Pepco 10-Q 2 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2019shares
Entity Registrant Name	EXELON CORP
Entity Central Index Key	0001109357
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock Shares Outstanding	970,954,879
Exelon Generation Co L L C [Member]
Entity Registrant Name	EXELON GENERATION CO LLC
Entity Central Index Key	0001168165
Entity Filer Category	Non-accelerated Filer
Commonwealth Edison Co [Member]
Entity Registrant Name	COMMONWEALTH EDISON CO
Entity Central Index Key	0000022606
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	127,021,331
PECO Energy Co [Member]
Entity Registrant Name	PECO ENERGY CO
Entity Central Index Key	0000078100
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	0000009466
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	1,000
Pepco Holdings LLC [Member]
Entity Registrant Name	PEPCO HOLDINGS LLC
Entity Central Index Key	0001135971
Entity Filer Category	Non-accelerated Filer
Potomac Electric Power Company [Member]
Entity Registrant Name	POTOMAC ELECTRIC POWER CO
Entity Central Index Key	0000079732
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	100
Delmarva Power and Light Company [Member]
Entity Registrant Name	DELMARVA POWER & LIGHT CO/DE
Entity Central Index Key	0000027879
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	1,000
Atlantic City Electric Company [Member]
Entity Registrant Name	ATLANTIC CITY ELECTRIC CO
Entity Central Index Key	0000008192
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	8,546,017

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income (Unaudited) - USD ($) shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Operating revenues
Competitive businesses revenues		$ 4,979	$ 5,113
Rate-regulated utility revenues		4,503	4,570
Revenues from alternative revenue programs		(5)	10
Operating revenues from affiliates	[1]	0	0
Total operating revenues		9,477	9,693
Operating expenses
Competitive businesses purchased power and fuel		3,204	3,289
Rate-regulated utility purchased power and fuel		1,349	1,438
Operating and maintenance		2,189	2,384
Depreciation and amortization		1,075	1,091
Taxes other than income		445	446
Total operating expenses		8,262	8,648
Gain on sales of assets and businesses		3	56
Operating income		1,218	1,101
Other income and (deductions)
Interest expense, net		(397)	(365)
Interest expense to affiliates		(6)	(6)
Other, net		467	(28)
Total other income and (deductions)		64	(399)
Income before income taxes		1,282	702
Income taxes		310	59
Equity in losses of unconsolidated affiliates		(6)	(7)
Net income		966	636
Net income attributable to noncontrolling interest		59	51
Net income (loss) attributable to common shareholders		907	585
Other comprehensive (loss) income, net of income taxes
Prior service benefit reclassified to periodic benefit cost		(16)	(17)
Actuarial loss reclassified to periodic benefit cost		36	61
Pension and non-pension postretirement benefit plan valuation adjustment		(38)	18
Unrealized gain on cash flow hedges		0	8
Unrealized (loss) gain on investments in unconsolidated affiliates		(2)	1
Unrealized gain (loss) on foreign currency translation		2	1
Other comprehensive (loss) income		(18)	72
Comprehensive income		948	708
Comprehensive income attributable to noncontrolling interests		58	52
Comprehensive income attributable to common shareholders		$ 890	$ 656
Average shares of common stock outstanding:
Basic average shares of common stock outstanding		971	966
Assumed exercise and/or distributions of stock-based awards		1	2
Diluted average shares of common stock outstanding	[2]	972	968
Earnings per average common share:
Basic earnings per average common share		$ 0.93	$ 0.61
Diluted earnings per average common share		$ 0.93	$ 0.60
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			5
Exelon Generation Co L L C [Member]
Operating revenues
Competitive businesses revenues		$ 4,979	$ 5,114
Operating revenues from affiliates		317	398
Total operating revenues		5,296	5,512
Operating expenses
Competitive businesses purchased power and fuel		3,204	3,289
Purchased power and fuel from affiliates		1	4
Operating and maintenance		1,068	1,178
Operating and maintenance from affiliates		150	161
Depreciation and amortization		405	448
Taxes other than income		135	138
Total operating expenses		4,963	5,218
Gain on sales of assets and businesses		0	53
Operating income		333	347
Other income and (deductions)
Interest expense, net		(102)	(91)
Interest expense to affiliates		(9)	(10)
Other, net		430	(44)
Total other income and (deductions)		319	(145)
Income before income taxes		652	202
Income taxes		224	9
Equity in losses of unconsolidated affiliates		(6)	(7)
Net income		422	186
Net income attributable to noncontrolling interest		59	50
Net income attributable to membership interest		363	136
Other comprehensive (loss) income, net of income taxes
Unrealized gain on cash flow hedges		1	7
Unrealized (loss) gain on investments in unconsolidated affiliates		(2)	1
Unrealized gain (loss) on foreign currency translation		2	(1)
Other comprehensive (loss) income		1	7
Comprehensive income		423	193
Comprehensive income attributable to noncontrolling interests		58	51
Comprehensive income attributable to common shareholders		365	142
Commonwealth Edison Co [Member]
Operating revenues
Electric operating revenues		1,432	1,493
Revenues from alternative revenue programs		(28)	5
Operating revenues from affiliates		4	14
Total operating revenues		1,408	1,512
Operating expenses
Purchased power		388	411
Purchased power and fuel from affiliates		97	194
Operating and maintenance		259	253
Operating and maintenance from affiliates		62	60
Depreciation and amortization		251	228
Taxes other than income		78	77
Total operating expenses		1,135	1,223
Gain on sales of assets and businesses		3	3
Operating income		276	292
Other income and (deductions)
Interest expense, net		(84)	(86)
Interest expense to affiliates		(3)	(3)
Other, net		8	8
Total other income and (deductions)		(79)	(81)
Income before income taxes		197	211
Income taxes		40	46
Net income		157	165
Other comprehensive (loss) income, net of income taxes
Comprehensive income		157	165
PECO Energy Co [Member]
Operating revenues
Electric operating revenues		622	633
Natural gas operating revenues		280	232
Revenues from alternative revenue programs		(3)	(1)
Operating revenues from affiliates		1	2
Total operating revenues		900	866
Operating expenses
Purchased power		152	199
Purchased fuel		135	98
Purchased power and fuel from affiliates		44	36
Operating and maintenance		187	233
Operating and maintenance from affiliates		38	42
Depreciation and amortization		81	75
Taxes other than income		41	41
Total operating expenses		678	724
Operating income		222	142
Other income and (deductions)
Interest expense, net		(30)	(30)
Interest expense to affiliates		(3)	(3)
Other, net		4	2
Total other income and (deductions)		(29)	(31)
Income before income taxes		193	111
Income taxes		25	(2)
Net income		168	113
Other comprehensive (loss) income, net of income taxes
Comprehensive income		168	113
Baltimore Gas and Electric Company [Member]
Operating revenues
Electric operating revenues		652	654
Natural gas operating revenues		308	330
Revenues from alternative revenue programs		10	(13)
Operating revenues from affiliates		6	6
Total operating revenues		976	977
Operating expenses
Purchased power		190	192
Purchased fuel		95	123
Purchased power and fuel from affiliates		75	65
Operating and maintenance		153	184
Operating and maintenance from affiliates		39	37
Depreciation and amortization		136	134
Taxes other than income		68	65
Total operating expenses		756	800
Operating income		220	177
Other income and (deductions)
Interest expense, net		(29)	(25)
Other, net		5	4
Total other income and (deductions)		(24)	(21)
Income before income taxes		196	156
Income taxes		36	28
Net income		160	128
Other comprehensive (loss) income, net of income taxes
Comprehensive income		160	128
Pepco Holdings LLC [Member]
Operating revenues
Electric operating revenues		1,139	1,151
Natural gas operating revenues		71	78
Revenues from alternative revenue programs		15	18
Operating revenues from affiliates		3	4
Total operating revenues		1,228	1,251
Operating expenses
Purchased power		355	374
Purchased fuel		34	41
Purchased power and fuel from affiliates		101	105
Operating and maintenance		239	271
Operating and maintenance from affiliates		33	38
Depreciation and amortization		180	183
Taxes other than income		111	113
Total operating expenses		1,053	1,125
Operating income		175	126
Other income and (deductions)
Interest expense, net		(65)	(63)
Other, net		12	11
Total other income and (deductions)		(53)	(52)
Income before income taxes		122	74
Income taxes		5	9
Net income		117	65
Other comprehensive (loss) income, net of income taxes
Comprehensive income attributable to common shareholders		117	65
Potomac Electric Power Company [Member]
Operating revenues
Electric operating revenues		559	536
Revenues from alternative revenue programs		14	19
Operating revenues from affiliates		2	2
Total operating revenues		575	557
Operating expenses
Purchased power		117	130
Purchased power and fuel from affiliates		70	52
Operating and maintenance		64	73
Operating and maintenance from affiliates		54	57
Depreciation and amortization		94	96
Taxes other than income		92	93
Total operating expenses		491	501
Operating income		84	56
Other income and (deductions)
Interest expense, net		(34)	(31)
Other, net		7	8
Total other income and (deductions)		(27)	(23)
Income before income taxes		57	33
Income taxes		2	2
Net income		55	31
Other comprehensive (loss) income, net of income taxes
Comprehensive income		55	31
Delmarva Power and Light Company [Member]
Operating revenues
Electric operating revenues		307	303
Natural gas operating revenues		71	78
Revenues from alternative revenue programs		0	1
Operating revenues from affiliates		2	2
Total operating revenues		380	384
Operating expenses
Purchased power		107	90
Purchased fuel		34	41
Purchased power and fuel from affiliates		23	46
Operating and maintenance		45	57
Operating and maintenance from affiliates		39	41
Depreciation and amortization		46	45
Taxes other than income		14	15
Total operating expenses		308	335
Operating income		72	49
Other income and (deductions)
Interest expense, net		(15)	(13)
Other, net		3	2
Total other income and (deductions)		(12)	(11)
Income before income taxes		60	38
Income taxes		7	7
Net income		53	31
Other comprehensive (loss) income, net of income taxes
Comprehensive income		53	31
Atlantic City Electric Company [Member]
Operating revenues
Electric operating revenues		271	311
Revenues from alternative revenue programs		1	(2)
Operating revenues from affiliates		1	1
Total operating revenues		273	310
Operating expenses
Purchased power		131	155
Purchased power and fuel from affiliates		8	6
Operating and maintenance		47	54
Operating and maintenance from affiliates		34	36
Depreciation and amortization		31	33
Taxes other than income		1	3
Total operating expenses		252	287
Operating income		21	23
Other income and (deductions)
Interest expense, net		(14)	(16)
Other, net		3	1
Total other income and (deductions)		(11)	(15)
Income before income taxes		10	8
Income taxes		0	1
Net income		10	7
Other comprehensive (loss) income, net of income taxes
Comprehensive income		$ 10	$ 7
[1]	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]	The number of stock options not included in the calculation of diluted common shares outstanding due to their antidilutive effect was immaterial for the three months ended March 31, 2019 and approximately 5 million for the three months ended March 31, 2018.

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities
Net income	$ 966	$ 636
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	1,460	1,501
Impairment of long-lived assets	7	0
Gain on sales of assets and businesses	0	(56)
Deferred income taxes and amortization of investment tax credits	187	(14)
Net fair value changes related to derivatives	31	259
Net realized and unrealized (gains) losses on NDT funds	(308)	68
Other non-cash operating activities	127	240
Changes in assets and liabilities:
Accounts receivable	79	133
Inventories	128	167
Accounts payable and accrued expenses	(764)	(451)
Option premiums received (paid), net	6	(27)
Collateral posted, net	(101)	(214)
Income taxes	141	86
Pension and non-pension postretirement benefit contributions	(328)	(331)
Other assets and liabilities	(587)	(495)
Net cash flows provided by operating activities	1,044	1,502
Cash flows from investing activities
Capital expenditures	(1,873)	(1,880)
Proceeds from NDT fund sales	3,713	1,189
Investment in NDT funds	(3,666)	(1,248)
Proceeds from sales of assets and businesses	8	79
Other investing activities	32	3
Net cash flows used in investing activities	(1,786)	(1,857)
Cash flows from financing activities
Changes in short-term borrowings	540	726
Proceeds from short-term borrowings with maturities greater than 90 days	0	1
Repayments on short-term borrowings with maturities greater than 90 days	0	(1)
Issuance of long-term debt	402	1,130
Retirement of long-term debt	(352)	(1,241)
Dividends paid on common stock	(352)	(333)
Proceeds from employee stock plans	51	12
Other financing activities	(14)	(30)
Net cash flows provided by (used in) financing activities	275	264
Increase (Decrease) in cash, cash equivalents and restricted cash	(467)	(91)
Cash, cash equivalents and restricted cash at beginning of period	1,781	1,190
Cash, cash equivalents and restricted cash at end of period	1,314	1,099
Exelon Generation Co L L C [Member]
Cash flows from operating activities
Net income	422	186
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	789	858
Impairment of long-lived assets	7	0
Gain on sales of assets and businesses	0	(53)
Deferred income taxes and amortization of investment tax credits	108	(68)
Net fair value changes related to derivatives	33	264
Net realized and unrealized (gains) losses on NDT funds	(308)	68
Other non-cash operating activities	(90)	45
Changes in assets and liabilities:
Accounts receivable	197	194
Receivables from and payables to affiliates, net	(5)	(15)
Inventories	103	122
Accounts payable and accrued expenses	(411)	(317)
Option premiums received (paid), net	6	(27)
Collateral posted, net	(87)	(214)
Income taxes	146	79
Pension and non-pension postretirement benefit contributions	(141)	(125)
Other assets and liabilities	(187)	(142)
Net cash flows provided by operating activities	582	855
Cash flows from investing activities
Capital expenditures	(511)	(628)
Proceeds from NDT fund sales	3,713	1,189
Investment in NDT funds	(3,666)	(1,248)
Proceeds from sales of assets and businesses	8	79
Other investing activities	23	(7)
Net cash flows used in investing activities	(433)	(615)
Cash flows from financing activities
Changes in short-term borrowings	0	165
Proceeds from short-term borrowings with maturities greater than 90 days	0	1
Repayments on short-term borrowings with maturities greater than 90 days	0	(1)
Issuance of long-term debt	2	4
Retirement of long-term debt	(47)	(29)
Changes in Exelon intercompany money pool	(100)	0
Distributions to member	(225)	(188)
Other financing activities	(6)	(9)
Net cash flows provided by (used in) financing activities	(376)	(57)
Increase (Decrease) in cash, cash equivalents and restricted cash	(227)	183
Cash, cash equivalents and restricted cash at beginning of period	903	554
Cash, cash equivalents and restricted cash at end of period	676	737
Commonwealth Edison Co [Member]
Cash flows from operating activities
Net income	157	165
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	251	228
Deferred income taxes and amortization of investment tax credits	34	50
Other non-cash operating activities	56	46
Changes in assets and liabilities:
Accounts receivable	14	39
Receivables from and payables to affiliates, net	(34)	(19)
Inventories	(3)	5
Accounts payable and accrued expenses	(188)	(158)
Collateral posted, net	(13)	(3)
Income taxes	5	(5)
Pension and non-pension postretirement benefit contributions	(67)	(38)
Other assets and liabilities	(121)	(176)
Net cash flows provided by operating activities	91	134
Cash flows from investing activities
Capital expenditures	(503)	(531)
Other investing activities	11	8
Net cash flows used in investing activities	(492)	(523)
Cash flows from financing activities
Changes in short-term borrowings	322	317
Issuance of long-term debt	400	800
Retirement of long-term debt	(300)	(700)
Dividends paid on common stock	(127)	(114)
Contributions from parent	63	113
Other financing activities	(9)	(9)
Net cash flows provided by (used in) financing activities	349	407
Increase (Decrease) in cash, cash equivalents and restricted cash	(52)	18
Cash, cash equivalents and restricted cash at beginning of period	330	144
Cash, cash equivalents and restricted cash at end of period	278	162
PECO Energy Co [Member]
Cash flows from operating activities
Net income	168	113
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	81	75
Deferred income taxes and amortization of investment tax credits	5	(4)
Other non-cash operating activities	16	21
Changes in assets and liabilities:
Accounts receivable	(86)	(51)
Receivables from and payables to affiliates, net	7	7
Inventories	23	12
Accounts payable and accrued expenses	(13)	6
Income taxes	20	5
Pension and non-pension postretirement benefit contributions	(25)	(24)
Other assets and liabilities	(119)	(141)
Net cash flows provided by operating activities	77	19
Cash flows from investing activities
Capital expenditures	(222)	(217)
Other investing activities	2	2
Net cash flows used in investing activities	(220)	(215)
Cash flows from financing activities
Changes in short-term borrowings	0	220
Issuance of long-term debt	0	325
Retirement of long-term debt	0	(500)
Dividends paid on common stock	(90)	(287)
Changes in Exelon intercompany money pool	0	194
Contributions from parent	145	0
Other financing activities	0	(5)
Net cash flows provided by (used in) financing activities	55	(53)
Increase (Decrease) in cash, cash equivalents and restricted cash	(88)	(249)
Cash, cash equivalents and restricted cash at beginning of period	135	275
Cash, cash equivalents and restricted cash at end of period	47	26
Baltimore Gas and Electric Company [Member]
Cash flows from operating activities
Net income	160	128
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	136	134
Deferred income taxes and amortization of investment tax credits	28	22
Other non-cash operating activities	27	20
Changes in assets and liabilities:
Accounts receivable	(39)	(32)
Receivables from and payables to affiliates, net	(10)	0
Inventories	17	20
Accounts payable and accrued expenses	(27)	(9)
Collateral posted, net	(1)	0
Income taxes	8	14
Pension and non-pension postretirement benefit contributions	(40)	(45)
Other assets and liabilities	(14)	61
Net cash flows provided by operating activities	245	313
Cash flows from investing activities
Capital expenditures	(258)	(224)
Other investing activities	1	1
Net cash flows used in investing activities	(257)	(223)
Cash flows from financing activities
Changes in short-term borrowings	71	(32)
Dividends paid on common stock	(56)	(52)
Net cash flows provided by (used in) financing activities	15	(84)
Increase (Decrease) in cash, cash equivalents and restricted cash	3	6
Cash, cash equivalents and restricted cash at beginning of period	13	18
Cash, cash equivalents and restricted cash at end of period	16	24
Pepco Holdings LLC [Member]
Cash flows from operating activities
Net income	117	65
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	180	183
Deferred income taxes and amortization of investment tax credits	0	17
Other non-cash operating activities	35	53
Changes in assets and liabilities:
Accounts receivable	(11)	(9)
Receivables from and payables to affiliates, net	(8)	10
Inventories	(12)	4
Accounts payable and accrued expenses	(9)	44
Income taxes	4	(9)
Pension and non-pension postretirement benefit contributions	(6)	(55)
Other assets and liabilities	(61)	(24)
Net cash flows provided by operating activities	229	279
Cash flows from investing activities
Capital expenditures	(358)	(258)
Other investing activities	1	0
Net cash flows used in investing activities	(357)	(258)
Cash flows from financing activities
Changes in short-term borrowings	147	57
Retirement of long-term debt	(5)	(12)
Changes in Exelon intercompany money pool	0	13
Distributions to member	(128)	(71)
Contributions from member	19	0
Net cash flows provided by (used in) financing activities	33	(13)
Increase (Decrease) in cash, cash equivalents and restricted cash	(95)	8
Cash, cash equivalents and restricted cash at beginning of period	186	95
Cash, cash equivalents and restricted cash at end of period	91	103
Potomac Electric Power Company [Member]
Cash flows from operating activities
Net income	55	31
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	94	96
Deferred income taxes and amortization of investment tax credits	(2)	4
Other non-cash operating activities	3	10
Changes in assets and liabilities:
Accounts receivable	(19)	0
Receivables from and payables to affiliates, net	3	(18)
Inventories	(14)	(2)
Accounts payable and accrued expenses	(2)	36
Income taxes	4	(3)
Pension and non-pension postretirement benefit contributions	(4)	(7)
Other assets and liabilities	(37)	(21)
Net cash flows provided by operating activities	81	126
Cash flows from investing activities
Capital expenditures	(144)	(127)
Other investing activities	1	0
Net cash flows used in investing activities	(143)	(127)
Cash flows from financing activities
Changes in short-term borrowings	65	34
Dividends paid on common stock	(24)	(25)
Contributions from parent	14	0
Net cash flows provided by (used in) financing activities	55	9
Increase (Decrease) in cash, cash equivalents and restricted cash	(7)	8
Cash, cash equivalents and restricted cash at beginning of period	53	40
Cash, cash equivalents and restricted cash at end of period	46	48
Delmarva Power and Light Company [Member]
Cash flows from operating activities
Net income	53	31
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	46	45
Deferred income taxes and amortization of investment tax credits	1	10
Other non-cash operating activities	11	19
Changes in assets and liabilities:
Accounts receivable	(5)	(1)
Receivables from and payables to affiliates, net	(15)	(16)
Inventories	1	7
Accounts payable and accrued expenses	11	18
Income taxes	5	(5)
Other assets and liabilities	(10)	7
Net cash flows provided by operating activities	98	115
Cash flows from investing activities
Capital expenditures	(78)	(65)
Net cash flows used in investing activities	(78)	(65)
Cash flows from financing activities
Changes in short-term borrowings	5	(5)
Retirement of long-term debt	0	(4)
Dividends paid on common stock	(41)	(36)
Net cash flows provided by (used in) financing activities	(36)	(45)
Increase (Decrease) in cash, cash equivalents and restricted cash	(16)	5
Cash, cash equivalents and restricted cash at beginning of period	24	2
Cash, cash equivalents and restricted cash at end of period	8	7
Atlantic City Electric Company [Member]
Cash flows from operating activities
Net income	10	7
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	31	33
Deferred income taxes and amortization of investment tax credits	0	2
Other non-cash operating activities	5	9
Changes in assets and liabilities:
Accounts receivable	13	(5)
Receivables from and payables to affiliates, net	(4)	(4)
Inventories	1	0
Accounts payable and accrued expenses	12	30
Income taxes	(1)	0
Pension and non-pension postretirement benefit contributions	0	(6)
Other assets and liabilities	(7)	(7)
Net cash flows provided by operating activities	60	59
Cash flows from investing activities
Capital expenditures	(128)	(63)
Other investing activities	0	(1)
Net cash flows used in investing activities	(128)	(64)
Cash flows from financing activities
Changes in short-term borrowings	77	28
Retirement of long-term debt	(4)	(8)
Dividends paid on common stock	(12)	(9)
Contributions from parent	5	0
Net cash flows provided by (used in) financing activities	66	11
Increase (Decrease) in cash, cash equivalents and restricted cash	(2)	6
Cash, cash equivalents and restricted cash at beginning of period	30	31
Cash, cash equivalents and restricted cash at end of period	$ 28	$ 37

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Current Assets
Cash and cash equivalents		$ 880	$ 1,349
Restricted cash and cash equivalents		223	247
Accounts receivable, net
Customer		4,564	4,607
Other		1,062	1,256
Mark-to-market derivative assets, current		652	804
Unamortized energy contract assets, current		49	48
Inventories, net
Fossil fuel and emission allowances		179	334
Materials and supplies		1,380	1,351
Regulatory assets, current		1,191	1,222
Assets held for sale		890	904
Other		1,406	1,238
Total current assets		12,476	13,360
Property, plant and equipment, net		77,460	76,707
Deferred debits and other assets
Regulatory assets, noncurrent		8,222	8,237
Nuclear decommissioning trust funds		12,302	11,661
Investments		620	625
Goodwill		6,677	6,677
Mark-to-market derivative assets, noncurrent		454	452
Unamortized energy contract assets, noncurrent		365	372
Other		3,017	1,575
Total deferred debits and other assets		31,657	29,599
Total assets	[1]	121,593	119,666
Current Liabilities
Short-term borrowings		1,254	714
Long-term debt due within one year		2,508	1,349
Accounts payable		3,327	3,800
Accrued expenses		1,725	2,112
Payable to affiliates, current		5	5
Regulatory liabilities, current		522	644
Mark-to-market derivative liabilities, current		345	475
Unamortized energy contract liabilities, current		151	149
Renewable energy credit obligation		348	344
Liabilities held for sale		799	777
Other		1,245	1,035
Total current liabilities		12,229	11,404
Long-term debt		32,960	34,075
Long-term debt to financing trusts		390	390
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		11,642	11,330
Asset retirement obligations, noncurrent		9,967	9,679
Pension obligations		3,734	3,988
Non-pension postretirement benefit obligations		1,984	1,928
Spent nuclear fuel obligation		1,178	1,171
Regulatory liabilities, noncurrent		9,781	9,559
Mark-to-market derivative liabilities, noncurrent		434	479
Unamortized energy contract liabilities, noncurrent		432	463
Other		3,158	2,130
Total deferred credits and other liabilities		42,310	40,727
Total liabilities	[1]	87,889	86,596
Commitments and contingencies
Shareholders' equity
Common stock		19,171	19,116
Treasury stock, at cost (2 shares at March 31, 2019 and December 31, 2018)		(123)	(123)
Retained earnings		15,321	14,766
Accumulated other comprehensive loss, net		(3,012)	(2,995)
Total shareholders’ equity		31,357	30,764
Member’s equity
Noncontrolling Interests		2,347	2,306
Total equity		33,704	33,070
Total liabilities and shareholders’ equity		121,593	119,666
Variable Interest Entity, Consolidated, Assets, Pledged		9,546	9,667
Variable Interest Entity, Consolidated, Liabilities, No Recourse		3,572	3,548
Exelon Generation Co L L C [Member]
Current Assets
Cash and cash equivalents		537	750
Restricted cash and cash equivalents		139	153
Accounts receivable, net
Customer		2,800	2,941
Other		367	562
Mark-to-market derivative assets, current		652	804
Receivable from affiliates, current		163	173
Unamortized energy contract assets, current		49	49
Inventories, net
Fossil fuel and emission allowances		146	251
Materials and supplies		965	963
Assets held for sale		890	904
Other		1,013	883
Total current assets		7,721	8,433
Property, plant and equipment, net		24,034	23,981
Deferred debits and other assets
Nuclear decommissioning trust funds		12,302	11,661
Investments		404	414
Goodwill		47	47
Mark-to-market derivative assets, noncurrent		454	452
Prepaid pension asset		1,525	1,421
Unamortized energy contract assets, noncurrent		364	371
Deferred income taxes		18	21
Other		1,813	755
Total deferred debits and other assets		16,927	15,142
Total assets	[2]	48,682	47,556
Current Liabilities
Long-term debt due within one year		2,365	906
Accounts payable		1,566	1,847
Accrued expenses		675	898
Payable to affiliates, current		136	139
Borrowings from Exelon intercompany money pool		0	100
Mark-to-market derivative liabilities, current		318	449
Unamortized energy contract liabilities, current		28	31
Renewable energy credit obligation		348	343
Liabilities held for sale		799	777
Other		425	279
Total current liabilities		6,660	5,769
Long-term debt		5,487	6,989
Long-term debt to affiliates		895	898
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		3,502	3,383
Asset retirement obligations, noncurrent		9,737	9,450
Non-pension postretirement benefit obligations		894	900
Spent nuclear fuel obligation		1,178	1,171
Payables to affiliates, noncurrent		2,870	2,606
Mark-to-market derivative liabilities, noncurrent		219	252
Unamortized energy contract liabilities, noncurrent		16	20
Other		1,528	610
Total deferred credits and other liabilities		19,944	18,392
Total liabilities	[2]	32,986	32,048
Commitments and contingencies
Shareholders' equity
Retained earnings		3,862	3,724
Accumulated other comprehensive loss, net		(36)	(38)
Member’s equity
Membership interest		9,525	9,518
Total members' equity		13,351	13,204
Noncontrolling Interests		2,345	2,304
Total equity		15,696	15,508
Total liabilities and shareholders’ equity		48,682	47,556
Variable Interest Entity, Consolidated, Assets, Pledged		9,515	9,634
Variable Interest Entity, Consolidated, Liabilities, No Recourse		3,508	3,480
Commonwealth Edison Co [Member]
Current Assets
Cash and cash equivalents		68	135
Restricted cash and cash equivalents		17	29
Accounts receivable, net
Customer		539	539
Other		336	320
Receivable from affiliates, current		21	20
Inventories, net
Inventories, net		152	148
Regulatory assets, current		285	293
Other		89	86
Total current assets		1,507	1,570
Property, plant and equipment, net		22,274	22,058
Deferred debits and other assets
Regulatory assets, noncurrent		1,338	1,307
Investments		6	6
Goodwill		2,625	2,625
Receivable from affiliates, noncurrent		2,412	2,217
Prepaid pension asset		1,073	1,035
Other		347	395
Total deferred debits and other assets		7,801	7,585
Total assets		31,582	31,213
Current Liabilities
Short-term borrowings		322	0
Long-term debt due within one year		0	300
Accounts payable		491	607
Accrued expenses		229	373
Payable to affiliates, current		74	119
Customer deposits		112	111
Regulatory liabilities, current		241	293
Mark-to-market derivative liabilities, current		27	26
Other		98	96
Total current liabilities		1,594	1,925
Long-term debt		8,194	7,801
Long-term debt to financing trusts		205	205
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		3,870	3,813
Asset retirement obligations, noncurrent		119	118
Non-pension postretirement benefit obligations		196	201
Regulatory liabilities, noncurrent		6,269	6,050
Mark-to-market derivative liabilities, noncurrent		213	223
Other		582	630
Total deferred credits and other liabilities		11,249	11,035
Total liabilities		21,242	20,966
Commitments and contingencies
Shareholders' equity
Common stock		1,588	1,588
Other paid-in capital		7,385	7,322
Retained deficit unappropriated		(1,639)	(1,639)
Retained earnings appropriated		3,006	2,976
Total shareholders’ equity		10,340	10,247
Member’s equity
Total liabilities and shareholders’ equity		31,582	31,213
PECO Energy Co [Member]
Current Assets
Cash and cash equivalents		41	130
Restricted cash and cash equivalents		6	5
Accounts receivable, net
Customer		394	321
Other		148	151
Inventories, net
Fossil fuel and emission allowances		15	38
Materials and supplies		37	37
Prepaid utility taxes		100	0
Regulatory assets, current		54	81
Other		21	19
Total current assets		816	782
Property, plant and equipment, net		8,766	8,610
Deferred debits and other assets
Regulatory assets, noncurrent		491	460
Investments		25	25
Receivable from affiliates, noncurrent		457	389
Prepaid pension asset		372	349
Other		29	27
Total deferred debits and other assets		1,374	1,250
Total assets		10,956	10,642
Current Liabilities
Accounts payable		379	370
Accrued expenses		119	113
Payable to affiliates, current		66	59
Customer deposits		68	68
Regulatory liabilities, current		123	175
Other		32	24
Total current liabilities		787	809
Long-term debt		3,084	3,084
Long-term debt to financing trusts		184	184
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		1,974	1,933
Asset retirement obligations, noncurrent		27	27
Non-pension postretirement benefit obligations		288	288
Regulatory liabilities, noncurrent		488	421
Other		81	76
Total deferred credits and other liabilities		2,858	2,745
Total liabilities		6,913	6,822
Commitments and contingencies
Shareholders' equity
Common stock		2,723	2,578
Retained earnings		1,320	1,242
Total shareholders’ equity		4,043	3,820
Member’s equity
Total liabilities and shareholders’ equity		10,956	10,642
Baltimore Gas and Electric Company [Member]
Current Assets
Cash and cash equivalents		12	7
Restricted cash and cash equivalents		4	6
Accounts receivable, net
Customer		385	353
Other		89	90
Receivable from affiliates, current		0	1
Inventories, net
Fossil fuel and emission allowances		16	36
Materials and supplies		42	39
Prepaid utility taxes		38	74
Regulatory assets, current		161	177
Other		6	3
Total current assets		753	786
Property, plant and equipment, net		8,408	8,243
Deferred debits and other assets
Regulatory assets, noncurrent		395	398
Investments		5	5
Prepaid pension asset		301	279
Other		105	5
Total deferred debits and other assets		806	687
Total assets		9,967	9,716
Current Liabilities
Short-term borrowings		106	35
Accounts payable		291	295
Accrued expenses		142	155
Payable to affiliates, current		54	65
Customer deposits		120	120
Regulatory liabilities, current		67	77
Other		54	27
Total current liabilities		834	774
Long-term debt		2,876	2,876
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		1,275	1,222
Asset retirement obligations, noncurrent		24	24
Non-pension postretirement benefit obligations		198	201
Regulatory liabilities, noncurrent		1,172	1,192
Other		130	73
Total deferred credits and other liabilities		2,799	2,712
Total liabilities		6,509	6,362
Commitments and contingencies
Shareholders' equity
Common stock		1,714	1,714
Retained earnings		1,744	1,640
Total shareholders’ equity		3,458	3,354
Member’s equity
Total liabilities and shareholders’ equity		9,967	9,716
Pepco Holdings LLC [Member]
Current Assets
Cash and cash equivalents		33	124
Restricted cash and cash equivalents		39	43
Accounts receivable, net
Customer		445	453
Other		189	177
Receivable from affiliates, current		1	0
Inventories, net
Fossil fuel and emission allowances		2	9
Materials and supplies		184	163
Regulatory assets, current		506	489
Other		54	75
Total current assets		1,453	1,533
Property, plant and equipment, net		13,619	13,446
Deferred debits and other assets
Regulatory assets, noncurrent		2,236	2,312
Investments		132	130
Goodwill		4,005	4,005
Prepaid pension asset		467	486
Deferred income taxes		12	12
Other		370	60
Total deferred debits and other assets		7,222	7,005
Total assets	[3]	22,294	21,984
Current Liabilities
Short-term borrowings		326	179
Long-term debt due within one year		125	125
Accounts payable		441	496
Accrued expenses		253	256
Payable to affiliates, current		87	94
Customer deposits		117	116
Regulatory liabilities, current		76	84
Unamortized energy contract liabilities, current		123	119
Other		127	123
Total current liabilities		1,675	1,592
Long-term debt		6,119	6,134
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		2,182	2,146
Asset retirement obligations, noncurrent		52	52
Non-pension postretirement benefit obligations		101	103
Regulatory liabilities, noncurrent		1,829	1,864
Unamortized energy contract liabilities, noncurrent		416	442
Other		630	369
Total deferred credits and other liabilities		5,210	4,976
Total liabilities	[3]	13,004	12,702
Commitments and contingencies
Shareholders' equity
Retained earnings		51	62
Member’s equity
Membership interest		9,239	9,220
Total members' equity		9,290	9,282
Total equity		9,290	9,282
Total liabilities and shareholders’ equity		22,294	21,984
Variable Interest Entity, Consolidated, Assets, Pledged		31	33
Variable Interest Entity, Consolidated, Liabilities, No Recourse		64	69
Potomac Electric Power Company [Member]
Current Assets
Cash and cash equivalents		11	16
Restricted cash and cash equivalents		35	37
Accounts receivable, net
Customer		219	225
Other		102	81
Receivable from affiliates, current		1	1
Inventories, net
Inventories, net		109	93
Regulatory assets, current		270	270
Other		22	37
Total current assets		769	760
Property, plant and equipment, net		6,534	6,460
Deferred debits and other assets
Regulatory assets, noncurrent		620	643
Investments		106	105
Prepaid pension asset		311	316
Other		80	15
Total deferred debits and other assets		1,117	1,079
Total assets		8,420	8,299
Current Liabilities
Short-term borrowings		105	40
Long-term debt due within one year		15	15
Accounts payable		188	214
Accrued expenses		139	126
Payable to affiliates, current		65	62
Customer deposits		55	54
Regulatory liabilities, current		6	7
Merger related obligation		38	38
Current portion of DC PLUG obligation		30	30
Other		17	42
Total current liabilities		658	628
Long-term debt		2,705	2,704
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		1,081	1,064
Non-pension postretirement benefit obligations		26	29
Regulatory liabilities, noncurrent		805	822
Other		360	312
Total deferred credits and other liabilities		2,272	2,227
Total liabilities		5,635	5,559
Commitments and contingencies
Shareholders' equity
Common stock		1,650	1,636
Retained earnings		1,135	1,104
Total shareholders’ equity		2,785	2,740
Member’s equity
Total liabilities and shareholders’ equity		8,420	8,299
Delmarva Power and Light Company [Member]
Current Assets
Cash and cash equivalents		7	23
Restricted cash and cash equivalents		1	1
Accounts receivable, net
Customer		141	134
Other		39	46
Receivable from affiliates, current		2	0
Inventories, net
Fossil fuel and emission allowances		2	9
Materials and supplies		43	37
Regulatory assets, current		60	59
Other		21	27
Total current assets		316	336
Property, plant and equipment, net		3,848	3,821
Deferred debits and other assets
Regulatory assets, noncurrent		225	231
Goodwill		8	8
Prepaid pension asset		182	186
Other		81	6
Total deferred debits and other assets		496	431
Total assets		4,660	4,588
Current Liabilities
Short-term borrowings		5	0
Long-term debt due within one year		91	91
Accounts payable		98	111
Accrued expenses		50	39
Payable to affiliates, current		21	33
Customer deposits		36	35
Regulatory liabilities, current		49	59
Other		16	7
Total current liabilities		366	375
Long-term debt		1,404	1,403
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		643	628
Non-pension postretirement benefit obligations		16	17
Regulatory liabilities, noncurrent		596	606
Other		114	50
Total deferred credits and other liabilities		1,369	1,301
Total liabilities		3,139	3,079
Commitments and contingencies
Shareholders' equity
Common stock		914	914
Retained earnings		607	595
Total shareholders’ equity		1,521	1,509
Member’s equity
Total liabilities and shareholders’ equity		4,660	4,588
Atlantic City Electric Company [Member]
Current Assets
Cash and cash equivalents		6	7
Restricted cash and cash equivalents		3	4
Accounts receivable, net
Customer		85	95
Other		52	55
Receivable from affiliates, current		1	1
Inventories, net
Inventories, net		32	33
Regulatory assets, current		53	40
Other		6	5
Total current assets		238	240
Property, plant and equipment, net		3,041	2,966
Deferred debits and other assets
Regulatory assets, noncurrent		377	386
Prepaid pension asset		63	67
Other		64	40
Total deferred debits and other assets		504	493
Total assets	[4]	3,783	3,699
Current Liabilities
Short-term borrowings		216	139
Long-term debt due within one year		19	18
Accounts payable		139	154
Accrued expenses		38	35
Payable to affiliates, current		24	28
Customer deposits		26	26
Regulatory liabilities, current		20	18
Other		10	4
Total current liabilities		492	422
Long-term debt		1,165	1,170
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		539	535
Non-pension postretirement benefit obligations		17	17
Regulatory liabilities, noncurrent		395	402
Other		46	27
Total deferred credits and other liabilities		997	981
Total liabilities	[4]	2,654	2,573
Commitments and contingencies
Shareholders' equity
Common stock		984	979
Retained earnings		145	147
Total shareholders’ equity		1,129	1,126
Member’s equity
Total liabilities and shareholders’ equity		3,783	3,699
Variable Interest Entity, Consolidated, Assets, Pledged		22	23
Variable Interest Entity, Consolidated, Liabilities, No Recourse		$ 54	$ 59
[1]	Exelon’s consolidated assets include $9,546 million and $9,667 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,572 million and $3,548 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2 — Variable Interest Entities for additional information.
[2]	Generation’s consolidated assets include $9,515 million and $9,634 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,508 million and $3,480 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2 — Variable Interest Entities for additional information.
[3]	PHI’s consolidated total assets include $31 million and $33 million at March 31, 2019 and December 31, 2018, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $64 million and $69 million at March 31, 2019 and December 31, 2018, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 2 — Variable Interest Entities for additional information.
[4]	ACE’s consolidated total assets include $22 million and $23 million at March 31, 2019 and December 31, 2018, respectively, of ACE's consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated total liabilities include $54 million and $59 million at March 31, 2019 and December 31, 2018, respectively, of ACE's consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 2 — Variable Interest Entities for additional information.

Consolidated Balance Sheets (_2

Consolidated Balance Sheets (Unaudited) (Parenthetical) - shares	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Common Stock, Shares Authorized	2,000,000,000	2,000,000,000
Common Stock, Shares, Outstanding	970,954,879	968,187,955
Treasury Stock, Shares held	1,832,457	1,832,457

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]	Exelon Generation Co L L C [Member]	Exelon Generation Co L L C [Member]Membership Interest [Member]	Exelon Generation Co L L C [Member]Retained/Undistributed Earnings (Losses), Unappropriated [Member]	Exelon Generation Co L L C [Member]Accumulated Other Comprehensive Income (Loss) [Member]		Exelon Generation Co L L C [Member]Noncontrolling Interest [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/Undistributed Earnings (Losses), Unappropriated [Member]	Commonwealth Edison Co [Member]Retained Earnings, Appropriated [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]	Baltimore Gas and Electric Company [Member]	Baltimore Gas and Electric Company [Member]Common Stock [Member]	Baltimore Gas and Electric Company [Member]Retained Earnings [Member]	Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member]Membership Interest [Member]	Pepco Holdings LLC [Member]Retained/Undistributed Earnings (Losses), Unappropriated [Member]	Potomac Electric Power Company [Member]	Potomac Electric Power Company [Member]Common Stock [Member]	Potomac Electric Power Company [Member]Retained Earnings [Member]	Delmarva Power and Light Company [Member]	Delmarva Power and Light Company [Member]Common Stock [Member]	Delmarva Power and Light Company [Member]Retained Earnings [Member]	Atlantic City Electric Company [Member]	Atlantic City Electric Company [Member]Common Stock [Member]	Atlantic City Electric Company [Member]Retained Earnings [Member]
Beginning balance (in shares) at Dec. 31, 2017	965,168,000
Beginning balance at Dec. 31, 2017	$ 32,187	$ 18,964	$ (123)	$ 14,081	$ (3,026)	[1]	$ 2,291
Beginning Balance at Dec. 31, 2017								$ 15,959	$ 9,357	$ 4,349	$ (37)	[1]	$ 2,290													$ 8,825	$ 8,835	$ (10)
Beginning Balance at Dec. 31, 2017														$ 9,542	$ 1,588	$ 6,822	$ (1,639)	$ 2,771	$ 3,577	$ 2,489	$ 1,087	$ 1	$ 3,141	$ 1,605	$ 1,536				$ 2,533	$ 1,470	$ 1,063	$ 1,335	$ 764	$ 571	$ 1,043	$ 912	$ 131
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 636			585			51	186		136	0		50	165			165		113		113		128		128	65		65	31		31	31		31	7		7
Stock issued during period, shares, long-term incentive plan activity	1,685,000
Stock issued during period, value, long-term incentive plan activity	$ (3)	(3)	0	0	0		0
Stock issued during period, shares, employee stock purchase plan	361,000
Stock issued during period, value, employee stock purchase plan	$ 12	12	0	0	0		0
Changes in equity of noncontrolling interests	(9)						(9)	(9)					(9)
Common stock dividends	(334)			(334)										(114)				(114)	(287)		(287)		(52)		(52)				(25)		(25)	(36)		(36)	(9)		(9)
Contributions from parent														113		113
Distributions to member								(188)		(188)																(71)		(71)
Other comprehensive income (loss), net of income taxes	72				71	[1]	1	7		0	6	[1]	1
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	$ 4			14	(10)			3		6	(3)								0		1	(1)
Ending balance (in shares) at Mar. 31, 2018	967,214,000
Ending balance at Mar. 31, 2018	$ 32,565	18,973	(123)	14,346	(2,965)	[1]	2,334
Ending Balance at Mar. 31, 2018								15,958	9,357	4,303	(34)	[1]	2,332													8,819	8,835	(16)
Ending Balance at Mar. 31, 2018														9,706	1,588	6,935	(1,639)	2,822	3,403	2,489	914	0	3,217	1,605	1,612				2,539	1,470	1,069	1,330	764	566	1,041	912	129
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Appropriation of retained earnings for future dividends																	(165)	165
Appropriation of retained earnings for future dividends														(2,976)
Beginning balance (in shares) at Dec. 31, 2018	970,020,000
Beginning balance at Dec. 31, 2018	$ 33,070	19,116	(123)	14,766	(2,995)	[1]	2,306
Beginning Balance at Dec. 31, 2018								15,508	9,518	3,724	(38)	[1]	2,304													9,282	9,220	62
Beginning Balance at Dec. 31, 2018	30,764													10,247	1,588	7,322	(1,639)	2,976	3,820	2,578	1,242	0	3,354	1,714	1,640				2,740	1,636	1,104	1,509	914	595	1,126	979	147
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 966			907			59	422		363	0		59	157			157		168		168		160		160	117		117	55		55	53		53	10		10
Stock issued during period, shares, long-term incentive plan activity	2,446,000
Stock issued during period, value, long-term incentive plan activity	$ (3)	(3)	0	0	0		0
Stock issued during period, shares, employee stock purchase plan	320,000
Stock issued during period, value, employee stock purchase plan	$ 51	51	0	0	0		0
Changes in equity of noncontrolling interests	(17)						(17)	(17)					(17)
Sale of noncontrolling interests	7	7						7	7
Common stock dividends	(352)			(352)										(127)				(127)	(90)		(90)		(56)		(56)				(24)		(24)	(41)		(41)	(12)		(12)
Contributions from parent														63		63			(145)	(145)						19	19		14	14					5	5
Distributions to member								(225)		(225)																(128)		(128)
Other comprehensive income (loss), net of income taxes	$ (18)				(17)	[1]	(1)	1		0	2	[1]	(1)
Ending balance (in shares) at Mar. 31, 2019	972,786,000
Ending balance at Mar. 31, 2019	$ 33,704	$ 19,171	$ (123)	$ 15,321	$ (3,012)	[1]	$ 2,347
Ending Balance at Mar. 31, 2019								$ 15,696	$ 9,525	$ 3,862	$ (36)	[1]	$ 2,345													$ 9,290	$ 9,239	$ 51
Ending Balance at Mar. 31, 2019	$ 31,357													10,340	$ 1,588	$ 7,385	(1,639)	3,006	$ 4,043	$ 2,723	$ 1,320	$ 0	$ 3,458	$ 1,714	$ 1,744				$ 2,785	$ 1,650	$ 1,135	$ 1,521	$ 914	$ 607	$ 1,129	$ 984	$ 145
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Appropriation of retained earnings for future dividends														$ (3,006)			$ (157)	$ 157
[1]	All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.

Consolidated Statement of Cha_2

Consolidated Statement of Changes in Shareholders Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Stockholders' Equity [Abstract]
Common Stock, Dividends, Per Share, Declared	$ 0.36	$ 0.35

Significant Accounting Policies

Significant Accounting Policies	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Significant Accounting Policies [Text Block]	Significant Accounting Policies (All Registrants) Description of Business (All Registrants) Exelon is a utility services holding company engaged in the generation, delivery and marketing of energy through Generation and the energy distribution and transmission businesses through ComEd, PECO, BGE, Pepco, DPL and ACE. Name of Registrant Business Service Territories Exelon Generation Generation, physical delivery and marketing of power across multiple geographical regions through its customer-facing business, Constellation, which sells electricity to both wholesale and retail customers. Generation also sells natural gas, renewable energy and other energy-related products and services. Five reportable segments: Mid-Atlantic, Midwest, New York, ERCOT and Other Power Regions Commonwealth Edison Company Purchase and regulated retail sale of electricity Northern Illinois, including the City of Chicago Transmission and distribution of electricity to retail customers PECO Energy Company Purchase and regulated retail sale of electricity and natural gas Southeastern Pennsylvania, including the City of Philadelphia (electricity) Transmission and distribution of electricity and distribution of natural gas to retail customers Pennsylvania counties surrounding the City of Philadelphia (natural gas) Baltimore Gas and Electric Company Purchase and regulated retail sale of electricity and natural gas Central Maryland, including the City of Baltimore (electricity and natural gas) Transmission and distribution of electricity and distribution of natural gas to retail customers Pepco Holdings LLC Utility services holding company engaged, through its reportable segments Pepco, DPL and ACE Service Territories of Pepco, DPL and ACE Potomac Electric Purchase and regulated retail sale of electricity District of Columbia, and major portions of Montgomery and Prince George’s Counties, Maryland Transmission and distribution of electricity to retail customers Delmarva Power & Light Company Purchase and regulated retail sale of electricity and natural gas Portions of Delaware and Maryland (electricity) Transmission and distribution of electricity and distribution of natural gas to retail customers Portions of New Castle County, Delaware (natural gas) Atlantic City Electric Company Purchase and regulated retail sale of electricity Portions of Southern New Jersey Transmission and distribution of electricity to retail customers Basis of Presentation (All Registrants) Each of the Registrant’s Consolidated Financial Statements includes the accounts of its subsidiaries. All intercompany transactions have been eliminated. 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. PHI also has a business services subsidiary, PHISCO, which provides a variety of support services at cost, including legal, accounting, engineering, customer operations, distribution and transmission planning, asset management, system operations, and power procurement, to PHI operating companies. The costs of BSC and PHISCO are directly charged or allocated to the applicable subsidiaries. The results of Exelon’s corporate operations are presented as “Other” within the consolidated financial statements and include intercompany eliminations unless otherwise disclosed. The accompanying consolidated financial statements as of March 31, 2019 and 2018 and for the three months then ended are unaudited but, in the opinion of the management of each Registrant include all adjustments that are considered necessary for a fair statement of the Registrants’ respective financial statements in accordance with GAAP. All adjustments are of a normal, recurring nature, except as otherwise disclosed. The December 31, 2018 Consolidated Balance Sheets were derived from audited financial statements. Financial results for interim periods are not necessarily indicative of results that may be expected for any other interim period or for the fiscal year ending December 31, 2019 . These Combined Notes to Consolidated Financial Statements have been prepared pursuant to the rules and regulations of the SEC for Quarterly Reports on Form 10-Q. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. New Accounting Standards (All Registrants) New Accounting Standards Adopted in 2019: In 2019, the Registrants have adopted the following new authoritative accounting guidance issued by the FASB. Leases. The Registrants applied the new guidance with the following transition practical expedients: • a "package of three" expedients that must be taken together and allow entities to (1) not reassess whether existing contracts contain leases, (2) carryforward the existing lease classification, and (3) not reassess initial direct costs associated with existing leases, • an implementation expedient which allows the requirements of the standard in the period of adoption with no restatement of prior periods, and • a land easement expedient which allows entities to not evaluate land easements under the new standard at adoption if they were not previously accounted for as leases. The standard materially impacted the Registrants' Consolidated Balance Sheets but did not have a material impact in the Registrants' Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows and Consolidated Statements of Changes in Shareholders' Equity. The most significant impact was the recognition of the ROU assets and lease liabilities for operating leases. The operating ROU assets and lease liabilities recognized upon adoption are materially consistent with the balances presented in the Combined Notes to the Consolidated Financial Statements. See Note 5 - Leases for additional information. See Note 1 — Significant Accounting Policies of the Exelon 2018 Form 10-K for additional information on new accounting standards issued and adopted as of January 1, 2019. New Accounting Standards Issued and Not Yet Adopted as of March 31, 2019 : The following new authoritative accounting guidance issued by the FASB has not yet been adopted and reflected by the Registrants in their consolidated financial statements as of March 31, 2019 . Unless otherwise indicated, the Registrants are currently assessing the impacts such guidance may have (which could be material) in 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 where applicable. The Registrants have assessed other FASB issuances of new standards which are not listed below given the current expectation that such standards will not significantly impact the Registrants' financial reporting. Goodwill Impairment (Issued January 2017). Simplifies the accounting for goodwill impairment by removing Step 2 of the current test, which requires calculation of a hypothetical purchase price allocation. Under the revised guidance, goodwill impairment will be measured as the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill (currently Step 1 of the two-step impairment test). Entities will continue to have the option to perform a qualitative assessment to determine if a quantitative impairment test is necessary. Exelon, Generation, ComEd, PHI and DPL have goodwill as of March 31, 2019 . This updated guidance is not currently expected to impact the Registrants’ financial reporting. The standard is effective January 1, 2020, with early adoption permitted, and must be applied on a prospective basis. Impairment of Financial Instruments (Issued June 2016). Provides for a new Current Expected Credit Loss (CECL) impairment model for specified financial instruments including loans, trade receivables, debt securities classified as held-to-maturity investments and net investments in leases recognized by a lessor. Under the new guidance, on initial recognition and at each reporting period, an entity is required to recognize an allowance that reflects the entity’s current estimate of credit losses expected to be incurred over the life of the financial instrument. The standard does not make changes to the existing impairment models for non-financial assets such as fixed assets, intangibles and goodwill. The standard will be effective January 1, 2020 (with early adoption as of January 1, 2019 permitted) and requires a modified retrospective transition approach through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Registrants are currently assessing the impacts of this standard. Leases (All Registrants) The Registrants recognize a ROU asset and lease liability for operating leases with a term of greater than one year. The ROU asset is included in Other deferred debits and other assets and the lease liability is included in Other current liabilities and Other deferred credits and other liabilities on the Consolidated Balance Sheets. The ROU asset is measured as the sum of (1) the present value of all remaining fixed and in-substance fixed payments using each Registrant’s incremental borrowing rate, (2) any lease payments made at or before the commencement date (less any lease incentives received) and (3) any initial direct costs incurred. The lease liability is measured the same as the ROU asset, but excludes any payments made before the commencement date and initial direct costs incurred. Lease terms include options to extend or terminate the lease if it is reasonably certain they will be exercised. The Registrants include non-lease components, which are service-related costs that are not integral to the use of the asset, in the measurement of the ROU asset and lease liability. Expense for operating leases and leases with a term of one year or less is recognized on a straight-line basis over the term of the lease, unless another systematic and rational basis is more representative of the derivation of benefit from use of the leased property. Variable lease payments are recognized in the period in which the related obligation is incurred and consist primarily of payments for purchases of electricity under contracted generation and are based on the electricity produced by those generating assets. Operating lease expense and variable lease payments are recorded to Purchased power and fuel expense for contracted generation or Operating and maintenance expense for all other lease agreements on the Registrants’ Statements of Operations and Comprehensive Income. Income from operating leases, including subleases, is recognized on a straight-line basis over the term of the lease, unless another systematic and rational basis is more representative of the pattern in which income is earned over the term of the lease. Variable lease payments are recognized in the period in which the related obligation is performed and consist primarily of payments received from sales of electricity under contracted generation and are based on the electricity produced by those generating assets. Operating lease income and variable lease payments are recorded to Operating revenues on the Registrants’ Statements of Operations and Comprehensive Income. The Registrants’ operating leases consist primarily of contracted generation, real estate including office buildings, and vehicles and equipment. The Registrants generally account for contracted generation in which the generating asset is not renewable as a lease if the customer has dispatch rights and obtains substantially all of the economic benefits. For new agreements entered after January 1, 2019, the Registrants will generally not account for contracted generation in which the generating asset is renewable as a lease if the customer does not design the generating asset. The Registrants account for land right arrangements that provide for exclusive use as leases while shared use land arrangements are generally not leases. The Registrants do not account for secondary use pole attachments as leases. See Note 5 — Leases for additional information.
Business Description [Text Block]	Description of Business (All Registrants) Exelon is a utility services holding company engaged in the generation, delivery and marketing of energy through Generation and the energy distribution and transmission businesses through ComEd, PECO, BGE, Pepco, DPL and ACE. Name of Registrant Business Service Territories Exelon Generation Generation, physical delivery and marketing of power across multiple geographical regions through its customer-facing business, Constellation, which sells electricity to both wholesale and retail customers. Generation also sells natural gas, renewable energy and other energy-related products and services. Five reportable segments: Mid-Atlantic, Midwest, New York, ERCOT and Other Power Regions Commonwealth Edison Company Purchase and regulated retail sale of electricity Northern Illinois, including the City of Chicago Transmission and distribution of electricity to retail customers PECO Energy Company Purchase and regulated retail sale of electricity and natural gas Southeastern Pennsylvania, including the City of Philadelphia (electricity) Transmission and distribution of electricity and distribution of natural gas to retail customers Pennsylvania counties surrounding the City of Philadelphia (natural gas) Baltimore Gas and Electric Company Purchase and regulated retail sale of electricity and natural gas Central Maryland, including the City of Baltimore (electricity and natural gas) Transmission and distribution of electricity and distribution of natural gas to retail customers Pepco Holdings LLC Utility services holding company engaged, through its reportable segments Pepco, DPL and ACE Service Territories of Pepco, DPL and ACE Potomac Electric Purchase and regulated retail sale of electricity District of Columbia, and major portions of Montgomery and Prince George’s Counties, Maryland Transmission and distribution of electricity to retail customers Delmarva Power & Light Company Purchase and regulated retail sale of electricity and natural gas Portions of Delaware and Maryland (electricity) Transmission and distribution of electricity and distribution of natural gas to retail customers Portions of New Castle County, Delaware (natural gas) Atlantic City Electric Company Purchase and regulated retail sale of electricity Portions of Southern New Jersey Transmission and distribution of electricity to retail customers

Variable Interest Entities (All

Variable Interest Entities (All Registrants)	3 Months Ended
	Mar. 31, 2019
Variable Interest Entity [Abstract]
Variable Interest Entity Disclosure (All Registrants)	Variable Interest Entities (All Registrants) 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 March 31, 2019 and December 31, 2018 , Exelon, Generation, PHI and ACE collectively consolidated five VIEs or VIE groups for which the applicable Registrant was the primary beneficiary (see Consolidated Variable Interest Entities below). As of March 31, 2019 and December 31, 2018 , Exelon and Generation collectively had significant interests in seven other VIEs for which the applicable Registrant does not have the power to direct the entities’ activities and, accordingly, was not the primary beneficiary (see Unconsolidated Variable Interest Entities below). Consolidated Variable Interest Entities As of March 31, 2019 and December 31, 2018 , Exelon's and Generation's consolidated VIEs consist of: • energy related companies involved in distributed generation, backup generation and energy development • renewable energy project companies formed by Generation to build, own and operate renewable power facilities • certain retail power and gas companies for which Generation is the sole supplier of energy, and • CENG. As of March 31, 2019 and December 31, 2018 , Exelon's, PHI's and ACE's consolidated VIE consist of: • ATF, a special purpose entity formed by ACE for the purpose of securitizing authorized portions of ACE’s recoverable stranded costs through the issuance and sale of transition bonds. As of March 31, 2019 and December 31, 2018 , ComEd, PECO, BGE, Pepco and DPL did not have any material consolidated VIEs. As of March 31, 2019 and December 31, 2018 , Exelon and Generation provided the following support to their respective consolidated VIEs: • Generation provides operating and capital funding to the renewable energy project companies and there is limited recourse to Generation related to certain renewable energy project companies. • Generation provides approximately $32 million in credit support for the retail power and gas companies for which Generation is the sole supplier of energy. • Exelon and Generation, where indicated, provide the following support to CENG: • under PPAs 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 were suspended during the term of the RSSA, through the end of March 31, 2017. With the expiration of the RSSA, the PPA was reinstated beginning April 1, 2017, • Generation provided a $400 million loan to CENG. The loan balance was fully repaid by CENG in January 2019. • 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 16 — Commitments and Contingencies for additional information), • Generation and EDF share in the $688 million of contingent payment obligations for the payment of contingent retrospective premium adjustments for the nuclear liability insurance, 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. As of March 31, 2019 and December 31, 2018 , Exelon, PHI and ACE provided the following support to their respective consolidated VIE: • In the case of ATF, proceeds from the sale of each series of transition bonds by ATF were transferred to ACE in exchange for the transfer by ACE to ATF of the right to collect a non-bypassable Transition Bond Charge from ACE customers pursuant to bondable stranded costs rate orders issued by the NJBPU in an amount sufficient to fund the principal and interest payments on transition bonds and related taxes, expenses and fees. During the three months ended March 31, 2019 , ACE transferred $4 million to ATF. During the three months ended March 31, 2018 , ACE transferred $8 million to ATF. 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, PHI and ACE did not provide any additional material financial support to the VIEs; • Exelon, Generation, PHI and ACE 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, PHI's or ACE's general credit. The carrying amounts and classification of the consolidated VIEs’ assets and liabilities included in the Registrants' consolidated financial statements at March 31, 2019 and December 31, 2018 are as follows: March 31, 2019 December 31, 2018 Exelon (a) Generation PHI (a) ACE Exelon (a) Generation PHI (a) ACE Current assets $ 645 $ 639 $ 6 $ 3 $ 938 $ 931 $ 7 $ 4 Noncurrent assets 9,235 9,210 25 19 9,071 9,045 26 19 Total assets $ 9,880 $ 9,849 $ 31 $ 22 $ 10,009 $ 9,976 $ 33 $ 23 Current liabilities $ 748 $ 725 $ 23 $ 19 $ 274 $ 252 $ 22 $ 19 Noncurrent liabilities 2,831 2,790 41 35 3,280 3,233 47 40 Total liabilities $ 3,579 $ 3,515 $ 64 $ 54 $ 3,554 $ 3,485 $ 69 $ 59 _________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. 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 March 31, 2019 and December 31, 2018 , these assets and liabilities primarily consisted of the following: March 31, 2019 December 31, 2018 Exelon (a) Generation PHI (a) ACE Exelon (a) Generation PHI (a) ACE Cash and cash equivalents $ 125 $ 125 $ — $ — $ 414 $ 414 $ — $ — Restricted cash and cash equivalents 58 55 3 3 66 62 4 4 Accounts receivable, net Customer 152 152 — — 146 146 — — Other 23 23 — — 23 23 — — Inventory, net Materials and supplies 213 213 — — 212 212 — — Other current assets 51 48 3 — 52 49 3 — Total current assets 622 616 6 3 913 906 7 4 Property, plant and equipment, net 6,147 6,147 — — 6,145 6,145 — — NDT funds 2,520 2,520 — — 2,351 2,351 — — Other noncurrent assets 257 232 25 19 258 232 26 19 Total noncurrent assets 8,924 8,899 25 19 8,754 8,728 26 19 Total assets $ 9,546 $ 9,515 $ 31 $ 22 $ 9,667 $ 9,634 $ 33 $ 23 Long-term debt due within one year $ 567 $ 545 $ 22 $ 19 $ 87 $ 66 $ 21 $ 18 Accounts payable 120 120 — — 96 96 — — Accrued expenses 42 41 1 — 72 72 1 1 Unamortized energy contract liabilities 13 13 — — 15 15 — — Other current liabilities 6 6 — — 3 3 — — Total current liabilities 748 725 23 19 273 252 22 19 Long-term debt 565 524 41 35 1,072 1,025 47 40 Asset retirement obligations 2,190 2,190 — — 2,160 2,160 — — Unamortized energy contract liabilities — — — — 1 1 — — Other noncurrent liabilities 69 69 — — 42 42 — — Total noncurrent liabilities 2,824 2,783 41 35 3,275 3,228 47 40 Total liabilities $ 3,572 $ 3,508 $ 64 $ 54 $ 3,548 $ 3,480 $ 69 $ 59 _________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. 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 in 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 March 31, 2019 and December 31, 2018 , Exelon's and Generation's unconsolidated VIEs consist of: • Energy purchase and sale agreements with VIEs for which Generation has concluded that consolidation is not required. • Asset sale agreement with ZionSolutions, LLC and EnergySolutions, Inc. in which Generation has a variable interest but has concluded that consolidation is not required. • Equity investments in distributed energy companies for which Generation has concluded that consolidation is not required. As of March 31, 2019 and December 31, 2018 , the Utility Registrants did not have any material unconsolidated VIEs. As of March 31, 2019 and December 31, 2018 , Exelon and Generation had significant unconsolidated variable interests in seven VIEs for which Exelon or Generation, as applicable, was not the primary beneficiary; including certain equity investments and certain commercial agreements. Exelon and Generation only include unconsolidated VIEs that are individually material in the tables below. However, Exelon and Generation have several individually immaterial VIEs that in aggregate represent a total investment of $16 million and $12 million , respectively, as of March 31, 2019 . These immaterial VIEs are equity and debt securities in energy development companies. As of March 31, 2019 , the maximum exposure to loss related to these securities included in Investments in Exelon’s and Generation’s Consolidated Balance Sheets is limited to $16 million and $12 million , respectively. The risk of a loss was assessed to be remote and, accordingly, Exelon and Generation have not recognized a liability associated with any portion of the maximum exposure to loss. The following tables present summary information about Exelon's and Generation’s significant unconsolidated VIE entities: March 31, 2019 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 601 $ 463 $ 1,064 Total liabilities (a) 42 223 265 Exelon's ownership interest in VIE (a) — 214 214 Other ownership interests in VIE (a) 559 26 585 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 214 214 Contract intangible asset 7 — 7 December 31, 2018 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 597 $ 472 $ 1,069 Total liabilities (a) 37 222 259 Exelon's ownership interest in VIE (a) — 223 223 Other ownership interests in VIE (a) 560 27 587 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 223 223 Contract intangible asset 7 — 7 _________ (a) These items represent amounts in the unconsolidated VIE balance sheets, not in Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs. For each of the unconsolidated VIEs, Exelon and Generation have 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 material agreements with, or commitments by, third parties that would affect the fair value or risk of their variable interests in these VIEs.

Mergers, Acquisitions and Dispo

Mergers, Acquisitions and Dispositions (Exelon and Generation)	3 Months Ended
	Mar. 31, 2019
Discontinued Operations and Disposal Groups [Abstract]
Disposal Groups, Including Discontinued Operations, Disclosure [Text Block]	Mergers, Acquisitions and Dispositions (Exelon and Generation) Disposition of Oyster Creek On July 31, 2018, Generation entered into an agreement with Holtec International (Holtec) and its indirect wholly owned subsidiary, Oyster Creek Environmental Protection, LLC (OCEP), for the sale and decommissioning of Oyster Creek located in Forked River, New Jersey. On September 17, 2018, Oyster Creek permanently ceased generation operations. Under the terms of the transaction, Generation will transfer to OCEP substantially all the assets associated with Oyster Creek, including assets held in NDT funds, along with the assumption of liability for all responsibility for the site, including full decommissioning and ongoing management of spent fuel until the spent fuel is moved offsite. In addition to the assumption of liability for the full decommissioning and ongoing management of spent fuel, other consideration to be received in the transaction is contingent on several factors, including a requirement that Generation deliver a minimum NDT fund balance at closing, subject to adjustment for specific terms that include income taxes that would be imposed on any net unrealized built-in gains and certain decommissioning activities to be performed during the pre-close period after the unit shuts down in the fall of 2018 and prior to the anticipated close of the transaction. The terms of the transaction also include various forms of performance assurance for the obligations of OCEP to timely complete the required decommissioning, including a parental guaranty from Holtec for all performance and payment obligations of OCEP, and a requirement for Holtec to deliver a letter of credit to Generation upon the occurrence of specified events. As a result of the transaction, in the third quarter of 2018, Exelon and Generation reclassified certain Oyster Creek assets and liabilities in Exelon’s and Generation’s Consolidated Balance Sheets as held for sale at their respective fair value s. Exelon and Generation had $888 million and $765 million of Assets and Liabilities held for sale, respectively, at March 31, 2019 and $897 million and $777 million of Assets and Liabilities held for sale, respectively, at December 31, 2018 . Upon remeasurement of the Oyster Creek ARO in the third quarter of 2018, Exelon and Generation recognized an $84 million pre-tax charge to Operating and maintenance expense. Completion of the transaction contemplated by the sale agreement is subject to the satisfaction of several closing conditions, including approval of the license transfer from the NRC and other regulatory approvals, and a private letter ruling from the IRS, which was received in April 2019. Generation currently anticipates satisfaction of the remaining closing conditions to occur in the second half of 2019. Other Asset Disposition On February 28, 2018, Generation completed the sale of its interest in an electrical contracting business that primarily installs, maintains and repairs underground and high-voltage cable transmission and distribution systems for $87 million , resulting in a pre-tax gain which is included within Gain on sales of assets and businesses in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income for the three months ended March 31, 2018 . In June 2018, additional proceeds were received, and a pre-tax gain was recorded within Gain on sales of assets and businesses in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income.

Revenue from Contracts with Cus

Revenue from Contracts with Customers (All Registrants)	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	Revenue from Contracts with Customers (All Registrants) The Registrants recognize revenue from contracts with customers to depict the transfer of goods or services to customers at an amount that the entities expect to be entitled to in exchange for those goods or services. Generation’s primary sources of revenue include competitive sales of power, natural gas, and other energy-related products and services. The Utility Registrants’ primary sources of revenue include regulated electric and gas tariff sales, distribution and transmission services. See Note 3 — Revenue from Contracts with Customers of the Exelon 2018 Form 10-K for additional information regarding the primary sources of revenue for the Registrants. Contract Balances (All Registrants) Contract Assets and Liabilities Generation records contract assets for the revenue recognized on the construction and installation of energy efficiency assets and new power generating facilities before Generation has an unconditional right to bill for and receive the consideration from the customer. These contract assets are subsequently reclassified to receivables when the right to payment becomes unconditional. Generation records contract assets and contract receivables within Other current assets and Accounts receivable, net - Customer, respectively, within Exelon’s and Generation’s Consolidated Balance Sheets. Generation records contract liabilities when consideration is received or due prior to the satisfaction of the performance obligations. These contract liabilities primarily relate to upfront consideration received or due for equipment service plans, solar panel leases and the Illinois ZEC program that introduces a cap on the total consideration to be received by Generation. Generation records contract liabilities within Other current liabilities and Other noncurrent liabilities within Exelon's and Generation's Consolidated Balance Sheets. The following table provides a rollforward of the contract assets and liabilities reflected in Exelon's and Generation's Consolidated Balance Sheets from January 1, 2018 to March 31, 2019 : Contract Assets Contract Liabilities Exelon Generation Exelon Generation Balance as of January 1, 2018 $ 283 $ 283 $ 35 $ 35 Increases as a result of changes in the estimate of the stage of completion 50 50 — — Increases as a result of additional cash received or due — — 179 465 Amounts reclassified into receivables or recognized into revenues (146 ) (146 ) (187 ) (458 ) Balance at December 31, 2018 187 187 27 42 Increases as a result of changes in the estimate of the stage of completion 26 26 — — Increases as a result of additional cash received or due — — 21 63 Amounts reclassified into receivables or recognized into revenues (26 ) (26 ) (23 ) (66 ) Balance at March 31, 2019 $ 187 $ 187 $ 25 $ 39 The Utility Registrants do not have any contract assets. The Utility Registrants also record contract liabilities when consideration is received prior to the satisfaction of the performance obligations. As of March 31, 2019 and December 31, 2018 , the Utility Registrants' contract liabilities were immaterial. Transaction Price Allocated to Remaining Performance Obligations (All Registrants) The following table shows the amounts of future revenues expected to be recorded in each year for performance obligations that are unsatisfied or partially unsatisfied as of March 31, 2019 . This disclosure only includes contracts for which the total consideration is fixed and determinable at contract inception. The average contract term varies by customer type and commodity but ranges from one month to several years. This disclosure excludes Generation's power and gas sales contracts as they contain variable volumes and/or variable pricing. This disclosure also excludes the Utility Registrants' gas and electric tariff sales contracts and transmission revenue contracts as they generally have an original expected duration of one year or less and, therefore, do not contain any future, unsatisfied performance obligations to be included in this disclosure. 2019 2020 2021 2022 2023 and thereafter Total Exelon $ 393 $ 273 $ 112 $ 50 $ 142 $ 970 Generation 493 331 126 50 142 1,142 Revenue Disaggregation (All Registrants) The Registrants disaggregate revenue recognized from contracts with customers into categories that depict how the nature, amount, timing, and uncertainty of revenue and cash flows are affected by economic factors. See Note 18 — Segment Information for the presentation of the Registrant's revenue disaggregation.

Leases (All Registrants)

Leases (All Registrants)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Lessee, Finance and Operating Leases [Text Block]	Leases (All Registrants) Lessee The Registrants have operating leases for which they are the lessees. The following tables outline the significant types of operating leases at each registrant and other terms and conditions of the lease agreements. The Registrants do not have material finance leases. Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Contracted generation ● ● Real estate ● ● ● ● ● ● ● ● ● Vehicles and equipment ● ● ● ● ● ● ● ● ● (in years) Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Remaining lease terms 1-87 1-37 1-34 1-15 1-87 1-13 1-13 1-13 1-8 Options to extend the term 3-30 3-30 3-10 N/A N/A 3-30 5 3-30 N/A Options to terminate within 1-3 2 N/A N/A 3 N/A N/A N/A N/A The components of lease costs for the three months ended March 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating lease costs $ 68 $ 46 $ 1 $ — $ 8 $ 10 $ 3 $ 3 $ 1 Variable lease costs 73 68 — — — 2 — 1 — Short-term lease costs 9 8 — — — — — — — Total lease costs (a) $ 150 $ 122 $ 1 $ — $ 8 $ 12 $ 3 $ 4 $ 1 __________ (a) Excludes $3 million , $2 million , $1 million and $1 million of sublease income recorded at Exelon, Generation, PHI and DPL. The following table provides additional information regarding the presentation of operating lease ROU assets and lease liabilities within the Registrants’ Consolidated Balance Sheets as of March 31, 2019 : Exelon (a) Generation (a) ComEd PECO BGE PHI Pepco DPL ACE Operating lease ROU assets Other deferred debits and other assets $ 1,465 $ 1,027 $ 5 $ 2 $ 97 $ 314 $ 67 $ 75 $ 26 Operating lease liabilities Other current liabilities 249 173 3 1 31 36 8 11 6 Other deferred credits and other liabilities 1,395 1,023 4 1 66 284 60 72 20 Total operating lease liabilities $ 1,644 $ 1,196 $ 7 $ 2 $ 97 $ 320 $ 68 $ 83 $ 26 __________ (a) Exelon's and Generation's operating ROU assets and lease liabilities include $631 million and $778 million , respectively, related to contracted generation. The weighted average remaining lease terms, in years, and discount rates for operating leases as of March 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Remaining lease term 10.0 10.7 2.9 4.4 5.6 9.4 9.9 9.8 5.3 Discount rate 4.6 % 4.8 % 3.3 % 3.4 % 3.6 % 4.1 % 3.9 % 3.9 % 3.5 % Future minimum lease payments for operating leases as of March 31, 2019 were as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2019 $ 214 $ 154 $ 2 $ 1 $ 19 $ 33 $ 8 $ 7 $ 5 2020 289 202 2 1 34 43 9 12 5 2021 244 162 2 — 32 42 9 11 5 2022 174 112 1 — 16 40 8 11 4 2023 139 99 — — — 39 8 10 3 Remaining years 1,052 840 — — 18 194 42 52 7 Total 2,112 1,569 7 2 119 391 84 103 29 Interest 468 373 — — 22 71 16 20 3 Total operating lease liabilities $ 1,644 $ 1,196 $ 7 $ 2 $ 97 $ 320 $ 68 $ 83 $ 26 Future minimum lease payments for operating leases under the prior lease accounting guidance as of December 31, 2018 were as follows: Exelon (a)(b) Generation (a)(b) ComEd (a)(c) PECO (a)(c) BGE (a)(c)(d)(e) PHI (a) Pepco (a) DPL (a)(c) ACE (a) 2019 $ 140 $ 33 $ 7 $ 5 $ 35 $ 48 $ 11 $ 14 $ 7 2020 149 46 5 5 35 46 10 13 6 2021 143 46 4 5 33 43 9 12 5 2022 126 47 4 5 18 42 8 12 5 2023 97 46 3 5 3 39 8 10 4 Remaining years 723 545 — — 19 159 40 35 5 Total minimum future lease payments $ 1,378 $ 763 $ 23 $ 25 $ 143 $ 377 $ 86 $ 96 $ 32 __________ (a) Includes amounts related to shared use land arrangements. (b) Excludes Generation’s contingent operating lease payments associated with contracted generation. (c) Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO, BGE and DPL have excluded these payments from the remaining years as such amounts would not be meaningful. ComEd's, PECO’s, BGE’s and DPL's average annual obligation for these arrangements, included in each of the years 2019 - 2023, was $3 million , $5 million , $1 million and $1 million respectively. Also includes amounts related to shared use land arrangements. (d) Includes all future lease payments on a 99-year real estate lease that expires in 2106. (e) The BGE column above includes minimum future lease payments associated with a 6-year lease for the Baltimore City conduit system that became effective during the fourth quarter of 2016. BGE's total commitments under the lease agreement are $26 million , $28 million , $28 million and $14 million related to years 2019 - 2022, respectively. Cash paid for amounts included in the measurement of lease liabilities for the three months ended March 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating cash flows from operating leases $ 78 $ 52 $ 1 $ — $ 14 $ 8 $ 2 $ 2 $ 1
Lessor, Operating Leases [Text Block]	The Registrants have operating leases for which they are the lessors. The following tables outline the significant types of leases at each registrant and other terms and conditions of their lease agreements. Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Contracted generation ● ● Real estate ● ● ● ● ● ● ● ● ● (in years) Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Remaining lease terms 1-84 1-33 1-18 1-84 24 1-14 2-7 13-14 1-3 Options to extend the term 1-79 1-5 5-79 5-50 N/A 5 N/A N/A N/A The components of lease income for the three months ended March 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating lease income $ 4 $ 3 $ — $ — $ — $ 1 $ — $ 1 $ — Variable lease income $ 52 $ 52 $ — $ — $ — $ — $ — $ — $ — Future minimum lease payments to be recovered under operating leases as of March 31, 2019 were as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2019 $ 47 $ 43 $ — $ — $ — $ 4 $ — $ 3 $ — 2020 51 46 — — — 4 — 3 — 2021 50 45 — — — 4 — 3 — 2022 50 45 — — — 4 — 3 — 2023 49 45 — — — 4 — 3 — Remaining years 315 271 1 3 1 39 1 38 — Total $ 562 $ 495 $ 1 $ 3 $ 1 $ 59 $ 1 $ 53 $ — Leases (All Registrants)

Regulatory Matters (All Registr

Regulatory Matters (All Registrants)	3 Months Ended
	Mar. 31, 2019
Regulated Operations [Abstract]
Regulatory Matters (All Registrants)	Regulatory Matters (All Registrants) As discussed in Note 4 — Regulatory Matters of the Exelon 2018 Form 10-K, the Registrants are involved in rate and regulatory proceedings at the FERC and their state commissions. The following discusses developments in 2019 and updates to the 2018 Form 10-K. Utility Regulatory Matters (Exelon and the Utility Registrants) Distribution Base Rate Case Proceedings The following tables show the completed and pending distribution base rate case proceedings in 2019. Completed Distribution Base Rate Case Proceedings Registrant/Jurisdiction Filing Date Requested Revenue Requirement Increase Approved Revenue Requirement Increase (Decrease) Approved ROE Approval Date Rate Effective Date BGE - Maryland (Natural Gas) June 8, 2018 (amended October 12, 2018) $ 61 $ 43 9.8 % January 4, 2019 January 4, 2019 ACE - New Jersey (Electric) August 21, 2018 (amended November 19, 2018) $ 122 (a) $ 70 (a) 9.6 % March 13, 2019 April 1, 2019 __________ (a) Requested and approved increases are before New Jersey sales and use tax. Pending Distribution Base Rate Case Proceedings Registrant/Jurisdiction Filing Date Requested Revenue Requirement Increase/(Decrease) Requested ROE Expected Approval Timing Pepco - Maryland (Electric) January 15, 2019 (amended April 30, 2019) $ 27 10.3 % Third quarter of 2019 ComEd - Illinois (Electric) (a) April 8, 2019 $ (6 ) 8.91 % December 2019 __________ (a) Reflects an increase of $57 million for the initial revenue requirement for 2019 and a decrease of $63 million related to the annual reconciliation for 2018. The revenue requirement for 2019 and annual reconciliation for 2018 provides for a weighted average debt and equity return on distribution rate base of 6.53% . See Note 4 — Regulatory Matters of the Exelon 2018 Form 10-K for additional information on ComEd's distribution formula rate filings. Transmission Formula Rates Pending Transmission Formula Rate (Exelon and PECO). On May 1, 2017, PECO filed a request with FERC seeking approval to update its transmission rates and change the manner in which PECO’s transmission rate is determined from a fixed rate to a formula rate. The formula rate will be updated annually to ensure that under this rate customers pay the actual costs of providing transmission services. The formula rate filing includes a requested increase of $22 million to PECO’s annual transmission revenues and a requested rate of return on common equity of 11% , inclusive of a 50 basis point adder for being a member of a regional transmission organization. PECO requested that the new transmission rate be effective as of July 2017. On June 27, 2017, FERC issued an Order accepting the filing and suspending the proposed rates until December 1, 2017, subject to refund, and set the matter for hearing and settlement judge procedures. On May 4, 2018, the Chief Administrative Law Judge terminated settlement judge procedures and designated a new presiding judge. On February 8, 2019, PECO and the active parties reached an agreement in principle to settle this case. The presiding Administrative Law Judge has since suspended the procedural schedule in order for PECO and the active parties to continue working towards finalizing a settlement. On April 15, 2019, PECO and the active parties filed a status update with the presiding Administrative Law Judge requesting an additional 45 days to file a settlement. PECO cannot predict the outcome of this proceeding, or the transmission formula FERC may approve. On May 11, 2018, pursuant to the transmission formula rate request discussed above, PECO made its first annual formula rate update, which included a revenue decrease of $6 million . The revenue decrease of $6 million included an approximately $20 million reduction as a result of the tax savings associated with the TCJA. The updated transmission rate was effective June 1, 2018, subject to refund. Other State Regulatory Matters New Jersey Regulatory Matters ACE Infrastructure Investment Program Filing (Exelon, PHI and ACE). On February 28, 2018, ACE filed with the NJBPU the company’s Infrastructure Investment Program (IIP) proposing to seek recovery of a series of investments through a new rider mechanism, totaling $338 million , between 2019-2022 to provide safe and reliable service for its customers. The IIP allows for more timely recovery of investments made to modernize and enhance ACE’s electric system. On April 15, 2019, ACE entered into a settlement agreement with other parties, which allows for a recovery totaling $96 million of reliability related capital investments from July 1, 2019 through June 30, 2023. On April 18, 2019, the NJBPU approved the settlement agreement. New Jersey Clean Energy Legislation (Exelon and ACE). On May 23, 2018, New Jersey enacted legislation that established and modified New Jersey’s clean energy and energy efficiency programs and solar and renewable energy portfolio standards. On the same day, New Jersey enacted legislation that established a ZEC program that provides compensation for nuclear plants that demonstrate to the NJBPU that they meet certain requirements, including that they make a significant contribution to air quality in the state and that their revenues are insufficient to cover their costs and risks. Electric distribution utilities in New Jersey, including ACE, must begin collecting from retail distribution customers, through a non-bypassable charge, all costs associated with the utility’s procurement of the ZECs effective April 18, 2019. See Generation Regulatory Matters below for additional information. Other Federal Regulatory Matters Transmission-Related Income Tax Regulatory Assets (Exelon, ComEd, BGE, PHI, Pepco, DPL and ACE). ComEd’s, BGE’s, Pepco’s, DPL’s and ACE’s transmission formula rates currently do not provide for the pass back or recovery of income tax-related regulatory liabilities or assets, including those established upon enactment of the TCJA. On December 13, 2016 (and as amended on March 13, 2017), BGE filed with FERC to begin recovering certain existing and future transmission-related income tax regulatory assets through its transmission formula rate. BGE’s existing regulatory assets included (1) amounts that, if BGE’s transmission formula rate provided for recovery, would have been previously amortized and (2) amounts that would be amortized and recovered prospectively. ComEd, Pepco, DPL and ACE had similar transmission-related income tax regulatory liabilities and assets also requiring FERC approval. On November 16, 2017, FERC issued an order rejecting BGE’s proposed revisions to its transmission formula rate to recover these transmission-related income tax regulatory assets. As a result of the FERC’s order, ComEd, BGE, Pepco, DPL and ACE took a charge to Income tax expense within their Consolidated Statements of Operations and Comprehensive Income in the fourth quarter of 2017 reducing their associated transmission-related income tax regulatory assets for the portion of the total transmission-related income tax regulatory assets that would have been previously amortized and recovered through rates. Similar regulatory assets and liabilities at PECO are not subject to the same FERC transmission rate recovery formula. See above for additional information regarding PECO's transmission formula rate filing. On December 18, 2017, BGE filed for clarification and rehearing of FERC’s November 16, 2017 order and on February 23, 2018 (as amended on July 9, 2018), ComEd, Pepco, DPL, and ACE each filed with FERC to revise their transmission formula rate mechanisms to permit recovery of transmission-related income tax regulatory assets, including those amounts that would have been previously amortized and recovered through rates had the transmission formula rate provided for such recovery. On September 7, 2018, FERC issued orders rejecting BGE’s December 18, 2017 request for rehearing and clarification and ComEd's, Pepco's, DPL's and ACE's February 23, 2018 (as amended on July 9, 2018) filings, citing the lack of timeliness of the requests to recover amounts that would have been previously amortized, but indicating that ongoing recovery of certain transmission-related income tax regulatory assets would provide for a more accurate revenue requirement, consistent with its November 16, 2017 order. On October 1, 2018, ComEd, BGE, Pepco, DPL, and ACE submitted filings to recover ongoing non-TCJA amortization amounts and refund TCJA transmission-related income tax regulatory liabilities for the prospective period starting on October 1, 2018. In addition, on October 9, 2018, ComEd, Pepco, DPL, and ACE sought rehearing of FERC's September 7, 2018 order. On November 2, 2018, BGE filed an appeal of FERC’s September 7, 2018 order to the Court of Appeals for the D.C. Circuit. On April 26, 2019, FERC issued an order accepting ComEd’s, BGE’s, Pepco’s, DPL’s, and ACE’s October 1, 2018 filings, effective October 1, 2018, subject to refund and established hearing and settlement judge procedures. ComEd, BGE, Pepco, DPL, and ACE cannot predict the outcome of these proceedings. If FERC ultimately rules that the future, ongoing non-TCJA amortization amounts are not recoverable, Exelon, ComEd, BGE, PHI, Pepco, DPL and ACE would record additional charges to Income tax expense, which could be up to approximately $76 million , $51 million , $15 million , $10 million , $3 million , $5 million and $2 million , respectively, as of March 31, 2019. Regulatory Assets and Liabilities Regulatory assets and liabilities have not changed materially since December 31, 2018. See Note 4 — Regulatory Matters of the Exelon 2018 Form 10-K for additional information on the specific regulatory assets and liabilities. Capitalized Ratemaking Amounts Not Recognized (Exelon and the Utility Registrants) The following table presents authorized amounts capitalized for ratemaking purposes related to earnings on shareholders’ investment that are not recognized for financial reporting purposes in Exelon's and the Utility Registrant's Consolidated Balance Sheets. These amounts will be recognized as revenues in the related Consolidated Statements of Operations and Comprehensive Income in the periods they are billable to our customers. Exelon ComEd (a) PECO BGE (b) PHI Pepco (c) DPL (c) ACE March 31, 2019 $ 64 $ 7 $ — $ 49 $ 8 $ 5 $ 3 $ — December 31, 2018 $ 65 $ 8 $ — $ 49 $ 8 $ 5 $ 3 $ — _________ (a) Reflects ComEd's unrecognized equity returns earned for ratemaking purposes on its electric distribution formula rate regulatory assets. (b) BGE's authorized amounts capitalized for ratemaking purposes primarily relate to earnings on shareholders' investment on its AMI programs. (c) Pepco's and DPL's authorized amounts capitalized for ratemaking purposes relate to earnings on shareholders' investment on their respective AMI Programs and Energy Efficiency and Demand Response Programs. The earnings on energy efficiency are on Pepco DC and DPL DE programs only. Generation Regulatory Matters (Exelon and Generation) Illinois Regulatory Matters Zero Emission Standard. Pursuant to FEJA, on January 25, 2018, the ICC announced that Generation’s Clinton Unit 1, Quad Cities Unit 1 and Quad Cities Unit 2 nuclear plants were selected as the winning bidders through the IPA's ZEC procurement event. Generation executed the ZEC procurement contracts with Illinois utilities, including ComEd, effective January 26, 2018 and began recognizing revenue with compensation for the sale of ZECs retroactive to the June 1, 2017 effective date of FEJA. During the three months ended March 31, 2018, Generation recognized $150 million of revenue related to ZECs generated from June 1, 2017 through December 31, 2017. On February 14, 2017, two lawsuits were filed in the Northern District of Illinois against the IPA alleging that the state’s ZEC program violates certain provisions of the U.S. Constitution. Both lawsuits argued that the Illinois ZEC program would distort PJM's FERC-approved energy and capacity market auction system of setting wholesale prices and sought a permanent injunction preventing the implementation of the program. The lawsuits were dismissed by the district court on July 14, 2017. On September 13, 2018, the U.S. Circuit Court of Appeals for the Seventh Circuit affirmed the lower court's dismissal of both lawsuits. On January 7, 2019, plaintiffs filed a petition seeking U.S. Supreme Court review of the case which was denied on April 15, 2019. New Jersey Regulatory Matters New Jersey Clean Energy Legislation. On May 23, 2018, New Jersey enacted legislation that established a ZEC program that will provide compensation for nuclear plants that demonstrate to the NJBPU that they meet certain requirements, including that they make a significant contribution to air quality in the state and that their revenues are insufficient to cover their costs and risks. Under the legislation, the NJBPU will issue ZECs to qualifying nuclear power plants and the electric distribution utilities in New Jersey, including ACE, will be required to purchase those ZECs. On November 19, 2018, NJBPU issued an order providing for the method and application process for determining the eligibility of nuclear power plants, a draft method and process for ranking and selecting eligible nuclear power plants, and the establishment of a mechanism for each regulated utility to purchase ZECs from selected nuclear power plants. On December 19, 2018, PSEG filed complete applications seeking NJBPU approval for Salem 1 and Salem 2, of which Generation owns a 42.59% ownership interest, to participate in the ZEC program. On the same day, Generation filed certain Supplemental Information with the NJBPU providing proprietary information that was requested in the application but which could not be shared with PSEG. On April 18, 2019, the NJBPU approved the award of ZECs to Salem 1 and Salem 2. See Note 8 — Early Plant Retirements for additional information related to Salem. New York Regulatory Matters New York Clean Energy Standard. On August 1, 2016, the NYPSC issued an order establishing the New York CES, a component of which is a Tier 3 ZEC program targeted at preserving the environmental attributes of zero-emissions nuclear-powered generating facilities that meet the criteria demonstrating public necessity as determined by the NYPSC. On October 19, 2016, a coalition of fossil-generation companies filed a complaint in federal district court against the NYPSC alleging that the ZEC program violates certain provisions of the U.S. Constitution; specifically, that the ZEC program interferes with FERC’s jurisdiction over wholesale rates and that it discriminates against out of state competitors, which was dismissed by the district court on July 25, 2017. On September 27, 2018, the U.S. Court of Appeals for the Second Circuit affirmed the lower court's dismissal of the complaint against the ZEC program. On January 7, 2019, the fossil-generation companies filed a petition seeking U.S. Supreme Court review of the case which was denied on April 15, 2019. In addition, on November 30, 2016 (as amended on January 13, 2017), a group of parties filed a Petition in New York State court seeking to invalidate the ZEC program, which argued that the NYPSC did not have authority to establish the program, that it violated state environmental law and that it violated certain technical provisions of the State Administrative Procedures Act when adopting the ZEC program. Subsequently, Generation, CENG and the NYPSC filed motions to dismiss the state court action, which were later opposed by the plaintiffs. On January 22, 2018, the court dismissed the environmental claims and the majority of the plaintiffs from the case but denied the motions to dismiss with respect to the remaining five plaintiffs and claims, without commenting on the merits of the case. Generation, CENG and the state’s answers and briefs were filed on March 30, 2018. On December 17, 2018, plaintiffs filed a reply brief introducing new arguments and new evidence. The State of New York filed a motion to strike on December 28, 2018. On January 4, 2019, Generation and CENG filed a motion to strike the new arguments and new evidence.The court must now decide whether or not to set the case for hearing. Other legal challenges remain possible, the outcomes of which remain uncertain. See Note 8 — Early Plant Retirements for additional information related to Ginna and Nine Mile Point. Federal Regulatory Matters Operating License Renewals Conowingo Hydroelectric Project. On August 29, 2012, Generation submitted a hydroelectric license application to FERC for a new license for the Conowingo Hydroelectric Project (Conowingo). In connection with Generation’s efforts to obtain a water quality certification pursuant to Section 401 of the Clean Water Act (401 Certification) with Maryland Department of the Environment (MDE) for Conowingo, Generation continues to work with MDE and other stakeholders to resolve water quality licensing issues, including: (1) water quality, (2) fish habitat, and (3) sediment. On April 27, 2018, the MDE issued its 401 Certification for Conowingo. As issued, the 401 Certification contains numerous conditions, including those relating to reduction of nutrients from upstream sources, removal of all visible trash and debris from upstream sources, and implementation of measures relating to fish passage, which could have a material, unfavorable impact in Exelon’s and Generation’s financial statements through an increase in capital expenditures and operating costs if implemented. On May 25, 2018, Generation filed complaints in federal and state court, along with a petition for reconsideration with MDE, alleging that the conditions are unfair and onerous violating MDE regulations, state, federal, and constitutional law. Generation also requested that FERC defer the issuance of the federal license while these significant state and federal law issues are pending. On February 28, 2019, Generation filed a Petition for Declaratory Order with FERC requesting that FERC issue an order declaring that MDE waived its right to issue a 401 Certification for Conowingo because it failed to timely act on Conowingo's 401 Certification application and requesting that FERC decline to include the conditions proposed by MDE in April 2018. Exelon also continues to challenge the 401 Certification through the administrative process and in state and federal court. Exelon and Generation cannot predict the final outcome or its financial impact, if any, on Exelon or Generation. As of March 31, 2019 , $38 million of direct costs associated with Conowingo licensing efforts have been capitalized. See Note 4 — Regulatory Matters of the Exelon 2018 Form 10-K for additional information on Generation's operating license renewal efforts.

Impairment of Long-Lived Assets

Impairment of Long-Lived Assets (Exelon and Generation)	3 Months Ended
	Mar. 31, 2019
Property, Plant and Equipment [Abstract]
Asset Impairment Charges [Text Block]	Impairment of Long-Lived Assets (Exelon and Generation) Registrants evaluate long-lived assets for recoverability whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. The fair value analysis is primarily based on the income approach using significant unobservable inputs (Level 3) including revenue and generation forecasts, projected capital and maintenance expenditures and discount rates. Changes in those inputs could potentially result in material future impairments of the Registrants' long-lived assets. Generation’s Antelope Valley, a 242 MW solar facility in Lancaster, CA, sells all of its output to Pacific Gas and Electric Company (PG&E) through a PPA. As of March 31, 2019 , Generation had approximately $750 million of net long-lived assets related to Antelope Valley. As a result of the PG&E bankruptcy filing in the first quarter of 2019, Generation completed a comprehensive review of Antelope Valley's estimated undiscounted future cash flows and no impairment charge was recorded. Significant changes in assumptions such as the likelihood of the PPA being rejected as part of the bankruptcy proceedings could potentially result in future impairments of Antelope Valley’s net long-lived assets, which could be material. Antelope Valley is a wholly owned indirect subsidiary of EGR IV, which had approximately $1,970 million of additional net long-lived assets as of March 31, 2019 . EGR IV is a wholly owned indirect subsidiary of Exelon and Generation and includes Generation's interest in EGRP and other projects with non-controlling interests. To date, there have been no indicators to suggest that the carrying amount of other net long-lived assets of EGR IV may not be recoverable. Generation will continue to monitor the bankruptcy proceedings for any changes in circumstances that may indicate the carrying amount of the net long-lived assets of Antelope Valley or other long-lived assets of EGR IV may not be recoverable. See Note 11 - Debt and Credit Agreements for additional information on the PG&E bankruptcy.

Early Plant Retirements (Exelon

Early Plant Retirements (Exelon and Generation)	3 Months Ended
	Mar. 31, 2019
Property, Plant and Equipment [Abstract]
Implications Of Potential Early Retirement Disclosure [Text Block]	Early Plant Retirements (Exelon and Generation) Exelon and Generation continuously evaluate factors that affect the current and expected economic value of Generation’s plants, including, but not limited to: market power prices, results of capacity auctions, potential legislative and regulatory solutions to ensure plants are fairly compensated for benefits they provide through their carbon-free emissions, reliability, or fuel security, and the impact of potential rules from the EPA requiring reduction of carbon and other emissions and the efforts of states to implement those final rules. The precise timing of an early retirement date for any plant, and the resulting financial statement impacts, may be affected by many factors, including the status of potential regulatory or legislative solutions, results of any transmission system reliability study assessments, the nature of any co-owner requirements and stipulations, and NDT fund requirements for nuclear plants, 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 or other obligations, and where applicable, just prior to its next scheduled nuclear refueling outage. Nuclear Generation In 2015 and 2016, Generation identified the Clinton and Quad Cities nuclear plants in Illinois, Ginna and Nine Mile Point nuclear plants in New York and Three Mile Island nuclear plant in Pennsylvania as having the greatest risk of early retirement based on economic valuation and other factors. In 2017, PSEG made public similar financial challenges facing its New Jersey nuclear plants, including Salem, of which Generation owns a 42.59% ownership interest. PSEG is the operator of Salem and also has the decision making authority to retire Salem. Assuming the continued effectiveness of the Illinois ZES, New Jersey ZEC program and the New York CES, Generation and CENG, through its ownership of Ginna and Nine Mile Point, no longer consider Clinton, Quad Cities, Salem, Ginna or Nine Mile Point to be at heightened risk for early retirement. However, to the extent the Illinois ZES, New Jersey ZEC program or the New York CES programs do not operate as expected over their full terms, each of these plants could again be at heightened risk for early retirement, which could have a material impact on Exelon’s and Generation’s future financial statements. See Note 6 — Regulatory Matters for additional information on the Illinois ZES, New Jersey ZEC program and New York CES. In Pennsylvania, the TMI nuclear plant did not clear in the May 2017 PJM capacity auction for the 2020-2021 planning year, the third consecutive year that TMI failed to clear the PJM base residual capacity auction and on May 30, 2017, based on these capacity auction results, prolonged periods of low wholesale power prices, and the absence of federal or state policies that place a value on nuclear energy for its ability to produce electricity without air pollution, Exelon announced that Generation will permanently cease generation operations at TMI on or about September 30, 2019. TMI is currently committed to operate through May 2019 and is licensed to operate through 2034. Generation has filed the required market and regulatory notifications to shut down the plant. PJM has subsequently notified Generation that it has not identified any reliability issues and has approved the deactivation of TMI as proposed. On April 5, 2019, Generation filed the post shutdown decommissioning activities report (PSDAR) with the NRC detailing the plans for TMI after its final shutdown. On February 2, 2018, Exelon announced that Generation will permanently cease generation operations at the Oyster Creek nuclear plant at the end of its current operating cycle and permanently ceased generation operations in September 2018. As a result of these early nuclear plant retirement decisions, Exelon and Generation recognized incremental non-cash charges to earnings stemming from shortening the expected economic useful lives primarily related to accelerated depreciation of plant assets (including any ARC) and accelerated amortization of nuclear fuel, as well as operating and maintenance expenses. See Note 13 — Nuclear Decommissioning for additional information on changes to the nuclear decommissioning ARO balance. The total impact for the three months ended March 31, 2019 and 2018 are summarized in the table below. Three Months Ended Income statement expense (pre-tax) 2019 2018 Depreciation and amortization (a) Accelerated depreciation (b) $ 74 $ 137 Accelerated nuclear fuel amortization 5 15 Operating and maintenance (c) (83 ) 26 Total $ (4 ) $ 178 _________ (a) Reflects incremental accelerated depreciation and amortization for TMI for the three months ended March 31, 2019 . Reflects incremental accelerated depreciation for TMI and Oyster Creek for the three months ended March 31, 2018 . The Oyster Creek amounts are from February 2, 2018 through March 31, 2018. (b) Reflects incremental accelerated depreciation of plant assets, including any ARC. (c) In 2019, primarily reflects decrease to estimated decommissioning costs for TMI. See Note 13 — Nuclear Decommissioning for additional information on the first quarter 2019 TMI ARO update. In 2018, primarily reflects materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments. Generation’s Dresden, Byron and Braidwood nuclear plants in Illinois are also showing increased signs of economic distress, which could lead to an early retirement, in a market that does not currently compensate them for their unique contribution to grid resiliency and their ability to produce large amounts of energy without carbon and air pollution. The May 2018 PJM capacity auction for the 2021-2022 planning year resulted in the largest volume of nuclear capacity ever not selected in the auction, including all of Dresden, and portions of Byron and Braidwood. Exelon continues to work with stakeholders on state policy solutions, while also advocating for broader market reforms at the regional and federal level. Other Generation On March 29, 2018, Generation notified grid operator ISO-NE of its plans to early retire its Mystic Generating Station assets absent regulatory reforms on June 1, 2022, at the end of the current capacity commitment for Mystic Units 7 and 8. Mystic Unit 9 is currently committed through May 2021. On May 16, 2018, Generation made a filing with FERC to establish cost-of-service compensation and terms and conditions of service for Mystic Units 8 and 9 for the period between June 1, 2022 - May 31, 2024. On December 20, 2018, FERC issued an order accepting the cost of service agreement reflecting a number of adjustments to the annual fixed revenue requirement and allowing for recovery of a substantial portion of the costs associated with the Everett Marine Terminal. Those adjustments were reflected in a compliance filing filed March 1, 2019. In the December 20, 2018 order, FERC also directed a paper hearing on ROE using a new methodology. Initial briefs in the ROE proceeding were filed on April 19, 2019 and reply briefs are due on July 18, 2019. On January 4, 2019, Generation notified ISO-NE that it will participate in the Forward Capacity Market auction for the 2022 - 2023 capacity commitment period. In addition, on January 22, 2019, Exelon and several other parties filed requests for rehearing of certain findings of the December 20, 2018 order, which does not alter Generation's commitment to participate in the Forward Capacity Auction for the 2022-2023 capacity commitment period. On March 25, 2019, ISO-NE filed the Inventoried Energy Program, which is intended to provide an interim fuel security program pending conclusion of the stakeholder process to develop a long-term, market-based solution to address fuel security. Exelon filed comments on the Inventoried Energy Program proposal on April 15, 2019. FERC has ordered ISO-NE to file the long-term, market-based fuel security rules by October 15, 2019. The following table provides the balance sheet amounts as of March 31, 2019 for Exelon's and Generation’s significant assets and liabilities associated with the Mystic Units 8 and 9 and Everett Marine Terminal assets that would potentially be impacted by a decision to permanently cease generation operations in the absence of long-term market rule changes. March 31, 2019 Asset Balances Materials and supplies inventory $ 30 Fuel inventory 22 Completed plant, net 900 Construction work in progress 2 Liability Balances Asset retirement obligation (1 )

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities (All Registrants)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities (All Registrants)	Fair Value of Financial Assets and Liabilities (All Registrants) Fair Value of Financial Liabilities Recorded at Amortized Cost 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 March 31, 2019 and December 31, 2018 : Exelon March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 1,254 $ — $ 1,254 $ — $ 1,254 Long-term debt (including amounts due within one year) (a) 35,468 — 35,066 2,188 37,254 Long-term debt to financing trusts (b) 390 — — 411 411 SNF obligation 1,178 — 989 — 989 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 714 $ — $ 714 $ — $ 714 Long-term debt (including amounts due within one year) (a) 35,424 — 33,711 2,158 35,869 Long-term debt to financing trusts (b) 390 — — 400 400 SNF obligation 1,171 — 949 — 949 Generation March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 8,747 $ — $ 7,641 $ 1,443 $ 9,084 SNF obligation 1,178 — 989 — 989 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 8,793 $ — $ 7,467 $ 1,443 $ 8,910 SNF obligation 1,171 — 949 — 949 ComEd March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 322 $ — $ 322 $ — $ 322 Long-term debt (including amounts due within one year) (a) 8,194 — 8,855 — 8,855 Long-term debt to financing trusts (b) 205 — — 215 215 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 8,101 $ — $ 8,390 $ — $ 8,390 Long-term debt to financing trusts (b) 205 — — 209 209 PECO March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 3,084 $ — $ 3,295 $ 50 $ 3,345 Long-term debt to financing trusts (b) 184 — — 196 196 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 3,084 $ — $ 3,157 $ 50 $ 3,207 Long-term debt to financing trusts (b) 184 — — 191 191 BGE March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 106 $ — $ 106 $ — $ 106 Long-term debt (including amounts due within one year) (a) 2,876 — 3,051 — 3,051 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 35 $ — $ 35 $ — $ 35 Long-term debt (including amounts due within one year) (a) 2,876 — 2,950 — 2,950 PHI March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 326 $ — $ 326 $ — $ 326 Long-term debt (including amounts due within one year) (a) 6,244 — 5,608 695 6,303 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 179 $ — $ 179 $ — $ 179 Long-term debt (including amounts due within one year) (a) 6,259 — 5,436 665 6,101 Pepco March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 105 $ — $ 105 $ — $ 105 Long-term debt (including amounts due within one year) (a) 2,720 — 3,000 208 3,208 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 40 $ — $ 40 $ — $ 40 Long-term debt (including amounts due within one year) (a) 2,719 — 2,901 196 3,097 DPL March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 5 $ — $ 5 $ — $ 5 Long-term debt (including amounts due within one year) (a) 1,495 — 1,345 204 1,549 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 1,494 $ — $ 1,303 $ 193 $ 1,496 ACE March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 216 $ — $ 216 $ — $ 216 Long-term debt (including amounts due within one year) (a) 1,184 — 1,004 283 1,287 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 139 $ — $ 139 $ — $ 139 Long-term debt (including amounts due within one year) (a) 1,188 — 987 275 1,262 _________ (a) Includes unamortized debt issuance costs which are not fair valued of $216 million , $49 million , $67 million , $22 million , $18 million , $14 million , $33 million , $12 million and $6 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of March 31, 2019 . Includes unamortized debt issuance costs which are not fair valued of $216 million , $51 million , $63 million , $23 million , $18 million , $14 million , $34 million , $12 million and $7 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of December 31, 2018 . (b) Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of March 31, 2019 . Includes unamortized debt issuance costs which are not fair valued of less than $1 million and $1 million for Exelon and ComEd, respectively, as of December 31, 2018 . 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. Generation and Exelon In accordance with the applicable guidance on fair value measurement, certain investments that are measured at fair value using the NAV per share as a practical expedient are no longer classified within the fair value hierarchy and are included under "Not subject to leveling" in the table below. The following tables present assets and liabilities measured and recorded at fair value in Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of March 31, 2019 and December 31, 2018 : Generation Exelon As of March 31, 2019 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Assets Cash equivalents (a) $ 370 $ — $ — $ — $ 370 $ 817 $ — $ — $ — $ 817 NDT fund investments Cash equivalents (b) 369 74 — — 443 369 74 — — 443 Equities 3,060 1,753 1 1,545 6,359 3,060 1,753 1 1,545 6,359 Fixed income Corporate debt — 1,545 236 1 1,782 — 1,545 236 1 1,782 U.S. Treasury and agencies 2,033 112 — — 2,145 2,033 112 — — 2,145 Foreign governments — 43 — — 43 — 43 — — 43 State and municipal debt — 110 — — 110 — 110 — — 110 Other (c) — 26 — 935 961 — 26 — 935 961 Fixed income subtotal 2,033 1,836 236 936 5,041 2,033 1,836 236 936 5,041 Middle market lending — — 303 406 709 — — 303 406 709 Private equity — — — 352 352 — — — 352 352 Real estate — — — 535 535 — — — 535 535 NDT fund investments subtotal (d) 5,462 3,663 540 3,774 13,439 5,462 3,663 540 3,774 13,439 Rabbi trust investments Cash equivalents 4 — — — 4 47 — — — 47 Mutual funds 25 — — — 25 74 — — — 74 Fixed income — — — — — — 14 — — 14 Life insurance contracts — 23 — — 23 — 71 39 — 110 Rabbi trust investments subtotal (e) 29 23 — — 52 121 85 39 — 245 Commodity derivative assets Economic hedges 273 2,164 1,442 — 3,879 273 2,164 1,442 — 3,879 Proprietary trading — 74 104 — 178 — 74 104 — 178 Effect of netting and allocation of collateral (f)(g) (294 ) (1,836 ) (820 ) — (2,950 ) (294 ) (1,836 ) (820 ) — (2,950 ) Commodity derivative assets subtotal (21 ) 402 726 — 1,107 (21 ) 402 726 — 1,107 Interest rate and foreign currency derivative assets Economic hedges — 4 — — 4 — 4 — — 4 Effect of netting and allocation of collateral — (5 ) — — (5 ) — (5 ) — — (5 ) Interest rate and foreign currency derivative assets subtotal — (1 ) — — (1 ) — (1 ) — — (1 ) Other investments — — 42 — 42 — — 42 — 42 Total assets 5,840 4,087 1,308 3,774 15,009 6,379 4,149 1,347 3,774 15,649 Generation Exelon As of March 31, 2019 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Liabilities Commodity derivative liabilities Economic hedges (350 ) (2,339 ) (1,164 ) — (3,853 ) (350 ) (2,339 ) (1,404 ) — (4,093 ) Proprietary trading — (79 ) (40 ) — (119 ) — (79 ) (40 ) — (119 ) Effect of netting and allocation of collateral (f)(g) 346 2,119 977 — 3,442 346 2,119 977 — 3,442 (4 ) (299 ) (227 ) — (530 ) (4 ) (299 ) (467 ) — (770 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — — — — — — (2 ) — — (2 ) Economic hedges — (12 ) — — (12 ) — (12 ) — — (12 ) Effect of netting and allocation of collateral — 5 — — 5 — 5 — — 5 Interest rate and foreign currency derivative liabilities subtotal — (7 ) — — (7 ) — (9 ) — — (9 ) Deferred compensation obligation — (36 ) — — (36 ) — (140 ) — — (140 ) Total liabilities (4 ) (342 ) (227 ) — (573 ) (4 ) (448 ) (467 ) — (919 ) Total net assets $ 5,836 $ 3,745 $ 1,081 $ 3,774 $ 14,436 $ 6,375 $ 3,701 $ 880 $ 3,774 $ 14,730 Generation Exelon As of December 31, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Assets Cash equivalents (a) $ 581 $ — $ — $ — $ 581 $ 1,243 $ — $ — $ — $ 1,243 NDT fund investments Cash equivalents (b) 252 86 — — 338 252 86 — — 338 Equities 2,918 1,591 — 1,381 5,890 2,918 1,591 — 1,381 5,890 Fixed income Corporate debt — 1,593 230 — 1,823 — 1,593 230 — 1,823 U.S. Treasury and agencies 2,081 99 — — 2,180 2,081 99 — — 2,180 Foreign governments — 50 — — 50 — 50 — — 50 State and municipal debt — 149 — — 149 — 149 — — 149 Other (c) — 30 — 846 876 — 30 — 846 876 Fixed income subtotal 2,081 1,921 230 846 5,078 2,081 1,921 230 846 5,078 Middle market lending — — 313 367 680 — — 313 367 680 Private equity — — — 329 329 — — — 329 329 Real estate — — — 510 510 — — — 510 510 NDT fund investments subtotal (d) 5,251 3,598 543 3,433 12,825 5,251 3,598 543 3,433 12,825 Rabbi trust investments Cash equivalents 5 — — — 5 48 — — — 48 Mutual funds 24 — — — 24 72 — — — 72 Fixed income — — — — — — 15 — — 15 Life insurance contracts — 22 — — 22 — 70 38 — 108 Rabbi trust investments subtotal (e) 29 22 — — 51 120 85 38 — 243 Commodity derivative assets Economic hedges 541 2,760 1,470 — 4,771 541 2,760 1,470 — 4,771 Proprietary trading — 69 77 — 146 — 69 77 — 146 Effect of netting and allocation of collateral (f)(g) (582 ) (2,357 ) (732 ) — (3,671 ) (582 ) (2,357 ) (732 ) — (3,671 ) Commodity derivative assets subtotal (41 ) 472 815 — 1,246 (41 ) 472 815 — 1,246 Interest rate and foreign currency derivative assets Economic hedges — 13 — — 13 — 13 — — 13 Effect of netting and allocation of collateral — (3 ) — — (3 ) — (3 ) — — (3 ) Interest rate and foreign currency derivative assets subtotal — 10 — — 10 — 10 — — 10 Other investments — — 42 — 42 — — 42 — 42 Total assets 5,820 4,102 1,400 3,433 14,755 6,573 4,165 1,438 3,433 15,609 Generation Exelon As of December 31, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Liabilities Commodity derivative liabilities Economic hedges (642 ) (2,963 ) (1,027 ) — (4,632 ) (642 ) (2,963 ) (1,276 ) — (4,881 ) Proprietary trading — (73 ) (21 ) — (94 ) — (73 ) (21 ) — (94 ) Effect of netting and allocation of collateral (f)(g) 639 2,581 808 — 4,028 639 2,581 808 — 4,028 Commodity derivative liabilities subtotal (3 ) (455 ) (240 ) — (698 ) (3 ) (455 ) (489 ) — (947 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — — — — — — (4 ) — — (4 ) Economic hedges — (6 ) — — (6 ) — (6 ) — — (6 ) Effect of netting and allocation of collateral — 3 — — 3 — 3 — — 3 Interest rate and foreign currency derivative liabilities subtotal — (3 ) — — (3 ) — (7 ) — — (7 ) Deferred compensation obligation — (35 ) — — (35 ) — (137 ) — — (137 ) Total liabilities (3 ) (493 ) (240 ) — (736 ) (3 ) (599 ) (489 ) — (1,091 ) Total net assets $ 5,817 $ 3,609 $ 1,160 $ 3,433 $ 14,019 $ 6,570 $ 3,566 $ 949 $ 3,433 $ 14,518 _________ (a) Generation excludes cash of $270 million and $283 million at March 31, 2019 and December 31, 2018 and restricted cash of $36 million and $39 million at March 31, 2019 and December 31, 2018 . Exelon excludes cash of $426 million and $458 million at March 31, 2019 and December 31, 2018 and restricted cash of $71 million and $80 million at March 31, 2019 and December 31, 2018 and includes long-term restricted cash of $211 million and $185 million at March 31, 2019 and December 31, 2018 , which is reported in Other deferred debits in the Consolidated Balance Sheets. (b) Includes $43 million and $50 million of cash received from outstanding repurchase agreements at March 31, 2019 and December 31, 2018 , respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below. (c) Includes derivative instruments of $7 million and $44 million , which have a total notional amount of $1,223 million and $1,432 million at March 31, 2019 and December 31, 2018 , 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 Exelon and Generation's exposure to credit or market loss. (d) Excludes net liabilities of $94 million and $130 million at March 31, 2019 and December 31, 2018 , 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) The amount of unrealized gains/(losses) at Generation totaled less than $1 million for the three months ended March 31, 2019 and March 31, 2018 , respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million for the three months ended March 31, 2019 and March 31, 2018 , respectively. (f) Collateral posted/(received) from counterparties totaled $52 million , $283 million and $157 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of March 31, 2019 . Collateral posted/(received) from counterparties, net of collateral paid to counterparties, totaled $57 million , $224 million and $76 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2018 . (g) Of the collateral posted/(received), $(33) million and $(94) million represents variation margin on the exchanges as of March 31, 2019 and December 31, 2018 , respectively. Exelon and Generation hold investments without readily determinable fair values with carrying amounts of $71 million as of March 31, 2019 . Changes were immaterial in fair value, cumulative adjustments and impairments for the three months ended March 31, 2019 . ComEd, PECO and BGE The following tables present assets and liabilities measured and recorded at fair value in ComEd's, PECO's and BGE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of March 31, 2019 and December 31, 2018 : ComEd PECO BGE As of March 31, 2019 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 194 $ — $ — $ 194 $ 16 $ — $ — $ 16 $ 3 $ — $ — $ 3 Rabbi trust investments Mutual funds — — — — 7 — — 7 6 — — 6 Life insurance contracts — — — — — 10 — 10 — — — — Rabbi trust investments subtotal (b) — — — — 7 10 — 17 6 — — 6 Total assets 194 — — 194 23 10 — 33 9 — — 9 Liabilities Deferred compensation obligation — (7 ) — (7 ) — (10 ) — (10 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (c) — — (240 ) (240 ) — — — — — — — — Total liabilities — (7 ) (240 ) (247 ) — (10 ) — (10 ) — (5 ) — (5 ) Total net assets (liabilities) $ 194 $ (7 ) $ (240 ) $ (53 ) $ 23 $ — $ — $ 23 $ 9 $ (5 ) $ — $ 4 ComEd PECO BGE As of December 31, 2018 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 209 $ — $ — $ 209 $ 111 $ — $ — $ 111 $ 4 $ — $ — $ 4 Rabbi trust investments Mutual funds — — — — 7 — — 7 6 — — 6 Life insurance contracts — — — — — 10 — 10 — — — — Rabbi trust investments subtotal (b) — — — — 7 10 — 17 6 — — 6 Total assets 209 — — 209 118 10 — 128 10 — — 10 Liabilities Deferred compensation obligation — (6 ) — (6 ) — (10 ) — (10 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (c) — — (249 ) (249 ) — — — — — — — — Total liabilities — (6 ) (249 ) (255 ) — (10 ) — (10 ) — (5 ) — (5 ) Total net assets (liabilities) $ 209 $ (6 ) $ (249 ) $ (46 ) $ 118 $ — $ — $ 118 $ 10 $ (5 ) $ — $ 5 _________ (a) ComEd excludes cash of $69 million and $93 million at March 31, 2019 and December 31, 2018 and restricted cash of $15 million and $28 million at March 31, 2019 and December 31, 2018 and includes long-term restricted cash of $193 million and $166 million at March 31, 2019 and December 31, 2018 , which is reported in Other deferred debits in the Consolidated Balance Sheets. PECO excludes cash of $31 million and $24 million at March 31, 2019 and December 31, 2018 . BGE excludes cash of $12 million and $7 million at March 31, 2019 and December 31, 2018 and restricted cash of $1 million and $2 million at March 31, 2019 and December 31, 2018 . (b) The amount of unrealized gains/(losses) at ComEd, PECO and BGE totaled less than $1 million for the three months ended March 31, 2019 and March 31, 2018 . (c) The Level 3 balance consists of the current and noncurrent liability of $27 million and $213 million , respectively, at March 31, 2019 , and $26 million and $223 million , respectively, at December 31, 2018 , related to floating-to-fixed energy swap contracts with unaffiliated suppliers. PHI, Pepco, DPL and ACE The following tables present assets and liabilities measured and recorded at fair value in PHI's, Pepco's, DPL's and ACE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of March 31, 2019 and December 31, 2018 : As of March 31, 2019 As of December 31, 2018 PHI Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 63 $ — $ — $ 63 $ 147 $ — $ — $ 147 Rabbi trust investments Cash equivalents 42 — — 42 42 — — 42 Mutual funds 14 — — 14 13 — — 13 Fixed income — 14 — 14 — 15 — 15 Life insurance contracts — 22 39 61 — 22 38 60 Rabbi trust investments subtotal (b) 56 36 39 131 55 37 38 130 Total assets 119 36 39 194 202 37 38 277 Liabilities Deferred compensation obligation — (20 ) — (20 ) — (21 ) — (21 ) Total liabilities — (20 ) — (20 ) — (21 ) — (21 ) Total net assets $ 119 $ 16 $ 39 $ 174 $ 202 $ 16 $ 38 $ 256 Pepco DPL ACE As of March 31, 2019 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 35 $ — $ — $ 35 $ 2 $ — $ — $ 2 $ 21 $ — $ — $ 21 Rabbi trust investments Cash equivalents 42 — — 42 — — — — — — — — Fixed income — 4 — 4 — — — — — — — — Life insurance contracts — 22 38 60 — — — — — — — — Rabbi trust investments subtotal (b) 42 26 38 106 — — — — — — — — Total assets 77 26 38 141 2 — — 2 21 — — 21 Liabilities Deferred compensation obligation — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total liabilities — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 77 $ 23 $ 38 $ 138 $ 2 $ (1 ) $ — $ 1 $ 21 $ — $ — $ 21 Pepco DPL ACE As of December 31, 2018 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 38 $ — $ — $ 38 $ 16 $ — $ — $ 16 $ 23 $ — $ — $ 23 Rabbi trust investments Cash equivalents 41 — — 41 — — — — — — — — Fixed income — 5 — 5 — — — — — — — — Life insurance contracts — 22 37 59 — — — — — — — — Rabbi trust investments subtotal (b) 41 27 37 105 — — — — — — — — Total assets 79 27 37 143 16 — — 16 23 — — 23 Liabilities Deferred compensation obligation — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total liabilities — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 79 $ 24 $ 37 $ 140 $ 16 $ (1 ) $ — $ 15 $ 23 $ — $ — $ 23 _________ (a) PHI excludes cash of $29 million and $39 million at March 31, 2019 and December 31, 2018 , respectively, and includes long-term restricted cash of $19 million at both March 31, 2019 and December 31, 2018 , which is reported in Other deferred debits in the Consolidated Balance Sheets. Pepco excludes cash of $11 million and $15 million at March 31, 2019 and December 31, 2018 , respectively. DPL excludes cash of $6 million and $8 million at March 31, 2019 and December 31, 2018 , respectively. ACE excludes cash of $7 million at both March 31, 2019 and December 31, 2018 , and includes long-term restricted cash of $19 million at both March 31, 2019 and December 31, 2018 , which is reported in Other deferred debits in the Consolidated Balance Sheets. (b) The amount of unrealized gains/(losses) at PHI totaled less than $1 million for both the three months ended March 31, 2019 and 2018 . The amount of unrealized gains/(losses) at Pepco totaled less than $1 million for both the three months ended March 31, 2019 and 2018 . The following tables present the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis during the three months ended March 31, 2019 and 2018 : Generation ComEd PHI Exelon Three Months Ended March 31, 2019 NDT Fund Investments Mark-to-Market Derivatives Other Investments Total Generation Mark-to-Market Derivatives Life Insurance Contracts (c) Eliminated in Consolidation Total Balance as of December 31, 2018 $ 543 $ 575 $ 42 $ 1,160 $ (249 ) $ 38 $ — $ 949 Total realized / unrealized gains (losses) Included in net income 2 (231 ) (a) — (229 ) — 1 — (228 ) Included in noncurrent payables to affiliates 11 — — 11 — — (11 ) — Included in regulatory assets/liabilities — — — — 9 (b) — 11 20 Change in collateral — 81 — 81 — — — 81 Purchases, sales, issuances and settlements Purchases 1 57 — 58 — — — 58 Sales — — — — — — — — Settlements (17 ) — — (17 ) — — — (17 ) Transfers into Level 3 — — (d) — — — — — — Transfers out of Level 3 — 17 (d) — 17 — — — 17 Balance at March 31, 2019 $ 540 $ 499 $ 42 $ 1,081 $ (240 ) $ 39 $ — $ 880 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of March 31, 2019 $ 2 $ (151 ) $ — $ (149 ) $ — $ 1 $ — $ (148 ) Generation ComEd PHI Exelon Three Months Ended March 31, 2018 NDT Fund Investments Mark-to-Market Derivatives Other Investments Total Generation Mark-to-Market Derivatives Life Insurance Contracts (c) Eliminated in Consolidation Total Balance as of December 31, 2017 $ 648 $ 552 $ 37 $ 1,237 $ (256 ) $ 22 $ — $ 1,003 Total realized / unrealized gains (losses) Included in net income — 184 (a) 1 185 — 1 — 186 Included in noncurrent payables to affiliates 7 — — 7 — — (7 ) — Included in regulatory assets — — — — (11 ) (b) — 7 (4 ) Change in collateral — 105 — 105 — — — 105 Purchases, sales, issuances and settlements Purchases 2 88 — 90 — — — 90 Sales — (3 ) — (3 ) — — — (3 ) Issuances — — — — — — — — Settlements (48 ) — — (48 ) — — — (48 ) Transfers into Level 3 — (8 ) (d) — (8 ) — — — (8 ) Transfers out of Level 3 — — (d) (2 ) (2 ) — — — (2 ) Balance as of March 31, 2018 $ 609 $ 918 $ 36 $ 1,563 $ (267 ) $ 23 $ — $ 1,319 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of March 31, 2018 $ — $ 256 $ 1 $ 257 $ — $ 1 $ — $ 258 __________ (a) Includes a reduction for the reclassification of $80 million and $72 million of realized gains due to the settlement of derivative contracts for the three months ended March 31, 2019 and 2018 , respectively. (b) Includes $14 million of decreases in fair value and an increase for realized losses due to settlements of $5 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2019 . Includes $17 million of increases in fair value and an increase for realized losses due to settlements of $6 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2018 . (c) The amounts represented are life insurance contracts at Pepco. (d) Transfers into and out of Level 3 generally occur when the contract tenor becomes less and more observable respectively, primarily due to changes in market liquidity or assumptions for certain commodity contracts. 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 three months ended March 31, 2019 and 2018 : Generation PHI Exelon Operating Purchased Other, net Operating and Maintenance Operating Purchased Operating and Maintenance Other, net Total gains (losses) included in net income for the three months ended March 31, 2019 $ (128 ) $ (103 ) $ 2 $ 1 $ (128 ) $ (103 ) $ 1 $ 2 Change in the unrealized gains (losses) relating to assets and liabilities held for the three months ended March 31, 2019 (91 ) (60 ) 2 1 (91 ) (60 ) 1 2 Generation PHI Exelon Operating Revenues Purchased Power and Fuel Other, net Operating and Maintenance Operating Revenues Purchased Power and Fuel Operating and Maintenance Other, net Total gains (losses) included in net income for the three months ended March 31, 2018 $ 335 $ (151 ) $ 1 $ 1 $ 335 $ (151 ) $ 1 $ 1 Change in the unrealized gains (losses) relating to assets and liabilities held for the three months ended March 31, 2018 309 (53 ) 1 1 309 (53 ) 1 1 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 (All Registrants). The Registrants’ cash equivalents include investments with original 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. NDT Fund Investments (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 and Fixed Income. 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 generally 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 which are based on quoted prices in active markets are categorized in Level 1. Certain equity securities have been categorized as Level 2 because they are based on evaluated prices that reflect observable market information, such as actual trade information or similar securities. 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 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 funds are valued using NAV as a practical expedient for fair value, which is primarily derived from the quoted prices in active markets on the underlying securities, and are not classified within the fair value hierarchy. These investments typically can be redeemed monthly with 30 or less days of notice and without further restrictions. Derivative instruments consisting primarily of futures and interest rate swaps to manage risk are recorded at fair value. Over the counter derivatives are valued daily based on quoted prices in active markets and trade in open markets and have been categorized as Level 1. Derivative instruments other than over the counter derivatives 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 loans 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. Managed funds are valued using NAV or its equivalent as a practical expedient, and therefore, are not classified within the fair value hierarchy. 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 partne

Derivative Financial Instrument

Derivative Financial Instruments (All Registrants)	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments (All Registrants)	Derivative Financial Instruments (All Registrants) The Registrants use derivative instruments to manage commodity price risk, interest rate risk and foreign exchange risk related to ongoing business operations. Commodity Price Risk (All Registrants) 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 commodity products. The Registrants believe these instruments, which are either determined to be non-derivative or classified as economic hedges, mitigate exposure to fluctuations in commodity prices. Derivative authoritative 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 immediately. 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 hedges and fair value hedges. For Generation, all derivative economic hedges related to commodities are recorded at fair value through earnings for the consolidated company, referred to as economic hedges in the following tables. 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. Fair value authoritative guidance and disclosures about offsetting assets and liabilities requires the fair value of derivative instruments to be shown in the Combined Notes to 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 margin on exchange positions, is aggregated in the collateral and netting column. As of March 31, 2019 , $6 million of cash collateral held, and as of December 31, 2018 , $2 million of cash collateral posted and an additional $12 million of cash collateral posted with ComEd, was not offset against derivative positions because such collateral was not associated with any energy-related derivatives, were associated with accrual positions, or had no positions to offset as of the balance sheet date. 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 an unaffiliated 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 March 31, 2019 : Generation ComEd Exelon Derivatives Economic Hedges Proprietary Trading Collateral and Netting (a)(d) Subtotal (b) Economic Hedges (c) Total Derivatives Mark-to-market derivative assets (current assets) $ 2,691 $ 118 $ (2,156 ) $ 653 $ — $ 653 Mark-to-market derivative assets (noncurrent assets) 1,188 60 (794 ) 454 — 454 Total mark-to-market derivative assets 3,879 178 (2,950 ) 1,107 — 1,107 Mark-to-market derivative liabilities (current liabilities) (2,711 ) (89 ) 2,485 (315 ) (27 ) (342 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,142 ) (30 ) 957 (215 ) (213 ) (428 ) Total mark-to-market derivative liabilities (3,853 ) (119 ) 3,442 (530 ) (240 ) (770 ) Total mark-to-market derivative net assets (liabilities) $ 26 $ 59 $ 492 $ 577 $ (240 ) $ 337 _________ (a) Exelon and Generation net all available amounts allowed under the derivative authoritative guidance in 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 $152 million and $63 million , respectively, and current and noncurrent liabilities are shown net of collateral of $177 million and $100 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $492 million at March 31, 2019 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Of the collateral posted/(received), $(33) million represents variation margin on the exchanges. The following table provides a summary of the derivative fair value balances recorded by the Registrants as of December 31, 2018 : Generation ComEd Exelon Description Economic Proprietary Collateral (a)(d) Subtotal (b) Economic (c) Total Mark-to-market derivative assets $ 3,505 $ 105 $ (2,809 ) $ 801 $ — $ 801 Mark-to-market derivative assets 1,266 41 (862 ) 445 — 445 Total mark-to-market derivative assets 4,771 146 (3,671 ) 1,246 — 1,246 Mark-to-market derivative liabilities (3,429 ) (74 ) 3,056 (447 ) (26 ) (473 ) Mark-to-market derivative liabilities (1,203 ) (20 ) 972 (251 ) (223 ) (474 ) Total mark-to-market derivative liabilities (4,632 ) (94 ) 4,028 (698 ) (249 ) (947 ) Total mark-to-market derivative net assets (liabilities) $ 139 $ 52 $ 357 $ 548 $ (249 ) $ 299 _________ (a) Exelon and Generation net all available amounts allowed under the derivative authoritative guidance in 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, and 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 $121 million and $51 million , respectively, and current and noncurrent liabilities are shown net of collateral of $125 million and $60 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $357 million at December 31, 2018 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Of the collateral posted/(received), $(94) million represents variation margin on the exchanges. Economic Hedges (Commodity Price Risk) 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 power purchases, natural gas transportation and pipeline capacity agreements and other energy-related products marketed and purchased. To manage these risks, Generation may enter into fixed-price derivative or non-derivative contracts to hedge the variability in future cash flows from expected sales of power and gas and purchases of power and fuel. The objectives for executing such hedges include fixing the price for a portion of anticipated future electricity sales at a level that provides an acceptable return. 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. For the three months ended March 31, 2019 and 2018 , Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses) which are also located in the "Net fair value changes related to derivatives" in the Consolidated Statements of Cash Flows. Three Months Ended 2019 2018 Income Statement Location Gain (Loss) Operating revenues $ (50 ) $ (100 ) Purchased power and fuel 30 (167 ) Total Exelon and Generation $ (20 ) $ (267 ) 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 March 31, 2019 , the percentage of expected generation hedged for the Mid-Atlantic, Midwest, New York and ERCOT reportable segments is 90% - 93% , 64% - 67% and 38% - 41% for 2019 , 2020 and 2021 , respectively. On December 17, 2010, ComEd executed 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. 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 in 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 4 — Regulatory Matters of the Exelon 2018 Form 10-K for additional information. 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 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 2018 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 2018 and previous PGC settlements, 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 20% 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 results of operations and financial position 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. BGE’s commodity 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. BGE’s natural gas supply and asset management agreements qualify for the NPNS scope exception and result in physical delivery. Pepco has contracts to procure SOS electric supply that are executed through a competitive procurement process approved by the MDPSC and DCPSC. The SOS rates charged recover Pepco's wholesale power supply costs and include an administrative fee. The administrative fee includes an incremental cost component and a shareholder return component for residential and commercial rate classes. Pepco’s commodity price risk related to electric supply procurement is limited. Pepco locks in fixed prices for its SOS requirements through full requirements contracts. Certain of Pepco’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other Pepco full requirements contracts are not derivatives. DPL has contracts to procure SOS electric supply that are executed through a competitive procurement process approved by the MDPSC and the DPSC. The SOS rates charged recover DPL's wholesale power supply costs. In Delaware, DPL is also entitled to recover a Reasonable Allowance for Retail Margin (RARM). The RARM includes a fixed annual margin of approximately $2.75 million , plus an incremental cost component and a cash working capital allowance. In Maryland, DPL charges an administrative fee intended to allow it to recover its administrative costs. DPL locks in fixed prices for its SOS requirements through full requirements contracts. DPL’s commodity price risk related to electric supply procurement is limited. Certain of DPL’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other DPL full requirements contracts are not derivatives. DPL provides natural gas to its customers under an Annual GCR mechanism approved by the DPSC. Under this mechanism, DPL’s Annual GCR Filing establishes a future GCR for firm bundled sales customers by using a forecast of demand and commodity costs. The actual costs are trued up against forecasts on a monthly basis and any shortfall or excess is carried forward as a recovery balance in the next GCR filing. The demand portion of the GCR is based upon DPL’s firm transportation and storage contracts. DPL has firm deliverability of swing and seasonal storage, a liquefied natural gas facility and firm transportation capacity to meet customer demand and provide a reserve margin. The commodity portion of the GCR includes a commission approved hedging program which is intended to reduce gas commodity price volatility while limiting the firm natural gas customers’ exposure to adverse changes in the market price of natural gas. The hedge program requires that DPL hedge, on a non-discretionary basis, an amount equal to 50% of estimated purchase requirements for each month, including estimated monthly purchases for storage injections. The 50% hedge monthly target is achieved by hedging 1/12th of the 50% target each month beginning 12-months prior to the month in which the physical gas is to be purchased. Currently, DPL uses only exchange traded futures for its gas hedging program, which are considered derivatives, however, it retains the capability to employ other physical and financial hedges if needed. DPL has not elected hedge accounting for these derivative financial instruments. Because of the DPSC-approved fuel adjustment clause for DPL's derivatives, the change in fair value of the derivatives each period, in addition to all premiums paid and other transaction costs incurred as part of the gas hedging program, are fully recoverable and are recorded by DPL as regulatory assets or liabilities. DPL’s physical gas purchases are currently all daily, monthly or intra-month transactions. From time to time, DPL will enter into seasonal purchase or sale arrangements, however, there are none currently in the portfolio. Certain of DPL's full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other DPL full requirements contracts are not derivatives. ACE has contracts to procure BGS electric supply that are executed through a competitive procurement process approved by the NJBPU. The BGS rates charged recover ACE's wholesale power supply costs. ACE does not make any profit or incur any loss on the supply component of the BGS it supplies to customers. ACE’s commodity price risk related to electric supply procurement is limited. ACE locks in fixed prices for all of its BGS requirements through full requirements contracts. Certain of ACE’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other ACE full requirements contracts are not derivatives. Proprietary Trading (Commodity Price Risk) Generation also executes commodity derivatives for proprietary trading purposes. Proprietary trading includes all contracts executed with the intent of benefiting from shifts or changes in market prices as opposed to those executed with the intent of hedging or managing risk. Proprietary trading activities are subject to limits established by Exelon’s RMC. The proprietary trading portfolio is subject to a risk management policy that includes stringent risk management limits to manage exposure to market risk. Additionally, the Exelon risk management group and Exelon's RMC monitor the financial risks of the 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 revenue from energy marketing activities. Gains and losses associated with proprietary trading are reported as Operating revenues in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. For the three months ended March 31, 2019 and 2018 Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses) which are also included in the "Net fair value changes related to derivatives" in the Consolidated Statements of Cash Flows. The Utility Registrants do not execute derivatives for proprietary trading purposes. Three Months Ended 2019 2018 Income Statement Location Gain (Loss) Operating revenues $ 2 $ 2 Interest Rate and Foreign Exchange Risk (Exelon and Generation) Exelon and Generation utilize interest rate swaps, which are treated as economic hedges, to manage their interest rate exposure. On July 1, 2018, Exelon de-designated its fair value hedges related to interest rate risk and Generation de-designated its cash flow hedges related to interest rate risk. The notional amounts were $1,419 million and $1,420 million at March 31, 2019 and December 31, 2018 , respectively, for Exelon and $619 million and $620 million at March 31, 2019 and December 31, 2018 , respectively, for Generation. Generation utilizes foreign currency derivatives to manage foreign exchange rate exposure associated with international commodity purchases in currencies other than U.S. dollars, which are treated as economic hedges. The notional amounts were $209 million and $268 million at March 31, 2019 and December 31, 2018 , respectively. The mark-to-market derivative assets and liabilities as of March 31, 2019 and December 31, 2018 and the mark-to-market gains and losses for the three months ended March 31, 2019 and 2018 were not material for Exelon and Generation. Credit Risk, Collateral and Contingent-Related Features (All Registrants) The Registrants would be exposed to credit-related losses in the event of non-performance by counterparties on executed derivative instruments. The credit exposure of derivative contracts, before collateral, is represented by the fair value of contracts at the reporting date. For commodity derivatives, Generation enters into enabling agreements that allow for payment netting with its counterparties, which reduces Generation’s exposure to counterparty risk by providing for the offset of amounts payable to the counterparty against amounts receivable from the counterparty. Typically, each enabling agreement is for a specific commodity and so, with respect to each individual counterparty, netting is limited to transactions involving that specific commodity product, except where master netting agreements exist with a counterparty that allow for cross product netting. In addition to payment netting language in the enabling agreement, Generation’s credit department establishes credit limits, margining thresholds and collateral requirements for each counterparty, which are defined in the derivative contracts. Counterparty credit limits are based on an internal credit review process that considers a variety of factors, including the results of a scoring model, leverage, liquidity, profitability, credit ratings by credit rating agencies, and risk management capabilities. To the extent that a counterparty’s margining thresholds are exceeded, the counterparty is required to post collateral with Generation as specified in each enabling agreement. Generation’s credit department monitors current and forward credit exposure to counterparties and their affiliates, both on an individual and an aggregate basis. The following tables provide information on Generation’s credit exposure for all derivative instruments, NPNS and applicable payables and receivables, net of collateral and instruments that are subject to master netting agreements, as of March 31, 2019 . The tables further delineate that exposure by credit rating of the counterparties and provide guidance on the concentration of credit risk to individual counterparties. 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, NASDAQ, NGX and Nodal commodity exchanges. Additionally, the figures in the tables below exclude exposures with affiliates, including net receivables with ComEd, PECO, BGE, Pepco, DPL and ACE of $36 million , $31 million , $27 million , $37 million , $5 million and $4 million as of March 31, 2019 , respectively. Rating as of March 31, 2019 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 $ 819 $ 11 $ 808 1 $ 135 Non-investment grade 86 39 47 No external ratings Internally rated — investment grade 162 — 162 Internally rated — non-investment grade 87 7 80 Total $ 1,154 $ 57 $ 1,097 1 $ 135 Net Credit Exposure by Type of Counterparty As of Financial institutions $ 13 Investor-owned utilities, marketers, power producers 762 Energy cooperatives and municipalities 287 Other 35 Total $ 1,097 _________ (a) As of March 31, 2019 , credit collateral held from counterparties where Generation had credit exposure included $37 million of cash and $19 million of letters of credit. The credit collateral does not include non-liquid collateral. ComEd’s power procurement contracts provide suppliers with a certain amount of unsecured credit. The credit position is based on daily, updated forward market prices compared to the benchmark prices. The benchmark prices are the forward prices of energy projected through the contract term and are set at the point of supplier bid submittals. If the forward market price of energy exceeds the benchmark price on a given day, the suppliers are required to post collateral for the secured credit portion after adjusting for any unpaid deliveries and unsecured credit allowed under the contract. The unsecured credit used by the suppliers represents ComEd’s net credit exposure. As of March 31, 2019 , ComEd’s net credit exposure to suppliers was $2 million . ComEd is permitted to recover its costs of procuring energy through the Illinois Settlement Legislation. ComEd’s counterparty credit risk is mitigated by its ability to recover realized energy costs through customer rates. See Note 4 — Regulatory Matters of the Exelon 2018 Form 10-K for additional information. PECO’s unsecured credit used by the suppliers represents PECO’s net credit exposure. As of March 31, 2019 , PECO had no material net credit exposure to its electric suppliers. PECO’s natural gas procurement plan is reviewed and approved annually on a prospective basis by the PAPUC. PECO’s counterparty credit risk under its natural gas supply and asset management agreements is mitigated by its ability to recover its natural gas costs through the PGC, which allows PECO to adjust rates quarterly to reflect realized natural gas prices. As of March 31, 2019 , PECO had no material credit exposure under its natural gas supply and asset management agreements with investment grade suppliers. BGE is permitted to recover its costs of procuring energy through the MDPSC-approved procurement tariffs. BGE’s counterparty credit risk is mitigated by its ability to recover realized energy costs through customer rates. See Note 4 — Regulatory Matters of the Exelon 2018 Form 10-K for additional information. BGE’s full requirement wholesale electric power agreements that govern the terms of its electric supply procurement contracts, which define a supplier’s performance assurance requirements, allow a supplier, or its guarantor, to meet its credit requirements with a certain amount of unsecured credit. As of March 31, 2019 , BGE's net credit exposure to suppliers was immaterial. BGE’s regulated gas business is exposed to market-price risk. At March 31, 2019 , BGE's credit exposure related to off-system sales, which is mitigated by parental guarantees, letters of credit or right to offset clauses within other contracts with those third-party suppliers, was immaterial. Pepco’s, DPL's and ACE's power procurement contracts provide suppliers with a certain amount of unsecured credit. The amount of unsecured credit is determined based on the supplier’s lowest credit rating from the major credit rating agencies and the supplier’s tangible net worth. The credit position is based on the initial market price, which is the forward price of energy on the day a transaction is executed, compared to the current forward price curve for energy. To the extent that the forward price curve for energy exceeds the initial market price, the supplier is required to post collateral to the extent the credit exposure is greater than the supplier’s unsecured credit limit. The unsecured credit used by the suppliers represents Pepco’s, DPL's and ACE's net credit exposure. As of March 31, 2019 , Pepco’s, DPL's and ACE's net credit exposures to suppliers were immaterial. Pepco is permitted to recover its costs of procuring energy through the MDPSC-approved and DCPSC-approved procurement tariffs. DPL is permitted to recover its costs of procuring energy through the MDPSC-approved and DPSC-approved procurement tariffs. ACE is permitted to recover its costs of procuring energy through the NJBPU-approved procurement tariffs. Pepco’s, DPL's and ACE's counterparty credit risks are mitigated by their ability to recover realized energy costs through customer rates. See Note 2 — Regulatory Matters of the Exelon 2018 Form 10-K for additional information. DPL’s natural gas procurement plan is reviewed and approved annually on a prospective basis by the DPSC. DPL’s counterparty credit risk under its natural gas supply and asset management agreements is mitigated by its ability to recover its natural gas costs through the GCR, which allows DPL to adjust rates annually to reflect realized natural gas prices. To the extent that the fair value of the transactions in a net loss position exceeds the unsecured credit threshold, then collateral is required to be posted in an amount equal to the amount by which the unsecured credit threshold is exceeded. Exchange-traded contracts are required to be fully collateralized without regard to the credit rating of the holder. As of March 31, 2019 , DPL's credit exposure under its natural gas supply and asset management agreements with investment grade suppliers was immaterial. Collateral (All Registrants) As part of the normal course of business, Generation routinely enters into physically or financially settled contracts for the purchase and sale of electric capacity, electricity, fuels, emissions allowances and other energy-related products. Certain of Generation’s derivative instruments contain provisions that require Generation to post collateral. Generation also enters into commodity transactions on exchanges where the exchanges act as the counterparty to each trade. Transactions on the exchanges must adhere to comprehensive collateral and margining requirements. This collateral may be posted in the form of cash or credit support with thresholds contingent upon Generation’s credit rating from each of the major credit rating agencies. The collateral and credit support requirements vary by contract and by counterparty. These credit-risk related contingent features stipulate that if Generation were to be downgraded or lose its investment grade credit rating (based on its senior unsecured debt rating), it would be required to provide additional collateral. This incremental collateral requirement allows for the offsetting of derivative instruments that are assets with the same counterparty, where the contractual right of offset exists under applicable master netting agreements. In the absence of expressly agreed-to provisions that specify the collateral that must be provided, collateral requested will be a function of the facts and circumstances of the situation at the time of the demand. In this case, Generation believes an amount of several months of future payments (i.e., capacity payments) rather than a calculation of fair value is the best estimate for the contingent collateral obligation, which has been factored into the disclosure below. 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: Credit-Risk Related Contingent Featu

Debt and Credit Agreements (All

Debt and Credit Agreements (All Registrants)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Debt and Credit Agreements (All Registrants)	Debt and Credit Agreements (All Registrants) Short-Term Borrowings Exelon Corporate, ComEd, BGE, Pepco, DPL and ACE 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 Exelon intercompany money pool. PHI Corporate meets its short-term liquidity requirements primarily through the issuance of short-term notes and the Exelon intercompany money pool. The Registrants may use their respective credit facilities for general corporate purposes, including meeting short-term funding requirements and the issuance of letters of credit. Commercial Paper The following table reflects the Registrants' commercial paper programs as of March 31, 2019 and December 31, 2018 . Generation and PECO had no commercial paper borrowings as of both March 31, 2019 and December 31, 2018 . Outstanding Average Interest Rate on Commercial Paper Issuer March 31, 2019 December 31, 2018 March 31, 2019 December 31, 2018 Exelon $ 629 $ 89 2.63 % 2.15 % ComEd 322 — 2.64 % 2.14 % BGE 106 35 2.59 % 2.18 % PHI 201 54 2.62 % 2.15 % PEPCO 105 40 2.62 % 2.24 % DPL 5 — 2.61 % 2.07 % ACE 91 14 2.62 % 2.21 % See Note 13 — Debt and Credit Agreements of the Exelon 2018 Form 10-K for additional information on the Registrants’ credit facilities. Short-Term Loan Agreements On March 23, 2017, Exelon Corporate entered into a term loan agreement for $500 million , which was renewed on March 22, 2018 with an expiration of March 21, 2019. The loan agreement was renewed on March 20, 2019 and will expire on March 19, 2020. Pursuant to the loan agreement, loans made thereunder bear interest at a variable rate equal to LIBOR plus 0.95% and all indebtedness thereunder is unsecured. The loan agreement is reflected in Exelon's Consolidated Balance Sheet within Short-Term borrowings. Credit Agreements On February 21, 2019, Generation entered into a credit agreement establishing a $100 million bilateral credit facility. The facility will mature in March 2021. This facility will solely be used by Generation to issue letters of credit. Long-Term Debt Issuance of Long-Term Debt During the three months ended March 31, 2019 , the following long-term debt was issued: Company Type Interest Rate Maturity Amount Use of Proceeds Generation Energy Efficiency Project Financing 3.95 % August 31, 2020 $ 2 Funding to install energy conservation measures for the Fort Meade project. ComEd First Mortgage Bonds, Series 126 4.00 % March 1, 2049 $ 400 Repay a portion of ComEd’s outstanding commercial paper obligations and fund other general corporate purposes. Debt Covenants As of March 31, 2019 , the Registrants are in compliance with debt covenants, except for Antelope Valley's nonrecourse debt event of default as discussed below. Nonrecourse Debt Exelon and Generation have issued nonrecourse debt financing. 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. 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 2014. The loan will mature on January 5, 2037. As of March 31, 2019 , $ 502 million was outstanding. In 2017, Generation’s interests in Antelope Valley were also contributed to and are pledged as collateral for the EGR IV financing structure referenced below. Antelope Valley sells all of its output to Pacific Gas and Electric Company (PG&E) through a PPA. On January 29, 2019, PG&E filed for protection under Chapter 11 of the U.S. Bankruptcy Code, which created an event of default for Antelope Valley’s nonrecourse debt that provides the lender with a right to accelerate amounts outstanding under the loan such that they would become immediately due and payable. As a result of the ongoing event of default and the absence of a waiver from the lender foregoing their acceleration rights, the debt was reclassified as current in Exelon’s and Generation’s Consolidated Balance Sheets as of March 31, 2019 . Further, distributions from Antelope Valley to EGR IV are currently suspended. ExGen Renewables IV. In November 2017, EGR IV, an indirect subsidiary of Exelon and Generation, entered into an $ 850 million nonrecourse senior secured term loan credit facility agreement. Generation’s interests in EGRP, Antelope Valley, SolGen, and Albany Green Energy were all contributed to and are pledged as collateral for this financing. The loan is scheduled to mature on November 28, 2024. As of March 31, 2019 , $ 834 million was outstanding. Although Antelope Valley’s debt is in default, it is nonrecourse to EGR IV. However, if in the future Antelope Valley were to file for bankruptcy protection as a result of events culminating from PG&E’s bankruptcy proceedings this would represent an event of default for EGR IV’s debt that would provide the lender with an opportunity to accelerate EGR IV’s debt. See Note 13 — Debt and Credit Agreements of the Exelon 2018 Form 10-K for additional information on nonrecourse debt.

Income Taxes (All Registrants)

Income Taxes (All Registrants)	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes (All Registrants)	Income Taxes (All Registrants) Rate Reconciliation The effective income tax rate from continuing operations varies from the U.S. Federal statutory rate principally due to the following: Three Months Ended March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE U.S. Federal statutory rate 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% Increase (decrease) due to: State income taxes, net of Federal income tax benefit 3.9 3.1 8.2 1.0 6.3 4.7 2.1 6.5 6.7 Qualified NDT fund income 7.2 14.2 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.5) (0.9) (0.2) — (0.1) (0.2) (0.1) (0.2) (0.3) Plant basis differences (1.4) — (0.5) (6.7) (0.9) (1.7) (2.0) (0.7) (2.3) Production tax credits and other credits (0.8) (1.5) — — — — — — — Noncontrolling interests (0.6) (1.1) — — — — — — — Excess deferred tax amortization (4.7) — (8.5) (2.5) (7.9) (19.4) (17.9) (15.6) (23.9) Other 0.1 (0.5) 0.3 0.2 — (0.3) 0.4 0.7 (1.2) Effective income tax rate 24.2% 34.3% 20.3% 13.0% 18.4% 4.1% 3.5% 11.7% —% Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE U.S. Federal statutory rate 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% Increase (decrease) due to: State income taxes, net of Federal income tax benefit 4.1 2.4 8.2 (3.9) 6.3 4.6 1.7 6.3 6.6 Qualified NDT fund income (0.4) (1.3) — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.3) (4.3) (0.2) (0.1) (0.1) (0.2) (0.1) (0.2) (0.3) Plant basis differences (2.7) — 0.1 (14.2) (0.7) (2.6) (3.4) (1.3) (2.6) Production tax credits and other credits (2.8) (9.5) (0.1) — — — — — — Noncontrolling interests (0.7) (2.5) — — — — — — — Excess deferred tax amortization (6.0) — (7.5) (4.8) (8.6) (10.6) (12.8) (7.9) (8.7) Other (2.8) (1.3) 0.3 0.2 — — (0.3) 0.5 (3.5) Effective income tax rate 8.4% 4.5% 21.8% (1.8)% 17.9% 12.2% 6.1% 18.4% 12.5% Accounting for Uncertainty in Income Taxes The Registrants have the following unrecognized tax benefits as of March 31, 2019 and December 31, 2018 : Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE March 31, 2019 $ 448 $ 411 $ — $ — $ — $ 45 $ — $ — $ 14 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2018 $ 477 $ 408 $ 2 $ — $ — $ 45 $ — $ — $ 14 In 2016, the Tax Court held that Exelon was not entitled to defer a gain on its 1999 like-kind exchange transaction. In addition to the tax and interest related to the gain deferral, the Tax Court also ruled that Exelon was liable for penalties and interest on the penalties. Exelon had fully paid the amounts assessed resulting from the Tax Court decision in 2017. In September 2017, Exelon appealed the Tax Court decision to the U.S. Court of Appeals for the Seventh Circuit. In October 2018, the U.S. Court of Appeals for the Seventh Circuit affirmed the Tax Court’s decision. Exelon filed a petition seeking rehearing of the Seventh Circuit’s decision, but the Seventh Circuit denied that petition in December 2018. In the first quarter of 2019, Exelon elected not to seek a further review by the U.S. Supreme Court. As a result, Exelon's and ComEd's unrecognized tax benefits decreased by approximately $33 million and $2 million , respectively, in the first quarter of 2019. Reasonably possible the total amount of unrecognized tax benefits could significantly increase or decrease within 12 months after the reporting date Settlement of Income Tax Audits, Refund Claims, and Litigation As of March 31, 2019 , Exelon, Generation, PHI and ACE have approximately $425 million , $411 million , $14 million and $14 million of unrecognized federal and state tax benefits that could significantly decrease within the 12 months after the reporting date as a result of completing audits, potential settlements, and the outcomes of pending court cases. Of the above unrecognized tax benefits, Exelon and Generation have $411 million that, if recognized, would decrease the effective tax rate. The unrecognized tax benefits related to PHI and ACE, if recognized, may be included in future regulated base rates and that portion would have no impact to the effective tax rate.

Nuclear Decommissioning (Exelon

Nuclear Decommissioning (Exelon and Generation)	3 Months Ended
	Mar. 31, 2019
Environmental Remediation Obligations [Abstract]
Nuclear Decommissioning (Exelon and Generation)	Nuclear Decommissioning (Exelon and Generation) Nuclear Decommissioning Asset Retirement Obligations (Exelon and Generation) 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 updates its ARO annually, 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 in Exelon’s and Generation’s Consolidated Balance Sheets from December 31, 2018 to March 31, 2019 : Nuclear decommissioning ARO at December 31, 2018 (a)(b) $ 10,005 Net increase due to changes in, and timing of, estimated future cash flows 223 Accretion expense 120 Costs incurred related to decommissioning plants (19 ) Nuclear decommissioning ARO at March 31, 2019 (a)(b) $ 10,329 _________ (a) Includes $41 million and $22 million as the current portion of the ARO at March 31, 2019 and December 31, 2018 , respectively, which is included in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets. (b) Includes $760 million and $772 million of ARO related to Oyster Creek which is classified as Liabilities held for sale in Exelon's and Generation's Consolidated Balance Sheets at March 31, 2019 and December 31, 2018 , respectively. See Note 3 — Mergers, Acquisitions and Dispositions for additional information. During the three months ended March 31, 2019 , Exelon's and Generation’s total nuclear ARO increased by approximately $324 million , primarily reflecting the impacts of ARO updates completed during first quarter 2019 and the accretion of the ARO liability due to the passage of time. The first quarter 2019 ARO update includes an increase of approximately $330 million for a change in the assumed retirement timing probabilities for certain economically challenged nuclear plants and a $110 million decrease for the impacts of revised decommissioning cost estimates for TMI which incorporate site specific decommissioning planning activities in anticipation of its September 2019 shutdown date. Approximately $85 million of the TMI ARO adjustment resulted in a decrease in Operating and maintenance expense within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. See Note 8 — Early Plant Retirements for additional information. NDT Funds (Exelon and Generation) Exelon and Generation had NDT funds totaling $13,345 million and $12,695 million at March 31, 2019 and December 31, 2018 , respectively. The NDT funds include $881 million and $890 million at March 31, 2019 and December 31, 2018 , respectively, related to Oyster Creek NDT funds which are classified as Assets held for sale in Exelon's and Generation's Consolidated Balance Sheets. See Note 3 — Mergers, Acquisitions and Dispositions for additional information regarding the announced pending sale of Oyster Creek. The NDT funds also include $163 million and $144 million for the current portion of the NDT funds at March 31, 2019 and December 31, 2018 , respectively, which are included in Other current assets in Exelon's and Generation's Consolidated Balance Sheets. See Note 17 — Supplemental Financial Information for additional information on activities of the NDT funds. NRC Minimum Funding Requirements (Exelon and Generation) 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. Generation filed its biennial decommissioning funding status report with the NRC on April 1, 2019 for all units except for Zion Station which is included in a separate report to the NRC submitted by ZionSolutions, LLC. The status report demonstrated adequate decommissioning funding assurance as of December 31, 2018 for all units except for Clinton and Peach Bottom Unit 1. As of February 28, 2019, Clinton demonstrated adequate minimum funding assurance due to market recovery and no further action is required. This demonstration was also included in the April 1, 2019 submittal. As a former PECO plant, financial assurance for decommissioning Peach Bottom Unit 1 is provided by the NDT fund, collections from PECO ratepayers, and the ability to adjust those collections in accordance with the approved PAPUC tariff. No additional actions are required aside from the PAPUC filing in accordance with the tariff. See Note 15 — Asset Retirement Obligations of the Exelon 2018 Form 10-K for information regarding the amount collected from PECO ratepayers for decommissioning cost.

Retirement Benefits (All Regist

Retirement Benefits (All Registrants)	3 Months Ended
	Mar. 31, 2019
Retirement Benefits [Abstract]
Retirement Benefits (Exelon, Generation, ComEd, PECO and BGE)	Retirement Benefits (All Registrants) Exelon sponsors defined benefit pension plans and other postretirement benefit plans for essentially all current employees. 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. Effective February 1, 2018, most newly-hired Generation and BSC non-represented employees are not eligible for pension benefits and will instead be eligible to receive an enhanced non-discretionary employer contribution in an Exelon defined contribution savings plan. Effective January 1, 2018, most newly-hired non-represented employees are not eligible for OPEB benefits and employees represented by Local 614 are not eligible for retiree health care benefits. Effective January 1, 2019, Exelon merged the Exelon Corporation Cash Balance Pension Plan (CBPP) into the Exelon Corporation Retirement Program (ECRP). The merging of the plans is not changing the benefits offered to the plan participants and, thus, has no impact on Exelon's pension obligation. However, beginning in 2019, actuarial losses and gains related to the CBPP and ECRP are being amortized over participants’ average remaining service period of the merged ECRP rather than each individual plan. Defined Benefit Pension and Other Postretirement Benefits During the first quarter of 2019, Exelon received an updated valuation of its pension and OPEB to reflect actual census data as of January 1, 2019. This valuation resulted in an increase to the pension and OPEB obligations of $75 million and $36 million , respectively. Additionally, accumulated other comprehensive loss increased by $39 million (after-tax) and regulatory assets and liabilities increased by $53 million and decreased by $5 million , respectively. The majority of the 2019 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 4.31% . The majority of the 2019 other postretirement benefit cost is calculated using an expected long-term rate of return on plan assets of 6.67% for funded plans and a discount rate of 4.30% . A portion of the net periodic benefit cost for all plans is capitalized within the Consolidated Balance Sheets. The following table presents the components of Exelon's net periodic benefit costs, prior to capitalization, for the three months ended March 31, 2019 and 2018 . Pension Benefits Other Postretirement Benefits 2019 2018 2019 2018 Components of net periodic benefit cost: Service cost $ 89 $ 101 $ 24 $ 28 Interest cost 221 201 47 43 Expected return on assets (307 ) (312 ) (38 ) (43 ) Amortization of: Prior service cost (benefit) — — (45 ) (46 ) Actuarial loss 104 157 11 16 Net periodic benefit cost $ 107 $ 147 $ (1 ) $ (2 ) The amounts below represent Exelon's, Generation's, ComEd's, PECO's, BGE's, PHI's, Pepco's, DPL's, and ACE's pension and postretirement benefit plan costs. For Exelon, the service cost component is included in Operating and maintenance expense and Property, plant and equipment, net, for the three months ended March 31, 2019 and 2018, while the non-service cost components are included in Other, net and Regulatory assets for the three months ended March 31, 2019 and 2018. For the Registrants other than Exelon, the service cost and non-service cost components are included in Operating and maintenance expense and Property, plant and equipment, net in their consolidated financial statements for the three months ended March 31, 2019 and 2018. Three Months Ended Pension and Other Postretirement Benefit Costs 2019 2018 Exelon $ 106 $ 145 Generation 31 51 ComEd 24 45 PECO 2 5 BGE 16 15 PHI 23 15 Pepco 6 4 DPL 4 — ACE 4 3 Defined Contribution Savings Plans The Registrants participate in various 401(k) defined contribution savings plans that are sponsored by Exelon. The plans are qualified under applicable sections of the IRC and allow employees to contribute a portion of their pre-tax and/or after-tax income in accordance with specified guidelines. All Registrants match a percentage of the employee contributions up to certain limits. The following table presents the matching contributions to the savings plans during the three months ended March 31, 2019 and 2018 , respectively. Three Months Ended Savings Plan Matching Contributions 2019 2018 Exelon $ 31 $ 32 Generation 13 15 ComEd 7 7 PECO 2 2 BGE 2 2 PHI 4 3 Pepco 1 1 DPL 1 1 ACE 1 —

Changes in Accumulated Other Co

Changes in Accumulated Other Comprehensive Income (Exelon and Generation)	3 Months Ended
	Mar. 31, 2019
Changes in Accumulated Other Comprehensive Income [Abstract]
Comprehensive Income (Loss) Note [Text Block]	Changes in Accumulated Other Comprehensive Income (Exelon and Generation) The following tables present changes in accumulated other comprehensive income (loss) (AOCI) by component for the three months ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 Gains (Losses) on Cash Flow Hedges Unrealized Gains (Losses) on Marketable Securities Pension and Non-Pension Postretirement Benefit Plan Items Foreign Currency Items AOCI of Investments in Unconsolidated Affiliates Total Exelon (a) Beginning balance $ (2 ) $ — $ (2,960 ) $ (33 ) $ — $ (2,995 ) OCI before reclassifications — — (38 ) 2 (1 ) (37 ) Amounts reclassified from AOCI (b) — — 20 — — 20 Net current-period OCI — — (18 ) 2 (1 ) (17 ) Ending balance $ (2 ) $ — $ (2,978 ) $ (31 ) $ (1 ) $ (3,012 ) Generation (a) Beginning balance $ (4 ) $ — $ — $ (33 ) $ (1 ) $ (38 ) OCI before reclassifications — — — 2 (1 ) 1 Amounts reclassified from AOCI 1 — — — — 1 Net current-period OCI 1 — — 2 (1 ) 2 Ending balance $ (3 ) $ — $ — $ (31 ) $ (2 ) $ (36 ) Three Months Ended March 31, 2018 Gains (Losses) on Cash Flow Hedges Unrealized gains (losses) on Marketable Securities Pension and Non-Pension Postretirement Benefit Plan Items Foreign Currency Items AOCI of Investments in Unconsolidated Affiliates Total Exelon (a) Beginning balance $ (14 ) $ 10 $ (2,998 ) (d) $ (23 ) $ (1 ) $ (3,026 ) OCI before reclassifications 8 — 18 1 — 27 Amounts reclassified from AOCI (b) — — 44 — — 44 Net current-period OCI 8 — 62 1 — 71 Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard (c) — (10 ) — — — (10 ) Ending balance $ (6 ) $ — $ (2,936 ) $ (22 ) $ (1 ) $ (2,965 ) Generation (a) Beginning balance $ (16 ) $ 3 $ — $ (23 ) $ (1 ) $ (37 ) OCI before reclassifications 7 — — (1 ) — 6 Amounts reclassified from AOCI — — — — — — Net current-period OCI 7 — — (1 ) — 6 Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard (c) — (3 ) — — — (3 ) Ending balance $ (9 ) $ — $ — $ (24 ) $ (1 ) $ (34 ) _________ (a) All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI. (b) See next tables for details about these reclassifications. (c) Exelon prospectively adopted the new standard Recognition and Measurement of Financial Assets and Liabilities. The standard was adopted as of January 1, 2018, which resulted in an increase to Retained earnings and Accumulated other comprehensive loss of $10 million and $3 million for Exelon and Generation, respectively. The amounts reclassified related to Rabbi Trusts. See Note 1 — Significant Accounting Policies of the Exelon 2018 Form 10-K for additional information. (d) Exelon early adopted the new standard Reclassification of Certain Tax Effects from AOCI. The standard was adopted retrospectively as of December 31, 2017, which resulted in an increase to Exelon’s Retained earnings and Accumulated other comprehensive loss of $539 million , primarily related to deferred income taxes associated with Exelon’s pension and OPEB obligations. See Note 1 — Significant Accounting Policies of the Exelon 2018 Form 10-K for additional information. Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE did not have any reclassifications out of AOCI to Net income during the three months ended March 31, 2019 and 2018 . The following tables present amounts reclassified out of AOCI to Net income for Exelon during the three months ended March 31, 2019 and 2018 . Three Months Ended March 31, 2019 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 22 Actuarial losses (b) (49 ) (27 ) Total before tax 7 Tax benefit $ (20 ) Net of tax Total Reclassifications $ (20 ) Net of tax Three Months Ended March 31, 2018 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 23 Actuarial losses (b) (83 ) (60 ) Total before tax 16 Tax benefit $ (44 ) Net of tax Total Reclassifications $ (44 ) Net of tax _________ (a) Amounts in parenthesis represent a decrease in net income. (b) This AOCI component is included in the computation of net periodic pension and OPEB cost. See Note 14 — Retirement Benefits for additional information. The following table presents income tax benefit (expense) allocated to each component of other comprehensive income (loss) during the three months ended March 31, 2019 and 2018 : Three Months Ended 2019 2018 Exelon Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 6 $ 6 Actuarial loss reclassified to periodic benefit cost (13 ) (22 ) Pension and non-pension postretirement benefit plans valuation adjustment 14 (7 ) Change in unrealized loss on cash flow hedges — (3 ) Change in unrealized loss on investments in unconsolidated affiliates — (1 ) Total $ 7 $ (27 ) Generation Change in unrealized gain (loss) on cash flow hedges $ 1 $ (3 ) Change in unrealized loss on investments in unconsolidated affiliates — (1 ) Total $ 1 $ (4 )

Commitments and Contingencies (

Commitments and Contingencies (All Registrants)	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies (All Registrants)	Commitments and Contingencies (All Registrants) The following is an update to the current status of commitments and contingencies set forth in Note 22 of the Exelon 2018 Form 10-K. See Note 5 — Mergers, Acquisitions and Dispositions of the Exelon 2018 Form 10-K for additional information on the PHI Merger commitments. Commitments PHI Merger Commitments (Exelon, PHI, Pepco, DPL and ACE). The merger of Exelon and PHI was approved in Delaware, New Jersey, Maryland and the District of Columbia. Exelon and PHI agreed to certain commitments including where applicable: customer rate credits, funding for energy efficiency and delivery system modernization programs, a green sustainability fund, workforce development initiatives, charitable contributions, renewable generation and other required commitments. In addition, the orders approving the merger in Delaware, New Jersey, and Maryland include a “most favored nation” provision which, generally, requires allocation of merger benefits proportionally across all the jurisdictions. The following amounts represent total commitment costs for Exelon, PHI, Pepco, DPL and ACE that have been recorded since the acquisition date and the remaining obligations as of March 31, 2019 : Description Expected Payment Period Exelon PHI Pepco DPL ACE Rate credits 2016 - 2021 $ 264 $ 264 $ 91 $ 72 $ 101 Energy efficiency 2016 - 2021 117 — — — — Charitable contributions 2016 - 2026 50 50 28 12 10 Delivery system modernization Q2 2017 22 — — — — Green sustainability fund Q2 2017 14 — — — — Workforce development 2016 - 2020 17 — — — — Other 29 6 1 5 — Total commitments $ 513 $ 320 $ 120 $ 89 $ 111 Remaining commitments $ 123 $ 90 $ 71 $ 12 $ 7 In addition, Exelon is committed to develop or to assist in the commercial development of approximately 37 MWs of new solar generation in Maryland, District of Columbia, and Delaware at an estimated cost of approximately $127 million, which will generate future earnings at Exelon and Generation. Investment costs, which are expected to be primarily capital in nature, will be recognized as incurred and recorded in Exelon's and Generation's financial statements. As of March 31, 2019 , 27 MWs of new generation were developed and Exelon and Generation have incurred costs of $97 million . Exelon has also committed to purchase 100 MWs of wind energy in PJM. DPL has committed to conducting three RFPs to procure up to a total of 120 MWs of wind RECs for the purpose of meeting Delaware's renewable portfolio standards. DPL has conducted two of the three wind REC RFPs. The first 40 MW wind REC tranche was conducted in 2017 and did not result in a purchase agreement. The second 40 MW wind REC tranche was conducted in 2018 and resulted in a proposed REC purchase agreement that was approved by the DPSC in March 2019. The third and final 40 MW wind REC tranche will be conducted in 2022. Pursuant to the various jurisdictions' merger approval conditions, over specified periods Pepco, DPL and ACE are not permitted to reduce employment levels due to involuntary attrition associated with the merger integration process and have made other commitments regarding hiring and relocation of positions. Commercial Commitments (All Registrants). The Registrants’ commercial commitments as of March 31, 2019 , representing commitments potentially triggered by future events were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Letters of credit $ 1,480 $ 1,455 $ 6 $ — $ 2 $ 8 $ 8 $ — $ — Surety bonds (a) 1,597 1,376 51 9 17 40 32 5 3 Financing trust guarantees 378 — 200 178 — — — — — Guaranteed lease residual values (b) 26 — — — — 26 8 11 7 Total commercial commitments $ 3,481 $ 2,831 $ 257 $ 187 $ 19 $ 74 $ 48 $ 16 $ 10 _________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (b) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $68 million , $22 million of which is a guarantee by Pepco, $28 million by DPL and $17 million by ACE. The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote. Nuclear Insurance (Exelon and Generation). Generation is subject to liability, property damage and other risks associated with major incidents at any of its 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 March 31, 2019 , the current liability limit per incident is $14.1 billion and is subject to change to account for the effects of inflation and changes in the number of licensed reactors. Changes to account for the effects of inflation occur at least once every five years with the last adjustment effective November 1, 2018. 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. Effective January 1, 2017, the required amount of nuclear energy liability insurance purchased is $450 million for each operating site. Claims exceeding that amount are covered through mandatory participation in a financial protection pool, as required by the Price Anderson-Act, which provides the additional $13.6 billion per incident 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. Exelon’s share of this secondary layer would be approximately $3.1 billion , however any amounts payable under this secondary layer would be capped at $454 million per year. In addition, the U.S. Congress could impose revenue-raising measures on the nuclear industry to pay public liability claims exceeding the $14.1 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 2 — Variable Interest Entities of the Exelon 2018 Form 10-K 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. Premiums paid to NEIL by its members are also subject to a potential assessment for adverse loss experience in the form of a retrospective premium obligation. NEIL has never assessed this retrospective premium since its formation in 1973, and Generation cannot predict the level of future assessments if any. The current maximum aggregate annual retrospective premium obligation for Generation is approximately $335 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 by Exelon 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 cash flows. Environmental Remediation Matters General (All Registrants). The Registrants’ operations have in the past, and may in the future, require substantial expenditures 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. Unless otherwise disclosed, the Registrants cannot reasonably estimate whether they will incur 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. Additional costs could have a material, unfavorable impact in the Registrants' financial statements. MGP Sites (Exelon, ComEd, PECO, BGE, PHI and DPL). ComEd, PECO, BGE and DPL have identified sites where former MGP or gas purification 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, 21 of which have been remediated and approved by the Illinois EPA or the U.S. EPA and 21 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 2023. • PECO has identified 26 sites, 17 of which have been remediated in accordance with applicable PA DEP regulatory requirements and 9 that 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 2022. • BGE has identified 13 sites, 9 of which have been remediated and approved by the MDE and 4 that require some level of remediation and/or ongoing activity. BGE expects the majority of the remediation at these sites to continue through at least 2019. • DPL has identified 3 sites, for 2 of which remediation has been completed and approved by the MDE or the Delaware Department of Natural Resources and Environmental Control. The remaining site is under study and the required cost at the site is not expected to be material. The historical nature of the MGP and gas purification 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. 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 6 — Regulatory Matters for additional information regarding the associated regulatory assets. While BGE and DPL do not have riders for MGP clean-up costs, they have historically received recovery of actual clean-up costs in distribution rates. As of March 31, 2019 and December 31, 2018 , 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: March 31, 2019 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 486 $ 347 Generation 108 — ComEd 320 318 PECO 27 25 BGE 5 4 PHI 26 — Pepco 24 — DPL 1 — ACE 1 — December 31, 2018 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 496 $ 356 Generation 108 — ComEd 329 327 PECO 27 25 BGE 5 4 PHI 27 — Pepco 25 — DPL 1 — ACE 1 — Cotter Corporation (Exelon and Generation). The EPA has advised Cotter Corporation (Cotter), a former ComEd subsidiary, that it is potentially liable in connection with radiological contamination at a site known as the West Lake Landfill in Missouri. In 2000, ComEd sold Cotter to an unaffiliated third-party. As part of the sale, ComEd agreed to indemnify Cotter for any liability arising in connection with the West Lake Landfill. In connection with Exelon’s 2001 corporate restructuring, this responsibility to indemnify Cotter was transferred to Generation. Including Cotter, there are three PRPs participating in the West Lake Landfill remediation proceeding. Investigation by Generation has identified a number of other parties who also may be PRPs and could be liable to contribute to the final remedy. Further investigation is ongoing. In September 2018 the EPA issued its Record of Decision (ROD) Amendment for the selection of the final remedy. The ROD modified the EPA’s previously proposed plan for partial excavation of the radiological materials by reducing the depths of the excavation. The ROD also allows for variation in depths of excavation depending on radiological concentrations. The EPA and the PRPs are negotiating Consent Agreements to design and implement the ROD remedy, and negotiations are expected to be completed in the first quarter of 2020. The estimated cost of the remedy, taking into account the current EPA technical requirements and the total costs expected to be incurred by the PRPs in fully executing the remedy, is approximately $280 million , including cost escalation on an undiscounted basis, which would be allocated among the final group of PRPs. Generation has determined that a loss associated with the EPA’s partial excavation and enhanced landfill cover remedy is probable and has recorded a liability included in the table above, that reflects management’s best estimate of Cotter’s allocable share of the ultimate cost. Given the joint and several nature of this liability, the magnitude of Generation’s ultimate liability will depend on the actual costs incurred to implement the required remediation remedy as well as on the nature and terms of any cost-sharing arrangements with the final group of PRPs. Therefore, it is reasonably possible that the ultimate cost and Generation’s associated allocable share could differ significantly once these uncertainties are resolved, which could have a material impact on Exelon's and Generation's future financial statements. One of the other PRPs has indicated it will be making a contribution claim against Cotter for costs that it has incurred to prevent the subsurface fire from spreading to those areas of the West Lake Landfill where radiological materials are believed to have been disposed. At this time, Exelon and Generation do not possess sufficient information to assess this claim and therefore are unable to estimate a range of loss, if any. As such, no liability has been recorded for the potential contribution claim. It is reasonably possible, however, that resolution of this matter could have a material, unfavorable impact on Exelon’s and Generation's financial statements. In January 2018, the PRPs were advised by the EPA that it will begin an additional investigation and evaluation of groundwater conditions at the West Lake Landfill. In September 2018, the PRPs agreed to an Administrative Settlement Agreement and Order on Consent for the performance by the PRPs of the groundwater RI/FS. The purpose of this RI/FS is to define the nature and extent of any groundwater contamination from the West Lake Landfill site and evaluate remedial alternatives. Generation estimates the undiscounted cost for the groundwater RI/FS to be approximately $20 million . Generation determined a loss associated with the RI/FS is probable and has recorded a liability included in the table above that reflects management’s best estimate of Cotter’s allocable share of the cost among the PRPs. At this time Generation cannot predict the likelihood or the extent to which, if any, remediation activities may be required and therefore cannot estimate a reasonably possible range of loss for response costs beyond those associated with the RI/FS component. It is reasonably possible, however, that resolution of this matter could have a material, unfavorable impact on Exelon’s and Generation’s future financial statements. In August, 2011, Cotter was notified by the DOJ that Cotter is considered a PRP with respect to the government’s clean-up costs for contamination attributable to low level radioactive residues at a former storage and reprocessing facility named Latty Avenue near St. Louis, Missouri. The Latty Avenue site is included in ComEd’s indemnification responsibilities discussed above as part of the sale of Cotter. The radioactive residues had been generated initially in connection with the processing of uranium ores as part of the U.S. Government’s Manhattan Project. Cotter purchased the residues in 1969 for initial processing at the Latty Avenue facility for the subsequent extraction of uranium and metals. In 1976, the NRC found that the Latty Avenue site had radiation levels exceeding NRC criteria for decontamination of land areas. Latty Avenue was investigated and remediated by the United States Army Corps of Engineers pursuant to funding under FUSRAP. The DOJ has not yet formally advised the PRPs of the amount that it is seeking, but it is believed to be approximately $90 million from all PRPs. Pursuant to a series of annual agreements since 2011, the DOJ and the PRPs have tolled the statute of limitations until August 2019 so that settlement discussions could proceed. Generation has determined that a loss associated with this matter is probable under its indemnification agreement with Cotter and has recorded an estimated liability, which is included in the table above. Commencing in February 2012, a number of lawsuits have been filed in the U.S. District Court for the Eastern District of Missouri. Among the defendants were Exelon, Generation and ComEd, all of which were subsequently dismissed from the case, as well as Cotter, which remains a defendant. The suits allege that individuals living in the North St. Louis area developed some form of cancer or other serious illness due to Cotter's negligent or reckless conduct in processing, transporting, storing, handling and/or disposing of radioactive materials. Plaintiffs are asserting public liability claims under the Price-Anderson Act. Their state law claims for negligence, strict liability, emotional distress, and medical monitoring have been dismissed. In the event of a finding of liability against Cotter, it is probable that Generation would be financially responsible due to its indemnification responsibilities of Cotter described above. The court has dismissed a number of the lawsuits as untimely, which has been upheld on appeal. Cotter and the remaining plaintiffs have engaged in settlement discussions pursuant to court-ordered mediation. During the second quarter of 2018, Generation determined a loss was probable based on the advancement of settlement proceedings and recorded an immaterial liability. Benning Road Site (Exelon, Generation, PHI and Pepco). In September 2010, PHI received a letter from EPA identifying the Benning Road site as one of six land-based sites potentially contributing to contamination of the lower Anacostia River. A portion of the site was formerly the location of a Pepco Energy Services electric generating facility. That generating facility was deactivated in June 2012 and plant structure demolition was completed in July 2015. The remaining portion of the site consists of a Pepco transmission and distribution service center that remains in operation. In December 2011, the U.S. District Court for the District of Columbia approved a Consent Decree entered into by Pepco and Pepco Energy Services with the DOEE, which requires Pepco and Pepco Energy Services to conduct a Remediation Investigation (RI)/ Feasibility Study (FS) for the Benning Road site and an approximately 10 to 15-acre portion of the adjacent Anacostia River. The RI/FS will form the basis for the remedial actions for the Benning Road site and for the Anacostia River sediment associated with the site. The Consent Decree does not obligate Pepco or Pepco Energy Services to pay for or perform any remediation work, but it is anticipated that DOEE will look to Pepco and Pepco Energy Services to assume responsibility for cleanup of any conditions in the river that are determined to be attributable to past activities at the Benning Road site. Pursuant to Exelon's March 23, 2016 acquisition of PHI, Pepco Energy Services was transferred to Generation. Since 2013, Pepco and Pepco Energy Services (now Generation) have been performing RI work and have submitted multiple draft RI reports to the DOEE. Once the RI work is completed, Pepco and Generation will issue a draft “final” RI report for review and comment by DOEE and the public. Pepco and Generation will then proceed to develop an FS to evaluate possible remedial alternatives for submission to DOEE. The Court has established a schedule for completion of the RI and FS, and approval by the DOEE, by September 16, 2021. Upon DOEE’s approval of the final RI and FS Reports, Pepco and Generation will have satisfied their obligations under the Consent Decree. At that point, DOEE will prepare a Proposed Plan regarding further response actions. After considering public comment on the Proposed Plan, DOEE will issue a Record of Decision identifying any further response actions determined to be necessary. PHI, Pepco and Generation have determined that a loss associated with this matter is probable and have accrued an estimated liability, which is included in the table above. Anacostia River Tidal Reach (Exelon, PHI and Pepco). Contemporaneous with the Benning RI/FS being performed by Pepco and Generation, DOEE and certain federal agencies have been conducting a separate RI/FS focused on the entire tidal reach of the Anacostia River extending from just north of the Maryland-D.C. boundary line to the confluence of the Anacostia and Potomac Rivers. In March 2016, DOEE released a draft of the river-wide RI Report for public review and comment. The river-wide RI incorporated the results of the river sampling performed by Pepco and Pepco Energy Services as part of the Benning RI/FS, as well as similar sampling efforts conducted by owners of other sites adjacent to this segment of the river and supplemental river sampling conducted by DOEE’s contractor. DOEE asked Pepco, along with parties responsible for other sites along the river, to participate in a “Consultative Working Group” to provide input into the process for future remedial actions addressing the entire tidal reach of the river and to ensure proper coordination with the other river cleanup efforts currently underway, including cleanup of the river segment adjacent to the Benning Road site resulting from the Benning RI/FS. Pepco responded that it will participate in the Consultative Working Group, but its participation is not an acceptance of any financial responsibility beyond the work that will be performed at the Benning Road site described above. In April 2018, DOEE released a draft remedial investigation report for public review and comment. Pepco submitted written comments to the draft RI and participated in a public hearing. Pepco continues outreach efforts as appropriate to the agencies, governmental officials, community organizations and other key stakeholders. In May 2018 the District of Columbia Council extended the deadline for completion of the Record of Decision from June 30, 2018 until December 31, 2019. An appropriate liability for Pepco’s share of investigation costs has been accrued and is included in the table above. Although Pepco has determined that it is probable that costs for remediation will be incurred, Pepco cannot estimate the reasonably possible range of loss at this time and no liability has been accrued for those future costs. A draft Feasibility Study of potential remedies and their estimated costs is being prepared by the agencies and is expected later in 2019, at which time Pepco will likely be in a better position to estimate the range of loss. In addition to the activities associated with the remedial process outlined above, there is a complementary statutory program that requires an assessment to determine if any natural resources have been damaged as a result of the contamination that is being remediated, and, if so, that a plan be developed by the federal, state and local Trustees responsible for those resources to restore them to their condition before injury from the environmental contaminants. If natural resources are not restored, then compensation for the injury can be sought from the party responsible for the release of the contaminants. The assessment of Natural Resource Damages (NRD) typically takes place following cleanup because cleanups sometimes also effectively restore habitat. During the second quarter of 2018, Pepco became aware that the Trustees are in the beginning stages of this process that often takes many years beyond the remedial decision to complete. Pepco has concluded that a loss associated with the eventual NRD assessment is reasonably possible. Due to the very early stage of the assessment process it cannot reasonably estimate the range of loss. Litigation and Regulatory Matters Asbestos Personal Injury Claims (Exelon and Generation). Generation maintains a reserve for claims associated with asbestos-related personal injury actions in certain facilities that are currently owned by Generation or were previously owned by ComEd and PECO. The estimated liabilities are recorded on an undiscounted basis and exclude the estimated legal costs associated with handling these matters, which could be material. At March 31, 2019 and December 31, 2018 , Generation had recorded estimated liabilities of approximately $77 million and $79 million , respectively, in total for asbestos-related bodily injury claims. As of March 31, 2019 , approximately $25 million of this amount related to 239 open claims presented to Generation, while the remaining $52 million is for estimated future asbestos-related bodily injury claims anticipated to arise through 2050, based on actuarial assumptions and analyses, which are updated on an annual basis. On a quarterly basis, Generation monitors actual experience against the number of forecasted claims to be received and expected claim payments and evaluates whether adjustments to the estimated liabilities are necessary. There is a reasonable possibility that Exelon may have additional exposure to estimated future asbestos-related bodily injury claims in excess of the amount accrued and the increases could have a material unfavorable impact on Exelon's and Generation's financial statements. City of Everett Tax Increment Financing Agreement (Exelon and Generation). On April 10, 2017, the City of Everett petitioned the Massachusetts Economic Assistance Coordinating Council (EACC) to revoke the 1999 tax increment financing agreement (TIF Agreement) relating to Mystic Units 8 and 9 on the grounds that the total investment in Mystic Units 8 and 9 materially deviates from the investment set forth in the TIF Agreement. On October 31, 2017, a three-member panel of the EACC conducted an administrative hearing on the City’s petition. On November 30, 2017, the hearing panel issued a tentative decision denying the City’s petition, finding that there was no material misrepresentation that would justify revocation of the TIF Agreement. On December 13, 2017, the tentative decision was adopted by the full EACC. On January 12, 2018, the City filed a complaint in Massachusetts Superior Court requesting, among other things, that the court set aside the EACC’s decision, grant the City’s request to decertify the Project and the TIF Agreement, and award the City damages for alleged underpaid taxes over the period of the TIF Agreement. Generation vigorously contested the City’s claims before the EACC and will continue to do so in the Massachusetts Superior Court proceeding. Generation continues to believe that the City’s claim lacks merit. Accordingly, Generation has not recorded a liability for payment resulting from such a revocation, nor can Generation estimate a reasonably possible range of loss, if any, associated with any such revocation. Further, it is reasonably possible that property taxes assessed in future periods, including those following the expiration of the current TIF Agreement in 2019, could be material to Generation’s results of operations and cash flows. General (All Registrants). The Registrants are involved in various other litigation matters that are being defended and handled in the ordinary course of business. The assessment of whether a loss is probable or reasonably possible, and whether the loss or a range of loss is estimable, often involves a series of complex judgments about future events. The Registrants maintain accruals for such losses that are probable of being incurred and subject to reasonable estimation. Management is sometimes unable to estimate an amount or range of reasonably possible loss, particularly where (1) the damages sought are indeterminate, (2) the proceedings are in the early stages, or (3) the matters involve novel or unsettled legal theories. In such cases, there is considerable uncertainty regarding the timing or ultimate resolution of such matters, including a possible eventual loss.

Supplemental Financial Informat

Supplemental Financial Information (All Registrants)	3 Months Ended
	Mar. 31, 2019
Supplemental Financial Information [Abstract]
Supplemental Financial Information (All Registrants)	Supplemental Financial Information (All Registrants) Supplemental Statement of Operations Information The following tables provide additional information about the Registrants’ Consolidated Statements of Operations and Comprehensive Income for the three months ended March 31, 2019 and 2018 . Three Months Ended March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on NDT funds (a) Regulatory agreement units (b) $ 54 $ 54 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 54 54 — — — — — — — Net unrealized gains on NDT funds Regulatory agreement units (b) 379 379 — — — — — — — Non-regulatory agreement units 280 280 — — — — — — — Regulatory offset to NDT fund-related activities (c) (348 ) (348 ) — — — — — — — Total decommissioning-related activities 419 419 — — — — — — — Investment income 12 7 — 1 — — — — — Interest income related to uncertain income tax positions 1 — — — — — — — — AFUDC — Equity 22 — 5 3 5 9 6 1 2 Non-service net periodic benefit cost 5 — — — — — — — — Other 8 4 3 — — 3 1 2 1 Other, net $ 467 $ 430 $ 8 $ 4 $ 5 $ 12 $ 7 $ 3 $ 3 Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on NDT funds (a) Regulatory agreement units (b) $ 46 $ 46 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 56 56 — — — — — — — Net unrealized losses on NDT funds Regulatory agreement units (b) (75 ) (75 ) — — — — — — — Non-regulatory agreement units (96 ) (96 ) — — — — — — — Regulatory offset to NDT fund-related activities (c) 24 24 — — — — — — — Total decommissioning-related activities (45 ) (45 ) — — — — — — — Investment income 4 2 — — — — — — — Interest income related to uncertain income tax positions 2 1 — — — — — — — AFUDC — Equity 18 — 6 2 4 6 5 1 — Non-service net periodic benefit cost (10 ) — — — — — — — — Other 3 (2 ) 2 — — 5 3 1 1 Other, net $ (28 ) $ (44 ) $ 8 $ 2 $ 4 $ 11 $ 8 $ 2 $ 1 _________ (a) Realized income includes interest, dividends and realized gains and losses on sales of NDT fund investments. (b) Net realized and unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities in Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates in Generation’s Consolidated Balance Sheets. (c) Includes the elimination of decommissioning-related activities for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 15 — Asset Retirement Obligations of the Exelon 2018 Form 10-K for additional information regarding the accounting for nuclear decommissioning. The following utility taxes are included in revenues and expenses for the three months ended March 31, 2019 and 2018 . Generation’s utility tax expense represents gross receipts tax related to its retail operations, and the Utility Registrants' utility tax expense represents 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 in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Three Months Ended March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 223 $ 26 $ 62 $ 34 $ 27 $ 74 $ 69 $ 5 $ — Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 235 $ 32 $ 61 $ 33 $ 26 $ 83 $ 77 $ 6 $ — Supplemental Cash Flow Information The following tables provide additional information regarding the Registrants’ Consolidated Statements of Cash Flows for the three months ended March 31, 2019 and 2018 . Three Months Ended March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment (a) $ 917 $ 392 $ 219 $ 74 $ 85 $ 127 $ 58 $ 35 $ 25 Amortization of regulatory assets (a) 143 — 32 7 51 53 36 11 6 Amortization of intangible assets, net (a) 15 13 — — — — — — — Nuclear fuel (c) 261 261 — — — — — — — ARO accretion (d) 124 123 — — — — — — — Total depreciation, amortization and accretion $ 1,460 $ 789 $ 251 $ 81 $ 136 $ 180 $ 94 $ 46 $ 31 Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment (a) $ 926 $ 436 $ 201 $ 68 $ 82 $ 117 $ 53 $ 32 $ 23 Amortization of regulatory assets (a) 152 — 27 7 52 66 43 13 10 Amortization of intangible assets, net (a) 13 12 — — — — — — — Amortization of energy contract assets and liabilities (b) 3 3 — — — — — — — Nuclear fuel (c) 287 287 — — — — — — — ARO accretion (d) 120 120 — — — — — — — Total depreciation, amortization and accretion $ 1,501 $ 858 $ 228 $ 75 $ 134 $ 183 $ 96 $ 45 $ 33 _________ (a) Included in Depreciation and amortization in the Registrants' Consolidated Statements of Operations and Comprehensive Income. (b) Included in Operating revenues or Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (c) Included in Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (d) Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Three Months Ended March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 106 $ 31 $ 24 $ 2 $ 15 $ 23 $ 6 $ 4 $ 4 Loss from equity method investments 6 6 — — — — — — — Provision for uncollectible accounts 43 — 9 16 8 10 4 4 2 Stock-based compensation costs 28 — — — — — — — — Other decommissioning-related activity (a) (202 ) (202 ) — — — — — — — Energy-related options (b) 37 37 — — — — — — — Amortization of regulatory asset related to debt costs 3 — — — — 1 — — — Amortization of rate stabilization deferral (6 ) — — — — (6 ) (7 ) 1 — Amortization of debt fair value adjustment (4 ) (3 ) — — — (1 ) — — — Discrete impacts from EIMA and FEJA (c) 28 — 28 — — — — — — Amortization of debt costs 9 3 1 — — 1 1 — — Long-term incentive plan 25 — — — — — — — — Amortization of operating ROU asset 53 34 1 — 8 9 2 2 1 Other 1 4 (7 ) (2 ) (4 ) (2 ) (3 ) — (2 ) Total other non-cash operating activities $ 127 $ (90 ) $ 56 $ 16 $ 27 $ 35 $ 3 $ 11 $ 5 Non-cash investing and financing activities: Change in capital expenditures not paid $ (229 ) $ (93 ) $ (80 ) $ 8 $ 2 $ (55 ) $ (15 ) $ (17 ) $ (24 ) Change in PPE related to ARO update 301 301 — — — — — — — Dividends on stock compensation 1 — — — — — — — — Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 145 $ 51 $ 45 $ 5 $ 14 $ 15 $ 4 $ — $ 3 Loss from equity method investments 7 7 — — — — — — — Provision for uncollectible accounts 64 11 8 17 8 20 6 8 5 Stock-based compensation costs 29 — — — — — — — — Other decommissioning-related activity (a) (31 ) (31 ) — — — — — — — Energy-related options (b) (7 ) (7 ) — — — — — — — Amortization of regulatory asset related to debt costs 2 — 1 — — 1 — — — Amortization of rate stabilization deferral 7 — — — — 7 1 6 — Amortization of debt fair value adjustment (3 ) (3 ) — — — — — — — Discrete impacts from EIMA and FEJA (c) (4 ) — (4 ) — — — — — — Amortization of debt costs 9 3 1 — — 1 — — — Provision for excess and obsolete inventory 13 12 1 — — — — — — Other 9 2 (6 ) (1 ) (2 ) 9 (1 ) 5 1 Total other non-cash operating activities $ 240 $ 45 $ 46 $ 21 $ 20 $ 53 $ 10 $ 19 $ 9 Non-cash investing and financing activities: Change in capital expenditures not paid $ (177 ) $ (131 ) $ (48 ) $ (25 ) $ (11 ) $ 61 $ 19 $ 14 $ 27 Change in PPE related to ARO update 32 32 — — — — — — — Dividends on stock compensation 1 — — — — — — — — _________ (a) Includes the elimination of decommissioning-related 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 15 — Asset Retirement Obligations of the Exelon 2018 Form 10-K 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 in Operating revenues and expenses. (c) Reflects the change in ComEd's distribution and energy efficiency formula rates. See Note 6 — Regulatory Matters for additional information. The following tables provide a reconciliation of cash, cash equivalents and restricted cash reported within the Registrants’ Consolidated Balance Sheets that sum to the total of the same amounts in their Consolidated Statements of Cash Flows. March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 880 $ 537 $ 68 $ 41 $ 12 $ 33 $ 11 $ 7 $ 6 Restricted cash 223 139 17 6 4 39 35 1 3 Restricted cash included in other long-term assets 211 — 193 — — 19 — — 19 Total cash, cash equivalents and restricted cash $ 1,314 $ 676 $ 278 $ 47 $ 16 $ 91 $ 46 $ 8 $ 28 December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 1,349 $ 750 $ 135 $ 130 $ 7 $ 124 $ 16 $ 23 $ 7 Restricted cash 247 153 29 5 6 43 37 1 4 Restricted cash included in other long-term assets 185 — 166 — — 19 — — 19 Total cash, cash equivalents and restricted cash $ 1,781 $ 903 $ 330 $ 135 $ 13 $ 186 $ 53 $ 24 $ 30 March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 787 $ 610 $ 70 $ 21 $ 22 $ 43 $ 15 $ 7 $ 10 Restricted cash 209 127 9 5 2 40 33 — 7 Restricted cash included in other long-term assets 103 — 83 — — 20 — — 20 Total cash, cash equivalents and restricted cash $ 1,099 $ 737 $ 162 $ 26 $ 24 $ 103 $ 48 $ 7 $ 37 December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 898 $ 416 $ 76 $ 271 $ 17 $ 30 $ 5 $ 2 $ 2 Restricted cash 207 138 5 4 1 42 35 — 6 Restricted cash included in other long-term assets 85 — 63 — — 23 — — 23 Total cash, cash equivalents and restricted cash $ 1,190 $ 554 $ 144 $ 275 $ 18 $ 95 $ 40 $ 2 $ 31 For additional information on restricted cash see Note 1 — Significant Accounting Policies of the Exelon 2018 Form 10-K. Supplemental Balance Sheet Information The following tables provide additional information about assets and liabilities of the Registrants as of March 31, 2019 and December 31, 2018 . March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Property, plant and equipment: Accumulated depreciation and amortization $ 23,695 (a) $ 12,663 (a) $ 4,833 $ 3,598 $ 3,670 $ 930 $ 3,392 $ 1,354 $ 1,154 Accounts receivable: Allowance for uncollectible accounts $ 340 $ 87 $ 97 $ 72 $ 27 $ 57 $ 23 $ 15 $ 19 December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Property, plant and equipment: Accumulated depreciation and amortization $ 22,902 (b) $ 12,206 (b) $ 4,684 $ 3,561 $ 3,633 $ 841 $ 3,354 $ 1,329 $ 1,137 Accounts receivable: Allowance for uncollectible accounts $ 319 $ 104 $ 81 $ 61 $ 20 $ 53 $ 21 $ 13 $ 19 _________ (a) Includes accumulated amortization of nuclear fuel in the reactor core of $3,040 million . (b) Includes accumulated amortization of nuclear fuel in the reactor core of $2,969 million . The Utility Registrants are required, under separate legislation and regulations in Illinois, Pennsylvania, Maryland, District of Columbia and New Jersey, to purchase certain receivables from alternative retail electric and, as applicable, natural gas suppliers that participate in the utilities' consolidated billing. ComEd, BGE, Pepco and DPL purchase receivables at a discount to recover primarily uncollectible accounts expense from the suppliers. PECO and ACE purchase receivables at face value and recover uncollectible accounts expense, including those from alternative retail electric and natural gas supplies, through base distribution rates and a rate rider, respectively. Exelon and the Utility Registrants do not record unbilled commodity receivables under their POR programs. Purchased billed receivables are recorded on a net basis in Exelon’s and the Utility Registrant's Consolidated Statements of Operations and Comprehensive Income and are classified in Other accounts receivable, net in their Consolidated Balance Sheets. The following tables provide information about the purchased receivables of those companies as of March 31, 2019 and December 31, 2018 . March 31, 2019 Exelon ComEd PECO BGE PHI Pepco DPL ACE Purchased receivables $ 332 $ 105 $ 77 $ 65 $ 85 $ 58 $ 8 $ 19 Allowance for uncollectible accounts (a) (38 ) (19 ) (6 ) (4 ) (9 ) (5 ) (1 ) (3 ) Purchased receivables, net $ 294 $ 86 $ 71 $ 61 $ 76 $ 53 $ 7 $ 16 December 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Purchased receivables $ 313 $ 94 $ 74 $ 61 $ 84 $ 57 $ 8 $ 19 Allowance for uncollectible accounts (a) (34 ) (17 ) (5 ) (3 ) (9 ) (5 ) (1 ) (3 ) Purchased receivables, net $ 279 $ 77 $ 69 $ 58 $ 75 $ 52 $ 7 $ 16 __________ (a) For ComEd, BGE, Pepco and DPL, 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 a rate rider. BGE, Pepco and DPL recover actual write-offs which are reflected in the POR discount rate.

Segment Information (All Regist

Segment Information (All Registrants)	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Segment Information (All Registrants)	Segment Information (All Registrants) Operating segments for each of the Registrants are determined based on information used by the CODM in deciding how to evaluate performance and allocate resources at each of the Registrants. Exelon has eleven reportable segments, which include Generation's five reportable segments consisting of the Mid-Atlantic, Midwest, New York, ERCOT and all other power regions referred to collectively as “Other Power Regions” and ComEd, PECO, BGE, and PHI's three reportable segments consisting of Pepco, DPL and ACE. ComEd, PECO, BGE, Pepco, DPL and ACE each represent a single reportable segment, and as such, no separate segment information is provided for these Registrants. Exelon, ComEd, PECO, BGE, Pepco, DPL and ACE's CODMs evaluate the performance of and allocate resources to ComEd, PECO, BGE, Pepco, DPL and ACE based on net income. 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 five 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 and the United States footprint of MISO, excluding MISO’s Southern Region. • New York represents operations within ISO-NY. • ERCOT represents operations within Electric Reliability Council of Texas. • Other Power Regions: • New England represents the operations within ISO-NE. • South represents operations in the FRCC, MISO’s Southern Region, and the remaining portions of the SERC not included within MISO or PJM. • West represents operations in the WECC, which includes California ISO. • 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 electric business activities and allocate resources based on 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 the Utility Registrants. 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 excluded from 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. During the first quarter of 2019, due to a change in economics in our New England region, Generation changed the way that information is reviewed by the CODM. The New England region is no longer regularly reviewed as a separate region by the CODM nor is it presented separately in any external information presented to third parties. Information for the New England region is reviewed by the CODM as part of Other Power Regions. Exelon and Generation retrospectively applied this change. An analysis and reconciliation of the Registrants’ reportable segment information to the respective information in the consolidated financial statements for the three months ended March 31, 2019 and 2018 is as follows: Three Months Ended March 31, 2019 and 2018 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon Operating revenues (c) : 2019 Competitive businesses electric revenues $ 4,337 $ — $ — $ — $ — $ — $ (315 ) $ 4,022 Competitive businesses natural gas revenues 879 — — — — — (1 ) 878 Competitive businesses other revenues 80 — — — — — (1 ) 79 Rate-regulated electric revenues — 1,408 620 658 1,153 — (8 ) 3,831 Rate-regulated natural gas revenues — — 280 318 71 — (4 ) 665 Shared service and other revenues — — — — 4 455 (457 ) 2 Total operating revenues $ 5,296 $ 1,408 $ 900 $ 976 $ 1,228 $ 455 $ (786 ) $ 9,477 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon 2018 Competitive businesses electric revenues $ 4,509 $ — $ — $ — $ — $ — $ (391 ) $ 4,118 Competitive businesses natural gas revenues 955 — — — — — (8 ) 947 Competitive businesses other revenues 48 — — — — — — 48 Rate-regulated electric revenues — 1,512 634 658 1,169 — (18 ) 3,955 Rate-regulated natural gas revenues — — 232 319 78 — (4 ) 625 Shared service and other revenues — — — — 4 451 (455 ) — Total operating revenues $ 5,512 $ 1,512 $ 866 $ 977 $ 1,251 $ 451 $ (876 ) $ 9,693 Intersegment revenues (d) : 2019 $ 317 $ 4 $ 1 $ 6 $ 4 $ 453 $ (785 ) $ — 2018 400 14 2 6 4 450 (876 ) — Depreciation and amortization: 2019 $ 405 $ 251 $ 81 $ 136 $ 180 $ 22 $ — $ 1,075 2018 448 228 75 134 183 23 — 1,091 Operating expenses: 2019 $ 4,963 $ 1,135 $ 678 $ 756 $ 1,054 $ 459 $ (783 ) $ 8,262 2018 5,218 1,223 724 800 1,125 444 (886 ) 8,648 Interest expense, net: 2019 $ 111 $ 87 $ 33 $ 29 $ 65 $ 78 $ — $ 403 2018 101 89 33 25 63 60 — 371 Income (loss) before income taxes: 2019 $ 652 $ 197 $ 193 $ 196 $ 122 $ (78 ) $ — $ 1,282 2018 202 211 111 156 74 (52 ) — 702 Income Taxes: 2019 $ 224 $ 40 $ 25 $ 36 $ 5 $ (20 ) $ — $ 310 2018 9 46 (2 ) 28 9 (31 ) — 59 Net income (loss): 2019 $ 422 $ 157 $ 168 $ 160 $ 117 $ (58 ) $ — $ 966 2018 186 165 113 128 65 (21 ) — 636 Capital Expenditures 2019 $ 511 $ 503 $ 222 $ 258 $ 358 $ 21 $ — $ 1,873 2018 628 531 217 224 258 22 — 1,880 Total assets: March 31, 2019 $ 48,682 $ 31,582 $ 10,956 $ 9,967 $ 22,294 $ 8,325 $ (10,213 ) $ 121,593 December 31, 2018 47,556 31,213 10,642 9,716 21,984 8,355 (9,800 ) 119,666 __________ (a) Intersegment revenues for Generation in 2019 include revenue from sales to PECO of $45 million , sales to BGE of $76 million , sales to Pepco of $70 million , sales to DPL of $23 million and sales to ACE of $8 million in the Mid-Atlantic region, and sales to ComEd of $94 million in the Midwest region, which eliminate upon consolidation. Intersegment revenues for Generation in 2018 include revenue from sales to PECO of $37 million , sales to BGE of $65 million , sales to Pepco of $52 million , sales to DPL of $46 million and sales to ACE of $6 million in the Mid-Atlantic region, and sales to ComEd of $194 million in the Midwest region, which eliminate upon consolidation. (b) Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities. (c) Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 17 — Supplemental Financial Information for additional information on total utility taxes. (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. PHI: Pepco DPL ACE Other (b) Intersegment PHI Operating revenues (a) : 2019 Rate-regulated electric revenues $ 575 $ 310 $ 273 $ — $ (5 ) $ 1,153 Rate-regulated natural gas revenues — 70 — — 1 71 Shared service and other revenues — — — 106 (102 ) 4 Total operating revenues $ 575 $ 380 $ 273 $ 106 $ (106 ) $ 1,228 2018 Rate-regulated electric revenues $ 557 $ 306 $ 310 $ — $ (4 ) $ 1,169 Rate-regulated natural gas revenues — 78 — — — 78 Shared service and other revenues — — — 113 (109 ) 4 Total operating revenues $ 557 $ 384 $ 310 $ 113 $ (113 ) $ 1,251 Intersegment revenues: 2019 $ 2 $ 2 $ 1 $ 105 $ (106 ) $ 4 2018 2 2 1 112 (113 ) 4 Depreciation and amortization: 2019 $ 94 $ 46 $ 31 $ 10 $ (1 ) $ 180 2018 96 45 33 9 — 183 Operating expenses: 2019 $ 491 $ 308 $ 252 $ 108 $ (105 ) $ 1,054 2018 501 335 287 114 (112 ) 1,125 Interest expense, net: 2019 $ 34 $ 15 $ 14 $ 3 $ (1 ) $ 65 2018 31 13 16 2 1 63 Income (loss) before income taxes: 2019 $ 57 $ 60 $ 10 $ 113 $ (118 ) $ 122 2018 33 38 8 64 (69 ) 74 Income Taxes: 2019 $ 2 $ 7 $ — $ (4 ) $ — $ 5 2018 2 7 1 (1 ) — 9 Net income (loss): 2019 $ 55 $ 53 $ 10 $ (5 ) $ 4 $ 117 2018 31 31 7 (8 ) 4 65 Capital Expenditures 2019 $ 144 $ 78 $ 128 $ 8 $ — $ 358 2018 127 65 63 3 — 258 Total assets: March 31, 2019 $ 8,420 $ 4,660 $ 3,783 $ 10,909 $ (5,478 ) $ 22,294 December 31, 2018 8,299 4,588 3,699 10,819 (5,421 ) 21,984 __________ (a) Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 17 — Supplemental Financial Information for additional information on total utility taxes. (b) Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities. The following tables disaggregate the Registrants' revenue recognized from contracts with customers into categories that depict how the nature, amount, timing, and uncertainty of revenue and cash flows are affected by economic factors. For Generation, the disaggregation of revenues reflects Generation’s two primary products of power sales and natural gas sales, with further disaggregation of power sales provided by geographic region. For the Utility Registrants, the disaggregation of revenues reflects the two primary utility services of rate-regulated electric sales and rate-regulated natural gas sales (where applicable), with further disaggregation of these tariff sales provided by major customer groups. Exelon’s disaggregated revenues are consistent with Generation and the Utility Registrants, but exclude any intercompany revenues. Competitive Business Revenues (Generation): Three Months Ended March 31, 2019 Revenues from external parties (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 1,286 $ (24 ) $ 1,262 $ (6 ) $ 1,256 Midwest 1,055 59 1,114 (6 ) 1,108 New York 409 (16 ) 393 — 393 ERCOT 130 79 209 3 212 Other Power Regions 1,165 194 1,359 (6 ) 1,353 Total Competitive Businesses Electric Revenues 4,045 292 4,337 (15 ) 4,322 Competitive Businesses Natural Gas Revenues 584 295 879 15 894 Competitive Businesses Other Revenues (c) 120 (40 ) 80 — 80 Total Generation Consolidated Operating Revenues $ 4,749 $ 547 $ 5,296 $ — $ 5,296 Three Months Ended March 31, 2018 Revenues from external customers (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 1,355 $ 80 $ 1,435 $ 5 $ 1,440 Midwest 1,273 71 1,344 2 1,346 New York 439 (29 ) 410 (1 ) 409 ERCOT 149 59 208 1 209 Other Power Regions 935 177 1,112 (32 ) 1,080 Total Competitive Businesses Electric Revenues 4,151 358 4,509 (25 ) 4,484 Competitive Businesses Natural Gas Revenues 522 433 955 25 980 Competitive Businesses Other Revenues (c) 134 (86 ) 48 — 48 Total Generation Consolidated Operating Revenues $ 4,807 $ 705 $ 5,512 $ — $ 5,512 __________ (a) Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants. (b) Includes revenues from derivatives and leases. (c) Other represents activities not allocated to a region. See text above for a description of included activities. Includes unrealized mark-to-market losses of $52 million and $98 million in 2019 and 2018 , respectively, and elimination of intersegment revenues. Revenues net of purchased power and fuel expense (Generation): Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 RNF (a) Intersegment RNF Total RNF RNF (a) Intersegment RNF Total RNF Mid-Atlantic $ 679 $ 4 $ 683 $ 836 $ 14 $ 850 Midwest 769 2 771 847 13 860 New York 262 3 265 282 1 283 ERCOT 98 (24 ) 74 106 (70 ) 36 Other Power Regions 174 (18 ) 156 279 (43 ) 236 Total Revenues net of purchased power and fuel for Reportable Segments 1,982 (33 ) 1,949 2,350 (85 ) 2,265 Other (b) 109 33 142 (131 ) 85 (46 ) Total Generation Revenues net of purchased power and fuel expense $ 2,091 $ — $ 2,091 $ 2,219 $ — $ 2,219 __________ (a) Includes purchases and sales from/to third parties and affiliated sales to the Utility Registrants. (b) Other represents activities not allocated to a region. See text above for a description of included activities. Includes unrealized mark-to-market losses of $28 million and $266 million in 2019 and 2018 , respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 8 — Early Plant Retirements of $5 million and $15 million decrease to RNF in 2019 and 2018, respectively, and the elimination of intersegment RNF. Electric and Gas Revenue by Customer Class (Utility Registrants): Three Months Ended March 31, 2019 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 710 $ 409 $ 385 $ 579 $ 256 $ 185 $ 138 Small commercial & industrial 360 96 70 120 38 48 34 Large commercial & industrial 132 48 110 267 204 24 39 Public authorities & electric railroads 13 7 7 14 8 3 3 Other (a) 217 62 80 157 53 47 57 Total rate-regulated electric revenues (b) $ 1,432 $ 622 $ 652 $ 1,137 $ 559 $ 307 $ 271 Rate-regulated natural gas revenues Residential $ — $ 198 $ 219 $ 44 $ — $ 44 $ — Small commercial & industrial — 72 35 19 — 19 — Large commercial & industrial — 1 50 1 — 1 — Transportation — 7 — 4 — 4 — Other (c) — 2 4 3 — 3 — Total rate-regulated natural gas revenues (d) $ — $ 280 $ 308 $ 71 $ — $ 71 $ — Total rate-regulated revenues from contracts with customers $ 1,432 $ 902 $ 960 $ 1,208 $ 559 $ 378 $ 271 Other revenues Revenues from alternative revenue programs $ (28 ) $ (3 ) $ 10 $ 15 $ 14 $ — $ 1 Other rate-regulated electric revenues (e) 4 1 3 4 2 1 1 Other rate-regulated natural gas revenues (e) — — 3 1 — 1 — Total other revenues $ (24 ) $ (2 ) $ 16 $ 20 $ 16 $ 2 $ 2 Total rate-regulated revenues for reportable segments $ 1,408 $ 900 $ 976 $ 1,228 $ 575 $ 380 $ 273 Three Months Ended March 31, 2018 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 717 $ 403 $ 393 $ 610 $ 259 $ 191 $ 160 Small commercial & industrial 385 101 68 115 32 46 37 Large commercial & industrial 152 58 106 259 190 23 46 Public authorities & electric railroads 14 8 7 14 7 4 3 Other (a) 230 62 78 156 49 41 66 Total rate-regulated electric revenues (b) $ 1,498 $ 632 $ 652 $ 1,154 $ 537 $ 305 $ 312 Rate-regulated natural gas revenues Residential $ — $ 161 $ 224 $ 47 $ — $ 47 $ — Small commercial & industrial — 62 34 18 — 18 — Large commercial & industrial — 1 47 4 — 4 — Transportation — 6 — 5 — 5 — Other (c) — 2 27 4 — 4 — Total rate-regulated natural gas revenues (d) $ — $ 232 $ 332 $ 78 $ — $ 78 $ — Total rate-regulated revenues from contracts with customers $ 1,498 $ 864 $ 984 $ 1,232 $ 537 $ 383 $ 312 Other revenues Revenues from alternative revenue programs $ 5 $ (1 ) $ (13 ) $ 18 $ 19 $ 1 $ (2 ) Other rate-regulated electric revenues (e) 9 3 4 1 1 — — Other rate-regulated natural gas revenues (e) — — 2 — — — — Total other revenues $ 14 $ 2 $ (7 ) $ 19 $ 20 $ 1 $ (2 ) Total rate-regulated revenues for reportable segments $ 1,512 $ 866 $ 977 $ 1,251 $ 557 $ 384 $ 310 __________ (a) Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue. (b) Includes operating revenues from affiliates of $4 million , $1 million , $2 million , $3 million , $2 million , $2 million and $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2019 and $14 million , $2 million , $2 million , $4 million $2 million , $2 million and 1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2018 . (c) Includes revenues from off-system natural gas sales. (d) Includes operating revenues from affiliates of less than $1 million and $4 million at PECO and BGE, respectively, in 2019 and 2018 . (e) Includes late payment charge revenues.

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Accounting, Policy [Policy Text Block]	Basis of Presentation (All Registrants) Each of the Registrant’s Consolidated Financial Statements includes the accounts of its subsidiaries. All intercompany transactions have been eliminated. 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. PHI also has a business services subsidiary, PHISCO, which provides a variety of support services at cost, including legal, accounting, engineering, customer operations, distribution and transmission planning, asset management, system operations, and power procurement, to PHI operating companies. The costs of BSC and PHISCO are directly charged or allocated to the applicable subsidiaries. The results of Exelon’s corporate operations are presented as “Other” within the consolidated financial statements and include intercompany eliminations unless otherwise disclosed. The accompanying consolidated financial statements as of March 31, 2019 and 2018 and for the three months then ended are unaudited but, in the opinion of the management of each Registrant include all adjustments that are considered necessary for a fair statement of the Registrants’ respective financial statements in accordance with GAAP. All adjustments are of a normal, recurring nature, except as otherwise disclosed. The December 31, 2018 Consolidated Balance Sheets were derived from audited financial statements. Financial results for interim periods are not necessarily indicative of results that may be expected for any other interim period or for the fiscal year ending December 31, 2019 . These Combined Notes to Consolidated Financial Statements have been prepared pursuant to the rules and regulations of the SEC for Quarterly Reports on Form 10-Q. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations.
New Accounting Pronouncements, Policy [Policy Text Block]	New Accounting Standards (All Registrants) New Accounting Standards Adopted in 2019: In 2019, the Registrants have adopted the following new authoritative accounting guidance issued by the FASB. Leases. The Registrants applied the new guidance with the following transition practical expedients: • a "package of three" expedients that must be taken together and allow entities to (1) not reassess whether existing contracts contain leases, (2) carryforward the existing lease classification, and (3) not reassess initial direct costs associated with existing leases, • an implementation expedient which allows the requirements of the standard in the period of adoption with no restatement of prior periods, and • a land easement expedient which allows entities to not evaluate land easements under the new standard at adoption if they were not previously accounted for as leases. The standard materially impacted the Registrants' Consolidated Balance Sheets but did not have a material impact in the Registrants' Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows and Consolidated Statements of Changes in Shareholders' Equity. The most significant impact was the recognition of the ROU assets and lease liabilities for operating leases. The operating ROU assets and lease liabilities recognized upon adoption are materially consistent with the balances presented in the Combined Notes to the Consolidated Financial Statements. See Note 5 - Leases for additional information. See Note 1 — Significant Accounting Policies of the Exelon 2018 Form 10-K for additional information on new accounting standards issued and adopted as of January 1, 2019. New Accounting Standards Issued and Not Yet Adopted as of March 31, 2019 : The following new authoritative accounting guidance issued by the FASB has not yet been adopted and reflected by the Registrants in their consolidated financial statements as of March 31, 2019 . Unless otherwise indicated, the Registrants are currently assessing the impacts such guidance may have (which could be material) in 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 where applicable. The Registrants have assessed other FASB issuances of new standards which are not listed below given the current expectation that such standards will not significantly impact the Registrants' financial reporting. Goodwill Impairment (Issued January 2017). Simplifies the accounting for goodwill impairment by removing Step 2 of the current test, which requires calculation of a hypothetical purchase price allocation. Under the revised guidance, goodwill impairment will be measured as the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill (currently Step 1 of the two-step impairment test). Entities will continue to have the option to perform a qualitative assessment to determine if a quantitative impairment test is necessary. Exelon, Generation, ComEd, PHI and DPL have goodwill as of March 31, 2019 . This updated guidance is not currently expected to impact the Registrants’ financial reporting. The standard is effective January 1, 2020, with early adoption permitted, and must be applied on a prospective basis. Impairment of Financial Instruments (Issued June 2016). Provides for a new Current Expected Credit Loss (CECL) impairment model for specified financial instruments including loans, trade receivables, debt securities classified as held-to-maturity investments and net investments in leases recognized by a lessor. Under the new guidance, on initial recognition and at each reporting period, an entity is required to recognize an allowance that reflects the entity’s current estimate of credit losses expected to be incurred over the life of the financial instrument. The standard does not make changes to the existing impairment models for non-financial assets such as fixed assets, intangibles and goodwill. The standard will be effective January 1, 2020 (with early adoption as of January 1, 2019 permitted) and requires a modified retrospective transition approach through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Registrants are currently assessing the impacts of this standard.
Revenues [Policy Text Block]	The Registrants recognize revenue from contracts with customers to depict the transfer of goods or services to customers at an amount that the entities expect to be entitled to in exchange for those goods or services. Generation’s primary sources of revenue include competitive sales of power, natural gas, and other energy-related products and services. The Utility Registrants’ primary sources of revenue include regulated electric and gas tariff sales, distribution and transmission services.
Fair Value of Financial Instruments, Policy [Policy Text Block]	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 (All Registrants). The Registrants’ cash equivalents include investments with original 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. NDT Fund Investments (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 and Fixed Income. 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 generally 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 which are based on quoted prices in active markets are categorized in Level 1. Certain equity securities have been categorized as Level 2 because they are based on evaluated prices that reflect observable market information, such as actual trade information or similar securities. 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 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 funds are valued using NAV as a practical expedient for fair value, which is primarily derived from the quoted prices in active markets on the underlying securities, and are not classified within the fair value hierarchy. These investments typically can be redeemed monthly with 30 or less days of notice and without further restrictions. Derivative instruments consisting primarily of futures and interest rate swaps to manage risk are recorded at fair value. Over the counter derivatives are valued daily based on quoted prices in active markets and trade in open markets and have been categorized as Level 1. Derivative instruments other than over the counter derivatives 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 loans 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. Managed funds are valued using NAV or its equivalent as a practical expedient, and therefore, are not classified within the fair value hierarchy. 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, and therefore, are not classified within the fair value hierarchy. 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. These valuation inputs are unobservable. As of March 31, 2019 , Exelon and Generation have outstanding commitments to invest in fixed income, middle market lending, private equity and real estate investments of approximately $127 million , $179 million , $301 million , and $268 million , respectively. These commitments will be funded by Generation’s existing NDT funds. Concentrations of Credit Risk. Generation evaluated its NDT portfolios for the existence of significant concentrations of credit risk as of March 31, 2019 . 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 March 31, 2019 , there were no significant concentrations (generally defined as greater than 10 percent) of risk in Generation's NDT assets. See Note 13 — Nuclear Decommissioning for additional information on the NDT fund investments. Rabbi Trust Investments (Exelon, Generation, PECO, BGE, PHI, and Pepco). 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 money market funds, mutual funds, fixed income securities 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. Money market funds and mutual funds are publicly quoted and have been categorized as Level 1 given the clear observability of the prices. The fair values of fixed income 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 life insurance policies are valued using the cash surrender value of the policies, net of loans against those policies, which is provided by a third-party. Certain life insurance policies, which consist primarily of mutual funds that are priced based on observable market data, have been categorized as Level 2 because the life insurance policies can be liquidated at the reporting date for the value of the underlying assets. Life insurance policies that are valued using unobservable inputs have been categorized as Level 3. Mark-to-Market Derivatives (Exelon, Generation, ComEd, PHI and DPL). Derivative contracts are traded in both exchange-based and non-exchange-based markets. Exchange-based derivatives that are valued using unadjusted quoted prices in active markets are categorized in Level 1 in the fair value hierarchy. Certain derivatives’ pricing is verified using indicative price quotations available through brokers or over-the-counter, on-line exchanges and are categorized in Level 2. These price quotations reflect the average of the bid-ask, mid-point prices and are obtained from sources that the Registrants believe provide the most liquid market for the commodity. The price quotations are reviewed and corroborated to ensure the prices are observable and representative of an orderly transaction between market participants. This includes consideration of actual transaction volumes, market delivery points, bid-ask spreads and contract duration. The remainder of derivative contracts are valued using the Black model, an industry standard option valuation model. The Black model takes into account inputs such as contract terms, including maturity, and market parameters, including assumptions of the future prices of energy, interest rates, volatility, credit worthiness and credit spread. For derivatives that trade in liquid markets, such as generic forwards, swaps and options, model inputs are generally observable. Such instruments are categorized in Level 2. The Registrants’ derivatives are predominantly at liquid trading points. For derivatives that trade in less liquid markets with limited pricing information model inputs generally would include both observable and unobservable inputs. These valuations may include an estimated basis adjustment from an illiquid trading point to a liquid trading point for which active price quotations are available. Such instruments are categorized in Level 3. Exelon may utilize fixed-to-floating interest rate swaps as a means to achieve its targeted level of variable-rate debt as a percent of total debt. In addition, the Registrants may utilize interest rate derivatives to lock in interest rate levels in anticipation of future financings. Exelon determines the current fair value by calculating the net present value of expected payments and receipts under the swap agreement, based on and discounted by the market's expectation of future interest rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk and other market parameters. As these inputs are based on observable data and valuations of similar instruments, the interest rate swaps are categorized in Level 2 in the fair value hierarchy. See Note 10 — Derivative Financial Instruments for additional information on mark-to-market derivatives. Deferred Compensation Obligations (All Registrants). The Registrants’ deferred compensation plans allow participants to defer certain cash compensation into a notional investment account. The Registrants include such plans in other current and noncurrent liabilities in their Consolidated Balance Sheets. The value of the Registrants’ deferred compensation obligations is based on the market value of the participants’ notional investment accounts. The underlying notional investments are comprised primarily of equities, mutual funds, commingled funds, and fixed income securities which are based on directly and indirectly observable market prices. Since the deferred compensation obligations themselves are not exchanged in an active market, they are categorized as Level 2 in the fair value hierarchy. The value of certain employment agreement obligations (which are included with the Deferred Compensation Obligation in the tables above) are based on a known and certain stream of payments to be made over time and are categorized as Level 2 within the fair value hierarchy. Additional Information Regarding Level 3 Fair Value Measurements (Exelon, Generation, ComEd, PHI, Pepco, DPL and ACE) NDT Fund Investments (Exelon and Generation). For middle market lending and certain corporate debt securities investments, the fair value is determined using a combination of valuation models including cost models, market models and income models. The valuation estimates are based on discounting the forecasted cash flows, market-based comparable data, credit and liquidity factors, as well as other factors that may impact value. Significant judgment is required in the application of discounts or premiums applied for factors such as size, marketability, credit risk and relative performance. Because Generation relies on third-party fund managers to develop the quantitative unobservable inputs without adjustment for the valuations of its Level 3 investments, quantitative information about significant unobservable inputs used in valuing these investments is not reasonably available to Generation. This includes information regarding the sensitivity of the fair values to changes in the unobservable inputs. Therefore, Generation has not disclosed such inputs. Rabbi Trust Investments - Life insurance contracts (Exelon, PHI, and Pepco). For life insurance policies categorized as Level 3, the fair value is determined based on the cash surrender value of the policy, which contains unobservable inputs and assumptions. Because Exelon relies on its third-party insurance provider to develop the inputs without adjustment for the valuations of its Level 3 investments, quantitative information about significant unobservable inputs used in valuing these investments is not reasonably available to Exelon. Therefore, Exelon has not disclosed such inputs. Mark-to-Market Derivatives (Exelon, Generation and ComEd). For valuations that include both observable and unobservable inputs, if the unobservable input is determined to be significant to the overall inputs, the entire valuation is categorized in Level 3. This includes derivatives valued using indicative price quotations whose contract tenure extends into unobservable periods. In instances where observable data is unavailable, consideration is given to the assumptions that market participants would use in valuing the asset or liability. This includes assumptions about market risks such as liquidity, volatility and contract duration. Such instruments are categorized in Level 3 as the model inputs generally are not observable. Forward price curves for the power market utilized by the front office to manage the portfolio, are reviewed and verified by the middle office, and used for financial reporting by the back office. The Registrants consider credit and nonperformance risk in the valuation of derivative contracts categorized in Level 2 and 3, including both historical and current market data in its assessment of credit and nonperformance risk by counterparty. Due to master netting agreements and collateral posting requirements, the impacts of credit and nonperformance risk were not material to the financial statements.
Lessee, Leases [Policy Text Block]	Leases (All Registrants) The Registrants recognize a ROU asset and lease liability for operating leases with a term of greater than one year. The ROU asset is included in Other deferred debits and other assets and the lease liability is included in Other current liabilities and Other deferred credits and other liabilities on the Consolidated Balance Sheets. The ROU asset is measured as the sum of (1) the present value of all remaining fixed and in-substance fixed payments using each Registrant’s incremental borrowing rate, (2) any lease payments made at or before the commencement date (less any lease incentives received) and (3) any initial direct costs incurred. The lease liability is measured the same as the ROU asset, but excludes any payments made before the commencement date and initial direct costs incurred. Lease terms include options to extend or terminate the lease if it is reasonably certain they will be exercised. The Registrants include non-lease components, which are service-related costs that are not integral to the use of the asset, in the measurement of the ROU asset and lease liability. Expense for operating leases and leases with a term of one year or less is recognized on a straight-line basis over the term of the lease, unless another systematic and rational basis is more representative of the derivation of benefit from use of the leased property. Variable lease payments are recognized in the period in which the related obligation is incurred and consist primarily of payments for purchases of electricity under contracted generation and are based on the electricity produced by those generating assets. Operating lease expense and variable lease payments are recorded to Purchased power and fuel expense for contracted generation or Operating and maintenance expense for all other lease agreements on the Registrants’ Statements of Operations and Comprehensive Income. Income from operating leases, including subleases, is recognized on a straight-line basis over the term of the lease, unless another systematic and rational basis is more representative of the pattern in which income is earned over the term of the lease. Variable lease payments are recognized in the period in which the related obligation is performed and consist primarily of payments received from sales of electricity under contracted generation and are based on the electricity produced by those generating assets. Operating lease income and variable lease payments are recorded to Operating revenues on the Registrants’ Statements of Operations and Comprehensive Income. The Registrants’ operating leases consist primarily of contracted generation, real estate including office buildings, and vehicles and equipment. The Registrants generally account for contracted generation in which the generating asset is not renewable as a lease if the customer has dispatch rights and obtains substantially all of the economic benefits. For new agreements entered after January 1, 2019, the Registrants will generally not account for contracted generation in which the generating asset is renewable as a lease if the customer does not design the generating asset. The Registrants account for land right arrangements that provide for exclusive use as leases while shared use land arrangements are generally not leases. The Registrants do not account for secondary use pole attachments as leases. See Note 5 — Leases for additional information.

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	3 Months Ended
	Mar. 31, 2019
Variable Interest Entity [Abstract]
Schedule of Variable Interest Entities	The carrying amounts and classification of the consolidated VIEs’ assets and liabilities included in the Registrants' consolidated financial statements at March 31, 2019 and December 31, 2018 are as follows: March 31, 2019 December 31, 2018 Exelon (a) Generation PHI (a) ACE Exelon (a) Generation PHI (a) ACE Current assets $ 645 $ 639 $ 6 $ 3 $ 938 $ 931 $ 7 $ 4 Noncurrent assets 9,235 9,210 25 19 9,071 9,045 26 19 Total assets $ 9,880 $ 9,849 $ 31 $ 22 $ 10,009 $ 9,976 $ 33 $ 23 Current liabilities $ 748 $ 725 $ 23 $ 19 $ 274 $ 252 $ 22 $ 19 Noncurrent liabilities 2,831 2,790 41 35 3,280 3,233 47 40 Total liabilities $ 3,579 $ 3,515 $ 64 $ 54 $ 3,554 $ 3,485 $ 69 $ 59 _________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. March 31, 2019 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 601 $ 463 $ 1,064 Total liabilities (a) 42 223 265 Exelon's ownership interest in VIE (a) — 214 214 Other ownership interests in VIE (a) 559 26 585 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 214 214 Contract intangible asset 7 — 7 December 31, 2018 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 597 $ 472 $ 1,069 Total liabilities (a) 37 222 259 Exelon's ownership interest in VIE (a) — 223 223 Other ownership interests in VIE (a) 560 27 587 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 223 223 Contract intangible asset 7 — 7 _________ (a) These items represent amounts in the unconsolidated VIE balance sheets, not in Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated 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 March 31, 2019 and December 31, 2018 , these assets and liabilities primarily consisted of the following: March 31, 2019 December 31, 2018 Exelon (a) Generation PHI (a) ACE Exelon (a) Generation PHI (a) ACE Cash and cash equivalents $ 125 $ 125 $ — $ — $ 414 $ 414 $ — $ — Restricted cash and cash equivalents 58 55 3 3 66 62 4 4 Accounts receivable, net Customer 152 152 — — 146 146 — — Other 23 23 — — 23 23 — — Inventory, net Materials and supplies 213 213 — — 212 212 — — Other current assets 51 48 3 — 52 49 3 — Total current assets 622 616 6 3 913 906 7 4 Property, plant and equipment, net 6,147 6,147 — — 6,145 6,145 — — NDT funds 2,520 2,520 — — 2,351 2,351 — — Other noncurrent assets 257 232 25 19 258 232 26 19 Total noncurrent assets 8,924 8,899 25 19 8,754 8,728 26 19 Total assets $ 9,546 $ 9,515 $ 31 $ 22 $ 9,667 $ 9,634 $ 33 $ 23 Long-term debt due within one year $ 567 $ 545 $ 22 $ 19 $ 87 $ 66 $ 21 $ 18 Accounts payable 120 120 — — 96 96 — — Accrued expenses 42 41 1 — 72 72 1 1 Unamortized energy contract liabilities 13 13 — — 15 15 — — Other current liabilities 6 6 — — 3 3 — — Total current liabilities 748 725 23 19 273 252 22 19 Long-term debt 565 524 41 35 1,072 1,025 47 40 Asset retirement obligations 2,190 2,190 — — 2,160 2,160 — — Unamortized energy contract liabilities — — — — 1 1 — — Other noncurrent liabilities 69 69 — — 42 42 — — Total noncurrent liabilities 2,824 2,783 41 35 3,275 3,228 47 40 Total liabilities $ 3,572 $ 3,508 $ 64 $ 54 $ 3,548 $ 3,480 $ 69 $ 59 _________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Contract with Customer, Asset and Liability [Table Text Block]	The following table provides a rollforward of the contract assets and liabilities reflected in Exelon's and Generation's Consolidated Balance Sheets from January 1, 2018 to March 31, 2019 : Contract Assets Contract Liabilities Exelon Generation Exelon Generation Balance as of January 1, 2018 $ 283 $ 283 $ 35 $ 35 Increases as a result of changes in the estimate of the stage of completion 50 50 — — Increases as a result of additional cash received or due — — 179 465 Amounts reclassified into receivables or recognized into revenues (146 ) (146 ) (187 ) (458 ) Balance at December 31, 2018 187 187 27 42 Increases as a result of changes in the estimate of the stage of completion 26 26 — — Increases as a result of additional cash received or due — — 21 63 Amounts reclassified into receivables or recognized into revenues (26 ) (26 ) (23 ) (66 ) Balance at March 31, 2019 $ 187 $ 187 $ 25 $ 39
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]	2019 2020 2021 2022 2023 and thereafter Total Exelon $ 393 $ 273 $ 112 $ 50 $ 142 $ 970 Generation 493 331 126 50 142 1,142

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Components of Lease Cost [Table Text Block]	ROU assets obtained in exchange for lease obligations for the three months ended March 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating leases $ 20 $ 9 $ — $ — $ — $ 11 $ 4 $ 4 $ 3 The weighted average remaining lease terms, in years, and discount rates for operating leases as of March 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Remaining lease term 10.0 10.7 2.9 4.4 5.6 9.4 9.9 9.8 5.3 Discount rate 4.6 % 4.8 % 3.3 % 3.4 % 3.6 % 4.1 % 3.9 % 3.9 % 3.5 % The components of lease costs for the three months ended March 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating lease costs $ 68 $ 46 $ 1 $ — $ 8 $ 10 $ 3 $ 3 $ 1 Variable lease costs 73 68 — — — 2 — 1 — Short-term lease costs 9 8 — — — — — — — Total lease costs (a) $ 150 $ 122 $ 1 $ — $ 8 $ 12 $ 3 $ 4 $ 1 __________ (a) Excludes $3 million , $2 million , $1 million and $1 million of sublease income recorded at Exelon, Generation, PHI and DPL.
Supplemental Balance Sheet Information Related to Lessee Right-of-Use Assets and Lease Liabilities [Table Text Block]	The following table provides additional information regarding the presentation of operating lease ROU assets and lease liabilities within the Registrants’ Consolidated Balance Sheets as of March 31, 2019 : Exelon (a) Generation (a) ComEd PECO BGE PHI Pepco DPL ACE Operating lease ROU assets Other deferred debits and other assets $ 1,465 $ 1,027 $ 5 $ 2 $ 97 $ 314 $ 67 $ 75 $ 26 Operating lease liabilities Other current liabilities 249 173 3 1 31 36 8 11 6 Other deferred credits and other liabilities 1,395 1,023 4 1 66 284 60 72 20 Total operating lease liabilities $ 1,644 $ 1,196 $ 7 $ 2 $ 97 $ 320 $ 68 $ 83 $ 26 __________ (a) Exelon's and Generation's operating ROU assets and lease liabilities include $631 million and $778 million , respectively, related to contracted generation.
Lessee, Operating Lease, Liability, Maturity [Table Text Block]	Future minimum lease payments for operating leases as of March 31, 2019 were as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2019 $ 214 $ 154 $ 2 $ 1 $ 19 $ 33 $ 8 $ 7 $ 5 2020 289 202 2 1 34 43 9 12 5 2021 244 162 2 — 32 42 9 11 5 2022 174 112 1 — 16 40 8 11 4 2023 139 99 — — — 39 8 10 3 Remaining years 1,052 840 — — 18 194 42 52 7 Total 2,112 1,569 7 2 119 391 84 103 29 Interest 468 373 — — 22 71 16 20 3 Total operating lease liabilities $ 1,644 $ 1,196 $ 7 $ 2 $ 97 $ 320 $ 68 $ 83 $ 26
Schedule of Future Minimum Lease Payments for Operating Leases [Table Text Block]	Future minimum lease payments for operating leases under the prior lease accounting guidance as of December 31, 2018 were as follows: Exelon (a)(b) Generation (a)(b) ComEd (a)(c) PECO (a)(c) BGE (a)(c)(d)(e) PHI (a) Pepco (a) DPL (a)(c) ACE (a) 2019 $ 140 $ 33 $ 7 $ 5 $ 35 $ 48 $ 11 $ 14 $ 7 2020 149 46 5 5 35 46 10 13 6 2021 143 46 4 5 33 43 9 12 5 2022 126 47 4 5 18 42 8 12 5 2023 97 46 3 5 3 39 8 10 4 Remaining years 723 545 — — 19 159 40 35 5 Total minimum future lease payments $ 1,378 $ 763 $ 23 $ 25 $ 143 $ 377 $ 86 $ 96 $ 32 __________ (a) Includes amounts related to shared use land arrangements. (b) Excludes Generation’s contingent operating lease payments associated with contracted generation. (c) Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO, BGE and DPL have excluded these payments from the remaining years as such amounts would not be meaningful. ComEd's, PECO’s, BGE’s and DPL's average annual obligation for these arrangements, included in each of the years 2019 - 2023, was $3 million , $5 million , $1 million and $1 million respectively. Also includes amounts related to shared use land arrangements. (d) Includes all future lease payments on a 99-year real estate lease that expires in 2106. (e) The BGE column above includes minimum future lease payments associated with a 6-year lease for the Baltimore City conduit system that became effective during the fourth quarter of 2016. BGE's total commitments under the lease agreement are $26 million , $28 million , $28 million and $14 million related to years 2019 - 2022, respectively.
Schedule of Supplemental Cash Flow Information Related to Leases [Table Text Block]	Cash paid for amounts included in the measurement of lease liabilities for the three months ended March 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating cash flows from operating leases $ 78 $ 52 $ 1 $ — $ 14 $ 8 $ 2 $ 2 $ 1
Components of Operating Lease Income [Table Text Block]	The components of lease income for the three months ended March 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating lease income $ 4 $ 3 $ — $ — $ — $ 1 $ — $ 1 $ — Variable lease income $ 52 $ 52 $ — $ — $ — $ — $ — $ — $ —
Lessor, Operating Lease, Payments to be Received, Maturity [Table Text Block]	Future minimum lease payments to be recovered under operating leases as of March 31, 2019 were as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2019 $ 47 $ 43 $ — $ — $ — $ 4 $ — $ 3 $ — 2020 51 46 — — — 4 — 3 — 2021 50 45 — — — 4 — 3 — 2022 50 45 — — — 4 — 3 — 2023 49 45 — — — 4 — 3 — Remaining years 315 271 1 3 1 39 1 38 — Total $ 562 $ 495 $ 1 $ 3 $ 1 $ 59 $ 1 $ 53 $ —

Regulatory Matters (Tables)

Regulatory Matters (Tables)	3 Months Ended
	Mar. 31, 2019
Regulated Operations [Abstract]
Public Utilities General Disclosures [Table Text Block]	The following table presents authorized amounts capitalized for ratemaking purposes related to earnings on shareholders’ investment that are not recognized for financial reporting purposes in Exelon's and the Utility Registrant's Consolidated Balance Sheets. These amounts will be recognized as revenues in the related Consolidated Statements of Operations and Comprehensive Income in the periods they are billable to our customers. Exelon ComEd (a) PECO BGE (b) PHI Pepco (c) DPL (c) ACE March 31, 2019 $ 64 $ 7 $ — $ 49 $ 8 $ 5 $ 3 $ — December 31, 2018 $ 65 $ 8 $ — $ 49 $ 8 $ 5 $ 3 $ — _________ (a) Reflects ComEd's unrecognized equity returns earned for ratemaking purposes on its electric distribution formula rate regulatory assets. (b) BGE's authorized amounts capitalized for ratemaking purposes primarily relate to earnings on shareholders' investment on its AMI programs. (c) Pepco's and DPL's authorized amounts capitalized for ratemaking purposes relate to earnings on shareholders' investment on their respective AMI Programs and Energy Efficiency and Demand Response Programs. The earnings on energy efficiency are on Pepco DC and DPL DE programs only.

Early Plant Retirements (Tables

Early Plant Retirements (Tables)	3 Months Ended
	Mar. 31, 2019
Property, Plant and Equipment [Abstract]
Schedule of Other Operating Cost and Expense, by Component [Table Text Block]	Three Months Ended Income statement expense (pre-tax) 2019 2018 Depreciation and amortization (a) Accelerated depreciation (b) $ 74 $ 137 Accelerated nuclear fuel amortization 5 15 Operating and maintenance (c) (83 ) 26 Total $ (4 ) $ 178 _________ (a) Reflects incremental accelerated depreciation and amortization for TMI for the three months ended March 31, 2019 . Reflects incremental accelerated depreciation for TMI and Oyster Creek for the three months ended March 31, 2018 . The Oyster Creek amounts are from February 2, 2018 through March 31, 2018. (b) Reflects incremental accelerated depreciation of plant assets, including any ARC. (c) In 2019, primarily reflects decrease to estimated decommissioning costs for TMI. See Note 13 — Nuclear Decommissioning for additional information on the first quarter 2019 TMI ARO update. In 2018, primarily reflects materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments.
Implications of Potential Early Plant Retirement on Balance Sheet [Table Text Block]	The following table provides the balance sheet amounts as of March 31, 2019 for Exelon's and Generation’s significant assets and liabilities associated with the Mystic Units 8 and 9 and Everett Marine Terminal assets that would potentially be impacted by a decision to permanently cease generation operations in the absence of long-term market rule changes. March 31, 2019 Asset Balances Materials and supplies inventory $ 30 Fuel inventory 22 Completed plant, net 900 Construction work in progress 2 Liability Balances Asset retirement obligation (1 )

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
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 March 31, 2019 and December 31, 2018 : Exelon March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 1,254 $ — $ 1,254 $ — $ 1,254 Long-term debt (including amounts due within one year) (a) 35,468 — 35,066 2,188 37,254 Long-term debt to financing trusts (b) 390 — — 411 411 SNF obligation 1,178 — 989 — 989 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 714 $ — $ 714 $ — $ 714 Long-term debt (including amounts due within one year) (a) 35,424 — 33,711 2,158 35,869 Long-term debt to financing trusts (b) 390 — — 400 400 SNF obligation 1,171 — 949 — 949 Generation March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 8,747 $ — $ 7,641 $ 1,443 $ 9,084 SNF obligation 1,178 — 989 — 989 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 8,793 $ — $ 7,467 $ 1,443 $ 8,910 SNF obligation 1,171 — 949 — 949 ComEd March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 322 $ — $ 322 $ — $ 322 Long-term debt (including amounts due within one year) (a) 8,194 — 8,855 — 8,855 Long-term debt to financing trusts (b) 205 — — 215 215 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 8,101 $ — $ 8,390 $ — $ 8,390 Long-term debt to financing trusts (b) 205 — — 209 209 PECO March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 3,084 $ — $ 3,295 $ 50 $ 3,345 Long-term debt to financing trusts (b) 184 — — 196 196 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 3,084 $ — $ 3,157 $ 50 $ 3,207 Long-term debt to financing trusts (b) 184 — — 191 191 BGE March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 106 $ — $ 106 $ — $ 106 Long-term debt (including amounts due within one year) (a) 2,876 — 3,051 — 3,051 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 35 $ — $ 35 $ — $ 35 Long-term debt (including amounts due within one year) (a) 2,876 — 2,950 — 2,950 PHI March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 326 $ — $ 326 $ — $ 326 Long-term debt (including amounts due within one year) (a) 6,244 — 5,608 695 6,303 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 179 $ — $ 179 $ — $ 179 Long-term debt (including amounts due within one year) (a) 6,259 — 5,436 665 6,101 Pepco March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 105 $ — $ 105 $ — $ 105 Long-term debt (including amounts due within one year) (a) 2,720 — 3,000 208 3,208 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 40 $ — $ 40 $ — $ 40 Long-term debt (including amounts due within one year) (a) 2,719 — 2,901 196 3,097 DPL March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 5 $ — $ 5 $ — $ 5 Long-term debt (including amounts due within one year) (a) 1,495 — 1,345 204 1,549 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 1,494 $ — $ 1,303 $ 193 $ 1,496 ACE March 31, 2019 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 216 $ — $ 216 $ — $ 216 Long-term debt (including amounts due within one year) (a) 1,184 — 1,004 283 1,287 December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 139 $ — $ 139 $ — $ 139 Long-term debt (including amounts due within one year) (a) 1,188 — 987 275 1,262 _________ (a) Includes unamortized debt issuance costs which are not fair valued of $216 million , $49 million , $67 million , $22 million , $18 million , $14 million , $33 million , $12 million and $6 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of March 31, 2019 . Includes unamortized debt issuance costs which are not fair valued of $216 million , $51 million , $63 million , $23 million , $18 million , $14 million , $34 million , $12 million and $7 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of December 31, 2018 . (b) Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of March 31, 2019 . Includes unamortized debt issuance costs which are not fair valued of less than $1 million and $1 million for Exelon and ComEd, respectively, as of December 31, 2018 .
Assets and liabilities measured and recorded at fair value on recurring basis	The following tables present assets and liabilities measured and recorded at fair value in Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of March 31, 2019 and December 31, 2018 : Generation Exelon As of March 31, 2019 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Assets Cash equivalents (a) $ 370 $ — $ — $ — $ 370 $ 817 $ — $ — $ — $ 817 NDT fund investments Cash equivalents (b) 369 74 — — 443 369 74 — — 443 Equities 3,060 1,753 1 1,545 6,359 3,060 1,753 1 1,545 6,359 Fixed income Corporate debt — 1,545 236 1 1,782 — 1,545 236 1 1,782 U.S. Treasury and agencies 2,033 112 — — 2,145 2,033 112 — — 2,145 Foreign governments — 43 — — 43 — 43 — — 43 State and municipal debt — 110 — — 110 — 110 — — 110 Other (c) — 26 — 935 961 — 26 — 935 961 Fixed income subtotal 2,033 1,836 236 936 5,041 2,033 1,836 236 936 5,041 Middle market lending — — 303 406 709 — — 303 406 709 Private equity — — — 352 352 — — — 352 352 Real estate — — — 535 535 — — — 535 535 NDT fund investments subtotal (d) 5,462 3,663 540 3,774 13,439 5,462 3,663 540 3,774 13,439 Rabbi trust investments Cash equivalents 4 — — — 4 47 — — — 47 Mutual funds 25 — — — 25 74 — — — 74 Fixed income — — — — — — 14 — — 14 Life insurance contracts — 23 — — 23 — 71 39 — 110 Rabbi trust investments subtotal (e) 29 23 — — 52 121 85 39 — 245 Commodity derivative assets Economic hedges 273 2,164 1,442 — 3,879 273 2,164 1,442 — 3,879 Proprietary trading — 74 104 — 178 — 74 104 — 178 Effect of netting and allocation of collateral (f)(g) (294 ) (1,836 ) (820 ) — (2,950 ) (294 ) (1,836 ) (820 ) — (2,950 ) Commodity derivative assets subtotal (21 ) 402 726 — 1,107 (21 ) 402 726 — 1,107 Interest rate and foreign currency derivative assets Economic hedges — 4 — — 4 — 4 — — 4 Effect of netting and allocation of collateral — (5 ) — — (5 ) — (5 ) — — (5 ) Interest rate and foreign currency derivative assets subtotal — (1 ) — — (1 ) — (1 ) — — (1 ) Other investments — — 42 — 42 — — 42 — 42 Total assets 5,840 4,087 1,308 3,774 15,009 6,379 4,149 1,347 3,774 15,649 Generation Exelon As of March 31, 2019 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Liabilities Commodity derivative liabilities Economic hedges (350 ) (2,339 ) (1,164 ) — (3,853 ) (350 ) (2,339 ) (1,404 ) — (4,093 ) Proprietary trading — (79 ) (40 ) — (119 ) — (79 ) (40 ) — (119 ) Effect of netting and allocation of collateral (f)(g) 346 2,119 977 — 3,442 346 2,119 977 — 3,442 (4 ) (299 ) (227 ) — (530 ) (4 ) (299 ) (467 ) — (770 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — — — — — — (2 ) — — (2 ) Economic hedges — (12 ) — — (12 ) — (12 ) — — (12 ) Effect of netting and allocation of collateral — 5 — — 5 — 5 — — 5 Interest rate and foreign currency derivative liabilities subtotal — (7 ) — — (7 ) — (9 ) — — (9 ) Deferred compensation obligation — (36 ) — — (36 ) — (140 ) — — (140 ) Total liabilities (4 ) (342 ) (227 ) — (573 ) (4 ) (448 ) (467 ) — (919 ) Total net assets $ 5,836 $ 3,745 $ 1,081 $ 3,774 $ 14,436 $ 6,375 $ 3,701 $ 880 $ 3,774 $ 14,730 Generation Exelon As of December 31, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Assets Cash equivalents (a) $ 581 $ — $ — $ — $ 581 $ 1,243 $ — $ — $ — $ 1,243 NDT fund investments Cash equivalents (b) 252 86 — — 338 252 86 — — 338 Equities 2,918 1,591 — 1,381 5,890 2,918 1,591 — 1,381 5,890 Fixed income Corporate debt — 1,593 230 — 1,823 — 1,593 230 — 1,823 U.S. Treasury and agencies 2,081 99 — — 2,180 2,081 99 — — 2,180 Foreign governments — 50 — — 50 — 50 — — 50 State and municipal debt — 149 — — 149 — 149 — — 149 Other (c) — 30 — 846 876 — 30 — 846 876 Fixed income subtotal 2,081 1,921 230 846 5,078 2,081 1,921 230 846 5,078 Middle market lending — — 313 367 680 — — 313 367 680 Private equity — — — 329 329 — — — 329 329 Real estate — — — 510 510 — — — 510 510 NDT fund investments subtotal (d) 5,251 3,598 543 3,433 12,825 5,251 3,598 543 3,433 12,825 Rabbi trust investments Cash equivalents 5 — — — 5 48 — — — 48 Mutual funds 24 — — — 24 72 — — — 72 Fixed income — — — — — — 15 — — 15 Life insurance contracts — 22 — — 22 — 70 38 — 108 Rabbi trust investments subtotal (e) 29 22 — — 51 120 85 38 — 243 Commodity derivative assets Economic hedges 541 2,760 1,470 — 4,771 541 2,760 1,470 — 4,771 Proprietary trading — 69 77 — 146 — 69 77 — 146 Effect of netting and allocation of collateral (f)(g) (582 ) (2,357 ) (732 ) — (3,671 ) (582 ) (2,357 ) (732 ) — (3,671 ) Commodity derivative assets subtotal (41 ) 472 815 — 1,246 (41 ) 472 815 — 1,246 Interest rate and foreign currency derivative assets Economic hedges — 13 — — 13 — 13 — — 13 Effect of netting and allocation of collateral — (3 ) — — (3 ) — (3 ) — — (3 ) Interest rate and foreign currency derivative assets subtotal — 10 — — 10 — 10 — — 10 Other investments — — 42 — 42 — — 42 — 42 Total assets 5,820 4,102 1,400 3,433 14,755 6,573 4,165 1,438 3,433 15,609 Generation Exelon As of December 31, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Liabilities Commodity derivative liabilities Economic hedges (642 ) (2,963 ) (1,027 ) — (4,632 ) (642 ) (2,963 ) (1,276 ) — (4,881 ) Proprietary trading — (73 ) (21 ) — (94 ) — (73 ) (21 ) — (94 ) Effect of netting and allocation of collateral (f)(g) 639 2,581 808 — 4,028 639 2,581 808 — 4,028 Commodity derivative liabilities subtotal (3 ) (455 ) (240 ) — (698 ) (3 ) (455 ) (489 ) — (947 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — — — — — — (4 ) — — (4 ) Economic hedges — (6 ) — — (6 ) — (6 ) — — (6 ) Effect of netting and allocation of collateral — 3 — — 3 — 3 — — 3 Interest rate and foreign currency derivative liabilities subtotal — (3 ) — — (3 ) — (7 ) — — (7 ) Deferred compensation obligation — (35 ) — — (35 ) — (137 ) — — (137 ) Total liabilities (3 ) (493 ) (240 ) — (736 ) (3 ) (599 ) (489 ) — (1,091 ) Total net assets $ 5,817 $ 3,609 $ 1,160 $ 3,433 $ 14,019 $ 6,570 $ 3,566 $ 949 $ 3,433 $ 14,518 _________ (a) Generation excludes cash of $270 million and $283 million at March 31, 2019 and December 31, 2018 and restricted cash of $36 million and $39 million at March 31, 2019 and December 31, 2018 . Exelon excludes cash of $426 million and $458 million at March 31, 2019 and December 31, 2018 and restricted cash of $71 million and $80 million at March 31, 2019 and December 31, 2018 and includes long-term restricted cash of $211 million and $185 million at March 31, 2019 and December 31, 2018 , which is reported in Other deferred debits in the Consolidated Balance Sheets. (b) Includes $43 million and $50 million of cash received from outstanding repurchase agreements at March 31, 2019 and December 31, 2018 , respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below. (c) Includes derivative instruments of $7 million and $44 million , which have a total notional amount of $1,223 million and $1,432 million at March 31, 2019 and December 31, 2018 , 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 Exelon and Generation's exposure to credit or market loss. (d) Excludes net liabilities of $94 million and $130 million at March 31, 2019 and December 31, 2018 , 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) The amount of unrealized gains/(losses) at Generation totaled less than $1 million for the three months ended March 31, 2019 and March 31, 2018 , respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million for the three months ended March 31, 2019 and March 31, 2018 , respectively. (f) Collateral posted/(received) from counterparties totaled $52 million , $283 million and $157 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of March 31, 2019 . Collateral posted/(received) from counterparties, net of collateral paid to counterparties, totaled $57 million , $224 million and $76 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2018 . (g) Of the collateral posted/(received), $(33) million and $(94) million represents variation margin on the exchanges as of March 31, 2019 and December 31, 2018 , respectively. Exelon and Generation hold investments without readily determinable fair values with carrying amounts of $71 million as of March 31, 2019 . Changes were immaterial in fair value, cumulative adjustments and impairments for the three months ended March 31, 2019 . ComEd, PECO and BGE The following tables present assets and liabilities measured and recorded at fair value in ComEd's, PECO's and BGE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of March 31, 2019 and December 31, 2018 : ComEd PECO BGE As of March 31, 2019 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 194 $ — $ — $ 194 $ 16 $ — $ — $ 16 $ 3 $ — $ — $ 3 Rabbi trust investments Mutual funds — — — — 7 — — 7 6 — — 6 Life insurance contracts — — — — — 10 — 10 — — — — Rabbi trust investments subtotal (b) — — — — 7 10 — 17 6 — — 6 Total assets 194 — — 194 23 10 — 33 9 — — 9 Liabilities Deferred compensation obligation — (7 ) — (7 ) — (10 ) — (10 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (c) — — (240 ) (240 ) — — — — — — — — Total liabilities — (7 ) (240 ) (247 ) — (10 ) — (10 ) — (5 ) — (5 ) Total net assets (liabilities) $ 194 $ (7 ) $ (240 ) $ (53 ) $ 23 $ — $ — $ 23 $ 9 $ (5 ) $ — $ 4 ComEd PECO BGE As of December 31, 2018 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 209 $ — $ — $ 209 $ 111 $ — $ — $ 111 $ 4 $ — $ — $ 4 Rabbi trust investments Mutual funds — — — — 7 — — 7 6 — — 6 Life insurance contracts — — — — — 10 — 10 — — — — Rabbi trust investments subtotal (b) — — — — 7 10 — 17 6 — — 6 Total assets 209 — — 209 118 10 — 128 10 — — 10 Liabilities Deferred compensation obligation — (6 ) — (6 ) — (10 ) — (10 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (c) — — (249 ) (249 ) — — — — — — — — Total liabilities — (6 ) (249 ) (255 ) — (10 ) — (10 ) — (5 ) — (5 ) Total net assets (liabilities) $ 209 $ (6 ) $ (249 ) $ (46 ) $ 118 $ — $ — $ 118 $ 10 $ (5 ) $ — $ 5 _________ (a) ComEd excludes cash of $69 million and $93 million at March 31, 2019 and December 31, 2018 and restricted cash of $15 million and $28 million at March 31, 2019 and December 31, 2018 and includes long-term restricted cash of $193 million and $166 million at March 31, 2019 and December 31, 2018 , which is reported in Other deferred debits in the Consolidated Balance Sheets. PECO excludes cash of $31 million and $24 million at March 31, 2019 and December 31, 2018 . BGE excludes cash of $12 million and $7 million at March 31, 2019 and December 31, 2018 and restricted cash of $1 million and $2 million at March 31, 2019 and December 31, 2018 . (b) The amount of unrealized gains/(losses) at ComEd, PECO and BGE totaled less than $1 million for the three months ended March 31, 2019 and March 31, 2018 . (c) The Level 3 balance consists of the current and noncurrent liability of $27 million and $213 million , respectively, at March 31, 2019 , and $26 million and $223 million , respectively, at December 31, 2018 , related to floating-to-fixed energy swap contracts with unaffiliated suppliers. PHI, Pepco, DPL and ACE The following tables present assets and liabilities measured and recorded at fair value in PHI's, Pepco's, DPL's and ACE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of March 31, 2019 and December 31, 2018 : As of March 31, 2019 As of December 31, 2018 PHI Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 63 $ — $ — $ 63 $ 147 $ — $ — $ 147 Rabbi trust investments Cash equivalents 42 — — 42 42 — — 42 Mutual funds 14 — — 14 13 — — 13 Fixed income — 14 — 14 — 15 — 15 Life insurance contracts — 22 39 61 — 22 38 60 Rabbi trust investments subtotal (b) 56 36 39 131 55 37 38 130 Total assets 119 36 39 194 202 37 38 277 Liabilities Deferred compensation obligation — (20 ) — (20 ) — (21 ) — (21 ) Total liabilities — (20 ) — (20 ) — (21 ) — (21 ) Total net assets $ 119 $ 16 $ 39 $ 174 $ 202 $ 16 $ 38 $ 256 Pepco DPL ACE As of March 31, 2019 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 35 $ — $ — $ 35 $ 2 $ — $ — $ 2 $ 21 $ — $ — $ 21 Rabbi trust investments Cash equivalents 42 — — 42 — — — — — — — — Fixed income — 4 — 4 — — — — — — — — Life insurance contracts — 22 38 60 — — — — — — — — Rabbi trust investments subtotal (b) 42 26 38 106 — — — — — — — — Total assets 77 26 38 141 2 — — 2 21 — — 21 Liabilities Deferred compensation obligation — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total liabilities — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 77 $ 23 $ 38 $ 138 $ 2 $ (1 ) $ — $ 1 $ 21 $ — $ — $ 21 Pepco DPL ACE As of December 31, 2018 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 38 $ — $ — $ 38 $ 16 $ — $ — $ 16 $ 23 $ — $ — $ 23 Rabbi trust investments Cash equivalents 41 — — 41 — — — — — — — — Fixed income — 5 — 5 — — — — — — — — Life insurance contracts — 22 37 59 — — — — — — — — Rabbi trust investments subtotal (b) 41 27 37 105 — — — — — — — — Total assets 79 27 37 143 16 — — 16 23 — — 23 Liabilities Deferred compensation obligation — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total liabilities — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 79 $ 24 $ 37 $ 140 $ 16 $ (1 ) $ — $ 15 $ 23 $ — $ — $ 23 _________ (a) PHI excludes cash of $29 million and $39 million at March 31, 2019 and December 31, 2018 , respectively, and includes long-term restricted cash of $19 million at both March 31, 2019 and December 31, 2018 , which is reported in Other deferred debits in the Consolidated Balance Sheets. Pepco excludes cash of $11 million and $15 million at March 31, 2019 and December 31, 2018 , respectively. DPL excludes cash of $6 million and $8 million at March 31, 2019 and December 31, 2018 , respectively. ACE excludes cash of $7 million at both March 31, 2019 and December 31, 2018 , and includes long-term restricted cash of $19 million at both March 31, 2019 and December 31, 2018 , which is reported in Other deferred debits in the Consolidated Balance Sheets. (b) The amount of unrealized gains/(losses) at PHI totaled less than $1 million for both the three months ended March 31, 2019 and 2018 . The amount of unrealized gains/(losses) at Pepco totaled less than $1 million for both the three months ended March 31, 2019 and 2018
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis	The following tables present the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis during the three months ended March 31, 2019 and 2018 : Generation ComEd PHI Exelon Three Months Ended March 31, 2019 NDT Fund Investments Mark-to-Market Derivatives Other Investments Total Generation Mark-to-Market Derivatives Life Insurance Contracts (c) Eliminated in Consolidation Total Balance as of December 31, 2018 $ 543 $ 575 $ 42 $ 1,160 $ (249 ) $ 38 $ — $ 949 Total realized / unrealized gains (losses) Included in net income 2 (231 ) (a) — (229 ) — 1 — (228 ) Included in noncurrent payables to affiliates 11 — — 11 — — (11 ) — Included in regulatory assets/liabilities — — — — 9 (b) — 11 20 Change in collateral — 81 — 81 — — — 81 Purchases, sales, issuances and settlements Purchases 1 57 — 58 — — — 58 Sales — — — — — — — — Settlements (17 ) — — (17 ) — — — (17 ) Transfers into Level 3 — — (d) — — — — — — Transfers out of Level 3 — 17 (d) — 17 — — — 17 Balance at March 31, 2019 $ 540 $ 499 $ 42 $ 1,081 $ (240 ) $ 39 $ — $ 880 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of March 31, 2019 $ 2 $ (151 ) $ — $ (149 ) $ — $ 1 $ — $ (148 ) Generation ComEd PHI Exelon Three Months Ended March 31, 2018 NDT Fund Investments Mark-to-Market Derivatives Other Investments Total Generation Mark-to-Market Derivatives Life Insurance Contracts (c) Eliminated in Consolidation Total Balance as of December 31, 2017 $ 648 $ 552 $ 37 $ 1,237 $ (256 ) $ 22 $ — $ 1,003 Total realized / unrealized gains (losses) Included in net income — 184 (a) 1 185 — 1 — 186 Included in noncurrent payables to affiliates 7 — — 7 — — (7 ) — Included in regulatory assets — — — — (11 ) (b) — 7 (4 ) Change in collateral — 105 — 105 — — — 105 Purchases, sales, issuances and settlements Purchases 2 88 — 90 — — — 90 Sales — (3 ) — (3 ) — — — (3 ) Issuances — — — — — — — — Settlements (48 ) — — (48 ) — — — (48 ) Transfers into Level 3 — (8 ) (d) — (8 ) — — — (8 ) Transfers out of Level 3 — — (d) (2 ) (2 ) — — — (2 ) Balance as of March 31, 2018 $ 609 $ 918 $ 36 $ 1,563 $ (267 ) $ 23 $ — $ 1,319 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of March 31, 2018 $ — $ 256 $ 1 $ 257 $ — $ 1 $ — $ 258 __________ (a) Includes a reduction for the reclassification of $80 million and $72 million of realized gains due to the settlement of derivative contracts for the three months ended March 31, 2019 and 2018 , respectively. (b) Includes $14 million of decreases in fair value and an increase for realized losses due to settlements of $5 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2019 . Includes $17 million of increases in fair value and an increase for realized losses due to settlements of $6 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2018 . (c) The amounts represented are life insurance contracts at Pepco. (d) Transfers into and out of Level 3 generally occur when the contract tenor becomes less and more observable respectively, primarily due to changes in market liquidity or assumptions for certain commodity contracts.
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 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 three months ended March 31, 2019 and 2018 : Generation PHI Exelon Operating Purchased Other, net Operating and Maintenance Operating Purchased Operating and Maintenance Other, net Total gains (losses) included in net income for the three months ended March 31, 2019 $ (128 ) $ (103 ) $ 2 $ 1 $ (128 ) $ (103 ) $ 1 $ 2 Change in the unrealized gains (losses) relating to assets and liabilities held for the three months ended March 31, 2019 (91 ) (60 ) 2 1 (91 ) (60 ) 1 2 Generation PHI Exelon Operating Revenues Purchased Power and Fuel Other, net Operating and Maintenance Operating Revenues Purchased Power and Fuel Operating and Maintenance Other, net Total gains (losses) included in net income for the three months ended March 31, 2018 $ 335 $ (151 ) $ 1 $ 1 $ 335 $ (151 ) $ 1 $ 1 Change in the unrealized gains (losses) relating to assets and liabilities held for the three months ended March 31, 2018 309 (53 ) 1 1 309 (53 ) 1 1
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 March 31, 2019 Valuation Technique Unobservable Input Range Mark-to-market derivatives — Economic Hedges (Exelon and Generation) (a)(b) $ 278 Discounted Forward power $9 - $164 Forward gas $1.76 - $11.63 Option Model Volatility 10% - 334% Mark-to-market derivatives — Proprietary trading (Exelon and Generation) (a)(b) $ 64 Discounted Forward power $9 - $162 Mark-to-market derivatives (Exelon and ComEd) $ (240 ) Discounted Forward heat (c) 10x - 11x Marketability 4% - 8% Renewable 85% - 120% Type of trade Fair Value at December 31, 2018 Valuation Technique Unobservable Input Range Mark-to-market derivatives — Economic Hedges (Exelon and Generation) (a)(b) $ 443 Discounted Forward power price $12 - $174 Forward gas price $0.78 - $12.38 Option Model Volatility percentage 10% - 277% Mark-to-market derivatives — Proprietary trading (Exelon and Generation) (a)(b) $ 56 Discounted Forward power price $14 - $174 Mark-to-market derivatives (Exelon and ComEd) $ (249 ) Discounted Cash Flow Forward heat (c) 10x - 11x Marketability reserve 4% - 8% Renewable factor 86% - 120% _________ (a) The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions. (b) The fair values do not include cash collateral posted on level three positions of $157 million and $76 million as of March 31, 2019 and December 31, 2018 , respectively. (c) 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 Instrume_2

Derivative Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Summary of the derivative fair value	The following table provides a summary of the derivative fair value balances recorded by the Registrants as of March 31, 2019 : Generation ComEd Exelon Derivatives Economic Hedges Proprietary Trading Collateral and Netting (a)(d) Subtotal (b) Economic Hedges (c) Total Derivatives Mark-to-market derivative assets (current assets) $ 2,691 $ 118 $ (2,156 ) $ 653 $ — $ 653 Mark-to-market derivative assets (noncurrent assets) 1,188 60 (794 ) 454 — 454 Total mark-to-market derivative assets 3,879 178 (2,950 ) 1,107 — 1,107 Mark-to-market derivative liabilities (current liabilities) (2,711 ) (89 ) 2,485 (315 ) (27 ) (342 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,142 ) (30 ) 957 (215 ) (213 ) (428 ) Total mark-to-market derivative liabilities (3,853 ) (119 ) 3,442 (530 ) (240 ) (770 ) Total mark-to-market derivative net assets (liabilities) $ 26 $ 59 $ 492 $ 577 $ (240 ) $ 337 _________ (a) Exelon and Generation net all available amounts allowed under the derivative authoritative guidance in 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 $152 million and $63 million , respectively, and current and noncurrent liabilities are shown net of collateral of $177 million and $100 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $492 million at March 31, 2019 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Of the collateral posted/(received), $(33) million represents variation margin on the exchanges. The following table provides a summary of the derivative fair value balances recorded by the Registrants as of December 31, 2018 : Generation ComEd Exelon Description Economic Proprietary Collateral (a)(d) Subtotal (b) Economic (c) Total Mark-to-market derivative assets $ 3,505 $ 105 $ (2,809 ) $ 801 $ — $ 801 Mark-to-market derivative assets 1,266 41 (862 ) 445 — 445 Total mark-to-market derivative assets 4,771 146 (3,671 ) 1,246 — 1,246 Mark-to-market derivative liabilities (3,429 ) (74 ) 3,056 (447 ) (26 ) (473 ) Mark-to-market derivative liabilities (1,203 ) (20 ) 972 (251 ) (223 ) (474 ) Total mark-to-market derivative liabilities (4,632 ) (94 ) 4,028 (698 ) (249 ) (947 ) Total mark-to-market derivative net assets (liabilities) $ 139 $ 52 $ 357 $ 548 $ (249 ) $ 299 _________ (a) Exelon and Generation net all available amounts allowed under the derivative authoritative guidance in 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, and 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 $121 million and $51 million , respectively, and current and noncurrent liabilities are shown net of collateral of $125 million and $60 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $357 million at December 31, 2018 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Of the collateral posted/(received), $(94) million represents variation margin on the exchanges.
Derivative Instruments, Gain (Loss) [Table Text Block]	For the three months ended March 31, 2019 and 2018 , Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses) which are also located in the "Net fair value changes related to derivatives" in the Consolidated Statements of Cash Flows. Three Months Ended 2019 2018 Income Statement Location Gain (Loss) Operating revenues $ (50 ) $ (100 ) Purchased power and fuel 30 (167 ) Total Exelon and Generation $ (20 ) $ (267 )
Schedule of Derivative Instruments Included in Trading Activities [Table Text Block]	For the three months ended March 31, 2019 and 2018 Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses) which are also included in the "Net fair value changes related to derivatives" in the Consolidated Statements of Cash Flows. The Utility Registrants do not execute derivatives for proprietary trading purposes. Three Months Ended 2019 2018 Income Statement Location Gain (Loss) Operating revenues $ 2 $ 2
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 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: Credit-Risk Related Contingent Features March 31, 2019 December 31, 2018 Gross fair value of derivative contracts containing this feature (a) $ (1,667 ) $ (1,723 ) Offsetting fair value of in-the-money contracts under master netting arrangements (b) 1,177 1,105 Net fair value of derivative contracts containing this feature (c) $ (490 ) $ (618 ) _________ (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. The following tables provide information on Generation’s credit exposure for all derivative instruments, NPNS and applicable payables and receivables, net of collateral and instruments that are subject to master netting agreements, as of March 31, 2019 . The tables further delineate that exposure by credit rating of the counterparties and provide guidance on the concentration of credit risk to individual counterparties. 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, NASDAQ, NGX and Nodal commodity exchanges. Additionally, the figures in the tables below exclude exposures with affiliates, including net receivables with ComEd, PECO, BGE, Pepco, DPL and ACE of $36 million , $31 million , $27 million , $37 million , $5 million and $4 million as of March 31, 2019 , respectively. Rating as of March 31, 2019 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 $ 819 $ 11 $ 808 1 $ 135 Non-investment grade 86 39 47 No external ratings Internally rated — investment grade 162 — 162 Internally rated — non-investment grade 87 7 80 Total $ 1,154 $ 57 $ 1,097 1 $ 135 Net Credit Exposure by Type of Counterparty As of Financial institutions $ 13 Investor-owned utilities, marketers, power producers 762 Energy cooperatives and municipalities 287 Other 35 Total $ 1,097 _________ (a) As of March 31, 2019 , credit collateral held from counterparties where Generation had credit exposure included $37 million of cash and $19 million of letters of credit. The credit collateral does not include non-liquid collateral.

Debt and Credit Agreements (Tab

Debt and Credit Agreements (Tables)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Commercial Paper Borrowings	The following table reflects the Registrants' commercial paper programs as of March 31, 2019 and December 31, 2018 . Generation and PECO had no commercial paper borrowings as of both March 31, 2019 and December 31, 2018 . Outstanding Average Interest Rate on Commercial Paper Issuer March 31, 2019 December 31, 2018 March 31, 2019 December 31, 2018 Exelon $ 629 $ 89 2.63 % 2.15 % ComEd 322 — 2.64 % 2.14 % BGE 106 35 2.59 % 2.18 % PHI 201 54 2.62 % 2.15 % PEPCO 105 40 2.62 % 2.24 % DPL 5 — 2.61 % 2.07 % ACE 91 14 2.62 % 2.21 %
Schedule of Long-term Debt Instruments [Table Text Block]	During the three months ended March 31, 2019 , the following long-term debt was issued: Company Type Interest Rate Maturity Amount Use of Proceeds Generation Energy Efficiency Project Financing 3.95 % August 31, 2020 $ 2 Funding to install energy conservation measures for the Fort Meade project. ComEd First Mortgage Bonds, Series 126 4.00 % March 1, 2049 $ 400 Repay a portion of ComEd’s outstanding commercial paper obligations and fund other general corporate purposes.

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The effective income tax rate from continuing operations varies from the U.S. Federal statutory rate principally due to the following: Three Months Ended March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE U.S. Federal statutory rate 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% Increase (decrease) due to: State income taxes, net of Federal income tax benefit 3.9 3.1 8.2 1.0 6.3 4.7 2.1 6.5 6.7 Qualified NDT fund income 7.2 14.2 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.5) (0.9) (0.2) — (0.1) (0.2) (0.1) (0.2) (0.3) Plant basis differences (1.4) — (0.5) (6.7) (0.9) (1.7) (2.0) (0.7) (2.3) Production tax credits and other credits (0.8) (1.5) — — — — — — — Noncontrolling interests (0.6) (1.1) — — — — — — — Excess deferred tax amortization (4.7) — (8.5) (2.5) (7.9) (19.4) (17.9) (15.6) (23.9) Other 0.1 (0.5) 0.3 0.2 — (0.3) 0.4 0.7 (1.2) Effective income tax rate 24.2% 34.3% 20.3% 13.0% 18.4% 4.1% 3.5% 11.7% —% Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE U.S. Federal statutory rate 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% 21.0% Increase (decrease) due to: State income taxes, net of Federal income tax benefit 4.1 2.4 8.2 (3.9) 6.3 4.6 1.7 6.3 6.6 Qualified NDT fund income (0.4) (1.3) — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.3) (4.3) (0.2) (0.1) (0.1) (0.2) (0.1) (0.2) (0.3) Plant basis differences (2.7) — 0.1 (14.2) (0.7) (2.6) (3.4) (1.3) (2.6) Production tax credits and other credits (2.8) (9.5) (0.1) — — — — — — Noncontrolling interests (0.7) (2.5) — — — — — — — Excess deferred tax amortization (6.0) — (7.5) (4.8) (8.6) (10.6) (12.8) (7.9) (8.7) Other (2.8) (1.3) 0.3 0.2 — — (0.3) 0.5 (3.5) Effective income tax rate 8.4% 4.5% 21.8% (1.8)% 17.9% 12.2% 6.1% 18.4% 12.5%
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	The Registrants have the following unrecognized tax benefits as of March 31, 2019 and December 31, 2018 : Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE March 31, 2019 $ 448 $ 411 $ — $ — $ — $ 45 $ — $ — $ 14 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2018 $ 477 $ 408 $ 2 $ — $ — $ 45 $ — $ — $ 14

Nuclear Decommissioning (Tables

Nuclear Decommissioning (Tables)	3 Months Ended
	Mar. 31, 2019
Schedule Of Nuclear Decommissioning [Line Items]
Schedule of Change in Asset Retirement Obligation [Table Text Block]	The following table provides a rollforward of the nuclear decommissioning ARO reflected in Exelon’s and Generation’s Consolidated Balance Sheets from December 31, 2018 to March 31, 2019 : Nuclear decommissioning ARO at December 31, 2018 (a)(b) $ 10,005 Net increase due to changes in, and timing of, estimated future cash flows 223 Accretion expense 120 Costs incurred related to decommissioning plants (19 ) Nuclear decommissioning ARO at March 31, 2019 (a)(b) $ 10,329 _________ (a) Includes $41 million and $22 million as the current portion of the ARO at March 31, 2019 and December 31, 2018 , respectively, which is included in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets. (b) Includes $760 million and $772 million of ARO related to Oyster Creek which is classified as Liabilities held for sale in Exelon's and Generation's Consolidated Balance Sheets at March 31, 2019 and December 31, 2018 , respectively. See Note 3 — Mergers, Acquisitions and Dispositions for additional information.	[1]
[1]	Includes $41 million and $22 million as the current portion of the ARO at March 31, 2019 and December 31, 2018, respectively, which is included in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2019
Retirement Benefits [Abstract]
Schedule of Net Benefit Costs [Table Text Block]	The following table presents the components of Exelon's net periodic benefit costs, prior to capitalization, for the three months ended March 31, 2019 and 2018 . Pension Benefits Other Postretirement Benefits 2019 2018 2019 2018 Components of net periodic benefit cost: Service cost $ 89 $ 101 $ 24 $ 28 Interest cost 221 201 47 43 Expected return on assets (307 ) (312 ) (38 ) (43 ) Amortization of: Prior service cost (benefit) — — (45 ) (46 ) Actuarial loss 104 157 11 16 Net periodic benefit cost $ 107 $ 147 $ (1 ) $ (2 )
Schedule Of Pension And Other Postretirement Benefit Costs	The amounts below represent Exelon's, Generation's, ComEd's, PECO's, BGE's, PHI's, Pepco's, DPL's, and ACE's pension and postretirement benefit plan costs. For Exelon, the service cost component is included in Operating and maintenance expense and Property, plant and equipment, net, for the three months ended March 31, 2019 and 2018, while the non-service cost components are included in Other, net and Regulatory assets for the three months ended March 31, 2019 and 2018. For the Registrants other than Exelon, the service cost and non-service cost components are included in Operating and maintenance expense and Property, plant and equipment, net in their consolidated financial statements for the three months ended March 31, 2019 and 2018. Three Months Ended Pension and Other Postretirement Benefit Costs 2019 2018 Exelon $ 106 $ 145 Generation 31 51 ComEd 24 45 PECO 2 5 BGE 16 15 PHI 23 15 Pepco 6 4 DPL 4 — ACE 4 3
Schedule Of Defined Contributions	Defined Contribution Savings Plans The Registrants participate in various 401(k) defined contribution savings plans that are sponsored by Exelon. The plans are qualified under applicable sections of the IRC and allow employees to contribute a portion of their pre-tax and/or after-tax income in accordance with specified guidelines. All Registrants match a percentage of the employee contributions up to certain limits. The following table presents the matching contributions to the savings plans during the three months ended March 31, 2019 and 2018 , respectively. Three Months Ended Savings Plan Matching Contributions 2019 2018 Exelon $ 31 $ 32 Generation 13 15 ComEd 7 7 PECO 2 2 BGE 2 2 PHI 4 3 Pepco 1 1 DPL 1 1 ACE 1 —

Changes in Accumulated Other _2

Changes in Accumulated Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2019
Changes in Accumulated Other Comprehensive Income [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The following tables present changes in accumulated other comprehensive income (loss) (AOCI) by component for the three months ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 Gains (Losses) on Cash Flow Hedges Unrealized Gains (Losses) on Marketable Securities Pension and Non-Pension Postretirement Benefit Plan Items Foreign Currency Items AOCI of Investments in Unconsolidated Affiliates Total Exelon (a) Beginning balance $ (2 ) $ — $ (2,960 ) $ (33 ) $ — $ (2,995 ) OCI before reclassifications — — (38 ) 2 (1 ) (37 ) Amounts reclassified from AOCI (b) — — 20 — — 20 Net current-period OCI — — (18 ) 2 (1 ) (17 ) Ending balance $ (2 ) $ — $ (2,978 ) $ (31 ) $ (1 ) $ (3,012 ) Generation (a) Beginning balance $ (4 ) $ — $ — $ (33 ) $ (1 ) $ (38 ) OCI before reclassifications — — — 2 (1 ) 1 Amounts reclassified from AOCI 1 — — — — 1 Net current-period OCI 1 — — 2 (1 ) 2 Ending balance $ (3 ) $ — $ — $ (31 ) $ (2 ) $ (36 ) Three Months Ended March 31, 2018 Gains (Losses) on Cash Flow Hedges Unrealized gains (losses) on Marketable Securities Pension and Non-Pension Postretirement Benefit Plan Items Foreign Currency Items AOCI of Investments in Unconsolidated Affiliates Total Exelon (a) Beginning balance $ (14 ) $ 10 $ (2,998 ) (d) $ (23 ) $ (1 ) $ (3,026 ) OCI before reclassifications 8 — 18 1 — 27 Amounts reclassified from AOCI (b) — — 44 — — 44 Net current-period OCI 8 — 62 1 — 71 Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard (c) — (10 ) — — — (10 ) Ending balance $ (6 ) $ — $ (2,936 ) $ (22 ) $ (1 ) $ (2,965 ) Generation (a) Beginning balance $ (16 ) $ 3 $ — $ (23 ) $ (1 ) $ (37 ) OCI before reclassifications 7 — — (1 ) — 6 Amounts reclassified from AOCI — — — — — — Net current-period OCI 7 — — (1 ) — 6 Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard (c) — (3 ) — — — (3 ) Ending balance $ (9 ) $ — $ — $ (24 ) $ (1 ) $ (34 ) _________ (a) All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI. (b) See next tables for details about these reclassifications. (c) Exelon prospectively adopted the new standard Recognition and Measurement of Financial Assets and Liabilities. The standard was adopted as of January 1, 2018, which resulted in an increase to Retained earnings and Accumulated other comprehensive loss of $10 million and $3 million for Exelon and Generation, respectively. The amounts reclassified related to Rabbi Trusts. See Note 1 — Significant Accounting Policies of the Exelon 2018 Form 10-K for additional information. (d) Exelon early adopted the new standard Reclassification of Certain Tax Effects from AOCI. The standard was adopted retrospectively as of December 31, 2017, which resulted in an increase to Exelon’s Retained earnings and Accumulated other comprehensive loss of $539 million , primarily related to deferred income taxes associated with Exelon’s pension and OPEB obligations. See Note 1 — Significant Accounting Policies of the Exelon 2018 Form 10-K for additional information.
Reclassification out of Accumulated Other Comprehensive Income	Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE did not have any reclassifications out of AOCI to Net income during the three months ended March 31, 2019 and 2018 . The following tables present amounts reclassified out of AOCI to Net income for Exelon during the three months ended March 31, 2019 and 2018 . Three Months Ended March 31, 2019 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 22 Actuarial losses (b) (49 ) (27 ) Total before tax 7 Tax benefit $ (20 ) Net of tax Total Reclassifications $ (20 ) Net of tax Three Months Ended March 31, 2018 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 23 Actuarial losses (b) (83 ) (60 ) Total before tax 16 Tax benefit $ (44 ) Net of tax Total Reclassifications $ (44 ) Net of tax _________ (a) Amounts in parenthesis represent a decrease in net income. (b) This AOCI component is included in the computation of net periodic pension and OPEB cost. See Note 14 — Retirement Benefits for additional information.
Schedule Of Other Comprehensive Income Loss Tax	The following table presents income tax benefit (expense) allocated to each component of other comprehensive income (loss) during the three months ended March 31, 2019 and 2018 : Three Months Ended 2019 2018 Exelon Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 6 $ 6 Actuarial loss reclassified to periodic benefit cost (13 ) (22 ) Pension and non-pension postretirement benefit plans valuation adjustment 14 (7 ) Change in unrealized loss on cash flow hedges — (3 ) Change in unrealized loss on investments in unconsolidated affiliates — (1 ) Total $ 7 $ (27 ) Generation Change in unrealized gain (loss) on cash flow hedges $ 1 $ (3 ) Change in unrealized loss on investments in unconsolidated affiliates — (1 ) Total $ 1 $ (4 )

Commitments and Contingencies_2

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2019
Commitments And Contingencies Tables Disclosure [Line Items]
Other Commitments	The following amounts represent total commitment costs for Exelon, PHI, Pepco, DPL and ACE that have been recorded since the acquisition date and the remaining obligations as of March 31, 2019 : Description Expected Payment Period Exelon PHI Pepco DPL ACE Rate credits 2016 - 2021 $ 264 $ 264 $ 91 $ 72 $ 101 Energy efficiency 2016 - 2021 117 — — — — Charitable contributions 2016 - 2026 50 50 28 12 10 Delivery system modernization Q2 2017 22 — — — — Green sustainability fund Q2 2017 14 — — — — Workforce development 2016 - 2020 17 — — — — Other 29 6 1 5 — Total commitments $ 513 $ 320 $ 120 $ 89 $ 111 Remaining commitments $ 123 $ 90 $ 71 $ 12 $ 7 The Registrants’ commercial commitments as of March 31, 2019 , representing commitments potentially triggered by future events were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Letters of credit $ 1,480 $ 1,455 $ 6 $ — $ 2 $ 8 $ 8 $ — $ — Surety bonds (a) 1,597 1,376 51 9 17 40 32 5 3 Financing trust guarantees 378 — 200 178 — — — — — Guaranteed lease residual values (b) 26 — — — — 26 8 11 7 Total commercial commitments $ 3,481 $ 2,831 $ 257 $ 187 $ 19 $ 74 $ 48 $ 16 $ 10 _________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (b) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $68 million , $22 million of which is a guarantee by Pepco, $28 million by DPL and $17 million by ACE. The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote.
Accrued environmental liabilities	As of March 31, 2019 and December 31, 2018 , 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: March 31, 2019 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 486 $ 347 Generation 108 — ComEd 320 318 PECO 27 25 BGE 5 4 PHI 26 — Pepco 24 — DPL 1 — ACE 1 — December 31, 2018 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 496 $ 356 Generation 108 — ComEd 329 327 PECO 27 25 BGE 5 4 PHI 27 — Pepco 25 — DPL 1 — ACE 1 —

Supplemental Financial Inform_2

Supplemental Financial Information (Tables)	3 Months Ended
	Mar. 31, 2019
Supplemental Financial Information [Abstract]
Schedule of Other Nonoperating Income, by Component	The following tables provide additional information about the Registrants’ Consolidated Statements of Operations and Comprehensive Income for the three months ended March 31, 2019 and 2018 . Three Months Ended March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on NDT funds (a) Regulatory agreement units (b) $ 54 $ 54 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 54 54 — — — — — — — Net unrealized gains on NDT funds Regulatory agreement units (b) 379 379 — — — — — — — Non-regulatory agreement units 280 280 — — — — — — — Regulatory offset to NDT fund-related activities (c) (348 ) (348 ) — — — — — — — Total decommissioning-related activities 419 419 — — — — — — — Investment income 12 7 — 1 — — — — — Interest income related to uncertain income tax positions 1 — — — — — — — — AFUDC — Equity 22 — 5 3 5 9 6 1 2 Non-service net periodic benefit cost 5 — — — — — — — — Other 8 4 3 — — 3 1 2 1 Other, net $ 467 $ 430 $ 8 $ 4 $ 5 $ 12 $ 7 $ 3 $ 3 Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on NDT funds (a) Regulatory agreement units (b) $ 46 $ 46 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 56 56 — — — — — — — Net unrealized losses on NDT funds Regulatory agreement units (b) (75 ) (75 ) — — — — — — — Non-regulatory agreement units (96 ) (96 ) — — — — — — — Regulatory offset to NDT fund-related activities (c) 24 24 — — — — — — — Total decommissioning-related activities (45 ) (45 ) — — — — — — — Investment income 4 2 — — — — — — — Interest income related to uncertain income tax positions 2 1 — — — — — — — AFUDC — Equity 18 — 6 2 4 6 5 1 — Non-service net periodic benefit cost (10 ) — — — — — — — — Other 3 (2 ) 2 — — 5 3 1 1 Other, net $ (28 ) $ (44 ) $ 8 $ 2 $ 4 $ 11 $ 8 $ 2 $ 1 _________ (a) Realized income includes interest, dividends and realized gains and losses on sales of NDT fund investments. (b) Net realized and unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities in Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates in Generation’s Consolidated Balance Sheets. (c) Includes the elimination of decommissioning-related activities for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 15 — Asset Retirement Obligations of the Exelon 2018 Form 10-K for additional information regarding the accounting for nuclear decommissioning.
Schedule Of Taxes Excluding Income And Excise Taxes [Table Text Block]	The following utility taxes are included in revenues and expenses for the three months ended March 31, 2019 and 2018 . Generation’s utility tax expense represents gross receipts tax related to its retail operations, and the Utility Registrants' utility tax expense represents 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 in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Three Months Ended March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 223 $ 26 $ 62 $ 34 $ 27 $ 74 $ 69 $ 5 $ — Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 235 $ 32 $ 61 $ 33 $ 26 $ 83 $ 77 $ 6 $ —
Cash Flow Supplemental Disclosures	The following tables provide additional information regarding the Registrants’ Consolidated Statements of Cash Flows for the three months ended March 31, 2019 and 2018 . Three Months Ended March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment (a) $ 917 $ 392 $ 219 $ 74 $ 85 $ 127 $ 58 $ 35 $ 25 Amortization of regulatory assets (a) 143 — 32 7 51 53 36 11 6 Amortization of intangible assets, net (a) 15 13 — — — — — — — Nuclear fuel (c) 261 261 — — — — — — — ARO accretion (d) 124 123 — — — — — — — Total depreciation, amortization and accretion $ 1,460 $ 789 $ 251 $ 81 $ 136 $ 180 $ 94 $ 46 $ 31 Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment (a) $ 926 $ 436 $ 201 $ 68 $ 82 $ 117 $ 53 $ 32 $ 23 Amortization of regulatory assets (a) 152 — 27 7 52 66 43 13 10 Amortization of intangible assets, net (a) 13 12 — — — — — — — Amortization of energy contract assets and liabilities (b) 3 3 — — — — — — — Nuclear fuel (c) 287 287 — — — — — — — ARO accretion (d) 120 120 — — — — — — — Total depreciation, amortization and accretion $ 1,501 $ 858 $ 228 $ 75 $ 134 $ 183 $ 96 $ 45 $ 33 _________ (a) Included in Depreciation and amortization in the Registrants' Consolidated Statements of Operations and Comprehensive Income. (b) Included in Operating revenues or Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (c) Included in Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (d) Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Three Months Ended March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 106 $ 31 $ 24 $ 2 $ 15 $ 23 $ 6 $ 4 $ 4 Loss from equity method investments 6 6 — — — — — — — Provision for uncollectible accounts 43 — 9 16 8 10 4 4 2 Stock-based compensation costs 28 — — — — — — — — Other decommissioning-related activity (a) (202 ) (202 ) — — — — — — — Energy-related options (b) 37 37 — — — — — — — Amortization of regulatory asset related to debt costs 3 — — — — 1 — — — Amortization of rate stabilization deferral (6 ) — — — — (6 ) (7 ) 1 — Amortization of debt fair value adjustment (4 ) (3 ) — — — (1 ) — — — Discrete impacts from EIMA and FEJA (c) 28 — 28 — — — — — — Amortization of debt costs 9 3 1 — — 1 1 — — Long-term incentive plan 25 — — — — — — — — Amortization of operating ROU asset 53 34 1 — 8 9 2 2 1 Other 1 4 (7 ) (2 ) (4 ) (2 ) (3 ) — (2 ) Total other non-cash operating activities $ 127 $ (90 ) $ 56 $ 16 $ 27 $ 35 $ 3 $ 11 $ 5 Non-cash investing and financing activities: Change in capital expenditures not paid $ (229 ) $ (93 ) $ (80 ) $ 8 $ 2 $ (55 ) $ (15 ) $ (17 ) $ (24 ) Change in PPE related to ARO update 301 301 — — — — — — — Dividends on stock compensation 1 — — — — — — — — Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 145 $ 51 $ 45 $ 5 $ 14 $ 15 $ 4 $ — $ 3 Loss from equity method investments 7 7 — — — — — — — Provision for uncollectible accounts 64 11 8 17 8 20 6 8 5 Stock-based compensation costs 29 — — — — — — — — Other decommissioning-related activity (a) (31 ) (31 ) — — — — — — — Energy-related options (b) (7 ) (7 ) — — — — — — — Amortization of regulatory asset related to debt costs 2 — 1 — — 1 — — — Amortization of rate stabilization deferral 7 — — — — 7 1 6 — Amortization of debt fair value adjustment (3 ) (3 ) — — — — — — — Discrete impacts from EIMA and FEJA (c) (4 ) — (4 ) — — — — — — Amortization of debt costs 9 3 1 — — 1 — — — Provision for excess and obsolete inventory 13 12 1 — — — — — — Other 9 2 (6 ) (1 ) (2 ) 9 (1 ) 5 1 Total other non-cash operating activities $ 240 $ 45 $ 46 $ 21 $ 20 $ 53 $ 10 $ 19 $ 9 Non-cash investing and financing activities: Change in capital expenditures not paid $ (177 ) $ (131 ) $ (48 ) $ (25 ) $ (11 ) $ 61 $ 19 $ 14 $ 27 Change in PPE related to ARO update 32 32 — — — — — — — Dividends on stock compensation 1 — — — — — — — — _________ (a) Includes the elimination of decommissioning-related 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 15 — Asset Retirement Obligations of the Exelon 2018 Form 10-K 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 in Operating revenues and expenses. (c) Reflects the change in ComEd's distribution and energy efficiency formula rates. See Note 6 — Regulatory Matters for additional information. The following tables provide a reconciliation of cash, cash equivalents and restricted cash reported within the Registrants’ Consolidated Balance Sheets that sum to the total of the same amounts in their Consolidated Statements of Cash Flows. March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 880 $ 537 $ 68 $ 41 $ 12 $ 33 $ 11 $ 7 $ 6 Restricted cash 223 139 17 6 4 39 35 1 3 Restricted cash included in other long-term assets 211 — 193 — — 19 — — 19 Total cash, cash equivalents and restricted cash $ 1,314 $ 676 $ 278 $ 47 $ 16 $ 91 $ 46 $ 8 $ 28 December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 1,349 $ 750 $ 135 $ 130 $ 7 $ 124 $ 16 $ 23 $ 7 Restricted cash 247 153 29 5 6 43 37 1 4 Restricted cash included in other long-term assets 185 — 166 — — 19 — — 19 Total cash, cash equivalents and restricted cash $ 1,781 $ 903 $ 330 $ 135 $ 13 $ 186 $ 53 $ 24 $ 30 March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 787 $ 610 $ 70 $ 21 $ 22 $ 43 $ 15 $ 7 $ 10 Restricted cash 209 127 9 5 2 40 33 — 7 Restricted cash included in other long-term assets 103 — 83 — — 20 — — 20 Total cash, cash equivalents and restricted cash $ 1,099 $ 737 $ 162 $ 26 $ 24 $ 103 $ 48 $ 7 $ 37 December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 898 $ 416 $ 76 $ 271 $ 17 $ 30 $ 5 $ 2 $ 2 Restricted cash 207 138 5 4 1 42 35 — 6 Restricted cash included in other long-term assets 85 — 63 — — 23 — — 23 Total cash, cash equivalents and restricted cash $ 1,190 $ 554 $ 144 $ 275 $ 18 $ 95 $ 40 $ 2 $ 31 For additional information on restricted cash see Note 1 — Significant Accounting Policies of the Exelon 2018 Form 10-K.
Supplemental Balance Sheet Disclosures	The following tables provide additional information about assets and liabilities of the Registrants as of March 31, 2019 and December 31, 2018 . March 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Property, plant and equipment: Accumulated depreciation and amortization $ 23,695 (a) $ 12,663 (a) $ 4,833 $ 3,598 $ 3,670 $ 930 $ 3,392 $ 1,354 $ 1,154 Accounts receivable: Allowance for uncollectible accounts $ 340 $ 87 $ 97 $ 72 $ 27 $ 57 $ 23 $ 15 $ 19 December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Property, plant and equipment: Accumulated depreciation and amortization $ 22,902 (b) $ 12,206 (b) $ 4,684 $ 3,561 $ 3,633 $ 841 $ 3,354 $ 1,329 $ 1,137 Accounts receivable: Allowance for uncollectible accounts $ 319 $ 104 $ 81 $ 61 $ 20 $ 53 $ 21 $ 13 $ 19 _________ (a) Includes accumulated amortization of nuclear fuel in the reactor core of $3,040 million . (b) Includes accumulated amortization of nuclear fuel in the reactor core of $2,969 million . The Utility Registrants are required, under separate legislation and regulations in Illinois, Pennsylvania, Maryland, District of Columbia and New Jersey, to purchase certain receivables from alternative retail electric and, as applicable, natural gas suppliers that participate in the utilities' consolidated billing. ComEd, BGE, Pepco and DPL purchase receivables at a discount to recover primarily uncollectible accounts expense from the suppliers. PECO and ACE purchase receivables at face value and recover uncollectible accounts expense, including those from alternative retail electric and natural gas supplies, through base distribution rates and a rate rider, respectively. Exelon and the Utility Registrants do not record unbilled commodity receivables under their POR programs. Purchased billed receivables are recorded on a net basis in Exelon’s and the Utility Registrant's Consolidated Statements of Operations and Comprehensive Income and are classified in Other accounts receivable, net in their Consolidated Balance Sheets. The following tables provide information about the purchased receivables of those companies as of March 31, 2019 and December 31, 2018 . March 31, 2019 Exelon ComEd PECO BGE PHI Pepco DPL ACE Purchased receivables $ 332 $ 105 $ 77 $ 65 $ 85 $ 58 $ 8 $ 19 Allowance for uncollectible accounts (a) (38 ) (19 ) (6 ) (4 ) (9 ) (5 ) (1 ) (3 ) Purchased receivables, net $ 294 $ 86 $ 71 $ 61 $ 76 $ 53 $ 7 $ 16 December 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Purchased receivables $ 313 $ 94 $ 74 $ 61 $ 84 $ 57 $ 8 $ 19 Allowance for uncollectible accounts (a) (34 ) (17 ) (5 ) (3 ) (9 ) (5 ) (1 ) (3 ) Purchased receivables, net $ 279 $ 77 $ 69 $ 58 $ 75 $ 52 $ 7 $ 16 __________ (a) For ComEd, BGE, Pepco and DPL, 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 a rate rider. BGE, Pepco and DPL recover actual write-offs which are reflected in the POR discount rate.

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2019
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 three months ended March 31, 2019 and 2018 is as follows: Three Months Ended March 31, 2019 and 2018 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon Operating revenues (c) : 2019 Competitive businesses electric revenues $ 4,337 $ — $ — $ — $ — $ — $ (315 ) $ 4,022 Competitive businesses natural gas revenues 879 — — — — — (1 ) 878 Competitive businesses other revenues 80 — — — — — (1 ) 79 Rate-regulated electric revenues — 1,408 620 658 1,153 — (8 ) 3,831 Rate-regulated natural gas revenues — — 280 318 71 — (4 ) 665 Shared service and other revenues — — — — 4 455 (457 ) 2 Total operating revenues $ 5,296 $ 1,408 $ 900 $ 976 $ 1,228 $ 455 $ (786 ) $ 9,477 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon 2018 Competitive businesses electric revenues $ 4,509 $ — $ — $ — $ — $ — $ (391 ) $ 4,118 Competitive businesses natural gas revenues 955 — — — — — (8 ) 947 Competitive businesses other revenues 48 — — — — — — 48 Rate-regulated electric revenues — 1,512 634 658 1,169 — (18 ) 3,955 Rate-regulated natural gas revenues — — 232 319 78 — (4 ) 625 Shared service and other revenues — — — — 4 451 (455 ) — Total operating revenues $ 5,512 $ 1,512 $ 866 $ 977 $ 1,251 $ 451 $ (876 ) $ 9,693 Intersegment revenues (d) : 2019 $ 317 $ 4 $ 1 $ 6 $ 4 $ 453 $ (785 ) $ — 2018 400 14 2 6 4 450 (876 ) — Depreciation and amortization: 2019 $ 405 $ 251 $ 81 $ 136 $ 180 $ 22 $ — $ 1,075 2018 448 228 75 134 183 23 — 1,091 Operating expenses: 2019 $ 4,963 $ 1,135 $ 678 $ 756 $ 1,054 $ 459 $ (783 ) $ 8,262 2018 5,218 1,223 724 800 1,125 444 (886 ) 8,648 Interest expense, net: 2019 $ 111 $ 87 $ 33 $ 29 $ 65 $ 78 $ — $ 403 2018 101 89 33 25 63 60 — 371 Income (loss) before income taxes: 2019 $ 652 $ 197 $ 193 $ 196 $ 122 $ (78 ) $ — $ 1,282 2018 202 211 111 156 74 (52 ) — 702 Income Taxes: 2019 $ 224 $ 40 $ 25 $ 36 $ 5 $ (20 ) $ — $ 310 2018 9 46 (2 ) 28 9 (31 ) — 59 Net income (loss): 2019 $ 422 $ 157 $ 168 $ 160 $ 117 $ (58 ) $ — $ 966 2018 186 165 113 128 65 (21 ) — 636 Capital Expenditures 2019 $ 511 $ 503 $ 222 $ 258 $ 358 $ 21 $ — $ 1,873 2018 628 531 217 224 258 22 — 1,880 Total assets: March 31, 2019 $ 48,682 $ 31,582 $ 10,956 $ 9,967 $ 22,294 $ 8,325 $ (10,213 ) $ 121,593 December 31, 2018 47,556 31,213 10,642 9,716 21,984 8,355 (9,800 ) 119,666 __________ (a) Intersegment revenues for Generation in 2019 include revenue from sales to PECO of $45 million , sales to BGE of $76 million , sales to Pepco of $70 million , sales to DPL of $23 million and sales to ACE of $8 million in the Mid-Atlantic region, and sales to ComEd of $94 million in the Midwest region, which eliminate upon consolidation. Intersegment revenues for Generation in 2018 include revenue from sales to PECO of $37 million , sales to BGE of $65 million , sales to Pepco of $52 million , sales to DPL of $46 million and sales to ACE of $6 million in the Mid-Atlantic region, and sales to ComEd of $194 million in the Midwest region, which eliminate upon consolidation. (b) Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities. (c) Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 17 — Supplemental Financial Information for additional information on total utility taxes. (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. PHI: Pepco DPL ACE Other (b) Intersegment PHI Operating revenues (a) : 2019 Rate-regulated electric revenues $ 575 $ 310 $ 273 $ — $ (5 ) $ 1,153 Rate-regulated natural gas revenues — 70 — — 1 71 Shared service and other revenues — — — 106 (102 ) 4 Total operating revenues $ 575 $ 380 $ 273 $ 106 $ (106 ) $ 1,228 2018 Rate-regulated electric revenues $ 557 $ 306 $ 310 $ — $ (4 ) $ 1,169 Rate-regulated natural gas revenues — 78 — — — 78 Shared service and other revenues — — — 113 (109 ) 4 Total operating revenues $ 557 $ 384 $ 310 $ 113 $ (113 ) $ 1,251 Intersegment revenues: 2019 $ 2 $ 2 $ 1 $ 105 $ (106 ) $ 4 2018 2 2 1 112 (113 ) 4 Depreciation and amortization: 2019 $ 94 $ 46 $ 31 $ 10 $ (1 ) $ 180 2018 96 45 33 9 — 183 Operating expenses: 2019 $ 491 $ 308 $ 252 $ 108 $ (105 ) $ 1,054 2018 501 335 287 114 (112 ) 1,125 Interest expense, net: 2019 $ 34 $ 15 $ 14 $ 3 $ (1 ) $ 65 2018 31 13 16 2 1 63 Income (loss) before income taxes: 2019 $ 57 $ 60 $ 10 $ 113 $ (118 ) $ 122 2018 33 38 8 64 (69 ) 74 Income Taxes: 2019 $ 2 $ 7 $ — $ (4 ) $ — $ 5 2018 2 7 1 (1 ) — 9 Net income (loss): 2019 $ 55 $ 53 $ 10 $ (5 ) $ 4 $ 117 2018 31 31 7 (8 ) 4 65 Capital Expenditures 2019 $ 144 $ 78 $ 128 $ 8 $ — $ 358 2018 127 65 63 3 — 258 Total assets: March 31, 2019 $ 8,420 $ 4,660 $ 3,783 $ 10,909 $ (5,478 ) $ 22,294 December 31, 2018 8,299 4,588 3,699 10,819 (5,421 ) 21,984 __________ (a) Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 17 — Supplemental Financial Information for additional information on total utility taxes. (b) Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities. The following tables disaggregate the Registrants' revenue recognized from contracts with customers into categories that depict how the nature, amount, timing, and uncertainty of revenue and cash flows are affected by economic factors. For Generation, the disaggregation of revenues reflects Generation’s two primary products of power sales and natural gas sales, with further disaggregation of power sales provided by geographic region. For the Utility Registrants, the disaggregation of revenues reflects the two primary utility services of rate-regulated electric sales and rate-regulated natural gas sales (where applicable), with further disaggregation of these tariff sales provided by major customer groups. Exelon’s disaggregated revenues are consistent with Generation and the Utility Registrants, but exclude any intercompany revenues. Competitive Business Revenues (Generation): Three Months Ended March 31, 2019 Revenues from external parties (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 1,286 $ (24 ) $ 1,262 $ (6 ) $ 1,256 Midwest 1,055 59 1,114 (6 ) 1,108 New York 409 (16 ) 393 — 393 ERCOT 130 79 209 3 212 Other Power Regions 1,165 194 1,359 (6 ) 1,353 Total Competitive Businesses Electric Revenues 4,045 292 4,337 (15 ) 4,322 Competitive Businesses Natural Gas Revenues 584 295 879 15 894 Competitive Businesses Other Revenues (c) 120 (40 ) 80 — 80 Total Generation Consolidated Operating Revenues $ 4,749 $ 547 $ 5,296 $ — $ 5,296
Analysis and reconciliation of reportable segment revenues for Generation	etitive Business Revenues (Generation): Three Months Ended March 31, 2019 Revenues from external parties (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 1,286 $ (24 ) $ 1,262 $ (6 ) $ 1,256 Midwest 1,055 59 1,114 (6 ) 1,108 New York 409 (16 ) 393 — 393 ERCOT 130 79 209 3 212 Other Power Regions 1,165 194 1,359 (6 ) 1,353 Total Competitive Businesses Electric Revenues 4,045 292 4,337 (15 ) 4,322 Competitive Businesses Natural Gas Revenues 584 295 879 15 894 Competitive Businesses Other Revenues (c) 120 (40 ) 80 — 80 Total Generation Consolidated Operating Revenues $ 4,749 $ 547 $ 5,296 $ — $ 5,296 Three Months Ended March 31, 2018 Revenues from external customers (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 1,355 $ 80 $ 1,435 $ 5 $ 1,440 Midwest 1,273 71 1,344 2 1,346 New York 439 (29 ) 410 (1 ) 409 ERCOT 149 59 208 1 209 Other Power Regions 935 177 1,112 (32 ) 1,080 Total Competitive Businesses Electric Revenues 4,151 358 4,509 (25 ) 4,484 Competitive Businesses Natural Gas Revenues 522 433 955 25 980 Competitive Businesses Other Revenues (c) 134 (86 ) 48 — 48 Total Generation Consolidated Operating Revenues $ 4,807 $ 705 $ 5,512 $ — $ 5,512 __________ (a) Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants. (b) Includes revenues from derivatives and leases. (c) Other represents activities not allocated to a region. See text above for a description of included activities. Includes unrealized mark-to-market losses of $52 million and $98 million in 2019 and 2018 , respectively, and elimination of intersegment revenues. Revenues net of purchased power and fuel expense (Generation): Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 RNF (a) Intersegment RNF Total RNF RNF (a) Intersegment RNF Total RNF Mid-Atlantic $ 679 $ 4 $ 683 $ 836 $ 14 $ 850 Midwest 769 2 771 847 13 860 New York 262 3 265 282 1 283 ERCOT 98 (24 ) 74 106 (70 ) 36 Other Power Regions 174 (18 ) 156 279 (43 ) 236 Total Revenues net of purchased power and fuel for Reportable Segments 1,982 (33 ) 1,949 2,350 (85 ) 2,265 Other (b) 109 33 142 (131 ) 85 (46 ) Total Generation Revenues net of purchased power and fuel expense $ 2,091 $ — $ 2,091 $ 2,219 $ — $ 2,219 __________ (a) Includes purchases and sales from/to third parties and affiliated sales to the Utility Registrants. (b) Other represents activities not allocated to a region. See text above for a description of included activities. Includes unrealized mark-to-market losses of $28 million and $266 million in 2019 and 2018 , respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 8 — Early Plant Retirements of $5 million and $15 million decrease to RNF in 2019 and 2018, respectively, and the elimination of intersegment RNF. Electric and Gas Revenue by Customer Class (Utility Registrants)
Schedule of Revenue by Major Customers by Reporting Segments [Table Text Block]	ric and Gas Revenue by Customer Class (Utility Registrants): Three Months Ended March 31, 2019 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 710 $ 409 $ 385 $ 579 $ 256 $ 185 $ 138 Small commercial & industrial 360 96 70 120 38 48 34 Large commercial & industrial 132 48 110 267 204 24 39 Public authorities & electric railroads 13 7 7 14 8 3 3 Other (a) 217 62 80 157 53 47 57 Total rate-regulated electric revenues (b) $ 1,432 $ 622 $ 652 $ 1,137 $ 559 $ 307 $ 271 Rate-regulated natural gas revenues Residential $ — $ 198 $ 219 $ 44 $ — $ 44 $ — Small commercial & industrial — 72 35 19 — 19 — Large commercial & industrial — 1 50 1 — 1 — Transportation — 7 — 4 — 4 — Other (c) — 2 4 3 — 3 — Total rate-regulated natural gas revenues (d) $ — $ 280 $ 308 $ 71 $ — $ 71 $ — Total rate-regulated revenues from contracts with customers $ 1,432 $ 902 $ 960 $ 1,208 $ 559 $ 378 $ 271 Other revenues Revenues from alternative revenue programs $ (28 ) $ (3 ) $ 10 $ 15 $ 14 $ — $ 1 Other rate-regulated electric revenues (e) 4 1 3 4 2 1 1 Other rate-regulated natural gas revenues (e) — — 3 1 — 1 — Total other revenues $ (24 ) $ (2 ) $ 16 $ 20 $ 16 $ 2 $ 2 Total rate-regulated revenues for reportable segments $ 1,408 $ 900 $ 976 $ 1,228 $ 575 $ 380 $ 273 Three Months Ended March 31, 2018 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 717 $ 403 $ 393 $ 610 $ 259 $ 191 $ 160 Small commercial & industrial 385 101 68 115 32 46 37 Large commercial & industrial 152 58 106 259 190 23 46 Public authorities & electric railroads 14 8 7 14 7 4 3 Other (a) 230 62 78 156 49 41 66 Total rate-regulated electric revenues (b) $ 1,498 $ 632 $ 652 $ 1,154 $ 537 $ 305 $ 312 Rate-regulated natural gas revenues Residential $ — $ 161 $ 224 $ 47 $ — $ 47 $ — Small commercial & industrial — 62 34 18 — 18 — Large commercial & industrial — 1 47 4 — 4 — Transportation — 6 — 5 — 5 — Other (c) — 2 27 4 — 4 — Total rate-regulated natural gas revenues (d) $ — $ 232 $ 332 $ 78 $ — $ 78 $ — Total rate-regulated revenues from contracts with customers $ 1,498 $ 864 $ 984 $ 1,232 $ 537 $ 383 $ 312 Other revenues Revenues from alternative revenue programs $ 5 $ (1 ) $ (13 ) $ 18 $ 19 $ 1 $ (2 ) Other rate-regulated electric revenues (e) 9 3 4 1 1 — — Other rate-regulated natural gas revenues (e) — — 2 — — — — Total other revenues $ 14 $ 2 $ (7 ) $ 19 $ 20 $ 1 $ (2 ) Total rate-regulated revenues for reportable segments $ 1,512 $ 866 $ 977 $ 1,251 $ 557 $ 384 $ 310 __________ (a) Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue. (b) Includes operating revenues from affiliates of $4 million , $1 million , $2 million , $3 million , $2 million , $2 million and $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2019 and $14 million , $2 million , $2 million , $4 million $2 million , $2 million and 1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2018 . (c) Includes revenues from off-system natural gas sales. (d) Includes operating revenues from affiliates of less than $1 million and $4 million at PECO and BGE, respectively, in 2019 and 2018 . (e) Includes late payment charge revenues.

Variable Interest Entities - Na

Variable Interest Entities - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)VIE	Mar. 31, 2018USD ($)	Dec. 31, 2018VIE	Apr. 01, 2014USD ($)
Variable Interest Entity [Line Items]
Number Of Variable Interest Entities Consolidated | VIE	5		5
Number of Variable Interest Entities not consolidated by equity holders | VIE	7		7
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 68
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	16
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	16
Payment Guarantee [Member] | CENG [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted				$ 245
Financial Guarantee [Member] | CENG [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted				165
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value	32
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	12
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	12
Exelon Generation Co L L C [Member] | CENG [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value	$ 688
Equity Method Investment, Ownership Percentage	50.01%
Due from Affiliates				$ 400
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 17
Atlantic City Electric Company [Member] | ATF [Member]
Variable Interest Entity [Line Items]
Cash Remitted To VIE	$ 4	$ 8

Variable Interest Entities - Ca

Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Current assets		$ 645	$ 938
Noncurrent assets		9,235	9,071
Total assets	[1]	9,880	10,009
Current liabilities		748	274
Noncurrent liabilities		2,831	3,280
Total liabilities	[1]	3,579	3,554
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		639	931
Noncurrent assets		9,210	9,045
Total assets		9,849	9,976
Current liabilities		725	252
Noncurrent liabilities		2,790	3,233
Total liabilities		3,515	3,485
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Current assets		6	7
Noncurrent assets		25	26
Total assets	[1]	31	33
Current liabilities		23	22
Noncurrent liabilities		41	47
Total liabilities	[1]	64	69
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		3	4
Noncurrent assets		19	19
Total assets		22	23
Current liabilities		19	19
Noncurrent liabilities		35	40
Total liabilities		$ 54	$ 59
[1]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.

Variable Interest Entities - As

Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 880	$ 1,349	$ 787	$ 898
Restricted cash and cash equivalents		223	247	209	207
Accounts receivable, net
Customer		4,564	4,607
Other		1,062	1,256
Inventory, net
Materials and Supplies		1,380	1,351
Other current assets		1,406	1,238
Total current assets		12,476	13,360
Property, plant and equipment, net		77,460	76,707
NDT funds		12,302	11,661
Other Assets, Noncurrent		3,017	1,575
Total assets	[1]	121,593	119,666
Long-term debt due within one year		2,508	1,349
Accounts payable		3,327	3,800
Accrued expenses		1,725	2,112
Unamortized energy contract liabilities		151	149
Other Liabilities, Current		1,245	1,035
Total current liabilities		12,229	11,404
Long-term debt		32,960	34,075
Asset retirement obligations		9,967	9,679
Unamortized energy contract liabilities		432	463
Other Liabilities, Noncurrent		3,158	2,130
Total liabilities	[1]	87,889	86,596
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		125	414
Restricted cash and cash equivalents		58	66
Accounts receivable, net
Customer		152	146
Other		23	23
Inventory, net
Materials and Supplies		213	212
Other current assets		51	52
Total current assets	[2]	622	913
Property, plant and equipment, net		6,147	6,145
NDT funds		2,520	2,351
Other Assets, Noncurrent		257	258
Total noncurrent assets	[2]	8,924	8,754
Total assets	[2]	9,546	9,667
Long-term debt due within one year		567	87
Accounts payable		120	96
Accrued expenses		42	72
Unamortized energy contract liabilities		13	15
Other Liabilities, Current		6	3
Total current liabilities	[2]	748	273
Long-term debt		565	1,072
Asset retirement obligations		2,190	2,160
Unamortized energy contract liabilities		0	1
Other Liabilities, Noncurrent		69	42
Total noncurrent liabilities	[2]	2,824	3,275
Total liabilities	[2]	3,572	3,548
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		537	750	610	416
Restricted cash and cash equivalents		139	153	127	138
Accounts receivable, net
Customer		2,800	2,941
Other		367	562
Inventory, net
Materials and Supplies		965	963
Other current assets		1,013	883
Total current assets		7,721	8,433
Property, plant and equipment, net		24,034	23,981
NDT funds		12,302	11,661
Other Assets, Noncurrent		1,813	755
Total assets	[3]	48,682	47,556
Long-term debt due within one year		2,365	906
Accounts payable		1,566	1,847
Accrued expenses		675	898
Unamortized energy contract liabilities		28	31
Other Liabilities, Current		425	279
Total current liabilities		6,660	5,769
Long-term debt		5,487	6,989
Asset retirement obligations		9,737	9,450
Unamortized energy contract liabilities		16	20
Other Liabilities, Noncurrent		1,528	610
Total liabilities	[3]	32,986	32,048
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		125	414
Restricted cash and cash equivalents		55	62
Accounts receivable, net
Customer		152	146
Other		23	23
Inventory, net
Materials and Supplies		213	212
Other current assets		48	49
Total current assets		616	906
Property, plant and equipment, net		6,147	6,145
NDT funds		2,520	2,351
Other Assets, Noncurrent		232	232
Total noncurrent assets		8,899	8,728
Total assets		9,515	9,634
Long-term debt due within one year		545	66
Accounts payable		120	96
Accrued expenses		41	72
Unamortized energy contract liabilities		13	15
Other Liabilities, Current		6	3
Total current liabilities		725	252
Long-term debt		524	1,025
Asset retirement obligations		2,190	2,160
Unamortized energy contract liabilities		0	1
Other Liabilities, Noncurrent		69	42
Total noncurrent liabilities		2,783	3,228
Total liabilities		3,508	3,480
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		33	124	43	30
Restricted cash and cash equivalents		39	43	40	42
Accounts receivable, net
Customer		445	453
Other		189	177
Inventory, net
Materials and Supplies		184	163
Other current assets		54	75
Total current assets		1,453	1,533
Property, plant and equipment, net		13,619	13,446
Other Assets, Noncurrent		370	60
Total assets	[4]	22,294	21,984
Long-term debt due within one year		125	125
Accounts payable		441	496
Accrued expenses		253	256
Unamortized energy contract liabilities		123	119
Other Liabilities, Current		127	123
Total current liabilities		1,675	1,592
Long-term debt		6,119	6,134
Asset retirement obligations		52	52
Unamortized energy contract liabilities		416	442
Other Liabilities, Noncurrent		630	369
Total liabilities	[4]	13,004	12,702
Pepco Holdings LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0	0
Restricted cash and cash equivalents		3	4
Accounts receivable, net
Customer		0	0
Other		0	0
Inventory, net
Materials and Supplies		0	0
Other current assets		3	3
Total current assets	[2]	6	7
Property, plant and equipment, net		0	0
NDT funds		0	0
Other Assets, Noncurrent		25	26
Total noncurrent assets	[2]	25	26
Total assets	[2]	31	33
Long-term debt due within one year		22	21
Accounts payable		0	0
Accrued expenses		1	1
Unamortized energy contract liabilities		0	0
Other Liabilities, Current		0	0
Total current liabilities	[2]	23	22
Long-term debt		41	47
Asset retirement obligations		0	0
Unamortized energy contract liabilities		0	0
Other Liabilities, Noncurrent		0	0
Total noncurrent liabilities	[2]	41	47
Total liabilities	[2]	64	69
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		6	7	10	2
Restricted cash and cash equivalents		3	4	$ 7	$ 6
Accounts receivable, net
Customer		85	95
Other		52	55
Inventory, net
Other current assets		6	5
Total current assets		238	240
Property, plant and equipment, net		3,041	2,966
Other Assets, Noncurrent		64	40
Total assets	[5]	3,783	3,699
Long-term debt due within one year		19	18
Accounts payable		139	154
Accrued expenses		38	35
Other Liabilities, Current		10	4
Total current liabilities		492	422
Long-term debt		1,165	1,170
Other Liabilities, Noncurrent		46	27
Total liabilities	[5]	2,654	2,573
Atlantic City Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0	0
Restricted cash and cash equivalents		3	4
Accounts receivable, net
Customer		0	0
Other		0	0
Inventory, net
Materials and Supplies		0	0
Other current assets		0	0
Total current assets		3	4
Property, plant and equipment, net		0	0
NDT funds		0	0
Other Assets, Noncurrent		19	19
Total noncurrent assets		19	19
Total assets		22	23
Long-term debt due within one year		19	18
Accounts payable		0	0
Accrued expenses		0	1
Unamortized energy contract liabilities		0	0
Other Liabilities, Current		0	0
Total current liabilities		19	19
Long-term debt		35	40
Asset retirement obligations		0	0
Unamortized energy contract liabilities		0	0
Other Liabilities, Noncurrent		0	0
Total noncurrent liabilities		35	40
Total liabilities		$ 54	$ 59
[1]	Exelon’s consolidated assets include $9,546 million and $9,667 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,572 million and $3,548 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2 — Variable Interest Entities for additional information.
[2]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.
[3]	Generation’s consolidated assets include $9,515 million and $9,634 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,508 million and $3,480 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2 — Variable Interest Entities for additional information.
[4]	PHI’s consolidated total assets include $31 million and $33 million at March 31, 2019 and December 31, 2018, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $64 million and $69 million at March 31, 2019 and December 31, 2018, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 2 — Variable Interest Entities for additional information.
[5]	ACE’s consolidated total assets include $22 million and $23 million at March 31, 2019 and December 31, 2018, respectively, of ACE's consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated total liabilities include $54 million and $59 million at March 31, 2019 and December 31, 2018, respectively, of ACE's consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 2 — Variable Interest Entities for additional information.

Variable Interest Entities - Su

Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Total assets	[1]	$ 1,064	$ 1,069
Total liabilities	[1]	265	259
Exelon's ownership interest in VIE	[1]	214	223
Other ownership interests in VIE	[1]	585	587
Registrants' maximum exposure to loss		16
Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		214	223
Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		7	7
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets		601	597
Total liabilities		42	37
Exelon's ownership interest in VIE		0	0
Other ownership interests in VIE		559	560
Commercial Agreement Variable Interest Entities [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		0	0
Commercial Agreement Variable Interest Entities [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		7	7
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets		463	472
Total liabilities		223	222
Exelon's ownership interest in VIE		214	223
Other ownership interests in VIE		26	27
Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		214	223
Equity Investment VIE [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		0	$ 0
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		$ 12
[1]	These items represent amounts in the unconsolidated VIE balance sheets, not in Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs.

Mergers, Acquisitions and Dis_2

Mergers, Acquisitions and Dispositions - Narrative (Details) - USD ($) $ in Millions	Feb. 28, 2018	Sep. 30, 2018	Mar. 31, 2019	Dec. 31, 2018
Business Dispositions [Line Items]
Assets held for sale			$ 890	$ 904
Liabilities held for sale			799	777
Proceeds from Divestiture of Businesses	$ 87
Exelon Generation Co L L C [Member]
Business Dispositions [Line Items]
Assets held for sale			890	904
Liabilities held for sale			799	777
Proceeds from Divestiture of Businesses	$ 87
Oyster Creek [Member]
Business Dispositions [Line Items]
Assets held for sale			888	897
Liabilities held for sale			765	777
Oyster Creek [Member] | Exelon Generation Co L L C [Member]
Business Dispositions [Line Items]
Assets held for sale			888	897
Liabilities held for sale			$ 765	$ 777
Asset Retirement Obligation Revision Of Estimate In Operating And Maintenance Expense		$ 84

Revenue from Contracts with C_3

Revenue from Contracts with Customers Change in Contract with Customer, Asset and Liability (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in Contract with Customer, Asset and Liability [Line Items]
Contract with Customer, Asset, Net, Current	$ 187	$ 187	$ 283
Contract with Customer, Liability, Current	25	27	35
Increases (decreases) as a result of changes in the estimate of the stage of completion, contract assets	26	50
Increases (decreases) as a result of changes in the estimate of the stage of completion, contract liabilities	0	0
Increases (decreases) as a result of additional cash received or due, contract assets	0	0
Increases (decreases) as a result of additional cash received or due, contract liabilities	21	179
Amounts reclassified to receivables, contract assets	(26)	(146)
Amounts recognized into revenues, contract liabilities	(23)	(187)
Exelon Generation Co L L C [Member]
Change in Contract with Customer, Asset and Liability [Line Items]
Contract with Customer, Asset, Net, Current	187	187	283
Contract with Customer, Liability, Current	39	42	$ 35
Increases (decreases) as a result of changes in the estimate of the stage of completion, contract assets	26	50
Increases (decreases) as a result of changes in the estimate of the stage of completion, contract liabilities	0	0
Increases (decreases) as a result of additional cash received or due, contract assets	0	0
Increases (decreases) as a result of additional cash received or due, contract liabilities	63	465
Amounts reclassified to receivables, contract assets	(26)	(146)
Amounts recognized into revenues, contract liabilities	$ (66)	$ (458)

Revenue from Contracts with C_4

Revenue from Contracts with Customers Performance Obligations (Details) $ in Millions	Mar. 31, 2019USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	$ 393
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01 | Exelon Generation Co L L C [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	493
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	273
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01 | Exelon Generation Co L L C [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	331
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	112
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01 | Exelon Generation Co L L C [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	126
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	50
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01 | Exelon Generation Co L L C [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	50
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	142
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01 | Exelon Generation Co L L C [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	142
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	970
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil) | Exelon Generation Co L L C [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	$ 1,142

Leases Lessee - Narrative (Deta

Leases Lessee - Narrative (Details)	3 Months Ended
	Mar. 31, 2019
Contracted Generation [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Real Estate [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Vehicles & Equipment [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Minimum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	1 year
Options to extend the term, Lessee, Operating Lease	3 years
Options to terminate within, Lessee, Operating Lease	1 years
Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	87 years
Options to extend the term, Lessee, Operating Lease	30 years
Options to terminate within, Lessee, Operating Lease	3 years
Atlantic City Electric Company [Member] | Real Estate [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Atlantic City Electric Company [Member] | Vehicles & Equipment [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Atlantic City Electric Company [Member] | Minimum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	1 year
Atlantic City Electric Company [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	8 years
Delmarva Power and Light Company [Member] | Real Estate [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Delmarva Power and Light Company [Member] | Vehicles & Equipment [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Delmarva Power and Light Company [Member] | Minimum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	1 year
Options to extend the term, Lessee, Operating Lease	3 years
Delmarva Power and Light Company [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	13 years
Options to extend the term, Lessee, Operating Lease	30 years
Potomac Electric Power Company [Member] | Real Estate [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Potomac Electric Power Company [Member] | Vehicles & Equipment [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Potomac Electric Power Company [Member] | Minimum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	1 year
Options to extend the term, Lessee, Operating Lease	5 years
Potomac Electric Power Company [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	13 years
Options to extend the term, Lessee, Operating Lease	5 years
Pepco Holdings LLC [Member] | Real Estate [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Pepco Holdings LLC [Member] | Vehicles & Equipment [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Pepco Holdings LLC [Member] | Minimum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	1 year
Options to extend the term, Lessee, Operating Lease	3 years
Pepco Holdings LLC [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	13 years
Options to extend the term, Lessee, Operating Lease	30 years
Baltimore Gas and Electric Company [Member] | Real Estate [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Baltimore Gas and Electric Company [Member] | Vehicles & Equipment [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Baltimore Gas and Electric Company [Member] | Minimum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	1 year
Options to terminate within, Lessee, Operating Lease	3 years
Baltimore Gas and Electric Company [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	87 years
Options to terminate within, Lessee, Operating Lease	3 years
PECO Energy Co [Member] | Real Estate [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
PECO Energy Co [Member] | Vehicles & Equipment [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
PECO Energy Co [Member] | Minimum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	1 year
PECO Energy Co [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	15 years
Commonwealth Edison Co [Member] | Real Estate [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Commonwealth Edison Co [Member] | Vehicles & Equipment [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Commonwealth Edison Co [Member] | Minimum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	1 year
Options to extend the term, Lessee, Operating Lease	3 years
Commonwealth Edison Co [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	34 years
Options to extend the term, Lessee, Operating Lease	10 years
Exelon Generation Co L L C [Member] | Contracted Generation [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Exelon Generation Co L L C [Member] | Real Estate [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Exelon Generation Co L L C [Member] | Vehicles & Equipment [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Exelon Generation Co L L C [Member] | Minimum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	1 year
Options to extend the term, Lessee, Operating Lease	3 years
Options to terminate within, Lessee, Operating Lease	2 years
Exelon Generation Co L L C [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	37 years
Options to extend the term, Lessee, Operating Lease	30 years
Options to terminate within, Lessee, Operating Lease	2 years

Leases Components of Lease Cost

Leases Components of Lease Cost (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	$ 68
Variable Lease Cost	73
Short-term Lease Cost	9
Total Lease Cost	150	[1]
Sublease Income	$ 3
Operating Lease, Weighted Average Remaining Lease Term	10 years
Operating Lease Weighted Average Discount Rate, Percent	4.60%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 20
Exelon Generation Co L L C [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	46
Variable Lease Cost	68
Short-term Lease Cost	8
Total Lease Cost	122	[1]
Sublease Income	$ 2
Operating Lease, Weighted Average Remaining Lease Term	10 years 8 months 12 days
Operating Lease Weighted Average Discount Rate, Percent	4.80%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 9
Commonwealth Edison Co [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	1
Variable Lease Cost	0
Short-term Lease Cost	0
Total Lease Cost	$ 1
Operating Lease, Weighted Average Remaining Lease Term	2 years 10 months 24 days
Operating Lease Weighted Average Discount Rate, Percent	3.30%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 0
PECO Energy Co [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	0
Variable Lease Cost	0
Short-term Lease Cost	0
Total Lease Cost	$ 0
Operating Lease, Weighted Average Remaining Lease Term	4 years 4 months 24 days
Operating Lease Weighted Average Discount Rate, Percent	3.40%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 0
Baltimore Gas and Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	8
Variable Lease Cost	0
Short-term Lease Cost	0
Total Lease Cost	$ 8
Operating Lease, Weighted Average Remaining Lease Term	5 years 7 months 6 days
Operating Lease Weighted Average Discount Rate, Percent	3.60%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 0
Pepco Holdings LLC [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	10
Variable Lease Cost	2
Short-term Lease Cost	0
Total Lease Cost	12	[1]
Sublease Income	$ 1
Operating Lease, Weighted Average Remaining Lease Term	9 years 4 months 24 days
Operating Lease Weighted Average Discount Rate, Percent	4.10%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 11
Potomac Electric Power Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	3
Variable Lease Cost	0
Short-term Lease Cost	0
Total Lease Cost	$ 3
Operating Lease, Weighted Average Remaining Lease Term	9 years 10 months 24 days
Operating Lease Weighted Average Discount Rate, Percent	3.90%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 4
Delmarva Power and Light Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	3
Variable Lease Cost	1
Short-term Lease Cost	0
Total Lease Cost	4	[1]
Sublease Income	$ 1
Operating Lease, Weighted Average Remaining Lease Term	9 years 9 months 18 days
Operating Lease Weighted Average Discount Rate, Percent	3.90%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 4
Atlantic City Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	1
Variable Lease Cost	0
Short-term Lease Cost	0
Total Lease Cost	$ 1
Operating Lease, Weighted Average Remaining Lease Term	5 years 3 months 18 days
Operating Lease Weighted Average Discount Rate, Percent	3.50%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 3
[1]	Excludes $3 million, $2 million, $1 million and $1 million of sublease income recorded at Exelon, Generation, PHI and DPL.

Leases Supplemental Balance She

Leases Supplemental Balance Sheet Information Related to Lessee Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		$ 3,017	$ 1,575
Other current liabilities		1,245	1,035
Other deferred credits and other liabilities		3,158	2,130
Total Operating Lease Liabilities	[1]	1,644
Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		1,813	755
Other current liabilities		425	279
Other deferred credits and other liabilities		1,528	610
Total Operating Lease Liabilities	[1]	1,196
Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		347	395
Other current liabilities		98	96
Other deferred credits and other liabilities		582	630
Total Operating Lease Liabilities		7
PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		29	27
Other current liabilities		32	24
Other deferred credits and other liabilities		81	76
Total Operating Lease Liabilities		2
Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		105	5
Other current liabilities		54	27
Other deferred credits and other liabilities		130	73
Total Operating Lease Liabilities		97
Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		370	60
Other current liabilities		127	123
Other deferred credits and other liabilities		630	369
Total Operating Lease Liabilities		320
Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		80	15
Other current liabilities		17	42
Other deferred credits and other liabilities		360	312
Total Operating Lease Liabilities		68
Delmarva Power and Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		81	6
Other current liabilities		16	7
Other deferred credits and other liabilities		114	50
Total Operating Lease Liabilities		83
Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		64	40
Other current liabilities		10	4
Other deferred credits and other liabilities		46	$ 27
Total Operating Lease Liabilities		26
Contracted Generation [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		631
Total Operating Lease Liabilities		778
Contracted Generation [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		631
Total Operating Lease Liabilities		778
Other Deferred Debits and Other Assets [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	[1]	1,465
Other Deferred Debits and Other Assets [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets	[1]	1,027
Other Deferred Debits and Other Assets [Member] | Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		5
Other Deferred Debits and Other Assets [Member] | PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		2
Other Deferred Debits and Other Assets [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		97
Other Deferred Debits and Other Assets [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		314
Other Deferred Debits and Other Assets [Member] | Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		67
Other Deferred Debits and Other Assets [Member] | Delmarva Power and Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		75
Other Deferred Debits and Other Assets [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred debits and other assets		26
Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	[1]	249
Other Current Liabilities [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	[1]	173
Other Current Liabilities [Member] | Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities		3
Other Current Liabilities [Member] | PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities		1
Other Current Liabilities [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities		31
Other Current Liabilities [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities		36
Other Current Liabilities [Member] | Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities		8
Other Current Liabilities [Member] | Delmarva Power and Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities		11
Other Current Liabilities [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities		6
Other Deferred Credits and Other Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	[1]	1,395
Other Deferred Credits and Other Liabilities [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	[1]	1,023
Other Deferred Credits and Other Liabilities [Member] | Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities		4
Other Deferred Credits and Other Liabilities [Member] | PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities		1
Other Deferred Credits and Other Liabilities [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities		66
Other Deferred Credits and Other Liabilities [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities		284
Other Deferred Credits and Other Liabilities [Member] | Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities		60
Other Deferred Credits and Other Liabilities [Member] | Delmarva Power and Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities		72
Other Deferred Credits and Other Liabilities [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities		$ 20
[1]	Exelon's and Generation's operating ROU assets and lease liabilities include $631 million and $778 million, respectively, related to contracted generation.

Leases Lessee Future Minimum Op

Leases Lessee Future Minimum Operating Lease Maturity Payments (Details) $ in Millions	Mar. 31, 2019USD ($)
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	$ 214
2020	289
2021	244
2022	174
2023	139
Remaining Years	1,052
Lessee, Operating Lease, Liability, Payments, Due	2,112
Interest	468
Operating Lease, Liability	1,644	[1]
Exelon Generation Co L L C [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	154
2020	202
2021	162
2022	112
2023	99
Remaining Years	840
Lessee, Operating Lease, Liability, Payments, Due	1,569
Interest	373
Operating Lease, Liability	1,196	[1]
Commonwealth Edison Co [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	2
2020	2
2021	2
2022	1
2023	0
Remaining Years	0
Lessee, Operating Lease, Liability, Payments, Due	7
Interest	0
Operating Lease, Liability	7
PECO Energy Co [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	1
2020	1
2021	0
2022	0
2023	0
Remaining Years	0
Lessee, Operating Lease, Liability, Payments, Due	2
Interest	0
Operating Lease, Liability	2
Baltimore Gas and Electric Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	19
2020	34
2021	32
2022	16
2023	0
Remaining Years	18
Lessee, Operating Lease, Liability, Payments, Due	119
Interest	22
Operating Lease, Liability	97
Pepco Holdings LLC [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	33
2020	43
2021	42
2022	40
2023	39
Remaining Years	194
Lessee, Operating Lease, Liability, Payments, Due	391
Interest	71
Operating Lease, Liability	320
Potomac Electric Power Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	8
2020	9
2021	9
2022	8
2023	8
Remaining Years	42
Lessee, Operating Lease, Liability, Payments, Due	84
Interest	16
Operating Lease, Liability	68
Delmarva Power and Light Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	7
2020	12
2021	11
2022	11
2023	10
Remaining Years	52
Lessee, Operating Lease, Liability, Payments, Due	103
Interest	20
Operating Lease, Liability	83
Atlantic City Electric Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	5
2020	5
2021	5
2022	4
2023	3
Remaining Years	7
Lessee, Operating Lease, Liability, Payments, Due	29
Interest	3
Operating Lease, Liability	$ 26
[1]	Exelon's and Generation's operating ROU assets and lease liabilities include $631 million and $778 million, respectively, related to contracted generation.

Leases Lessee 2018 Schedule of

Leases Lessee 2018 Schedule of Minimum Future Operating Lease Payments (Details) $ in Millions	Dec. 31, 2018USD ($)
Operating Leases Future Minimum Payments Due [Line Items]
2019	$ 140	[1],[2]
2020	149	[1],[2]
2021	143	[1],[2]
2022	126	[1],[2]
2023	97	[1],[2]
Remaining Years	723	[1],[2]
Total Minimum Future Operating Lease Payments Due	1,378	[1],[2]
Exelon Generation Co L L C [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	33	[1],[2]
2020	46	[1],[2]
2021	46	[1],[2]
2022	47	[1],[2]
2023	46	[1],[2]
Remaining Years	545	[1],[2]
Total Minimum Future Operating Lease Payments Due	763	[1],[2]
Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	7	[2],[3]
2020	5	[2],[3]
2021	4	[2],[3]
2022	4	[2],[3]
2023	3	[2],[3]
Remaining Years	0	[2],[3]
Total Minimum Future Operating Lease Payments Due	23	[2],[3]
PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	5	[2],[3]
2020	5	[2],[3]
2021	5	[2],[3]
2022	5	[2],[3]
2023	5	[2],[3]
Remaining Years	0	[2],[3]
Total Minimum Future Operating Lease Payments Due	25	[2],[3]
Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	35	[2],[3],[4],[5]
2020	35	[2],[3],[4],[5]
2021	33	[2],[3],[4],[5]
2022	18	[2],[3],[4],[5]
2023	3	[2],[3],[4],[5]
Remaining Years	19	[2],[3],[4],[5]
Total Minimum Future Operating Lease Payments Due	143	[2],[3],[4],[5]
Pepco Holdings LLC [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	48	[2]
2020	46	[2]
2021	43	[2]
2022	42	[2]
2023	39	[2]
Remaining Years	159	[2]
Total Minimum Future Operating Lease Payments Due	377	[2]
Potomac Electric Power Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	11	[2]
2020	10	[2]
2021	9	[2]
2022	8	[2]
2023	8	[2]
Remaining Years	40	[2]
Total Minimum Future Operating Lease Payments Due	86	[2]
Delmarva Power and Light Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	14	[2],[3]
2020	13	[2],[3]
2021	12	[2],[3]
2022	12	[2],[3]
2023	10	[2],[3]
Remaining Years	35	[2],[3]
Total Minimum Future Operating Lease Payments Due	96	[2],[3]
Atlantic City Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	7	[2]
2020	6	[2]
2021	5	[2]
2022	5	[2]
2023	4	[2]
Remaining Years	5	[2]
Total Minimum Future Operating Lease Payments Due	32	[2]
Real Estate Leases and Railroad Licenses [Member] | Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total Minimum Future Operating Lease Payments Due	3
Real Estate Leases and Railroad Licenses [Member] | PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total Minimum Future Operating Lease Payments Due	5
Real Estate Leases and Railroad Licenses [Member] | Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total Minimum Future Operating Lease Payments Due	1
Real Estate Leases and Railroad Licenses [Member] | Delmarva Power and Light Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total Minimum Future Operating Lease Payments Due	1
Electrical Conduit System [Member] | Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	26
2020	28
2021	28
2022	$ 14
[1]	Excludes Generation’s contingent operating lease payments associated with contracted generation.
[2]	Includes amounts related to shared use land arrangements.
[3]	Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO, BGE and DPL have excluded these payments from the remaining years as such amounts would not be meaningful. ComEd's, PECO’s, BGE’s and DPL's average annual obligation for these arrangements, included in each of the years 2019 - 2023, was $3 million, $5 million, $1 million and $1 million respectively. Also includes amounts related to shared use land arrangements.
[4]	Includes all future lease payments on a 99-year real estate lease that expires in 2106.
[5]	The BGE column above includes minimum future lease payments associated with a 6-year lease for the Baltimore City conduit system that became effective during the fourth quarter of 2016. BGE's total commitments under the lease agreement are $26 million, $28 million, $28 million and $14 million related to years 2019 - 2022, respectively.

Leases Supplemental Cash Flow I

Leases Supplemental Cash Flow Information Related to Leases (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	$ 78
Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	52
Commonwealth Edison Co [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	1
PECO Energy Co [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	0
Baltimore Gas and Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	14
Pepco Holdings LLC [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	8
Potomac Electric Power Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	2
Delmarva Power and Light Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	2
Atlantic City Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	$ 1

Leases Lessor - Narrative (Deta

Leases Lessor - Narrative (Details)	3 Months Ended
	Mar. 31, 2019
Minimum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	1 year
Options to extend the term, Lessor, Operating Lease	1 years
Maximum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	84 years
Options to extend the term, Lessor, Operating Lease	79 years
Exelon Generation Co L L C [Member] | Minimum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	1 year
Options to extend the term, Lessor, Operating Lease	1 years
Exelon Generation Co L L C [Member] | Maximum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	33 years
Options to extend the term, Lessor, Operating Lease	5 years
Commonwealth Edison Co [Member] | Minimum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	1 year
Options to extend the term, Lessor, Operating Lease	5 years
Commonwealth Edison Co [Member] | Maximum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	18 years
Options to extend the term, Lessor, Operating Lease	79 years
PECO Energy Co [Member] | Minimum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	1 year
Options to extend the term, Lessor, Operating Lease	5 years
PECO Energy Co [Member] | Maximum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	84 years
Options to extend the term, Lessor, Operating Lease	50 years
Baltimore Gas and Electric Company [Member] | Minimum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	24 years
Baltimore Gas and Electric Company [Member] | Maximum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	24 years
Pepco Holdings LLC [Member] | Minimum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	1 year
Options to extend the term, Lessor, Operating Lease	5 years
Pepco Holdings LLC [Member] | Maximum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	14 years
Options to extend the term, Lessor, Operating Lease	5 years
Potomac Electric Power Company [Member] | Minimum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	2 years
Potomac Electric Power Company [Member] | Maximum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	7 years
Delmarva Power and Light Company [Member] | Minimum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	13 years
Delmarva Power and Light Company [Member] | Maximum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	14 years
Atlantic City Electric Company [Member] | Minimum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	1 year
Atlantic City Electric Company [Member] | Maximum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	3 years
Contracted Generation [Member]
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Description	●
Contracted Generation [Member] | Exelon Generation Co L L C [Member]
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Description	●
Real Estate [Member]
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Description	●
Real Estate [Member] | Exelon Generation Co L L C [Member]
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Description	●
Real Estate [Member] | Commonwealth Edison Co [Member]
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Description	●
Real Estate [Member] | PECO Energy Co [Member]
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Description	●
Real Estate [Member] | Baltimore Gas and Electric Company [Member]
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Description	●
Real Estate [Member] | Pepco Holdings LLC [Member]
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Description	●
Real Estate [Member] | Potomac Electric Power Company [Member]
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Description	●
Real Estate [Member] | Delmarva Power and Light Company [Member]
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Description	●
Real Estate [Member] | Atlantic City Electric Company [Member]
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Description	●

Leases Components of Operating

Leases Components of Operating Lease Income (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	$ 4
Variable Lease Income	52
Exelon Generation Co L L C [Member]
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	3
Variable Lease Income	52
Commonwealth Edison Co [Member]
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	0
Variable Lease Income	0
PECO Energy Co [Member]
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	0
Variable Lease Income	0
Baltimore Gas and Electric Company [Member]
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	0
Variable Lease Income	0
Pepco Holdings LLC [Member]
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	1
Variable Lease Income	0
Potomac Electric Power Company [Member]
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	0
Variable Lease Income	0
Delmarva Power and Light Company [Member]
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	1
Variable Lease Income	0
Atlantic City Electric Company [Member]
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	0
Variable Lease Income	$ 0

Leases Lessor Future Minimum Op

Leases Lessor Future Minimum Operating Lease Maturity Payments (Details) $ in Millions	Mar. 31, 2019USD ($)
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	$ 47
2020	51
2021	50
2022	50
2023	49
Remaining years	315
Total Lessor, Operating Lease, Payments to be Received	562
Exelon Generation Co L L C [Member]
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	43
2020	46
2021	45
2022	45
2023	45
Remaining years	271
Total Lessor, Operating Lease, Payments to be Received	495
Commonwealth Edison Co [Member]
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	0
2020	0
2021	0
2022	0
2023	0
Remaining years	1
Total Lessor, Operating Lease, Payments to be Received	1
PECO Energy Co [Member]
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	0
2020	0
2021	0
2022	0
2023	0
Remaining years	3
Total Lessor, Operating Lease, Payments to be Received	3
Baltimore Gas and Electric Company [Member]
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	0
2020	0
2021	0
2022	0
2023	0
Remaining years	1
Total Lessor, Operating Lease, Payments to be Received	1
Pepco Holdings LLC [Member]
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	4
2020	4
2021	4
2022	4
2023	4
Remaining years	39
Total Lessor, Operating Lease, Payments to be Received	59
Potomac Electric Power Company [Member]
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	0
2020	0
2021	0
2022	0
2023	0
Remaining years	1
Total Lessor, Operating Lease, Payments to be Received	1
Delmarva Power and Light Company [Member]
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	3
2020	3
2021	3
2022	3
2023	3
Remaining years	38
Total Lessor, Operating Lease, Payments to be Received	53
Atlantic City Electric Company [Member]
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	0
2020	0
2021	0
2022	0
2023	0
Remaining years	0
Total Lessor, Operating Lease, Payments to be Received	$ 0

Regulatory Matters - Narrative

Regulatory Matters - Narrative (Details) - USD ($) $ in Millions	Apr. 15, 2019	Feb. 28, 2019	May 01, 2017	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2018
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment				$ 1,873	$ 1,880
Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets							$ 76
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment				511	628
License Costs				38
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment				503	531
Commonwealth Edison Co [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets							51
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 22
Public Utilities, Requested Equity Capital Structure, Percentage			11.00%
Prior Year Revenue Adjustment				6
Payments to Acquire Property, Plant, and Equipment				222	217
PECO Energy Co [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act				20
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment				258	224
Baltimore Gas and Electric Company [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets							15
Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment				358	258
Pepco Holdings LLC [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets							10
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment				144	127
Potomac Electric Power Company [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets							3
Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment				78	65
Delmarva Power and Light Company [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets							5
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment		$ 338		$ 128	$ 63
Atlantic City Electric Company [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets							$ 2
Atlantic City Electric Company [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment	$ 96
Zero Emission Standard [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Revenue, Net						$ 150
Nuclear Plant [Member] | Exelon Generation Co L L C [Member] | Salem [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share				42.59%

Regulatory Matters Schedule of

Regulatory Matters Schedule of Completed Rate Cases (Details) (Details) - USD ($) $ in Millions		Mar. 13, 2019	Jan. 04, 2019	Nov. 19, 2018	Jun. 08, 2018
Baltimore Gas and Electric Company [Member] | Gas Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 61
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 43
Public Utilities, Requested Return on Equity, Percentage			9.80%
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[1]			$ 122
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]	$ 70
Public Utilities, Requested Return on Equity, Percentage		9.60%
[1]	Requested and approved increases are before New Jersey sales and use tax

Regulatory Matters Schedule o_2

Regulatory Matters Schedule of Pending Rate Cases (Details) (Details) - Electric Distribution [Member] - USD ($) $ in Millions		Apr. 08, 2019	Jan. 15, 2019	Dec. 31, 2018
Potomac Electric Power Company [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 27
Public Utilities, Requested Return on Equity, Percentage			10.30%
Commonwealth Edison Co [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 57
Public Utilities, Approved Rate Increase (Decrease), Amount				$ (63)
Public Utilities, Requested Equity Capital Structure, Percentage				6.53%
Subsequent Event [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]	$ (6)
Public Utilities, Requested Return on Equity, Percentage	[1]	8.90%
[1]	Reflects an increase of $57 million for the initial revenue requirement for 2019 and a decrease of $63 million related to the annual reconciliation for 2018. The revenue requirement for 2019 and annual reconciliation for 2018 provides for a weighted average debt and equity return on distribution rate base of 6.53%. See Note 4 — Regulatory Matters of the Exelon 2018 Form 10-K for additional information on ComEd's distribution formula rate filings.

Regulatory Matters - Capitalize

Regulatory Matters - Capitalized Ratemaking Amount Not Recognized (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		$ 64	$ 65
Commonwealth Edison Co [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[1]	7	8
PECO Energy Co [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		0	0
Baltimore Gas and Electric Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[2]	49	49
Pepco Holdings LLC [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		8	8
Potomac Electric Power Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[3]	5	5
Delmarva Power and Light Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[3]	3	3
Atlantic City Electric Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		$ 0	$ 0
[1]	Reflects ComEd's unrecognized equity returns earned for ratemaking purposes on its electric distribution formula rate regulatory assets.
[2]	BGE's authorized amounts capitalized for ratemaking purposes primarily relate to earnings on shareholders' investment on its AMI programs.
[3]	Pepco's and DPL's authorized amounts capitalized for ratemaking purposes relate to earnings on shareholders' investment on their respective AMI Programs and Energy Efficiency and Demand Response Programs. The earnings on energy efficiency are on Pepco DC and DPL DE programs only.

Regulatory Matters - Annual Ele

Regulatory Matters - Annual Electric Transmission Fillings (Details) - USD ($) $ in Millions		Mar. 13, 2019	Jan. 04, 2019	Nov. 19, 2018	Jun. 08, 2018
Baltimore Gas and Electric Company [Member] | Gas Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase					$ 61
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 43
Public Utilities, Requested Return on Equity, Percentage			9.80%
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase	[1]			$ 122
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]	$ 70
Public Utilities, Requested Return on Equity, Percentage		9.60%
[1]	Requested and approved increases are before New Jersey sales and use tax

Impairment of Long-Lived Asse_2

Impairment of Long-Lived Assets - Narrative (Details) $ in Millions	Mar. 31, 2019USD ($)
Antelope Valley [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	$ 750
Exelon Generation Co L L C [Member] | Antelope Valley [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	750
ExGen Renewables IV, LLC [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	1,970
ExGen Renewables IV, LLC [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	$ 1,970

Early Plant Retirements - Narra

Early Plant Retirements - Narrative (Details)	Mar. 31, 2019
Salem [Member] | Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	42.59%

Early Plant Retirements - Preta

Early Plant Retirements - Pretax Expense (Details) - Facility Closing [Member] - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Three Mile Island [Member]
Accelerated depreciation	[1],[2]	$ 74
Accelerated nuclear fuel amortization	[1]	5
Operating and maintenance	[3]	(83)
Restructuring and Related Cost, Incurred Cost		(4)
TMI,OysterCreek [Member]
Accelerated depreciation	[1],[2]		$ 137
Accelerated nuclear fuel amortization	[1]		15
Operating and maintenance	[3]		26
Restructuring and Related Cost, Incurred Cost			178
Exelon Generation Co L L C [Member] | Three Mile Island [Member]
Accelerated depreciation	[1],[2]	74
Accelerated nuclear fuel amortization	[1]	5
Operating and maintenance	[3]	(83)
Restructuring and Related Cost, Incurred Cost		$ (4)
Exelon Generation Co L L C [Member] | TMI,OysterCreek [Member]
Accelerated depreciation	[1],[2]		137
Accelerated nuclear fuel amortization	[1]		15
Operating and maintenance	[3]		26
Restructuring and Related Cost, Incurred Cost			$ 178
[1]	Reflects incremental accelerated depreciation and amortization for TMI for the three months ended March 31, 2019. Reflects incremental accelerated depreciation for TMI and Oyster Creek for the three months ended March 31, 2018. The Oyster Creek amounts are from February 2, 2018 through March 31, 2018.
[2]	Reflects incremental accelerated depreciation of plant assets, including any ARC.
[3]	In 2019, primarily reflects decrease to estimated decommissioning costs for TMI. See Note 13 — Nuclear Decommissioning for additional information on the first quarter 2019 TMI ARO update. In 2018, primarily reflects materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments.

Early Plant Retirements - Impli

Early Plant Retirements - Implications of Potential Early Plant Retirement on Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Implications of Potential Early Plant Retirement [Line Items]
Completed plant, net	$ 77,460	$ 76,707
Mystic Generating Station [Member] | Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory	30
Fuel inventory	22
Completed plant, net	900
Construction work in progress	2
Asset retirement obligation	(1)
Exelon Generation Co L L C [Member]
Implications of Potential Early Plant Retirement [Line Items]
Completed plant, net	24,034	$ 23,981
Exelon Generation Co L L C [Member] | Mystic Generating Station [Member] | Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory	30
Fuel inventory	22
Completed plant, net	900
Construction work in progress	2
Asset retirement obligation	$ (1)

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities - Narrative (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net	$ 216,000,000	$ 216,000,000
EquitySecuritiesWithoutReadilyDeterminableFairValueAmount	71,000,000
Forward Power Basis	2.52
Forward Gas Basis	0.46
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net	49,000,000	$ 51,000,000
EquitySecuritiesWithoutReadilyDeterminableFairValueAmount	71,000,000
Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	127,000,000
Fixed Income Securities [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	127,000,000
Middle Market Lending [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	179,000,000
Middle Market Lending [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	179,000,000
Private Equity Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	301,000,000
Private Equity Funds [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	301,000,000
Real Estate Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	268,000,000
Real Estate Funds [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 268,000,000

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust		$ 390	$ 390
Spent Nuclear Fuel Obligation, Noncurrent		1,178	1,171
Debt Issuance Costs, Net		216	216
Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Debt Issuance Costs, Net		1	0
Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		1,254	714
Long-term debt (including amounts due within one year)	[1]	35,468	35,424
Long-term debt to financing trust	[2]	390	390
Spent Nuclear Fuel Obligation, Noncurrent		1,178	1,171
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		1,254	714
Long-term debt (including amounts due within one year)	[1]	37,254	35,869
Long-term debt to financing trust	[2]	411	400
Spent Nuclear Fuel Obligation, Noncurrent		989	949
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0	0
Long-term debt (including amounts due within one year)	[1]	0	0
Long-term debt to financing trust	[2]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		1,254	714
Long-term debt (including amounts due within one year)	[1]	35,066	33,711
Long-term debt to financing trust	[2]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		989	949
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0	0
Long-term debt (including amounts due within one year)	[1]	2,188	2,158
Long-term debt to financing trust	[2]	411	400
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Exelon Generation Co L L C [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Spent Nuclear Fuel Obligation, Noncurrent		1,178	1,171
Debt Issuance Costs, Net		49	51
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[1]	8,747	8,793
Spent Nuclear Fuel Obligation, Noncurrent		1,178	1,171
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[1]	9,084	8,910
Spent Nuclear Fuel Obligation, Noncurrent		989	949
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[1]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[1]	7,641	7,467
Spent Nuclear Fuel Obligation, Noncurrent		989	949
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[1]	1,443	1,443
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Commonwealth Edison Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust		205	205
Debt Issuance Costs, Net		67	63
Commonwealth Edison Co [Member] | Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Debt Issuance Costs, Net		1	1
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		322
Long-term debt (including amounts due within one year)	[1]	8,194	8,101
Long-term debt to financing trust	[2]	205	205
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		322
Long-term debt (including amounts due within one year)	[1]	8,855	8,390
Long-term debt to financing trust	[2]	215	209
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0
Long-term debt (including amounts due within one year)	[1]	0	0
Long-term debt to financing trust	[2]	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		322
Long-term debt (including amounts due within one year)	[1]	8,855	8,390
Long-term debt to financing trust	[2]	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0
Long-term debt (including amounts due within one year)	[1]	0	0
Long-term debt to financing trust	[2]	215	209
PECO Energy Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust		184	184
Debt Issuance Costs, Net		22	23
PECO Energy Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[1]	3,084	3,084
Long-term debt to financing trust	[2]	184	184
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[1]	3,345	3,207
Long-term debt to financing trust	[2]	196	191
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[1]	0	0
Long-term debt to financing trust	[2]	0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[1]	3,295	3,157
Long-term debt to financing trust	[2]	0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[1]	50	50
Long-term debt to financing trust	[2]	196	191
Baltimore Gas and Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Debt Issuance Costs, Net		18	18
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		106	35
Long-term debt (including amounts due within one year)	[1]	2,876	2,876
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		106	35
Long-term debt (including amounts due within one year)	[1]	3,051	2,950
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0	0
Long-term debt (including amounts due within one year)	[1]	0	0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		106	35
Long-term debt (including amounts due within one year)	[1]	3,051	2,950
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0	0
Long-term debt (including amounts due within one year)	[1]	0	0
Pepco Holdings LLC [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Debt Issuance Costs, Net		14	14
Pepco Holdings LLC [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		326	179
Long-term debt (including amounts due within one year)	[1]	6,244	6,259
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		326	179
Long-term debt (including amounts due within one year)	[1]	6,303	6,101
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0	0
Long-term debt (including amounts due within one year)	[1]	0	0
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		326	179
Long-term debt (including amounts due within one year)	[1]	5,608	5,436
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0	0
Long-term debt (including amounts due within one year)	[1]	695	665
Potomac Electric Power Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Debt Issuance Costs, Net		33	34
Potomac Electric Power Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		105	40
Long-term debt (including amounts due within one year)	[1]	2,720	2,719
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		105	40
Long-term debt (including amounts due within one year)	[1]	3,208	3,097
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0	0
Long-term debt (including amounts due within one year)	[1]	0	0
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		105	40
Long-term debt (including amounts due within one year)	[1]	3,000	2,901
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0	0
Long-term debt (including amounts due within one year)	[1]	208	196
Delmarva Power and Light Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Debt Issuance Costs, Net		12	12
Delmarva Power and Light Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		5
Long-term debt (including amounts due within one year)	[1]	1,495	1,494
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		5
Long-term debt (including amounts due within one year)	[1]	1,549	1,496
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0
Long-term debt (including amounts due within one year)	[1]	0	0
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		5
Long-term debt (including amounts due within one year)	[1]	1,345	1,303
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0
Long-term debt (including amounts due within one year)	[1]	204	193
Atlantic City Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Debt Issuance Costs, Net		6	7
Atlantic City Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		216	139
Long-term debt (including amounts due within one year)	[1]	1,184	1,188
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		216	139
Long-term debt (including amounts due within one year)	[1]	1,287	1,262
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0	0
Long-term debt (including amounts due within one year)	[1]	0	0
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		216	139
Long-term debt (including amounts due within one year)	[1]	1,004	987
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities		0	0
Long-term debt (including amounts due within one year)	[1]	$ 283	$ 275
[1]	Includes unamortized debt issuance costs which are not fair valued of $216 million, $49 million, $67 million, $22 million, $18 million, $14 million, $33 million, $12 million and $6 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of March 31, 2019. Includes unamortized debt issuance costs which are not fair valued of $216 million, $51 million, $63 million, $23 million, $18 million, $14 million, $34 million, $12 million and $7 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of December 31, 2018.
[2]	Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of March 31, 2019. Includes unamortized debt issuance costs which are not fair valued of less than $1 million and $1 million for Exelon and ComEd, respectively, as of December 31, 2018.

Fair Value of Financial Asset_5

Fair Value of Financial Assets and Liabilities - Fair Value Measurements of Assets and Liabilities, Recurring and Nonrecurring (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)		$ 345		$ 475
Derivative Liability, Noncurrent		434		479
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Collateral, Right to Reclaim Cash		43		50
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value		(7)		(44)
Derivative Asset, Notional Amount		1,223		1,432
Debt Issuance Costs, Net		216		216
Margin Deposit Assets		(33)		(94)
Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		426		458
Restricted cash member [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		71		80
Other Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		211		185
Nuclear Decommissioning Trust Fund Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments		94		130
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[1]	817		1,243
Total Assets		15,649		15,609
Deferred Compensation Liability, Current and Noncurrent		(140)		(137)
Total Liabilities		(919)		(1,091)
Total net assets (liabilities)		14,730		14,518
Alternative Investment, Fair Value Disclosure		3,774		3,433
Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		(770)		(947)
Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		(4,093)		(4,881)
Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		(119)		(94)
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]
Total mark-to-market derivative liabilities	[2],[3]	3,442		4,028
Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		(9)		(7)
Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		(2)		(4)
Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		(12)		(6)
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]
Total mark-to-market derivative liabilities		5		3
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]	13,439		12,825
Alternative Investment, Fair Value Disclosure	[4]	3,774		3,433
Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[5]	443		338
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6,359		5,890
Alternative Investment, Fair Value Disclosure		1,545		1,381
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		5,041		5,078
Alternative Investment, Fair Value Disclosure		936		846
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		1,782		1,823
Alternative Investment, Fair Value Disclosure		1
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		2,145		2,180
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		43		50
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		110		149
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	[6]	961		876
Alternative Investment, Fair Value Disclosure	[6]	935		846
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		709		680
Alternative Investment, Fair Value Disclosure		406		367
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		352		329
Alternative Investment, Fair Value Disclosure		352		329
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		535		510
Alternative Investment, Fair Value Disclosure		535		510
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	[7]	245		243
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		47		48
Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		74		72
Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		110		108
Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		3,879		4,771
Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		178		146
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],[3]	(2,950)		(3,671)
Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,107		1,246
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		(1)		10
Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		4		13
Fair Value, Measurements, Recurring [Member] | Effectsofnettingandallocationofcollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(5)		(3)
Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		42		42
Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		14		15
Fair Value, Inputs, Level 1 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Collateral received from counterparties, net of collateral paid to counterparties		52		57
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[1]	817		1,243
Total Assets		6,379		6,573
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		(4)		(3)
Total net assets (liabilities)		6,375		6,570
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]
Total mark-to-market derivative liabilities		(4)		(3)
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]
Total mark-to-market derivative liabilities		(350)		(642)
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]
Total mark-to-market derivative liabilities		0		0
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]
Total mark-to-market derivative liabilities	[2],[3]	346		639
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		0		0
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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		0		0
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]
Total mark-to-market derivative liabilities		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]	5,462		5,251
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[5]	369		252
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		3,060		2,918
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		2,033		2,081
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
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		2,033		2,081
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
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
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	[6]	0		0
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
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
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
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	[7]	121		120
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]
Investments, Fair Value Disclosure		47		48
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		74		72
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
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		273		541
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		0		0
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	[2],[3]	(294)		(582)
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		(21)		(41)
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		0		0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [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] | Effectsofnettingandallocationofcollateral1 [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] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Fair Value, Inputs, Level 2 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Collateral received from counterparties, net of collateral paid to counterparties		283		224
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[1]	0		0
Total Assets		4,149		4,165
Deferred Compensation Liability, Current and Noncurrent		(140)		(137)
Total Liabilities		(448)		(599)
Total net assets (liabilities)		3,701		3,566
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]
Total mark-to-market derivative liabilities		(299)		(455)
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]
Total mark-to-market derivative liabilities		(2,339)		(2,963)
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]
Total mark-to-market derivative liabilities		(79)		(73)
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]
Total mark-to-market derivative liabilities	[2],[3]	2,119		2,581
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		(9)		(7)
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]
Total mark-to-market derivative liabilities		(2)		(4)
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]
Total mark-to-market derivative liabilities		(12)		(6)
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]
Total mark-to-market derivative liabilities		5		3
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]	3,663		3,598
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[5]	74		86
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,753		1,591
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		1,836		1,921
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		1,545		1,593
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		112		99
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		43		50
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		110		149
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	[6]	26		30
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
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
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
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	[7]	85		85
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]
Investments, Fair Value Disclosure		0		0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		71		70
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		2,164		2,760
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		74		69
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],[3]	(1,836)		(2,357)
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		402		472
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		(1)		10
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		4		13
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		(5)		(3)
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
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		14		15
Fair Value, Inputs, Level 3 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Collateral received from counterparties, net of collateral paid to counterparties		157		76
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[1]	0		0
Total Assets		1,347		1,438
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		(467)		(489)
Total net assets (liabilities)		880		949
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]
Total mark-to-market derivative liabilities		(467)		(489)
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]
Total mark-to-market derivative liabilities		(1,404)		(1,276)
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]
Total mark-to-market derivative liabilities		(40)		(21)
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]
Total mark-to-market derivative liabilities	[2],[3]	977		808
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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	[4]	540		543
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[5]	0		0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1		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		236		230
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		236		230
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
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
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
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	[6]	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		303		313
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		0		0
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		0		0
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	[7]	39		38
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]
Investments, Fair Value Disclosure		0		0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		39		38
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		1,442		1,470
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		104		77
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	[2],[3]	(820)		(732)
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		726		815
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] | 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] | 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] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		42		42
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Exelon Generation Co L L C [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)		318		449
Derivative Liability, Noncurrent		219		252
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Collateral, Right to Reclaim Cash		43		50
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value		(7)		(44)
Derivative Asset, Notional Amount		1,223		1,432
Debt Issuance Costs, Net		49		51
Margin Deposit Assets		(33)		(94)
Exelon Generation Co L L C [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		270		283
Exelon Generation Co L L C [Member] | Restricted cash member [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		36		39
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments		94		130
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[1]	370		581
Total Assets		15,009		14,755
Deferred Compensation Liability, Current and Noncurrent		(36)		(35)
Total Liabilities		(573)		(736)
Total net assets (liabilities)		14,436		14,019
Alternative Investment, Fair Value Disclosure		3,774		3,433
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]
Total mark-to-market derivative liabilities		(530)		(698)
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]
Total mark-to-market derivative liabilities		(3,853)		(4,632)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		(119)		(94)
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]
Total mark-to-market derivative liabilities	[2],[3]	3,442		4,028
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		(7)		(3)
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]
Total mark-to-market derivative liabilities		0		0
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]
Total mark-to-market derivative liabilities		(12)		(6)
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]
Total mark-to-market derivative liabilities		5		3
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	[4]	13,439		12,825
Alternative Investment, Fair Value Disclosure	[4]	3,774		3,433
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[5]	443		338
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6,359		5,890
Alternative Investment, Fair Value Disclosure		1,545		1,381
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		5,041		5,078
Alternative Investment, Fair Value Disclosure		936		846
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		1,782		1,823
Alternative Investment, Fair Value Disclosure		1
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		2,145		2,180
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		43		50
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		110		149
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	[6]	961		876
Alternative Investment, Fair Value Disclosure	[6]	935		846
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		709		680
Alternative Investment, Fair Value Disclosure		406		367
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		352		329
Alternative Investment, Fair Value Disclosure		352		329
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		535		510
Alternative Investment, Fair Value Disclosure		535		510
Exelon Generation Co L L C [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	[7]	52		51
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]
Investments, Fair Value Disclosure		4		5
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		25		24
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		23		22
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		3,879		4,771
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		178		146
Exelon Generation Co L L C [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],[3]	(2,950)		(3,671)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,107		1,246
Exelon Generation Co L L C [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		(1)		10
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		4		13
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Effectsofnettingandallocationofcollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(5)		(3)
Exelon Generation Co L L C [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		42		42
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Collateral received from counterparties, net of collateral paid to counterparties		52		57
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[1]	370		581
Total Assets		5,840		5,820
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		(4)		(3)
Total net assets (liabilities)		5,836		5,817
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]
Total mark-to-market derivative liabilities		(4)		(3)
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]
Total mark-to-market derivative liabilities		(350)		(642)
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]
Total mark-to-market derivative liabilities		0		0
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]
Total mark-to-market derivative liabilities	[2],[3]	346		639
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		0		0
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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		0		0
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]
Total mark-to-market derivative liabilities		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]	5,462		5,251
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[5]	369		252
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		3,060		2,918
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		2,033		2,081
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
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		2,033		2,081
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
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
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	[6]	0		0
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
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
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
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	[7]	29		29
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]
Investments, Fair Value Disclosure		4		5
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		25		24
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity 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] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		273		541
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		0		0
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	[2],[3]	(294)		(582)
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		(21)		(41)
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		0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [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] | 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 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
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Collateral received from counterparties, net of collateral paid to counterparties		283		224
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[1]	0		0
Total Assets		4,087		4,102
Deferred Compensation Liability, Current and Noncurrent		(36)		(35)
Total Liabilities		(342)		(493)
Total net assets (liabilities)		3,745		3,609
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]
Total mark-to-market derivative liabilities		(299)		(455)
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]
Total mark-to-market derivative liabilities		(2,339)		(2,963)
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]
Total mark-to-market derivative liabilities		(79)		(73)
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]
Total mark-to-market derivative liabilities	[2],[3]	2,119		2,581
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		(7)		(3)
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]
Total mark-to-market derivative liabilities		0		0
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]
Total mark-to-market derivative liabilities		(12)		(6)
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]
Total mark-to-market derivative liabilities		5		3
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]	3,663		3,598
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[5]	74		86
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,753		1,591
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		1,836		1,921
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		1,545		1,593
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		112		99
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		43		50
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		110		149
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	[6]	26		30
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
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
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
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	[7]	23		22
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]
Investments, Fair Value Disclosure		0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity 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] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		23		22
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		2,164		2,760
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		74		69
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],[3]	(1,836)		(2,357)
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		402		472
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		(1)		10
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		4		13
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		(5)		(3)
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
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Collateral received from counterparties, net of collateral paid to counterparties		157		76
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[1]	0		0
Total Assets		1,308		1,400
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		(227)		(240)
Total net assets (liabilities)		1,081		1,160
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]
Total mark-to-market derivative liabilities		(227)		(240)
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]
Total mark-to-market derivative liabilities		(1,164)		(1,027)
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]
Total mark-to-market derivative liabilities		(40)		(21)
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]
Total mark-to-market derivative liabilities	[2],[3]	977		808
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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	[4]	540		543
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[5]	0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1		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		236		230
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		236		230
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
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
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
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	[6]	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		303		313
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		0		0
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		0		0
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	[7]	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]
Investments, Fair Value Disclosure		0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity 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] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity 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] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,442		1,470
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		104		77
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	[2],[3]	(820)		(732)
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		726		815
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] | 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] | 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] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		42		42
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Commonwealth Edison Co [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)		27		26
Derivative Liability, Noncurrent		213		223
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Debt Issuance Costs, Net		67		63
Commonwealth Edison Co [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		69		93
Commonwealth Edison Co [Member] | Restricted cash member [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		15		28
Commonwealth Edison Co [Member] | Other Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		193		166
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[8]	194		209
Total Assets		194		209
Total mark-to-market derivative liabilities	[9]	240		249
Deferred Compensation Liability, Current and Noncurrent		(7)		(6)
Total Liabilities		(247)		(255)
Total net assets (liabilities)		(53)		(46)
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	[10]	0		0
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[8]	194		209
Total Assets		194		209
Total mark-to-market derivative liabilities	[9]	0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		194		209
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	[10]	0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[8]	0		0
Total Assets		0		0
Total mark-to-market derivative liabilities	[9]	0		0
Deferred Compensation Liability, Current and Noncurrent		(7)		(6)
Total Liabilities		(7)		(6)
Total net assets (liabilities)		(7)		(6)
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	[10]	0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[8]	0		0
Total Assets		0		0
Total mark-to-market derivative liabilities	[9]	240		249
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		(240)		(249)
Total net assets (liabilities)		(240)		(249)
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	[10]	0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
PECO Energy Co [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Debt Issuance Costs, Net		22		23
PECO Energy Co [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		31		24
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[8]	16		111
Total Assets		33		128
Total mark-to-market derivative liabilities	[9]	0		0
Deferred Compensation Liability, Current and Noncurrent		(10)		(10)
Total Liabilities		(10)		(10)
Total net assets (liabilities)		23		118
PECO Energy 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	[10]	17		17
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		7		7
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		10		10
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[8]	16		111
Total Assets		23		118
Total mark-to-market derivative liabilities	[9]	0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		23		118
PECO Energy 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	[10]	7		7
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		7		7
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[8]	0		0
Total Assets		10		10
Total mark-to-market derivative liabilities	[9]	0		0
Deferred Compensation Liability, Current and Noncurrent		(10)		(10)
Total Liabilities		(10)		(10)
Total net assets (liabilities)		0		0
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	[10]	10		10
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		10		10
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[8]	0		0
Total Assets		0		0
Total mark-to-market derivative liabilities	[9]	0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		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	[10]	0		0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Baltimore Gas and Electric Company [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Debt Issuance Costs, Net		18		18
Baltimore Gas and Electric Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		12		7
Baltimore Gas and Electric Company [Member] | Restricted cash member [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		1		2
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[8]	3		4
Total Assets		9		10
Total mark-to-market derivative liabilities	[9]	0		0
Deferred Compensation Liability, Current and Noncurrent		(5)		(5)
Total Liabilities		(5)		(5)
Total net assets (liabilities)		4		5
Baltimore Gas and Electric Company [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	[10]	6		6
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6		6
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[8]	3		4
Total Assets		9		10
Total mark-to-market derivative liabilities	[9]	0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		9		10
Baltimore Gas and Electric Company [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	[10]	6		6
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6		6
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, 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, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[8]	0		0
Total Assets		0		0
Total mark-to-market derivative liabilities	[9]	0		0
Deferred Compensation Liability, Current and Noncurrent		(5)		(5)
Total Liabilities		(5)		(5)
Total net assets (liabilities)		(5)		(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	[10]	0		0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity 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, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[8]	0		0
Total Assets		0		0
Total mark-to-market derivative liabilities	[9]	0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		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	[10]	0		0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity 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, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Debt Issuance Costs, Net		14		14
Pepco Holdings LLC [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		29		39
Pepco Holdings LLC [Member] | Other Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		19		19
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	63		147
Total Assets		194		277
Deferred Compensation Liability, Current and Noncurrent		(20)		(21)
Total Liabilities		(20)		(21)
Total net assets (liabilities)		174		256
Pepco Holdings LLC [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	[12]	131		130
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		42		42
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		14		13
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		61		60
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		14		15
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	63		147
Total Assets		119		202
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		119		202
Pepco Holdings LLC [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	[12]	56		55
Pepco Holdings LLC [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]
Investments, Fair Value Disclosure		42		42
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		14		13
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	0		0
Total Assets		36		37
Deferred Compensation Liability, Current and Noncurrent		(20)		(21)
Total Liabilities		(20)		(21)
Total net assets (liabilities)		16		16
Pepco Holdings LLC [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	[12]	36		37
Pepco Holdings LLC [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]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22		22
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		14		15
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	0		0
Total Assets		39		38
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		39		38
Pepco Holdings LLC [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	[12]	39		38
Pepco Holdings LLC [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]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		39		38
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Potomac Electric Power Company [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Debt Issuance Costs, Net		33		34
Potomac Electric Power Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		11		15
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	35		38
Total Assets		141		143
Deferred Compensation Liability, Current and Noncurrent		(3)		(3)
Total Liabilities		(3)		(3)
Total net assets (liabilities)		138		140
Potomac Electric Power Company [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	[12]	106		105
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		42		41
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		60		59
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4		5
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	35		38
Total Assets		77		79
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		77		79
Potomac Electric Power Company [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	[12]	42		41
Potomac Electric Power Company [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]
Investments, Fair Value Disclosure		42		41
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	0		0
Total Assets		26		27
Deferred Compensation Liability, Current and Noncurrent		(3)		(3)
Total Liabilities		(3)		(3)
Total net assets (liabilities)		23		24
Potomac Electric Power 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	[12]	26		27
Potomac Electric Power Company [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]
Investments, Fair Value Disclosure		0		0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22		22
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4		5
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	0		0
Total Assets		38		37
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		38		37
Potomac Electric Power 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	[12]	38		37
Potomac Electric Power Company [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]
Investments, Fair Value Disclosure		0		0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		38		37
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Debt Issuance Costs, Net		12		12
Delmarva Power and Light Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		6		8
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	2		16
Total Assets		2		16
Deferred Compensation Liability, Current and Noncurrent		(1)		(1)
Total Liabilities		(1)		(1)
Total net assets (liabilities)		1		15
Delmarva Power and Light Company [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	[12]	0		0
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	2		16
Investments, Fair Value Disclosure		0		0
Total Assets		2		16
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		2		16
Delmarva Power and Light Company [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	[12]	0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	0		0
Total Assets		0		0
Deferred Compensation Liability, Current and Noncurrent		(1)		(1)
Total Liabilities		(1)		(1)
Total net assets (liabilities)		(1)		(1)
Delmarva Power and Light 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	[12]	0		0
Delmarva Power and Light Company [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]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	0		0
Total Assets		0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		0		0
Delmarva Power and Light 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	[12]	0		0
Delmarva Power and Light Company [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]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Atlantic City Electric Company [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Debt Issuance Costs, Net		6		7
Atlantic City Electric Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		7		7
Atlantic City Electric Company [Member] | Other Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		19		19
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	21		23
Total Assets		21		23
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		21		23
Atlantic City Electric Company [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	[12]	0		0
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	21		23
Investments, Fair Value Disclosure		0		0
Total Assets		21		23
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		21		23
Atlantic City Electric Company [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	[12]	0		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	0		0
Total Assets		0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		0		0
Atlantic City 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	[12]	0		0
Atlantic City Electric Company [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]
Investments, Fair Value Disclosure		0		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[11]	0		0
Total Assets		0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Total Liabilities		0		0
Total net assets (liabilities)		0		0
Atlantic City 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	[12]	0		0
Atlantic City Electric Company [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]
Investments, Fair Value Disclosure		0		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		$ 0
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)			$ (10)
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		1	1
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Exelon Generation Co L L C [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)			(3)
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Exelon Generation Co L L C [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		0	0
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Commonwealth Edison Co [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		0	0
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | PECO Energy Co [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		0	0
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Baltimore Gas and Electric Company [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		0	0
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Pepco Holdings LLC [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		0	0
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Potomac Electric Power Company [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		$ 0	$ 0
[1]	Generation excludes cash of $270 million and $283 million at March 31, 2019 and December 31, 2018 and restricted cash of $36 million and $39 million at March 31, 2019 and December 31, 2018. Exelon excludes cash of $426 million and $458 million at March 31, 2019 and December 31, 2018 and restricted cash of $71 million and $80 million at March 31, 2019 and December 31, 2018 and includes long-term restricted cash of $211 million and $185 million at March 31, 2019 and December 31, 2018, which is reported in Other deferred debits in the Consolidated Balance Sheets.
[2]	Collateral posted/(received) from counterparties totaled $52 million, $283 million and $157 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of March 31, 2019. Collateral posted/(received) from counterparties, net of collateral paid to counterparties, totaled $57 million, $224 million and $76 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2018.
[3]	Of the collateral posted/(received), $(33) million and $(94) million represents variation margin on the exchanges as of March 31, 2019 and December 31, 2018, respectively.
[4]	Excludes net liabilities of $94 million and $130 million at March 31, 2019 and December 31, 2018, 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.
[5]	Includes $43 million and $50 million of cash received from outstanding repurchase agreements at March 31, 2019 and December 31, 2018, respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below.
[6]	Includes derivative instruments of $7 million and $44 million, which have a total notional amount of $1,223 million and $1,432 million at March 31, 2019 and December 31, 2018, 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 Exelon and Generation's exposure to credit or market loss.
[7]	The amount of unrealized gains/(losses) at Generation totaled less than $1 million for the three months ended March 31, 2019 and March 31, 2018, respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million for the three months ended March 31, 2019 and March 31, 2018, respectively.
[8]	ComEd excludes cash of $69 million and $93 million at March 31, 2019 and December 31, 2018 and restricted cash of $15 million and $28 million at March 31, 2019 and December 31, 2018 and includes long-term restricted cash of $193 million and $166 million at March 31, 2019 and December 31, 2018, which is reported in Other deferred debits in the Consolidated Balance Sheets. PECO excludes cash of $31 million and $24 million at March 31, 2019 and December 31, 2018. BGE excludes cash of $12 million and $7 million at March 31, 2019 and December 31, 2018 and restricted cash of $1 million and $2 million at March 31, 2019 and December 31, 2018
[9]	The Level 3 balance consists of the current and noncurrent liability of $27 million and $213 million, respectively, at March 31, 2019, and $26 million and $223 million, respectively, at December 31, 2018, related to floating-to-fixed energy swap contracts with unaffiliated suppliers.
[10]	The amount of unrealized gains/(losses) at ComEd, PECO and BGE totaled less than $1 million for the three months ended March 31, 2019 and March 31, 2018.
[11]	PHI excludes cash of $29 million and $39 million at March 31, 2019 and December 31, 2018, respectively, and includes long-term restricted cash of $19 million at both March 31, 2019 and December 31, 2018, which is reported in Other deferred debits in the Consolidated Balance Sheets. Pepco excludes cash of $11 million and $15 million at March 31, 2019 and December 31, 2018, respectively. DPL excludes cash of $6 million and $8 million at March 31, 2019 and December 31, 2018, respectively. ACE excludes cash of $7 million at both March 31, 2019 and December 31, 2018, and includes long-term restricted cash of $19 million at both March 31, 2019 and December 31, 2018, which is reported in Other deferred debits in the Consolidated Balance Sheets.
[12]	The amount of unrealized gains/(losses) at PHI totaled less than $1 million for both the three months ended March 31, 2019 and 2018. The amount of unrealized gains/(losses) at Pepco totaled less than $1 million for both the three months ended March 31, 2019 and 2018.

Fair Value of Financial Asset_6

Fair Value of Financial Assets and Liabilities - Fair Value Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ 880	$ 1,319	$ 949	$ 1,003
Total realized / unrealized gains (losses)
Included in net income		(228)	186
Included in noncurrent payables to affiliates		0	0
Included in regulatory assets		20	(4)
Change in collateral		81	105
Purchases, sales, issuances and settlements
Purchases		58	90
Sales		0	(3)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0
Settlements		(17)	(48)
Transfers into Level 3		0	(8)
Transfers out of Level 3		17	(2)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(148)	258
Fair Value, Inputs, Level 3 [Member] | Consolidation, Eliminations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		0	0	0	0
Total realized / unrealized gains (losses)
Included in net income		0	0
Included in noncurrent payables to affiliates		(11)	(7)
Included in regulatory assets		11	7
Change in collateral		0
Purchases, sales, issuances and settlements
Purchases		0	0
Sales		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0
Settlements		0	0
Transfers into Level 3		0	0
Transfers out of Level 3		0	0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0	0
Exelon Generation Co L L C [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings		80	72
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		1,081	1,563	1,160	1,237
Total realized / unrealized gains (losses)
Included in net income		(229)	185
Included in noncurrent payables to affiliates		11	7
Included in regulatory assets		0	0
Change in collateral		81	105
Purchases, sales, issuances and settlements
Purchases		58	90
Sales		0	(3)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0
Settlements		(17)	(48)
Transfers into Level 3		0	(8)
Transfers out of Level 3		17	(2)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(149)	257
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		540	609	543	648
Total realized / unrealized gains (losses)
Included in net income		2	0
Included in noncurrent payables to affiliates		11	7
Included in regulatory assets			0
Change in collateral		0	0
Purchases, sales, issuances and settlements
Purchases		1	2
Sales		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0
Settlements		(17)	(48)
Transfers into Level 3		0	0
Transfers out of Level 3		0	0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		2	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		499	918	575	552
Total realized / unrealized gains (losses)
Included in net income	[1]	(231)	184
Included in noncurrent payables to affiliates		0	0
Included in regulatory assets			0
Change in collateral		81	105
Purchases, sales, issuances and settlements
Purchases		57	88
Sales		0	(3)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0
Settlements		0	0
Transfers into Level 3	[2]	0	(8)
Transfers out of Level 3	[2]	17	0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(151)	256
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Other Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		42	36	42	37
Total realized / unrealized gains (losses)
Included in net income		0	1
Included in noncurrent payables to affiliates		0	0
Included in regulatory assets			0
Change in collateral		0	0
Purchases, sales, issuances and settlements
Purchases		0	0
Sales		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0
Settlements		0	0
Transfers into Level 3		0	0
Transfers out of Level 3		0	(2)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0	1
Commonwealth Edison Co [Member] | Derivative [Member] | Interest Rate Swap [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Realized Investment Gains (Losses)		(5)	(6)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(240)	(267)	(249)	(256)
Total realized / unrealized gains (losses)
Included in net income		0	0
Included in noncurrent payables to affiliates		0	0
Included in regulatory assets	[3]	9	11
Change in collateral		0	0
Purchases, sales, issuances and settlements
Purchases		0	0
Sales		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0
Settlements		0	0
Transfers into Level 3		0	0
Transfers out of Level 3		0	0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Period Increase (Decrease)		(14)	17
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	[4]	39	23	$ 38	$ 22
Total realized / unrealized gains (losses)
Included in net income	[4]	1	1
Included in noncurrent payables to affiliates	[4]	0	0
Included in regulatory assets	[4]	0	0
Change in collateral	[4]	0	0
Purchases, sales, issuances and settlements
Purchases	[4]	0	0
Sales	[4]	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	[4]		0
Settlements	[4]	0	0
Transfers into Level 3	[4]	0	0
Transfers out of Level 3	[4]	0	0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[4]	$ 1	$ 1
[1]	Includes a reduction for the reclassification of $80 million and $72 million of realized gains due to the settlement of derivative contracts for the three months ended March 31, 2019 and 2018, respectively.
[2]	Transfers into and out of Level 3 generally occur when the contract tenor becomes less and more observable respectively, primarily due to changes in market liquidity or assumptions for certain commodity contracts.
[3]	Includes $14 million of decreases in fair value and an increase for realized losses due to settlements of $5 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2019. Includes $17 million of increases in fair value and an increase for realized losses due to settlements of $6 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2018.
[4]	The amounts represented are life insurance contracts at Pepco.

Fair Value of Financial Asset_7

Fair Value of Financial Assets and Liabilities - Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pepco Holdings LLC [Member] | Operating and Maintenance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	$ 1	$ 1
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	1	1
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	228	(186)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(148)	258
Fair Value, Inputs, Level 3 [Member] | Operating Revenue [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	(128)	335
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(91)	309
Fair Value, Inputs, Level 3 [Member] | Purchased Power And Fuel [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	(103)	(151)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(60)	(53)
Fair Value, Inputs, Level 3 [Member] | Other, net [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	2	1
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	2	1
Fair Value, Inputs, Level 3 [Member] | Operating and Maintenance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	1	1
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	1	1
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	229	(185)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(149)	257
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	(128)	335
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(91)	309
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	(103)	(151)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(60)	(53)
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Other, net [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	2	1
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 2	$ 1

Fair Value of Financial Asset_8

Fair Value of Financial Assets and Liabilities - Fair Value Inputs Assets Quantitative Information (Details) - USD ($)		3 Months Ended	12 Months Ended
		Mar. 31, 2019	Dec. 31, 2018
Derivatives Fair Value Footnotes [Abstract]
Cash Collateral Posted		$ 37,000,000
Fair Value, Inputs, Level 3 [Member]
Derivatives Fair Value Footnotes [Abstract]
Cash Collateral Posted		157,000,000	$ 76,000,000
Fair Value, Inputs, Level 3 [Member] | Economic Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	[1],[2]	278,000,000	443,000,000
Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		(240,000,000)	(249,000,000)
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	[1],[2]	9	12
Forward gas price assets	[1],[2]	$ 1.76	$ 0.78
Forward heat rate	[3]	1000.00%	1000.00%
Fair Value Inputs, Discount for Lack of Marketability		4.00%	4.00%
Fair Value Inputs Renewable Factor		85.00%	86.00%
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	[1],[2]	$ 164	$ 174
Forward gas price assets	[1],[2]	$ 11.63	$ 12.38
Forward heat rate	[3]	1100.00%	1100.00%
Fair Value Inputs, Discount for Lack of Marketability		8.00%	8.00%
Fair Value Inputs Renewable Factor		120.00%	120.00%
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Volatility percentage	[1],[2]	9.84%	10.00%
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Volatility percentage	[1],[2]	334.36%	277.00%
Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	[1],[2]	$ 64,000,000	$ 56,000,000
Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	[1],[2]	9	14
Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	[1],[2]	162	174
Exelon Generation Co L L C [Member]
Derivatives Fair Value Footnotes [Abstract]
Cash Collateral Posted		542,000,000	418,000,000
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member]
Derivatives Fair Value Footnotes [Abstract]
Cash Collateral Posted		157,000,000	76,000,000
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Economic Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	[1],[2]	278,000,000	443,000,000
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	[1],[2]	9	12
Forward gas price assets	[1],[2]	1.76	0.78
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	[1],[2]	164	174
Forward gas price assets	[1],[2]	$ 11.63	$ 12.38
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Volatility percentage	[1],[2]	9.84%	10.00%
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Volatility percentage	[1],[2]	334.36%	277.00%
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	[1],[2]	$ 64,000,000	$ 56,000,000
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	[1],[2]	9	14
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	[1],[2]	162	174
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		$ (240,000,000)	$ (249,000,000)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward heat rate	[3]	1000.00%	1000.00%
Fair Value Inputs, Discount for Lack of Marketability		4.00%	4.00%
Fair Value Inputs Renewable Factor		85.00%	86.00%
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward heat rate	[3]	1100.00%	1100.00%
Fair Value Inputs, Discount for Lack of Marketability		8.00%	8.00%
Fair Value Inputs Renewable Factor		120.00%	120.00%
[1]	The fair values do not include cash collateral posted on level three positions of $157 million and $76 million as of March 31, 2019 and December 31, 2018, respectively.
[2]	The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions.
[3]	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 Instrume_3

Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions		Mar. 31, 2019		Dec. 31, 2018
Derivative [Line Items]
Mark-to-market derivatives assets		$ 652		$ 804
Derivative Asset, Noncurrent		454		452
Derivative Liability, Current		(345)		(475)
Derivative Liability, Noncurrent		(434)		(479)
Derivative, Collateral, Right to Reclaim Cash		43		50
Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		653		801
Derivative Asset, Noncurrent		454		445
Total mark-to-market derivative assets		1,107		1,246
Derivative Liability, Current		(342)		(473)
Derivative Liability, Noncurrent		(428)		(474)
Total mark-to-market derivative liabilities		(770)		(947)
Total mark-to-market derivative net assets (liabilities)		337		299
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		652		804
Derivative Asset, Noncurrent		454		452
Derivative Liability, Current		(318)		(449)
Derivative Liability, Noncurrent		(219)		(252)
Derivative, Collateral, Right to Reclaim Cash		43		50
Derivative Liability, Fair Value, Amount Offset Against Collateral		(1,177)	[1]	1,105
Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		653	[2]	801	[3]
Derivative Asset, Noncurrent		454	[2]	445	[3]
Total mark-to-market derivative assets		1,107	[2]	1,246	[3]
Derivative Liability, Current		(315)	[2]	(447)	[3]
Derivative Liability, Noncurrent		(215)	[2]	(251)	[3]
Total mark-to-market derivative liabilities		(530)	[2]	(698)	[3]
Total mark-to-market derivative net assets (liabilities)		577	[2]	548	[3]
Commonwealth Edison Co [Member]
Derivative [Line Items]
Derivative Liability, Current		(27)		(26)
Derivative Liability, Noncurrent		(213)		(223)
Collateral And Netting [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets	[4]	(2,156)	[5]	(2,809)	[6]
Derivative Asset, Noncurrent	[4]	(794)	[5]	(862)	[6]
Total mark-to-market derivative assets	[4]	(2,950)	[5]	(3,671)	[6]
Derivative Liability, Current	[4]	2,485	[5]	3,056	[6]
Derivative Liability, Noncurrent	[4]	957	[5]	972	[6]
Total mark-to-market derivative liabilities	[4]	3,442	[5]	4,028	[6]
Total mark-to-market derivative net assets (liabilities)	[4]	492	[5]	357	[6]
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		2,691		3,505
Derivative Asset, Noncurrent		1,188		1,266
Total mark-to-market derivative assets		3,879		4,771
Derivative Liability, Current		(2,711)		(3,429)
Derivative Liability, Noncurrent		(1,142)		(1,203)
Total mark-to-market derivative liabilities		(3,853)		(4,632)
Total mark-to-market derivative net assets (liabilities)		26		139
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commonwealth Edison Co [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets	[7]	0		0
Derivative Asset, Noncurrent	[7]	0		0
Total mark-to-market derivative assets	[7]	0		0
Derivative Liability, Current	[7]	(27)		(26)
Derivative Liability, Noncurrent	[7]	(213)		(223)
Total mark-to-market derivative liabilities	[7]	(240)		(249)
Total mark-to-market derivative net assets (liabilities)	[7]	(240)		(249)
Not Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		118		105
Derivative Asset, Noncurrent		60		41
Total mark-to-market derivative assets		178		146
Derivative Liability, Current		(89)		(74)
Derivative Liability, Noncurrent		(30)		(20)
Total mark-to-market derivative liabilities		(119)		(94)
Total mark-to-market derivative net assets (liabilities)		59		52
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Liability, Collateral, Right to Reclaim Cash, Offset		(492)		(357)
Current liabilities collateral offset		177		125
Noncurrent liabilities collateral offset		100		60
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member] | Other Current Assets [Member]
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash		152		121
Derivative Liability, Fair Value, Amount Offset Against Collateral		(33)		(94)
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member] | Other Noncurrent Assets [Member]
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash		$ 63		$ 51
[1]	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.
[2]	Current and noncurrent assets are shown net of collateral of $152 million and $63 million, respectively, and current and noncurrent liabilities are shown net of collateral of $177 million and $100 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $492 million at March 31, 2019.
[3]	Current and noncurrent assets are shown net of collateral of $121 million and $51 million, respectively, and current and noncurrent liabilities are shown net of collateral of $125 million and $60 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $357 million at December 31, 2018.
[4]	Exelon and Generation net all available amounts allowed under the derivative authoritative guidance in 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.
[5]	Of the collateral posted/(received), $(33) million represents variation margin on the exchanges.
[6]	Of the collateral posted/(received), $(94) million represents variation margin on the exchanges.
[7]	Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.

Derivative Financial Instrume_4

Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (31)	$ (259)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(33)	(264)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(20)	(267)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(50)	(100)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ 30	$ (167)

Derivative Financial Instrume_5

Derivative Financial Instruments - Summary of Proprietary Trading Activities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (31)	$ (259)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(33)	(264)
Not Designated as Hedging Instrument [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ 2	$ 2

Derivative Financial Instrume_6

Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Cash Collateral Posted		$ 37
Letters Of Credit Posted		19
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Financial institutions		13
Investor-owned utilities, marketers and power producers		762
Energy Cooperatives And Municipalities		287
Other		35
Cash Collateral Posted		542	$ 418
Letters Of Credit Posted		289	$ 367
Exelon Generation Co L L C [Member] | Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade		819
Non-investment grade		86
No external ratings - internally rated - investment grade		162
No external ratings - internally rated - non-investment grade		87
Total		1,154
Exelon Generation Co L L C [Member] | Credit Collateral [Member]
Derivative [Line Items]
Investment grade		11
Non-investment grade		39
No external ratings - internally rated - investment grade		0
No external ratings - internally rated - non-investment grade		7
Total	[1]	57
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Derivative [Line Items]
Investment grade		808
Non-investment grade		47
No external ratings - internally rated - investment grade		162
No external ratings - internally rated - non-investment grade		80
Total		1,097
Exelon Generation Co L L C [Member] | Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade		1
Non-investment grade
No external ratings - internally rated - investment grade
No external ratings - internally rated - non-investment grade
Total		1
Exelon Generation Co L L C [Member] | Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade		135
Non-investment grade
No external ratings - internally rated - investment grade
No external ratings - internally rated - non-investment grade
Total		$ 135
[1]	As of March 31, 2019, credit collateral held from counterparties where Generation had credit exposure included $37 million of cash and $19 million of letters of credit. The credit collateral does not include non-liquid collateral.

Derivative Financial Instrume_7

Derivative Financial Instruments - Summary of Credit Risk Related Contingent Features (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		Mar. 31, 2019		Dec. 31, 2018
Derivative [Line Items]
Aggregate fair value of derivatives with credit-risk-related contingent features		$ (1,667)	[1]	$ 1,723
Contractual right of offset related to derivative assets		1,177	[2]	(1,105)
Net liability position after contractual right of offset	[3]	$ (490)		$ (618)
[1]	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]	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]	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.

Derivative Financial Instrume_8

Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Cash Collateral Posted	$ 37,000
Letters of credit posted	19,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral received not offset against net derivative positions	(6,000)	$ 2,000
Cash Collateral Posted	542,000	418,000
Letters of credit held	26,000	44,000
Letters of credit posted	289,000	367,000
Cash collateral held	56,000	47,000
Incremental collateral for loss of investment grade credit rating	1,900,000	2,100,000
Commonwealth Edison Co [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	8,000
Credit Exposure Under Off System Sales	$ 2,000
PECO Energy Co [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	20.00%
Incremental collateral for loss of investment grade credit rating	$ 34,000
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	46,000
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	$ 14,000
Minimum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months	90.00%
Expected Generation Hedged In Year Two	64.00%
Expected generation hedged in year three	38.00%
Minimum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	10.00%
Maximum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months	93.00%
Expected Generation Hedged In Year Two	67.00%
Expected generation hedged in year three	41.00%
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	20.00%
Other Contract [Member] | Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	19000000
Energy Related Derivative [Member] | Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	11000000
Energy Related Derivative [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Brokered Natural Gas Margin Revenue	$ 2,750
Renewable Energy Program [Member] | Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	31000000
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral received not offset against net derivative positions		12,000
Net receivable from electric utility	$ 36,000
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility	31,000
Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility	27,000
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	37,000
Delmarva Power and Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	5,000
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	4,000
Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	1,419,000	1,420,000
Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Notional Amount	619,000	620,000
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 209,000	$ 268,000

Debt and Credit Agreements - Na

Debt and Credit Agreements - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Corporate, Non-Segment [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	$ 500
Debt Instrument, Interest Rate Terms	LIBOR plus 0.95%
Exelon Generation Co L L C [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 100
DOE Project Financing, 2.82% January 5, 2037 [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Non-Recourse Debt	502
DOE Project Financing, 2.82% January 5, 2037 [Member] | Exelon Generation Co L L C [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	646
Non-Recourse Debt	502
ExGenRenewablesIVNov2024 [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Non-Recourse Debt	834
ExGenRenewablesIVNov2024 [Member] | Exelon Generation Co L L C [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	850
Non-Recourse Debt	$ 834

Debt and Credit Agreements - Co

Debt and Credit Agreements - Commercial Paper Borrowings (Details) - Commercial Paper [Member] - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 629	$ 89
Average Interest Rate on Commercial Paper Borrowings	2.63%	2.15%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 0	$ 0
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 322	$ 0
Average Interest Rate on Commercial Paper Borrowings	2.64%	2.14%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 0	$ 0
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 106	$ 35
Average Interest Rate on Commercial Paper Borrowings	2.59%	2.18%
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 201	$ 54
Average Interest Rate on Commercial Paper Borrowings	2.62%	2.15%
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 105	$ 40
Average Interest Rate on Commercial Paper Borrowings	2.62%	2.24%
Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 5	$ 0
Average Interest Rate on Commercial Paper Borrowings	2.61%	2.07%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 91	$ 14
Average Interest Rate on Commercial Paper Borrowings	2.62%	2.21%

Debt and Credit Agreements - Is

Debt and Credit Agreements - Issuance of Long-Term Debt (Details) $ in Millions	Mar. 31, 2019USD ($)
Exelon Generation Co L L C [Member] | EEPF395Aug2020 [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Interest Rate	3.95%
Debt Instrument, Face Amount	$ 2
Commonwealth Edison Co [Member] | FMB400Mar2049 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	4.00%
Debt Instrument, Face Amount	$ 400

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Period Increase (Decrease)	$ 33
Decrease in Unrecognized Tax Benefits is Reasonably Possible	425
Unrecognized tax benefits that if recognized would affect the effective tax rate	411
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	411
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Period Increase (Decrease)	2
Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	14
Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 14

Income Taxes - Reconciliation t

Income Taxes - Reconciliation to Effective Tax Rate (Details)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	3.90%	4.10%
Qualified nuclear decommissioning trust fund income	7.20%	(0.40%)
Amortization of investment tax credit, including deferred taxes on basis difference	(0.50%)	(1.30%)
Plant basis differences	(1.40%)	(2.70%)
Production tax credits and other credits	(0.80%)	(2.80%)
Noncontrolling interests	(0.60%)	(0.70%)
Excess deferred tax amortization	(4.70%)	(6.00%)
Other	0.10%	(2.80%)
Effective income tax rate	24.20%	8.40%
Exelon Generation Co L L C [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	3.10%	2.40%
Qualified nuclear decommissioning trust fund income	14.20%	(1.30%)
Amortization of investment tax credit, including deferred taxes on basis difference	(0.90%)	(4.30%)
Plant basis differences	(0.00%)	(0.00%)
Production tax credits and other credits	(1.50%)	(9.50%)
Noncontrolling interests	(1.10%)	(2.50%)
Excess deferred tax amortization	0.00%	0.00%
Other	(0.50%)	(1.30%)
Effective income tax rate	34.30%	4.50%
Commonwealth Edison Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	8.20%	8.20%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)
Plant basis differences	(0.50%)	0.10%
Production tax credits and other credits	(0.00%)	(0.10%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(8.50%)	(7.50%)
Other	0.30%	0.30%
Effective income tax rate	20.30%	21.80%
PECO Energy Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	1.00%	(3.90%)
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.00%)	(0.10%)
Plant basis differences	(6.70%)	(14.20%)
Production tax credits and other credits	(0.00%)	(0.00%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(2.50%)	(4.80%)
Other	0.20%	0.20%
Effective income tax rate	13.00%	(1.80%)
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	6.30%	6.30%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)
Plant basis differences	(0.90%)	(0.70%)
Production tax credits and other credits	(0.00%)	(0.00%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(7.90%)	(8.60%)
Other	0.00%	0.00%
Effective income tax rate	18.40%	17.90%
Pepco Holdings LLC [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	4.70%	4.60%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)
Plant basis differences	(1.70%)	(2.60%)
Production tax credits and other credits	(0.00%)	(0.00%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(19.40%)	(10.60%)
Other	(0.30%)	0.00%
Effective income tax rate	4.10%	12.20%
Potomac Electric Power Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	2.10%	1.70%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)
Plant basis differences	(2.00%)	(3.40%)
Production tax credits and other credits	(0.00%)	(0.00%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(17.90%)	(12.80%)
Other	0.40%	(0.30%)
Effective income tax rate	3.50%	6.10%
Delmarva Power and Light Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	6.50%	6.30%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)
Plant basis differences	(0.70%)	(1.30%)
Production tax credits and other credits	(0.00%)	(0.00%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(15.60%)	(7.90%)
Other	0.70%	0.50%
Effective income tax rate	11.70%	18.40%
Atlantic City Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	6.70%	6.60%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.30%)	(0.30%)
Plant basis differences	(2.30%)	(2.60%)
Production tax credits and other credits	(0.00%)	(0.00%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(23.90%)	(8.70%)
Other	(1.20%)	(3.50%)
Effective income tax rate	0.00%	12.50%

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	$ 448	$ 477
Exelon Generation Co L L C [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	411	408
Commonwealth Edison Co [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	0	2
PECO Energy Co [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	0	0
Baltimore Gas and Electric Company [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	0	0
Pepco Holdings LLC [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	45	45
Potomac Electric Power Company [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	0	0
Delmarva Power and Light Company [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	0	0
Atlantic City Electric Company [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	$ 14	$ 14

Nuclear Decommissioning - Narra

Nuclear Decommissioning - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2018
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)	$ 324
Asset Retirement Obligation, Revision of Estimate	330		$ 84
Decommissioning Fund Investments	12,302			$ 11,661
Assets held for sale	890			904
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)	324
Asset Retirement Obligation, Revision of Estimate	330
Decommissioning Fund Investments	12,302			11,661
Assets held for sale	890			904
Nuclear Decommissioning [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation, Revision of Estimate	223
Nuclear Decommissioning [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation, Revision of Estimate	223
Oyster Creek [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Assets held for sale	888			897
Oyster Creek [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation Revision Of Estimate In Operating And Maintenance Expense		$ (84)
Assets held for sale	888			897
Three Mile Island [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)	(110)
Asset Retirement Obligation Revision Of Estimate In Operating And Maintenance Expense	(85)
Three Mile Island [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)	(110)
Asset Retirement Obligation Revision Of Estimate In Operating And Maintenance Expense	(85)
Assets, Total [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Decommissioning Fund Investments	13,345			12,695
Assets, Total [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Decommissioning Fund Investments	13,345			12,695
Nuclear Decommissioning Trust Fund Investments [Member] | Oyster Creek [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Assets held for sale	881			890
Nuclear Decommissioning Trust Fund Investments [Member] | Oyster Creek [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Assets held for sale	881			890
Other Current Assets [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Decommissioning Fund Investments	163			144
Other Current Assets [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Decommissioning Fund Investments	$ 163			$ 144

Nuclear Decommissioning - Rollf

Nuclear Decommissioning - Rollforward of Nuclear Decommissioning ARO (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2018
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Net increase due to changes in, and timing of, estimated future cash flows		$ 330		$ 84
Accretion expense	[1]	124	$ 120
Liabilities held for sale		799			$ 777
Nuclear Decommissioning [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Nuclear decommissioning ARO, beginning balance	[2],[3]	10,005
Net increase due to changes in, and timing of, estimated future cash flows		223
Accretion expense		120
Costs incurred related to decommissioning plants		(19)
Nuclear decommissioning ARO, ending balance	[2],[3]	10,329
Current portion of ARO		41			22
Oyster Creek [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liabilities held for sale		765			777
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Net increase due to changes in, and timing of, estimated future cash flows		330
Accretion expense	[1]	123	$ 120
Liabilities held for sale		799			777
Exelon Generation Co L L C [Member] | Nuclear Decommissioning [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Nuclear decommissioning ARO, beginning balance	[2],[3]	10,005
Net increase due to changes in, and timing of, estimated future cash flows		223
Accretion expense		120
Costs incurred related to decommissioning plants		(19)
Nuclear decommissioning ARO, ending balance	[2],[3]	10,329
Current portion of ARO		41			22
Exelon Generation Co L L C [Member] | Oyster Creek [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liabilities held for sale		765			777
Nuclear Decommissioning Asset Retirement Obligation [Member] | Oyster Creek [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liabilities held for sale		760			772
Nuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Generation Co L L C [Member] | Oyster Creek [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liabilities held for sale		$ 760			$ 772
[1]	Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[2]	Includes $41 million and $22 million as the current portion of the ARO at March 31, 2019 and December 31, 2018, respectively, which is included in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets.
[3]	Includes $760 million and $772 million of ARO related to Oyster Creek which is classified as Liabilities held for sale in Exelon's and Generation's Consolidated Balance Sheets at March 31, 2019 and December 31, 2018, respectively. See Note 3 — Mergers, Acquisitions and Dispositions for additional information.

Retirement Benefits - Narrative

Retirement Benefits - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Defined Benefit Plan Disclosure [Line Items]
Increase (Decrease) in Obligation, Pension Benefits	$ 75
Increase (Decrease) in Obligation, Other Postretirement Benefits	36
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax	(39)
Defined Benefit Plan Amounts Recognized In Regulatory Assets Before Tax	53
Defined Benefit Plan Amounts Recognized In Regulatory Liabilities Before Tax	$ (5)
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on assets	7.00%
Discount rate	4.31%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on assets	6.67%
Discount rate	4.30%

Retirement Benefits - Calculati

Retirement Benefits - Calculation of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Amortization of:
Net periodic benefit cost	$ (5)	$ 10
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	89	101
Interest cost	221	201
Expected return on assets	(307)	(312)
Amortization of:
Prior service cost (benefit)	0	0
Actuarial loss	104	157
Net periodic benefit cost	107	147
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	24	28
Interest cost	47	43
Expected return on assets	(38)	(43)
Amortization of:
Prior service cost (benefit)	(45)	(46)
Actuarial loss	11	16
Net periodic benefit cost	$ (1)	$ (2)

Retirement Benefits - Allocated

Retirement Benefits - Allocated Portion of Pension and Postretirement Benefit Plan Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	$ 106	$ 145
Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	106	145
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	31	51
Exelon Generation Co L L C [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	31	51
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	24	45
Commonwealth Edison Co [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	24	45
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	2	5
PECO Energy Co [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	2	5
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	15	14
Baltimore Gas and Electric Company [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	16	15
Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	23	15
Pepco Holdings LLC [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	23	15
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	6	4
Potomac Electric Power Company [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	6	4
Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	4	0
Delmarva Power and Light Company [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	4	0
Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	4	3
Atlantic City Electric Company [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	$ 4	$ 3

Retirement Benefits - Defined C

Retirement Benefits - Defined Contribution Savings Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	$ 31	$ 32
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	13	15
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	7	7
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	2	2
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	2	2
Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	4	3
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	1	1
Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	1	1
Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	$ 1	$ 0

Changes in Accumulated Other _3

Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		$ 33,070	$ 32,187
Beginning Balance		30,764
Amounts reclassified from AOCI	[1]	20	44
Other comprehensive (loss) income		(18)	72
Ending balance		33,704	32,565
Ending Balance		31,357
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings			539
Gains (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]	(2)	(14)
OCI before reclassifications	[2]	0	8
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	0	8
Ending balance	[2]	(2)	(6)
Gains (Losses) on Cash Flow Hedges | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)			0
Unrealized Gains (Losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]	0	10
OCI before reclassifications	[2]	0	0
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	0	0
Ending balance	[2]	0	0
Unrealized Gains (Losses) on Marketable Securities | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)			(10)
Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]	(2,960)	(2,998)
OCI before reclassifications	[2]	(38)	18
Amounts reclassified from AOCI	[1],[2],[3]	20	44
Other comprehensive (loss) income	[2]	(18)	62
Ending balance	[2]	(2,978)	(2,936)
Pension and Non-Pension Postretirement Benefit Plan Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)			0
Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]	(33)	(23)
OCI before reclassifications	[2]	2	1
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	2	1
Ending balance	[2]	(31)	(22)
Foreign Currency Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)			0
AOCI of Investments in Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]	0	(1)
OCI before reclassifications	[2]	(1)	0
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	(1)	0
Ending balance	[2]	(1)	(1)
AOCI of Investments in Unconsolidated Affiliates | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)			0
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]	(2,995)	(3,026)
OCI before reclassifications	[2]	(37)	27
Amounts reclassified from AOCI	[2],[3]	20	44
Other comprehensive (loss) income	[2]	(17)	71
Ending balance	[2]	(3,012)	(2,965)
Total | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)			(10)
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		15,508	15,959
Other comprehensive (loss) income		1	7
Ending Balance		15,696	15,958
Exelon Generation Co L L C [Member] | Gains (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(4)	(16)
OCI before reclassifications	[2]	0	7
Amounts reclassified from AOCI	[2],[3]	1	0
Other comprehensive (loss) income	[2]	1	7
Ending Balance	[2]	(3)	(9)
Exelon Generation Co L L C [Member] | Gains (Losses) on Cash Flow Hedges | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)			0
Exelon Generation Co L L C [Member] | Unrealized Gains (Losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	0	3
OCI before reclassifications	[2]	0	0
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	0	0
Ending Balance	[2]	0	0
Exelon Generation Co L L C [Member] | Unrealized Gains (Losses) on Marketable Securities | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)			(3)
Exelon Generation Co L L C [Member] | Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	0	0
OCI before reclassifications	[2]	0	0
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	0	0
Ending Balance	[2]	0	0
Exelon Generation Co L L C [Member] | Pension and Non-Pension Postretirement Benefit Plan Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)			0
Exelon Generation Co L L C [Member] | Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(33)	(23)
OCI before reclassifications	[2]	2	(1)
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	2	(1)
Ending Balance	[2]	(31)	(24)
Exelon Generation Co L L C [Member] | Foreign Currency Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)			0
Exelon Generation Co L L C [Member] | AOCI of Investments in Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(1)	(1)
OCI before reclassifications	[2]	(1)	0
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	(1)	0
Ending Balance	[2]	(2)	(1)
Exelon Generation Co L L C [Member] | AOCI of Investments in Unconsolidated Affiliates | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)			0
Exelon Generation Co L L C [Member] | Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(38)	(37)
OCI before reclassifications	[2]	1	6
Amounts reclassified from AOCI	[2],[3]	1	0
Other comprehensive (loss) income	[2]	2	6
Ending Balance	[2]	$ (36)	(34)
Exelon Generation Co L L C [Member] | Total | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)			$ (3)
[1]	Amounts in parenthesis represent a decrease in net income.
[2]	All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.
[3]	See next tables for details about these reclassifications.

Changes in Accumulated Other _4

Changes in Accumulated Other Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense (Benefit)		$ 310	$ 59
Amortization of pension and other postretirement benefit plan items			4
Amounts reclassified from AOCI	[1]	(20)	(44)
Gains (Losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	[2],[3]	0	0
Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	22	23
Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	(49)	(83)
Pension and Non-Pension Postretirement Benefit Plan Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1]	(27)	(60)
Tax benefit	[1]	7	16
Amounts reclassified from AOCI	[1],[2],[3]	$ (20)	$ (44)
[1]	Amounts in parenthesis represent a decrease in net income.
[2]	All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.
[3]	See next tables for details about these reclassifications.
[4]	This AOCI component is included in the computation of net periodic pension and OPEB cost. See Note 14 — Retirement Benefits for additional information.

Changes in Accumulated Other _5

Changes in Accumulated Other Comprehensive Income - Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	$ 7	$ (27)
Prior service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	6	6
Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	(13)	(22)
Pension and Non-Pension Postretirement Benefit Plan Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	14	(7)
Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	0	(3)
Unrealized Gains (Losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	0	(1)
Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	1	(4)
Exelon Generation Co L L C [Member] | Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	1	(3)
Exelon Generation Co L L C [Member] | Unrealized Gains (Losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in unrealized gains (losses) on investments in unconsolidated affiliates	$ 0	$ (1)

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019USD ($)MGPSiteOpen_claimgalMW	Dec. 31, 2022MW	Dec. 31, 2018USD ($)MW	Dec. 31, 2017MW
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 3,481
Accrual for Environmental Loss Contingencies, Gross	486		$ 496
Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	2,831
Accrued Insurance, Current	14,100
Loss Contingency, Undiscounted Amount of Insurance-related Assessment Liability	450
Maximum liability per nuclear incident	13,600
Prepaid Reinsurance Premiums	335
Estimated Insurance Recoveries	3,200
Accrual for Environmental Loss Contingencies, Gross	108		108
Accrual for Environmental Loss Contingencies, Component Amount	90
Liability for Asbestos and Environmental Claims, Gross	$ 77		79
Open Asbestos Related Personal Injury Claims | Open_claim	239
Pepco Holdings LLC [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 74
Accrual for Environmental Loss Contingencies, Gross	26		27
Commonwealth Edison Co [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 257
Mgp Site Contingency Approved Cleanup Count | MGPSite	42
Mgp Site Contingency Count | MGPSite	21
Mgp Site Contingency Monitoring Count | MGPSite	21
Accrual for Environmental Loss Contingencies, Gross	$ 320		329
Potomac Electric Power Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	48
Accrual for Environmental Loss Contingencies, Gross	24		25
PECO Energy Co [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 187
Mgp Site Contingency Approved Cleanup Count | MGPSite	26
Mgp Site Contingency Count | MGPSite	17
Mgp Site Contingency Monitoring Count | MGPSite	9
Accrual for Environmental Loss Contingencies, Gross	$ 27		27
Baltimore Gas and Electric Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 19
Mgp Site Contingency Approved Cleanup Count | MGPSite	13
Mgp Site Contingency Count | MGPSite	9
Mgp Site Contingency Monitoring Count | MGPSite	4
Accrual for Environmental Loss Contingencies, Gross	$ 5		5
Delmarva Power and Light Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 16
Mgp Site Contingency Approved Cleanup Count | gal	3
Mgp Site Contingency Count | MGPSite	2
Accrual for Environmental Loss Contingencies, Gross	$ 1		$ 1
Open Claims [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Liability for Asbestos and Environmental Claims, Gross	25
Estimated Future Claims [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Liability for Asbestos and Environmental Claims, Gross	52
Nuclear Insurance Premiums [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Nuclear financial protection pool value	3,100
Nuclear Insurance Premiums [Member] | Maximum [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Nuclear financial protection pool value	454
Pepco Holdings Inc [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	513
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	320
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	120
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	89
West Lake [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Accrual for Environmental Loss Contingencies, Gross	280
West Lake [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 20
Other Solar Projects [Member] | Pepco Holdings Inc [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Business Acquisition, Expected New Generation Mwh | MW	37
Other Non-Financial Commitment | MW	27
Other Commitment	$ 97
Other Solar Projects [Member] | Pepco Holdings Inc [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 97
Wind Assets [Member] | Pepco Holdings Inc [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Non-Financial Commitment | MW	100
Wind Assets [Member] | Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Purchase Commitment | MW	120		40	40
Subsequent Event [Member] | Wind Assets [Member] | Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Purchase Commitment | MW		40

Commitments and Contingencies_3

Commitments and Contingencies - Merger Commitment (Details) $ in Millions	Mar. 31, 2019USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,481
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	74
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	48
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	16
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	10
Pepco Holdings Inc [Member]
Other Commitments [Line Items]
Other Commitment	513
Pepco Holdings Inc [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	264
Pepco Holdings Inc [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	117
Pepco Holdings Inc [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings Inc [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	22
Pepco Holdings Inc [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	14
Pepco Holdings Inc [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	17
Pepco Holdings Inc [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	29
Pepco Holdings Inc [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	123
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	320
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	264
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	6
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	90
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	120
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	91
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	28
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	1
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	71
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	89
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	72
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	12
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	5
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	12
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	111
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	101
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	10
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	$ 7

Commitments and Contingencies_4

Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Mar. 31, 2019USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,481
Guarantor Obligations, Maximum Exposure, Undiscounted	68
Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1,480
Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	1,597	[1]
Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	378
Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	26	[2]
Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Commitment	2,831
Exelon Generation Co L L C [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1,455
Exelon Generation Co L L C [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	1,376	[1]
Exelon Generation Co L L C [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Exelon Generation Co L L C [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	0	[2]
Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Other Commitment	257
Commonwealth Edison Co [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	6
Commonwealth Edison Co [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	51	[1]
Commonwealth Edison Co [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	200
Commonwealth Edison Co [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	0	[2]
PECO Energy Co [Member]
Other Commitments [Line Items]
Other Commitment	187
PECO Energy Co [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	0
PECO Energy Co [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	9	[1]
PECO Energy Co [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	178
PECO Energy Co [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	0	[2]
Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	19
Baltimore Gas and Electric Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	2
Baltimore Gas and Electric Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	17	[1]
Baltimore Gas and Electric Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Baltimore Gas and Electric Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	0	[2]
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	74
Pepco Holdings LLC [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	8
Pepco Holdings LLC [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	40	[1]
Pepco Holdings LLC [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	26	[2]
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	48
Guarantor Obligations, Maximum Exposure, Undiscounted	22
Potomac Electric Power Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	8
Potomac Electric Power Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	32	[1]
Potomac Electric Power Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Potomac Electric Power Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	8	[2]
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	16
Guarantor Obligations, Maximum Exposure, Undiscounted	28
Delmarva Power and Light Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	0
Delmarva Power and Light Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	5	[1]
Delmarva Power and Light Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Delmarva Power and Light Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	11	[2]
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	10
Guarantor Obligations, Maximum Exposure, Undiscounted	17
Atlantic City Electric Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	0
Atlantic City Electric Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	3	[1]
Atlantic City Electric Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Atlantic City Electric Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	$ 7	[2]
[1]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[2]	Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $68 million, $22 million of which is a guarantee by Pepco, $28 million by DPL and $17 million by ACE. The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote.

Commitments and Contingencies_5

Commitments and Contingencies - Schedule of Accruals for Environmental Matters (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 486	$ 496
Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	108	108
Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	320	329
PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	27	27
Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	5	5
Pepco Holdings LLC [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	26	27
Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	24	25
Delmarva Power and Light Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	1
Atlantic City Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	1
Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	347	356
Accrual For MGP Investigation And Remediation [Member] | Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	318	327
Accrual For MGP Investigation And Remediation [Member] | PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	25	25
Accrual For MGP Investigation And Remediation [Member] | Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	4	4
Accrual For MGP Investigation And Remediation [Member] | Pepco Holdings LLC [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Delmarva Power and Light Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Atlantic City Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 0	$ 0

Supplemental Financial Inform_3

Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	[1],[2]	$ 54	$ 46
Net realized income on NDT funds - Non-regulatory agreement units	[2]	54	56
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	[1]	379	(75)
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement units		280	(96)
Regulatory offset to NDT fund-related activities	[3]	(348)	24
Total decommissioning-related activities		419	(45)
Investment income		12	4
Interest income related to uncertain income tax positions		1	2
AFUDC - Equity		22	18
Non-service net periodic benefit cost		5	(10)
Other		8	3
Other, net		467	(28)
Exelon Generation Co L L C [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	[1],[2]	54	46
Net realized income on NDT funds - Non-regulatory agreement units	[2]	54	56
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	[1]	379	(75)
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement units		280	(96)
Regulatory offset to NDT fund-related activities	[3]	(348)	24
Total decommissioning-related activities		419	(45)
Investment income		7	2
Interest income related to uncertain income tax positions		0	1
AFUDC - Equity		0	0
Other		4	(2)
Other, net		430	(44)
Commonwealth Edison Co [Member]
Decommissioning-Related Activities [Abstract]
Investment income		0	0
Interest income related to uncertain income tax positions		0	0
AFUDC - Equity		5	6
Other		3	2
Other, net		8	8
PECO Energy Co [Member]
Decommissioning-Related Activities [Abstract]
Investment income		1	0
Interest income related to uncertain income tax positions		0	0
AFUDC - Equity		3	2
Other		0	0
Other, net		4	2
Baltimore Gas and Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income		0	0
Interest income related to uncertain income tax positions		0	0
AFUDC - Equity		5	4
Other		0	0
Other, net		5	4
Pepco Holdings LLC [Member]
Decommissioning-Related Activities [Abstract]
Investment income		0	0
Interest income related to uncertain income tax positions		0	0
AFUDC - Equity		9	6
Other		3	5
Other, net		12	11
Potomac Electric Power Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income		0	0
Interest income related to uncertain income tax positions		0	0
AFUDC - Equity		6	5
Other		1	3
Other, net		7	8
Delmarva Power and Light Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income		0	0
Interest income related to uncertain income tax positions		0	0
AFUDC - Equity		1	1
Other		2	1
Other, net		3	2
Atlantic City Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income		0	0
Interest income related to uncertain income tax positions		0	0
AFUDC - Equity		2	0
Other		1	1
Other, net		$ 3	$ 1
[1]	Net realized and unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities in Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates in Generation’s Consolidated Balance Sheets.
[2]	Realized income includes interest, dividends and realized gains and losses on sales of NDT fund investments.
[3]	Includes the elimination of decommissioning-related activities for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 15 — Asset Retirement Obligations of the Exelon 2018 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

Supplemental Financial Inform_4

Supplemental Financial Information - Utility Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Supplemental Statement of Operations Information [Line Items]
Utility taxes	$ 223	$ 235
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	26	32
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	62	61
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	34	33
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	27	26
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	74	83
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	69	77
Delmarva Power and Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	5	6
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	$ 0	$ 0

Supplemental Financial Inform_5

Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	$ 917	$ 926
Amortization of regulatory assets	[1]	143	152
Amortization of intangible assets, net	[1]	15	13
Amortization of energy contract assets and liabilities	[2]		3
Amortization of nuclear fuel	[3]	261	287
ARO accretion	[4]	124	120
Total depreciation, amortization and accretion		1,460	1,501
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		106	145
Loss on equity method investments		6	7
Provision for uncollectible accounts		43	64
Stock-based compensation costs		28	29
Other decommissioning-related activity	[5]	(202)	(31)
Energy-related options	[6]	37	(7)
Amortization of regulatory asset related to debt costs		3	2
Amortization of rate stabilization deferral		(6)	7
Amortization of debt fair value adjustment		(4)	(3)
Discrete impacts from EIMA and FEJA	[7]	28	(4)
Amortization of debt costs		9	9
Provision for excess and obsolete inventory			13
Long-term incentive plan		25
Amortization of operating ROU asset		53
Other		1	9
Total other noncash operating activities		127	240
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(229)	(177)
Change in PPE related to ARO update		301	32
Dividends on stock compensation		1	1
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	392	436
Amortization of regulatory assets	[1]	0	0
Amortization of intangible assets, net	[1]	13	12
Amortization of energy contract assets and liabilities	[2]		3
Amortization of nuclear fuel	[3]	261	287
ARO accretion	[4]	123	120
Total depreciation, amortization and accretion		789	858
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		31	51
Loss on equity method investments		6	7
Provision for uncollectible accounts		0	11
Other decommissioning-related activity	[5]	(202)	(31)
Energy-related options	[6]	37	(7)
Amortization of regulatory asset related to debt costs		0	0
Amortization of rate stabilization deferral		0	0
Amortization of debt fair value adjustment		(3)	(3)
Amortization of debt costs		3	3
Provision for excess and obsolete inventory			12
Amortization of operating ROU asset		34
Other		4	2
Total other noncash operating activities		(90)	45
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(93)	(131)
Change in PPE related to ARO update		301	32
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	219	201
Amortization of regulatory assets	[1]	32	27
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		251	228
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		24	45
Loss on equity method investments		0	0
Provision for uncollectible accounts		9	8
Amortization of regulatory asset related to debt costs		0	1
Amortization of rate stabilization deferral		0	0
Amortization of debt fair value adjustment		0	0
Discrete impacts from EIMA and FEJA	[7]	28	(4)
Amortization of debt costs		1	1
Provision for excess and obsolete inventory			1
Amortization of operating ROU asset		1
Other		(7)	(6)
Total other noncash operating activities		56	46
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(80)	(48)
Change in PPE related to ARO update		0	0
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	74	68
Amortization of regulatory assets	[1]	7	7
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		81	75
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		2	5
Loss on equity method investments		0	0
Provision for uncollectible accounts		16	17
Amortization of regulatory asset related to debt costs		0	0
Amortization of rate stabilization deferral		0	0
Amortization of debt fair value adjustment		0	0
Amortization of debt costs		0	0
Provision for excess and obsolete inventory			0
Amortization of operating ROU asset		0
Other		(2)	(1)
Total other noncash operating activities		16	21
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		8	(25)
Change in PPE related to ARO update		0	0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	85	82
Amortization of regulatory assets	[1]	51	52
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		136	134
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		15	14
Loss on equity method investments		0	0
Provision for uncollectible accounts		8	8
Amortization of regulatory asset related to debt costs		0	0
Amortization of rate stabilization deferral		0	0
Amortization of debt fair value adjustment		0	0
Amortization of debt costs		0	0
Provision for excess and obsolete inventory			0
Amortization of operating ROU asset		8
Other		(4)	(2)
Total other noncash operating activities		27	20
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		2	(11)
Change in PPE related to ARO update		0	0
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	127	117
Amortization of regulatory assets	[1]	53	66
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		180	183
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		23	15
Loss on equity method investments		0	0
Provision for uncollectible accounts		10	20
Amortization of regulatory asset related to debt costs		1	1
Amortization of rate stabilization deferral		(6)	7
Amortization of debt fair value adjustment		(1)	0
Amortization of debt costs		1	1
Provision for excess and obsolete inventory			0
Amortization of operating ROU asset		9
Other		(2)	9
Total other noncash operating activities		35	53
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(55)	61
Change in PPE related to ARO update		0	0
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	58	53
Amortization of regulatory assets	[1]	36	43
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		94	96
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		6	4
Loss on equity method investments		0	0
Provision for uncollectible accounts		4	6
Amortization of regulatory asset related to debt costs		0	0
Amortization of rate stabilization deferral		(7)	1
Amortization of debt fair value adjustment		0	0
Amortization of debt costs		1	0
Provision for excess and obsolete inventory			0
Amortization of operating ROU asset		2
Other		(3)	(1)
Total other noncash operating activities		3	10
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(15)	19
Change in PPE related to ARO update		0	0
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	35	32
Amortization of regulatory assets	[1]	11	13
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		46	45
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		4	0
Loss on equity method investments		0	0
Provision for uncollectible accounts		4	8
Amortization of regulatory asset related to debt costs		0	0
Amortization of rate stabilization deferral		1	6
Amortization of debt fair value adjustment		0	0
Amortization of debt costs		0	0
Provision for excess and obsolete inventory			0
Amortization of operating ROU asset		2
Other		0	5
Total other noncash operating activities		11	19
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(17)	14
Change in PPE related to ARO update		0	0
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	25	23
Amortization of regulatory assets	[1]	6	10
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		31	33
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		4	3
Loss on equity method investments		0	0
Provision for uncollectible accounts		2	5
Amortization of regulatory asset related to debt costs		0	0
Amortization of rate stabilization deferral		0	0
Amortization of debt fair value adjustment		0	0
Amortization of debt costs		0	0
Provision for excess and obsolete inventory			0
Amortization of operating ROU asset		1
Other		(2)	1
Total other noncash operating activities		5	9
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(24)	27
Change in PPE related to ARO update		$ 0	$ 0
[1]	Included in Depreciation and amortization in the Registrants' Consolidated Statements of Operations and Comprehensive Income.
[2]	Included in Operating revenues or Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[3]	Included in Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[4]	Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[5]	Includes the elimination of decommissioning-related 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 15 — Asset Retirement Obligations of the Exelon 2018 Form 10-K for additional information regarding the accounting for nuclear decommissioning.
[6]	Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded in Operating revenues and expenses.
[7]	Reflects the change in ComEd's distribution and energy efficiency formula rates. See Note 6 — Regulatory Matters for additional information.

Supplemental Financial Inform_6

Supplemental Financial Information - Balance Sheet (Details) - USD ($) $ in Millions		Mar. 31, 2019		Dec. 31, 2018		Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		$ 23,695	[1]	$ 22,902	[2]
Accounts receivable, net
Allowance for uncollectible accounts		340		319
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		880		1,349		$ 787	$ 898
Restricted cash and cash equivalents		223		247		209	207
Restricted cash included in other long-term assets		211		185		103	85
Total cash, cash equivalents and restricted cash		1,314		1,781		1,099	1,190
Purchased Receivables [Abstract]
Purchased receivables		332		313
Allowance for uncollectible accounts	[3]	(38)		(34)
Purchased receivables, net		294		279
Nuclear Fuel [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		3,040		2,969
Exelon Generation Co L L C [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		12,663	[1]	12,206	[2]
Accounts receivable, net
Allowance for uncollectible accounts		87		104
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		537		750		610	416
Restricted cash and cash equivalents		139		153		127	138
Restricted cash included in other long-term assets		0		0		0	0
Total cash, cash equivalents and restricted cash		676		903		737	554
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		3,040		2,969
Commonwealth Edison Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		4,833		4,684
Accounts receivable, net
Allowance for uncollectible accounts		97		81
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		68		135		70	76
Restricted cash and cash equivalents		17		29		9	5
Restricted cash included in other long-term assets		193		166		83	63
Total cash, cash equivalents and restricted cash		278		330		162	144
Purchased Receivables [Abstract]
Purchased receivables		105		94
Allowance for uncollectible accounts	[3]	(19)		(17)
Purchased receivables, net		86		77
PECO Energy Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		3,598		3,561
Accounts receivable, net
Allowance for uncollectible accounts		72		61
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		41		130		21	271
Restricted cash and cash equivalents		6		5		5	4
Restricted cash included in other long-term assets		0		0		0	0
Total cash, cash equivalents and restricted cash		47		135		26	275
Purchased Receivables [Abstract]
Purchased receivables		77		74
Allowance for uncollectible accounts	[3]	(6)		(5)
Purchased receivables, net		71		69
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		3,670		3,633
Accounts receivable, net
Allowance for uncollectible accounts		27		20
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		12		7		22	17
Restricted cash and cash equivalents		4		6		2	1
Restricted cash included in other long-term assets		0		0		0	0
Total cash, cash equivalents and restricted cash		16		13		24	18
Purchased Receivables [Abstract]
Purchased receivables		65		61
Allowance for uncollectible accounts	[3]	(4)		(3)
Purchased receivables, net		61		58
Pepco Holdings LLC [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		930		841
Accounts receivable, net
Allowance for uncollectible accounts		57		53
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		33		124		43	30
Restricted cash and cash equivalents		39		43		40	42
Restricted cash included in other long-term assets		19		19		20	23
Total cash, cash equivalents and restricted cash		91		186		103	95
Purchased Receivables [Abstract]
Purchased receivables		85		84
Allowance for uncollectible accounts	[3]	(9)		(9)
Purchased receivables, net		76		75
Potomac Electric Power Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		3,392		3,354
Accounts receivable, net
Allowance for uncollectible accounts		23		21
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		11		16		15	5
Restricted cash and cash equivalents		35		37		33	35
Restricted cash included in other long-term assets		0		0		0	0
Total cash, cash equivalents and restricted cash		46		53		48	40
Purchased Receivables [Abstract]
Purchased receivables		58		57
Allowance for uncollectible accounts	[3]	(5)		(5)
Purchased receivables, net		53		52
Delmarva Power and Light Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		1,354		1,329
Accounts receivable, net
Allowance for uncollectible accounts		15		13
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		7		23		7	2
Restricted cash and cash equivalents		1		1		0	0
Restricted cash included in other long-term assets		0		0		0	0
Total cash, cash equivalents and restricted cash		8		24		7	2
Purchased Receivables [Abstract]
Purchased receivables		8		8
Allowance for uncollectible accounts	[3]	(1)		(1)
Purchased receivables, net		7		7
Atlantic City Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		1,154		1,137
Accounts receivable, net
Allowance for uncollectible accounts		19		19
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		6		7		10	2
Restricted cash and cash equivalents		3		4		7	6
Restricted cash included in other long-term assets		19		19		20	23
Total cash, cash equivalents and restricted cash		28		30		$ 37	$ 31
Purchased Receivables [Abstract]
Purchased receivables		19		19
Allowance for uncollectible accounts	[3]	(3)		(3)
Purchased receivables, net		$ 16		$ 16
[1]	Includes accumulated amortization of nuclear fuel in the reactor core of $3,040 million.
[2]	Includes accumulated amortization of nuclear fuel in the reactor core of $2,969 million.
[3]	For ComEd, BGE, Pepco and DPL, 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 a rate rider. BGE, Pepco and DPL recover actual write-offs which are reflected in the POR discount rate.

Segment Information - Narrative

Segment Information - Narrative (Details)	3 Months Ended
	Mar. 31, 2019Reportable_segment
Segment Reporting Information [Line Items]
Number of reportable segments	11
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	5
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	3

Segment Information - Reconcili

Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019		Mar. 31, 2018		Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues		$ 9,477		$ 9,693
Operating revenues from affiliates	[1]	0		0
Depreciation, Depletion and Amortization		1,075		1,091
Operating Expenses		8,262		8,648
Interest Revenue (Expense), Net		403		371
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		1,282		702
Income taxes		310		59
Net income (loss)		966		636
Payments to Acquire Property, Plant, and Equipment		1,873		1,880
Assets	[2]	121,593				$ 119,666
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		1,139		1,151
Rate-regulated natural gas revenues		71		78
Revenues		1,228		1,251
Operating revenues from affiliates		3		4
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		122		74
Income taxes		5		9
Net income (loss)		117		65
Payments to Acquire Property, Plant, and Equipment		358		258
Assets	[3]	22,294				21,984
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues		5,296		5,512
Operating revenues from affiliates		317		398
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		652		202
Income taxes		224		9
Net income (loss)		422		186
Payments to Acquire Property, Plant, and Equipment		511		628
Assets	[4]	48,682				47,556
Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	4,022		4,118
Competitive businesses natural gas revenues	[5]	878		947
Competitive businesses other revenues	[5]	79		48
Rate-regulated electric revenues	[5]	3,831		3,955
Rate-regulated natural gas revenues	[5]	665		625
Shared service and other revenues	[5]	2		0
Revenues	[5]	9,477		9,693
Net income (loss)		966		636
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	(315)		(391)
Competitive businesses natural gas revenues	[5]	(1)		(8)
Competitive businesses other revenues	[5]	(1)		0
Rate-regulated electric revenues	[5]	(8)		(18)
Rate-regulated natural gas revenues	[5]	(4)		(4)
Shared service and other revenues	[5]	(457)		(455)
Revenues	[5]	(786)		(876)
Operating revenues from affiliates	[1]	(785)		(876)
Depreciation, Depletion and Amortization		0		0
Operating Expenses		(783)		(886)
Interest Revenue (Expense), Net		0		0
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		0		0
Income taxes		0		0
Net income (loss)		0		0
Payments to Acquire Property, Plant, and Equipment		0		0
Assets		(10,213)				(9,800)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]	(5)		(4)
Rate-regulated natural gas revenues	[6]	1		0
Shared service and other revenues	[6]	(102)		(109)
Revenues	[6]	(106)		(113)
Operating revenues from affiliates		(106)		(113)
Depreciation, Depletion and Amortization		(1)		0
Operating Expenses		(105)		(112)
Interest Revenue (Expense), Net		(1)		1
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		(118)		(69)
Income taxes		0		0
Net income (loss)		4		4
Payments to Acquire Property, Plant, and Equipment		0		0
Assets		(5,478)				(5,421)
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5],[7]	4,337		4,509
Competitive businesses natural gas revenues	[5],[7]	879		955
Competitive businesses other revenues	[5],[7]	80		48
Rate-regulated electric revenues	[5],[7]	0		0
Rate-regulated natural gas revenues	[5],[7]	0		0
Shared service and other revenues	[5],[7]	0		0
Revenues	[5],[7]	5,296		5,512
Depreciation, Depletion and Amortization		405		448
Operating Expenses		4,963		5,218
Interest Revenue (Expense), Net		111		101
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		652		202
Income taxes		224		9
Net income (loss)	[7]	422		186
Payments to Acquire Property, Plant, and Equipment		511		628
Assets	[7]	48,682				47,556
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1],[7]	317		400
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	0		0
Competitive businesses natural gas revenues	[5]	0		0
Competitive businesses other revenues	[5]	0		0
Rate-regulated electric revenues	[5]	1,408		1,512
Rate-regulated natural gas revenues	[5]	0		0
Shared service and other revenues	[5]	0		0
Revenues	[5]	1,408		1,512
Depreciation, Depletion and Amortization		251		228
Operating Expenses		1,135		1,223
Interest Revenue (Expense), Net		87		89
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		197		211
Income taxes		40		46
Net income (loss)		157		165
Payments to Acquire Property, Plant, and Equipment		503		531
Assets		31,582				31,213
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]	4		14
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	0		0
Competitive businesses natural gas revenues	[5]	0		0
Competitive businesses other revenues	[5]	0		0
Rate-regulated electric revenues	[5]	620		634
Rate-regulated natural gas revenues	[5]	280		232
Shared service and other revenues	[5]	0		0
Revenues	[5]	900		866
Depreciation, Depletion and Amortization		81		75
Operating Expenses		678		724
Interest Revenue (Expense), Net		33		33
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		193		111
Income taxes		25		(2)
Net income (loss)		168		113
Payments to Acquire Property, Plant, and Equipment		222		217
Assets		10,956				10,642
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]	1		2
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	0		0
Competitive businesses natural gas revenues	[5]	0		0
Competitive businesses other revenues	[5]	0		0
Rate-regulated electric revenues	[5]	658		658
Rate-regulated natural gas revenues	[5]	318		319
Shared service and other revenues	[5]	0		0
Revenues	[5]	976		977
Depreciation, Depletion and Amortization		136		134
Operating Expenses		756		800
Interest Revenue (Expense), Net		29		25
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		196		156
Income taxes		36		28
Net income (loss)		160		128
Payments to Acquire Property, Plant, and Equipment		258		224
Assets		9,967				9,716
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]	6		6
Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	0		0
Competitive businesses natural gas revenues	[5]	0		0
Competitive businesses other revenues	[5]	0		0
Rate-regulated electric revenues	[5],[6]	1,153		1,169
Rate-regulated natural gas revenues	[5],[6]	71		78
Shared service and other revenues	[5],[6]	4		4
Revenues	[5],[6]	1,228		1,251
Depreciation, Depletion and Amortization		180		183
Operating Expenses		1,054		1,125
Interest Revenue (Expense), Net		65		63
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		122		74
Income taxes		5		9
Net income (loss)		117		65
Payments to Acquire Property, Plant, and Equipment		358		258
Assets		22,294				21,984
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]	4		4
Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]	575		557
Rate-regulated natural gas revenues	[6]	0		0
Shared service and other revenues	[6]	0		0
Revenues	[6]	575		557
Depreciation, Depletion and Amortization		94		96
Operating Expenses		491		501
Interest Revenue (Expense), Net		34		31
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		57		33
Income taxes		2		2
Net income (loss)		55		31
Payments to Acquire Property, Plant, and Equipment		144		127
Assets		8,420				8,299
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2		2
Delmarva Power and Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]	310		306
Rate-regulated natural gas revenues	[6]	70		78
Shared service and other revenues	[6]	0		0
Revenues	[6]	380		384
Depreciation, Depletion and Amortization		46		45
Operating Expenses		308		335
Interest Revenue (Expense), Net		15		13
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		60		38
Income taxes		7		7
Net income (loss)		53		31
Payments to Acquire Property, Plant, and Equipment		78		65
Assets		4,660				4,588
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2		2
Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]	273		310
Rate-regulated natural gas revenues	[6]	0		0
Shared service and other revenues	[6]	0		0
Revenues	[6]	273		310
Depreciation, Depletion and Amortization		31		33
Operating Expenses		252		287
Interest Revenue (Expense), Net		14		16
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		10		8
Income taxes		0		1
Net income (loss)		10		7
Payments to Acquire Property, Plant, and Equipment		128		63
Assets		3,783				3,699
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1		1
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5],[8]	0		0
Competitive businesses natural gas revenues	[5],[8]	0		0
Competitive businesses other revenues	[5],[8]	0		0
Rate-regulated electric revenues	[8]	0	[7]	0	[5]
Rate-regulated natural gas revenues	[5],[8]	0		0
Shared service and other revenues	[5],[8]	455		451
Revenues	[5],[8]	455		451
Depreciation, Depletion and Amortization	[8]	22		23
Operating Expenses	[8]	459		444
Interest Revenue (Expense), Net	[8]	78		60
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	[8]	(78)		(52)
Income taxes	[8]	(20)		(31)
Net income (loss)	[8]	(58)		(21)
Payments to Acquire Property, Plant, and Equipment	[8]	21		22
Assets	[8]	8,325				8,355
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6],[9]	0		0
Rate-regulated natural gas revenues	[6],[9]	0		0
Shared service and other revenues	[6],[9]	106		113
Revenues	[6],[9]	106		113
Depreciation, Depletion and Amortization		10		9
Operating Expenses		108		114
Interest Revenue (Expense), Net		3		2
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		113		64
Income taxes		(4)		(1)
Net income (loss)	[9]	(5)		(8)
Payments to Acquire Property, Plant, and Equipment		8		3
Assets		10,909				$ 10,819
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1],[8]	453		450
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[9]	105		112
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,256		1,440
Generation Mid Atlantic [Member] | PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		45		37
Generation Mid Atlantic [Member] | Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		76		65
Generation Mid Atlantic [Member] | PotomacElectricPowerCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		70		52
Generation Mid Atlantic [Member] | DelmarvaPowerandLightCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		23		46
Generation Mid Atlantic [Member] | AtlanticCityElectricCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		8		6
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[10]	1,262		1,435
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(6)		5
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,108		1,346
Generation Midwest [Member] | Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		94		194
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[10]	1,114		1,344
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		$ (6)		$ 2
[1]	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]	Exelon’s consolidated assets include $9,546 million and $9,667 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,572 million and $3,548 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2 — Variable Interest Entities for additional information.
[3]	PHI’s consolidated total assets include $31 million and $33 million at March 31, 2019 and December 31, 2018, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $64 million and $69 million at March 31, 2019 and December 31, 2018, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 2 — Variable Interest Entities for additional information.
[4]	Generation’s consolidated assets include $9,515 million and $9,634 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,508 million and $3,480 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2 — Variable Interest Entities for additional information.
[5]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 17 — Supplemental Financial Information for additional information on total utility taxes.
[6]	ncludes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 17 — Supplemental Financial Information for additional information on total utility taxes.
[7]	Intersegment revenues for Generation in 2019 include revenue from sales to PECO of $45 million, sales to BGE of $76 million, sales to Pepco of $70 million, sales to DPL of $23 million and sales to ACE of $8 million in the Mid-Atlantic region, and sales to ComEd of $94 million in the Midwest region, which eliminate upon consolidation. Intersegment revenues for Generation in 2018 include revenue from sales to PECO of $37 million, sales to BGE of $65 million, sales to Pepco of $52 million, sales to DPL of $46 million and sales to ACE of $6 million in the Mid-Atlantic region, and sales to ComEd of $194 million in the Midwest region, which eliminate upon consolidation.
[8]	Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities.
[9]	ther primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities.The following tables disaggregate the Registrants' revenue recognized from contracts with customers into categories that depict how the nature, amount, timing, and uncertainty of revenue and cash flows are affected by economic factors. For Generation, the disaggregation of revenues reflects Generation’s two primary products of power sales and natural gas sales, with further disaggregation of power sales provided by geographic region. For the Utility Registrants, the disaggregation of revenues reflects the two primary utility services of rate-regulated electric sales and rate-regulated natural gas sales (where applicable), with further disaggregation of these tariff sales provided by major customer groups. Exelon’s disaggregated revenues are consistent with Generation and the Utility Registrants, but exclude any intercompany revenues.Competitive Business Revenues (Generation):
[10]	des all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants.(b)

Segment Information - Generatio

Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Revenues		$ 9,477	$ 9,693
Operating revenues from affiliates	[1]	0	0
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,256	1,440
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,108	1,346
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		393	409
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		212	209
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		1,353	1,080
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		4,322	4,484
Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues		894	980
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2]	80	48
Unrealized Gain (Loss) on Securities		(52)	(98)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		5,296	5,512
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[3]	9,477	9,693
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,262	1,435
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,114	1,344
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	393	410
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	209	208
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,359	1,112
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	4,337	4,509
Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	879	955
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Unrealized Gain (Loss) on Securities		(28)	(266)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	5,296	5,512
Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	80	48
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	[3]	(786)	(876)
Operating revenues from affiliates	[1]	(785)	(876)
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(6)	5
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(6)	2
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0	(1)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		3	1
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(6)	(32)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(15)	(25)
Intersegment Eliminations [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		15	25
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[2]	0	0
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0	0
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,286	1,355
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,055	1,273
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	409	439
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	130	149
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,165	935
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	4,045	4,151
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	584	522
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	4,749	4,807
Revenue from Contract with Customer [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	120	134
Other [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	(24)	80
Other [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	59	71
Other [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	(16)	(29)
Other [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	79	59
Other [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	194	177
Other [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	292	358
Other [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	295	433
Other [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	547	705
Other [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5],[6]	$ (40)	$ (86)
[1]	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]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjhiOGQyMzgxMWZiYjQ2YjNiZDRmMDg0ZmFhZDBiZGFjfFRleHRTZWxlY3Rpb246Nzg0RjkwRDlGOTIxNTBDQkFGM0EzREE2MkIyMjdEOTEM}
[3]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 17 — Supplemental Financial Information for additional information on total utility taxes.
[4]	des all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants.(b)
[5]	represents activities not allocated to a region. See text above for a description of included activities. Includes unrealized mark-to-market losses of $52 million and $98 million in 2019 and 2018, respectively, and elimination of intersegment revenues.Reve
[6]	des revenues from derivatives and leases. (c)

Segment Information - Generat_2

Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		$ 683	$ 850
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		771	860
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		265	283
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		74	36
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		156	236
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		1,949	2,265
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	[1]	142	(46)
Unrealized Gain (Loss) on Securities		(52)	(98)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		2,091	2,219
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	679	836
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	769	847
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	262	282
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	98	106
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	174	279
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	1,982	2,350
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[1],[2]	109	(131)
Unrealized Gain (Loss) on Securities		(28)	(266)
Nuclear Fuel Amortization		5	15
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	2,091	2,219
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		4	14
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		2	13
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		3	1
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(24)	(70)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(18)	(43)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(33)	(85)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	[1]	33	85
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		$ 0	$ 0
[1]	Other represents activities not allocated to a region. See text above for a description of included activities. Includes unrealized mark-to-market losses of $28 million and $266 million in 2019 and 2018, respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 8 — Early Plant Retirements of $5 million and $15 million decrease to RNF in 2019 and 2018, respectively, and the elimination of intersegment RNF.
[2]	Includes purchases and sales from/to third parties and affiliated sales to the Utility Registrants.

Segment Information - Electric

Segment Information - Electric and Gas Revenue by Customer Class (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs		$ (5)	$ 10
Revenues		9,477	9,693
Revenue from Related Parties	[1]	0	0
Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[2]	3,831	3,955
Rate-regulated natural gas revenues	[2]	665	625
Revenues	[2]	9,477	9,693
Commonwealth Edison Co [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		1,432	1,493
Revenues from alternative revenue programs		(28)	5
Revenues		1,408	1,512
Revenue from Related Parties		4	14
Commonwealth Edison Co [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs		(28)	5
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	1,432	1,498
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	4	9
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		710	717
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		360	385
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		132	152
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		13	14
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	217	230
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[4]	0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues			0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	0	0
Commonwealth Edison Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		1,432	1,498
Commonwealth Edison Co [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues		(24)	14
PECO Energy Co [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		622	633
Rate-regulated natural gas revenues		280	232
Revenues from alternative revenue programs		(3)	(1)
Revenues		900	866
Revenue from Related Parties		1	2
PECO Energy Co [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs		(3)	(1)
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	622	632
Revenue from Related Parties		1	2
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	1	3
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		409	403
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		96	101
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		48	58
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		7	8
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	62	62
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	280	232
Revenue from Related Parties		0	0
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[4]	0	0
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		198	161
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		72	62
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		1	1
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		7	6
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	2	2
PECO Energy Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		902	864
PECO Energy Co [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues		(2)	2
Baltimore Gas and Electric Company [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		652	654
Rate-regulated natural gas revenues		308	330
Revenues from alternative revenue programs		10	(13)
Revenues		976	977
Revenue from Related Parties		6	6
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs		10	(13)
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	652	652
Revenue from Related Parties		2	2
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	3	4
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		385	393
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		70	68
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		110	106
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		7	7
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	80	78
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	308	332
Revenue from Related Parties
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[4]	3	2
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		219	224
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		35	34
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		50	47
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	4	27
Baltimore Gas and Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		960	984
Baltimore Gas and Electric Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues		16	(7)
Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		1,139	1,151
Rate-regulated natural gas revenues		71	78
Revenues from alternative revenue programs		15	18
Revenues		1,228	1,251
Revenue from Related Parties		3	4
Pepco Holdings LLC [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs		15	18
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	1,137	1,154
Revenue from Related Parties			4
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	4	1
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		579	610
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		120	115
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		267	259
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		14	14
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	157	156
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	71	78
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[4]	1	0
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		44	47
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		19	18
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		1	4
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		4	5
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	3	4
Pepco Holdings LLC [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		1,208	1,232
Pepco Holdings LLC [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues		20	19
Potomac Electric Power Company [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		559	536
Revenues from alternative revenue programs		14	19
Revenues		575	557
Revenue from Related Parties		2	2
Potomac Electric Power Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs		14	19
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	559	537
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	2	1
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		256	259
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		38	32
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		204	190
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		8	7
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	53	49
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[4]	0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	0	0
Potomac Electric Power Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		559	537
Potomac Electric Power Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues		16	20
Delmarva Power and Light Company [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		307	303
Rate-regulated natural gas revenues		71	78
Revenues from alternative revenue programs		0	1
Revenues		380	384
Revenue from Related Parties		2	2
Delmarva Power and Light Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs		0	1
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	307	305
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	1	0
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		185	191
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		48	46
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		24	23
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		3	4
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	47	41
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	71	78
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[4]	1	0
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		44	47
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		19	18
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		1	4
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		4	5
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	3	4
Delmarva Power and Light Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		378	383
Delmarva Power and Light Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues		2	1
Atlantic City Electric Company [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		271	311
Revenues from alternative revenue programs		1	(2)
Revenues		273	310
Revenue from Related Parties		1	1
Atlantic City Electric Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs		1	(2)
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	271	312
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	1	0
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		138	160
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		34	37
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		39	46
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		3	3
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	57	66
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[4]	0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	0	0
Atlantic City Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		271	312
Atlantic City Electric Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues		$ 2	(2)
Atlantic City Electric Co Affiliate [Member]
Revenue, Major Customer [Line Items]
Revenue from Related Parties			$ 0
[1]	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 gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 17 — Supplemental Financial Information for additional information on total utility taxes.
[3]	Includes operating revenues from affiliates of $4 million, $1 million, $2 million, $3 million, $2 million, $2 million and $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2019 and $14 million, $2 million, $2 million, $4 million $2 million, $2 million and 1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2018.
[4]	Includes late payment charge revenues.
[5]	Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue.
[6]	Includes operating revenues from affiliates of less than $1 million and $4 million at PECO and BGE, respectively, in 2019 and 2018.
[7]	Includes revenues from off-system natural gas sales.