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		122	101
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		37	42
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		37	42
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		765	729
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		765	729
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		850	788
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		850	788
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		830
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		830
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		242	239
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		242	239
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | CorporateDebtSecuritiesZoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | State and Municipal Debt Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure			0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed income Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		428	366
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		428	366
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		35	3
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		35	3
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		127	184
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		127	184
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds, Domestic [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		242	239
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		242	239
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zoin Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		127	184
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		127	184
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Investments, Fair Value Disclosure			0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Investments, Fair Value Disclosure			0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		125	83
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		125	83
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,173	1,151
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,707	1,681
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		30	27
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(564)	(557)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		33	3
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		33	3
Commonwealth Edison Co [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		29	25
Derivative Liability, Noncurrent		224	187
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		224	187
Derivative Liability, Current		23	20
Cash and Cash Equivalents, Fair Value Disclosure		29	25
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		(226)	(190)
FinancialAssetsFairValueDisclosure1		29	25
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		247	207
Deferred Compensation Liability, Current and Noncurrent		8	8
Financial Liabilities Fair Value Disclosure		255	215
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		247	207
Financial Liabilities Fair Value Disclosure		255	215
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		29	25
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		29	25
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		29	25
FinancialAssetsFairValueDisclosure1		29	25
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		(8)	(8)
FinancialAssetsFairValueDisclosure1		0	0
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Deferred Compensation Liability, Current and Noncurrent		8	8
Financial Liabilities Fair Value Disclosure		8	8
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		8	8
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		(247)	(207)
FinancialAssetsFairValueDisclosure1		0	0
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent			207
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		247	207
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent			207
Financial Liabilities Fair Value Disclosure		247	207
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
PECO Energy Co [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		271	12
Derivative Liability, Noncurrent		12
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		12
Cash and Cash Equivalents, Fair Value Disclosure		271	12
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		267	6
FinancialAssetsFairValueDisclosure1		279	21
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		8	9
Derivative Liability, Noncurrent		0	0
Deferred Compensation Liability, Current and Noncurrent		12	15
Financial Liabilities Fair Value Disclosure		12	15
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Investments, Fair Value Disclosure		8	9
Financial Liabilities Fair Value Disclosure		12	15
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		271	12
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		271	12
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		279	21
FinancialAssetsFairValueDisclosure1		279	21
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		8	9
Derivative Liability, Noncurrent		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Investments, Fair Value Disclosure		8	9
Financial Liabilities Fair Value Disclosure		0	0
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		(12)	(15)
FinancialAssetsFairValueDisclosure1		0	0
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Deferred Compensation Liability, Current and Noncurrent		12	15
Financial Liabilities Fair Value Disclosure		12	15
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		12	15
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		0	0
FinancialAssetsFairValueDisclosure1		0	0
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		25	103
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		25	103
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		25	103
FinancialAssetsFairValueDisclosure1		29	108
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4	5
Derivative Liability, Noncurrent		0	0
Deferred Compensation Liability, Current and Noncurrent		4	5
Financial Liabilities Fair Value Disclosure		4	5
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Investments, Fair Value Disclosure		4	5
Financial Liabilities Fair Value Disclosure		4	5
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		25	103
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		25	103
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		29	108
FinancialAssetsFairValueDisclosure1		29	108
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4	5
Derivative Liability, Noncurrent		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Investments, Fair Value Disclosure		4	5
Financial Liabilities Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		(4)	(5)
FinancialAssetsFairValueDisclosure1		0	0
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Deferred Compensation Liability, Current and Noncurrent		4	5
Financial Liabilities Fair Value Disclosure		4	5
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		4	5
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items]
FinancialAssetLiabilitiesNetFairValueDisclosure1		0	0
FinancialAssetsFairValueDisclosure1		0	0
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Investments, Fair Value Disclosure		$ 0	$ 0
[1]	Excludes certain cash equivalents considered to be held-to-maturity and not reported at fair value.

Fair Value of Financial Asse102

Fair Value of Financial Assets and Liabilities - Fair Value Reconciliation of Level 3 Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Exelon Generation Co L L C [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings		$ (834)	$ (114)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ (1,794)	$ (1,721)	$ (749)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		27	532
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral		$ 29	$ 198
Purchases		420	598
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(106)	(64)
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities		860	644
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		860	644
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning		2	(2)
Included in regulatory assets/liabilities		(17)	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		(108)	(80)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		84	(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(254)	(207)
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Consolidation, Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		(23)	(14)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ 0	$ 0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		0	0
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral		$ 0	$ 0
Purchases		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0	0
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning		0	0
Included in regulatory assets/liabilities		23	14
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0	0
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		23	14
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ (2,041)	$ (1,928)	(942)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		27	532
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Included in other comprehensive income			$ 0
Change in collateral		$ 29	198
Purchases		420	598
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities		860	644
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		860	644
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Decrease in Fair Value Adjustment		55	13
Included in payable for Zion Station decommissioning		2	(2)
Included in regulatory assets/liabilities		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		(108)	(80)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements		106	64
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		84	(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(254)	(207)
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		23	14
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ (830)	$ (691)	(350)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		4	6
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral		$ 0	$ 0
Purchases		226	400
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(106)
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities		4	4
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		4	4
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning		0	0
Included in regulatory assets/liabilities		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		(8)	(15)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			64
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		4	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(4)	0
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ (127)	$ (184)	(112)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		0	0
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral		$ 0	$ 0
Purchases		20	120
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning		2	(2)
Included in regulatory assets/liabilities		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		(75)	(50)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0	0
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ (1,051)	$ (1,050)	(465)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		22	526
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral		$ 29	$ 198
Purchases		144	76
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0	0
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities		856	640
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		856	640
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning		0	0
Included in regulatory assets/liabilities		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		(25)	(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		80	(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(249)	(201)
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Other Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ (33)	$ (3)	(15)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		1	0
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral		$ 0	$ 0
Purchases		30	2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning		0	0
Included in regulatory assets/liabilities		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0	(8)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(1)	(6)
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member]
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Included in other comprehensive income			0
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Included in other comprehensive income			0
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Derivative [Member]
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Included in other comprehensive income	[1]		0
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Other Investments [Member]
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Included in other comprehensive income			0
Fair Value, Inputs, Level 3 [Member] | Commonwealth Edison Co [Member] | Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value		(247)	(207)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			$ (207)	$ (193)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		0	0
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral		$ 0	$ 0
Purchases		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0	0
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning		0	0
Included in regulatory assets/liabilities		(40)	(14)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		$ 0	$ 0
[1]	Includes $55 million of decreases in fair value and an increase for realized losses due to settlements of $(15) million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2015. Includes $13 million of decreases in fair value and a reduction for realized gains due to settlements of $1 million for the year ended December 31, 2014.

Fair Value of Financial Asse103

Fair Value of Financial Assets and Liabilities - Narrative (Details)	Dec. 31, 2015USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward Power Basis	$ 2.91
Forward Gas Basis	$ 0.27

Fair Value of Financial Asse104

Fair Value of Financial Assets and Liabilities - Fair Value Assets and Liabilities Measure on Recurring Basis Gain Loss Included in Earnings (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Revenue [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		$ 67	$ 614
Included in other comprehensive income		858	663
Purchased Fuel and Electric [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		(45)	(88)
Included in other comprehensive income		(2)	(23)
Other, net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		4	6
Included in other comprehensive income		4	4
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings		(834)	(114)
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		67	614
Included in other comprehensive income		858	663
Exelon Generation Co L L C [Member] | Purchased Fuel and Electric [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		(45)	(88)
Included in other comprehensive income		(2)	(23)
Exelon Generation Co L L C [Member] | Other, net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		4	6
Included in other comprehensive income		4	4
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(1,794)	(1,721)	$ (749)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ (108)	$ (80)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		27	532
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 0	$ 0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		(2)	2
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		(17)	0
Change in collateral		29	198
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		420	598
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(106)	(64)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		84	(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(254)	(207)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		860	644
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(2,041)	(1,928)	(942)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		(108)	(80)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements		$ (106)	(64)
Included in other comprehensive income			$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		27	532
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 23	$ 14
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		(2)	2
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		0	0
Change in collateral		29	198
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		420	598
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		84	(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(254)	(207)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		860	644
Other Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(33)	(3)	(15)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ 0	(8)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		1	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 0	$ 0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		0	0
Change in collateral		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		30	2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(1)	(6)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		0	0
Nuclear Decommissioning Trust Fund Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(830)	(691)	(350)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ (8)	(15)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			$ (64)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		4	6
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 23	$ 14
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		0	0
Change in collateral		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		226	400
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(106)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		4	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(4)	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		4	4
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(1,051)	(1,050)	(465)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ (25)	$ (7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		22	526
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 0	$ 0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		0	0
Change in collateral		29	198
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		144	76
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		80	(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(249)	(201)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		856	640
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Commonwealth Edison Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			(207)	(193)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ 0	$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 0	$ 0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		(40)	(14)
Change in collateral		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value		(247)	(207)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		0	0
Pledged Assets For Zion Station Decommissioning [Member] | Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(127)	(184)	(112)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ (75)	(50)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 0	$ 0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		(2)	2
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		0	0
Change in collateral		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		20	120
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		0	0
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in other comprehensive income	[1]		0
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Consolidation, Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		0	0	$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ 0	$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ (23)	$ (14)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		23	14
Change in collateral		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		0	0
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements		$ (15)	$ (1)
[1]	Includes $55 million of decreases in fair value and an increase for realized losses due to settlements of $(15) million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2015. Includes $13 million of decreases in fair value and a reduction for realized gains due to settlements of $1 million for the year ended December 31, 2014.

Fair Value of Financial Asse105

Fair Value of Financial Assets and Liabilities - Fair Value Inputs Assets Quantitative Information (Details) - USD ($)		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash collateral excluded		$ 201,000,000		$ 172,000,000
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value	[1]	248,000,000		293,000,000
Exelon Generation Co L L C [Member] | Proprietary Trading [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value		(7,000,000)	[2],[3]	(15,000,000)	[4],[5]
Exelon Generation Co L L C [Member] | Derivative [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value		857,000,000	[2],[3]	893,000,000	[4],[5]
Exelon Generation Co L L C [Member] | Income Approach Valuation Technique [Member] | Minimum [Member] | Proprietary Trading [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward power price assets		13	[3],[6]	15	[5]
Exelon Generation Co L L C [Member] | Income Approach Valuation Technique [Member] | Minimum [Member] | Derivative [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward power price assets		11	[3],[6]	15	[5]
Forward gas price assets		1.18	[3],[6]	1.52	[7]
Exelon Generation Co L L C [Member] | Income Approach Valuation Technique [Member] | Maximum [Member] | Proprietary Trading [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward power price assets		78	[3],[6]	117	[5],[7]
Exelon Generation Co L L C [Member] | Income Approach Valuation Technique [Member] | Maximum [Member] | Derivative [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward power price assets		88	[3],[6]	120	[5],[7]
Forward gas price assets		$ 8.95	[3],[6]	14.02	[7]
Exelon Generation Co L L C [Member] | Income Approach Valuation Technique [Member] | Maximum [Member] | Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | All Regions excluding New England [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward power price assets				97
Forward gas price assets				$ 8.14
Exelon Generation Co L L C [Member] | Option Model Valuation Technique [Member] | Minimum [Member] | Derivative [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Volatility percentage		5.00%	[3]	8.00%
Exelon Generation Co L L C [Member] | Option Model Valuation Technique [Member] | Maximum [Member] | Derivative [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Volatility percentage		152.00%	[3]	257.00%
Commonwealth Edison Co [Member] | Derivative [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value		$ (247,000,000)	[2]	$ (207,000,000)	[4]
Commonwealth Edison Co [Member] | Income Approach Valuation Technique [Member] | Minimum [Member] | Derivative [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward heat rate		8.00%	[8]	8.00%	[9]
Marketability Reserve		3.50%		3.50%
Renewable factor		87.00%		86.00%
Commonwealth Edison Co [Member] | Income Approach Valuation Technique [Member] | Maximum [Member] | Derivative [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward heat rate		9.00%	[8]	9.00%	[9]
Marketability Reserve		7.00%		8.00%
Renewable factor		128.00%		126.00%
[1]	(c)Amount represents the net fair value of out-of-the-money derivative contracts containing credit-risk related contingent features after considering the mitigating effects of offsetting positions under master netting arrangements and reflects the actual net liability upon which any potential contingent collateral obligations would be based.
[2]	The fair values do not include cash collateral posted on level three positions of $201 million as of December 31, 2015.
[3]	The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions.
[4]	The fair values do not include cash collateral posted on level three positions of $172 million as of December 31, 2014
[5]	The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions.
[6]	he
[7]	The upper ends of the ranges are driven by the winter power and gas prices in the New England region. Without the New England region, the upper ends of the ranges for power and gas would be approximately $97 and $8.14, respectively and would be approximately $76 for power proprietary trading.
[8]	Quoted forward natural gas rates are utilized to project the forward power curve for the delivery of energy at specified future dates. The natural gas curve is extrapolated beyond its observable period to the end of the contract’s delivery.
[9]	Quoted forward natural gas rates are utilized to project the forward power curve for the delivery of energy at specified future dates. The natural gas curve is extrapolated beyond its observable period to the end of the contract’s delivery.

Derivative Financial Instrum106

Derivative Financial Instruments - Narrative (Details) MWh in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)MWh		Dec. 31, 2014USD ($)MWh		Dec. 31, 2013USD ($)MWh	Jun. 30, 2015USD ($)
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	30.00%
Derivative, notional amount	$ 1,774		$ 1,491
Pre-tax net income impact associated with a hypothetical 10% increase in interest rates - exclusive upper bound	6
Ineffective portion recognized in income	17		18
Notional amount of interest rate swaps acquired from merger	2,400
Mark-to-market derivative liabilities	374		403
Mark-to-market derivative liabilities	205		234
Derivative, collateral, right to reclaim cash	52		43
Cash collateral held	13
Letters of credit held	69
Net Asset Liability Position After Contractual Right Of Offset	38
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional amount of preissuance interest rate cash flow hedge derivatives	738
Reclassification out of Accumulated Other Comprehensive Income [Member] | Energy Related Hedges [Member] | Operating Revenue One [Member]
Derivative [Line Items]
Cash flow hedge activity impact on pre-tax net income based on reclassification adjustment from accumulated other comprehensive income	2		195		$ 464
Designated as Hedging Instrument [Member] | PHI Merger [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	64
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Derivative, notional amount	800		1,450
Derivative Asset	25		29
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | ExGen Texas Power [Member]
Derivative [Line Items]
Derivative, notional amount	500
Interest Rate Swap [Member] | Derivative [Member]
Derivative [Line Items]
Derivative, notional amount	800
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | ExGen Texas Power [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities	12
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	26
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Notional amount of preissuance interest rate cash flow hedge derivatives			400
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Net receivable from electric utility	31
Credit exposure under off system sales	4
Incremental collateral for loss of investment grade credit rating	$ 35
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net			$ 4
Proprietary trading activities volume | MWh	10,571		8,762		12,958
Hypothetical increase in interest rates associated with variable-rate debt	50.00%
Mark-to-market derivative liabilities	$ 150		$ 105
Mark-to-market derivative liabilities	182		214
Derivative, collateral, right to reclaim cash	3		8
Letters of credit posted	497		672
Cash collateral held	21		77
Letters of credit held	78		24
Cash collateral posted			1,497
Incremental collateral for loss of investment grade credit rating	2,000		2,400
Net Asset Liability Position After Contractual Right Of Offset	13
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset	7,096		6,813
Mark-to-market derivative liabilities	1,673		1,540
Mark-to-market derivative liabilities	4,907		4,947
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member] | Other Solar Projects [Member]
Derivative [Line Items]
Derivative, notional amount	24
Exelon Generation Co L L C [Member] | Total Cash Flow Hedges [Member]
Derivative [Line Items]
Cash flow hedge activity impact on pre-tax net income based on reclassification adjustment from accumulated other comprehensive income	2		195		$ 683
Exelon Generation Co L L C [Member] | Derivative [Member]
Derivative [Line Items]
Derivative, collateral, right to reclaim cash	1,267
Exelon Generation Co L L C [Member] | Derivative [Member] | Other Solar Projects [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities	2
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities	2
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Derivative, notional amount			550
Derivative Asset			7
Exelon Generation Co L L C [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative, notional amount	189
Notional amount of interest rate swaps acquired from merger	25
Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, notional amount	$ 30
Commonwealth Edison Co [Member]
Derivative [Line Items]
Term of contract	20 years
Mark-to-market derivative liabilities	$ 224		187
Mark-to-market derivative liabilities	23		20
Net receivable from electric utility	15
Cash collateral held	19
Commonwealth Edison Co [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset	0	[1]	0
Mark-to-market derivative liabilities	224	[1]	187	[2]
Mark-to-market derivative liabilities	23	[1]	$ 20	[2]
PECO Energy Co [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities	12
Net receivable from electric utility	36
Incremental collateral for loss of investment grade credit rating	$ 25
Minimum [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months	90.00%
Expected generation hedged in year two	60.00%
Expected generation hedged in year three	28.00%
Minimum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	10.00%
Maximum [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months	93.00%
Expected generation hedged in year two	63.00%
Expected generation hedged in year three	31.00%
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	20.00%
Senior Notes [Member]
Derivative [Line Items]
Debt Instrument, Face Amount	$ 3,300					$ 4,200
Senior Notes [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Debt Instrument, Face Amount	$ 750
[1]	Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.
[2]	Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.

Derivative Financial Instrum107

Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) - USD ($) $ in Millions		Dec. 31, 2015		Dec. 31, 2014
Interest Rate Swap [Member] | Derivative [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		$ 15		$ 15
Mark-to-market derivative assets (noncurrent assets)		39		8
Total mark-to-market derivative assets		54		23
Mark-to-market derivative liabilities (current liabilities)		(8)		1
Mark-to-market derivative liabilities (noncurrent liabilities)		(8)		(114)
Total mark-to-market derivative liabilities		(16)		(113)
Interest Rate Derivative Fair Value Of Derivative Net		38		(90)
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		15		12
Mark-to-market derivative assets (noncurrent assets)		14		6
Total mark-to-market derivative assets		29		18
Mark-to-market derivative liabilities (current liabilities)		(8)		1
Mark-to-market derivative liabilities (noncurrent liabilities)		(8)		(3)
Total mark-to-market derivative liabilities		(16)		(2)
Interest Rate Derivative Fair Value Of Derivative Net		13		16
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member] | Derivative [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		10		7
Mark-to-market derivative assets (noncurrent assets)		10		5
Total mark-to-market derivative assets		20		12
Mark-to-market derivative liabilities (current liabilities)		(2)		(2)
Mark-to-market derivative liabilities (noncurrent liabilities)		(1)		0
Total mark-to-market derivative liabilities		(3)		(2)
Interest Rate Derivative Fair Value Of Derivative Net		17		10
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member] | Proprietary Trading [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		10	[1]	20	[2]
Mark-to-market derivative assets (noncurrent assets)		5	[1]	7	[2]
Total mark-to-market derivative assets		15	[1]	27	[2]
Mark-to-market derivative liabilities (current liabilities)		(9)	[1]	(14)	[2]
Mark-to-market derivative liabilities (noncurrent liabilities)		(3)	[1]	(9)	[2]
Total mark-to-market derivative liabilities		(12)	[1]	(23)	[2]
Interest Rate Derivative Fair Value Of Derivative Net		3	[1]	4	[2]
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member] | Collateral And Netting [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		(5)	[3]	(22)	[4]
Mark-to-market derivative assets (noncurrent assets)		(1)	[3]	(7)	[4]
Total mark-to-market derivative assets		(6)	[3]	(29)	[4]
Mark-to-market derivative liabilities (current liabilities)		11	[3]	25	[4]
Mark-to-market derivative liabilities (noncurrent liabilities)		4	[3]	10	[4]
Total mark-to-market derivative liabilities		15	[3]	35	[4]
Interest Rate Derivative Fair Value Of Derivative Net		9	[3]	6	[4]
Other Segments [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0		3
Mark-to-market derivative assets (noncurrent assets)		25		2
Total mark-to-market derivative assets		25		5
Mark-to-market derivative liabilities (current liabilities)		0		0
Mark-to-market derivative liabilities (noncurrent liabilities)		0		(111)
Total mark-to-market derivative liabilities		0		(111)
Interest Rate Derivative Fair Value Of Derivative Net		25		(106)
Other Segments [Member] | Interest Rate Swap [Member] | Derivative [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0		0
Mark-to-market derivative assets (noncurrent assets)		0		1
Total mark-to-market derivative assets		0		1
Mark-to-market derivative liabilities (current liabilities)		0		0
Mark-to-market derivative liabilities (noncurrent liabilities)		0		(101)
Total mark-to-market derivative liabilities		0		(101)
Interest Rate Derivative Fair Value Of Derivative Net		0		(100)
Other Segments [Member] | Interest Rate Swap [Member] | Collateral And Netting [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0	[3]	0
Mark-to-market derivative assets (noncurrent assets)		0	[3]	(19)
Total mark-to-market derivative assets	[3]	0		(19)
Mark-to-market derivative liabilities (current liabilities)		0	[3]	0
Mark-to-market derivative liabilities (noncurrent liabilities)		0	[3]	19
Total mark-to-market derivative liabilities	[3]	0		19
Interest Rate Derivative Fair Value Of Derivative Net	[3]	0		0
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0		7
Mark-to-market derivative assets (noncurrent assets)		0		1
Total mark-to-market derivative assets		0		8
Mark-to-market derivative liabilities (current liabilities)		(8)		(8)
Mark-to-market derivative liabilities (noncurrent liabilities)		(8)		(4)
Total mark-to-market derivative liabilities		(16)		(12)
Interest Rate Derivative Fair Value Of Derivative Net		(16)		(4)
Designated as Hedging Instrument [Member] | Other Segments [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (current liabilities)		0
Designated as Hedging Instrument [Member] | Other Segments [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0		3
Mark-to-market derivative assets (noncurrent assets)		25		20
Total mark-to-market derivative assets		25		23
Mark-to-market derivative liabilities (current liabilities)				0
Mark-to-market derivative liabilities (noncurrent liabilities)		0		(29)
Total mark-to-market derivative liabilities		0		(29)
Interest Rate Derivative Fair Value Of Derivative Net		$ 25		$ (6)
[1]	Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The characterization of the interest rate derivative contracts between the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure. Generation does not utilize proprietary trading interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates.
[2]	Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The characterization of the interest rate derivative contracts between the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure. Generation does not utilize proprietary trading interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates.
[3]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246MzVENkZDQ0ZEODdBMDc2NzU3MUMxMjI1RThCMzEwMDYM}
[4]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246NENEMjJCRjRDMzEyNTE4NUUyNjIxMjI1RThCMzBFMjEM}

Derivative Financial Instrum108

Derivative Financial Instruments - Summary of Gains and Losses on Hedges (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net			$ 4
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Gain (Loss) on Swaps/Borrowings		$ (9)	15	$ (3)
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Gain (Loss) on Swaps/Borrowings		2	3	(24)
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Gain (Loss) on Swaps/Borrowings	[1]	0	2	(6)
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member] | Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Gain (Loss) on Swaps/Borrowings	[1]	(1)	(16)	$ (15)
Gain (Loss) on Fair Value Hedges Recognized in Earnings		$ 1	$ (17)
[1]	For the years ended December 31, 2015 and 2014, the loss on Generation swaps included $(1) million and $(17) million realized in earnings, respectively, with an immaterial amount and $4 million excluded from hedge effectiveness testing, respectively.

Derivative Financial Instrum109

Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	$ 1,365		$ 1,279
Mark-to-market derivative assets (noncurrent assets)	758		773
Mark-to-market derivative liabilities (current liabilities)	(205)		(234)
Mark-to-market derivative liabilities (noncurrent liabilities)	(374)		(403)
Total mark-to-market derivative net assets (liabilities)	5		(3)
Total cash collateral received net of cash collateral posted			1,406
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	1,365		1,276
Mark-to-market derivative assets (noncurrent assets)	733		771
Mark-to-market derivative liabilities (current liabilities)	(182)		(214)
Mark-to-market derivative liabilities (noncurrent liabilities)	(150)		(105)
Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (current liabilities)	(23)		(20)
Mark-to-market derivative liabilities (noncurrent liabilities)	(224)		(187)
Proprietary Trading [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	108		456
Mark-to-market derivative assets (noncurrent assets)	22		56
Total mark-to-market derivative assets	130		512
Mark-to-market derivative liabilities (current liabilities)	(94)		(468)
Mark-to-market derivative liabilities (noncurrent liabilities)	(33)		(64)
Total mark-to-market derivative liabilities	(127)		(532)
Total mark-to-market derivative net assets (liabilities)	3		(20)
Collateral And Netting [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	(3,994)	[1]	(4,184)	[2]
Mark-to-market derivative assets (noncurrent assets)	(1,163)	[1]	(1,112)	[2]
Total mark-to-market derivative assets	(5,157)	[1]	(5,296)	[2]
Mark-to-market derivative liabilities (current liabilities)	4,827	[1]	5,200	[2]
Mark-to-market derivative liabilities (noncurrent liabilities)	1,564	[1]	1,502	[2]
Total mark-to-market derivative liabilities	6,391	[1]	6,702	[2]
Total mark-to-market derivative net assets (liabilities)	1,234	[1]	1,406	[2]
Derivative [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	1,350		1,264
Mark-to-market derivative assets (noncurrent assets)	719		765
Total mark-to-market derivative assets	2,069		2,029
Mark-to-market derivative liabilities (current liabilities)	(197)		(235)
Mark-to-market derivative liabilities (noncurrent liabilities)	(366)		(289)
Total mark-to-market derivative liabilities	(563)		(524)
Total mark-to-market derivative net assets (liabilities)	1,506		1,505
Derivative [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	1,350	[3]	1,264	[4]
Mark-to-market derivative assets (noncurrent assets)	719	[3]	765	[4]
Total mark-to-market derivative assets	2,069	[3]	2,029	[4]
Mark-to-market derivative liabilities (current liabilities)	(174)	[3]	(215)	[4]
Mark-to-market derivative liabilities (noncurrent liabilities)	(142)	[3]	(102)	[4]
Total mark-to-market derivative liabilities	(316)	[3]	(317)	[4]
Total mark-to-market derivative net assets (liabilities)	1,753	[3]	1,712	[4]
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	5,236		4,992
Mark-to-market derivative assets (noncurrent assets)	1,860		1,821
Total mark-to-market derivative assets	7,096		6,813
Mark-to-market derivative liabilities (current liabilities)	(4,907)		(4,947)
Mark-to-market derivative liabilities (noncurrent liabilities)	(1,673)		(1,540)
Total mark-to-market derivative liabilities	(6,580)		(6,487)
Total mark-to-market derivative net assets (liabilities)	516		326
Current assets collateral offset	(352)		(416)
Noncurrent assets collateral offset	(180)		(171)
Current liabilities collateral offset	(480)		(599)
Collateral Amount Offset Against Fair Value Of Derivative Current Noncurrent Liability	(222)		(220)
Total cash collateral received net of cash collateral posted	1,234
Designated as Hedging Instrument [Member] | Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0		0
Mark-to-market derivative assets (noncurrent assets)	0	[5]	0	[6]
Total mark-to-market derivative assets	0	[5]	0
Mark-to-market derivative liabilities (current liabilities)	(23)	[5]	(20)	[6]
Mark-to-market derivative liabilities (noncurrent liabilities)	(224)	[5]	(187)	[6]
Total mark-to-market derivative liabilities	(247)	[5]	(207)	[6]
Total mark-to-market derivative net assets (liabilities)	(247)	[5]	(207)	[6]
Total Cash Flow Hedges [Member]
Derivative [Line Items]
Effective portion of changes in fair value	(12)		(31)
Total Cash Flow Hedges [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Effective portion of changes in fair value	$ (8)		$ (15)
[1]	Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above.
[2]	Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above.
[3]	Current and noncurrent assets are shown net of collateral of $352 million and $180 million, respectively, and current and noncurrent liabilities are shown net of collateral of $480 million and $222 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $1,234 million at December 31, 2015.
[4]	Current and noncurrent assets are shown net of collateral of $416 million and $171 million, respectively, and current and noncurrent liabilities are shown net of collateral of $599 million and $220 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $1,406 million at December 31, 2014.
[5]	Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.
[6]	Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.

Derivative Financial Instrum110

Derivative Financial Instruments - Summary of AOCI related to Cash Flow Hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	$ 4	$ 78
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Reclassifications from accumulated OCI to net income	18,395	16,637	$ 14,277
Ineffective portion recognized in income	17	18
Exelon Generation Co L L C [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Reclassifications from accumulated OCI to net income	18,386	16,614	14,207
Total Cash Flow Hedges [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Accumulated OCI derivative gain - Beginning Balance	(28)	120
Effective portion of changes in fair value	(12)	(31)
Accumulated OCI derivative gain - Ending Balance	(19)	(28)	120
Total Cash Flow Hedges [Member] | Exelon Generation Co L L C [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Accumulated OCI derivative gain - Beginning Balance	(18)
Effective portion of changes in fair value	(8)	(15)
Accumulated OCI derivative gain - Ending Balance	(21)	(18)
Energy Related Hedges [Member] | Exelon Generation Co L L C [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Accumulated OCI derivative gain - Beginning Balance		114
Accumulated OCI derivative gain - Ending Balance			$ 114
Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	10
Other, net [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Total Cash Flow Hedges [Member] | Exelon Generation Co L L C [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion	0
Other, net [Member] | Operating Revenue [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Total Cash Flow Hedges [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion	16
Interest Expense [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Total Cash Flow Hedges [Member] | Exelon Generation Co L L C [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion	7
Interest Expense [Member] | Operating Revenue [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Total Cash Flow Hedges [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion	7
Operating Revenue [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Total Cash Flow Hedges [Member] | Exelon Generation Co L L C [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion	(2)	(117)
Operating Revenue [Member] | Operating Revenue One [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Total Cash Flow Hedges [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion	$ (2)
Operating Revenue [Member] | Operating Revenue [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Total Cash Flow Hedges [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion		$ (117)

Derivative Financial Instrum111

Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Change in fair value of commodity positions	$ 49	$ (92)	$ (5)
Reclassification to realized at settlement	58	(2)	(1)
Net mark-to market gains (losses)	357	(693)	507
Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	404	(607)	460
Reclassification to realized at settlement		8	53
Net mark-to market gains (losses)		(599)	513
Operating Revenue [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	0	0	7
Intersegment Eliminations [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	0	(6)
Reclassification to realized at settlement	0	0	13
Net mark-to market gains (losses)	0	0	7
Intersegment Eliminations [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	0	0
Reclassification to realized at settlement	0	0	0
Interest Rate Swap [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	107	(94)	(6)
Interest Rate Swap [Member] | Intersegment Eliminations [Member] | Operating Revenue [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	0	0	0
Other Segments [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	0	0
Reclassification to realized at settlement	0	0	0
Net mark-to market gains (losses)	0	0	0
Other Segments [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in fair value of commodity positions	36	(100)	0
Reclassification to realized at settlement	64	0	0
Net mark-to market gains (losses)	100	(100)	0
Other Segments [Member] | Interest Rate Swap [Member] | Interest Expense [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	100	(100)	0
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value of commodity positions	404	(607)	466
Reclassification to realized at settlement	(154)	8	40
Net mark-to market gains (losses)	250	(599)	506
Exelon Generation Co L L C [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	0	0
Reclassification to realized at settlement	0	0	0
Net mark-to market gains (losses)	0	0	0
Exelon Generation Co L L C [Member] | Purchased Power [Member]
Derivative [Line Items]
Change in fair value of commodity positions	13	8	(5)
Reclassification to realized at settlement	(6)	(2)	(1)
Net mark-to market gains (losses)	257	(593)	500
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	759	(413)	286
Reclassification to realized at settlement	(563)	231	(64)
Net mark-to market gains (losses)	196	(182)	222
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Change in fair value of commodity positions	(355)	(194)	180
Reclassification to realized at settlement	409	(223)	104
Net mark-to market gains (losses)	54	(417)	284
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	13	10	(1)
Reclassification to realized at settlement	(6)	(2)	(1)
Net mark-to market gains (losses)	203	(174)	220
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	0	0
Reclassification to realized at settlement	0	0	0
Net mark-to market gains (losses)	54	(417)	284
Exelon Generation Co L L C [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	(2)	(4)
Reclassification to realized at settlement	0	0	0
Net mark-to market gains (losses)	0	(2)	(4)
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Purchased Power [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	7	6	(6)
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Operating Revenue [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	7	8	(2)
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	0	0	0
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Interest Expense [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	$ 0	$ (2)	$ (4)

Derivative Financial Instrum112

Derivative Financial Instruments - Summary of Proprietary Trading Activities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Net mark-to-market gains (losses)	$ (8)	$ (26)	$ (39)
Change in fair value	8	1	1
Reclassification to realized at settlement	(10)	3	(3)
Operating Revenue [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)	(6)	(30)	(37)
Change in fair value	8	(1)	(22)
Reclassification to realized at settlement	(14)	(29)	(15)
Interest Rate Swap [Member] | Operating Revenue [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)	$ (2)	$ 4	$ (2)

Derivative Financial Instrum113

Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - Exelon Generation Co L L C [Member] $ in Millions	Dec. 31, 2015USD ($)
Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	$ 1,397
Non-investment grade	67
Internally rated—investment grade	521
Internally rated—non-investment grade	77
Total	2,062
Credit Collateral [Member]
Derivative [Line Items]
Investment grade	50
Non-investment grade	25
Internally rated—investment grade	0
Internally rated—non-investment grade	7
Total	82
Net Exposure [Member]
Derivative [Line Items]
Investment grade	1,347
Non-investment grade	42
Internally rated—investment grade	521
Internally rated—non-investment grade	70
Total	1,980
Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	1
Non-investment grade	0
Internally rated—investment grade	0
Internally rated—non-investment grade	0
Total	1
Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	432
Non-investment grade	0
Internally rated—investment grade	0
Internally rated—non-investment grade	0
Total	$ 432

Derivative Financial Instrum114

Derivative Financial Instruments - Net Credit Exposure by Type of Counterparty (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Cash collateral held	$ 13
Letters of credit held	69
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral held	21	$ 77
Letters of credit held	78	$ 24
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Derivative [Line Items]
Financial institutions	187
Investor-owned utilities, marketers, power producers	886
Energy cooperatives and municipalities	872
Other	35
Total	$ 1,980

Derivative Financial Instrum115

Derivative Financial Instruments - Summary of Credit Risk Related Contingent Features (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	[1]	$ (932)	$ (1,433)
Offsetting Fair Value of In-the-Money Contracts Under Master Netting Arrangements	[2]	684	1,140
Derivative liabilities, fair value	[3]	$ (248)	$ (293)
[1]	(a)Amount represents the gross fair value of out-of-the-money derivative contracts containing credit-risk-related contingent features ignoring the effects of master netting agreements.
[2]	(b)Amount represents the offsetting fair value of in-the-money derivative contracts under legally enforceable master netting agreements with the same counterparty, which reduces the amount of any liability for which a Registrant could potentially be required to post collateral.
[3]	(c)Amount represents the net fair value of out-of-the-money derivative contracts containing credit-risk related contingent features after considering the mitigating effects of offsetting positions under master netting arrangements and reflects the actual net liability upon which any potential contingent collateral obligations would be based.

Debt and Credit Agreements - Co

Debt and Credit Agreements - Commercial Paper Borrowings Outstanding (Details) - USD ($)		Dec. 31, 2015		Dec. 31, 2014	May. 30, 2014		Mar. 28, 2014	[1],[2]	Dec. 31, 2013
Commercial Paper [Member]
Short-term Debt [Line Items]
Maximum Program Size	[1],[2]	$ 8,150,000,000		$ 8,300,000,000
Outstanding commercial paper		504,000,000		$ 424,000,000
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size	[3]	$ 8,425,000,000
Exelon Corporate [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		0.88%		0.53%					0.35%
Exelon Corporate [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Maximum Program Size	[1],[2]			$ 500,000,000
Outstanding commercial paper		$ 0		0
Exelon Corporate [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size		500,000,000	[3]		$ 500,000,000	[1],[2]
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Bilateral letters of credit		275,000,000		200,000,000
Exelon Generation Co L L C [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Maximum Program Size	[1],[2]	5,450,000,000		5,600,000,000
Outstanding commercial paper		$ 0		$ 0
Average Interest Rate on Commercial Paper Borrowings		0.49%		0.32%
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size	[3]	$ 5,725,000,000
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		0.89%		0.50%					0.37%
Commonwealth Edison Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Maximum Program Size	[1],[2]			$ 1,000,000,000
Outstanding commercial paper		$ 294,000,000		$ 304,000,000
Average Interest Rate on Commercial Paper Borrowings		0.53%		0.33%
Commonwealth Edison Co [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size		$ 1,000,000,000	[3]				$ 1,000,000,000
PECO Energy Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Maximum Program Size	[1],[2]			$ 600,000,000
Outstanding commercial paper		0		$ 0
PECO Energy Co [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size		$ 600,000,000	[3]		600,000,000	[1],[2]
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		0.87%		0.61%					0.31%
Baltimore Gas and Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Maximum Program Size	[1],[2]			$ 600,000,000	$ 600,000,000
Outstanding commercial paper		$ 210,000,000		$ 120,000,000
Average Interest Rate on Commercial Paper Borrowings		0.48%		0.29%
Baltimore Gas and Electric Company [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size	[3]	$ 600,000,000
[1]	Excludes additional credit facilities for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. The agreements for these facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of December 31, 2015, letters of credit issued under these facilities totaled $7 million, $14 million, $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively.
[2]	Reflects aggregate bank commitments under the revolving and bilateral credit agreements (with the exception of $275 million and $200 million bilateral agreements for Generation as of December 31, 2015 and 2014, respectively) that backstop the commercial paper program. See discussion and Credit Facilities table below for items affecting effective program size.
[3]	Excludes additional credit facilities for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. The agreements for these facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of December 31, 2015, letters of credit issued under these facilities totaled $7 million, $14 million, $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively.

Debt and Credit Agreements - Su

Debt and Credit Agreements - Summary of Bank Commitments, Credit Facility Borrowings and Available Capacity (Details) - USD ($)		Dec. 31, 2015		Dec. 31, 2014	May. 30, 2014	[4],[5]	Mar. 28, 2014	[4],[5]
Short-term Debt [Line Items]
Facility draws		$ 0
Outstanding letters of credit	[1]	1,478,000,000
Actual available capacity		6,947,000,000
To Support Additional Commercial Paper	[2]	6,341,000,000
Exelon Corporate [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	26,000,000
Actual available capacity		474,000,000
To Support Additional Commercial Paper	[2]	474,000,000
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	1,449,000,000
Actual available capacity		4,276,000,000
To Support Additional Commercial Paper	[2]	4,174,000,000
Credit facility agreements with minority and community banks		50,000,000
Letters of credit		7,000,000
Bilateral letters of credit		275,000,000		$ 200,000,000
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	2,000,000
Actual available capacity		998,000,000
To Support Additional Commercial Paper	[2]	704,000,000
Credit facility agreements with minority and community banks		34,000,000
Letters of credit		14,000,000
PECO Energy Co [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	1,000,000
Actual available capacity		599,000,000
To Support Additional Commercial Paper	[2]	599,000,000
Credit facility agreements with minority and community banks		34,000,000
Letters of credit		21,000,000
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	0
Actual available capacity		600,000,000
To Support Additional Commercial Paper	[2]	390,000,000
Credit facility agreements with minority and community banks		5,000,000
Letters of credit		2,000,000
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size	[3]	8,425,000,000
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Short-term Debt [Line Items]
Maximum Program Size		500,000,000	[3]		$ 500,000,000
Revolving Credit Facility [Member] | Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Maximum Program Size	[3]	5,725,000,000
Revolving Credit Facility [Member] | Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Maximum Program Size		1,000,000,000	[3]				$ 1,000,000,000
Revolving Credit Facility [Member] | PECO Energy Co [Member]
Short-term Debt [Line Items]
Maximum Program Size		600,000,000	[3]		$ 600,000,000
Revolving Credit Facility [Member] | Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Maximum Program Size	[3]	$ 600,000,000
[1]	Excludes nonrecourse debt letters of credit, see discussion below on Continental Wind.
[2]	Excludes $275 million bilateral credit facilities that do not back Generation’s commercial paper program
[3]	Excludes additional credit facilities for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. The agreements for these facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of December 31, 2015, letters of credit issued under these facilities totaled $7 million, $14 million, $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively.
[4]	Excludes additional credit facilities for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. The agreements for these facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of December 31, 2015, letters of credit issued under these facilities totaled $7 million, $14 million, $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively.
[5]	Reflects aggregate bank commitments under the revolving and bilateral credit agreements (with the exception of $275 million and $200 million bilateral agreements for Generation as of December 31, 2015 and 2014, respectively) that backstop the commercial paper program. See discussion and Credit Facilities table below for items affecting effective program size.

Debt and Credit Agreements -118

Debt and Credit Agreements - Summary of Short-term Borrowing Activities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average borrowings	$ 461	$ 415	$ 203
Maximum borrowings outstanding	$ 684	$ 597	$ 446
Average interest rates, computed on a daily basis	0.53%	0.33%	0.40%
Average interest rates at year end	0.89%	0.50%	0.37%
Exelon Corporate [Member]
Short-term Debt [Line Items]
Average borrowings	$ 499	$ 571	$ 254
Maximum borrowings outstanding	$ 739	$ 1,164	$ 682
Average interest rates, computed on a daily basis	0.53%	0.32%	0.37%
Average interest rates at year end	0.88%	0.53%	0.35%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Average borrowings	$ 1	$ 93	$ 42
Maximum borrowings outstanding	$ 50	$ 552	$ 291
Average interest rates, computed on a daily basis	0.49%	0.32%	0.32%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 37	$ 64	$ 35
Maximum borrowings outstanding	$ 210	$ 180	$ 135
Average interest rates, computed on a daily basis	0.48%	0.29%	0.31%
Average interest rates at year end	0.87%	0.61%	0.31%

Debt and Credit Agreements - Na

Debt and Credit Agreements - Narrative (Details) $ / shares in Units, shares in Millions

Dec. 02, 2015USD ($)

Sep. 30, 2013USD ($)MW

Jun. 30, 2014USD ($)$ / sharesshares

Sep. 30, 2012USD ($)MW

Jul. 31, 2011USD ($)MW

Dec. 31, 2015USD ($)

Jan. 05, 2016USD ($)

Oct. 30, 2015USD ($)

Jun. 30, 2015USD ($)

Dec. 31, 2014USD ($)

Sep. 30, 2014USD ($)

Sep. 18, 2014USD ($)

May. 31, 2014USD ($)

May. 30, 2014USD ($)

[3],[4]

Mar. 28, 2014USD ($)

[3],[4]

Feb. 06, 2014USD ($)

Dec. 31, 2011USD ($)

Oct. 31, 2011USD ($)

Jun. 30, 2011USD ($)

Debt Instrument [Line Items]

Outstanding letters of credit

[1]

$ 1,478,000,000

Bridge loan

$ 3,200,000,000

$ 7,200,000,000

Long-term debt, gross

25,113,000,000

$ 20,864,000,000

Long-term debt

25,761,000,000

Redemption of debt

44,000,000

Collateral amount of debt

2,400,000,000

Outstanding borrowings/facility draws

0

Debt Instrument, Fee Amount

$ 5,000,000

Payments of Debt Issuance Costs

4,000,000

Write off of Deferred Debt Issuance Cost

9,000,000

Redemption Premium

9,000,000

Designated as Hedging Instrument [Member]

Debt Instrument [Line Items]

Notional amount of preissuance interest rate cash flow hedge derivatives

738,000,000

Senior Notes [Member]

Debt Instrument [Line Items]

Long-term debt, gross

9,803,000,000

7,071,000,000

Principal amount of debt

3,300,000,000

$ 4,200,000,000

Redemption of debt

868,000,000

Junior Subordinated Debt [Member]

Debt Instrument [Line Items]

Long-term debt, gross

$ 1,150,000,000

$ 1,150,000,000

1,150,000,000

Equity units issued | shares

23

Conversion price | $ / shares

$ 50

Proceeds from issuance of subordinated long-term debt

$ 1,110,000,000

Underwriting fee

35,000,000

Long-term debt

$ 131,000,000

Maximum [Member]

Debt Instrument [Line Items]

Basis points adders for prime-based borrowings

0.065%

Basis points adders for LIBOR-based borrowings

0.00165

Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

[2]

$ 8,425,000,000

Commonwealth Edison Co [Member]

Debt Instrument [Line Items]

Outstanding letters of credit

[1]

$ 2,000,000

Basis points adders for prime-based borrowings

0.075%

Basis points adders for LIBOR-based borrowings

0.01075

Long-term debt, gross

$ 6,567,000,000

5,977,000,000

Long-term debt

6,773,000,000

Outstanding borrowings/facility draws

0

Commonwealth Edison Co [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

1,000,000,000

[2]

$ 1,000,000,000

Exelon Corporate [Member]

Debt Instrument [Line Items]

Outstanding letters of credit

[1]

$ 26,000,000

Basis points adders for prime-based borrowings

0.275%

Basis points adders for LIBOR-based borrowings

0.01275

Long-term debt, gross

$ 5,853,000,000

3,916,000,000

Long-term debt

5,853,000,000

Principal amount of debt

$ 1,900,000,000

Outstanding borrowings/facility draws

0

Exelon Corporate [Member] | Junior Subordinated Debt [Member]

Debt Instrument [Line Items]

Long-term debt, gross

1,150,000,000

1,150,000,000

Exelon Corporate [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

500,000,000

[2]

$ 500,000,000

Exelon Generation Co L L C [Member]

Debt Instrument [Line Items]

Outstanding letters of credit

[1]

$ 1,449,000,000

Basis points adders for prime-based borrowings

0.275%

Basis points adders for LIBOR-based borrowings

0.01275

Long-term debt, gross

$ 8,919,000,000

8,134,000,000

Long-term debt

8,919,000,000

Outstanding borrowings/facility draws

0

Exelon Generation Co L L C [Member] | ExGen Texas Power [Member] | Interest Rate Swap [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

2.34%

Non-recourse debt, interest rate swap

$ 505,000,000

Exelon Generation Co L L C [Member] | ExgenRenewablesI425June62021[Member] | Interest Rate Swap [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

2.03%

Non-recourse debt, interest rate swap

$ 240,000,000

Exelon Generation Co L L C [Member] | Constellation Solar Horizons Financing [Member]

Debt Instrument [Line Items]

Non-recourse debt, interest rate swap

$ 29,000,000

Non-recourse debt, commitment

$ 38,000,000

Generation capacity of portfolio | MW

16

Outstanding borrowings/facility draws

32,000,000

Non-recourse debt, hedge percentage

75.00%

Exelon Generation Co L L C [Member] | Senior Notes [Member]

Debt Instrument [Line Items]

Long-term debt, gross

5,971,000,000

5,771,000,000

Principal amount of debt

750,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Continetal Wind [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

$ 131,000,000

Outstanding letters of credit

99,000,000

Interest rate on long-term debt

6.00%

Principal amount of debt

$ 613,000,000

Generation capacity of portfolio | MW

667

Aggregate bank commitments under unsecured revolving credit facilities

$ 10,000,000

Non-recourse debt

572,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExGen Texas Power [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

4.75%

Principal amount of debt

$ 675,000,000

Non-recourse debt

666,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExgenRenewablesI425June62021[Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

4.25%

Long-term debt

$ 300,000,000

Non-recourse debt

258,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | DOE Project Financing, 3.092% January 2, 2037 [Member]

Debt Instrument [Line Items]

Outstanding letters of credit

69,000,000

Non-recourse debt, commitment

$ 646,000,000

Non-recourse debt

574,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Sacramento PV Energy [Member]

Debt Instrument [Line Items]

Non-recourse debt, interest rate swap

$ 30,000,000

Generation capacity of portfolio | MW

30

Outstanding borrowings/facility draws

33,000,000

Non-recourse debt

$ 41,000,000

Non-recourse debt, hedge percentage

75.00%

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Denver International Airport [Member]

Debt Instrument [Line Items]

Outstanding borrowings/facility draws

$ 7,000,000

Non-recourse debt

7,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Holyoke [Member]

Debt Instrument [Line Items]

Outstanding borrowings/facility draws

$ 11,000,000

Non-recourse debt

10,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Upstream Gas Property [Member]

Debt Instrument [Line Items]

Non-recourse debt, commitment

$ 85,000,000

Non-recourse debt, commitment increase available

$ 500,000,000

Outstanding borrowings/facility draws

68,000,000

Exelon Generation Co L L C [Member] | Sumitomo Bank [Member]

Debt Instrument [Line Items]

Outstanding letters of credit

$ 100,000,000

Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member]

Debt Instrument [Line Items]

Outstanding letters of credit

$ 150,000,000

Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

[2]

5,725,000,000

PECO Energy Co [Member]

Debt Instrument [Line Items]

Outstanding letters of credit

[1]

$ 1,000,000

Basis points adders for prime-based borrowings

0.00%

Basis points adders for LIBOR-based borrowings

0.009

Long-term debt, gross

$ 2,600,000,000

2,250,000,000

Long-term debt

2,784,000,000

Outstanding borrowings/facility draws

0

PECO Energy Co [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

600,000,000

[2]

$ 600,000,000

Baltimore Gas and Electric Company [Member]

Debt Instrument [Line Items]

Outstanding letters of credit

[1]

$ 0

Basis points adders for prime-based borrowings

0.00%

Basis points adders for LIBOR-based borrowings

0.01

Long-term debt, gross

$ 1,870,000,000

$ 1,945,000,000

Long-term debt

2,128,000,000

Outstanding borrowings/facility draws

0

Baltimore Gas and Electric Company [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

[2]

$ 600,000,000

[1]

Excludes nonrecourse debt letters of credit, see discussion below on Continental Wind.

[2]

Excludes additional credit facilities for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. The agreements for these facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of December 31, 2015, letters of credit issued under these facilities totaled $7 million, $14 million, $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively.

[3]

Excludes additional credit facilities for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. The agreements for these facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of December 31, 2015, letters of credit issued under these facilities totaled $7 million, $14 million, $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively.

[4]

Reflects aggregate bank commitments under the revolving and bilateral credit agreements (with the exception of $275 million and $200 million bilateral agreements for Generation as of December 31, 2015 and 2014, respectively) that backstop the commercial paper program. See discussion and Credit Facilities table below for items affecting effective program size.

Debt and Credit Agreements -120

Debt and Credit Agreements - Summary of Credit Facility Thresholds (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	$ 1,478	[1]
Credit agreement threshold	2.50 to 1
Credit agreement threshold	2.50
Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	$ 1,449	[1]
Credit agreement threshold	3.00 to 1
Credit agreement threshold	3
Commonwealth Edison Co [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	$ 2	[1]
Credit agreement threshold	2.00 to 1
Credit agreement threshold	2
PECO Energy Co [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	$ 1	[1]
Credit agreement threshold	2.00 to 1
Credit agreement threshold	2
Baltimore Gas and Electric Company [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	$ 0	[1]
Credit agreement threshold	2.00 to 1
Credit agreement threshold	2
[1]	Excludes nonrecourse debt letters of credit, see discussion below on Continental Wind.

Debt and Credit Agreements -121

Debt and Credit Agreements - Summary of Interest Coverage Ratios (Details)	Dec. 31, 2015
Debt Instrument [Line Items]
Interest coverage ratio	977.00%
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Interest coverage ratio	1231.00%
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Interest coverage ratio	725.00%
PECO Energy Co [Member]
Debt Instrument [Line Items]
Interest coverage ratio	894.00%
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Interest coverage ratio	1066.00%

Debt and Credit Agreements -122

Debt and Credit Agreements - Summary of Outstanding Long-term Debt (Details) - USD ($)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Jun. 30, 2014
Debt Instrument [Line Items]
Maximum interest rate on long-term debt		3.95%
Long-term Debt, Gross		$ 25,113,000,000	$ 20,864,000,000
Unamortized debt discount and premium, net		(63,000,000)	(37,000,000)
Long-term debt (including amounts due within one year) (a)		275,000,000	333,000,000
Fair value hedge carrying value adjustment, net		0	4,000,000
Long-term debt due within one year		(1,500,000,000)	(1,802,000,000)
Long-term debt		23,645,000,000	19,212,000,000
Long-term debt to financing trusts	[1]	641,000,000	641,000,000
Total long-term debt to financing trusts		648,000,000	648,000,000
Unamortized Debt Issuance Expense	[2]	$ (180,000,000)	(150,000,000)
ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[1]	6.35%
Long-term debt to financing trusts	[1]	$ 206,000,000	206,000,000
PECO Trust Three Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[1]	7.38%
Long-term debt to financing trusts	[1]	$ 81,000,000	81,000,000
PECO Trust Four Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[1]	5.75%
Long-term debt to financing trusts	[1]	$ 103,000,000	103,000,000
BGE Trust Member [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[1]	6.20%
Long-term debt to financing trusts	[1]	$ 258,000,000	258,000,000
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Maximum interest rate on long-term debt		6.50%
Long-term Debt, Gross		$ 1,150,000,000	1,150,000,000	$ 1,150,000,000
Secured Debt [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	[3]	1.20%
Maximum interest rate on long-term debt	[3]	6.45%
Long-term Debt, Gross	[3]	$ 9,019,000,000	8,079,000,000
Unsecured Debt [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.80%
Maximum interest rate on long-term debt		6.35%
Long-term Debt, Gross		$ 1,750,000,000	1,750,000,000
Rate Stabilization Bonds [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		5.72%
Maximum interest rate on long-term debt		5.82%
Long-term Debt, Gross		$ 120,000,000	195,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		1.55%
Maximum interest rate on long-term debt		7.60%
Long-term Debt, Gross		$ 9,803,000,000	7,071,000,000
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		3.15%
Maximum interest rate on long-term debt		3.35%
Long-term Debt, Gross		$ 127,000,000	70,000,000
Pollution Control Notes [Member]
Debt Instrument [Line Items]
Maximum interest rate on long-term debt		2.70%
Long-term Debt, Gross		$ 435,000,000	0
Non Recourse Fixed Rate [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.293%
Maximum interest rate on long-term debt		6.00%
Long-term Debt, Gross		$ 1,162,000,000	1,166,000,000
Non Recourse Variable Rate [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.418%
Maximum interest rate on long-term debt		5.00%
Long-term Debt, Gross		$ 1,058,000,000	1,101,000,000
Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	[4]	1.43%
Maximum interest rate on long-term debt	[4]	7.825%
Long-term Debt, Gross	[4],[5]	$ 314,000,000	174,000,000
Unamortized Debt Issuance Expense	[2]	(7,000,000)	(7,000,000)
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, noncurrent		$ 29,000,000	32,000,000
Due in 2015
Due in 2016		$ 4,000,000
Due in 2017		4,000,000
Due in 2018		5,000,000
Due in 2019		4,000,000
Due in 2020		8,000,000
Software License Arrangement [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 111,000,000
contract Payments Junior Subordinate Debt [Member]
Debt Instrument [Line Items]
Maximum interest rate on long-term debt		2.50%
Long-term Debt, Gross		$ 64,000,000	108,000,000
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		8,919,000,000	8,134,000,000
Unamortized debt discount and premium, net		(17,000,000)	(14,000,000)
Long-term debt (including amounts due within one year) (a)		127,000,000	146,000,000
Long-term debt due within one year		(90,000,000)	(614,000,000)
Long-term debt		7,936,000,000	6,639,000,000
Long-term debt to financing trusts		933,000,000	943,000,000
Debt and Capital Lease Obligations		8,869,000,000	7,582,000,000
Capital lease obligations, noncurrent		21,000,000	24,000,000
Due in 2016		4,000,000
Due in 2017		4,000,000
Due in 2018		5,000,000
Due in 2019		4,000,000
Unamortized Debt Issuance Expense	[6]	$ (70,000,000)	(70,000,000)
Exelon Generation Co L L C [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.00%
Maximum interest rate on long-term debt		7.60%
Long-term Debt, Gross		$ 5,971,000,000	5,771,000,000
Exelon Generation Co L L C [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		3.15%
Long-term Debt, Gross			70,000,000
Exelon Generation Co L L C [Member] | Pollution Control Notes [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.50%
Long-term Debt, Gross		$ 435,000,000	0
Exelon Generation Co L L C [Member] | Non Recourse Fixed Rate [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.293%
Maximum interest rate on long-term debt		6.00%
Long-term Debt, Gross		$ 1,162,000,000	1,166,000,000
Exelon Generation Co L L C [Member] | Non Recourse Variable Rate [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.418%
Maximum interest rate on long-term debt		5.00%
Long-term Debt, Gross		$ 1,058,000,000	1,101,000,000
Exelon Generation Co L L C [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		1.43%
Maximum interest rate on long-term debt	[7]	7.825%
Long-term Debt, Gross	[7],[8]	$ 166,000,000	26,000,000
Long-term debt		100,000,000
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		6,567,000,000	5,977,000,000
Unamortized debt discount and premium, net		(20,000,000)	(19,000,000)
Long-term debt due within one year		(665,000,000)	(260,000,000)
Long-term debt		5,844,000,000	5,665,000,000
Long-term debt to financing trusts		205,000,000	205,000,000
Total long-term debt to financing trusts		206,000,000	206,000,000
Debt and Capital Lease Obligations		5,844,000,000	5,665,000,000
Unamortized Debt Issuance Expense	[9]	$ (38,000,000)	(33,000,000)
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[10]	6.35%
Long-term debt to financing trusts		$ 206,000,000
Total long-term debt to financing trusts		205,000,000	205,000,000
Unamortized Debt Issuance Expense	[9]	$ (1,000,000)	(1,000,000)
Commonwealth Edison Co [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	[11]	6.95%
Maximum interest rate on long-term debt	[11]	7.4865%
Long-term Debt, Gross	[11]	$ 148,000,000	148,000,000
Commonwealth Edison Co [Member] | Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, noncurrent		8,000,000	8,000,000
Due in 2020		$ 1,000,000
Commonwealth Edison Co [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	[12]	1.95%
Maximum interest rate on long-term debt	[12]	6.45%
Long-term Debt, Gross	[12]	$ 6,419,000,000	5,829,000,000
PECO Energy Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		2,600,000,000	2,250,000,000
Unamortized debt discount and premium, net		(5,000,000)	(4,000,000)
Long-term debt		2,280,000,000	2,232,000,000
Long-term debt to financing trusts		184,000,000	184,000,000
Long-term debt due within one year		(300,000,000)	0
Debt and Capital Lease Obligations		2,280,000,000	2,232,000,000
Unamortized Debt Issuance Expense	[13]	$ (15,000,000)	(14,000,000)
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[14]	7.38%
Long-term debt to financing trusts	[14]	$ 81,000,000	81,000,000
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[14]	5.75%
Long-term debt to financing trusts	[14]	$ 103,000,000	103,000,000
PECO Energy Co [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	[15]	1.20%
Maximum interest rate on long-term debt	[15]	5.95%
Long-term Debt, Gross	[15]	$ 2,600,000,000	2,250,000,000
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		1,870,000,000	1,945,000,000
Unamortized debt discount and premium, net		(3,000,000)	(3,000,000)
Long-term debt (including amounts due within one year) (a)			1,932,000,000
Long-term debt		1,480,000,000	1,857,000,000
Long-term debt to financing trusts		252,000,000	252,000,000
Total long-term debt to financing trusts		258,000,000	258,000,000
Long-term debt due within one year		(378,000,000)	(75,000,000)
Long-term debt		1,480,000,000	1,857,000,000
Unamortized Debt Issuance Expense	[16]	$ (9,000,000)	(10,000,000)
Baltimore Gas and Electric Company [Member] | BGE Trust Member [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[17]	6.20%
Long-term debt to financing trusts			252,000,000
Total long-term debt to financing trusts		$ 258,000,000	258,000,000
Unamortized Debt Issuance Expense	[16]	$ (6,000,000)	(6,000,000)
Baltimore Gas and Electric Company [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.80%
Maximum interest rate on long-term debt		6.35%
Long-term Debt, Gross		$ 1,750,000,000	1,750,000,000
Baltimore Gas and Electric Company [Member] | Rate Stabilization Bonds [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		5.72%
Maximum interest rate on long-term debt		5.82%
Long-term Debt, Gross		$ 120,000,000	$ 195,000,000
[1]	Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets.
[2]	Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information.
[3]	Substantially all of ComEd’s assets other than expressly excepted property and substantially all of PECO’s assets are subject to the liens of their respective mortgage indentures.
[4]	Includes capital lease obligations of $29 million and $32 million at December 31, 2015 and 2014, respectively. Lease payments of $4 million, $4 million, $4 million, $5 million, $4 million, and $8 million will be made in 2016, 2017, 2018, 2019, 2020 and thereafter, respectively.
[5]	Includes financing related to Albany Green Energy, LLC (AGE), which is a consolidated variable interest entity (see Note 2 - Variable Interest Entities for additional information). The agreement is scheduled to expire on November 17, 2017, at a variable rate equal to LIBOR plus 1.25%. As of December 31, 2015, $100 million was outstanding.
[6]	Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information.
[7]	Includes Generation’s capital lease obligations of $21 million and $24 million at December 31, 2015 and 2014, respectively. Generation will make lease payments of $4 million, $4 million, $4 million, $5 million and $4 million in 2016, 2017, 2018, 2019, 2020, respectively. The capital lease matures in 2020.
[8]	Includes financing related to Albany Green Energy, LLC (AGE), which is a consolidated variable interest entity (see Note 2 - Variable Interest Entities for additional information). The agreement is scheduled to expire on November 17, 2017, at a variable rate equal to LIBOR plus 1.25%. As of December 31, 2015, $100 million was outstanding.
[9]	Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information.
[10]	Amount owed to this financing trust is recorded as Long-term debt to financing trust within ComEd’s Consolidated Balance Sheets.
[11]	Includes ComEd’s capital lease obligations of $8 million at both December 31, 2015 and 2014, respectively. Lease payments of less than $1 million will be made from 2016 through expiration at 2053.
[12]	Substantially all of ComEd’s assets other than expressly excepted property are subject to the lien of its mortgage indenture.
[13]	Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information.
[14]	Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets.
[15]	Substantially all of PECO’s assets are subject to the lien of its mortgage indenture.
[16]	Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information.
[17]	Amount owed to this financing trust is recorded as Long-term debt to financing trust within BGE’s Consolidated Balance Sheets.

Debt and Credit Agreements - Sc

Debt and Credit Agreements - Schedule of Long-term Debt Maturities (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
2,015		$ 1,487
2,016		1,841
2,017		1,393
2,018		973
2,019		3,311
Thereafter	[1]	16,756
Total		25,761
Long-term debt to financing trusts	[2]	641	$ 641
BGE Trust Member [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	[2]	258	258
ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	[2]	206	206
PECO Financing Trusts [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	[2]	184
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
2,015		90
2,016		805
2,017		53
2,018		673
2,019		1,911
Thereafter		5,387
Total		8,919
Long-term debt to financing trusts		933	943
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
2,015		665
2,016		425
2,017		840
2,018		300
2,019		500
Thereafter	[3]	4,043
Total		6,773
Long-term debt to financing trusts		205	205
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts		206
PECO Energy Co [Member]
Debt Instrument [Line Items]
2,015		300
2,016		0
2,017		500
2,018		0
2,019		0
Thereafter	[4]	1,984
Total		2,784
Long-term debt to financing trusts		184	184
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
2,015		378
2,016		42
2,017		0
2,018		0
2,019		0
Thereafter	[5]	1,708
Total		2,128
Long-term debt to financing trusts		$ 252	252
Baltimore Gas and Electric Company [Member] | BGE Trust Member [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts			$ 252
[1]	Includes $648 million due to ComEd, PECO and BGE financing trusts.
[2]	Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets.
[3]	Includes $206 million due to ComEd financing trust.
[4]	Includes $184 million due to PECO financing trusts.
[5]	ncludes $258 million due to BGE financing trust.

Income Taxes - Components of In

Income Taxes - Components of Income Tax Expense (Benefit) from Continuing Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Income taxes	$ 1,073	$ 666	$ 1,044
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Income taxes	502	207	615
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Income taxes	280	268	152
PECO Energy Co [Member]
Income Taxes [Line Items]
Income taxes	143	114	162
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current	0	0	0
Income taxes	189	140	134
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Current	407	121	744
Deferred	566	576	140
Investment Tax Credit	22	20	15
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current	546	360	250
Deferred	16	(35)	360
Investment Tax Credit	19	16	11
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current	(80)	(171)	160
Deferred	310	395	(27)
Investment Tax Credit	2	2	2
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Current	64	28	126
Deferred	69	87	23
Investment Tax Credit	0	0	1
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current	25	24	9
Deferred	126	90	100
Investment Tax Credit	1	1	1
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Current	(86)	42	181
Deferred	208	(53)	(6)
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current	(90)	35	50
Deferred	49	(137)	(34)
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current	7	7	50
Deferred	45	39	(29)
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Current	(10)	(2)	16
Deferred	20	1	(2)
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Deferred	$ 39	$ 27	$ 26

Income Taxes - Reconciliation t

Income Taxes - Reconciliation to Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
U.S. Federal statutory rate	35.00%	35.00%	35.00%	[1]
State income taxes, net of Federal income tax benefit	3.70%	1.30%	4.80%	[1]
Qualified nuclear decommissioning trust fund loss	0.40%	(2.40%)	(3.70%)	[1]
Domestic production activities deduction	(0.70%)	(2.00%)	(0.00%)
Health care reform legislation	(0.00%)	(0.10%)	(0.10%)	[1]
Amortization of investment tax credit, including deferred taxes on basis difference	(0.90%)	(1.10%)	(1.90%)	[1]
Plant basis differences	(1.50%)	(1.90%)	(2.10%)	[1]
Statute of limitations expiration	(1.40%)	(2.60%)	(0.10%)
Production tax credits and other credits	(1.90%)	(2.40%)	(1.60%)	[1]
Non-controlling interest	0.30%	(1.80%)
Other	(0.00%)	0.20%	0.30%
Effective income tax rate	32.20%	26.80%	37.60%	[1]
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate	35.00%	35.00%	35.00%	[1]
State income taxes, net of Federal income tax benefit	1.00%	(1.90%)	1.80%	[1]
Qualified nuclear decommissioning trust fund loss	0.80%	(4.80%)	(6.10%)	[1]
Domestic production activities deduction	(1.30%)	(4.10%)	(0.00%)
Health care reform legislation	(0.00%)	(0.00%)	(0.00%)	[1]
Amortization of investment tax credit, including deferred taxes on basis difference	(1.50%)	(2.00%)	(3.00%)	[1]
Plant basis differences	(0.00%)	(0.00%)	(3.40%)	[1]
Statute of limitations expiration	(2.40%)	(5.30%)	(0.20%)
Production tax credits and other credits	(3.40%)	(4.80%)	(0.00%)	[1]
Non-controlling interest	0.50%	(3.70%)
Other	(0.00%)	1.10%	(0.40%)
Effective income tax rate	27.10%	16.90%	36.70%	[1]
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate	35.00%	35.00%	35.00%
State income taxes, net of Federal income tax benefit	4.90%	4.50%	3.40%
Qualified nuclear decommissioning trust fund loss	(0.00%)	(0.00%)	(0.00%)
Domestic production activities deduction	(0.00%)	(0.00%)	(0.00%)
Health care reform legislation	(0.00%)	(0.20%)	(0.70%)
Amortization of investment tax credit, including deferred taxes on basis difference	(0.30%)	(0.30%)	(0.60%)
Plant basis differences	(0.10%)	(0.10%)	(0.10%)
Statute of limitations expiration	(0.00%)	(0.00%)	(0.00%)
Production tax credits and other credits	(0.00%)	(0.00%)	(0.80%)
Non-controlling interest	0.00%
Other	(0.20%)	(0.30%)	(0.30%)
Effective income tax rate	39.70%	39.60%	37.90%
PECO Energy Co [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate	35.00%	35.00%	35.00%
State income taxes, net of Federal income tax benefit	1.00%	(0.10%)	1.60%
Qualified nuclear decommissioning trust fund loss	(0.00%)	(0.00%)	(0.00%)
Domestic production activities deduction	(0.00%)	(0.00%)	(0.00%)
Health care reform legislation	(0.00%)	(0.00%)	(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)	(0.10%)
Plant basis differences	(8.70%)	(10.40%)	(0.00%)
Statute of limitations expiration		(0.00%)	(0.00%)
Production tax credits and other credits	(0.00%)	(0.00%)	(7.10%)
Non-controlling interest	0.00%
Other	(0.20%)	(0.10%)	0.30%
Effective income tax rate	27.40%	24.50%	29.10%
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate	35.00%	35.00%	35.00%	[2]
State income taxes, net of Federal income tax benefit	5.30%	5.00%	4.90%	[2]
Qualified nuclear decommissioning trust fund loss	(0.00%)	(0.00%)	(0.00%)	[2]
Domestic production activities deduction	(0.00%)	(0.00%)	(0.00%)
Health care reform legislation	(0.10%)	(0.20%)	(0.20%)	[2]
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.30%)	(0.00%)	[2]
Plant basis differences	(0.70%)	0.20%	(0.00%)	[2]
Statute of limitations expiration	(0.00%)	(0.00%)	(0.00%)
Production tax credits and other credits	(0.00%)	(0.00%)	(0.20%)	[2]
Non-controlling interest	0.00%
Other	(0.00%)	0.20%	0.90%
Effective income tax rate	39.60%	39.90%	39.00%	[2]
[1]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246QzQzNkQ0QjY1NjJBRURBNTg3NjQxMjI1RThCMzFDMkMM}
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246QTM3RjVDOEFBRTExN0QzNDRCRUQxMjI1RThCRDk5NTcM}

Income Taxes - Tax Effects of T

Income Taxes - Tax Effects of Temporary Differences and Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Plant basis differences	$ (13,393)	$ (12,143)
Accrual based contracts	(136)	(178)
Derivatives and other financial instruments	(203)	(46)
Deferred pension and postretirement obligation	1,801	1,914
Nuclear decommissioning activities	(592)	(726)
Deferred debt refinancing costs	133	112
Regulatory assets and liabilities	(1,706)	(1,824)
Tax loss carryforward	103	111
Tax credit carryforward	327	97
Investment in CENG	(595)	(563)
Other, net	1,112	1,029
Deferred income tax liabilities (net)	13,149	12,217
Unamortized investment tax credits	(622)	(555)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(13,771)	(12,772)
Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(4,269)	(3,834)
Accrual based contracts	(136)	(178)
Derivatives and other financial instruments	(181)	(79)
Deferred pension and postretirement obligation	(371)	(390)
Nuclear decommissioning activities	(592)	(726)
Deferred debt refinancing costs	48	57
Regulatory assets and liabilities	0	0
Tax loss carryforward	56	48
Tax credit carryforward	374	143
Investment in CENG	(595)	(563)
Other, net	425	346
Deferred income tax liabilities (net)	5,241	5,176
Unamortized investment tax credits	(598)	(528)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(5,839)	(5,704)
Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(4,424)	(3,945)
Accrual based contracts	0	0
Derivatives and other financial instruments	(4)	(4)
Deferred pension and postretirement obligation	(505)	(543)
Nuclear decommissioning activities	0	0
Deferred debt refinancing costs	(15)	(18)
Regulatory assets and liabilities	(219)	(286)
Tax loss carryforward	0	0
Tax credit carryforward	0	0
Investment in CENG	0	0
Other, net	270	255
Deferred income tax liabilities (net)	4,897	4,541
Unamortized investment tax credits	(17)	(20)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(4,914)	(4,561)
PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(2,901)	(2,749)
Accrual based contracts	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(9)	2
Nuclear decommissioning activities	0	0
Deferred debt refinancing costs	(1)	(2)
Regulatory assets and liabilities	16	27
Tax loss carryforward	0	11
Tax credit carryforward	0	0
Investment in CENG	0	0
Other, net	105	111
Deferred income tax liabilities (net)	2,790	2,600
Unamortized investment tax credits	(2)	(2)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(2,792)	(2,602)
Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,821)	(1,660)
Accrual based contracts	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(47)	(53)
Nuclear decommissioning activities	0	0
Deferred debt refinancing costs	(4)	(4)
Regulatory assets and liabilities	(264)	(258)
Tax loss carryforward	33	39
Tax credit carryforward	0	0
Investment in CENG	0	0
Other, net	27	30
Deferred income tax liabilities (net)	2,076	1,906
Unamortized investment tax credits	(5)	(5)
Total deferred income tax liabilities (net) and unamortized investment tax credits	$ (2,081)	$ (1,911)

Income Taxes - Schedule of Carr

Income Taxes - Schedule of Carryforwards and Corresponding Valuation Allowances (Details) $ in Millions	Dec. 31, 2015USD ($)
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Amount	$ 416	[1]
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Amount	415	[1]
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Amount	0	[1]
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Amount	0	[1]
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Amount	0	[1]
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforward	2,086	[2]
State net operating losses and other credit carryforwards	117
Valuation allowance on state tax attributes	13
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforward	1,259	[3]
State net operating losses and other credit carryforwards	66
Valuation allowance on state tax attributes	11
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforward	0
State net operating losses and other credit carryforwards	0
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforward	0
State net operating losses and other credit carryforwards	0
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforward	618
State net operating losses and other credit carryforwards	34
Valuation allowance on state tax attributes	$ 1
[1]	Exelon’s and Generation's state net operating losses and other carryforwards, which are presented on a post-apportioned basis, will expire beginning in 201
[2]	6
[3]	6

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	$ 1,829	$ 2,175	$ 1,024
Increases based on tax positions related to current year	108	15	19
Changes to tax positions that only affect timing	(705)	(255)	649
Increases based on tax positions prior to current year	79	18	493
Decreases based on tax positions prior to current year	(116)	(1)	(6)
Decrease from settlements with taxing authorities	(31)	(35)
Decreases from expiration of statute of limitations	(86)	(88)	(4)
Unrecognized tax benefits - ending balance	1,078	1,829	2,175
Exelon Generation Co L L C [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	1,357	1,415	876
Increases based on tax positions related to current year	0	15	19
Changes to tax positions that only affect timing	(659)	33	36
Increases based on tax positions prior to current year	65	18	493
Decreases based on tax positions prior to current year	(112)	(2)	(5)
Decrease from settlements with taxing authorities	(31)	(34)
Decreases from expiration of statute of limitations	(86)	(88)	(4)
Unrecognized tax benefits - ending balance	534	1,357	1,415
Commonwealth Edison Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	149	324	67
Increases based on tax positions related to current year	0	0	0
Changes to tax positions that only affect timing	(7)	(175)	257
Increases based on tax positions prior to current year	0	0	0
Decreases based on tax positions prior to current year	0	0	0
Decrease from settlements with taxing authorities	0	0
Decreases from expiration of statute of limitations	0	0	0
Unrecognized tax benefits - ending balance	142	149	324
PECO Energy Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	44	44	44
Increases based on tax positions related to current year	0	0	0
Changes to tax positions that only affect timing	(44)	0	0
Increases based on tax positions prior to current year	0	0	0
Decreases based on tax positions prior to current year	0	0	0
Decrease from settlements with taxing authorities	0	0
Decreases from expiration of statute of limitations	0	0	0
Unrecognized tax benefits - ending balance	0	44	44
Baltimore Gas and Electric Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	0	0	0
Increases based on tax positions related to current year	106	0	0
Changes to tax positions that only affect timing	0	0	0
Increases based on tax positions prior to current year	14	0	0
Decreases based on tax positions prior to current year	0	0	0
Decrease from settlements with taxing authorities	0	0
Decreases from expiration of statute of limitations	0	0	0
Unrecognized tax benefits - ending balance	$ 120	$ 0	$ 0

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Mar. 31, 2015	Dec. 31, 1999
Income Taxes [Line Items]
Tax positions for which there is uncertainty about the timing of tax benefits		$ 540	$ 1,129
Unrecognized Tax Benefits		116	1	$ 6
Deferred gain on sale of property						$ 1,200
IRS asserted penalties for understatement of tax		90
Expected non-cash charge to earnings	$ 265
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position		760
Potential interest expense from a successful IRS challenge of the like-kind exchange position		280
Taxes accrued		293	305		$ 65
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits		112	2	5
Taxes accrued		186	248
Allocation of federal tax benefit under tax sharing agreement	77		55
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits		0	0	0
Taxes accrued		23	42
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits		0	0	0
Deferred gain on sale of property					$ 35
Expected non-cash charge to earnings	172
Noncash contributions from parent	$ 172
Taxes accrued		63	59
Intercompany Non Cash Allocation Of Tax Benefit		202	273	0
PECO Energy Co [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits		0	0	$ 0
Taxes accrued		4	3
Allocation of federal tax benefit under tax sharing agreement			$ 25
Maximum [Member]
Income Taxes [Line Items]
Cash tax benefit (detriment) as a result of repair costs deduction		$ 120

Income Taxes - Summary of Inter

Income Taxes - Summary of Interest Receivable (Payable) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Net interest receivable (payable) recognized related to uncertain tax positions	$ (288)	$ (310)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Net interest receivable (payable) recognized related to uncertain tax positions	80	40
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Net interest receivable (payable) recognized related to uncertain tax positions	(210)	(203)
PECO Energy Co [Member]
Income Taxes [Line Items]
Net interest receivable (payable) recognized related to uncertain tax positions	3	3
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Net interest receivable (payable) recognized related to uncertain tax positions	$ (1)	$ (1)

Income Taxes - Summary of In131

Income Taxes - Summary of Interest Expense (Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	$ (13)	$ (36)	$ 391
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	(31)	(50)	17
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	7	6	281
PECO Energy Co [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	0	0	(1)
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	$ 0	$ 1	$ 0

Asset Retirement Obligations -

Asset Retirement Obligations - Nuclear Decommissioning Asset Retirement Obligation Rollforward (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Net increase (decrease) resulting from updates to estimated future cash flows		$ 8		$ 16
Asset Retirement Obligation, Current		5		1
Nuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance		6,961	[1]	4,855
Accretion expense		387		334
Net increase (decrease) resulting from updates to estimated future cash flows		901		19
Costs incurred to decommission retired plants		(3)		(7)
ARO ending balance	[1]	8,246		6,961
Asset Retirement Obligation, Current		$ 7		8
CENG [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Consolidation of CENG	[2]			$ 1,760
[1]	Includes $7 million and $8 million as the current portion of the ARO at December 31, 2015 and 2014, respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.
[2]	(a)Represents the fair value of the CENG ARO liability as of April 1, 2014, the date of consolidation. See Note 5 — Investment in Constellation Energy Nuclear Group, LLC for additional information.

Asset Retirement Obligations133

Asset Retirement Obligations - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Asset Retirement Obligations [Line Items]
Nuclear decommissioning annual recovery current	$ 24,000,000
Percent of additional decommissioning shortfall with recourse	50.00%
Nuclear decommissioning trust funds	$ 10,342,000,000	$ 10,537,000,000
Minimum [Member]
Asset Retirement Obligations [Line Items]
Years after cessation of plant operations	20 years
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Increase (decrease) in asset retirement obligation		2,100,000,000
AssetRetirementObligationPeriodIncreaseSiteSecurity	$ 630,000,000
Net increase (decrease) resulting from updates to estimated future cash flows	8,000,000	16,000,000
Shortfall of decommissioning funds with recourse	$ 50,000,000
Percent of additional decommissioning shortfall with recourse	5.00%
Nuclear decommissioning trust funds	$ 10,342,000,000	10,537,000,000
Zion Station spent nuclear fuel obligation	84,000,000
ZionSolutions rent payable	1
EnergySolutions letter of credit	$ 200,000,000
Assumed annual after-tax return on NDT funds	2.00%
Assumed annual after-tax return on NDT funds for former PECO units	3.00%
Annual average accretion of the ARO	5.00%
Number of years used in present value measurement	30 years
Estimated annual after tax return on nuclear decommissioning funds lower bound	6.10%
Estimated annual after tax return on nuclear decommissioning funds upper bound	6.30%
Historical five-year annual average after-tax return on NDT funds	7.00%
AssetRetirementObligationPeriodIncreaseSNF	$ 285,000,000
Exelon Generation Co L L C [Member] | Minimum [Member]
Asset Retirement Obligations [Line Items]
Years after cessation of plant operations	10 years
Exelon Generation Co L L C [Member] | Maximum [Member]
Asset Retirement Obligations [Line Items]
Years after cessation of plant operations	70 years
Nuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Net increase (decrease) resulting from updates to estimated future cash flows	$ 901,000,000	$ 19,000,000
Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Increase (decrease) in asset retirement obligation	$ 1,300,000,000

Asset Retirement Obligations134

Asset Retirement Obligations - Unrealized Gain on NDT Funds (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Asset Retirement Obligations [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - Regulatory Agreement Units	[1]	$ (282)	$ 180	$ 406
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units	[2],[3]	(197)	134	146
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Unrealized Gain Loss Investment Income Pledged Assets		$ 7	$ 29	$ 7
[1]	Net unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities on Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates on Generation’s Consolidated Balance Sheets.
[2]	Excludes $7 million, $29 million and $7 million of net unrealized gains related to the Zion Station pledged assets in 2015, 2014 and 2013, respectively. Net unrealized gains related to Zion Station pledged assets are included in the Payable for Zion Station decommissioning on Exelon’s and Generation’s Consolidated Balance Sheets.
[3]	Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included within Other, net in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.

Asset Retirement Obligations135

Asset Retirement Obligations - Pledged Assets and Payables to ZionSolutions (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Asset Retirement Obligations [Line Items]
Carrying value of Zion Station pledged assets		$ 206	$ 319
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Carrying value of Zion Station pledged assets		206	319
Payable to Zion Solutions	[1]	189	292
Current portion of payable to Zion Solutions	[2]	99	137
Withdrawals by Zion Solutions to pay decommissioning costs	[3]	$ 786	$ 666
[1]	Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT Funds. The NDT Funds will be utilized to satisfy the tax obligations as gains and losses are realized.
[2]	Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets.
[3]	(c)Includes project expenses to decommission Zion Station and estimated tax payments on Zion Station NDT fund earnings.

Asset Retirement Obligations136

Asset Retirement Obligations - Non-Nuclear Asset Retirement Obligations Rollforward (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014
Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance		$ 346	[1]	$ 351
Net increase (decrease) resulting from updates to estimated future cash flows	[2]	(10)		(1)
Development projects	[3]	10		11
Accretion expense	[4]	16		15
Payments		(5)		(6)
Reclassified to liabilities held for sale	[5]			(4)
Asset Divestitures	[6]	(2)		(20)
ARO ending balance	[1]	355		346
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Net increase (decrease) resulting from updates to estimated future cash flows		8		16
Reduction to operating and maintenance expense due to updates to estimated future cash flows		(2)		(2)
Asset Retirement Obligation, Current		5		1
Exelon Generation Co L L C [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance		194	[1]	201
Net increase (decrease) resulting from updates to estimated future cash flows	[2]	(12)		(2)
Development projects	[3]	10		11
Accretion expense	[4]	10		11
Payments		(3)		(3)
Reclassified to liabilities held for sale	[5]			(4)
Asset Divestitures	[6]	(2)		(20)
ARO ending balance	[1]	197		194
Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Reduction to operating and maintenance expense due to updates to estimated future cash flows				1
Asset Retirement Obligation, Current		2		1
Commonwealth Edison Co [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance		104	[1]	101
Net increase (decrease) resulting from updates to estimated future cash flows	[2]	6		2
Development projects	[3]	0		0
Accretion expense	[4]	5		3
Payments		(2)		(2)
Reclassified to liabilities held for sale	[5]			0
Asset Divestitures	[6]	0		0
ARO ending balance	[1]	113		104
PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Current		0		1
PECO Energy Co [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance		30	[1]	30
Net increase (decrease) resulting from updates to estimated future cash flows	[2]	(4)		0
Development projects	[3]	0		0
Accretion expense	[4]	1		1
Payments		0		(1)
Reclassified to liabilities held for sale	[5]			0
Asset Divestitures	[6]	0		0
ARO ending balance	[1]	27		30
Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Current		1		1
Baltimore Gas and Electric Company [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance		18	[1]	19
Net increase (decrease) resulting from updates to estimated future cash flows	[2]	0		(1)
Development projects	[3]	0		0
Accretion expense	[4]	0		0
Payments		0		0
Reclassified to liabilities held for sale	[5]			0
Asset Divestitures	[6]	0		0
ARO ending balance	[1]	$ 18		$ 18
[1]	Excludes $1 million, $1 million, $1 million and $1 million as the current portion of the ARO at December 31, 2014 for Generation, ComEd, PECO and BGE, respectively. This is included in Other current liabilities on the Registrants' respective Consolidated Balance Sheets.
[2]	During the year ended December 31, 2015, Generation recorded a decrease of $(2) million in Operating and maintenance expense. ComEd, PECO, and BGE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2015. During the year ended December 31, 2014, Generation recorded a decrease of $(2) million and ComEd recorded an increase of $1 million in Operating and maintenance expense. PECO and BGE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2014.
[3]	Relates to new AROs recorded due to the construction of solar, wind and other non-nuclear generating sites.
[4]	For ComEd, PECO, and BGE, the majority of the accretion is recorded as an increase to a regulatory asset due to the associated regulatory treatment.
[5]	Represents AROs related to generating stations classified as held for sale. See Note 4 — Mergers, Acquisitions, and Dispositions for further information.
[6]	Reflects a reduction to the ARO resulting primarily from the sales of Schuylkill generating station in 2015 and Keystone and Conemaugh generating stations in 2014. See Note 4 — Mergers, Acquisitions, and Dispositions for further information.

Implications of Potential Ea137

Implications of Potential Early Plant Retirements Implications of Potential Early Plant Retirements (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	$ 1,104	$ 1,024
Property, plant and equipment, net	57,439	52,170
Quad Cities [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	50
Nuclear Fuel, Net of Amortization	218
Construction work in progress	11
Asset Retirement Obligation	(698)
Property, plant and equipment, net	1,030
Clinton [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	57
Nuclear Fuel, Net of Amortization	107
Construction work in progress	9
Asset Retirement Obligation	(401)
Property, plant and equipment, net	579
Ginna [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	29
Nuclear Fuel, Net of Amortization	60
Construction work in progress	11
Asset Retirement Obligation	(644)
Property, plant and equipment, net	127
Nuclear Plant [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	136
Nuclear Fuel, Net of Amortization	385
Construction work in progress	31
Asset Retirement Obligation	(1,743)
Property, plant and equipment, net	1,736
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	880	847
Property, plant and equipment, net	$ 25,843	$ 23,028

Retirement Benefits - Narrative

Retirement Benefits - Narrative (Details) - USD ($)		Dec. 31, 2014	Apr. 30, 2014	Mar. 31, 2015	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, amounts recognized In regulatory liabilities, before tax				$ 11,000,000
Effect of federal subsidy on net periodic postretirement benefit costs under the Prescription Drug Act					$ 0		$ 0
Expected qualified pension plan contributions					250,000,000
Expected other postretirement benefit plan contributions					$ 35,000,000
Projected Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Funded status of the pension and other postretirement benefit obligations					81.00%		81.00%
Accumulated Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Funded status of the pension and other postretirement benefit obligations					85.00%		87.00%
Exelon Generation Co L L C [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions					$ 134,000,000
Expected other postretirement benefit plan contributions					13,000,000
Commonwealth Edison Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions					30,000,000
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months					2,000,000
Expected other postretirement benefit plan contributions					3,000,000
PECO Energy Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions					28,000,000
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months					1,000,000
Expected other postretirement benefit plan contributions					1,000,000
Baltimore Gas and Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions					31,000,000
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months					1,000,000
Expected other postretirement benefit plan contributions					$ 18,000,000
Exelon Legacy Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory asset increase (decrease) due to updated valuation adjustment				48,000,000
Constellation Legacy Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
AOCI valuation adjustment				27,000,000
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets	[1]				7.00%		7.00%		7.50%
Discount rate					3.94%	[2]	4.80%	[3]	3.92%	[4]
Increase (decrease) in pension obligation		$ 361,000,000
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months					$ 1,153,000,000
Healthcare cost trend on covered charges					7.00%
Pension Plan, Defined Benefit [Member] | Exelon Generation Co L L C [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months					$ 9,000,000
Pension Plan, Defined Benefit [Member] | Exelon Legacy Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefit obligation increase (decrease) reflecting actual census data				45,000,000
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets			6.46%		6.50%	[1]	6.59%	[1]	6.45%	[1]
Discount rate					3.92%	[2]	4.90%	[3]	4.00%	[4]
Increase (decrease) in pension obligation		$ 117,000,000
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months					$ 217,000,000
Healthcare cost trend on covered charges					6.71%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Exelon Legacy Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefit obligation increase (decrease) reflecting actual census data				$ 57,000,000
Non-Qualified Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months					$ 21,000,000
[1]	Not applicable to pension and other postretirement benefit plans that do not have plan asset
[2]	)The discount rates above represent the initial discount rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2015. Discount rates for CENG's legacy pension and OPEB plans ranged from 3.68%-4.14% and 4.32%-4.43%, respectivel
[3]	The discount rates above represent the initial discount rates used to establish the majority of Exelon's pension and other postretirement benefits costs for the year ended December 31, 2014. Certain of the other postretirement benefit plans were remeasured as of April 30, 2014 using an expected long-term rate of return on plan assets of 6.59% and a discount rate of 4.30%. Costs of the year ended December 31, 2014 reflect the impact of this remeasurement. On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, Exelon became the sponsor of CENG’s legacy pension and OPEB plans effective July 14, 2014; discount rates for those plans, impacting 2014 costs, ranged from 3.60%-4.30% and 4.09%-4.55%, respectively. See Note 5 - Investment in Constellation Energy Nuclear Group, LLC for further information.
[4]	The discount rates above represent the initial discounts rates used to establish Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2013. Certain of the benefit plans were remeasured during the year using discount rates of 4.21% and 4.66% for pension and other postretirement benefits, respectively. Costs for the year ended December 31, 2013 reflect the impact of these remeasurement

Retirement Benefits - Summary o

Retirement Benefits - Summary of Changes in Benefit Obligations (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Net benefit obligation at beginning of year		$ 18,256	$ 15,459
Service cost		326	293	$ 317
Interest cost		710	749	650
Plan participants’ contributions		0	0
Actuarial (gain) loss		(582)	2,095
Plan amendments		0	0
Acquisitions/divestitures(a)		0	594
Curtailments		0	(8)
Settlements	[1]	(34)	(30)
Gross benefits paid		(923)	(896)
Net benefit obligation at end of year		17,753	18,256	15,459
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Net benefit obligation at beginning of year		4,197	4,451
Service cost		119	117	162
Interest cost		167	186	194
Plan participants’ contributions		42	42
Actuarial (gain) loss		(341)	502
Plan amendments		(23)	(1,012)
Acquisitions/divestitures(a)		0	142
Curtailments		0	0
Settlements	[1]	0	0
Gross benefits paid		(223)	(231)
Net benefit obligation at end of year		$ 3,938	$ 4,197	$ 4,451
[1]	_______________________ (a)On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, Exelon became a sponsor of CENG’s pension and OPEB plans effective July 14, 2014. See Note 5 - Investment in Constellation Energy Nuclear Group, LLC for further information.

Retirement Benefits - Summar140

Retirement Benefits - Summary of Changes in Plan Assets (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		$ 14,874	$ 13,571
Actual return on plan assets		(32)	1,443
Employer contributions		462	332
Plan participants’ contributions		0	0
Gross benefits paid		(923)	(896)
Acquisitions/divestitures(a)		0	454
Settlements	[1]	(34)	(30)
Fair value of net plan assets at end of year		14,347	14,874
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		2,430	2,238
Actual return on plan assets		4	90
Employer contributions		40	291
Plan participants’ contributions		42	42
Gross benefits paid		(223)	(231)
Acquisitions/divestitures(a)		0	0
Settlements	[1]	0	0
Fair value of net plan assets at end of year		$ 2,293	$ 2,430
[1]	_______________________ (a)On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, Exelon became a sponsor of CENG’s pension and OPEB plans effective July 14, 2014. See Note 5 - Investment in Constellation Energy Nuclear Group, LLC for further information.

Retirement Benefits - Balance S

Retirement Benefits - Balance Sheet locations of Benefit Obligations and Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities	$ 21	$ 16
Pension obligations	3,385	3,366
Non-pension postretirement benefit obligations	0	0
Unfunded status (net benefit obligation less net plan assets)	3,406	3,382
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities	27	25
Pension obligations	0	0
Non-pension postretirement benefit obligations	1,618	1,742
Unfunded status (net benefit obligation less net plan assets)	$ 1,645	$ 1,767

Retirement Benefits - Projected

Retirement Benefits - Projected Benefit Obligations and Accumulated Benefit Obligations in Excess of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Projected Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 17,753	$ 18,256
Fair value of net plan assets	14,347	14,874
Accumulated Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	17,753	18,256
Fair value of net plan assets	14,347	14,874
Accumulated benefit obligation	$ 16,792	$ 17,191

Retirement Benefits - Component

Retirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 326	$ 293	$ 317
Interest cost	710	749	650
Expected return on assets	(1,026)	(994)	(1,015)
Prior service cost (credit)	13	14	14
Actuarial loss	571	420	562
Settlement charges	2	2	9
Net periodic benefit cost	596	484	537
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	119	117	162
Interest cost	167	186	194
Expected return on assets	(151)	(154)	(132)
Prior service cost (credit)	(174)	(122)	(19)
Actuarial loss	80	50	83
Settlement charges	0	0	0
Net periodic benefit cost	$ 41	$ 77	$ 288

Retirement Benefits - Compon144

Retirement Benefits - Components of Accumulated Other Comprehensive Income and Regulatory Assets (Liabilities) related to Retirement Plans (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial loss (gain)		$ 476	$ 1,639	$ (1,169)
Amortization of actuarial loss		(571)	(420)	(562)
Current year prior service (credit) cost		0	0	0
Amortization of prior service (cost) credit		(13)	(14)	(14)
Settlements		(2)	(2)	(8)
Total recognized in AOCI and regulatory assets (liabilities)	[1]	(110)	1,203	(1,753)
Defined benefit plan, amounts recognized in OCI, before tax		64	788	1,071
Defined benefit plan, amounts recognized in regulatory assets, before tax		46	415	682
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial loss (gain)		(194)	561	(628)
Amortization of actuarial loss		(80)	(50)	(83)
Current year prior service (credit) cost		(23)	(1,012)	15
Amortization of prior service (cost) credit		174	122	19
Settlements		0	0	0
Total recognized in AOCI and regulatory assets (liabilities)	[1]	(123)	(379)	(677)
Defined benefit plan, amounts recognized in OCI, before tax		63	162	352
Defined benefit plan, amounts recognized in regulatory assets, before tax		$ 60	$ 217	$ 325
[1]	)Of the $110 million gain related to pension benefits, $64 million and $46 million were recognized in AOCI and regulatory assets, respectively, during 2015. Of the $123 million gain related to other postretirement benefits, $63 million and $60 million were recognized in AOCI and regulatory assets (liabilities), respectively, during 2015. Of the $1,203 million loss related to pension benefits, $788 million and $415 million were recognized in AOCI and regulatory assets, respectively, during 2014. Of the $379 million gain related to other postretirement benefits, $162 million and $217 million were recognized in AOCI and regulatory assets (liabilities), respectively, during 2014. Of the $1,753 million gain related to pension benefits, $1,071 million and $682 million were recognized in AOCI and regulatory assets, respectively, during 2013. Of the $677 million gain related to other postretirement benefits, $352 million and $325 million were recognized in AOCI and regulatory assets, respectively, during 2013.

Retirement Benefits - Gross Acc

Retirement Benefits - Gross Accumulated Other Comprehensive Loss and Regulatory Assets (Liabilities) not Recognized as Components of Periodic Benefit Cost (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		$ 36	$ 49
Actuarial loss		7,310	7,407
Total	[1]	7,346	7,456
Benefits included in accumulated other comprehensive income		4,246	4,310
Benefits included in regulatory assets		3,100	3,146
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		(812)	(963)
Actuarial loss		711	985
Total	[1]	(101)	$ 22
Benefits included in accumulated other comprehensive income		(63)
Benefits included in regulatory assets		$ (38)
[1]	)Of the $7,346 million related to pension benefits, $4,246 million and $3,100 million are included in AOCI and regulatory assets, respectively, at December 31, 2015. Of the $(101) million related to other postretirement benefits, $(63) million and $(38) million are included in AOCI and regulatory assets (liabilities), respectively, at December 31, 2015. Of the $7,456 million related to pension benefits, $4,310 million and $3,146 million are included in AOCI and regulatory assets, respectively, at December 31, 2014. The $22 million related to other postretirement benefits is included in regulatory assets (liabilities) at December 31, 2014.

Retirement Benefits - Compon146

Retirement Benefits - Components of Accumulated Other Comprehensive Income and Regulatory Assets expected to be Amortized as Components of Periodic Benefit Cost (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Amounts That Will Be Amortized From Accumulated Other Comprehensive Income Loss And Regulatory Assets In Next Fiscal Year	$ (125)
Benefits included in accumulated other comprehensive income	(64)
Benefits included in regulatory assets	(61)
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Future Amortization of Prior Service Cost (Credit)	13
Defined Benefit Plan, Future Amortization of Gain (Loss)	501
Benefits included in accumulated other comprehensive income	514	[1]
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax	290
Pension Plan, Defined Benefit [Member] | Regulatory Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax	224
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Future Amortization of Prior Service Cost (Credit)	(175)
Defined Benefit Plan, Future Amortization of Gain (Loss)	50
Benefits included in accumulated other comprehensive income	$ (125)	[1]
[1]	___________________ (a)Of the $514 million related to pension benefits at December 31, 2015, $290 million and $224 million are expected to be amortized from AOCI and regulatory assets in 2016, respectively. Of the $(125) million related to other postretirement benefits at December 31, 2015, $(64) million and $(61) million are expected to be amortized from AOCI and regulatory assets (liabilities) in 2016, respectively.

Retirement Benefits - Assumptio

Retirement Benefits - Assumptions Used in Calculations (Details)		1 Months Ended	12 Months Ended
		Apr. 30, 2014	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate			4.29%		3.94%		4.80%
Discount rate			3.94%	[1]	4.80%	[2]	3.92%	[3]
Expected return on plan assets	[4]		7.00%		7.00%		7.50%
Pension Plan, Defined Benefit [Member] | Remeasurement [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate used for remeasurement due to design changes					6.59%		4.21%
Pension Plan, Defined Benefit [Member] | First Five Years [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Rate of compensation increase					3.25%		3.25%
Rate of compensation increase			3.25%		3.25%		3.25%
Pension Plan, Defined Benefit [Member] | Thereafter [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Rate of compensation increase			3.75%				3.75%
Rate of compensation increase			3.75%		3.75%		3.75%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate			4.29%		3.92%		4.90%
Discount rate			3.92%	[1]	4.90%	[2]	4.00%	[3]
Expected return on plan assets		6.46%	6.50%	[4]	6.59%	[4]	6.45%	[4]
Health care cost trend rate			6.00%		6.50%		6.50%
Ultimate health care cost trend rate			5.00%		5.00%		5.00%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate used for remeasurement due to design changes					4.30%		4.66%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate used for remeasurement due to design changes			4.32%		4.09%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate used for remeasurement due to design changes			4.43%		4.55%
CENG Legacy Benefit Plans [Member] | Remeasurement [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate used for remeasurement due to design changes			3.68%		3.60%
CENG Legacy Benefit Plans [Member] | Remeasurement [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate used for remeasurement due to design changes			4.14%		4.30%
[1]	)The discount rates above represent the initial discount rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2015. Discount rates for CENG's legacy pension and OPEB plans ranged from 3.68%-4.14% and 4.32%-4.43%, respectivel
[2]	The discount rates above represent the initial discount rates used to establish the majority of Exelon's pension and other postretirement benefits costs for the year ended December 31, 2014. Certain of the other postretirement benefit plans were remeasured as of April 30, 2014 using an expected long-term rate of return on plan assets of 6.59% and a discount rate of 4.30%. Costs of the year ended December 31, 2014 reflect the impact of this remeasurement. On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, Exelon became the sponsor of CENG’s legacy pension and OPEB plans effective July 14, 2014; discount rates for those plans, impacting 2014 costs, ranged from 3.60%-4.30% and 4.09%-4.55%, respectively. See Note 5 - Investment in Constellation Energy Nuclear Group, LLC for further information.
[3]	The discount rates above represent the initial discounts rates used to establish Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2013. Certain of the benefit plans were remeasured during the year using discount rates of 4.21% and 4.66% for pension and other postretirement benefits, respectively. Costs for the year ended December 31, 2013 reflect the impact of these remeasurement
[4]	Not applicable to pension and other postretirement benefit plans that do not have plan asset

Retirement Benefits - Effects o

Retirement Benefits - Effects of One Percentage Point Change in Assumed Health Care Cost Trend Rates (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Compensation and Retirement Disclosure [Abstract]
Effect of a one percentage point increase in assumed healthcare cost trend on 2010 total service and interest cost components	$ 12
Effect of a one percentage point increase in assumed healthcare cost trend on postretirement benefit obligation at December 31, 2010	100
Effect of a one percentage point decrease in assumed healthcare cost trend on 2010 total service and interest cost components	(9)
Effect of a one percentage point decrease in assumed healthcare cost trend on postretirement benefit obligation at December 31, 2010	$ (89)

Retirement Benefits - Contribut

Retirement Benefits - Contributions made to Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		$ 502		$ 617		$ 422
Expected qualified pension plan contributions		250
Service cost		148		103		85
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		462	[1]	332		339
Service cost		250
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		40		291	[2]	83	[2]
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		245		297		149
Expected qualified pension plan contributions		134
Service cost		80		51		40
Exelon Generation Co L L C [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		231	[1]	173		119
Exelon Generation Co L L C [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		14		124	[2]	30	[2]
Exelon Corporate [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		5	[1]	9		72
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		150		248		122
Expected qualified pension plan contributions		30
Service cost		32		26		22
Commonwealth Edison Co [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		143	[1]	122		118
Commonwealth Edison Co [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		7		125	[2]	4	[2]
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		40		16		31
Expected qualified pension plan contributions		28
Service cost		11		8		8
PECO Energy Co [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		40	[1]	11		11
PECO Energy Co [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		0		5	[2]	20	[2]
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		17		16		24
Expected qualified pension plan contributions		31
Service cost	[3]	14		8		8
Baltimore Gas and Electric Company [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		1	[1]	0		0
Baltimore Gas and Electric Company [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		16		17	[2]	24	[2]
Business Services Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	[4]	11		10		7
Business Services Company [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		47	[1]	26		91
Business Services Company [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		3		20	[2]	$ 5	[2]
Constellation Legacy Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[1]	$ 36		$ 43
Remeasurement [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				6.59%		4.21%
Remeasurement [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				4.30%		4.66%
Remeasurement [Member] | Maximum [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes		4.43%		4.55%
[1]	Includes $5 million, $9 million, and $72 million of pension contributions funded by Exelon Corporate, for the years ended December 31, 2015, 2014, and 2013, respectively.
[2]	_________________________(a)Exelon's and Generation's pension contributions include $36 million and $43 million related to the legacy CENG plans that was funded by CENG as provided in an Employee Matters Agreement (EMA) between Exelon and CENG for the years ended December 31, 2015 and 2014, respectively.
[3]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246OTgxRUZBRTQwMEE3OERGNjRCMzUxMjI1RThCRDY3N0QM}
[4]	These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These costs are not included in the Generation, ComEd, PECO, or BGE amounts above.

Retirement Benefits - Estimated

Retirement Benefits - Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2015USD ($)
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,015	$ 1,153
2,016	997
2,017	1,009
2,018	1,036
2,019	1,071
2020 through 2024	5,923
Total estimated future benefit payments through 2025	11,189
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,015	217
2,016	223
2,017	228
2,018	235
2,019	244
2020 through 2024	1,341
Total estimated future benefit payments through 2025	$ 2,488

Retirement Benefits - Allocated

Retirement Benefits - Allocated Portion of Pension and Postretirement Benefit Plan Costs (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense		$ 637	$ 561	$ 825
Exelon Generation Co L L C [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense		269	250	347
Commonwealth Edison Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense		206	162	309
PECO Energy Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense		39	36	43
Business Services Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense	[1]	57	46	71
Baltimore Gas and Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense		$ 66	$ 67	$ 55
[1]	These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO or BGE amounts above.

Retirement Benefits - Pension a

Retirement Benefits - Pension and Other Postretirement Benefit Plan Target Asset Allocations (Details)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets		100.00%	100.00%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets		43.00%	42.00%
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets		35.00%	33.00%
Equity Securities [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage		39.00%
Equity Securities [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage		32.00%
Fixed Income Securities [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage		26.00%
Percentage of Plan Assets		27.00%	34.00%
Fixed Income Securities [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage		37.00%
Percentage of Plan Assets		34.00%	37.00%
Alternative Investments [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	[1]	35.00%
Percentage of Plan Assets	[1]	30.00%	24.00%
Alternative Investments [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	[1]	31.00%
Percentage of Plan Assets	[1]	31.00%	30.00%
[1]	Alternative investments include private equity, hedge funds, real estate, and private credit.

Retirement Benefits - Fair Valu

Retirement Benefits - Fair Value Measurements of Pension and Postretirement Benefit Plan Assets (Details) - USD ($) $ in Millions		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Derivative, Fair Value, Net		$ 5		$ (3)
Derivative, notional amount		1,774		1,491
Net assets pending transactions excluded		27		42
Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		2,293		2,430		$ 2,238
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		14,347		14,874		13,571
Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		373		226		115
Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		3,513		3,251		2,470
Equity Security Individually Held [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0		0		0
Equity Security Individually Held [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		2		2		2
Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0		0		0
Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		368		272		41
Private Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0		0		2
Private Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		924		900		806
Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		139		0		0
Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		795		785		706
Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		131		116		109
Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		725		685		544
Private Placement [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		103		110		4
Private Placement [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		699		607		$ 371
Fair Value, Measurements, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1],[2]	16,613		17,261
Fair Value, Measurements, Recurring [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	2,291		2,427
Fair Value, Measurements, Recurring [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	14,322		14,834
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1],[2]	5,473		5,323
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	691		767
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	4,782		4,556
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1],[2]	7,254		8,461
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	1,227		1,434
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	6,027		7,027
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1],[2]	3,886		3,477
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	373		226
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	3,513		3,251
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	15		11
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	210		1
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		15		11	[2]
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		210	[2]	1
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0		0	[2]
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0	[2]	0
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0		0	[2]
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0	[2]	0
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	992		1,005
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	5,035		4,712
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		510		480
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		3,571		3,261
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		482		525
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		1,462		1,449
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0		0
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		2		2
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	64		74
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	1,080		1,139
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	11		15
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	1,001		1,051
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	53		59
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	79		88
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	131		197
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	61		80
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	131		197
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	61		80
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	44		42
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	3,066		3,245
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	44		42
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	2,901		3,125
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	165		120
Fair Value, Measurements, Recurring [Member] | Other Debt Obligations [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	360		525
Fair Value, Measurements, Recurring [Member] | Other Debt Obligations [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	598		1,082
Fair Value, Measurements, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 1 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		155		253	[2]
Fair Value, Measurements, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		205		272	[2]
Fair Value, Measurements, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	395		930
Fair Value, Measurements, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0		0	[2]
Fair Value, Measurements, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	203		152
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	599		838
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	4,805		5,546
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	166		268
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	1,001		1,051
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	433		570
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	3,436		4,223
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	368		272
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	924		900
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	924		900
Fair Value, Measurements, Recurring [Member] | Hedge Funds [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	451		339
Fair Value, Measurements, Recurring [Member] | Hedge Funds [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	1,924		2,140
Fair Value, Measurements, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	312		339
Fair Value, Measurements, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	1,129		1,355
Fair Value, Measurements, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	139		0
Fair Value, Measurements, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	795		785
Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	131		124
Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	725		928
Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0		8	[2]
Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		243
Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0		0	[2]
Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		131		116	[2]
Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	725		685
Fair Value, Measurements, Recurring [Member] | Private Placement [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	103		110
Fair Value, Measurements, Recurring [Member] | Private Placement [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	699		607
Fair Value, Measurements, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 1 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 2 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0
Fair Value, Measurements, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	103		110
Fair Value, Measurements, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	$ 699		$ 607
[1]	Excludes net assets of $27 million and $42 million at December 31, 2015 and 2014, respectively, which are required to reconcile to the fair value of net plan assets. These items consist primarily of receivables related to pending securities sales, interest and dividends receivable, and payables related to pending securities purchases.
[2]	See Note 12—Fair Value of Financial Assets and Liabilities for a description of levels within the fair value hierarchy.

Retirement Benefits - Reconcili

Retirement Benefits - Reconciliation of Level 3 Assets and Liabilities measured at Fair Value for Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		$ 14,874	$ 13,571
Purchases		0	454
Fair value of net plan assets at end of year		14,347	14,874
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		2,430	2,238
Purchases		0	0
Fair value of net plan assets at end of year		2,293	2,430
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Transfers into (out of) Level 3		56
Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		3,251	2,470
Relating to assets still held at the reporting date		64	279
Relating to assets sold during the period		13	3
Purchases		731	847
Sales		(123)	(60)
Settlements	[1]	(423)	(301)
Transfers into (out of) Level 3	[2]		13
Fair value of net plan assets at end of year		3,513	3,251
Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		226	115
Relating to assets still held at the reporting date		9	14
Purchases		200	111
Sales			(13)
Settlements	[1]	(62)	(1)
Fair value of net plan assets at end of year		373	226
Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		785	706
Relating to assets still held at the reporting date		(39)	59
Relating to assets sold during the period		4	2
Purchases		104	74
Sales		(57)	(25)
Settlements	[1]	(2)	(1)
Transfers into (out of) Level 3	[2]		(30)
Fair value of net plan assets at end of year		795	785
Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		0	0
Relating to assets still held at the reporting date		1	0
Purchases		138	0
Sales			0
Settlements	[1]	0	0
Fair value of net plan assets at end of year		139	0
Private Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		900	806
Relating to assets still held at the reporting date		60	112
Relating to assets sold during the period		0	0
Purchases		186	169
Sales		0	0
Settlements	[1]	(222)	(203)
Transfers into (out of) Level 3	[2]		16
Fair value of net plan assets at end of year		924	900
Private Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		0	2
Relating to assets still held at the reporting date		0	0
Purchases		0	1
Sales			(2)
Settlements	[1]	0	(1)
Fair value of net plan assets at end of year		0	0
Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		685	544
Relating to assets still held at the reporting date		76	81
Relating to assets sold during the period		9	0
Purchases		116	112
Sales		(54)	(19)
Settlements	[1]	(107)	(60)
Transfers into (out of) Level 3	[2]		27
Fair value of net plan assets at end of year		725	685
Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		116	109
Relating to assets still held at the reporting date		15	13
Purchases		62	1
Sales			(7)
Settlements	[1]	(62)	0
Fair value of net plan assets at end of year		131	116
Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		272	41
Relating to assets still held at the reporting date		(14)	7
Relating to assets sold during the period		0	0
Purchases		125	227
Sales		(7)	(3)
Settlements	[1]	(8)	0
Transfers into (out of) Level 3	[2]		0
Fair value of net plan assets at end of year		368	272
Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		0	0
Relating to assets still held at the reporting date		0	0
Purchases		0	0
Sales			0
Settlements	[1]	0	0
Fair value of net plan assets at end of year		0	0
Equity Security Individually Held [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		2	2
Relating to assets still held at the reporting date		0	0
Relating to assets sold during the period		0	0
Purchases		0	0
Sales		0	0
Settlements	[1]	0	0
Transfers into (out of) Level 3	[2]		0
Fair value of net plan assets at end of year		2	2
Equity Security Individually Held [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		0	0
Relating to assets still held at the reporting date		0	0
Purchases		0	0
Sales			0
Settlements	[1]	0	0
Fair value of net plan assets at end of year		0	0
Private Placement [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		607	371
Relating to assets still held at the reporting date		(19)	20
Relating to assets sold during the period		0	1
Purchases		200	265
Sales		(5)	(13)
Settlements	[1]	(84)	(37)
Transfers into (out of) Level 3	[2],[3]		0
Fair value of net plan assets at end of year		699	607
Private Placement [Member] | Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net plan assets at beginning of year		110	4
Relating to assets still held at the reporting date		(7)	1
Purchases		0	109
Sales			(4)
Settlements	[1]	0	0
Fair value of net plan assets at end of year		$ 103	110
Hedge Fund Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Transfers into (out of) Level 3			$ 43
[1]	Represents cash settlements only.
[2]	As of January 1, 2015 and January 1, 2014, hedge fund investments that contained redemption restrictions limiting Exelon’s ability to redeem the investments within a reasonable period of time were classified as Level 3 investments. As of December 31, 2014, restrictions for certain investments no longer applied, therefore allowing redemption within a reasonable period of time from the measurement date at NAV. As such, these hedge fund investments are reflected as transfers out of Level 3 to Level 2 of $43 million in 2014.
[3]	In connection with the Employee Matters Agreement between EDF and Exelon, Exelon assumed the pension plan assets of Nine Mile Point Nuclear Station, LLC and Constellation Energy Nuclear Group, LLC resulting in transfers into Level 3 of $56 million.

Retirement Benefits - Summar155

Retirement Benefits - Summary of Defined Contribution Savings Plan (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions		$ 148	$ 103	$ 85
Exelon Generation Co L L C [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions		80	51	40
Commonwealth Edison Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions		32	26	22
PECO Energy Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions		11	8	8
Baltimore Gas and Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	[1]	14	8	8
Business Services Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	[2]	11	10	$ 7
CENG [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contributions		$ 9	$ 5
[1]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246OTgxRUZBRTQwMEE3OERGNjRCMzUxMjI1RThCRDY3N0QM}
[2]	These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These costs are not included in the Generation, ComEd, PECO, or BGE amounts above.

Contingently Redeemable Nonc156

Contingently Redeemable Noncontrolling Interest Contingently Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Noncontrolling Interest [Line Items]
Noncontrolling Interest, Increase from Sale of Parent Equity Interest		$ 1,548
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount	$ 28	0
Temporary Equity, Other Changes	(4)
Exelon Generation Co L L C [Member]
Noncontrolling Interest [Line Items]
Noncontrolling Interest, Increase from Sale of Parent Equity Interest	32	$ 116
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount	28
Temporary Equity, Other Changes	$ (4)

Shareholder Equity Schedule of

Shareholder Equity Schedule of Common Stock Authorided and Outstanding (Details) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Common Stock, Par or Stated Value Per Share	$ 12.50
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common Stock, Shares, Outstanding	919,924,742	859,833,343
Commonwealth Edison Co [Member]
Class of Stock [Line Items]
Common stock, shares authorized	250,000,000
Common Stock, Shares, Outstanding	127,016,973	127,016,947
PECO Energy Co [Member]
Class of Stock [Line Items]
Common stock, shares authorized	500,000,000
Common Stock, Shares, Outstanding	170,478,507	170,478,507
Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Common stock, shares authorized	175,000,000
Common Stock, Shares, Outstanding	1,000	1,000

Shareholder Equity Shareholder

Shareholder Equity Shareholder Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Schedule of Capitalization, Equity [Line Items]
Shares Issued, Price Per Share		$ 35
Junior Subordinated Notes, Noncurrent		$ 1,150
Treasury stock, at cost	$ 2,327		$ 2,327
Treasury Stock, Number of Shares Held	35,000,000
Forward Contract Indexed to Issuer's Equity, Indexed Shares		23,000,000
Sale of Stock, Price Per Share		$ 32.48
Temporary Equity, Share Subscriptions		57,500,000
Baltimore Gas and Electric Company [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Shares Authorized	6,500,000

Shareholder Equity Preferred an

Shareholder Equity Preferred and Preference Securities (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Preferred Stock, Value, Outstanding	$ 190	$ 190
Preferred Stock, Shares Outstanding	1,900,000	1,900,000
Preferred Stock, Shares Authorized	6,500,000
Preference Stock [Member] | Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Preferred Stock, Par or Stated Value Per Share		$ 100
Preferred Stock, Shares Authorized		6,500,000
Series 6.97% Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	6.97%
Series 6.97% Preferred Stock [Member] | Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Preferred Stock, Value, Outstanding	$ 50	$ 50
Preferred Stock, Redemption Price Per Share	$ 100
Preferred Stock, Shares Outstanding	500,000	500,000
Series 6.7% Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	6.70%
Series 6.7% Preferred Stock [Member] | Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Preferred Stock, Value, Outstanding	$ 40	$ 40
Preferred Stock, Redemption Price Per Share	$ 100
Preferred Stock, Shares Outstanding	400,000	400,000
Series 6.99% Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	6.99%
Series 6.99% Preferred Stock [Member] | Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Preferred Stock, Value, Outstanding	$ 60	$ 60
Preferred Stock, Redemption Price Per Share	$ 100
Preferred Stock, Shares Outstanding	600,000	600,000
Series 7.125% Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	7.125%
Series 7.125% Preferred Stock [Member] | Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Preferred Stock, Value, Outstanding	$ 40
Preferred Stock, Redemption Price Per Share	$ 100
Preferred Stock, Shares Outstanding	400,000	400,000
Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	100,000,000	100,000,000
Preferred Stock [Member] | Commonwealth Edison Co [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	850,000	850,000
Preferred Stock [Member] | Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Preferred Stock, Par or Stated Value Per Share	$ 100
Cumulative Preferred Stock [Member] | Commonwealth Edison Co [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized		6,810,451

- Schedule of Common Stock Auth

- Schedule of Common Stock Authorized and Outstanding (Details) - shares	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common Stock, Shares, Outstanding	919,924,742	859,833,343
Commonwealth Edison Co [Member]
Class of Stock [Line Items]
Common stock, shares authorized	250,000,000
Common Stock, Shares, Outstanding	127,016,973	127,016,947
PECO Energy Co [Member]
Class of Stock [Line Items]
Common stock, shares authorized	500,000,000
Common Stock, Shares, Outstanding	170,478,507	170,478,507
Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Common stock, shares authorized	175,000,000
Common Stock, Shares, Outstanding	1,000	1,000

Stock-Based Compensation Pla161

Stock-Based Compensation Plans - Narrative (Details)	12 Months Ended
	Dec. 31, 2015USD ($)warrant$ / sharesshares	Dec. 31, 2014USD ($)warrant$ / sharesshares	Dec. 31, 2013USD ($)$ / shares		Dec. 31, 2012	Jun. 30, 2015USD ($)$ / sharesshares
Common Stock Narrative Information [Line Items]
Allocated Share-based Compensation Expense	$ 119,000,000	$ 127,000,000	$ 118,000,000	[1]
Common stock shares reserved for warrant conversion | shares	24,478
Equity offering | shares						57,500,000
Price per share (in usd per share) | $ / shares						$ 35
Junior Subordinated Notes, Noncurrent						$ 1,150,000,000
Forward Contract Indexed to Issuer's Equity, Indexed Shares | shares						23,000,000
Treasury Stock, Number of Shares Held | shares	35,000,000
Treasury stock, at cost	$ 2,327,000,000	2,327,000,000
Expiration period	10 years
Obligations of outstanding restricted stock not settled	$ 97,000,000	85,000,000
Settlement of restricted stock	75,000,000	43,000,000	28,000,000
Unrecognized compensation costs of nonvested restricted stock	56,000,000
Weighted average grant date fair value of performance shares (in usd per share)	35.88	28.75	31.55
Settlement of performance shares	46,000,000	27,000,000	26,000,000
Settlement of performance shares in cash	29,000,000	13,000,000	12,000,000
Unrecognized compensation costs of performance based shares	$ 27,000,000
Weighted-average period of recognition of unrecognized compensation costs of performance based shares	1 year 4 months 24 days
Commonwealth Edison Co [Member]
Common Stock Narrative Information [Line Items]
Allocated Share-based Compensation Expense	$ 6,000,000	$ 7,000,000	9,000,000	[1]
Warrants outstanding | warrant	73,434	73,533
Common stock shares reserved for warrant conversion | shares		24,511
Performance Shares [Member]
Common Stock Narrative Information [Line Items]
Allocated Share-based Compensation Expense	$ 41,000,000	$ 59,000,000	$ 48,000,000
Mix of awards			67.00%
Percentage to be settled as common stock	50.00%
Percentage to be settled as cash	50.00%
Percentage to be settled as cash if ownership requirements are met	100.00%
Weighted average grant date fair value (in usd per share) | $ / shares	$ 35.88
Nonvested Stock Option [Member]
Common Stock Narrative Information [Line Items]
Unrecognized compensation costs	$ 0
Employee Stock Option [Member]
Common Stock Narrative Information [Line Items]
Allocated Share-based Compensation Expense	$ 1,000,000	$ 2,000,000	$ 3,000,000
Requisite service period	4 years
Restricted Stock [Member]
Common Stock Narrative Information [Line Items]
Mix of awards			33.00%
Weighted-average period of recognition of unrecognized compensation costs	2 years
Weighted average grant date fair value (in usd per share) | $ / shares	$ 36.55	$ 28.71	$ 31.06
Restricted Stock Units (RSUs) [Member]
Common Stock Narrative Information [Line Items]
Allocated Share-based Compensation Expense	$ 71,000,000	$ 61,000,000	$ 61,000,000
Stock Compensation Plan [Member]
Common Stock Narrative Information [Line Items]
Allocated Share-based Compensation Expense	$ 6,000,000	$ 5,000,000	$ 6,000,000
Minimum [Member]
Common Stock Narrative Information [Line Items]
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value						$ 1,870,000,000
Minimum [Member] | Restricted Stock [Member]
Common Stock Narrative Information [Line Items]
Requisite service period	3 years
Maximum [Member] | Restricted Stock [Member]
Common Stock Narrative Information [Line Items]
Requisite service period	5 years
LTIP [Member]
Common Stock Narrative Information [Line Items]
Shares authorized | shares	16,000,000
2013 Plan [Member] | Performance Shares [Member]
Common Stock Narrative Information [Line Items]
Vesting period			3 years
2012 Plan [Member] | Performance Shares [Member]
Common Stock Narrative Information [Line Items]
Vesting period					3 years
Performance period					1 year
Performance Share Transition Award [Member]
Common Stock Narrative Information [Line Items]
Percentage to be settled as common stock			50.00%
Percentage to be settled as cash			50.00%
Percentage to be settled as cash if ownership requirements are met			100.00%
Performance Share Transition Award [Member] | Performance Shares [Member]
Common Stock Narrative Information [Line Items]
Vesting period			1 year
Performance period			2 years
[1]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246QUY1RTYxOTI4NTg4NjNCODc2RTgxMjI1RThCREM3QzMM}

Stock-Based Compensation Pla162

Stock-Based Compensation Plans - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 119	$ 127	$ 118	[1]
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	$ (46)	$ (47)	$ (44)
[1]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246QUY1RTYxOTI4NTg4NjNCODc2RTgxMjI1RThCREM3QzMM}

Stock-Based Compensation Pla163

Stock-Based Compensation Plans - Schedule of Pre-Tax Stock-based Compensation Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	[1]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		$ 119	$ 127	$ 118
Exelon Generation Co L L C [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		64	52	48
Commonwealth Edison Co [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		6	7	9
PECO Energy Co [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		3	3	5
Baltimore Gas and Electric Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		3	5	6
Business Services Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	[2]	$ 43	$ 60	$ 50
[1]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246QUY1RTYxOTI4NTg4NjNCODc2RTgxMjI1RThCREM3QzMM}
[2]	These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO and BGE amounts above.

Stock-Based Compensation Pla164

Stock-Based Compensation Plans - Components of Tax Benefits from Stock-based Compensation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common Stock [Abstract]
Restricted stock units	$ 30	$ 17	$ 11
Performance share awards	18	11	11
Stock deferral plan	$ 0	$ 0	$ 1

Stock-Based Compensation Pla165

Stock-Based Compensation Plans - Assumptions used in Calculating Fair Value of Options (Details)	12 Months Ended
	Dec. 31, 2012$ / shares
Common Stock [Abstract]
Dividend yield	5.28%
Expected volatility	23.20%
Risk-free interest rate	1.30%
Expected life (years)	6 years 3 months
Weighted average grant date fair value (per share)	$ 4.18

Stock-Based Compensation Pla166

Stock-Based Compensation Plans - Summary of Stock Option Activity (Details) - Employee Stock Option [Member] - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
December 31, 2014		18,830,967
Options exercised		(7,133)
Options forfeited		(5,250)
Options expired		(3,245,827)
December 31, 2015		15,572,757
Weighted Average Exercise Price (in usd per share)		$ 46.68	$ 46.85
Options Reinstated, Weighted Average Exercise Price (in usd per share)		21.25
Options Forfeited, Weighted Average Exercise Price (in usd per share)		39.81
Options Expired, Weighted Average Exercise Price (in usd per share)		$ 47.75
Shares Outstanding, Weighted Average Remaining Contractual Life		3 years 10 months 6 days
Shares Outstanding, Aggregate Intrinsic Value		$ 9
Exercisable at December 31, 2014	[1]	15,490,507
Shares Exercisable, Weighted Average Exercise Price (in usd per share)	[1]	$ 46.72
Shares Exercisable, Weighted Average Remaining Contractual Life	[1]	3 years 10 months 2 days
Shares Exercisable, Aggregate Intrinsic Value	[1]	$ 9
[1]	Includes stock options issued to retirement eligible employees.

Stock-Based Compensation Pla167

Stock-Based Compensation Plans - Summary of Information of Stock Options Exercised (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common Stock [Abstract]
Aggregate value	[1]	$ 0	$ 3	$ 4
Cash received for exercise price		$ 0	$ 7	$ 19
[1]	Includes stock options issued to retirement eligible employees.

Stock-Based Compensation Pla168

Stock-Based Compensation Plans - Summary of Nonvested Stock Option Activity (Details) - Nonvested Stock Option [Member] - $ / shares		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance	[1]	432,035
Vested		(344,535)
Forfeited		(5,250)
Ending Balance	[1]	82,250
Nonvested, Weighted Average Exercise Price (in usd per share)	[1]	$ 39.81	$ 39.91
Vested, Weighted Average Exercise Price (in usd per share)		39.93
Forfeited, Weighted Average Exercise Price (in usd per share)		$ 39.81
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees		279,000	746,140
[1]	Excludes 279,000 and 746,140 of stock options issued to retirement-eligible employees as of December 31, 2015 and 2014, respectively, as they are fully vested.

Stock-Based Compensation Pla169

Stock-Based Compensation Plans - Summary of Nonvested Restrict Stock Unit Activity (Details) - Restricted Stock [Member] - $ / shares		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance	[1]	3,758,218
Granted		2,132,856
Vested		(1,597,255)
Forfeited		(76,232)
Undistributed vested awards	[2]	(654,333)
Ending Balance	[1]	3,563,254	3,758,218
Nonvested, Weighted Average Exercise Price (in usd per share)	[1]	$ 31.27
Granted, Weighted Average Grant Date Fair Value (in usd per share)		36.55	$ 28.71	$ 31.06
Vested, Weighted Average Exercise Price (in usd per share)		32.88
Forfeited, Weighted Average Exercise Price (in usd per share)		33.06
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	[2]	35.35
Nonvested, Weighted Average Exercise Price (in usd per share)	[1]	$ 32.92	$ 31.27
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees		1,097,630	975,116
[1]	Excludes 1,097,630 and 975,116 of restricted stock units issued to retirement-eligible employees as of December 31, 2015 and 2014, respectively, as they are fully vested.
[2]	Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2015.

Stock-Based Compensation Pla170

Stock-Based Compensation Plans - Summary of Nonvested Performance Share Awards Activity (Details) - Performance Shares [Member] - $ / shares		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance	[1]	2,696,097
Granted		1,556,273
Change in performance		(118,398)
Vested		(704,141)
Forfeited		(52,167)
Undistributed vested awards	[2]	(820,505)
Ending Balance	[1]	2,557,159	2,696,097
Nonvested, Weighted Average Exercise Price (in usd per share)	[1]	$ 31.88	$ 30.62
Granted, Weighted Average Grant Date Fair Value (in usd per share)		35.88
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Change in Performance, Weighted Average Grant Date Fair Value		35.88
Vested, Weighted Average Exercise Price (in usd per share)		32.80
Forfeited, Weighted Average Exercise Price (in usd per share)		32.25
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	[2]	$ 33.95
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees		1,817,883	1,535,791
[1]	Excludes 1,817,883 and 1,535,791 of performance share awards issued to retirement-eligible employees as of December 31, 2015 and 2014, respectively, as they are fully vested.
[2]	Represents performance share awards that vested but were not distributed to retirement-eligible employees during 2015.

Stock-Based Compensation Pla171

Stock-Based Compensation Plans - Balance Sheet Classification of Obligations related to Outstanding Performance Share Awards Not Yet Settled (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Common Stock [Abstract]
Current liabilities	[1]	$ 28	$ 28
Deferred credits and other liabilities	[2]	32	36
Common stock		35	33
Total		$ 95	$ 97
[1]	Represents the current liability related to performance share awards expected to be settled in cash.
[2]	Represents the long-term liability related to performance share awards expected to be settled in cash.

Earnings Per Share and Equity -

Earnings Per Share and Equity - Schedule of Earnings per Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income attributable to common shareholders									$ 2,269	$ 1,623	$ 1,719
Weighted average common shares outstanding—basic	921	913	863	862	861	861	860	858	890	860	856
Assumed exercise and/or distributions of stock-based awards									3	4	4
Weighted average common shares outstanding—diluted	924	915	866	867	868	863	864	861	893	864	860

Earnings Per Share and Equit173

Earnings Per Share and Equity - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock options not included in the calculation of diluted common shares outstanding (less than 1 million related to PHI merger)	16,000,000	17,000,000	20,000,000
Treasury Stock, Shares held	35,000,000	35,000,000
Treasury stock, at cost	$ 2,327	$ 2,327
Pepco Holdings [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock options not included in the calculation of diluted common shares outstanding (less than 1 million related to PHI merger)	3,000,000	1,000,000

Changes in Accumulated Other174

Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	$ (2,684)		$ (2,040)
OCI before reclassifications		(136)		(528)	[1]
Amounts reclassified from AOCI		196		(116)	[1],[2]
Other comprehensive income (loss)		60		(644)	[1]	$ 727
Ending balance		(2,624)		(2,684)	[1]	(2,040)	[1]
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	(28)		120
OCI before reclassifications		(12)		(31)	[1]
Amounts reclassified from AOCI		21		(117)	[1],[2]
Other comprehensive income (loss)		9		(148)	[1]
Ending balance		(19)		(28)	[1]	120	[1]
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		3	[1]	2
OCI before reclassifications		0		(1)
Amounts reclassified from AOCI		0		2
Other comprehensive income (loss)		0		1	[1]
Ending balance		3		3	[1]	2
Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		(2,640)	[1]	(2,260)
OCI before reclassifications		(100)		(498)	[1]
Amounts reclassified from AOCI		175		118	[1],[2]
Other comprehensive income (loss)		75		(380)	[1]
Ending balance		(2,565)		(2,640)	[1]	(2,260)
Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		(19)	[1]	(10)
OCI before reclassifications		(21)		(9)
Other comprehensive income (loss)		(21)		(9)	[1]
Ending balance		(40)		(19)	[1]	(10)
Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	0		108
OCI before reclassifications		(3)		11	[1]
Amounts reclassified from AOCI		0		(119)	[1],[2]
Other comprehensive income (loss)		(3)		(108)	[1]
Ending balance		(3)		0	[1]	108	[1]
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	(36)		214
OCI before reclassifications		(32)		(14)	[1]
Amounts reclassified from AOCI		5		(236)	[1],[2]
Other comprehensive income (loss)		(27)		(250)	[1]	(299)
Ending balance		(63)		(36)	[1]	214	[1]
Exelon Generation Co L L C [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	(18)		114
OCI before reclassifications		(8)		(15)	[1]
Amounts reclassified from AOCI		5		(117)	[1],[2]
Other comprehensive income (loss)		(3)		(132)	[1]
Ending balance		(21)		(18)	[1]	114	[1]
Exelon Generation Co L L C [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	1		2
OCI before reclassifications		0		(1)
Other comprehensive income (loss)		0		(1)	[1]
Ending balance		1		1	[1]	2	[1]
Exelon Generation Co L L C [Member] | Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		(19)	[1]	(10)
OCI before reclassifications		(21)		(9)	[1]
Other comprehensive income (loss)		(21)		(9)	[1]
Ending balance		(40)		(19)	[1]	(10)
Exelon Generation Co L L C [Member] | Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	0		108
OCI before reclassifications		(3)		11	[1]
Amounts reclassified from AOCI		0		(119)	[1],[2]
Other comprehensive income (loss)		(3)		(108)	[1]
Ending balance		(3)		0	[1]	108	[1]
PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	1		1
Ending balance		1		1	[1]	1	[1]
PECO Energy Co [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	1		1
Ending balance		$ 1		$ 1	[1]	$ 1	[1]
[1]	All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.
[2]	See next tables for details about these reclassifications.

Changes in Accumulated Other175

Changes in Accumulated Other Comprehensive Income - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		2 Months Ended	3 Months Ended										12 Months Ended
		Dec. 31, 2014	Dec. 31, 2015		Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014		Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues			$ 6,702		$ 7,401	$ 6,514	$ 8,830	$ 7,255	$ 6,912	$ 6,024	$ 7,237		$ 29,447		$ 27,429	$ 24,888
Interest expense													(1,079)		(610)	(896)
Prior service costs													30		19	0
Sale of equity method investment													(46)		455	460
Total income (loss) in equity method investments															(20)	10
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain (Loss), Net													0		289	0
Income before income taxes													3,330		2,486	2,773
Income tax benefit (expense)													(1,073)		(666)	(1,044)
Net income			309	[1]	629	638	693	18	993	522	90	[2]	2,250		1,820	1,729
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income	[3]												(196)		116
Reclassification out of Accumulated Other Comprehensive Income [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income	[3]														(2)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues													(26)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	[3]														(2)
Income before income taxes	[3]												(35)		195
Income tax benefit (expense)	[3]												14		(78)
Net income	[3]												(21)		117
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	[3]												2		195
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense	[3]												(11)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity Method Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Total income (loss) in equity method investments	[3]														5
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain (Loss), Net															193
Income before income taxes	[3]														198
Income tax benefit (expense)	[3]														(79)
Net income	[3]														119
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues		$ 386	4,294		4,768	4,232	5,840	4,802	4,412	3,789	4,390		19,135		17,393	15,630
Interest expense													(425)		50	(2)
Sale of equity method investment													(60)		406	355
Total income (loss) in equity method investments													8		(20)	10
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain (Loss), Net													0		289	0
Income tax benefit (expense)													(502)		(207)	(615)
Net income		$ (42)	$ 154		$ 377	$ 398	$ 443	$ (91)	$ 771	$ 340	$ (185)		1,340		1,019	$ 1,060
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income	[3]												(5)		236
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before income taxes	[3]												(9)		195
Income tax benefit (expense)													4	[3]	78
Net income	[3]												(5)		117
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	[3]												2		195
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense	[3]												(11)
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity Method Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Total income (loss) in equity method investments	[3]														5
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain (Loss), Net															193
Income before income taxes	[3]														198
Income tax benefit (expense)	[3]														(79)
Net income	[3]														119
Pension Plan, Defined Benefit [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Prior service costs	[3],[4]												74		46
Actuarial gains/losses	[3],[4]												(361)
Income before income taxes	[3]												(287)		(193)
Income tax benefit (expense)	[3]												112		75
Net income	[3]												$ (175)		(118)
Pension Plan, Defined Benefit [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity Method Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Actuarial gains/losses	[3],[5]														$ (239)
[1]	Includes charges to earnings related to the impairments of certain generating assets which were held for sale and certain Upstream exploration assets. See Note 8—Impairment of Long-Lived Assets of the Combined Notes to Consolidated Financial Statements for additional information.
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246NEExNTZFREE4NkYwMUZCQUZDQTExMjI1RThCRDM3QzcM}
[3]	Amounts in parenthesis represent a decrease in net income.
[4]	This accumulated other comprehensive income component is included in the computation of net periodic pension and OPEB cost (see Note 17 — Retirement Benefits for additional details).
[5]	Amortization of the deferred compensation unit plan is allocated to capital and operating and maintenance expense.

Changes in Accumulated Other176

Changes in Accumulated Other Comprehensive Income - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Prior service costs	$ 30	$ 19	$ 0
Actuarial loss reclassified to periodic cost, taxes	(140)	(93)	(133)
Pension and non-pension postretirement benefit plan valuation adjustment, taxes	62	317	(430)
Change in unrealized gain (loss) on cash flow hedges, taxes	(6)	96	166
Change in unrealized gain (loss) on equity investments taxes	1	73	(71)
Other comprehensive income, income taxes	(53)	412	(468)
Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in unrealized gain (loss) on cash flow hedges, taxes	2	84	262
Change in unrealized gain (loss) on equity investments taxes	1	73	(72)
Other comprehensive income, income taxes	$ 3	$ 157	$ 190

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details)		1 Months Ended			3 Months Ended	12 Months Ended
		Jan. 31, 2013USD ($)	Oct. 31, 2007USD ($)	May. 31, 2006Principle_responsible_party	Sep. 30, 2015USD ($)	Dec. 31, 2015USD ($)aMGPSitereactorclaimantOpen_claimCustomer	Dec. 31, 2014USD ($)	Dec. 31, 1999Principle_responsible_party	May. 30, 2012USD ($)	Dec. 31, 2003
Commitments and Contingencies [Line Items]
Nuclear insurance liability limit per incident						$ 18,300,000
Cost surcharge to Price-Anderson Act nuclear incident assessment						5.00%
Guarantee obligations maximum exposure						$ 9,206,000,000
Asbestos liability reserve						95,000,000	$ 100,000,000
Probable contingency (liability)						$ 21,000,000
Open asbestos liability claims | Open_claim						228
Asbestos liability reserve related to anticipated claims						$ 74,000,000
Rossville ash site [Member]
Commitments and Contingencies [Line Items]
Area of property | a						32
Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Guarantee obligations maximum exposure	[1]					$ 3,060,000,000
Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Nuclear financial protection pool value						$ 375,000,000
United States licensed nuclear reactors total | reactor						103
Maximum recovery limit from a nuclear industry mutual insurance company in the event of multiple losses						$ 13,100,000,000
Cost surcharge to Price-Anderson Act nuclear incident assessment						12730000000.00%
Maximum assessment mandated by Price-Anderson Act per nuclear reactor for a nuclear incident						$ 19,000,000
Maximum annual assessment payment mandated by Price-Anderson Act for a nuclear incident						2,700,000,000
Total retrospective premium obligation under insurance from a nuclear industry mutual insurance company						365,000,000
Mutual Replacement Power Cost Insurance Maximum Retrospective Premium Obligation						3,200,000,000
Cost of spent nuclear fuel disposal per kWh of net nuclear generation						0.001
Net nuclear fuel disposal fees						136,000,000	49,000,000
Department of Energy SNF one-time fee applicable to nuclear generation						277,000,000
DOE SNF one-time fee with interest						$ 1,021,000,000
13-week Treasury Rate used to calculate DOE SNF one-time fee						0.112%
Guarantee obligations maximum exposure						$ 6,832,000,000
Consent decree penalty			$ 1,000,000
Environmental loss contingencies						$ 12,000,000	$ 13,000,000
Payments for operating leases		$ 14,000,000
Open asbestos liability claims | Open_claim						300
Exelon Generation Co L L C [Member] | Cotter Corporation [Member]
Commitments and Contingencies [Line Items]
Total cost of remediation to be shared by PRPs						$ 60,000,000
DOJ potential settlement						90,000,000
Exelon Generation Co L L C [Member] | Rossville ash site [Member]
Commitments and Contingencies [Line Items]
Estimate of possible loss						9,000,000
Exelon Generation Co L L C [Member] | Equity Method Investments [Member]
Commitments and Contingencies [Line Items]
Purchase obligations, due within two years						21,000,000
Unrecorded Unconditional Purchase Obligation, Due within Three Years						7,000,000
Unrecorded Unconditional Purchase Obligation, Due within Four Years						0
Unrecorded Unconditional Purchase Obligation						327,000,000
Unrecorded unconditional purchase obligation, due in next 12 months						299,000,000
Other unrecorded amounts						20,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Nuclear insurance liability limit per incident						13,500,000,000
Guarantee obligations maximum exposure	[2]					3,060,000,000
Exelon Generation Co L L C [Member] | Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Mutual Property Insurance Distribution To Members						18,500,000
Midwest Generation, LLC [Member]
Commitments and Contingencies [Line Items]
Percentage agreed to reimburse related parties										50.00%
Commonwealth Edison Co [Member]
Commitments and Contingencies [Line Items]
Guarantee obligations maximum exposure						$ 224,000,000
Total number of MGP sites | MGPSite						42
Sites approved for clean-up | MGPSite						17
Sites under study/remediation | MGPSite						25
Minimum number of customers ComEd can be held liable to for power interruption | Customer						30,000
Commonwealth Edison Co [Member] | Accrual For MGP Investigation And Remediation [Member]
Commitments and Contingencies [Line Items]
Increase (decrease) in accrual for environmental loss contingencies					$ 50,000,000
PECO Energy Co [Member]
Commitments and Contingencies [Line Items]
Guarantee obligations maximum exposure						$ 209,000,000
Total number of MGP sites | MGPSite						26
Sites approved for clean-up | MGPSite						16
Sites under study/remediation | MGPSite						10
Baltimore Gas and Electric Company [Member]
Commitments and Contingencies [Line Items]
Guarantee obligations maximum exposure						$ 262,000,000
Total number of MGP sites | MGPSite						13
Sites under study/remediation | MGPSite						2
Maximum estimated clean-up costs for all potentially responsible parties									$ 1,700,000
Number of claimants | claimant						454
Baltimore Gas and Electric Company [Member] | Deferrable Interest Subordinated Debentures [Member]
Commitments and Contingencies [Line Items]
Interest rate on long-term debt						6.20%
Baltimore Gas and Electric Company [Member] | Accrual For MGP Investigation And Remediation [Member]
Commitments and Contingencies [Line Items]
Increase (decrease) in accrual for environmental loss contingencies					$ 1,000,000
Baltimore Gas and Electric Company [Member] | Sixty-Eighth Street Dump [Member]
Commitments and Contingencies [Line Items]
Number of parties jointly and severally liable In environmental protection agency action | Principle_responsible_party				19				19
Minimum estimated clean-up costs for all potentially responsible parties						$ 50,000,000
Maximum estimated clean-up costs for all potentially responsible parties						$ 64,000,000
[1]	Nuclear insurance premiums—Represents the maximum amount that Generation would be required to pay for retrospective premiums in the event of nuclear disaster at any domestic site under the Secondary Financial Protection pool as required under the Price-Anderson Act as well as the current aggregate annual retrospective premium obligation that could be imposed by NEIL. See the Nuclear Insurance section within this note for additional details on Generation’s nuclear insurance premiums.
[2]	Nuclear insurance premiums — Represents the maximum amount that Generation would be required to pay for retrospective premiums in the event of nuclear disaster at any domestic site, including CENG sites, under the Secondary Financial Protection pool as required under the Price-Anderson Act as well as the current aggregate annual retrospective premium obligation that could be imposed by NEIL. See the Nuclear Insurance section within this note for additional details on Generation’s nuclear insurance premiums.

Commitments and Contingencie178

Commitments and Contingencies - Schedule of Government Agreement Settlements (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Dec. 31, 2014	Dec. 31, 2015
Schedule of Government Agreements [Line Items]
Nontrade Receivables, Current		$ 82	$ 76
Nontrade Receivables, Noncurrent		7	14
Accounts Payable, Other, Current		(5)	(5)
Exelon Generation Co L L C [Member]
Schedule of Government Agreements [Line Items]
Spent Nuclear Fuel Storage Reimbursement			945
Spent Nuclear Fuel Storage Reimbursement Net Co Owners			$ 804
Department of Energy [Member] | Exelon Generation Co L L C [Member]
Schedule of Government Agreements [Line Items]
Spent Nuclear Fuel Storage Reimbursement	[1]	53
Spent Nuclear Fuel Storage Reimbursement Net Co Owners	[1],[2]	$ 49
[1]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246NDZFNjY1NjNDNkE4N0FEQUQwMUMxMjI1RThCRDQ0RjkM}
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246MDBDNEZCMjM3MzFBMTJCOTZFMDExMjI1RThCRDA3MEYM}

Commitments and Contingencie179

Commitments and Contingencies - Schedule of Energy Supply Procurement, Curtailment Services, REC and AEC Purchase Commitments (Details)	12 Months Ended
	Dec. 31, 2015
Commonwealth Edison Co [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Term of contract	20 years

Commitments and Contingencie180

Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Dec. 31, 2015USD ($)
Guarantor Obligations [Line Items]
Total	$ 9,206
2,015	5,424
2,016	54
2,017	3
2,018	2
2,019	29
2020 and beyond	$ 3,694
Percentage ownership of common stock	100.00%
Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	$ 1,583	[1]
2,015	1,565	[1]
2,016	5	[1]
2,017	0	[1]
2,018	0	[1]
2,019	13	[1]
2020 and beyond	0	[1]
Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	809	[2]
2,015	733	[2]
2,016	49	[2]
2,017	3	[2]
2,018	2	[2]
2,019	16	[2]
2020 and beyond	6	[2]
Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	628	[3]
2,015	0	[2]
2,016	0	[2]
2,017	0	[2]
2,018	0	[2]
2,019	0	[2]
2020 and beyond	628	[2]
Energy Contract Guarantee [Member]
Guarantor Obligations [Line Items]
Total	3,126	[4]
2,015	3,126	[4]
2,016	0	[4]
2,017	0	[4]
2,018	0	[4]
2,019	0	[4]
2020 and beyond	0	[4]
Estimated total assumed for commercial transaction obligations	3,100
Nuclear Insurance Premiums [Member]
Guarantor Obligations [Line Items]
Total	3,060	[5]
2,015	0	[5]
2,016	0	[5]
2,017	0	[5]
2,018	0	[5]
2,019	0	[5]
2020 and beyond	3,060	[5]
Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Guarantor Obligations [Line Items]
Estimated net exposure for commercial transaction obligations	500
Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Total	262
2,015	12
2,016	0
2,017	0
2,018	0
2,019	0
2020 and beyond	250
Baltimore Gas and Electric Company [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	2	[6]
2,015	2	[6]
2,016	0	[6]
2,017	0	[6]
2,018	0	[6]
2,019	0	[6]
2020 and beyond	0	[6]
Baltimore Gas and Electric Company [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	10	[7]
2,015	10	[7]
2,016	0	[7]
2,017	0	[7]
2,018	0	[7]
2,019	0	[7]
2020 and beyond	0	[7]
Baltimore Gas and Electric Company [Member] | Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	250	[8]
2,015	0	[8]
2,016	0	[8]
2,017	0	[8]
2,018	0	[8]
2,019	0	[8]
2020 and beyond	250	[8]
Baltimore Gas and Electric Company [Member] | Trust Preferred Securities [Member]
Guarantor Obligations [Line Items]
Total	250
PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Total	209
2,015	31
2,016	0
2,017	0
2,018	0
2,019	0
2020 and beyond	178
PECO Energy Co [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	22	[9]
2,015	22	[9]
2,016	0	[9]
2,017	0	[9]
2,018	0	[9]
2,019	0	[9]
2020 and beyond	0	[9]
PECO Energy Co [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	9	[10]
2,015	9	[10]
2,016	0	[10]
2,017	0	[10]
2,018	0	[10]
2,019	0	[10]
2020 and beyond	0	[10]
PECO Energy Co [Member] | Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	178	[11]
2,015	0	[11]
2,016	0	[11]
2,017	0	[11]
2,018	0	[11]
2,019	0	[11]
2020 and beyond	178	[11]
PECO Energy Co [Member] | Trust Preferred Securities [Member]
Guarantor Obligations [Line Items]
Total	178
Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Total	224
2,015	22
2,016	0
2,017	2
2,018	0
2,019	0
2020 and beyond	200
Commonwealth Edison Co [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	16	[12]
2,015	16	[12]
2,016	0	[12]
2,017	0	[12]
2,018	0	[12]
2,019	0	[12]
2020 and beyond	0	[12]
Commonwealth Edison Co [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	8	[13]
2,015	6	[13]
2,016	0	[13]
2,017	2	[13]
2,018	0	[13]
2,019	0	[13]
2020 and beyond	0	[13]
Commonwealth Edison Co [Member] | Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	200	[14]
2,015	0	[14]
2,016	0	[14]
2,017	0	[14]
2,018	0	[14]
2,019	0	[14]
2020 and beyond	200	[14]
Commonwealth Edison Co [Member] | Trust Preferred Securities [Member]
Guarantor Obligations [Line Items]
Total	200
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Total	6,832
2,015	3,709
2,016	50
2,017	0
2,018	0
2,019	13
2020 and beyond	3,060
Exelon Generation Co L L C [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	1,503	[15]
2,015	1,485	[15]
2,016	5	[15]
2,017	0	[15]
2,018	0	[15]
2,019	13	[15]
2020 and beyond	0	[15]
Exelon Generation Co L L C [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	737
2,015	692
2,016	45
2,017	0
2,018	0
2,019	0
2020 and beyond	0
Exelon Generation Co L L C [Member] | Energy Contract Guarantee [Member]
Guarantor Obligations [Line Items]
Total	1,532
2,015	1,532	[16]
2,016	0	[16]
2,017	0	[16]
2,018	0	[16]
2,019	0	[16]
2020 and beyond	0	[16]
Estimated total assumed for commercial transaction obligations	1,500
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member]
Guarantor Obligations [Line Items]
Total	3,060	[17]
2,015	0	[17]
2,016	0	[17]
2,017	0	[17]
2,018	0	[17]
2,019	0	[17]
2020 and beyond	3,060	[17]
Exelon Generation Co L L C [Member] | Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Guarantor Obligations [Line Items]
Estimated net exposure for commercial transaction obligations	$ 300
Commonwealth Edison Three [Member] | Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Percentage ownership of common stock	100.00%
PECO Trust III and IV [Member] | PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Percentage ownership of common stock	100.00%
[1]	Letters of credit (non-debt)—Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties.
[2]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[3]	ncludes $200 million of Trust Preferred Securities of ComEd Financing III, $178 million of Trust Preferred Securities of PECO Trust III and IV and $250 million of Trust Preferred Securities of BGE Capital Trust II.
[4]	Energy marketing contract guarantees—Guarantees issued to ensure performance under energy commodity contracts. Amount includes approximately $3.1 billion of guarantees issued by Exelon and Generation on behalf of its Constellation businesses to allow it the flexibility needed to conduct business with counterparties without having to post other forms of collateral. The majority of these guarantees contain evergreen provisions that require the guarantee to remain in effect until cancelled. Exelon’s estimated net exposure for obligations under commercial transactions covered by these guarantees is approximately $0.5 billion at December 31, 2015, which represents the total amount Exelon could be required to fund based on December 31, 2015 market prices.
[5]	Nuclear insurance premiums—Represents the maximum amount that Generation would be required to pay for retrospective premiums in the event of nuclear disaster at any domestic site under the Secondary Financial Protection pool as required under the Price-Anderson Act as well as the current aggregate annual retrospective premium obligation that could be imposed by NEIL. See the Nuclear Insurance section within this note for additional details on Generation’s nuclear insurance premiums.
[6]	Letters of credit (non-debt)—BGE maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties.
[7]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[8]	Performance guarantee—Reflects full and unconditional guarantee of Trust Preferred Securities of BGE Capital Trust which is an unconsolidated VIE of BGE.
[9]	Letters of credit (non-debt)—PECO maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties.
[10]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[11]	Performance guarantees—Reflects full and unconditional guarantee of Trust Preferred Securities of PECO Trust III and IV, which are 100% owned finance subsidiaries of PECO.
[12]	Letters of credit (non-debt)—ComEd maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties.
[13]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[14]	Performance guarantees—Reflects full and unconditional guarantee of Trust Preferred Securities of ComEd Financing III which is a 100% owned finance subsidiary of ComEd.
[15]	Letters of credit (non-debt)—Non-debt letters of credit maintained to provide credit support for certain transactions as requested by third parties.
[16]	Energy marketing contract guarantees—Guarantees issued to ensure performance under energy commodity contracts. Amount includes approximately $1.5 billion of guarantees issued by Generation on behalf of its Constellation businesses to allow it the flexibility needed to conduct business with counterparties without having to post other forms of collateral. The majority of these guarantees contain evergreen provisions that require the guarantee to remain in effect until cancelled. Generation’s estimated net exposure for obligations under commercial transactions covered by these guarantees is approximately $0.3 billion at December 31, 2015, which represents the total amount Generation could be required to fund based on December 31, 2015 market prices.
[17]	Nuclear insurance premiums — Represents the maximum amount that Generation would be required to pay for retrospective premiums in the event of nuclear disaster at any domestic site, including CENG sites, under the Secondary Financial Protection pool as required under the Price-Anderson Act as well as the current aggregate annual retrospective premium obligation that could be imposed by NEIL. See the Nuclear Insurance section within this note for additional details on Generation’s nuclear insurance premiums.

Commitments and Contingencie181

Commitments and Contingencies - Schedule of Equity Investment Commitments (Details) - Equity Method Investments [Member] - Exelon Generation Co L L C [Member] $ in Millions	Dec. 31, 2015USD ($)
Guarantor Obligations [Line Items]
2,015	$ 299
2,016	21
2,017	7
2,018	0
Total	$ 327

Commitments and Contingencie182

Commitments and Contingencies - Schedule of Minimum Future Operating Lease Payments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Operating Leases Future Minimum Payments Due [Line Items]
2,015	$ 133
2,016	109
2,017	86
2,018	74
2,019	70
Remaining years	702
Total minimum future lease payments	1,174	[1]
Exelon Generation Co L L C [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,015	86	[2]
2,016	69	[2]
2,017	57	[2]
2,018	45	[2]
2,019	44	[2]
Remaining years	655	[2]
Total minimum future lease payments	956	[1],[2]
Exelon Generation Co L L C [Member] | Baltimore Headquarters [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,016	10
2,017	11
2,018	13
2,019	14
Remaining years	271
Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,015	14	[3]
2,016	9	[3]
2,017	5	[3]
2,018	5	[3]
2,019	3	[3]
Remaining years	1	[3]
Total minimum future lease payments	37	[3]
Commonwealth Edison Co [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments	2
PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,015	3	[3]
2,016	3	[3]
2,017	2	[3]
2,018	2	[3]
2,019	2	[3]
Remaining years	0	[3]
Total minimum future lease payments	12	[3]
PECO Energy Co [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments	3
Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,015	12	[3],[4]
2,016	10	[3],[4]
2,017	9	[3],[4]
2,018	8	[3],[4]
2,019	7	[3],[4]
Remaining years	19	[3],[4]
Total minimum future lease payments	$ 65	[3],[4]
Baltimore Gas and Electric Company [Member] | Baltimore Headquarters [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Term of lease	20 years
Baltimore Gas and Electric Company [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments	$ 1
[1]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246RjY0REJFRDkzMzlGREY0NDZBNjExMjI1RThCRDI3MDcM}
[2]	The Generation column above includes minimum future lease payments associated with a 20-year lease agreement for the Baltimore headquarters that became effective during the second quarter of 2015. Generation’s total commitments under the lease agreement are $4 million, $10 million, $11 million, $13 million, $14 million, and $271 million related to years 2016, 2017, 2018, 2019, 2020 and thereafter, respectively.
[3]	Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO and BGE have excluded these payments from the remaining years, as such amounts would not be meaningful. ComEd’s, PECO’s, and BGE’s annual obligation for these arrangements, included in each of the years 2016—2020, was $2 million, $3 million, and $1 million respectively.
[4]	Includes all future lease payments on a 99 year real estate lease that expires in 2106.

Commitments and Contingencie183

Commitments and Contingencies - Schedule of Future Rental Expense under Operating Leases (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense		$ 922	$ 865	$ 806
Exelon Generation Co L L C [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense	[1]	851	806	744
Long Term Contract For Purchase Of Electric Power Capacity		798	755	694
Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense		12	15	15
PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense		9	14	21
Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense		$ 32	$ 12	$ 11
[1]	Includes contingent operating lease payments associated with contracted generation agreements that are not included in the minimum future operating lease payments table above. Payments made under Generation’s contracted generation lease agreements totaled $798 million, $755 million and $694 million during 2015, 2014 and 2013, respectively.

Commitments and Contingencie184

Commitments and Contingencies - Schedule of Environmental Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Total Accrual For Environmental Loss Contingencies [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	$ 369	$ 347
Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	301	277
Exelon Generation Co L L C [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	63	63
Exelon Generation Co L L C [Member] | Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	0	0
Commonwealth Edison Co [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	266	238
Commonwealth Edison Co [Member] | Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	264	235
PECO Energy Co [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	37	45
PECO Energy Co [Member] | Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	35	42
Baltimore Gas and Electric Company [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	3	1
Baltimore Gas and Electric Company [Member] | Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	$ 2	$ 0

Supplemental Financial Infor185

Supplemental Financial Information - Summary of Taxes other than Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Financial Information Tables [Line Items]
Utility Taxes	[1]	$ 474	$ 456	$ 449
Property		407	396	302
Payroll		201	200	159
Other		118	102	185
Total taxes other than income		1,200	1,154	1,095
Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Utility Taxes	[1]	105	89	79
Property		250	240	205
Payroll		118	118	89
Other		16	18	16
Total taxes other than income		489	465	389
Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Utility Taxes	[1]	236	238	241
Property		27	25	24
Payroll		28	28	27
Other		5	2	7
Total taxes other than income		296	293	299
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Utility Taxes	[1]	133	128	129
Property		11	15	14
Payroll		14	14	13
Other		2	2	2
Total taxes other than income		160	159	158
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Utility Taxes	[1]	85	86	82
Property		119	114	112
Payroll		16	18	15
Other		4	3	4
Total taxes other than income		$ 224	$ 221	$ 213
[1]	Generation’s utility tax represents gross receipts tax related to its retail operations and ComEd’s, PECO’s and BGE’s utility taxes represent municipal and state utility taxes and gross receipts taxes related to their operating revenues. The offsetting collection of utility taxes from customers is recorded in revenues on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

Supplemental Financial Infor186

Supplemental Financial Information - Summary of Other Income (Expense) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Financial Information Tables [Line Items]
Gain (Loss) on Sale of Derivatives	[1]	$ (26)
Payments of Debt Restructuring Costs	[2]	(22)
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[3]	232	$ 216	$ 256
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[3]	156	159	77
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		(282)	180	406
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		(197)	134	146
Net unrealized income (losses) on pledged assets		7	29	7
Regulatory offset to decommissioning trust fund-related activities	[4]	21	(358)	(546)
Total decommissioning-related activities		(63)	360	346
Investment income		8	1	8
Long-term lease income		15	24	28
Interest income related to uncertain income tax positions		1	40	24
AFUDC—Equity		24	21	22
Other		17	9	32
Other, net		(46)	455	460
Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[3]	232	216	256
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[3]	156	159	77
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		(282)	180	406
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		(197)	134	146
Net unrealized income (losses) on pledged assets		7	29	7
Regulatory offset to decommissioning trust fund-related activities	[4]	21	(358)	(546)
Total decommissioning-related activities		(63)	360	346
Investment income		3	1	(1)
Long-term lease income		0	0	0
Interest income related to uncertain income tax positions		1	54	4
AFUDC—Equity		0	0	0
Other		(1)	(9)	6
Other, net		(60)	406	355
Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[3]	0	0	0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[3]	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0	0
Net unrealized income (losses) on pledged assets		0	0	0
Regulatory offset to decommissioning trust fund-related activities	[4]	0	0	0
Total decommissioning-related activities		0	0	0
Investment income		0	0	0
Long-term lease income		0	0	0
Interest income related to uncertain income tax positions		0	0	0
AFUDC—Equity		5	3	11
Other		16	14	15
Other, net		21	17	26
Other Income		21
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[3]	0	0	0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[3]	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0	0
Net unrealized income (losses) on pledged assets		0	$ 0	$ 0
Regulatory offset to decommissioning trust fund-related activities	[4]	0
Total decommissioning-related activities		0	$ 0	$ 0
Investment income			(1)	(1)
Long-term lease income		0	0	0
Interest income related to uncertain income tax positions		0	0	0
AFUDC—Equity		5	6	4
Other		2	2	3
Other, net		5	7	6
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[3]	0	0	0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[3]	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0	0
Net unrealized income (losses) on pledged assets		0	$ 0	0
Regulatory offset to decommissioning trust fund-related activities	[4]	0		0
Total decommissioning-related activities		0	$ 0	0
Investment income	[5]	4	7	9
Long-term lease income		0	0	0
Interest income related to uncertain income tax positions		0	0	0
AFUDC—Equity		14	12	7
Other		0	(1)	1
Other, net		$ 18	$ 18	$ 17
[1]	In January 2015, in connection with Generation's $750 million issuance of five-year Senior Unsecured Notes, Exelon terminated certain floating-to-fixed interest rate swaps. As the original forecasted transactions were a series of future interest payments over a ten year period, a portion of the anticipated interest payments are probable not to occur. As a result, $26 million of anticipated payments were reclassified from Accumulated OCI to Other, net in Exelon's Consolidated Statement of Operations and Comprehensive Income.
[2]	(e)See Note 14—Debt and Credit Agreements and 4—Mergers, Acquisitions, and Dispositions for additional information on the PHI merger related debt exchange.
[3]	Includes investment income and realized gains and losses on sales of investments within the nuclear decommissioning trust funds.
[4]	Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 16 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.
[5]	Relates to the cash return on BGE’s rate stabilization deferral. See Note 3 — Regulatory Matters for additional information regarding the rate stabilization deferral.

Supplemental Financial Infor187

Supplemental Financial Information - Summary of Depreciation, Amortization, Accretion and Depletion (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment		$ 2,227	$ 2,080	$ 1,893
Regulatory assets		170	191	212
Amortization of intangible assets, net		54	44	48
Nuclear fuel	[1]	1,116	1,073	921
ARO accretion	[2]	398	345	275
Total depreciation, amortization, accretion and depletion		3,987	3,868	3,779
Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment		1,007	922	813
Regulatory assets		0	0	0
Amortization of intangible assets, net		47	44	43
Nuclear fuel	[1]	1,116	1,073	921
ARO accretion	[2]	397	345	275
Total depreciation, amortization, accretion and depletion		2,589	2,519	2,559
Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment		635	588	545
Regulatory assets		72	99	119
Amortization of intangible assets, net		0	0	5
Amortization of Intangible Assets		7	7	7
Nuclear fuel	[1]	0	0	0
ARO accretion	[2]	0	0	0
Total depreciation, amortization, accretion and depletion		707	687	669
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment		240	227	219
Regulatory assets		20	9	9
Amortization of intangible assets, net		0	0	0
Nuclear fuel	[1]	0	0	0
ARO accretion	[2]	0	0	0
Total depreciation, amortization, accretion and depletion		260	236	228
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment		289	288	264
Regulatory assets		77	83	84
Amortization of intangible assets, net		0	0	0
Nuclear fuel	[1]	0	0	0
ARO accretion	[2]	0	0	0
Total depreciation, amortization, accretion and depletion		366	371	348
Unamortized Energy Contracts [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]	22	135	430
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]	22	135	507
Unamortized Energy Contracts [Member] | Commonwealth Edison Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]	0
Unamortized Energy Contracts [Member] | Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]		0	0
Unamortized Energy Contracts [Member] | PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]	0	0	0
Unamortized Energy Contracts [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]	$ 0	$ 0	$ 0
[1]	Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[2]	Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[3]	Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

Supplemental Financial Infor188

Supplemental Financial Information - Supplemental Cash Flow Information (Details) - USD ($)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)		$ 930,000,000	$ 940,000,000		$ 866,000,000
Income taxes (net of refunds)		342,000,000	314,000,000		112,000,000
Pension and non-pension postretirement benefit costs		637,000,000	560,000,000		825,000,000
Income (Loss) from Equity Method Investments			20,000,000		(10,000,000)
Provision for uncollectible accounts		120,000,000	156,000,000		101,000,000
Provision for excess and obsolete inventory		10,000,000	5,000,000		9,000,000
Stock-based compensation costs		97,000,000	91,000,000		120,000,000
Other decommissioning related-activity		(82,000,000)	(132,000,000)		(169,000,000)
Energy-related options		21,000,000	122,000,000		104,000,000
Amortization of regulatory asset related to debt costs		7,000,000	11,000,000		12,000,000
Amortization of rate stabilization deferral		73,000,000	65,000,000		66,000,000
Amortization of debt fair value adjustment		(17,000,000)	(23,000,000)		(34,000,000)
Merger-related commitments			44,000,000
Discrete impacts from EIMA		144,000,000	53,000,000		(271,000,000)
Amortization of debt costs		58,000,000	53,000,000		18,000,000
Lower of cost or market inventory adjustment		23,000,000	29,000,000
Other		11,000,000	(2,000,000)		(53,000,000)
Total other non-cash operating activities		1,109,000,000	1,054,000,000		718,000,000
Total changes in other assets and liabilities		387,000,000	157,000,000		(128,000,000)
Change in PPE related to ARO update		885,000,000	72,000,000		(128,000,000)
Change in capital expenditures not paid		96,000,000	220,000,000		(38,000,000)
Consolidated VIE dividend to noncontrolling			421,000,000
Noncash Purchase Accounting Adjustment			3,400,000,000
Fair value of net assets recorded upon CENG consolidation			(131,000,000)
Indemnification of like-kind exchange position					0
Other Cost and Expense, Operating		8,322,000,000	8,568,000,000		7,270,000,000
Non Cash Licensing Agreement	[1]	95,000,000
Antelope Valle [Member]
Supplemental Cash Flow Information [Line Items]
Change in capital expenditures not paid			170,000,000
Nuclear Fuel Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	[2]	57,000,000
Capital Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired		77,000,000
Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired			70,000,000
Indemnification of like-kind exchange position		0	0
Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)		348,000,000	322,000,000		291,000,000
Income taxes (net of refunds)		476,000,000	227,000,000		(18,000,000)
Pension and non-pension postretirement benefit costs		269,000,000	249,000,000		345,000,000
Income (Loss) from Equity Method Investments		(8,000,000)	20,000,000		(10,000,000)
Provision for uncollectible accounts		22,000,000	14,000,000		10,000,000
Provision for excess and obsolete inventory		9,000,000	5,000,000		9,000,000
Stock-based compensation costs		0	0		0
Other decommissioning related-activity		(82,000,000)	(132,000,000)		(169,000,000)
Energy-related options		21,000,000	122,000,000		104,000,000
Amortization of regulatory asset related to debt costs		0	0		0
Amortization of rate stabilization deferral		0	0		0
Amortization of debt fair value adjustment		(17,000,000)	(23,000,000)		(34,000,000)
Merger-related commitments			44,000,000
Discrete impacts from EIMA		0	0		0
Amortization of debt costs		15,000,000	12,000,000		10,000,000
Lower of cost or market inventory adjustment		23,000,000	29,000,000
Other		0	6,000,000		5,000,000
Total other non-cash operating activities		268,000,000	346,000,000		270,000,000
Total changes in other assets and liabilities		207,000,000	(57,000,000)		85,000,000
Change in PPE related to ARO update		885,000,000	72,000,000		(128,000,000)
Change in capital expenditures not paid		82,000,000	(61,000,000)		(107,000,000)
Consolidated VIE dividend to noncontrolling					63,000,000
Noncash Purchase Accounting Adjustment			3,400,000,000
Indemnification of like-kind exchange position					0
Other Cost and Expense, Operating		4,688,000,000	4,943,000,000		3,960,000,000
Exelon Generation Co L L C [Member] | Nuclear Fuel Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	[2]	57,000,000
Exelon Generation Co L L C [Member] | Capital Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired		77,000,000
Exelon Generation Co L L C [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired			70,000,000
Indemnification of like-kind exchange position		0	0
Commonwealth Edison Co [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)		308,000,000	292,000,000		283,000,000
Income taxes (net of refunds)		(265,000,000)	(6,000,000)		33,000,000
Pension and non-pension postretirement benefit costs		206,000,000	162,000,000		308,000,000
Income (Loss) from Equity Method Investments		0	0		0
Provision for uncollectible accounts		53,000,000	26,000,000		(15,000,000)
Provision for excess and obsolete inventory		1,000,000	0		0
Stock-based compensation costs		0	0		0
Other decommissioning related-activity		0	0		0
Energy-related options		0	0		0
Amortization of regulatory asset related to debt costs		5,000,000	8,000,000		9,000,000
Amortization of rate stabilization deferral		0	0		0
Amortization of debt fair value adjustment		0	0		0
Merger-related commitments			0
Discrete impacts from EIMA		144,000,000	53,000,000		(271,000,000)
Amortization of debt costs		4,000,000	4,000,000		1,000,000
Lower of cost or market inventory adjustment		0
Other		3,000,000	2,000,000		(4,000,000)
Total other non-cash operating activities		416,000,000	255,000,000		28,000,000
Total changes in other assets and liabilities		(69,000,000)	(1,000,000)		(171,000,000)
Change in PPE related to ARO update		0	0		0
Change in capital expenditures not paid		34,000,000	78,000,000		(8,000,000)
Issuance of equity units			0
Indemnification of like-kind exchange position		202,000,000	273,000,000		176,000,000
Other Cost and Expense, Operating		1,372,000,000	1,263,000,000		1,211,000,000
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options		0
Indemnification of like-kind exchange position		7,000,000	5,000,000
PECO Energy Co [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)		94,000,000	94,000,000		95,000,000
Income taxes (net of refunds)		64,000,000	85,000,000		70,000,000
Pension and non-pension postretirement benefit costs		39,000,000	36,000,000		43,000,000
Income (Loss) from Equity Method Investments		0	0		0
Provision for uncollectible accounts		30,000,000	52,000,000		61,000,000
Provision for excess and obsolete inventory		0	0		0
Stock-based compensation costs		0	0		0
Other decommissioning related-activity		0	0		0
Energy-related options		0	0		0
Amortization of regulatory asset related to debt costs		2,000,000	3,000,000		3,000,000
Amortization of rate stabilization deferral		0	0		0
Amortization of debt fair value adjustment		0	0		0
Merger-related commitments			0
Discrete impacts from EIMA		0	0		0
Amortization of debt costs		2,000,000	2,000,000		2,000,000
Lower of cost or market inventory adjustment		0
Other		(3,000,000)	(1,000,000)		(1,000,000)
Total other non-cash operating activities		70,000,000	92,000,000		108,000,000
Total changes in other assets and liabilities		4,000,000	21,000,000		(4,000,000)
Change in PPE related to ARO update		0	0		0
Change in capital expenditures not paid		(13,000,000)	0		13,000,000
Issuance of equity units			0
Indemnification of like-kind exchange position		16,000,000	24,000,000		27,000,000
Other Cost and Expense, Operating		684,000,000	767,000,000		647,000,000
PECO Energy Co [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options		0
Indemnification of like-kind exchange position		0	0
Baltimore Gas and Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)		120,000,000	111,000,000		130,000,000
Income taxes (net of refunds)		73,000,000	(21,000,000)		42,000,000
Pension and non-pension postretirement benefit costs		65,000,000	64,000,000		56,000,000
Income (Loss) from Equity Method Investments		0	0		0
Provision for uncollectible accounts		15,000,000	64,000,000		44,000,000
Provision for excess and obsolete inventory		0	0		0
Stock-based compensation costs		0	0		0
Other decommissioning related-activity		0	0	[3]	0	[4]
Energy-related options		0	0	[5]	0	[6]
Amortization of regulatory asset related to debt costs		0	0		0
Amortization of rate stabilization deferral		73,000,000	65,000,000		66,000,000
Amortization of debt fair value adjustment		0	0		0
Merger-related commitments			0
Discrete impacts from EIMA		0	0	[7]	0	[8]
Amortization of debt costs		2,000,000	2,000,000		2,000,000
Lower of cost or market inventory adjustment		0
Other		(18,000,000)	(15,000,000)		(15,000,000)
Total other non-cash operating activities		137,000,000	180,000,000		153,000,000
Total changes in other assets and liabilities		173,000,000	158,000,000		72,000,000
Change in PPE related to ARO update		0	0		4,000,000
Change in capital expenditures not paid		(9,000,000)	25,000,000		48,000,000
Noncash Purchase Accounting Adjustment			0
Issuance of equity units			0
Indemnification of like-kind exchange position		7,000,000	0		0
Other Cost and Expense, Operating		565,000,000	614,000,000		551,000,000
Baltimore Gas and Electric Company [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options		0
Indemnification of like-kind exchange position		0	0	[9]
Exelon Consolidations [Member]
Supplemental Cash Flow Information [Line Items]
Income (Loss) from Equity Method Investments		$ (7,000,000)	$ 22,000,000
Constellation Energy Group Acquisition [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling					63,000,000
Constellation Energy Group Acquisition [Member] | Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling					63,000,000
Constellation Energy Group Acquisition [Member] | Commonwealth Edison Co [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling					0
Constellation Energy Group Acquisition [Member] | PECO Energy Co [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling					0
Constellation Energy Group Acquisition [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling					$ 0
[1]	(f)Relates to a long-term software license agreement entered into on May 30, 2015. Exelon is required to make payments starting August of 2015 through May of 2024. See Note 14 — Debt and Credit Agreements for additional information.
[2]	(d)Relates to the nuclear fuel procurement contract for the purchase of fixed quantities of converted uranium, which was delivered to Generation in 2015. Generation is required to make payments starting September 28, 2018, with the final payment being due no later than September 30, 2020.
[3]	Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 16 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.
[4]	Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 16 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.
[5]	Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.
[6]	Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.
[7]	Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate tariff. See Note 3 — Regulatory Matters for more information.
[8]	(d)Includes $55 million of changes in capital expenditures not paid between December 31, 2013 and 2012 related to Antelope Valley.
[9]	Relates to the present value of the contract payments for the equity units issued by Exelon. See Note 20 — Stock-Based Compensation Plans for additional information.

Supplemental Financial Infor189

Supplemental Financial Information - Narrative (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Supplemental Financial Information Tables [Line Items]
Gain (Loss) on Sale of Derivatives	[1]	$ (26)
Amount included in capital expenditures			$ 74
Smart Grid Grant Reimbursements			95
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Amount included in capital expenditures		2	27
Smart Grid Grant Reimbursements		5	37
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Amount included in capital expenditures			47
Smart Grid Grant Reimbursements			$ 58
Reclassification out of Accumulated Other Comprehensive Income [Member]
Supplemental Financial Information Tables [Line Items]
Gain (Loss) on Sale of Derivatives		$ 26
[1]	In January 2015, in connection with Generation's $750 million issuance of five-year Senior Unsecured Notes, Exelon terminated certain floating-to-fixed interest rate swaps. As the original forecasted transactions were a series of future interest payments over a ten year period, a portion of the anticipated interest payments are probable not to occur. As a result, $26 million of anticipated payments were reclassified from Accumulated OCI to Other, net in Exelon's Consolidated Statement of Operations and Comprehensive Income.

Supplemental Financial Infor190

Supplemental Financial Information - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013	Mar. 31, 2015
Supplemental Balance Sheet Information [Line Items]
Change in capital expenditures not paid		$ 96	$ 220		$ (38)
Total equity method investments		112	50
Net investment in leases (b)		352	361
Total investments		639	544
Compensation-related accruals	[1]	1,014	832
Taxes accrued		293	305			$ 65
Interest accrued		915	240
Severance accrued		21	49
Other accrued expenses		133	113	[2]
Total accrued expenses		2,376	1,539
Antelope Valle [Member]
Supplemental Balance Sheet Information [Line Items]
Change in capital expenditures not paid			170
Other accrued expenses			19		55
Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	22	22
Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		63	13
Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		23	9
Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		4	1
Sunnyside [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments			5
Trust for Benefit of Employees [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[4]	85	85
Other Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Available-for-sale Securities, Noncurrent		29	5
Cost Method Investments		55	37
Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Change in capital expenditures not paid		82	(61)		(107)
Total equity method investments		89	28
Net investment in leases (b)	[5]	6	7
Total investments		210	104
Compensation-related accruals	[1]	547	447
Taxes accrued		186	248
Interest accrued		77	66
Severance accrued		11	33
Other accrued expenses		114	92	[2]
Total accrued expenses		935	886
Exelon Generation Co L L C [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	0	0
Exelon Generation Co L L C [Member] | Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		63	13
Exelon Generation Co L L C [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		23	9
Exelon Generation Co L L C [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		3	1
Exelon Generation Co L L C [Member] | Sunnyside [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments			5
Exelon Generation Co L L C [Member] | Trust for Benefit of Employees [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[4]	31	27
Exelon Generation Co L L C [Member] | Other Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Available-for-sale Securities, Noncurrent		29	5
Cost Method Investments		55	37
Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Change in capital expenditures not paid		34	78		(8)
Total equity method investments		6	6
Total investments		6	6
Compensation-related accruals	[1]	183	153
Taxes accrued		63	59
Interest accrued		443	102
Severance accrued		3	2
Other accrued expenses		14	15
Total accrued expenses		706	331
Commonwealth Edison Co [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	6	6
PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Change in capital expenditures not paid		(13)	0		13
Total equity method investments		8	8
Total investments		28	31
Compensation-related accruals	[1]	66	50
Taxes accrued		4	3
Interest accrued		35	33
Severance accrued		0	1
Other accrued expenses		4	4
Total accrued expenses		109	91
PECO Energy Co [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	8	8
PECO Energy Co [Member] | Trust for Benefit of Employees [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[4]	20	23
Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Change in capital expenditures not paid		(9)	25		$ 48
Total equity method investments		8	8
Total investments		12	12
Compensation-related accruals	[1]	57	58
Taxes accrued		23	42
Interest accrued		27	29
Severance accrued		1	2
Other accrued expenses		2	0
Total accrued expenses		110	131
Baltimore Gas and Electric Company [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	8	8
Baltimore Gas and Electric Company [Member] | Trust for Benefit of Employees [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[4]	4	4
Exelon Consolidations [Member]
Supplemental Balance Sheet Information [Line Items]
Net investment in leases (b)	[5]	$ 358	$ 367
[1]	Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits.
[2]	Includes $19 million for amounts accrued related to Antelope Valley as of December 31, 2014.
[3]	Includes investments in affiliated financing trusts, which were not consolidated within the financial statements of Exelon and are shown as investments on the Consolidated Balance Sheets. See Note 1 — Significant Accounting Policies for additional information.
[4]	(c)The Registrants’ investments in these marketable securities are recorded at fair market value.
[5]	Represents direct financing lease investments.

Segment Information - Narrative

Segment Information - Narrative (Details)	12 Months Ended
	Dec. 31, 2015Reportable_segment
Segment Reporting Information [Line Items]
Number of reportable segments	9
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	6

Segment Information - Analysis

Segment Information - Analysis and Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		2 Months Ended	3 Months Ended										12 Months Ended
		Dec. 31, 2014	Dec. 31, 2015		Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues			$ 6,702		$ 7,401	$ 6,514	$ 8,830	$ 7,255	$ 6,912	$ 6,024	$ 7,237		$ 29,447		$ 27,429		$ 24,888
Competitive Energy Revenue													15,200		13,773		12,496
Other Alternative Energy Sales Revenue															154
Electric Revenue													9,876		9,467		9,365
Gas Domestic Regulated Revenue													1,176		1,325		1,246
Other Operating Income													757				46
Revenue from Purchased Oil and Gas													2,433		2,704		1,721
Operating revenues from affiliates													9		23		70
Depreciation and amortization													2,450		2,314		2,153
Operating Expenses	[1]												25,056		25,039		21,242
Equity in earnings (losses) of unconsolidated affiliates													(7)		(20)		10
Interest expense, net													1,033		1,065		1,356
Income (loss) from continuing operations before income taxes													3,330		2,486		2,773
Income taxes													1,073		666		1,044
Net income			309	[2]	629	638	693	18	993	522	90	[3]	2,250		1,820		1,729
Assets	[4]	$ 86,416	95,384					86,416					95,384		86,416
Utility taxes	[5]												474		456		449
Payments to Acquire Property, Plant, and Equipment													7,624		6,077		5,395
Sales Revenue, Services, Other													5		6		14
PECO Energy Co Affiliate [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[6]												1		1		10
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues													4,710		4,475		4,270
Operating Segments [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue	[7]												15,944		14,533		13,862
Electric Revenue	[7]												0		0		0
Gas Domestic Regulated Revenue	[7]												0		0		0
Other Operating Income	[7]												758		155		47
Revenue from Purchased Oil and Gas	[7]												2,433		2,705		1,721
Depreciation and amortization	[7]												1,054		967		856
Operating Expenses	[1],[7]												16,872		16,923		13,976
Equity in earnings (losses) of unconsolidated affiliates	[7]												(8)		(20)		10
Interest expense, net	[7]												365		356		357
Income (loss) from continuing operations before income taxes	[7]												1,850		1,226		1,675
Income taxes	[7]												502		207		615
Net income	[7]												1,340		1,019		1,060
Assets	[7]	44,951	46,529					44,951					46,529		44,951
Payments to Acquire Property, Plant, and Equipment	[7]												3,841		3,012		2,752
Sales Revenue, Services, Other	[7]												0		0		0
Operating Segments [Member] | Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue													0		0		0
Electric Revenue													4,905		4,564		4,464
Gas Domestic Regulated Revenue													0		0		0
Other Operating Income													0		0		0
Revenue from Purchased Oil and Gas													0		0		0
Depreciation and amortization													707		687		669
Operating Expenses	[1]												3,889		3,586		3,510
Equity in earnings (losses) of unconsolidated affiliates													0		0		0
Interest expense, net													332		321		579
Income (loss) from continuing operations before income taxes													706		676		401
Income taxes													280		268		152
Net income													426		408		249
Assets		25,358	26,532					25,358					26,532		25,358
Payments to Acquire Property, Plant, and Equipment													2,398		1,689		1,433
Sales Revenue, Services, Other													0		0		0
Operating Segments [Member] | PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue													0		0		0
Electric Revenue													2,486		2,448		2,500
Gas Domestic Regulated Revenue													546		646		600
Other Operating Income													0		0		0
Revenue from Purchased Oil and Gas													0		0		0
Depreciation and amortization													260		236		228
Operating Expenses	[1]												2,404		2,522		2,434
Equity in earnings (losses) of unconsolidated affiliates													0		0		0
Interest expense, net													114		113		115
Income (loss) from continuing operations before income taxes													521		466		557
Income taxes													143		114		162
Net income													378		352		395
Assets		9,860	10,367					9,860					10,367		9,860
Payments to Acquire Property, Plant, and Equipment													601		661		537
Sales Revenue, Services, Other													0		0		0
Operating Segments [Member] | Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue	[8]												0		0		0
Electric Revenue	[8]												2,490		2,460		2,405
Gas Domestic Regulated Revenue	[8]												645		705		660
Other Operating Income	[8]												0		0		0
Revenue from Purchased Oil and Gas	[8]												0		0		0
Depreciation and amortization	[8]												366		371		348
Operating Expenses	[1],[8]												2,578		2,726		2,616
Equity in earnings (losses) of unconsolidated affiliates	[8]												0		0		0
Interest expense, net	[8]												99		106		122
Income (loss) from continuing operations before income taxes	[8]												477		351		344
Income taxes	[8]												189		140		134
Net income	[8]												288		211		210
Assets	[8]	8,056	8,295					8,056					8,295		8,056
Payments to Acquire Property, Plant, and Equipment	[8]												719		620		587
Sales Revenue, Services, Other	[8]												0		0		0
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[9]												4,712		4,488		4,298
Other Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue	[10]												0		0		0
Electric Revenue	[10]												0		0		0
Gas Domestic Regulated Revenue	[10]												0		0		0
Other Operating Income	[10]												0		0		0
Revenue from Purchased Oil and Gas	[10]												0		0		0
Depreciation and amortization	[10]												63		53		52
Operating Expenses	[1],[10]												1,444		1,353		1,324
Equity in earnings (losses) of unconsolidated affiliates	[10]												1		0		0
Interest expense, net	[10]												123		169		183
Income (loss) from continuing operations before income taxes	[10]												(219)		(227)		(191)
Income taxes	[10]												(41)		(63)		(20)
Net income	[10]												(177)		(164)		(171)
Assets	[10]	9,711	15,389					9,711					15,389		9,711
Payments to Acquire Property, Plant, and Equipment	[10]												65		95		86
Sales Revenue, Services, Other	[10]												1,372		1,285		1,241
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue													(744)		(760)		(1,366)
Electric Revenue													(5)		(5)		(4)
Gas Domestic Regulated Revenue													(15)		(26)		(14)
Other Operating Income													(1)		(1)		(1)
Revenue from Purchased Oil and Gas													0		(1)		0
Operating revenues from affiliates	[11]												5		6		14
Depreciation and amortization													0		0		0
Operating Expenses	[1]												(2,131)		(2,071)		(2,618)
Equity in earnings (losses) of unconsolidated affiliates													0		0		0
Interest expense, net													0		0		0
Income (loss) from continuing operations before income taxes													(5)		(6)		(13)
Income taxes													0		0		1
Net income													(5)		(6)		(14)
Assets		(11,520)	(11,728)					(11,520)					(11,728)		(11,520)
Payments to Acquire Property, Plant, and Equipment													0		0		0
Sales Revenue, Services, Other													(1,367)		(1,279)		(1,227)
Intersegment Eliminations [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates													745		762	[7],[11]	1,367	[7],[11]
Intersegment Eliminations [Member] | Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates													4		4	[11]	3	[11]
Intersegment Eliminations [Member] | PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates													2	[12]	2	[11]	1	[11]
Intersegment Eliminations [Member] | Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates													14	[13]	25	[8],[11]	13	[8],[11]
Intersegment Eliminations [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[10],[11]												1,367		1,280		1,237
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates													(2)		(13)		(28)
Intersegment Eliminations [Member] | Segment Elimination [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11]												(2,127)		(2,067)		(2,607)
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues		386	4,294		4,768	4,232	5,840	4,802	4,412	3,789	4,390		19,135		17,393		15,630
Operating revenues from affiliates													749		779		1,423
Equity in earnings (losses) of unconsolidated affiliates													(8)
Income (loss) from continuing operations before income taxes													1,850		1,226		1,675
Income taxes													502		207		615
Net income		(42)	154		377	398	443	(91)	771	340	(185)		1,340		1,019		1,060
Assets	[14]	44,951	46,529					44,951					46,529		44,951
Utility taxes	[5]												105		89		79
Payments to Acquire Property, Plant, and Equipment													3,841		3,012		2,752
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[15]												224		198		405
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[16]												502		387		455
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[17]												18		176		506
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member] | Commonwealth Edison Co Affiliate [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[17]																7
Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Revenues			1,196		1,376	1,148	1,185	1,079	1,222	1,128	1,134		4,905		4,564		4,464
Operating revenues from affiliates													4		4		3
Income taxes													280		268		152
Net income			87		149	99	90	73	126	111	98		426		408		249
Assets		25,358	26,532					25,358					26,532		25,358
Utility taxes	[5]												236		238		241
Payments to Acquire Property, Plant, and Equipment													2,398		1,689		1,433
PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Revenues			645		740	661	985	750	693	656	993		3,032		3,094		3,100
Electric Revenue													2,485		2,446		2,499
Gas Domestic Regulated Revenue													545		646		600
Operating revenues from affiliates													2		2		1
Income (loss) from continuing operations before income taxes													521		466		557
Income taxes													143		114		162
Net income			79		90	70	139	98	81	84	89		378		352		395
Assets		9,860	10,367					9,860					10,367		9,860
Utility taxes	[5]												133		128		129
Payments to Acquire Property, Plant, and Equipment													601		661		537
Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Revenues			746		725	628	1,036	761	697	653	1,054		3,135		3,165		3,065
Electric Revenue													2,490		2,460		2,405
Gas Domestic Regulated Revenue													631		680		647
Operating revenues from affiliates													14		25		13
Income (loss) from continuing operations before income taxes													477		351		344
Income taxes													189		140		134
Net income			74		$ 51	$ 44	$ 106	52	$ 46	$ 16	$ 85		288		211		210
Assets	[18]	$ 8,056	$ 8,295					$ 8,056					8,295		8,056
Utility taxes	[5]												85		86		82
Payments to Acquire Property, Plant, and Equipment													$ 719		$ 620		$ 587
[1]	d)Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations and Comprehensive Income.
[2]	Includes charges to earnings related to the impairments of certain generating assets which were held for sale and certain Upstream exploration assets. See Note 8—Impairment of Long-Lived Assets of the Combined Notes to Consolidated Financial Statements for additional information.
[3]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246NEExNTZFREE4NkYwMUZCQUZDQTExMjI1RThCRDM3QzcM}
[4]	Exelon’s consolidated assets include $8,268 million and $8,159 million at December 31, 2015 and December 31, 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,264 million and $2,728 million at December 31, 2015 and December 31, 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.
[5]	Generation’s utility tax represents gross receipts tax related to its retail operations and ComEd’s, PECO’s and BGE’s utility taxes represent municipal and state utility taxes and gross receipts taxes related to their operating revenues. The offsetting collection of utility taxes from customers is recorded in revenues on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[6]	The intersegment profit associated with the sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statement of Operations. See Note 3—Regulatory Matters for additional information.
[7]	Generation includes the six power marketing reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. For the year ended December 31, 2015, intersegment revenues for Generation include revenue from sales to PECO of $224 million and sales to BGE of $502 million in the Mid-Atlantic region, and sales to ComEd of $18 million in the Midwest region, which eliminate upon consolidation. For the year ended December 31, 2014, intersegment revenues for Generation include revenue from sales to PECO of $198 million and sales to BGE of $387 million in the Mid-Atlantic region, and sales to ComEd of $176 million in the Midwest region, which eliminate upon consolidation. For the year ended December 31, 2013, intersegment revenues for Generation include revenue from sales to PECO of $405 million and sales to BGE of $455 million in the Mid-Atlantic region, and sales to ComEd of $506 million in the Midwest region, net of $7 million related to the unrealized mark-to-market losses related to the ComEd swap, which eliminate upon consolidation.
[8]	(b)Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities.
[9]	(a)On April 1, 2014, Generation assumed operational control of CENG's nuclear fleet. As a result, beginning on April 1, 2014, CENG's revenues are included on a fully consolidated basis.
[10]	(c)For the years ended December 31, 2015, 2014 and 2013, utility taxes of $105 million, $89 million and $79 million, respectively, are included in revenues and expenses for Generation. For the years ended December 31, 2015, 2014 and 2013, utility taxes of $236 million, $238 million and $241 million, respectively, are included in revenues and expenses for ComEd. For the years ended December 31, 2015, 2014 and 2013, utility taxes of $133 million, $128 million and $129 million, respectively, are included in revenues and expenses for PECO. For the years ended December 31, 2015, 2014 and 2013, utility taxes of $85 million, $86 million and $82 million are included in revenues and expenses for BGE, respectively.
[11]	Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations and Comprehensive Income.
[12]	PECO provides energy to Generation for Generation’s own use.
[13]	BGE provides energy to Generation for Generation’s own use.
[14]	Generation’s consolidated assets include $8,235 million and $8,118 million at December 31, 2015 and 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,135 million and $2,512 million at December 31, 2015 and 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities.
[15]	Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has five-year and ten-year agreements with PECO to sell non-solar and solar AECs, respectively. See Note 3—Regulatory Matters for additional information.
[16]	Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[17]	Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3—Regulatory Matters for additional information.
[18]	BGE’s consolidated assets include $26 million and $24 million at December 31, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE that can only be used to settle the liabilities of the VIE. BGE’s consolidated liabilities include $122 million and $197 million at December 31, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. See Note 2 - Variable Interest Entities.

Segment Information - Generatio

Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues		$ 6,702	$ 7,401	$ 6,514	$ 8,830	$ 7,255	$ 6,912	$ 6,024	$ 7,237	$ 29,447	$ 27,429	$ 24,888
Revenue from Related Parties										9	23	70
Amortization of intangible assets related to commodity contracts										7	289	767
Net mark-to market gains (losses)										357	(693)	507
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues										5,900	5,259	5,204
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues										4,710	4,475	4,270
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues										2,212	1,422	1,237
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues										985	843	714
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues										857	935	1,216
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[1]									1,102	1,309	968
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues										15,766	14,243	13,609
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									3,369	3,150	2,021
Net mark-to market gains (losses)										257	(591)	504
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues										19,135	17,393	15,630
Scenario, Adjustment [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties											(284)	(252)
Scenario, Adjustment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties											284	252
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									5,974	5,414	5,261
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									4,712	4,488	4,298
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									2,217	1,468	1,279
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									996	846	717
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									863	938	1,223
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[3]									1,182	1,379	1,084
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									15,944	14,533	13,862
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2],[3]									3,191	2,860	1,768
Net mark-to market gains (losses)										203	(174)	220
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									19,135	17,393	15,630
Operating Segments [Member] | Scenario, Adjustment [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues											284	252
Operating Segments [Member] | Scenario, Adjustment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues											(284)	(252)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	[4]									5	6	14
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(74)	(155)	(57)
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(2)	(13)	(28)
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(5)	(46)	(42)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(11)	(3)	(3)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(6)	(3)	(7)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	[1]									(80)	(70)	(116)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(178)	(290)	(253)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	[2]									178	290	253
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										$ 0	$ 0	$ 0
[1]	(b)Includes all wholesale and retail electric sales to third parties and affiliated sales to ComEd, PECO and BGE.
[2]	(c)Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $7 million increase to revenues, a $289 million decrease to revenues, and a $767 million decrease to revenues for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2015, 2014, and 2013, respectively, unrealized mark-to-market gains of $203 million, losses of $174 million, and gains of $220 million for the years ended December 31, 2015, 2014, and 2013, respectively, and elimination of intersegment revenues.
[3]	(a)On April 1, 2014, Generation assumed operational control of CENG's nuclear fleet. As a result, beginning on April 1, 2014, CENG's revenues are included on a fully consolidated basis.
[4]	Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations and Comprehensive Income.

Segment Information - Genera194

Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel		$ 8	$ 124	$ 488
Net mark-to market gains (losses)		357	(693)	507
Scenario, Adjustment [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total			19
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		3,571	3,431	3,270
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		2,892	2,599	2,586
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		461	351	185
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		634	483	(4)
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		293	317	436
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total	[1]	250	327	201
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		8,101	7,508	6,674
Generation Reportable Segments Total [Member] | Scenario, Adjustment [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers			11	134
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity			8	(134)
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total	[2]	1,013	(40)	759
Net mark-to market gains (losses)		257	(591)	504
Generation All Other Segments [Member] | Scenario, Adjustment [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers			(11)	(134)
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity			(8)	134
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		9,114	7,468	7,433
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	3,556	3,544	3,287
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	2,912	2,607	2,606
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	519	450	299
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	584	439	(55)
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	425	573	627
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[1],[3]	440	517	397
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	8,436	8,130	7,161
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[2],[3]	678	(662)	272
Net mark-to market gains (losses)		203	(174)	220
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	9,114	7,468	7,433
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		15	(113)	(17)
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		(20)	(8)	(20)
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		(58)	(99)	(114)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		50	44	51
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		(132)	(256)	(191)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	[1]	(190)	(190)	(196)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		(335)	(622)	(487)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	[2]	335	622	487
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		$ 0	$ 0	$ 0
[1]	(b)Includes purchases and sales from third parties and affiliated sales to ComEd, PECO and BGE.
[2]	(c)Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $8 million increase in RNF, a $124 million decrease in RNF, and a $488 million decrease in RNF for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2015, 2014, and 2013, respectively, unrealized mark-to-market gains of $257 million, losses of $591 million, and gains of $504 million for the years ended December 31, 2015, 2014, and 2013, respectively, and the elimination of intersegment revenue net of purchased power and fuel expense.
[3]	(a)On April 1, 2014, Generation assumed operational control of CENG's nuclear fleet. As a result, beginning on April 1, 2014, CENG's revenue net of purchased power and fuel expense are included on a fully consolidated basis.

Related Party Transactions - Re

Related Party Transactions - Related Party Transactions included in Consolidated Income Statement (Details) - USD ($) $ in Millions		Apr. 01, 2014	Dec. 31, 2014	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Operating revenues from affiliates												$ 9	$ 23	$ 70
Revenues				$ 6,702	$ 7,401	$ 6,514	$ 8,830	$ 7,255	$ 6,912	$ 6,024	$ 7,237	29,447	27,429	24,888
Purchase power and fuel from affiliates												0	531	1,256
Total interest expense to affiliates, net												41	41	41
Total income (loss) in equity method investments													(20)	10
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions												(7)	(20)	10
Cash dividends paid to parent												$ 1,105	1,065	1,249
Contributions from parent														0
Required purchases of power from CENG's nuclear plants not sold to third parties												85.00%
Purchase of nuclear output of CENG												50.01%
Purchase of nuclear output by EDF												49.99%
PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]											$ 1	1	10
Constellation Energy Nuclear Group Llc Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[2]											0	17	56
Purchase power and fuel from affiliates	[3]											0	282	992
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates												4	5	4
Keystone Fuels LLC Affiliate [Member]
Related Party Transaction [Line Items]
Purchase power and fuel from affiliates	[4]											0	138	144
Conemaugh Fuels LLC Affiliate [Member]
Related Party Transaction [Line Items]
Purchase power and fuel from affiliates	[4]											0	99	98
SafeHarborWaterPowerCorp [Member]
Related Party Transaction [Line Items]
Purchase power and fuel from affiliates	[4]											0	12	22
PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net												6	6	6
ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net												13	13	13
PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net												6	6	6
BGE Capital Trust II [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net	[5]											16	16	16
CENG Equity Investment Income Affiliate [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments	[6]												(19)	9
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	[6]											0
Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates												4
Total income (loss) in equity method investments													(1)	1
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions												1
Qualifying Facilities And Domestic Power Projects Affiliate [Member]
Related Party Transaction [Line Items]
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions												(8)
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			$ 113	83				113				83	113
Operating revenues from affiliates												749	779	1,423
Revenues			386	4,294	4,768	4,232	5,840	4,802	4,412	3,789	4,390	19,135	17,393	15,630
Purchase power and fuel from affiliates												14	557	1,270
Operating and maintenance from affiliates												620	623	574
Total interest expense to affiliates, net												43	53	59
Total income (loss) in equity method investments												8	(20)	10
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions												(8)
Cash distribution paid to member												2,474	645	625
Contribution from member												47	53	26
Contributions from parent														0
Required purchases of power from CENG's nuclear plants not sold to third parties		85.00%
Purchase of nuclear output by EDF		49.99%
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	[7]		43	15				43				15	43
Operating revenues from affiliates	[7]											18	176	506
Purchase power and fuel from affiliates												0	1	1
Operating and maintenance from affiliates	[8]											4	3	2
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	[9]		29	36				29				36	29
Operating revenues from affiliates	[9]											224	198	405
Operating and maintenance from affiliates	[8]											2	2	1
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	[10]		40	31				40				31	40
Operating revenues from affiliates	[10]											502	387	455
Purchase power and fuel from affiliates												14	25	13
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group Llc Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[11]											0	17	56
Purchase power and fuel from affiliates	[12]											0	282	992
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates												1	1	1
Operating and maintenance from affiliates	[13]											614	618	571
Capitalized Costs	[14]											76	91	93
Exelon Generation Co L L C [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net												43	53	59
Exelon Generation Co L L C [Member] | Keystone Fuels LLC Affiliate [Member]
Related Party Transaction [Line Items]
Purchase power and fuel from affiliates	[15]											0	138	144
Exelon Generation Co L L C [Member] | Conemaugh Fuels LLC Affiliate [Member]
Related Party Transaction [Line Items]
Purchase power and fuel from affiliates	[15]											0	99	98
Exelon Generation Co L L C [Member] | SafeHarborWaterPowerCorp [Member]
Related Party Transaction [Line Items]
Purchase power and fuel from affiliates												0	12	22
Exelon Generation Co L L C [Member] | CENG Equity Investment Income Affiliate [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments	[16]											0	(19)	9
Exelon Generation Co L L C [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			1	1				1				1	1
Operating revenues from affiliates												4
Exelon Generation Co L L C [Member] | Qualifying Facilities And Domestic Power Projects Affiliate [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments												(8)	(1)	1
Exelon Generation Co L L C [Member] | Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments												(8)
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			14	199				14				199	14
Total receivable from affiliates (noncurrent)			2,571	2,172				2,571				2,172	2,571
Operating revenues from affiliates												4	4	3
Revenues				1,196	1,376	1,148	1,185	1,079	1,222	1,128	1,134	4,905	4,564	4,464
Operating and maintenance from affiliates												195	166	157
Total interest expense to affiliates, net												13	13	13
Total income (loss) in equity method investments												0	0	0
Cash dividends paid to parent												299	307	220
Non-cash contribution to equity												202	273	0
Contributions from parent												202	273	176
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)				9								9
Total receivable from affiliates (noncurrent)	[17]		2,389	2,172				2,389				2,172	2,389
Operating revenues from affiliates													4	3
Purchase power and fuel from affiliates	[18]											18	176	512
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[14]											195	166	157
Capitalized Costs	[14]											103	77	69
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net												13	13	13
Commonwealth Edison Co [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	[19]			188								188
Total receivable from affiliates (noncurrent)	[19]		182	0				182				0	182
Commonwealth Edison Co [Member] | Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			12					12					12
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates												14	25	13
Revenues				746	725	628	1,036	761	697	653	1,054	3,135	3,165	3,065
Operating and maintenance from affiliates												118	103	83
Total interest expense to affiliates, net												16	16	16
Total income (loss) in equity method investments												0	0	0
Cash dividends paid to parent												158	0	0
Contributions from parent												7	0	0
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[20]												25	13
Purchase power and fuel from affiliates	[21]											498	382	452
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[22]											118	103	83
Capitalized Costs	[22]											28	19	15
Baltimore Gas and Electric Company [Member] | BGE Capital Trust II [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net												16	16	16
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			3	2				3				2	3
Total receivable from affiliates (noncurrent)			490	405				490				405	490
Operating revenues from affiliates												2	2	1
Revenues				645	$ 740	$ 661	$ 985	750	$ 693	$ 656	$ 993	3,032	3,094	3,100
Operating and maintenance from affiliates												110	99	101
Total interest expense to affiliates, net												12	12	12
Total income (loss) in equity method investments												0	0	0
Cash dividends paid to parent												279	320	332
Contributions from parent												16	24	27
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)	[23]		490	405				490				405	490
Operating revenues from affiliates	[24]												2	1
Purchase power and fuel from affiliates	[25]											220	194	392
Operating and maintenance from affiliates												3	3	3
PECO Energy Co [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)			2	2				2				2	2
PECO Energy Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)			$ 1	$ 0				$ 1				0	1
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[26]											107	96	98
Capitalized Costs	[26]											40	39	46
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net												6	6	6
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net												$ 6	$ 6	$ 6
[1]	The intersegment profit associated with the sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statement of Operations. See Note 3—Regulatory Matters for additional information.
[2]	Beginning in 2012, Generation entered into a power services agency agreement (PSAA) with the CENG plants, which as of April 1, 2014, was amended and extended until the permanent cessation of power generation by the CENG generation plants. The PSAA is an agreement under which Generation provides scheduling, asset management and billing services to the CENG plants for a specified monthly fee. The charges for services reflect the cost of the services. On April 1, 2014, Generation and CENG entered into a Nuclear Operating Services Agreement (NOSA) pursuant to which Generation will operate the CENG nuclear generation fleet owned by CENG subsidiaries and provide corporate and administrative services for the remaining life of the CENG nuclear plants as if they were part of the Generation nuclear fleet. For further information regarding the Investment in CENG, see Note 5—Investment in Constellation Energy Nuclear Group, LLC.
[3]	CENG owns 100% of four nuclear units in Maryland and New York and 82% of Nine Mile Point Unit 2 in New York. Beginning in 2012, Generation had a PPA under which it purchased 85% of the nuclear plant output owned by CENG that was not sold to third parties under pre-existing unit-contingent PPAs through 2014. Beginning on January 1, 2015 and continuing to the end of the life of the respective plants, Generation will purchase on a unit-contingent basis 50.01% of the nuclear plant output owned by CENG and a subsidiary of EDF will purchase on a unit-contingent basis 49.99% of the nuclear plant output owned by CENG (EDF PPA) not sold to third parties. Beginning April 1, 2014, sales to Generation are eliminated in consolidation. For further information regarding the Investment in CENG, see Note 5—Investment in Constellation Energy Nuclear Group, LLC.
[4]	During 2014, Generation closed the sale of Safe Harbor Water Power Corporation, Keystone Fuels, LLC, and Conemaugh Fuels LLC. Generation recorded purchase power and fuel costs from affiliates related to these generating assets during the time these assets were still partially owned by Generation. See Note 4—Mergers, Acquisitions, and Dispositions for more information.
[5]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246ODNGMzQxQTRCMURCRDhFQkMxOEYxMjI1RThCRDNERDEM}
[6]	Prior to April 1, 2014, Generation’s total gain (loss) in equity method investments includes equity investment income (loss) and amortization of the basis difference established as a result of purchase accounting applied upon Constellation merger in 2012. CENG was fully consolidated on April 1, 2014. For further information regarding the Investment in CENG, see Note 5—Investment in Constellation Energy Nuclear Group, LLC
[7]	Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3—Regulatory Matters for additional information.
[8]	Generation requires electricity for its own use at its generating stations. Generation purchases electricity and distribution and transmission services from PECO and only distribution and transmission services from ComEd for the delivery of electricity to its generating stations.
[9]	Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has five-year and ten-year agreements with PECO to sell non-solar and solar AECs, respectively. See Note 3—Regulatory Matters for additional information.
[10]	Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[11]	Beginning in 2012, Generation entered into a power services agency agreement (PSAA) with the CENG plants, which as of April 1, 2014, was amended and extended until the permanent cessation of power generation by the CENG generation plants. The PSAA is an agreement under which Generation provides scheduling, asset management and billing services to the CENG plants for a specified monthly fee. The charges for services reflect the cost of the services. On April 1, 2014, Generation and CENG entered into a Nuclear Operating Services Agreement (NOSA) pursuant to which Generation will operate the CENG nuclear generation fleet owned by CENG subsidiaries and provide corporate and administrative services for the remaining life of the CENG nuclear plants as if they were part of the Generation nuclear fleet. For further information regarding the Investment in CENG, see Note 5—Investment in Constellation Energy Nuclear Group, LLC.
[12]	CENG owns 100% of four nuclear units in Maryland and New York and 82% of Nine Mile Point Unit 2 in New York. Beginning in 2012, Generation had a PPA under which it purchased 85% of the nuclear plant output owned by CENG that was not sold to third parties under pre-existing unit-contingent PPAs through 2014. Beginning on January 1, 2015 and continuing to the end of the life of the respective plants, Generation will purchase on a unit-contingent basis 50.01% of the nuclear plant output owned by CENG and a subsidiary of EDF will purchase on a unit-contingent basis 49.99% of the nuclear plant output owned by CENG (EDF PPA) not sold to third parties. Beginning April 1, 2014, sales to Generation are eliminated in consolidation. For further information regarding the Investment in CENG, see Note 5—Investment in Constellation Energy Nuclear Group, LLC.
[13]	Generation receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[14]	ComEd receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[15]	During 2014, Generation closed the sale of Safe Harbor Water Power Corporation, Keystone Fuels, LLC, and Conemaugh Fuels LLC. Generation recorded purchase power and fuel costs from affiliates related to these generating assets during the time these assets were still partially owned by Generation. See Note 4—Mergers, Acquisitions, and Dispositions for more information.
[16]	Prior to April 1, 2014, Generation’s total gain (loss) in equity method investments includes equity income (loss) and amortization of the basis difference established as a result of purchase accounting applied upon Constellation merger in 2012. CENG was fully consolidated on April 1, 2014. For further information regarding the Investment in CENG, see Note 5—Investment in Constellation Energy Nuclear Group, LLC.
[17]	ComEd has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct for generating facilities previously owned by ComEd. To the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to ComEd for payment to ComEd’s customers.
[18]	ComEd procures a portion of its electricity supply requirements from Generation under an ICC-approved RFP contract. ComEd also purchases RECs from Generation. In addition, purchased power expense includes the settled portion of the financial swap contract with Generation, which expired in 2013. See Note 3—Regulatory Matters and Note 13—Derivative Financial Instruments for additional information.
[19]	Represents indemnification from Exelon Corporate related to the like-kind exchange transaction.
[20]	BGE provides energy to Generation for Generation’s own use.
[21]	BGE procures a portion of its electricity and gas supply requirements from Generation under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[22]	BGE receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[23]	PECO has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct, whereby, to the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to PECO for payment to PECO’s customers.
[24]	PECO provides energy to Generation for Generation’s own use.
[25]	PECO purchases electric supply from Generation under contracts executed through its competitive procurement process. In addition, PECO has five-year and ten-year agreements with Generation to purchase non-solar and solar AECs, respectively. See Note 3—Regulatory Matters for additional information on AECs.
[26]	PECO receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.

Related Party Transactions -196

Related Party Transactions - Related Party Transactions included in Consolidated Balance Sheet (Details) - USD ($) $ in Millions		Apr. 01, 2014	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Total payables to affiliates (current)			$ (8)	$ (8)
Long-term debt to financing trusts			$ 641	641
Required purchases of power from CENG's nuclear plants not sold to third parties			85.00%
Purchase of nuclear output of CENG			50.01%
Purchase of nuclear output by EDF			49.99%
Accounts Payable, Related Parties, Current			$ 8	8
ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			205	205
Accounts Payable, Related Parties, Current			4	4
PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			81	81
Accounts Payable, Related Parties, Current			1	1
PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			103	103
BGE Capital Trust II [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			252	252
Accounts Payable, Related Parties, Current			3	3
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			83	113
Total payables to affiliates (current)			0	(556)
Due to Affiliate, Noncurrent			2,577	2,880
Required purchases of power from CENG's nuclear plants not sold to third parties		85.00%
Purchase of nuclear output by EDF		49.99%
Accounts Payable, Related Parties, Current			104	107
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	[1]		15	43
Due to Affiliate, Noncurrent	[2]		2,172	2,389
Accounts Payable, Related Parties, Current			9	12
Exelon Generation Co L L C [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			1	1
Accounts Payable, Related Parties, Current			1	0
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	[3]		36	29
Due to Affiliate, Noncurrent	[2]		405	490
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	[4]		31	40
Exelon Generation Co L L C [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)			(1,252)	(556)
Long Term Debt To Affiliate			933	943
Accounts Payable, Related Parties, Current	[5]		16	12
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	[6]		0	1
Accounts Payable, Related Parties, Current	[6]		78	83
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Prepaid voluntary employee beneficiary association trust	[7]		0	1
Accounts Payable, Related Parties, Current			52	66
Baltimore Gas and Electric Company [Member] | BGE Capital Trust II [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			252	252
Accounts Payable, Related Parties, Current			3	3
Baltimore Gas and Electric Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current			0	1
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[8]		31	40
Baltimore Gas and Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[7]		1	5
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[9]		17	17
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			2	3
Total receivable from affiliates (noncurrent)			405	490
Long-term debt to financing trusts			184	184
Prepaid voluntary employee beneficiary association trust	[10]		2	3
Accounts Payable, Related Parties, Current			55	52
PECO Energy Co [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)			2	2
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			81	81
Accounts Payable, Related Parties, Current			1	1
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			103	103
PECO Energy Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)			0	1
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)	[11]		405	490
Accounts Payable, Related Parties, Current	[12]		36	29
PECO Energy Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current			1	2
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[13]		17	20
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			199	14
Total receivable from affiliates (noncurrent)			2,172	2,571
Prepaid voluntary employee beneficiary association trust	[14]		11	13
Accounts Payable, Related Parties, Current			62	84
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			205	205
Accounts Payable, Related Parties, Current			4	4
Commonwealth Edison Co [Member] | Voluntary Employee Beneficiary Association Trust [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			2	2
Commonwealth Edison Co [Member] | Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)				12
Commonwealth Edison Co [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	[15]		188
Total receivable from affiliates (noncurrent)	[15]		0	182
Commonwealth Edison Co [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current			2	2
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			9
Total receivable from affiliates (noncurrent)	[16]		2,172	2,389
Accounts Payable, Related Parties, Current	[17]		15	43
Commonwealth Edison Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current			2	3
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[18]		$ 39	$ 32
[1]	Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3—Regulatory Matters for additional information.
[2]	Generation has long-term payables to ComEd and PECO as a result of the nuclear decommissioning contractual construct whereby, to the extent NDT funds are greater than the underlying ARO at the end of decommissioning, such amounts are due back to ComEd and PECO, as applicable, for payment to their respective customers. See Note 16—Asset Retirement Obligations
[3]	Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has five-year and ten-year agreements with PECO to sell non-solar and solar AECs, respectively. See Note 3—Regulatory Matters for additional information.
[4]	Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[5]	The balance consists of interest owed to Exelon Corporation related to the senior unsecured notes, as well as, expense related to certain invoices Exelon Corporation processed on behalf of Generation.
[6]	Generation receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[7]	The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for BGE’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets.
[8]	BGE procures a portion of its electricity and gas supply requirements from Generation under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[9]	BGE receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[10]	The voluntary employee beneficiary association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for PECO’s contributions to the plans, being higher than actual claim expense incurred by the plans over time.
[11]	PECO has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct, whereby, to the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to PECO for payment to PECO’s customers.
[12]	PECO purchases electric supply from Generation under contracts executed through its competitive procurement process. In addition, PECO has five-year and ten-year agreements with Generation to purchase non-solar and solar AECs, respectively. See Note 3—Regulatory Matters for additional information on AECs.
[13]	PECO receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[14]	The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for ComEd’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets.
[15]	Represents indemnification from Exelon Corporate related to the like-kind exchange transaction.
[16]	ComEd has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct for generating facilities previously owned by ComEd. To the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to ComEd for payment to ComEd’s customers.
[17]	ComEd procures a portion of its electricity supply requirements from Generation under an ICC-approved RFP contract. ComEd also purchases RECs from Generation. In addition, purchased power expense includes the settled portion of the financial swap contract with Generation, which expired in 2013. See Note 3—Regulatory Matters and Note 13—Derivative Financial Instruments for additional information.
[18]	ComEd receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.

Quarterly Data (Unaudited) - Qu

Quarterly Data (Unaudited) - Quarterly Operating Results (Details) - USD ($) $ in Millions	2 Months Ended	3 Months Ended												12 Months Ended
	Dec. 31, 2014	Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Selected Quarterly Financial Information [Line Items]
Operating Revenues		$ 6,702		$ 7,401		$ 6,514		$ 8,830	$ 7,255	$ 6,912	$ 6,024	$ 7,237		$ 29,447	$ 27,429	$ 24,888
Operating Income		707
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		309	[1]	629		638		693	18	993	522	90	[2]	2,250	1,820	1,729
Reclassifications to Operating Income (Loss)										2	7	(1)
Unrecognized Tax Benefits, Interest on Income Taxes Accrued												265
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	$ 386	4,294		4,768		4,232		5,840	4,802	4,412	3,789	4,390		19,135	17,393	15,630
Operating Income		230							(105)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ (42)	154		377		398		443	(91)	771	340	(185)		1,340	1,019	1,060
Reclassifications to Operating Income (Loss)										1	7	(1)
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		1,196		1,376		1,148		1,185	1,079	1,222	1,128	1,134		4,905	4,564	4,464
Operating Income		217		327	[3]	243	[3]	230	196	287	258	238
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		87		149		99		90	73	126	111	98		426	408	249
Reclassifications to Operating Income (Loss)				1
Unrecognized Tax Benefits, Interest on Income Taxes Accrued												172
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		645		740		661		985	750	693	656	993		3,032	3,094	3,100
Operating Income		128		154		124		223	156	133	134	149
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		79		90		70		139	98	81	84	89		378	352	395
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		746		725		628		1,036	761	697	653	1,054		3,135	3,165	3,065
Operating Income		144		110		99		204	113	102	55	169
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		$ 74		$ 51		$ 44		$ 106	$ 52	$ 46	$ 16	$ 85		$ 288	$ 211	$ 210
[1]	Includes charges to earnings related to the impairments of certain generating assets which were held for sale and certain Upstream exploration assets. See Note 8—Impairment of Long-Lived Assets of the Combined Notes to Consolidated Financial Statements for additional information.
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246NEExNTZFREE4NkYwMUZCQUZDQTExMjI1RThCRDM3QzcM}
[3]	In both the second and third quarter of 2014, ComEd reclassified $1 million to Operating income for presentation purposes in ComEd's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect ComEd's Net (Loss) Income.

Quarterly Data (Unaudited) -198

Quarterly Data (Unaudited) - Quarterly Per Share Information (Details) - $ / shares shares in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Data [Abstract]
Weighted average common shares outstanding—basic	921	913	863	862	861	861	860	858	890	860	856
Earnings Per Share, Basic	$ 0.34	$ 0.69	$ 0.74	$ 0.80	$ 0.02	$ 1.15	$ 0.61	$ 0.10
Weighted average common shares outstanding—diluted	924	915	866	867	868	863	864	861	893	864	860
Earnings Per Share, Diluted	$ 0.33	$ 0.69	$ 0.74	$ 0.80	$ 0.02	$ 1.15	$ 0.60	$ 0.10	$ 2.54	$ 1.88	$ 2

Quarterly Data (Unaudited) -199

Quarterly Data (Unaudited) - Quarterly Composite Common Stock Prices and Dividends (Details) - USD ($)	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014
Quarterly Financial Data [Abstract]
High price	$ 31.37	$ 34.44	$ 34.98	$ 38.25	$ 38.93	$ 36.26	$ 37.73	$ 33.94
Low price	$ 25.09	$ 28.41	$ 31.28	$ 31.71	$ 33.07	$ 30.66	$ 33.11	$ 26.45
Close	$ 27.77	$ 29.7	$ 31.42	$ 33.61	$ 37.08	$ 34.09	$ 36.48	$ 33.56
Dividends	$ 0.31	$ 0.31	$ 0.31	$ 0.31	$ 0.31	$ 0.31	$ 0.31	$ 0.31

Schedule I - Condensed Finan200

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Statements of Operations and Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended										12 Months Ended
	Dec. 31, 2015	[1]	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	[2]	Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Operating Expenses [Abstract]
Operating and maintenance											$ 8,322	$ 8,568		$ 7,270
Total operating expenses											25,056	25,039		21,242
Operating Income (Loss)											4,409	3,096		3,669
Other income and (deductions)
Interest expense, net											(992)	(1,024)		(1,315)
Equity in (losses) earnings of unconsolidated affiliates												(20)		10
Other, net											(46)	455		460
Total other income and (deductions)											(1,079)	(610)		(896)
Income before income taxes											3,330	2,486		2,773
Income taxes											1,073	666		1,044
Net income	$ 309		$ 629	$ 638	$ 693	$ 18	$ 993	$ 522	$ 90		2,250	1,820		1,729
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost, net of tax											46	30		0
Actuarial loss reclassified to periodic cost, net of tax											220	147		208
Pension and non-pension postretirement benefit plans valuation adjustment, net of tax											(99)	(497)		669
Unrealized gain (loss) on cash flow hedges, net of taxes											9	(148)		(248)
Unrealized gain (loss) on marketable securities, net of taxes											0	1		2
Unrealized gain (loss) on equity investments, net of taxes											(3)	8		106
Unrealized gain (loss) on foreign currency translation, net of taxes											(21)	(9)		(10)
Reversal of CENG equity method AOCI, net of taxes											0	(116)		0
Other comprehensive income (loss)											60	(644)	[3]	727
Comprehensive income											2,310	1,176		2,456
Exelon Corporate [Member]
Operating Expenses [Abstract]
Operating and maintenance											0	9		9
Operating and maintenance from affiliates											43	38		34
Other											4	3		12
Total operating expenses											47	50		55
Operating Income (Loss)											(47)	(50)		(55)
Other income and (deductions)
Interest expense, net											(168)	(237)		(116)
Equity in (losses) earnings of unconsolidated affiliates											2,461	1,779		1,903
Interest income from affiliates, net											43	53		36
Other, net											(43)	(2)		(78)
Total other income and (deductions)											2,293	1,593		1,745
Income before income taxes											2,246	1,543		1,690
Income taxes											(23)	(80)		(29)
Net income											2,269	1,623		1,719
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost, net of tax											46	30		0
Actuarial loss reclassified to periodic cost, net of tax											220	147		208
Transition obligation reclassified to periodic cost, net of tax											0	0		0
Pension and non-pension postretirement benefit plans valuation adjustment, net of tax											(99)	(497)		669
Unrealized gain (loss) on cash flow hedges, net of taxes											9	(148)		(248)
Unrealized gain (loss) on marketable securities, net of taxes											0	1		2
Unrealized gain (loss) on equity investments, net of taxes											(3)	8		106
Unrealized gain (loss) on foreign currency translation, net of taxes											(21)	(9)		(10)
Reversal of CENG equity method AOCI, net of taxes											0
Other comprehensive income (loss)											60	(644)		727
Comprehensive income											$ 2,329	$ 979		$ 2,446
[1]	Includes charges to earnings related to the impairments of certain generating assets which were held for sale and certain Upstream exploration assets. See Note 8—Impairment of Long-Lived Assets of the Combined Notes to Consolidated Financial Statements for additional information.
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246NEExNTZFREE4NkYwMUZCQUZDQTExMjI1RThCRDM3QzcM}
[3]	All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.

Schedule I - Condensed Finan201

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions	Feb. 26, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net cash flows provided by operating activities		$ 7,616	$ 4,457	$ 6,343
Cash flows from investing activities
Proceeds from termination of direct financing lease investment	$ 335	0	335	0
Capital expenditures		(7,624)	(6,077)	(5,395)
Cash and restricted cash acquired from Constellation		0	140	0
Change in restricted cash		66	(104)	(43)
Other investing activities		(119)	(88)	112
Net cash flows used in investing activities		(7,822)	(4,599)	(5,394)
Cash flows from financing activities
Changes in short-term borrowings		80	122	332
Issuance of long-term debt		6,709	3,463	2,055
Retirement of long-term debt		(2,687)	(1,545)	(1,589)
Dividends paid on common stock		(1,105)	(1,065)	(1,249)
Proceeds from employee stock plans		32	35	47
Other financing activities		(67)	(178)	(119)
Net cash flows provided by (used in) financing activities		4,830	411	(826)
Increase in cash and cash equivalents		4,624	269	123
Cash and cash equivalents at beginning of period		1,878	1,609	1,486
Cash and cash equivalents at end of period		6,502	1,878	1,609
Exelon Corporate [Member]
Net cash flows provided by operating activities		3,071	806	1,053
Cash flows from investing activities
Proceeds from termination of direct financing lease investment		0	335	0
Changes in Exelon intercompany money pool		(1,217)	(83)	(60)
Note receivable from affiliates		550	0	484
Capital expenditures		0	1	0
Change in restricted cash		0	0	38
Investment in affiliates		(212)	(70)	(38)
Other investing activities		(55)	(126)	15
Net cash flows used in investing activities		(934)	57	439
Cash flows from financing activities
Changes in short-term borrowings		0	0	10
Issuance of long-term debt		4,200	1,150	0
Retirement of long-term debt		(2,263)	(23)	(450)
Dividends paid on common stock		(1,105)	(1,065)	(1,249)
Proceeds from employee stock plans		32	35	47
Other financing activities		(58)	(84)	(6)
Net cash flows provided by (used in) financing activities		2,674	13	(1,648)
Increase in cash and cash equivalents		4,811	876	(156)
Cash and cash equivalents at beginning of period		879	3	159
Cash and cash equivalents at end of period		$ 5,690	$ 879	$ 3

Schedule I - Condensed Finan202

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Balance Sheet (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Current assets
Cash and cash equivalents		$ 6,502	$ 1,878		$ 1,609		$ 1,486
Accounts receivable, net
Other		912	1,227
Regulatory assets		759	847
Other		748	865
Total current assets		15,334	11,853
Property, plant and equipment, net		57,439	52,170
Deferred debits and other assets
Regulatory assets		6,065	6,076
Other		1,445	923
Total deferred debits and other assets		22,611	22,393
Total assets	[1]	95,384	86,416
Current liabilities
Short-term Debt		533	460
Long-term debt due within one year		1,500	1,802
Accounts payable		2,883	3,048
Unamortized energy contract liabilities		100	238
Accrued expenses		2,376	1,539
Regulatory liabilities		369	310
Other		842	931
Total current liabilities		9,118	8,762
Long-term debt		23,645	19,212
Deferred credits and other liabilities
Regulatory liabilities		4,201	4,550
Pension obligations		3,385	3,366
Non-pension postretirement benefit obligations		1,618	1,742
Other		1,491	2,147
Total deferred credits and other liabilities		34,658	33,668
Total liabilities	[1]	68,062	62,283
Shareholders’ equity
Common stock		18,676	16,709
Treasury stock, at cost (35 shares at December 31, 2015 and 2014, respectively)		(2,327)	(2,327)
Retained earnings		12,068	10,910
Accumulated other comprehensive loss, net		(2,624)	(2,684)	[2]	(2,040)	[2]
Total shareholders’ equity		25,793	22,608
BGE preference stock not subject to mandatory redemption		193	193
Total liabilities and shareholders’ equity		95,384	86,416
Exelon Corporate [Member]
Current assets
Cash and cash equivalents		5,690	879		$ 3		$ 159
Accounts receivable, net
Other		272	209
Accounts receivable from affiliates		20	24
Receivables from affiliates		1,478	818
Regulatory assets		241	254
Other		5	22
Total current assets		7,706	2,206
Property, plant and equipment, net		53	54
Deferred debits and other assets
Regulatory assets		3,072	3,186
Investments in affiliates		26,119	26,670
Deferred income taxes		2,036	2,147
Receivable from affiliates		933	943
Other		404	149
Total deferred debits and other assets		32,672	33,095
Total assets		40,431	35,355
Current liabilities
Short-term Debt		188	0
Long-term debt due within one year		60	1,409
Accounts payable		5	2
Accrued expenses		440	25
Regulatory liabilities		63	51
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities		52	45
Other		1	30
Total current liabilities		809	1,562
Long-term debt		6,017	2,818
Payables to affiliates		0	182
Deferred credits and other liabilities
Regulatory liabilities		31	37
Pension obligations		7,520	7,638
Non-pension postretirement benefit obligations		0	16
Deferred income taxes		134	93
Other		122	398
Total deferred credits and other liabilities		7,807	8,182
Total liabilities		$ 14,633	$ 12,744
Commitments and Contingencies
Shareholders’ equity
Common stock		$ 18,678	$ 16,709
Treasury stock, at cost (35 shares at December 31, 2015 and 2014, respectively)		(2,327)	(2,327)
Retained earnings		12,068	10,910
Accumulated other comprehensive loss, net		(2,624)	(2,684)
Total shareholders’ equity		25,795	22,608
BGE preference stock not subject to mandatory redemption		3	3
Total liabilities and shareholders’ equity		$ 40,431	$ 35,355
[1]	Exelon’s consolidated assets include $8,268 million and $8,159 million at December 31, 2015 and December 31, 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,264 million and $2,728 million at December 31, 2015 and December 31, 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.
[2]	All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.

Schedule I - Condensed Finan203

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Balance Sheet - Phantom (Details) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Common stock, par value	$ 0	$ 0
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common Stock, Shares, Outstanding	919,924,742	859,833,343
Treasury Stock, Shares held	35,000,000	35,000,000
Exelon Corporate [Member]
Common stock, par value	$ 0	$ 0
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common Stock, Shares, Outstanding	860,000,000	857,000,000
Treasury Stock, Shares held	35,000,000	35,000,000

Schedule I - Condensed Finan204

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Basis of Presentation - Narrative (Details) - Exelon Corporate [Member]	Dec. 31, 2015
Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage (more than 99% for ComEd)	100.00%
Commonwealth Edison Co [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage (more than 99% for ComEd)	99.00%
Baltimore Gas and Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage (more than 99% for ComEd)	100.00%
Baltimore Gas and Electric Company [Member] | Preferred Stock [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage (more than 99% for ComEd)	0.00%
PECO Energy Co [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage (more than 99% for ComEd)	100.00%
PECO Energy Co [Member] | Preferred Stock [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage (more than 99% for ComEd)	0.00%

Schedule I - Condensed Finan205

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Debt and Credit Agreements - Narrative (Details) - USD ($)		Dec. 31, 2015		May. 30, 2014	[3],[4]
Line of Credit Facility [Line Items]
Line of Credit Facility, Capacity Available for Trade Purchases	[1]	$ 6,341,000,000
Exelon Corporate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Capacity Available for Trade Purchases	[1]	474,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum Program Size	[2]	8,425,000,000
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Line of Credit Facility [Line Items]
Maximum Program Size		$ 500,000,000	[2]	$ 500,000,000
[1]	Excludes $275 million bilateral credit facilities that do not back Generation’s commercial paper program
[2]	Excludes additional credit facilities for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. The agreements for these facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of December 31, 2015, letters of credit issued under these facilities totaled $7 million, $14 million, $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively.
[3]	Excludes additional credit facilities for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. The agreements for these facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of December 31, 2015, letters of credit issued under these facilities totaled $7 million, $14 million, $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively.
[4]	Reflects aggregate bank commitments under the revolving and bilateral credit agreements (with the exception of $275 million and $200 million bilateral agreements for Generation as of December 31, 2015 and 2014, respectively) that backstop the commercial paper program. See discussion and Credit Facilities table below for items affecting effective program size.

Schedule I - Condensed Finan206

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Debt and Credit Agreements - Schedule of Outstanding Long-term Debt (Details) - USD ($)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Jun. 30, 2014
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 25,113,000,000	$ 20,864,000,000
Unamortized debt discount and premium, net		(63,000,000)	(37,000,000)
Long-term debt		$ 23,645,000,000	19,212,000,000
Maximum interest rate on long-term debt		3.95%
Unamortized Debt Issuance Expense	[1]	$ (180,000,000)	(150,000,000)
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 1,150,000,000	1,150,000,000	$ 1,150,000,000
Maximum interest rate on long-term debt		6.50%
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 9,803,000,000	7,071,000,000
Minimum interest rate on long-term debt		1.55%
Maximum interest rate on long-term debt		7.60%
contract Payments Junior Subordinate Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 64,000,000	108,000,000
Maximum interest rate on long-term debt		2.50%
Exelon Corporate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 5,853,000,000	3,916,000,000
Unamortized debt discount and premium, net		(4,000,000)	1,000,000
Fair value adjustment of consolidated subsidiary		275,000,000	333,000,000
Long-term debt due within one year		(60,000,000)	(1,409,000,000)
Long-term debt		6,017,000,000	2,818,000,000
Unamortized Debt Issuance Expense		(47,000,000)	(23,000,000)
Exelon Corporate [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 1,150,000,000	1,150,000,000
Maximum interest rate on long-term debt		6.50%
Exelon Corporate [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Unsecured Long Term Debt	[2]	$ 4,639,000,000	2,658,000,000
Minimum interest rate on long-term debt	[2]	1.55%
Maximum interest rate on long-term debt	[2]	7.60%
Exelon Corporate [Member] | contract Payments Junior Subordinate Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 64,000,000	$ 108,000,000
Maximum interest rate on long-term debt		2.50%
[1]	Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information.
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246QUM1QzUxNjBCNkEwMjA1MjMyMzgxMjI1RThCRDgwNEUM}

Schedule I - Condensed Finan207

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Debt and Credit Agreements - Schedule of Debt Maturities (Details) $ in Millions	Dec. 31, 2015USD ($)
Debt Instrument [Line Items]
2,015	$ 1,487
2,016	1,841
2,017	1,393
2,018	973
2,019	3,311
Thereafter	16,756	[1]
Total	25,761
Exelon Corporate [Member]
Debt Instrument [Line Items]
2,015	45
2,016	569
2,017	0
2,018	0
2,019	1,450
Thereafter	3,789
Total	$ 5,853
[1]	Includes $648 million due to ComEd, PECO and BGE financing trusts.

Schedule I - Condensed Finan208

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Related Party Transactions - Summary of Related Party Transactions (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Total income (loss) in equity method investments			$ (20)	$ 10
Due to Affiliate, Current		$ 8	8
Exelon Corporate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates		43	38	34
Interest income from affiliates, net		43	53	36
Total income (loss) in equity method investments		2,461	1,779	1,903
Cash contributions received from affiliates		3,209	1,370	1,175
Accounts receivable from affiliates		20	24
Receivables from affiliates		1,478	818
Investments in affiliates		26,119	26,670
Total receivable from affiliates (noncurrent)		933	943
Due to Affiliate, Noncurrent		0	182
Exelon Corporate [Member] | Business Services Company [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[1]	43	38	34
Accounts receivable from affiliates	[1]	0	2
Receivables from affiliates	[1]	226	262
Investments in affiliates	[1]	191	193
Exelon Corporate [Member] | Exelon Energy Delivery Company LLC [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments	[2]	1,079	958	834
Investments in affiliates	[2]	14,163	13,590
Exelon Corporate [Member] | Exelon Ventures Company LLC [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments	[3]	0	926	1,076
Exelon Corporate [Member] | UII LLC [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments		20	(6)	(2)
Investments in affiliates		102	130
Exelon Corporate [Member] | Exelon Transmission Company LLC [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments		(8)	(7)	(5)
Investments in affiliates		3	1
Exelon Corporate [Member] | ExelonEnterprise [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments		(1)	(1)	0
Investments in affiliates		22	23
Exelon Corporate [Member] | Exelon Generation Consolidated [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments		1,371	(91)	$ 0
Receivables from affiliates		1,252	556
Investments in affiliates		11,637	12,720
Exelon Corporate [Member] | Exelon Consolidations [Member]
Related Party Transaction [Line Items]
Investments in affiliates		(6)	4
Exelon Corporate [Member] | Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates		16	12
Total receivable from affiliates (noncurrent)		933	943
Exelon Corporate [Member] | Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates		2	3
Due to Affiliate, Current		188
Due to Affiliate, Noncurrent		0	182
Exelon Corporate [Member] | PECO Energy Co [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates		1	2
Exelon Corporate [Member] | Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates		1	5
Exelon Corporate [Member] | VEBA [Member]
Related Party Transaction [Line Items]
Investments in affiliates		$ 7	$ 9
[1]	Exelon Corporate receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead.
[2]	Exelon Energy Delivery Company, LLC consists of ComEd, PECO and BGE.
[3]	Exelon Ventures Company, LLC primarily consisted of Generation

Schedule II - Valuation and 209

Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[1]	$ 311		$ 272		$ 293
Charged to Costs and Expenses	[1]	113		175		121
Charged to Other Accounts	[1]	27		69	[2]	37	[2],[3]
Deductions	[1],[4]	167		205		179
Balance at End of Period	[1]	284		311		272
Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		50		13		36
Charged to Costs and Expenses		0		0		1
Charged to Other Accounts		(27)		37		0	[3]
Deductions		10		0		24
Balance at End of Period		13		50		13
Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		95		58		53
Charged to Costs and Expenses		10		5		17
Charged to Other Accounts		2		34		0	[3]
Deductions		2		2		12
Balance at End of Period		105		95		58
Exelon Generation Co L L C [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		60		57		84
Charged to Costs and Expenses		22		14		(16)
Charged to Other Accounts		0		8		0	[1]
Deductions		5		19		11
Balance at End of Period		77		60		57
Exelon Generation Co L L C [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		48		11		35
Charged to Costs and Expenses		0		0		1
Charged to Other Accounts		(27)		37		0
Deductions		10		0		25
Balance at End of Period		11		48		11
Exelon Generation Co L L C [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		93		55		50
Charged to Costs and Expenses		9		5		16
Charged to Other Accounts		0		32		0	[1]
Deductions		0		(1)		11
Balance at End of Period		102		93		55
Commonwealth Edison Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		84		62		70
Charged to Costs and Expenses		39		45		33
Charged to Other Accounts	[5]	18		33		29
Deductions	[6]	66		56		70
Balance at End of Period		75		84		62
Commonwealth Edison Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		2		2		2
Charged to Costs and Expenses		1		0		1
Charged to Other Accounts		2		2		0
Deductions		2		2		1
Balance at End of Period		3		2		2
PECO Energy Co [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Noncurrent portion of uncollectible installment plan receivables		8		8		9
PECO Energy Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[7]	100		107		99
Charged to Costs and Expenses	[7]	37		52		61
Charged to Other Accounts	[7],[8]	9		11		7
Deductions	[7],[9]	63		70		60
Balance at End of Period	[7]	83		100		107
PECO Energy Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		1		1		1
Charged to Costs and Expenses		0		0		0
Charged to Other Accounts		0		0		0
Deductions		0		0		0
Balance at End of Period		1		1		1
Baltimore Gas and Electric Company [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Charged to Costs and Expenses		19
Baltimore Gas and Electric Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		67		46		40
Charged to Costs and Expenses		15		64		43
Charged to Other Accounts		0	[10]	17		1
Deductions	[11]	33		60		38
Balance at End of Period		49		67		46
Baltimore Gas and Electric Company [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		1		1		0
Charged to Costs and Expenses		0		0		0
Charged to Other Accounts		0		0		0
Deductions		0		0		0
Balance at End of Period		1		1		1
Baltimore Gas and Electric Company [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		1		0
Charged to Costs and Expenses		0		0		0
Charged to Other Accounts		0		0		0
Deductions		0		1		0
Balance at End of Period		$ 0		$ 0		$ 1
[1]	Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $8 million, $8 million, and $9 million for the years ended December 31, 2015, 2014, and 2013, respectively.
[2]	Includes charges for late payments and non-service receivables.
[3]	.
[4]	Write-off of individual accounts receivable.
[5]	Primarily charges for late payments and non-service receivables.
[6]	Write-off of individual accounts receivable.
[7]	Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $8 million, $8 million, and $9 million for the years ended December 31, 2015, 2014, and 2013, respectively.
[8]	Primarily charges for late payments.
[9]	Write-off of individual accounts receivable.
[10]	Primarily charges for late payments.
[11]	Write-off of individual accounts receivable.

Uncategorized Items - exc-20141

Label	Element	Value
Merger Integration Costs [Member]
Regulatory Asset Recovery, Period One	exc_RegulatoryAssetRecoveryPeriodOne	$ 4,000,000
Regulatory Asset Recovery, Period Two	exc_RegulatoryAssetRecoveryPeriodTwo	$ 4,000,000
Non-severance Merger Integration Costs [Member]
Regulatory Asset, Amortization Period	us-gaap_RegulatoryAssetAmortizationPeriod	5 years
Regulatory Assets	us-gaap_RegulatoryAssets	$ 4,000,000
Baltimore Gas and Electric Company [Member] | Pension and Other Postretirement Benefits [Member]
Regulatory Asset, Amortization Period	us-gaap_RegulatoryAssetAmortizationPeriod	12 years
Baltimore Gas and Electric Company [Member] | Transmission Rate Formula [Member]
Net Regulatory Assets	us-gaap_NetRegulatoryAssets	$ 1,000,000
Net Regulatory Assets	us-gaap_NetRegulatoryAssets	12,000,000
Regulatory Assets	us-gaap_RegulatoryAssets	12,000,000
Commonwealth Edison Co [Member] | Transmission Rate Formula [Member]
Net Regulatory Assets	us-gaap_NetRegulatoryAssets	21,000,000
Net Regulatory Assets	us-gaap_NetRegulatoryAssets	31,000,000
Commonwealth Edison Co [Member] | Under Recovered Distribution Service Costs [Member]
Net Regulatory Asset	exc_NetRegulatoryAsset	371,000,000
Net Regulatory Asset	exc_NetRegulatoryAsset	189,000,000
Common Stock [Member]
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options	us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitRealizedFromExerciseOfStockOptions	$ (3,000,000)