Exelon Generation 10-K 11 Feb 20 2019 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2019	Jan. 31, 2020	Jun. 30, 2019
Document Type	10-K
Amendment Flag	false
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	001-16169
Entity Registrant Name	EXELON CORPORATION
Entity Incorporation, State or Country Code	PA
Entity Tax Identification Number	23-2990190
Entity Address, Address Line One	10 South Dearborn Street
Entity Address, Address Line Two	P.O. Box 805379
Entity Address, City or Town	Chicago
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60680-5379
City Area Code	(800)
Local Phone Number	483-3220
Title of 12(b) Security	Common Stock, without par value
Trading Symbol	EXC
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 46,542,193,363
Entity Common Stock Shares Outstanding		974,319,565
Documents Incorporated by Reference [Text Block]	Portions of the Exelon Proxy Statement for the 2019 Annual Meeting of Shareholders and the Commonwealth Edison Company 2019 Information Statement are incorporated by reference in Part III.
Entity Central Index Key	0001109357
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Exelon Generation Co L L C [Member]
Entity File Number	333-85496
Entity Registrant Name	EXELON GENERATION COMPANY, LLC
Entity Incorporation, State or Country Code	PA
Entity Tax Identification Number	23-3064219
Entity Address, Address Line One	300 Exelon Way
Entity Address, City or Town	Kennett Square
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19348-2473
City Area Code	(610)
Local Phone Number	765-5959
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Central Index Key	0001168165
Commonwealth Edison Co [Member]
Entity File Number	001-01839
Entity Registrant Name	COMMONWEALTH EDISON COMPANY
Entity Incorporation, State or Country Code	IL
Entity Tax Identification Number	36-0938600
Entity Address, Address Line One	440 South LaSalle Street
Entity Address, City or Town	Chicago
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60605-1028
City Area Code	(312)
Local Phone Number	394-4321
Title of 12(g) Security	Common Stock Purchase Warrants (1971 Warrants and Series B Warrants)
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock Shares Outstanding		127,021,349
Entity Central Index Key	0000022606
PECO Energy Co [Member]
Entity File Number	000-16844
Entity Registrant Name	PECO ENERGY COMPANY
Entity Incorporation, State or Country Code	PA
Entity Tax Identification Number	23-0970240
Entity Address, Address Line One	P.O. Box 8699
Entity Address, Address Line Two	2301 Market Street
Entity Address, City or Town	Philadelphia
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19101-8699
City Area Code	(215)
Local Phone Number	841-4000
Title of 12(b) Security	Cumulative Preferred Security, Series D,
Trading Symbol	EXC/28
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock Shares Outstanding		170,478,507
Entity Central Index Key	0000078100
Baltimore Gas and Electric Company [Member]
Entity File Number	001-01910
Entity Registrant Name	BALTIMORE GAS AND ELECTRIC COMPANY
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	52-0280210
Entity Address, Address Line One	2 Center Plaza
Entity Address, Address Line Two	110 West Fayette Street
Entity Address, City or Town	Baltimore
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	21201-3708
City Area Code	(410)
Local Phone Number	234-5000
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock Shares Outstanding		1,000
Entity Central Index Key	0000009466
Pepco Holdings LLC [Member]
Entity File Number	001-31403
Entity Registrant Name	PEPCO HOLDINGS LLC
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	52-2297449
Entity Address, Address Line One	701 Ninth Street, N.W.
Entity Address, City or Town	Washington, District of Columbia
Entity Address, Postal Zip Code	20068
City Area Code	(202)
Local Phone Number	872-2000
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Central Index Key	0001135971
Potomac Electric Power Company [Member]
Entity File Number	001-01072
Entity Registrant Name	POTOMAC ELECTRIC POWER COMPANY
Entity Tax Identification Number	53-0127880
Entity Address, Address Line One	701 Ninth Street, N.W.
Entity Address, City or Town	Washington, District of Columbia
Entity Address, Postal Zip Code	20068
City Area Code	(202)
Local Phone Number	872-2000
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock Shares Outstanding		100
Entity Central Index Key	0000079732
Delmarva Power & Light Company [Member]
Entity File Number	001-01405
Entity Registrant Name	DELMARVA POWER & LIGHT COMPANY
Entity Tax Identification Number	51-0084283
Entity Address, Address Line One	500 North Wakefield Drive
Entity Address, City or Town	Newark
Entity Address, State or Province	DE
Entity Address, Postal Zip Code	19702
City Area Code	(202)
Local Phone Number	872-2000
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock Shares Outstanding		1,000
Entity Central Index Key	0000027879
Atlantic City Electric Company [Member]
Entity File Number	001-03559
Entity Registrant Name	ATLANTIC CITY ELECTRIC COMPANY
Entity Incorporation, State or Country Code	NJ
Entity Tax Identification Number	21-0398280
Entity Address, Address Line One	500 North Wakefield Drive
Entity Address, City or Town	Newark
Entity Address, State or Province	DE
Entity Address, Postal Zip Code	19702
City Area Code	(202)
Local Phone Number	872-2000
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock Shares Outstanding		8,546,017
Entity Central Index Key	0000008192
VIRGINIA | Potomac Electric Power Company [Member]
Entity Incorporation, State or Country Code	VA
VIRGINIA | Delmarva Power & Light Company [Member]
Entity Incorporation, State or Country Code	VA
DELAWARE | Delmarva Power & Light Company [Member]
Entity Incorporation, State or Country Code	DE
DISTRICT OF COLUMBIA | Potomac Electric Power Company [Member]
Entity Incorporation, State or Country Code	DC

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating revenues
Revenue from alternative revenue programs	$ (155)	$ (69)	$ 200
Total operating revenues	34,438	35,978	33,558
Operating expenses
Operating and maintenance	8,615	9,337	10,025
Depreciation and Amortization	4,252	4,353	3,828
Taxes other than income	1,732	1,783	1,731
Total operating expenses	30,096	32,143	29,619
Gain on sales of assets and businesses	31	56	3
Bargain purchase gain	0	0	233
Gain on deconsolidation of business	1	0	213
Operating income (loss)	4,374	3,891	4,388
Other income and (deductions)
Interest expense, net	(1,591)	(1,529)	(1,524)
Interest expense to affiliates	(25)	(25)	(36)
Other, net	1,227	(112)	947
Total other income and (deductions)	(389)	(1,666)	(613)
Income (loss) before income taxes	3,985	2,225	3,775
Income taxes	774	118	(126)
Equity in losses of unconsolidated affiliates	(183)	(28)	(32)
Net income (loss)	3,028	2,079	3,869
Net income (loss) attributable to noncontrolling interests and/or preference stock dividends	92	74	90
Net income (loss) attributable to common shareholders	2,936	2,005	3,779
Other comprehensive income (loss), net of income taxes
Prior service benefit reclassified to periodic benefit cost	(65)	(66)	(56)
Actuarial loss reclassified to periodic cost	149	247	197
Pension and non-pension postretirement benefit plan valuation adjustment	(289)	(143)	10
Unrealized gain on cash flow hedges	0	12	3
Unrealized gain on marketable securities	0	0	6
Unrealized gain (loss) on investments in unconsolidated affiliates	1	2	4
Unrealized (loss) gain on foreign currency translation	6	(10)	7
Other comprehensive income (loss)	(198)	42	171
Comprehensive income (loss)	2,830	2,121	4,040
Comprehensive income attributable to noncontrolling interests and/or preference stock dividends	93	75	88
Comprehensive income (loss) attributable to common shareholders	$ 2,737	$ 2,046	$ 3,952
Average shares of common stock outstanding:
Weighted Average Number of Shares Outstanding, Basic	973	967	947
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	1	2	2
Weighted Average Number of Shares Outstanding, Diluted	974	969	949
Earnings per average common share:
Earnings Per Share, Basic	$ 3.02	$ 2.07	$ 3.99
Earnings Per Share, Diluted	$ 3.01	$ 2.07	$ 3.98
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		3	8
Exelon Generation Co L L C [Member]
Operating revenues
Operating revenues from affiliates	$ 1,172	$ 1,268	$ 1,115
Total operating revenues	18,924	20,437	18,500
Operating expenses
Purchased power and/or fuel from affiliates	7	14	19
Operating and maintenance	4,131	4,803	5,602
Operating and maintenance from affiliates	587	661	697
Depreciation and Amortization	1,535	1,797	1,457
Taxes other than income	519	556	555
Total operating expenses	17,628	19,510	18,001
Gain on sales of assets and businesses	27	48	2
Bargain purchase gain	0	0	233
Gain on deconsolidation of business	0	0	213
Operating income (loss)	1,323	975	947
Other income and (deductions)
Interest expense, net	(394)	(396)	(401)
Interest expense to affiliates	(35)	(36)	(39)
Other, net	1,023	(178)	948
Total other income and (deductions)	594	(610)	508
Income (loss) before income taxes	1,917	365	1,455
Income taxes	516	(108)	(1,376)
Equity in losses of unconsolidated affiliates	(184)	(30)	(33)
Net income (loss)	1,217	443	2,798
Net income (loss) attributable to noncontrolling interests	92	73	88
Net income (loss) attributable to membership interest	1,125	370	2,710
Other comprehensive income (loss), net of income taxes
Unrealized gain on cash flow hedges	0	12	3
Unrealized gain on marketable securities	0	0	1
Unrealized gain (loss) on investments in unconsolidated affiliates	1	1	4
Unrealized (loss) gain on foreign currency translation	6	(10)	7
Other comprehensive income (loss)	7	3	15
Comprehensive income (loss)	1,224	446	2,813
Comprehensive income attributable to noncontrolling interests and/or preference stock dividends	93	74	86
Comprehensive income (loss) attributable to common shareholders	1,131	372	2,727
Commonwealth Edison Co [Member]
Operating revenues
Revenue from alternative revenue programs	(133)	(29)	43
Operating revenues from affiliates	30	27	15
Total operating revenues	5,747	5,882	5,536
Operating expenses
Purchased power and/or fuel from affiliates	376	529	108
Operating and maintenance	1,041	1,068	1,157
Operating and maintenance from affiliates	264	267	270
Depreciation and Amortization	1,033	940	850
Taxes other than income	301	311	296
Total operating expenses	4,580	4,741	4,214
Gain on sales of assets and businesses	4	5	1
Operating income (loss)	1,171	1,146	1,323
Other income and (deductions)
Interest expense, net	(346)	(334)	(348)
Interest expense to affiliates	(13)	(13)	(13)
Other, net	39	33	22
Total other income and (deductions)	(320)	(314)	(339)
Income (loss) before income taxes	851	832	984
Income taxes	163	168	417
Net income (loss)	688	664	567
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)	688	664	567
PECO Energy Co [Member]
Operating revenues
Revenue from alternative revenue programs	(21)	(7)	0
Operating revenues from affiliates	6	8	7
Total operating revenues	3,100	3,038	2,870
Operating expenses
Purchased power and/or fuel from affiliates	157	126	135
Operating and maintenance	707	742	657
Operating and maintenance from affiliates	154	156	149
Depreciation and Amortization	333	301	286
Taxes other than income	165	163	154
Total operating expenses	2,388	2,452	2,215
Gain on sales of assets and businesses	1	1	0
Operating income (loss)	713	587	655
Other income and (deductions)
Interest expense, net	(124)	(115)	(115)
Interest expense to affiliates	(12)	(14)	(11)
Other, net	16	8	9
Total other income and (deductions)	(120)	(121)	(117)
Income (loss) before income taxes	593	466	538
Income taxes	65	6	104
Net income (loss)	528	460	434
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)	528	460	434
Baltimore Gas and Electric Company [Member]
Operating revenues
Revenue from alternative revenue programs	12	(26)	124
Operating revenues from affiliates	26	29	16
Total operating revenues	3,106	3,169	3,176
Operating expenses
Purchased power and/or fuel from affiliates	286	257	384
Operating and maintenance	600	615	563
Operating and maintenance from affiliates	160	162	153
Depreciation and Amortization	502	483	473
Taxes other than income	260	254	240
Total operating expenses	2,574	2,696	2,562
Gain on sales of assets and businesses	0	1	0
Operating income (loss)	532	474	614
Other income and (deductions)
Interest expense, net	(121)	(106)	(95)
Interest expense to affiliates	0	0	(10)
Other, net	28	19	16
Total other income and (deductions)	(93)	(87)	(89)
Income (loss) before income taxes	439	387	525
Income taxes	79	74	218
Net income (loss)	360	313	307
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)	360	313	307
Pepco Holdings LLC [Member]
Operating revenues
Revenue from alternative revenue programs	(14)	(7)	33
Operating revenues from affiliates	14	15	50
Total operating revenues	4,806	4,798	4,672
Operating expenses
Purchased power and/or fuel from affiliates	352	355	463
Operating and maintenance	939	978	918
Operating and maintenance from affiliates	143	152	150
Depreciation and Amortization	754	740	675
Taxes other than income	450	455	452
Total operating expenses	4,084	4,156	3,911
Gain on sales of assets and businesses	0	1	1
Operating income (loss)	722	643	762
Other income and (deductions)
Interest expense, net	(263)	(261)	(245)
Other, net	55	43	54
Total other income and (deductions)	(208)	(218)	(191)
Income (loss) before income taxes	514	425	571
Income taxes	38	33	217
Equity in losses of unconsolidated affiliates	1	1	1
Net income (loss)	477	393	355
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss) attributable to common shareholders	477	393	355
Potomac Electric Power Company [Member]
Operating revenues
Revenue from alternative revenue programs	(3)	(7)	19
Operating revenues from affiliates	5	6	6
Total operating revenues	2,260	2,232	2,151
Operating expenses
Purchased power and/or fuel from affiliates	264	206	255
Operating and maintenance	273	275	396
Operating and maintenance from affiliates	209	226	58
Depreciation and Amortization	374	385	321
Taxes other than income	378	379	371
Total operating expenses	1,899	1,919	1,760
Gain on sales of assets and businesses	0	0	1
Operating income (loss)	361	313	392
Other income and (deductions)
Interest expense, net	(133)	(128)	(121)
Other, net	31	31	32
Total other income and (deductions)	(102)	(97)	(89)
Income (loss) before income taxes	259	216	303
Income taxes	16	11	105
Net income (loss)	243	205	198
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)	243	205	198
Delmarva Power & Light Company [Member]
Operating revenues
Revenue from alternative revenue programs	(11)	4	6
Operating revenues from affiliates	7	8	8
Total operating revenues	1,306	1,332	1,300
Operating expenses
Purchased power and/or fuel from affiliates	70	120	179
Operating and maintenance	171	182	283
Operating and maintenance from affiliates	152	162	32
Depreciation and Amortization	184	182	167
Taxes other than income	56	56	57
Total operating expenses	1,089	1,143	1,071
Gain on sales of assets and businesses	0	1	0
Operating income (loss)	217	190	229
Other income and (deductions)
Interest expense, net	(61)	(58)	(51)
Other, net	13	10	14
Total other income and (deductions)	(48)	(48)	(37)
Income (loss) before income taxes	169	142	192
Income taxes	22	22	71
Net income (loss)	147	120	121
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)	147	120	121
Atlantic City Electric Company [Member]
Operating revenues
Revenue from alternative revenue programs	0	(4)	8
Operating revenues from affiliates	3	3	2
Total operating revenues	1,240	1,236	1,186
Operating expenses
Purchased power and/or fuel from affiliates	19	29	29
Operating and maintenance	187	188	279
Operating and maintenance from affiliates	133	142	28
Depreciation and Amortization	157	136	146
Taxes other than income	4	5	6
Total operating expenses	1,089	1,087	1,029
Operating income (loss)	151	149	157
Other income and (deductions)
Interest expense, net	(58)	(64)	(61)
Other, net	6	2	7
Total other income and (deductions)	(52)	(62)	(54)
Income (loss) before income taxes	99	87	103
Income taxes	0	12	26
Net income (loss)	99	75	77
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)	99	75	77
Generation commodities and services [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	17,754	19,168	17,394
Operating expenses
Purchased power and/or fuel	10,849	11,679	9,668
Generation commodities and services [Member] | Exelon Generation Co L L C [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	17,752	19,169	17,385
Operating expenses
Purchased power and/or fuel	10,849	11,679	9,671
Rate-regulated utility revenues [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	16,839	16,879	15,964
Operating expenses
Purchased power and/or fuel	4,648	4,991	4,367
Electricity, US Regulated [Member] | Commonwealth Edison Co [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	5,850	5,884	5,478
Operating expenses
Purchased power and/or fuel	1,565	1,626	1,533
Electricity, US Regulated [Member] | PECO Energy Co [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	2,505	2,469	2,369
Operating expenses
Purchased power and/or fuel	610	734	648
Electricity, US Regulated [Member] | Baltimore Gas and Electric Company [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	2,368	2,428	2,384
Operating expenses
Purchased power and/or fuel	585	671	566
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	4,639	4,609	4,428
Operating expenses
Purchased power and/or fuel	1,371	1,387	1,182
Electricity, US Regulated [Member] | Potomac Electric Power Company [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	2,258	2,233	2,126
Operating expenses
Purchased power and/or fuel	401	448	359
Electricity, US Regulated [Member] | Delmarva Power & Light Company [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	1,143	1,139	1,125
Operating expenses
Purchased power and/or fuel	381	352	282
Electricity, US Regulated [Member] | Atlantic City Electric Company [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	1,237	1,237	1,176
Operating expenses
Purchased power and/or fuel	589	587	541
Natural Gas, US Regulated [Member] | PECO Energy Co [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	610	568	494
Operating expenses
Purchased power and/or fuel	262	230	186
Natural Gas, US Regulated [Member] | Baltimore Gas and Electric Company [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	700	738	652
Operating expenses
Purchased power and/or fuel	181	254	183
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	167	181	161
Operating expenses
Purchased power and/or fuel	75	89	71
Natural Gas, US Regulated [Member] | Delmarva Power & Light Company [Member]
Operating revenues
Revenue from Contract with Customer, Including Assessed Tax	167	181	161
Operating expenses
Purchased power and/or fuel	$ 75	$ 89	$ 71

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net income (loss)	$ 3,028	$ 2,079	$ 3,869
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	5,780	5,971	5,427
Asset impairments	201	50	573
Gain on sales of assets and businesses	(27)	(56)	(3)
Bargain purchase gain	0	0	(233)
Gain on deconsolidation of business	0	0	(213)
Deferred income taxes and amortization of investment tax credits	681	(108)	(362)
Net fair value changes related to derivatives	222	294	151
Net realized and unrealized (gains) losses on NDT fund investments	(663)	303	(616)
Other non-cash operating activities	613	1,131	728
Changes in assets and liabilities:
Accounts receivable	(243)	(565)	(470)
Inventories	(87)	(37)	(72)
Accounts payable and accrued expenses	(425)	551	(388)
Option premiums (paid) received, net	(29)	(43)	28
Collateral (posted) received, net	(438)	82	(158)
Income taxes	(64)	340	299
Pension and non-pension postretirement benefit contributions	(408)	(383)	(405)
Other assets and liabilities	(1,482)	(965)	(675)
Net cash flows provided by operating activities	6,659	8,644	7,480
Cash flows from investing activities
Capital expenditures	(7,248)	(7,594)	(7,584)
Proceeds from NDT fund sales	10,051	8,762	7,845
Investment in NDT funds	(10,087)	(8,997)	(8,113)
Reduction of restricted cash from deconsolidation of business	0	0	(87)
Acquisitions of assets and businesses, net	(41)	(154)	(208)
Proceeds from sales of assets and businesses	53	91	219
Other investing activities	12	58	(43)
Net cash flows used in investing activities	(7,260)	(7,834)	(7,971)
Cash flows from financing activities
Changes in short-term borrowings	781	(338)	(261)
Proceeds from short-term borrowings with maturities greater than 90 days	0	126	621
Repayments on short-term borrowings with maturities greater than 90 days	(125)	(1)	(700)
Issuance of long-term debt	1,951	3,115	3,470
Retirement of long-term debt	(1,287)	(1,786)	(2,490)
Retirement of long-term debt to financing trust	0	0	(250)
Common stock issued from treasury stock	0	0	1,150
Dividends paid on common stock	(1,408)	(1,332)	(1,236)
Proceeds from employee stock plans	112	105	150
Sale of noncontrolling interest	0	0	396
Other financing activities	(82)	(108)	(83)
Net cash flows provided by (used in) financing activities	(58)	(219)	767
Increase (Decrease) in cash, cash equivalents and restricted cash	(659)	591	276
Cash, cash equivalents, and restricted cash at beginning of period	1,781	1,190	914
Cash, cash equivalents, and restricted cash at end of period	1,122	1,781	1,190
Capital Expenditures Incurred but Not yet Paid	(7)	(69)	42
Increase (decrease) in PPE related to ARO update	968	(107)	29
Exelon Generation Co L L C [Member]
Cash flows from operating activities
Net income (loss)	1,217	443	2,798
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	3,063	3,415	3,056
Asset impairments	201	50	510
Gain on sales of assets and businesses	(27)	(48)	(2)
Bargain purchase gain	0	0	(233)
Gain on deconsolidation of business	0	0	(213)
Deferred income taxes and amortization of investment tax credits	361	(451)	(2,023)
Net fair value changes related to derivatives	228	307	167
Net realized and unrealized (gains) losses on NDT fund investments	(663)	303	(616)
Other non-cash operating activities	(124)	298	112
Changes in assets and liabilities:
Accounts receivable	(186)	(359)	(320)
Receivables from and payables to affiliates, net	(52)	8	(7)
Inventories	(47)	(12)	(29)
Accounts payable and accrued expenses	(248)	376	4
Option premiums (paid) received, net	(29)	(43)	28
Collateral (posted) received, net	(481)	64	(129)
Income taxes	302	(193)	496
Pension and non-pension postretirement benefit contributions	(175)	(139)	(148)
Other assets and liabilities	(467)	(158)	(152)
Net cash flows provided by operating activities	2,873	3,861	3,299
Cash flows from investing activities
Capital expenditures	(1,845)	(2,242)	(2,259)
Proceeds from NDT fund sales	10,051	8,762	7,845
Investment in NDT funds	(10,087)	(8,997)	(8,113)
Reduction of restricted cash from deconsolidation of business	0	0	(87)
Acquisitions of assets and businesses, net	(41)	(154)	(208)
Proceeds from sales of assets and businesses	52	90	218
Other investing activities	3	10	(58)
Net cash flows used in investing activities	(1,867)	(2,531)	(2,662)
Cash flows from financing activities
Changes in short-term borrowings	320	0	(620)
Proceeds from short-term borrowings with maturities greater than 90 days	0	0	121
Repayments on short-term borrowings with maturities greater than 90 days	0	0	(200)
Issuance of long-term debt	42	15	1,645
Retirement of long-term debt	(813)	(141)	(1,261)
Changes in Exelon intercompany money pool	(100)	46	(1)
Contributions from member	41	155	102
Distributions to member	(899)	(1,001)	(659)
Sale of noncontrolling interest	0	0	396
Other financing activities	(51)	(55)	(54)
Net cash flows provided by (used in) financing activities	(1,460)	(981)	(531)
Increase (Decrease) in cash, cash equivalents and restricted cash	(454)	349	106
Cash, cash equivalents, and restricted cash at beginning of period	903	554	448
Cash, cash equivalents, and restricted cash at end of period	449	903	554
Increase (decrease) in capital expenditures not paid	(34)	(199)	73
Increase (decrease) in PPE related to ARO update	959	(130)	29
Commonwealth Edison Co [Member]
Cash flows from operating activities
Net income (loss)	688	664	567
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	1,033	940	850
Deferred income taxes and amortization of investment tax credits	109	259	659
Other non-cash operating activities	265	242	164
Changes in assets and liabilities:
Accounts receivable	(34)	(136)	(59)
Receivables from and payables to affiliates, net	(12)	26	8
Inventories	(16)	1	4
Accounts payable and accrued expenses	(51)	70	(297)
Collateral (posted) received, net	48	11	(26)
Income taxes	95	62	(308)
Pension and non-pension postretirement benefit contributions	(77)	(42)	(41)
Other assets and liabilities	(345)	(348)	6
Net cash flows provided by operating activities	1,703	1,749	1,527
Cash flows from investing activities
Capital expenditures	(1,915)	(2,126)	(2,250)
Other investing activities	29	29	20
Net cash flows used in investing activities	(1,886)	(2,097)	(2,230)
Cash flows from financing activities
Changes in short-term borrowings	130	0	0
Issuance of long-term debt	700	1,350	1,000
Retirement of long-term debt	(300)	(840)	(425)
Dividends paid on common stock	(508)	(459)	(422)
Contributions from parent	250	500	651
Other financing activities	(16)	(17)	(15)
Net cash flows provided by (used in) financing activities	256	534	789
Increase (Decrease) in cash, cash equivalents and restricted cash	73	186	86
Cash, cash equivalents, and restricted cash at beginning of period	330	144	58
Cash, cash equivalents, and restricted cash at end of period	403	330	144
Increase (decrease) in capital expenditures not paid	(37)	11	(61)
Increase (decrease) in PPE related to ARO update	7	7	0
PECO Energy Co [Member]
Cash flows from operating activities
Net income (loss)	528	460	434
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	333	301	286
Gain on sales of assets and businesses	(1)	0	0
Deferred income taxes and amortization of investment tax credits	20	(5)	19
Other non-cash operating activities	38	51	54
Changes in assets and liabilities:
Accounts receivable	(29)	(74)	(44)
Receivables from and payables to affiliates, net	(5)	7	(6)
Inventories	4	(14)	1
Accounts payable and accrued expenses	(11)	(3)	6
Income taxes	(34)	15	34
Pension and non-pension postretirement benefit contributions	(28)	(28)	(24)
Other assets and liabilities	(64)	29	(5)
Net cash flows provided by operating activities	751	739	755
Cash flows from investing activities
Capital expenditures	(939)	(849)	(732)
Changes in Exelon intercompany money pool	(68)	0	131
Other investing activities	(1)	9	4
Net cash flows used in investing activities	(1,008)	(840)	(597)
Cash flows from financing activities
Issuance of long-term debt	325	700	325
Retirement of long-term debt	0	(500)	0
Dividends paid on common stock	(358)	(306)	(288)
Contributions from parent	188	89	16
Other financing activities	(6)	(22)	(3)
Net cash flows provided by (used in) financing activities	149	(39)	50
Increase (Decrease) in cash, cash equivalents and restricted cash	(108)	(140)	208
Cash, cash equivalents, and restricted cash at beginning of period	135	275	67
Cash, cash equivalents, and restricted cash at end of period	27	135	275
Increase (decrease) in capital expenditures not paid	40	(12)	22
Baltimore Gas and Electric Company [Member]
Cash flows from operating activities
Net income (loss)	360	313	307
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	502	483	473
Asset impairments	0	0	7
Deferred income taxes and amortization of investment tax credits	130	76	145
Other non-cash operating activities	85	58	65
Changes in assets and liabilities:
Accounts receivable	25	8	(5)
Receivables from and payables to affiliates, net	1	12	(4)
Inventories	(1)	2	(9)
Accounts payable and accrued expenses	(43)	(1)	(15)
Collateral (posted) received, net	(4)	4	0
Income taxes	(67)	(20)	60
Pension and non-pension postretirement benefit contributions	(48)	(54)	(53)
Other assets and liabilities	(192)	(92)	(150)
Net cash flows provided by operating activities	748	789	821
Cash flows from investing activities
Capital expenditures	(1,145)	(959)	(882)
Other investing activities	8	9	7
Net cash flows used in investing activities	(1,137)	(950)	(875)
Cash flows from financing activities
Changes in short-term borrowings	40	(42)	32
Issuance of long-term debt	400	300	300
Retirement of long-term debt	0	0	(41)
Retirement of long-term debt to financing trust	0	0	(250)
Dividends paid on common stock	(224)	(209)	(198)
Contributions from parent	193	109	184
Other financing activities	(8)	(2)	(5)
Net cash flows provided by (used in) financing activities	401	156	22
Increase (Decrease) in cash, cash equivalents and restricted cash	12	(5)	(32)
Cash, cash equivalents, and restricted cash at beginning of period	13	18	50
Cash, cash equivalents, and restricted cash at end of period	25	13	18
Increase (decrease) in capital expenditures not paid	6	50	23
Pepco Holdings LLC [Member]
Cash flows from operating activities
Net income (loss)	477	393	355
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	754	740	675
Asset impairments	0	0	52
Deferred income taxes and amortization of investment tax credits	(7)	30	252
Other non-cash operating activities	161	150	65
Changes in assets and liabilities:
Accounts receivable	(39)	(2)	(26)
Receivables from and payables to affiliates, net	3	8	(2)
Inventories	(27)	(14)	(37)
Accounts payable and accrued expenses	(17)	45	(106)
Income taxes	16	34	79
Pension and non-pension postretirement benefit contributions	(25)	(74)	(99)
Other assets and liabilities	(179)	(178)	(258)
Net cash flows provided by operating activities	1,117	1,132	950
Cash flows from investing activities
Capital expenditures	(1,355)	(1,375)	(1,396)
Other investing activities	(3)	4	(1)
Net cash flows used in investing activities	(1,358)	(1,371)	(1,397)
Cash flows from financing activities
Changes in short-term borrowings	154	(296)	328
Proceeds from short-term borrowings with maturities greater than 90 days	0	125	0
Repayments on short-term borrowings with maturities greater than 90 days	(125)	0	(500)
Issuance of long-term debt	485	750	202
Retirement of long-term debt	(157)	(299)	(169)
Changes in Exelon intercompany money pool	12	0	0
Contributions from member	398	385	758
Distributions to member	(526)	(326)	(311)
Other financing activities	(5)	(9)	(2)
Net cash flows provided by (used in) financing activities	236	330	306
Increase (Decrease) in cash, cash equivalents and restricted cash	(5)	91	(141)
Cash, cash equivalents, and restricted cash at beginning of period	186	95	236
Cash, cash equivalents, and restricted cash at end of period	181	186	95
Increase (decrease) in capital expenditures not paid	2	93	(12)
Potomac Electric Power Company [Member]
Cash flows from operating activities
Net income (loss)	243	205	198
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	374	385	321
Asset impairments	0	0	14
Deferred income taxes and amortization of investment tax credits	1	(20)	113
Other non-cash operating activities	56	67	1
Changes in assets and liabilities:
Accounts receivable	(22)	(5)	(20)
Receivables from and payables to affiliates, net	5	(17)	0
Inventories	(19)	(6)	(24)
Accounts payable and accrued expenses	(39)	59	(63)
Income taxes	9	(13)	81
Pension and non-pension postretirement benefit contributions	(14)	(17)	(72)
Other assets and liabilities	(82)	(164)	(142)
Net cash flows provided by operating activities	512	474	407
Cash flows from investing activities
Capital expenditures	(626)	(656)	(628)
Other investing activities	3	2	0
Net cash flows used in investing activities	(623)	(654)	(628)
Cash flows from financing activities
Changes in short-term borrowings	42	14	3
Issuance of long-term debt	260	200	202
Retirement of long-term debt	(125)	(14)	(13)
Dividends paid on common stock	(213)	(169)	(133)
Contributions from parent	160	166	161
Other financing activities	(3)	(4)	(1)
Net cash flows provided by (used in) financing activities	121	193	219
Increase (Decrease) in cash, cash equivalents and restricted cash	10	13	(2)
Cash, cash equivalents, and restricted cash at beginning of period	53	40	42
Cash, cash equivalents, and restricted cash at end of period	63	53	40
Increase (decrease) in capital expenditures not paid	39	20	5
Delmarva Power & Light Company [Member]
Cash flows from operating activities
Net income (loss)	147	120	121
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	184	182	167
Asset impairments	0	0	6
Deferred income taxes and amortization of investment tax credits	(7)	24	89
Other non-cash operating activities	27	24	9
Changes in assets and liabilities:
Accounts receivable	(5)	8	(22)
Receivables from and payables to affiliates, net	(5)	(9)	11
Inventories	(6)	(3)	(5)
Accounts payable and accrued expenses	3	11	(8)
Income taxes	12	2	26
Pension and non-pension postretirement benefit contributions	(1)	0	(2)
Other assets and liabilities	(55)	(7)	(71)
Net cash flows provided by operating activities	294	352	321
Cash flows from investing activities
Capital expenditures	(348)	(364)	(428)
Other investing activities	1	2	(1)
Net cash flows used in investing activities	(347)	(362)	(429)
Cash flows from financing activities
Changes in short-term borrowings	56	(216)	216
Issuance of long-term debt	75	200	0
Retirement of long-term debt	(12)	(4)	(40)
Dividends paid on common stock	(139)	(96)	(112)
Contributions from parent	63	150	0
Other financing activities	(1)	(2)	0
Net cash flows provided by (used in) financing activities	42	32	64
Increase (Decrease) in cash, cash equivalents and restricted cash	(11)	22	(44)
Cash, cash equivalents, and restricted cash at beginning of period	24	2	46
Cash, cash equivalents, and restricted cash at end of period	13	24	2
Increase (decrease) in capital expenditures not paid	(4)	22	4
Atlantic City Electric Company [Member]
Cash flows from operating activities
Net income (loss)	99	75	77
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	157	136	146
Asset impairments	0	0	7
Deferred income taxes and amortization of investment tax credits	3	25	32
Other non-cash operating activities	22	24	17
Changes in assets and liabilities:
Accounts receivable	(13)	(8)	14
Receivables from and payables to affiliates, net	(6)	1	0
Inventories	(1)	(4)	(7)
Accounts payable and accrued expenses	26	(7)	(2)
Income taxes	2	(2)	(11)
Pension and non-pension postretirement benefit contributions	(1)	(6)	(20)
Other assets and liabilities	(27)	(6)	(47)
Net cash flows provided by operating activities	261	228	206
Cash flows from investing activities
Capital expenditures	(375)	(335)	(312)
Other investing activities	(1)	1	(1)
Net cash flows used in investing activities	(376)	(334)	(313)
Cash flows from financing activities
Changes in short-term borrowings	56	(94)	108
Proceeds from short-term borrowings with maturities greater than 90 days	0	125	0
Repayments on short-term borrowings with maturities greater than 90 days	(125)	0	0
Issuance of long-term debt	150	350	0
Retirement of long-term debt	(18)	(281)	(35)
Dividends paid on common stock	(124)	(59)	(68)
Contributions from parent	175	67	0
Other financing activities	(1)	(3)	0
Net cash flows provided by (used in) financing activities	113	105	5
Increase (Decrease) in cash, cash equivalents and restricted cash	(2)	(1)	(102)
Cash, cash equivalents, and restricted cash at beginning of period	30	31	133
Cash, cash equivalents, and restricted cash at end of period	28	30	31
Increase (decrease) in capital expenditures not paid	$ (29)	$ 46	$ (13)

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Dec. 31, 2019		Dec. 31, 2018
Current assets
Cash and cash equivalents		$ 587		$ 1,349
Restricted cash and cash equivalents		358		247
Accounts receivable, net
Customer		4,592		4,607
Other		1,583		1,256
Mark-to-market derivative assets, current		679		804
Unamortized energy contract assets, current		47		48
Inventories, net
Fossil fuel		312		334
Materials and supplies		1,456		1,351
Regulatory assets, current		1,170		1,190
Assets held for sale		0		904
Other		1,253		1,238
Total current assets		12,037		13,328
Property, plant and equipment, net		80,233		76,707
Deferred debits and other assets
Regulatory assets, noncurrent		8,335		8,237
Nuclear decommissioning trust funds		13,190		11,661
Investments		464		625
Goodwill		6,677		6,677
Mark-to-market derivative assets, noncurrent		508		452
Unamortized energy contract assets, noncurrent		336		372
Other		3,197		1,575
Total deferred debits and other assets		32,707		29,599
Total assets	[1]	124,977		119,634
Current liabilities
Short-term borrowings		1,370		714
Long-term debt due within one year		4,710		1,349
Accounts payable		3,560		3,800
Accrued expenses		1,981		2,112
Payables to affiliates, current		5		5
Regulatory Liability, Current		406		644
Mark-to-market derivative liabilities, current		247		475
Unamortized energy contract liabilities, current		132		149
Renewable energy credit obligation		443		344
Liabilities held for sale		0		777
Other		1,331		1,035
Total current liabilities		14,185		11,404
Long-term debt		31,329		34,075
Long-term debt to financing trusts		390		390
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		12,351		11,321
Asset retirement obligations, noncurrent		10,846		9,679
Pension obligations		4,247		3,988
Non-pension postretirement benefit obligations		2,076		1,928
Spent nuclear fuel obligation		1,199		1,171
Regulatory liabilities, noncurrent		9,986		9,559
Mark-to-market derivative liabilities, noncurrent		393		479
Unamortized energy contract liabilities, noncurrent		338		463
Other		3,064		2,130
Total deferred credits and other liabilities		44,500		40,718
Total liabilities		90,404		86,587	[1]
Commitments and Contingencies
Shareholders’ equity
Common stock		19,274		19,116
Treasury stock, at cost		(123)		(123)
Retained earnings/Undistributed earnings		16,267		14,743
Accumulated other comprehensive income (loss), net		(3,194)		(2,995)
Total shareholders’ equity		32,224		30,741
Member’s equity
Noncontrolling interests		2,349		2,306
Total equity		34,573		33,047
Total liabilities and equity		$ 124,977		$ 119,634
Common Stock, Shares Authorized		2,000,000,000		2,000,000,000
Common Stock, Shares, Outstanding		973,000,000		968,000,000
Variable Interest Entity, Consolidated, Assets, Pledged		$ 9,532		$ 9,667
Variable Interest Entity, Consolidated, Liabilities, No Recourse		3,473		3,548
Exelon Generation Co L L C [Member]
Current assets
Cash and cash equivalents		303		750
Restricted cash and cash equivalents		146		153
Accounts receivable, net
Customer		2,893		2,941
Other		619		562
Mark-to-market derivative assets, current		675		804
Receivables from affiliates, current		190		173
Unamortized energy contract assets, current		47		49
Inventories, net
Fossil fuel and emission allowances		236		251
Materials and supplies		1,026		963
Assets held for sale		0		904
Other		941		883
Total current assets		7,076		8,433
Property, plant and equipment, net		24,193		23,981
Deferred debits and other assets
Nuclear decommissioning trust funds		13,190		11,661
Investments		235		414
Goodwill		47		47
Mark-to-market derivative assets, noncurrent		508		452
Prepaid pension asset		1,438		1,421
Unamortized energy contract assets, noncurrent		336		371
Deferred income taxes		12		21
Other		1,960		755
Total deferred debits and other assets		17,726		15,142
Total assets	[2]	48,995		47,556
Current liabilities
Short-term borrowings		320		0
Long-term debt due within one year		2,624		906
Long-term debt to affiliates due within one year		558		0
Accounts payable		1,692		1,847
Accrued expenses		786		898
Payables to affiliates, current		117		139
Borrowings from Exelon intercompany money pool		0		100
Mark-to-market derivative liabilities, current		215		449
Unamortized energy contract liabilities, current		17		31
Renewable energy credit obligation		443		343
Liabilities held for sale		0		777
Other		517		279
Total current liabilities		7,289		5,769
Long-term debt		4,464		6,989
Long-term debt to affiliates		328		898
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		3,752		3,383
Asset retirement obligations, noncurrent		10,603		9,450
Non-pension postretirement benefit obligations		878		900
Spent nuclear fuel obligation		1,199		1,171
Payables to affiliates, noncurrent		3,103		2,606
Mark-to-market derivative liabilities, noncurrent		123		252
Unamortized energy contract liabilities, noncurrent		11		20
Other		1,415		610
Total deferred credits and other liabilities		21,084		18,392
Total liabilities	[2]	33,165		32,048
Commitments and Contingencies
Shareholders’ equity
Retained earnings/Undistributed earnings		3,950		3,724
Accumulated other comprehensive income (loss), net		(32)		(38)
Member’s equity
Membership interest		9,566		9,518
Total member’s equity		13,484		13,204
Noncontrolling interests		2,346		2,304
Total equity		15,830		15,508
Total liabilities and equity		48,995		47,556
Variable Interest Entity, Consolidated, Assets, Pledged		9,512		9,634
Variable Interest Entity, Consolidated, Liabilities, No Recourse		3,429		3,480
Commonwealth Edison Co [Member]
Current assets
Cash and cash equivalents		90		135
Restricted cash and cash equivalents		150		29
Accounts receivable, net
Customer		545		539
Other		286		320
Receivables from affiliates, current		28		20
Inventories, net
Inventories, net		159		148
Regulatory assets, current		281		293
Other		44		86
Total current assets		1,583		1,570
Property, plant and equipment, net		23,107		22,058
Deferred debits and other assets
Regulatory assets, noncurrent		1,480		1,307
Investments		6		6
Goodwill		2,625		2,625
Receivable from affiliates, noncurrent		2,622		2,217
Prepaid pension asset		995		1,035
Other		347		395
Total deferred debits and other assets		8,075		7,585
Total assets		32,765		31,213
Current liabilities
Short-term borrowings		130		0
Long-term debt due within one year		500		300
Accounts payable		527		607
Accrued expenses		385		373
Payables to affiliates, current		103		119
Customer deposits		118		111
Regulatory Liability, Current		200		293
Mark-to-market derivative liabilities, current		32		26
Other		122		96
Total current liabilities		2,117		1,925
Long-term debt		7,991		7,801
Long-term debt to financing trusts		205		205
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		4,021		3,813
Asset retirement obligations, noncurrent		128		118
Non-pension postretirement benefit obligations		180		201
Regulatory liabilities, noncurrent		6,542		6,050
Mark-to-market derivative liabilities, noncurrent		269		223
Other		635		630
Total deferred credits and other liabilities		11,775		11,035
Total liabilities		22,088		20,966
Commitments and Contingencies
Shareholders’ equity
Common stock		1,588		1,588
Other paid-in capital		7,572		7,322
Retained earnings (deficit) unappropriated		(1,639)		(1,639)
Retained earnings (deficit) appropriated		3,156		2,976
Total shareholders’ equity		10,677		10,247
Member’s equity
Total liabilities and equity		32,765		31,213
PECO Energy Co [Member]
Current assets
Cash and cash equivalents		21		130
Restricted cash and cash equivalents		6		5
Accounts receivable, net
Customer		357		321
Other		138		151
Receivables from affiliates, current		1		0
Due from Affiliates		68		0
Inventories, net
Fossil fuel		36		38
Materials and supplies		35		37
Regulatory assets, current		41		81
Other		19		19
Total current assets		722		782
Property, plant and equipment, net		9,292		8,610
Deferred debits and other assets
Regulatory assets, noncurrent		554		460
Investments		27		25
Receivable from affiliates, noncurrent		480		389
Prepaid pension asset		365		349
Other		29		27
Total deferred debits and other assets		1,455		1,250
Total assets		11,469		10,642
Current liabilities
Accounts payable		387		370
Accrued expenses		101		113
Payables to affiliates, current		55		59
Customer deposits		69		68
Regulatory Liability, Current		91		175
Other		19		24
Total current liabilities		722		809
Long-term debt		3,405		3,084
Long-term debt to financing trusts		184		184
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		2,080		1,933
Asset retirement obligations, noncurrent		28		27
Non-pension postretirement benefit obligations		288		288
Regulatory liabilities, noncurrent		510		421
Other		74		76
Total deferred credits and other liabilities		2,980		2,745
Total liabilities		7,291		6,822
Commitments and Contingencies
Shareholders’ equity
Common stock		2,766		2,578
Retained earnings/Undistributed earnings		1,412		1,242
Total shareholders’ equity		4,178		3,820
Member’s equity
Total liabilities and equity		11,469		10,642
Baltimore Gas and Electric Company [Member]
Current assets
Cash and cash equivalents		24		7
Restricted cash and cash equivalents		1		6
Accounts receivable, net
Customer		317		353
Other		147		90
Receivables from affiliates, current		1		1
Inventories, net
Fossil fuel and emission allowances		30		36
Materials and supplies		46		39
Prepaid utility taxes		78		74
Regulatory assets, current		183		177
Other		6		3
Total current assets		833		786
Property, plant and equipment, net		8,990		8,243
Deferred debits and other assets
Regulatory assets, noncurrent		454		398
Investments		7		5
Prepaid pension asset		264		279
Other		86		5
Total deferred debits and other assets		811		687
Total assets		10,634		9,716
Current liabilities
Short-term borrowings		76		35
Accounts payable		243		295
Accrued expenses		152		155
Payables to affiliates, current		66		65
Customer deposits		120		120
Regulatory Liability, Current		33		77
Other		63		27
Total current liabilities		753		774
Long-term debt		3,270		2,876
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		1,396		1,222
Asset retirement obligations, noncurrent		22		24
Non-pension postretirement benefit obligations		199		201
Regulatory liabilities, noncurrent		1,195		1,192
Other		116		73
Total deferred credits and other liabilities		2,928		2,712
Total liabilities		6,951		6,362
Commitments and Contingencies
Shareholders’ equity
Common stock		1,907	[3]	1,714
Retained earnings/Undistributed earnings		1,776		1,640
Total shareholders’ equity		3,683		3,354
Member’s equity
Total liabilities and equity		10,634		9,716
Pepco Holdings LLC [Member]
Current assets
Cash and cash equivalents		131		124
Restricted cash and cash equivalents		36		43
Accounts receivable, net
Customer		479		453
Other		174		177
Receivables from affiliates, current		1		0
Inventories, net
Fossil fuel and emission allowances		8		9
Materials and supplies		190		163
Regulatory assets, current		412		457
Other		49		75
Total current assets		1,480		1,501
Property, plant and equipment, net		14,296		13,446
Deferred debits and other assets
Regulatory assets, noncurrent		2,061		2,312
Investments		135		130
Goodwill		4,005		4,005
Prepaid pension asset		406		486
Deferred income taxes		13		12
Other		323		60
Total deferred debits and other assets		6,943		7,005
Total assets		22,719		21,952
Current liabilities
Short-term borrowings		208		179
Long-term debt due within one year		103		125
Accounts payable		462		496
Accrued expenses		296		256
Payables to affiliates, current		98		94
Other Short-term Borrowings		12		0
Customer deposits		117		116
Regulatory Liability, Current		70		84
Unamortized energy contract liabilities, current		115		119
Other		131		123
Total current liabilities		1,612		1,592
Long-term debt		6,460		6,134
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		2,278		2,137
Asset retirement obligations, noncurrent		57		52
Non-pension postretirement benefit obligations		93		103
Regulatory liabilities, noncurrent		1,707		1,864
Unamortized energy contract liabilities, noncurrent		327		442
Other		577		369
Total deferred credits and other liabilities		5,039		4,967
Total liabilities		13,111	[4]	12,693
Commitments and Contingencies
Shareholders’ equity
Retained earnings/Undistributed earnings		(10)		39
Member’s equity
Membership interest		9,618		9,220
Total member’s equity		9,608		9,259
Total equity		9,608		9,259
Total liabilities and equity		22,719		21,952
Variable Interest Entity, Consolidated, Assets, Pledged		20		33
Variable Interest Entity, Consolidated, Liabilities, No Recourse		44		69
Potomac Electric Power Company [Member]
Current assets
Cash and cash equivalents		30		16
Restricted cash and cash equivalents		33		37
Accounts receivable, net
Customer		231		225
Other		91		81
Receivables from affiliates, current		0		1
Inventories, net
Inventories, net		112		93
Regulatory assets, current		188		238
Other		11		37
Total current assets		696		728
Property, plant and equipment, net		6,909		6,460
Deferred debits and other assets
Regulatory assets, noncurrent		584		643
Investments		110		105
Prepaid pension asset		296		316
Other		66		15
Total deferred debits and other assets		1,056		1,079
Total assets		8,661		8,267
Current liabilities
Short-term borrowings		82		40
Long-term debt due within one year		2		15
Accounts payable		195		214
Accrued expenses		156		126
Payables to affiliates, current		66		62
Customer deposits		57		54
Regulatory Liability, Current		8		7
Merger related obligation		39		38
Current portion of DC PLUG obligation		30		30
Other		22		42
Total current liabilities		657		628
Long-term debt		2,862		2,704
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		1,131		1,055
Asset retirement obligations, noncurrent		41		37
Non-pension postretirement benefit obligations		20		29
Regulatory liabilities, noncurrent		746		822
Other		297		275
Total deferred credits and other liabilities		2,235		2,218
Total liabilities		5,754		5,550
Commitments and Contingencies
Shareholders’ equity
Common stock		1,796	[5]	1,636
Retained earnings/Undistributed earnings		1,111		1,081
Total shareholders’ equity		2,907		2,717
Member’s equity
Total liabilities and equity		8,661		8,267
Delmarva Power & Light Company [Member]
Current assets
Cash and cash equivalents		13		23
Restricted cash and cash equivalents		0		1
Accounts receivable, net
Customer		141		134
Other		38		46
Inventories, net
Fossil fuel and emission allowances		8		9
Materials and supplies		44		37
Prepaid utility taxes		18		17
Regulatory assets, current		52		59
Other		11		10
Total current assets		325		336
Property, plant and equipment, net		4,035		3,821
Deferred debits and other assets
Regulatory assets, noncurrent		222		231
Investments		0		0
Goodwill		8		8
Prepaid pension asset		171		186
Other		69		6
Total deferred debits and other assets		470		431
Total assets		4,830		4,588
Current liabilities
Short-term borrowings		56		0
Long-term debt due within one year		80		91
Accounts payable		112		111
Accrued expenses		46		39
Payables to affiliates, current		32		33
Customer deposits		36		35
Regulatory Liability, Current		37		59
Other		15		7
Total current liabilities		414		375
Long-term debt		1,487		1,403
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		655		628
Non-pension postretirement benefit obligations		16		17
Regulatory liabilities, noncurrent		574		606
Other		104		50
Total deferred credits and other liabilities		1,349		1,301
Total liabilities		3,250		3,079
Commitments and Contingencies
Shareholders’ equity
Common stock		977	[6]	914
Retained earnings/Undistributed earnings		603		595
Total shareholders’ equity		1,580		1,509
Member’s equity
Total liabilities and equity		4,830		4,588
Atlantic City Electric Company [Member]
Current assets
Cash and cash equivalents		12		7
Restricted cash and cash equivalents		2		4
Accounts receivable, net
Customer		108		95
Other		48		55
Receivables from affiliates, current		4		1
Inventories, net
Inventories, net		34		33
Regulatory assets, current		57		40
Other		5		5
Total current assets		270		240
Property, plant and equipment, net		3,190		2,966
Deferred debits and other assets
Regulatory assets, noncurrent		368		386
Investments		0		0
Prepaid pension asset		52		67
Other		53		40
Total deferred debits and other assets		473		493
Total assets	[7]	3,933		3,699
Current liabilities
Short-term borrowings		70		139
Long-term debt due within one year		20		18
Accounts payable		144		154
Accrued expenses		42		35
Payables to affiliates, current		25		28
Customer deposits		25		26
Regulatory Liability, Current		25		18
Other		9		4
Total current liabilities		360		422
Long-term debt		1,307		1,170
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		577		535
Non-pension postretirement benefit obligations		17		17
Regulatory liabilities, noncurrent		357		402
Other		39		27
Total deferred credits and other liabilities		990		981
Total liabilities		2,657		2,573
Commitments and Contingencies
Shareholders’ equity
Common stock		1,154		979
Retained earnings/Undistributed earnings		122		147
Total shareholders’ equity		1,276		1,126
Member’s equity
Total liabilities and equity		3,933		3,699
Variable Interest Entity, Consolidated, Assets, Pledged		17		23
Variable Interest Entity, Consolidated, Liabilities, No Recourse		$ 41		$ 59
Common Stock [Member] | Commonwealth Edison Co [Member]
Member’s equity
Common Stock, Shares Authorized		250,000,000		250,000,000
Common Stock, Shares, Outstanding		127,000,000		127,000,000
Common Stock [Member] | PECO Energy Co [Member]
Member’s equity
Common Stock, Shares Authorized		500,000,000		500,000,000
Common Stock, Shares, Outstanding		170,000,000		170,000,000
Common Stock [Member] | Baltimore Gas and Electric Company [Member]
Member’s equity
Common Stock, Shares Authorized		1,500		0
Common Stock, Shares, Outstanding		1,000
Common Stock [Member] | Potomac Electric Power Company [Member]
Member’s equity
Common Stock, Shares Authorized		200,000,000		200,000,000
Common Stock, Shares, Outstanding		100		100
Common Stock [Member] | Delmarva Power & Light Company [Member]
Member’s equity
Common Stock, Shares Authorized		1,000		1,000
Common Stock, Shares, Outstanding		1,000		1,000
Common Stock [Member] | Atlantic City Electric Company [Member]
Member’s equity
Common Stock, Shares Authorized		25,000,000		25,000,000
Common Stock, Shares, Outstanding		9,000,000		9,000,000
[1]	Exelon’s consolidated assets include $9,532 million and $9,667 million at December 31, 2019 and 2018 , respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,473 million and $3,548 million at December 31, 2019 and 2018 , respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 22 – Variable Interest Entities for additional information.
[2]	Generation’s consolidated assets include $9,512 million and $9,634 million at December 31, 2019 and 2018 , respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,429 million and $3,480 million at December 31, 2019 and 2018 , respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 22 – Variable Interest Entities for additional information.
[3]	In millions, shares round to zero. Number of shares is 1,500 authorized and 1,000 outstanding at December 31, 2019 and 2018 .
[4]	PHI’s consolidated total assets include $20 million and $33 million at December 31, 2019 and 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 $44 million and $69 million at December 31, 2019 and 2018 , respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 22 - Variable Interest Entities for additional information.
[5]	In millions, shares round to zero. Number of shares is 100 outstanding at December 31, 2019 and 2018 .
[6]	In millions, shares round to zero. Number of shares is 1,000 authorized and 1,000 outstanding at December 31, 2019 and 2018 .
[7]	ACE’s consolidated assets include $17 million and $23 million at December 31, 2019 and 2018 , respectively, of ACE’s consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated liabilities include $41 million and $59 million at December 31, 2019 and 2018 , respectively, of ACE’s consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 22 - Variable Interest Entities for additional information.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Customer allowance for uncollectible accounts	$ 243	$ 283
Other allowance for uncollectible accounts	48	36
Accumulated depreciation and amortization	$ 23,979	$ 22,902
Common Stock, No Par Value	$ 0	$ 0
Common Stock, Shares Authorized	2,000,000,000	2,000,000,000
Common Stock, Shares, Outstanding	973,000,000	968,000,000
Treasury stock, shares held	2,000,000	2,000,000
Exelon Generation Co L L C [Member]
Customer allowance for uncollectible accounts	$ 80	$ 103
Other allowance for uncollectible accounts	0	1
Accumulated depreciation and amortization	12,017	12,206
Commonwealth Edison Co [Member]
Customer allowance for uncollectible accounts	59	61
Other allowance for uncollectible accounts	20	20
Accumulated depreciation and amortization	$ 5,168	$ 4,684
Commonwealth Edison Co [Member] | Common Stock [Member]
Common Stock, Par or Stated Value Per Share	$ 12.50	$ 12.50
Common Stock, Shares Authorized	250,000,000	250,000,000
Common Stock, Shares, Outstanding	127,000,000	127,000,000
Baltimore Gas and Electric Company [Member]
Customer allowance for uncollectible accounts	$ 12	$ 16
Other allowance for uncollectible accounts	5	4
Accumulated depreciation and amortization	$ 3,834	$ 3,633
Baltimore Gas and Electric Company [Member] | Common Stock [Member]
Common Stock, No Par Value	$ 0	$ 0
Common Stock, Shares Authorized	1,500	0
Common Stock, Shares, Outstanding	1,000
PECO Energy Co [Member]
Customer allowance for uncollectible accounts	$ 55	$ 53
Other allowance for uncollectible accounts	7	8
Accumulated depreciation and amortization	$ 3,718	$ 3,561
PECO Energy Co [Member] | Common Stock [Member]
Common Stock, No Par Value	$ 0	$ 0
Common Stock, Shares Authorized	500,000,000	500,000,000
Common Stock, Shares, Outstanding	170,000,000	170,000,000
Pepco Holdings LLC [Member]
Customer allowance for uncollectible accounts	$ 37	$ 50
Other allowance for uncollectible accounts	16	3
Accumulated depreciation and amortization	1,213	841
Potomac Electric Power Company [Member]
Customer allowance for uncollectible accounts	13	20
Other allowance for uncollectible accounts	7	1
Accumulated depreciation and amortization	$ 3,517	$ 3,354
Potomac Electric Power Company [Member] | Common Stock [Member]
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	200,000,000	200,000,000
Common Stock, Shares, Outstanding	100	100
Delmarva Power & Light Company [Member]
Customer allowance for uncollectible accounts	$ 11	$ 12
Other allowance for uncollectible accounts	4	1
Accumulated depreciation and amortization	$ 1,425	$ 1,329
Delmarva Power & Light Company [Member] | Common Stock [Member]
Common Stock, Par or Stated Value Per Share	$ 2.25	$ 2.25
Common Stock, Shares Authorized	1,000	1,000
Common Stock, Shares, Outstanding	1,000	1,000
Atlantic City Electric Company [Member]
Customer allowance for uncollectible accounts	$ 13	$ 18
Other allowance for uncollectible accounts	5	1
Accumulated depreciation and amortization	$ 1,210	$ 1,137
Atlantic City Electric Company [Member] | Common Stock [Member]
Common Stock, Par or Stated Value Per Share	$ 3	$ 3
Common Stock, Shares Authorized	25,000,000	25,000,000
Common Stock, Shares, Outstanding	9,000,000	9,000,000

Consolidated Statement of Chang

Consolidated Statement of Changes in Shareholders Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Undistributed Earnings [Member]	Accumulated Other Comprehensive Income (Loss), net	Noncontrolling Interest [Member]	Other Comprehensive Income (Loss) [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]Undistributed Earnings [Member]	Exelon Generation Co L L C [Member]Accumulated Other Comprehensive Income (Loss), net	Exelon Generation Co L L C [Member]Noncontrolling Interest [Member]	Exelon Generation Co L L C [Member]Other Comprehensive Income (Loss) [Member]	Commonwealth Edison Co [Member]	Commonwealth Edison Co [Member]Common Stock [Member]	Commonwealth Edison Co [Member]Retained Earnings [Member]	Commonwealth Edison Co [Member]Other Additional Capital [Member]	Commonwealth Edison Co [Member]Retained Earnings, 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), net	Baltimore Gas and Electric Company [Member]	Baltimore Gas and Electric Company [Member]Common Stock [Member]	Baltimore Gas and Electric Company [Member]Retained Earnings [Member]	Baltimore Gas and Electric Company [Member]Membership Interest [Member]	Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member]Membership Interest [Member]	Pepco Holdings LLC [Member]Undistributed Earnings [Member]	Potomac Electric Power Company [Member]	Potomac Electric Power Company [Member]Common Stock [Member]	Potomac Electric Power Company [Member]Retained Earnings [Member]	Delmarva Power & Light Company [Member]	Delmarva Power & Light Company [Member]Common Stock [Member]	Delmarva Power & 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, 2016	958,778
Beginning Balance at Dec. 31, 2016	$ 27,629	$ 18,794	$ (2,327)	$ 12,042		$ (2,660)	$ 1,780
Beginning Balance at Dec. 31, 2016									$ 13,284	$ 9,261	$ 2,298	$ (54)	$ 1,779																$ 8,005	$ 8,077	$ (72)
Beginning Balance at Dec. 31, 2016															$ 8,725	$ 1,588		$ 6,150	$ (1,639)	$ 2,626	$ 3,415	$ 2,473	$ 941	$ 1		$ 1,421	$ 1,427	$ 2,848				$ 2,289	$ 1,309	$ 980	$ 1,326	$ 764	$ 562	$ 1,034	$ 912	$ 122
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 3,869			3,779			90		2,798		2,710		88		567				567		434		434		$ 307		307	307	355		355	198		198	121		121	77		77
Long-Term Incentive Plan Activity (shares)	5,066
Long-Term Incentive Plan Activity	$ 56	56	0	0		0	0
Employee stock purchase plan issuances, shares	1,324
Employee stock purchase plan issuances	$ 150	150	0	0		0	0
Stock Issued During Period, Value, Treasury Stock Reissued	1,150		2,204	(1,054)
Sale of noncontrolling interests	407	(36)					443		407	(36)			443
Changes in equity of noncontrolling interests	(20)						(20)		(18)				(18)
Common stock dividends	(1,243)			(1,243)											(422)					(422)	(288)		(288)				(198)	(198)				(133)		(133)	(112)		(112)	(68)		(68)
Other Comprehensive Income (Loss), Net of Tax	171					173	(2)		15			17	(2)
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	0			539		(539)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Paid									33	33
Distributions to member									(659)		(659)																		(311)		(311)
Contributions from parent	$ 0								99	99					651			651								184		184	758	758		161	161
Income Tax Effects Allocated Directly to Equity, Other																					16	16		0
Ending Balance (in shares) at Dec. 31, 2017	965,168
Ending Balance at Dec. 31, 2017	$ 32,169	18,964	(123)	14,063		(3,026)	2,291
Ending Balance at Dec. 31, 2017															9,542	1,588		6,822	(1,639)	2,771	3,577	2,489	1,087	1		1,605	1,536	3,141				2,515	1,470	1,045	1,335	764	571	1,043	912	131
Ending Balance at Dec. 31, 2017									15,959	9,357	4,349	(37)	2,290																8,807	8,835	(28)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained Earnings, Appropriated																	$ 0		(567)	567
Other Additional Capital															21			21
Net income (loss)	$ 2,079			2,005			74		443		370		73		664				664		460		460		313		313	313	393		393	205		205	120		120	75		75
Long-Term Incentive Plan Activity (shares)	3,534
Long-Term Incentive Plan Activity	$ 41	41	0	0		0	0
Employee stock purchase plan issuances, shares	1,318
Employee stock purchase plan issuances	$ 105	105	0	0		0	0
Sale of noncontrolling interests	6	6					0		6	6			0
Changes in equity of noncontrolling interests	(60)						(60)		(60)				(60)
Common stock dividends	(1,339)			(1,339)											(459)					(459)	(306)		(306)				(209)	(209)				(169)		(169)	(96)		(96)	(59)		(59)
Other Comprehensive Income (Loss), Net of Tax	42					41	1		3			2	1
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	4				$ 14	(10)			3		6	(3)	0										1	(1)
Distributions to member									(1,001)		(1,001)																		(326)		(326)
Contributions from parent	0								155	155					500			500								109		109	385	385		166	166		150	150		67	67
Income Tax Effects Allocated Directly to Equity, Other	$ 0																				89	89
Ending Balance (in shares) at Dec. 31, 2018	970,020
Ending Balance at Dec. 31, 2018	$ 33,047	19,116	(123)	14,743		(2,995)	2,306
Ending Balance at Dec. 31, 2018	30,741														10,247	1,588		7,322	(1,639)	2,976	3,820	2,578	1,242	0	3,354	1,714	1,640	3,354				2,717	1,636	1,081	1,509	914	595	1,126	979	147
Ending Balance at Dec. 31, 2018									15,508	9,518	3,724	(38)	2,304																9,259	9,220	39
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained Earnings, Appropriated															2,976		0		(664)	664
Net income (loss)	$ 3,028			2,936			92		1,217		1,125		92		688				688		528		528		360		360	360	477		477	243		243	147		147	99		99
Long-Term Incentive Plan Activity (shares)	3,111
Long-Term Incentive Plan Activity	$ 40	40	0	0		0	0
Employee stock purchase plan issuances, shares	1,285
Employee stock purchase plan issuances	$ 112	112	0	0		0	0
Sale of noncontrolling interests	6	6					0		7	7			0
Changes in equity of noncontrolling interests	(48)	0					(48)		(48)				(48)
Common stock dividends	(1,412)			(1,412)											(508)					(508)	(358)		(358)				(224)	(224)				(213)		(213)	(139)		(139)	(124)		(124)
Other Comprehensive Income (Loss), Net of Tax	(198)					(199)	(1)	$ (200)	7			6	(2)	$ 4
Distributions to member									(899)		(899)																		(526)		(526)
Contributions from parent	$ 0								41	41					250			250			188	188				193	0	193	398	398		160	160		63	63		175	175
Ending Balance (in shares) at Dec. 31, 2019	974,416
Ending Balance at Dec. 31, 2019	$ 34,573	$ 19,274	$ (123)	$ 16,267		$ (3,194)	$ 2,349
Ending Balance at Dec. 31, 2019	$ 32,224														10,677	$ 1,588		$ 7,572	(1,639)	3,156	$ 4,178	$ 2,766	$ 1,412	$ 0	$ 3,683	$ 1,907	$ 1,776	$ 3,683				$ 2,907	$ 1,796	$ 1,111	$ 1,580	$ 977	$ 603	$ 1,276	$ 1,154	$ 122
Ending Balance at Dec. 31, 2019									$ 15,830	$ 9,566	$ 3,950	$ (32)	$ 2,346																$ 9,608	$ 9,618	$ (10)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained Earnings, Appropriated															$ 3,156		$ 0		$ (688)	$ 688

Consolidated Statement of Cha_2

Consolidated Statement of Changes in Shareholders Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Stockholders' Equity [Abstract]
Common Stock, Dividends, Per Share, Declared	$ 1.45	$ 1.38	$ 1.31

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies (All Registrants)	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) This is a combined annual report of all Registrants. The Notes to the Consolidated Financial Statements apply to the Registrants as indicated above in the Index to Combined Notes to Consolidated Financial Statements and parenthetically next to each corresponding disclosure. When appropriate, the Registrants are named specifically for their related activities and disclosures. Each of the Registrant’s Consolidated Financial Statements includes the accounts of its subsidiaries. All intercompany transactions have been eliminated. 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. Exelon owns 100% of Generation, PECO, BGE and PHI and more than 99% of ComEd. PHI owns 100% of Pepco, DPL and ACE. Generation owns 100% of its significant consolidated subsidiaries, either directly or indirectly, except for certain consolidated VIEs, including CENG and EGRP, of which Generation holds a 50.01% and 51% interest, respectively. The remaining interests in these consolidated VIEs are included in noncontrolling interests on Exelon’s and Generation’s Consolidated Balance Sheets. See Note 22 — Variable Interest Entities for additional information of Exelon’s and Generation’s consolidated VIEs. The Registrants consolidate the accounts of entities in which a Registrant has a controlling financial interest, after the elimination of intercompany transactions. Where the Registrants do not have a controlling financial interest in an entity, proportionate consolidation, equity method accounting or accounting for investments in equity securities without readily determinable fair value is applied. The Registrants apply proportionate consolidation when they have an undivided interest in an asset and are proportionately liable for their share of each liability associated with the asset. The Registrants proportionately consolidate their undivided ownership interests in jointly owned electric plants and transmission facilities. Under proportionate consolidation, the Registrants separately record their proportionate share of the assets, liabilities, revenues and expenses related to the undivided interest in the asset. The Registrants apply equity method accounting when they have significant influence over an investee through an ownership in common stock, which generally approximates a 20% to 50% voting interest. The Registrants apply equity method accounting to certain investments and joint ventures, including certain financing trusts of ComEd and PECO. Under equity method accounting, the Registrants report their interest in the entity as an investment and the Registrants’ percentage share of the earnings from the entity as single line items in their financial statements. The Registrants use accounting for investments in equity securities without readily determinable fair values if they lack significant influence, which generally results when they hold less than 20% of the common stock of an entity. Under accounting for investments in equity securities without readily determinable fair values, the Registrants report their investments at cost adjusted for changes from observable transactions for identical or similar investments of the same issuer, less impairment. Changes in measurement are reported in earnings. The accompanying consolidated financial statements have been prepared in accordance with GAAP for annual financial statements and in accordance with the instructions to Form 10-K and Regulation S-X promulgated by the SEC. Use of Estimates (All Registrants) The preparation of financial statements of each of the Registrants in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Areas in which significant estimates have been made include, but are not limited to, the accounting for nuclear decommissioning costs and other AROs, pension and OPEB, the application of purchase accounting, inventory reserves, allowance for uncollectible accounts, goodwill and asset impairments, derivative instruments, unamortized energy contracts, fixed asset depreciation, environmental costs and other loss contingencies, taxes and unbilled energy revenues. Actual results could differ from those estimates. Prior Period Adjustments and Reclassifications (Exelon, PHI and Pepco) In the fourth quarter 2019, management identified an error related to an overstatement of the regulatory asset associated with Pepco’s decoupling mechanism for Maryland that originated in 2007 upon the inception of the program. Management has concluded that the error was not material to previously issued consolidated financial statements and the error was corrected through a revision to Exelon’s, PHI’s and Pepco’s consolidated financial statements contained herein for the years ended December 31, 2018 and 2017. The impact of the error correction was an $11 million reduction to Exelon’s, PHI’s and Pepco’s opening Retained earnings as of January 1, 2017 with a corresponding reduction to current Regulatory assets of $18 million and Deferred income taxes and unamortized investment tax credits of $7 million . In addition, Exelon’s, PHI’s and Pepco’s Total operating revenues decreased by $7 million for the years ended December 31, 2018 and 2017 and Net income decreased by $5 million and $7 million for the years ended December 31, 2018 and 2017, respectively, from originally reported amounts. The error did not impact net cash flows provided by operating activities, net cash flows used in investing activities or net cash flows provided by financing activities for the years ended December 31, 2018 and 2017 for Exelon, PHI and Pepco. Exelon’s diluted earnings per share of common stock remained unchanged from the originally reported amount for the year ended December 31, 2018. Exelon’s basic earnings per share of common stock for the year ended December 31, 2018 and basic and diluted earnings per share of common stock for the year ended December 31, 2017 decreased by $0.01 from the originally reported amount. Accounting for the Effects of Regulation (Exelon and the Utility Registrants) For their regulated electric and gas operations, Exelon and the Utility Registrants reflect the effects of cost-based rate regulation in their financial statements, which is required for entities with regulated operations that meet the following criteria: 1) rates are established or approved by a third-party regulator; (2) rates are designed to recover the entities’ cost of providing services or products; and (3) there is a reasonable expectation that rates designed to recover costs can be charged to and collected from customers. Exelon and the Utility Registrants account for their regulated operations in accordance with regulatory and legislative guidance from the regulatory authorities having jurisdiction, principally the ICC, PAPUC, MDPSC, DCPSC, DPSC and NJBPU, under state public utility laws and the FERC under various Federal laws. Regulatory assets and liabilities are amortized and the related expense or revenue is recognized in the Consolidated Statements of Operations consistent with the recovery or refund included in customer rates. Exelon's regulatory assets and liabilities as of the balance sheet date are probable of being recovered or settled in future rates. If a separable portion of the Registrants' business was no longer able to meet the criteria discussed above, the affected entities would be required to eliminate from their consolidated financial statements the effects of regulation for that portion, which could have a material impact on their financial statements. See Note 3 — Regulatory Matters for additional information. With the exception of income tax-related regulatory assets and liabilities, Exelon and the Utility Registrants classify regulatory assets and liabilities with a recovery or settlement period greater than one year as both current and non-current in their Consolidated Balance Sheets, with the current portion representing the amount expected to be recovered from or settled to customers over the next twelve-month period as of the balance sheet date. Income tax-related regulatory assets and liabilities are classified entirely as non-current in Exelon's and the Utility Registrants’ Consolidated Balance Sheets to align with the classification of the related deferred income tax balances. Exelon and the Utility Registrants treat the impacts of a final rate order received after the balance sheet date but prior to the issuance of the financial statements as a non-recognized subsequent event, as the receipt of a final rate order is a separate and distinct event that has future impacts on the parties affected by the order. Revenues (All Registrants) Operating Revenues. The Registrants’ operating revenues generally consist of revenues from contracts with customers involving the sale and delivery of energy commodities and related products and services, utility revenues from ARP, and realized and unrealized revenues recognized under mark-to-market energy commodity derivative contracts. The Registrants recognize revenue from contracts with customers to depict the transfer of goods or services to customers in 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 natural gas tariff sales, distribution and transmission services. At the end of each month, the Registrants accrue an estimate for the unbilled amount of energy delivered or services provided to customers. ComEd records ARP revenue for its best estimate of the electric distribution, energy efficiency, and transmission revenue impacts resulting from future changes in rates that ComEd believes are probable of approval by the ICC and FERC in accordance with its formula rate mechanisms. BGE, Pepco and DPL record ARP revenue for their best estimate of the electric and natural gas distribution revenue impacts resulting from future changes in rates that they believe are probable of approval by the MDPSC and/or DCPSC in accordance with their revenue decoupling mechanisms. PECO, BGE, Pepco, DPL and ACE record ARP revenue for their best estimate of the transmission revenue impacts resulting from future changes in rates that they believe are probable of approval by FERC in accordance with their formula rate mechanisms. See Note 3 — Regulatory Matters for additional information. Option Contracts, Swaps and Commodity Derivatives. Certain option contracts and swap arrangements that meet the definition of derivative instruments are recorded at fair value with subsequent changes in fair value recognized as revenue or expense. The classification of revenue or expense is based on the intent of the transaction. To the extent a Utility Registrant receives full cost recovery for energy procurement and related costs from retail customers, it records the fair value of its energy swap contracts with unaffiliated suppliers as well as an offsetting regulatory asset or liability in its Consolidated Balance Sheets. See Note 3 — Regulatory Matters and Note 15 — Derivative Financial Instruments for additional information. Taxes Directly Imposed on Revenue-Producing Transactions. The Registrants collect certain taxes from customers such as sales and gross receipts taxes, along with other taxes, surcharges and fees, that are levied by state or local governments on the sale or distribution of gas and electricity. Some of these taxes are imposed on the customer, but paid by the Registrants, while others are imposed on the Registrants. Where these taxes are imposed on the customer, such as sales taxes, they are reported on a net basis with no impact to the Consolidated Statements of Operations and Comprehensive Income. However, where these taxes are imposed on the Registrants, such as gross receipts taxes or other surcharges or fees, they are reported on a gross basis. Accordingly, revenues are recognized for the taxes collected from customers along with an offsetting expense. Se e Note 23 — Supplemental Financial Information for Generation’s, ComEd’s, PECO’s, BGE’s, Pepco's, DPL's and ACE's utility taxes that are presented on a gross basis. 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 for most asset classes, 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 generally do 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 10 — Leases for additional information. Income Taxes (All Registrants) Deferred Federal and state income taxes are recorded on significant temporary differences between the book and tax basis of assets and liabilities and for tax benefits carried forward. Investment tax credits have been deferred in the Registrants’ Consolidated Balance Sheets and are recognized in book income over the life of the related property. The Registrants account for uncertain income tax positions using a benefit recognition model with a two-step approach; a more-likely-than-not recognition criterion; and a measurement approach that measures the position as the largest amount of tax benefit that is greater than 50% likely of being realized upon ultimate settlement. If it is not more-likely-than-not that the benefit of the tax position will be sustained on its technical merits, no benefit is recorded. Uncertain tax positions that relate only to timing of when an item is included on a tax return are considered to have met the recognition threshold. The Registrants recognize accrued interest related to unrecognized tax benefits in Interest expense or Other income and deductions (interest income) and recognize penalties related to unrecognized tax benefits in Other, net in their Consolidated Statements of Operations and Comprehensive Income. Cash and Cash Equivalents (All Registrants) The Registrants consider investments purchased with an original maturity of three months or less to be cash equivalents. Restricted Cash and Cash Equivalents (All Registrants) Restricted cash and cash equivalents represent funds that are restricted to satisfy designated current liabilities. As of December 31, 2019 and 2018 , the Registrants' restricted cash and cash equivalents primarily represented the following items: Registrant Description Exelon Payment of medical, dental, vision and long-term disability benefits, in addition to the items listed for Generation and the Utility Registrants. Generation Project-specific nonrecourse financing structures for debt service and financing of operations of the underlying entities. ComEd Collateral held from suppliers associated with energy and REC procurement contracts, any over-recovered RPS costs and alternative compliance payments received from RES pursuant to FEJA and costs for the remediation of an MGP site. PECO Proceeds from the sales of assets that were subject to PECO’s mortgage indenture. BGE Proceeds from the loan program for the completion of certain energy efficiency measures and collateral held from energy suppliers. PHI Payment of merger commitments, collateral held from its energy suppliers associated with procurement contracts and repayment of transition bonds. Pepco Payment of merger commitments and collateral held from energy suppliers. DPL Collateral held from energy suppliers. ACE Repayment of transition bonds and collateral held from energy suppliers. Restricted cash and cash equivalents not available to satisfy current liabilities are classified as noncurrent assets. As of December 31, 2019 and 2018 , the Registrants' noncurrent restricted cash and cash equivalents primarily represented ComEd’s over-recovered RPS costs and alternative compliance payments received from RES pursuant to FEJA and costs for the remediation of an MGP site, and ACE’s repayment of transition bonds. See Note 23 — Supplemental Financial Information for additional information. Allowance for Uncollectible Accounts (All Registrants) The allowance for uncollectible accounts reflects the Registrants’ best estimates of losses on the customers' accounts receivable balances. For Generation, the allowance is based on accounts receivable aging historical experience and other currently available information. Utility Registrants estimate the allowance by applying loss rates developed specifically for each company to the outstanding receivable balance by customer risk segment. Utility Registrants' customer accounts are written off consistent with approved regulatory requirements. See Note 3 — Regulatory Matters for additional information regarding the regulatory recovery of uncollectible accounts receivable at ComEd and ACE. Variable Interest Entities (Exelon, Generation, PHI and ACE) Exelon accounts for its investments in and arrangements with VIEs based on the following specific requirements: • requires an entity to qualitatively assess whether it should consolidate a VIE based on whether the entity has a controlling financial interest, • requires an ongoing reconsideration of this assessment instead of only upon certain triggering events, and • requires the entity that consolidates a VIE (the primary beneficiary) to disclose (1) the assets of the consolidated VIE, if they can be used to only settle specific obligations of the consolidated VIE, and (2) the liabilities of a consolidated VIE for which creditors do not have recourse to the general credit of the primary beneficiary. See Note 22 — Variable Interest Entities for additional information. Inventories (All Registrants) Inventory is recorded at the lower of weighted average cost or net realizable value. Provisions are recorded for excess and obsolete inventory. Fossil fuel, materials and supplies, and emissions allowances are generally included in inventory when purchased. Fossil fuel and emissions allowances are expensed to purchased power and fuel expense when used or sold. Materials and supplies generally includes transmission, distribution and generating plant materials and are expensed to operating and maintenance or capitalized to property, plant and equipment, as appropriate, when installed or used. Debt and Equity Security Investments (Exelon and Generation ) Debt Security Investments. Debt securities are reported at fair value and classified as available-for-sale securities. Unrealized gains and losses, net of tax, are reported in OCI. Equity Security Investments without Readily Determinable Fair Values. Exelon has certain equity securities without readily determinable fair values. Exelon has elected to use the practicability exception to measure these investments, defined as cost adjusted for changes from observable transactions for identical or similar investments of the same issuer, less impairment. Changes in measurement are reported in earnings. Equity Security Investments with Readily Determinable Fair Values. Equity securities held in the NDT funds are classified as equity securities with readily determinable fair values. Realized and unrealized gains and losses, net of tax, on Generation’s NDT funds associated with the Regulatory Agreement Units are included in regulatory liabilities at Exelon, ComEd and PECO, in Noncurrent payables to affiliates at Generation and in Noncurrent receivables from affiliates at ComEd and PECO. Realized and unrealized gains and losses, net of tax, on Generation’s NDT funds associated with the Non-Regulatory Agreement Units are included in earnings at Exelon and Generation. Exelon's and Generation's NDT funds are classified as current or noncurrent assets, depending on the timing of the decommissioning activities and income taxes on trust earnings. See Note 3 — Regulatory Matters for additional information regarding ComEd’s and PECO’s regulatory assets and liabilities and Note 17 — Fair Value of Financial Assets and Liabilities and Note 9 — Asset Retirement Obligations for additional information regarding marketable securities held by NDT funds. Property, Plant and Equipment (All Registrants) Property, plant and equipment is recorded at original cost. Original cost includes construction-related direct labor and material costs. The Utility Registrants also include indirect construction costs including labor and related costs of departments associated with supporting construction activities. When appropriate, original cost also includes capitalized interest for Generation, Exelon Corporate and PHI and AFUDC for regulated property at the Utility Registrants. The cost of repairs and maintenance, including planned major maintenance activities and minor replacements of property, is charged to Operating and maintenance expense as incurred. Third parties reimburse the Utility Registrants for all or a portion of expenditures for certain capital projects. Such contributions in aid of construction costs (CIAC) are recorded as a reduction to Property, plant and equipment, net. DOE SGIG and other funds reimbursed to the Utility Registrants have been accounted for as CIAC. For Generation, upon retirement, the cost of property is generally charged to accumulated depreciation in accordance with the composite and group methods of depreciation. Upon replacement of an asset, the costs to remove the asset, net of salvage, are capitalized to gross plant when incurred as part of the cost of the newly-installed asset and recorded to depreciation expense over the life of the new asset. Removal costs, net of salvage, incurred for property that will not be replaced is charged to Operating and maintenance expense as incurred. For the Utility Registrants, upon retirement, the cost of property, net of salvage, is charged to accumulated depreciation consistent with the composite and group methods of depreciation. Depreciation expense at ComEd, BGE, Pepco, DPL and ACE includes the estimated cost of dismantling and removing plant from service upon retirement. Actual incurred removal costs are applied against a related regulatory liability or recorded to a regulatory asset if in excess of previously collected removal costs. PECO’s removal costs are capitalized to accumulated depreciation when incurred, and recorded to depreciation expense over the life of the new asset constructed consistent with PECO’s regulatory recovery method. Capitalized Software. Certain costs, such as design, coding, and testing incurred during the application development stage of software projects that are internally developed or purchased for operational use are capitalized within Property, plant and equipment. Similar costs incurred for cloud-based solutions treated as service arrangements are capitalized within Other Current Assets and Deferred Debits and Other Assets. Such capitalized amounts are amortized ratably over the expected lives of the projects when they become operational, generally not to exceed five years. Certain other capitalized software costs are being amortized over longer lives based on the expected life or pursuant to prescribed regulatory requirements. Capitalized Interest and AFUDC. During construction, Exelon and Generation capitalize the costs of debt funds used to finance non-regulated construction projects. Capitalization of debt funds is recorded as a charge to construction work in progress and as a non-cash credit to interest expense. AFUDC is the cost, during the period of construction, of debt and equity funds used to finance construction projects for regulated operations. AFUDC is recorded to construction work in progress and as a non-cash credit to an allowance that is included in interest expense for debt-related funds and other income and deductions for equity-related funds. The rates used for capitalizing AFUDC are computed under a method prescribed by regulatory authorities. See Note 7 — Property, Plant and Equipment , Note 8 — Jointly Owned Electric Utility Plant and Note 23 — Supplemental Financial Information for additional information regarding property, plant and equipment. Nuclear Fuel (Exelon and Generation) The cost of nuclear fuel is capitalized within Property, plant and equipment and charged to fuel expense using the unit-of-production method. Any potential future SNF disposal fees will be expensed through fuel expense. Additionally, certain on-site SNF storage costs are being reimbursed by the DOE since a DOE (or government-owned) long-term storage facility has not been completed. See Note 18 — Commitments and Contingencies for additional information regarding the cost of SNF storage and disposal. Nuclear Outage Costs (Exelon and Generation) Costs associated with nuclear outages, including planned major maintenance activities, are expensed to Operating and maintenance expense or capitalized to Property, plant and equipment (based on the nature of the activities) in the period incurred. Depreciation and Amortization (All Registrants) Except for the amortization of nuclear fuel, depreciation is generally recorded over the estimated service lives of property, plant and equipment on a straight-line basis using the group, composite or unitary methods of depreciation. The group approach is typically for groups of similar assets that have approximately the same useful lives and the composite approach is used for dissimilar assets that have different lives. Under both methods, a reporting entity depreciates the assets over the average life of the assets in the group. The Utility Registrants' depreciation expense includes the estimated cost of dismantling and removing plant from service upon retirement, which is consistent with each utility's regulatory recovery method. The estimated service lives for the Registrants are based on a combination of depreciation studies, historical retirements, site licenses and management estimates of operating costs and expected future energy market conditions. See Note 6 — Early Plant Retirements for additional information on the impacts of expected and potential early plant retirements. See Note 7 — Property, Plant and Equipment for additional information regarding depreciation. Amortization of regulatory assets and liabilities are recorded over the recovery or refund period specified in the related legislation or regulatory order or agreement. When the recovery or refund pe

Mergers, Acquisitions and Dispo

Mergers, Acquisitions and Dispositions (Exelon and Generation)	12 Months Ended
	Dec. 31, 2019
Business Combinations [Abstract]
Mergers, Acquisitions and Dispositions	Mergers, Acquisitions and Dispositions (Exelon and Generation) CENG Put Option (Exelon and Generation) Generation owns a 50.01% membership interest in CENG, a joint venture with EDF, which wholly owns the Calvert Cliffs and Ginna nuclear stations and Nine Mile Point Unit 1, in addition to an 82% undivided ownership interest in Nine Mile Point Unit 2. CENG is 100% consolidated in Exelon's and Generation's financial statements. See Note 22 — Variable Interest Entities for additional information. On April 1, 2014, Generation and EDF entered into various agreements including a Nuclear Operating Services Agreement, an amended LLC Operating Agreement, an Employee Matters Agreement, and a Put Option Agreement, among others. Under the amended Operating Agreement, CENG made a $400 million special distribution to EDF and committed to make preferred distributions to Generation until Generation has received aggregate distributions of $400 million plus a return of 8.50% per annum. Under the Put Option Agreement, EDF has the option to sell its 49.99% equity interest in CENG to Generation exercisable beginning on January 1, 2016 and thereafter until June 30, 2022. On November 20, 2019, Generation received notice of EDF’s intention to exercise the put option to sell its interest in CENG to Generation and the put automatically exercised on January 19, 2020 at the end of the sixty-day advance notice period. Under the terms of the Put Option Agreement, the purchase price is to be determined by agreement of the parties, or absent such agreement, by a third-party arbitration process. The third parties determining fair market value of EDF’s 49.99% interest are to take into consideration all rights and obligations under the LLC Operating Agreement and Employee Matters Agreement including but not limited to Generation’s rights with respect to any unpaid aggregate preferred distributions and the related return. As of December 31, 2019 , the total unpaid aggregate preferred distributions and related return owed to Generation is $571 million . At this time, Generation cannot reasonably predict the ultimate purchase price that will be paid to EDF for its interest in CENG. The transaction will require approval by the NYPSC, the FERC and the NRC. The process and regulatory approvals could take one to two years or more to complete. Acquisition of James A. FitzPatrick Nuclear Generating Station (Exelon and Generation) On March 31, 2017, Generation acquired the single-unit James A. FitzPatrick (FitzPatrick) nuclear generating station located in Scriba, New York from Entergy Nuclear FitzPatrick LLC (Entergy) for a total purchase price of $289 million , which consisted of a cash purchase price of $110 million and a net cost reimbursement to and on behalf of Entergy of $179 million . As part of the transaction, Generation received the FitzPatrick NDT fund assets and assumed the obligation to decommission FitzPatrick. The NRC license for FitzPatrick expires in 2034. An after-tax bargain purchase gain of $233 million was included within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income which primarily reflects differences in strategies between Generation and Entergy for the intended use and ultimate decommissioning of the plant. Exelon and Generation incurred $57 million of merger and integration related costs for FitzPatrick for the year ended December 31, 2017 which are included within Operating and maintenance expense in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. Disposition of Oyster Creek (Exelon and Generation) 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, which permanently ceased generation operations on September 17, 2018. Completion of the transaction contemplated by the sale agreement was 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 were satisfied in the second quarter 2019. The sale was completed on July 1, 2019. Exelon and Generation recognized a loss on the sale in the third quarter, which was immaterial. Under the terms of the transaction, Generation transferred 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. 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 values. Exelon and Generation had $897 million and $777 million of Assets and Liabilities held for sale, respectively, at December 31, 2018. Upon remeasurement of the Oyster Creek ARO, Exelon and Generation recognized an $84 million and a $9 million pre-tax charge to Operating and maintenance expense in the third quarter of 2018 and in the second quarter of 2019, respectively. See Note 9 — Asset Retirement Obligations for additional information. Disposition of EGTP and Acquisition of Handley Generating Station (Exelon and Generation) EGTP, a Delaware limited liability company, was formed in 2014 with the purpose of financing a portfolio of assets comprised of two combined-cycle gas turbines (CCGTs) and three peaking/simple cycle facilities consisting of approximately 3.4 GW of generation capacity in ERCOT North and Houston Zones. EGTP was an indirect wholly owned subsidiary of Exelon and Generation. EGTP’s operating cash flows were negatively impacted by certain market conditions and the seasonality of its cash flows. On May 2, 2017, as a result of the negative impacts of certain market conditions and the seasonality of its cash flows, EGTP entered into a consent agreement with its lenders to permit EGTP to draw on its revolving credit facility and initiate an orderly sales process to sell the assets of its wholly owned subsidiaries. As a result, Exelon and Generation classified certain of EGTP assets and liabilities as held for sale at their respective fair values less costs to sell and recorded a $460 million pre-tax impairment loss. See Note 16 — Debt and Credit Agreements for details regarding the nonrecourse debt associated with EGTP and Note 11 — Asset Impairments for additional information. On November 7, 2017, EGTP and all of its wholly owned subsidiaries filed voluntary petitions for relief under Chapter 11 of Title 11 of the United States Code in the United States Bankruptcy Court for the District of Delaware, which resulted in Exelon and Generation deconsolidating EGTP's assets and liabilities from their consolidated financial statements in the fourth quarter of 2017 that resulted in a pre-tax gain upon deconsolidation of $213 million . Concurrently with the Chapter 11 filings, Generation entered into an asset purchase agreement to acquire one of EGTP's generating plants, the Handley Generating Station, subject to a potential adjustment for fuel oil and assumption of certain liabilities. In the Chapter 11 Filings, EGTP requested that the proposed acquisition of the Handley Generating Station be consummated through a court-approved and supervised sales process. The acquisition closed on April 4, 2018 for a purchase price of $62 million . The Chapter 11 bankruptcy proceedings were finalized on April 17, 2018, resulting in the ownership of EGTP assets (other than the Handley Generating Station) being transferred to EGTP's lenders. Disposition of Electrical Contracting Business (Exelon and Generation) 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 year ended December 31, 2018.

Regulatory Matters (All Registr

Regulatory Matters (All Registrants)	12 Months Ended
	Dec. 31, 2019
Regulated Operations [Abstract]
Regulatory Matters (All Registrants)	Regulatory Matters (All Registrants) The following matters below discuss the status of material regulatory and legislative proceedings of the Registrants. 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 (Decrease) Increase Approved Revenue Requirement (Decrease) Increase Approved ROE Approval Date Rate Effective Date ComEd - Illinois (Electric) (a) April 16, 2018 $ (23 ) $ (24 ) 8.69 % December 4, 2018 January 1, 2019 ComEd - Illinois (Electric) (a) April 8, 2019 (6 ) (17 ) 8.91 % December 4, 2019 January 1, 2020 PECO - Pennsylvania (Electric) March 29, 2018 82 25 N/A (b) December 20, 2018 January 1, 2019 BGE - Maryland June 8, 2018 (amended October 12, 2018) 61 43 9.8 % January 4, 2019 January 4, 2019 BGE - Maryland (Electric) May 24, 2019 (amended December 17, 2019) 74 18 9.7 % (d) December 17, 2019 December 17, 2019 BGE - Maryland (Natural Gas) May 24, 2019 (amended December 17, 2019) 59 45 9.75 % (d) December 17, 2019 December 17, 2019 ACE - New Jersey (Electric) August 21, 2018 (amended November 19, 2018) 122 (c) 70 (c) 9.6 % March 13, 2019 April 1, 2019 Pepco - Maryland (Electric) January 15, 2019 (amended May 16, 2019) 27 10 9.6 % August 12, 2019 August 13, 2019 __________ (a) Pursuant to EIMA and FEJA, ComEd’s electric distribution rates are established through a performance-based formula, which sunsets at the end of 2022. ComEd is required to file an annual update to its electric distribution formula rate on or before May 1 st , with resulting rates effective in January of the following year. ComEd’s annual electric distribution formula rate update is based on prior year actual costs and current year projected capital additions (initial year revenue requirement). The update also reconciles any differences between the revenue requirement in effect for the prior year and actual costs incurred from the year (annual reconciliation). ComEd’s 2018 approved revenue requirement above reflects a decrease of $58 million for the initial year revenue requirement for 2018 and an increase of $34 million related to the annual reconciliation for 2017. The revenue requirement for 2018 and the annual reconciliation for 2017 provides for a weighted average debt and equity return on distribution rate base of 6.52% inclusive of an allowed ROE of 8.69% , reflecting the average rate on 30-year treasury notes plus 580 basis points. ComEd’s 2019 approved revenue requirement above reflects an increase of $51 million for the initial year revenue requirement for 2019 and a decrease of $68 million related to the annual reconciliation for 2018. The revenue requirement for 2019 and the annual reconciliation for 2018 provides for a weighted average debt and equity return on distribution rate base of 6.51% inclusive of an allowed ROE of 8.91% , reflecting the average rate on 30-year treasury notes plus 580 basis points. See table below for ComEd's regulatory assets associated with its electric distribution formula rate. During the first quarter of 2018, ComEd revised its electric distribution formula rate to implement revenue decoupling provisions provided for under FEJA. As a result of this revision, ComEd’s electric distribution formula rate revenues are not impacted by abnormal weather, usage per customer or numbers of customers. ComEd began reflecting the impacts of this change in its Operating revenues and electric distribution formula rate regulatory asset in the first quarter of 2017. (b) The PECO rate case proceeding was resolved through a settlement agreement, which did not specify an approved ROE. (c) Requested and approved increases are before New Jersey sales and use tax. (d) ROEs in approved settlement are for the purpose of calculating AFUDC and carrying charges. Pending Distribution Base Rate Case Proceedings Registrant/Jurisdiction Filing Date Requested Revenue Requirement Increase Requested ROE Expected Approval Timing Pepco - District of Columbia (Electric) (a) May 30, 2019 (amended September 16, 2019) $ 160 10.3 % Fourth quarter of 2020 DPL - Maryland (Electric) December 5, 2019 19 10.3 % Third quarter of 2020 _________ (a) Reflects a three-year cumulative multi-year plan and total requested revenue requirement increases of $84 million , $40 million and $36 million for years 2020, 2021, and 2022, respectively, to recover capital investments made in 2018 and 2019 and planned capital investments from 2020 to 2022. Transmission Formula Rates Transmission Formula Rate (Exelon, ComEd, BGE, PHI, Pepco, DPL and ACE). ComEd’s, BGE’s, Pepco's, DPL's and ACE's transmission rates are each established based on a FERC-approved formula. ComEd, BGE, Pepco, DPL and ACE are required to file an annual update to the FERC-approved formula on or before May 15, with the resulting rates effective on June 1 of the same year. The annual formula rate update is based on prior year actual costs and current year projected capital additions (initial year revenue requirement). The update also reconciles any differences between the revenue requirement in effect beginning June 1 of the prior year and actual costs incurred for that year (annual reconciliation). For 2019 , the following total increases/(decreases) were included in ComEd’s, BGE’s, Pepco's, DPL's and ACE's electric transmission formula rate filings: Registrant Initial Revenue Requirement Increase/(Decrease) Annual Reconciliation (Decrease)/Increase Total Revenue Requirement Increase/(Decrease) Allowed Return on Rate Base (c) Allowed ROE (d) ComEd (a) $ 21 $ (16 ) $ 5 8.21 % 11.50 % BGE (a) (10 ) (23 ) (19 ) (b) 7.35 % 10.50 % Pepco 15 11 26 7.75 % 10.50 % DPL 17 (1 ) 16 7.14 % 10.50 % ACE 11 (2 ) 9 7.79 % 10.50 % __________ (a) The time period for any formal challenges to the annual transmission formula rate update filings expired with no formal challenges submitted (b) The change in BGE's transmission revenue requirement includes a FERC approved dedicated facilities charge of $14 million to recover the costs of providing transmission service to specifically designated load by BGE. (c) Represents the weighted average debt and equity return on transmission rate bases. (d) As part of the FERC-approved settlement of ComEd’s 2007 transmission rate case, the rate of return on common equity is 11.50% , inclusive of a 50 -basis-point incentive adder for being a member of a RTO, and the common equity component of the ratio used to calculate the weighted average debt and equity return for the transmission formula rate is currently capped at 55% . As part of the FERC-approved settlement of the ROE complaint against BGE, Pepco, DPL and ACE, the rate of return on common equity is 10.50% , inclusive of a 50 -basis-point incentive adder for being a member of a RTO. 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. PECO’s initial formula rate filing included a requested increase of $22 million to PECO’s annual transmission revenue requirement, which reflected a ROE of 11% , inclusive of a 50 basis point adder for being a member of a RTO. 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 December 5, 2019, FERC issued an Order accepting without modification the settlement agreement filed by PECO and other parties in July 2019. The settlement results in an increase of approximately $14 million with a return on rate base of 7.62% compared to PECO's initial formula rate filing and allows for an ROE of 10.35% , inclusive of a 50 basis point adder for being a member of the RTO. The settlement did not have a material impact on PECO's 2017, 2018, or 2019 annual transmission revenue requirements. PECO will update its rates in 2020 and refund estimated overcollections totaling approximately $28 million related to the amounts billed under the proposed rates in effect since 2017. Pursuant to the transmission formula rate request discussed above, PECO made its annual formula rate updates in May 2018 and 2019, which included a decrease of $6 million and an increase of $8 million , respectively, to the annual transmission revenue requirement. The updated transmission formula rates were effective on June 1, 2018 and 2019, respectively, subject to refund. Other State Regulatory Matters Illinois Regulatory Matters Energy Efficiency Formula Rate (Exelon and ComEd). FEJA allows ComEd to defer energy efficiency costs (except for any voltage optimization costs which are recovered through the electric distribution formula rate) as a separate regulatory asset that is recovered through the energy efficiency formula rate over the weighted average useful life, as approved by the ICC, of the related energy efficiency measures. ComEd earns a return on the energy efficiency regulatory asset at a rate equal to its weighted average cost of capital, which is based on a year-end capital structure and calculated using the same methodology applicable to ComEd’s electric distribution formula rate. Beginning January 1, 2018 through December 31, 2030, the return on equity that ComEd earns on its energy efficiency regulatory asset is subject to a maximum downward or upward adjustment of 200 basis points if ComEd’s cumulative persisting annual MWh savings falls short of or exceeds specified percentage benchmarks of its annual incremental savings goal. ComEd is required to file an update to its energy efficiency formula rate on or before June 1 st each year, with resulting rates effective in January of the following year. The annual update is based on projected current year energy efficiency costs, PJM capacity revenues, and the projected year-end regulatory asset balance less any related deferred income taxes (initial year revenue requirement). The update also reconciles any differences between the revenue requirement in effect for the prior year and actual costs incurred from the year (annual reconciliation). The approved energy efficiency formula rate also provides for revenue decoupling provisions similar to those in ComEd’s electric distribution formula rate. During 2019, the ICC approved the following total increases in ComEd's requested energy efficiency revenue requirement: Filing Date Requested Revenue Requirement Increase Approved Revenue Requirement Increase Approved ROE Approval Date Rate Effective Date May 23, 2019 $ 51 $ 50 (a) 8.91 % November 26, 2019 January 1, 2020 _________ (a) ComEd’s 2020 approved revenue requirement above reflects an increase of $53 million for the initial year revenue requirement for 2020 and a decrease of $3 million related to the annual reconciliation for 2018. The revenue requirement for 2020 provides for a weighted average debt and equity return on the energy efficiency regulatory asset and rate base of 6.51% inclusive of an allowed ROE of 8.91% , reflecting the average rate on 30-year treasury notes plus 580 basis points. See table below for ComEd's regulatory assets associated with its energy efficiency formula rate. Maryland Regulatory Matters Maryland Alternative Rate Plans Rulemaking (Exelon, BGE, PHI, Pepco and DPL). On August 9, 2019, the MDPSC issued an order in which the MDPSC determined that it is now appropriate to move forward to implement alternative rate plans in Maryland. The MDPSC found that a multi-year rate plan, based on a historic test year and allowing up to three future test years, can produce just and reasonable rates. A working group was convened and submitted a detailed implementation report related to multi-year rate plans to the MDPSC on December 20, 2019. In response to the working group report, the MDPSC issued an order on February 4, 2020 establishing a multi-year rate plan pilot and an associated framework for a Maryland utility to use in the pilot multi-year rate plan filing. The working group was required to continue and discuss how best to integrate performance-based measures into a multi-year rate plan. The working group is currently discussing performance-based measures which could be combined with future multi-year rate plans and will submit its report to the MDPSC by April 1, 2020. BGE, Pepco and DPL cannot predict the outcome or the potential financial impact, if any, on BGE, Pepco or DPL. The Maryland Strategic Infrastructure Development and Enhancement Program (Exelon and BGE). On December 1, 2017 (as amended on January 22, 2018), BGE filed an application with the MDPSC seeking approval for a new gas infrastructure replacement plan and associated surcharge, effective for the five-year period from 2019 through 2023. On May 30, 2018, the MDPSC approved with modifications a new infrastructure plan and associated surcharge, subject to BGE's acceptance of the Order. On June 1, 2018, BGE accepted the MDPSC Order and the associated surcharge became effective January 2019. The five-year plan calls for capital expenditures over the 2019-2023 timeframe of $732 million with an associated revenue requirement of $200 million. Cash Working Capital Order (Exelon and BGE). On November 17, 2016, the MDPSC rendered a decision in the proceeding to review BGE’s request to recover its cash working capital (CWC) requirement for its Provider of Last Resort service, also known as Standard Offer Service (SOS), as well as other components that make up the Administrative Charge, the mechanism that enables BGE to recover its SOS-related costs. The Administrative Charge is comprised of five components: CWC, uncollectibles, incremental costs, return, and an administrative adjustment, which acts as a proxy for retail suppliers’ costs. The MDPSC accepted BGE's positions on recovery of CWC and pass-through recovery of BGE’s actual uncollectibles and incremental costs. The order also grants BGE a return on the SOS. Subsequently, the MDPSC Staff and residential consumer advocate sought clarification and appealed the amount of return awarded to BGE on the SOS. The appeal currently resides with the Maryland Court of Special Appeals. Also, in BGE’s 2019 electric and gas distribution base rate proceeding, the MDPSC established a normalized administrative adjustment. However, a group of electric suppliers appealed the MDPSC’s decision to the Circuit Court for Baltimore City. BGE cannot predict the outcome of these appeals. 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 will allow 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, PHI 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, began 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). 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 $79 million , $51 million , $17 million , $11 million , $4 million , $5 million and $2 million , respectively, as of December 31, 2019. PJM Transmission Rate Design (All Registrants). On June 15, 2016, several parties, including the Utility Registrants, filed a proposed settlement with FERC to resolve outstanding issues related to cost responsibility for charges to transmission customers for certain transmission facilities that operate at or above 500 kV. The settlement included provisions for monthly credits or charges related to the periods prior to January 1, 2016 that are expected to be refunded or recovered through PJM wholesale transmission rates through December 2025. On May 31, 2018, FERC issued an order approving the settlement. Pursuant to the order, similar charges for the period January 1, 2016 through June 30, 2018 would also be refunded or recovered through PJM wholesale transmission rates over the subsequent 12-month period. PJM commenced billing the refunds and charges associated with this settlement in August 2018. The Utility Registrants recorded the following payables to/receivables from PJM and related regulatory assets/liabilities in 2018 and have been refunding or recovering these amounts through electric distribution customer rates. Generation recorded a $41 million net payable to PJM and a pre-tax charge within Purchased power and fuel expense in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. PJM Receivable PJM Payable Regulatory Asset Regulatory Liability Exelon $ 220 $ 176 $ 136 $ 221 Generation (a) — 41 — — ComEd 122 — — 122 PECO 85 — — 85 BGE — 51 51 — PHI 13 84 85 14 Pepco — 84 84 — DPL 10 — — 10 ACE 3 — 1 4 __________ (a) Does not include an offsetting receivable from New Jersey Utilities of $16 million as of December 31, 2018. Regulatory Assets and Liabilities Regulatory assets represent incurred costs that have been deferred because of their probable future recovery from customers through regulated rates. Regulatory liabilities represent the excess recovery of costs or accrued credits that have been deferred because it is probable such amounts will be returned to customers through future regulated rates or represent billings in advance of expenditures for approved regulatory programs. The following tables provide information about the regulatory assets and liabilities of Exelon, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE as of December 31, 2019 and December 31, 2018 : December 31, 2019 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits $ 2,784 $ — $ — $ — $ — $ — $ — $ — Pension and other postretirement benefits - Merger related 1,138 — — — — — — — Deferred income taxes 528 — 518 — 10 10 — — AMI programs - Deployment costs 207 — — 129 78 43 35 — AMI programs - Legacy Meters 276 113 12 45 106 79 27 — Electric distribution formula rate annual reconciliations 34 34 — — — — — — Electric distribution formula rate significant one-time events 66 66 — — — — — — Energy efficiency costs 746 746 — — — — — — Fair value of long-term debt 650 — — — 523 — — — Fair value of PHI's unamortized energy contracts 443 — — — 443 — — — Asset retirement obligations 127 85 23 16 3 2 — 1 MGP remediation costs 302 287 11 4 — — — — Renewable energy 301 301 — — — — — — Electric Energy and Natural Gas Costs 110 — 6 36 68 43 5 20 Transmission formula rate annual reconciliations 11 — — 1 10 1 2 7 Energy efficiency and demand response programs 572 — — 303 269 196 73 — Merger integration costs 32 — — 2 30 15 8 7 Under-recovered revenue decoupling 37 — — 8 29 29 — — Securitized stranded costs 37 — — — 37 — — 37 Removal costs 641 — — 67 574 152 100 324 DC PLUG charge 126 — — — 126 126 — — Other 337 129 25 26 167 76 24 29 Total regulatory assets 9,505 1,761 595 637 2,473 772 274 425 Less: current portion 1,170 281 41 183 412 188 52 57 Total noncurrent regulatory assets $ 8,335 $ 1,480 $ 554 $ 454 $ 2,061 $ 584 $ 222 $ 368 December 31, 2019 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Deferred income taxes $ 4,944 $ 2,297 $ — $ 1,089 $ 1,558 $ 725 $ 477 $ 356 Nuclear decommissioning 3,102 2,622 480 — — — — — Removal costs 1,621 1,435 — 58 128 20 108 — Electric Energy and Natural Gas Costs 109 45 56 — 8 — 8 — Transmission formula rate annual reconciliations 34 6 28 — — — — — Other 582 337 37 81 83 9 18 26 Total regulatory liabilities 10,392 6,742 601 1,228 1,777 754 611 382 Less: current portion 406 200 91 33 70 8 37 25 Total noncurrent regulatory liabilities $ 9,986 $ 6,542 $ 510 $ 1,195 $ 1,707 $ 746 $ 574 $ 357 December 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits $ 2,553 $ — $ — $ — $ — $ — $ — $ — Pension and other postretirement benefits - Merger related 1,266 — — — — — — — Deferred income taxes 414 — 404 — 10 10 — — AMI programs - Deployment costs 234 — — 145 89 50 39 — AMI programs - Legacy Meters 328 136 24 48 120 90 30 — Electric distribution formula rate annual reconciliations 158 158 — — — — — — Electric distribution formula rate significant one-time events 81 81 — — — — — — Energy efficiency costs 472 472 — — — — — — Fair value of long-term debt 702 — — — 569 — — — Fair value of PHI's unamortized energy contracts 561 — — — 561 — — — Asset retirement obligations 118 79 22 16 1 1 — — MGP remediation costs 326 309 17 — — — — — Renewable energy 249 249 — — — — — — Electric Energy and Natural Gas Costs 193 — 49 51 93 84 — 9 Transmission formula rate annual reconciliations 41 6 — 4 31 10 14 7 Energy efficiency and demand response programs 545 — 1 289 255 188 67 — Merger integration costs 42 — — 3 39 18 11 10 Under-recovered revenue decoupling 27 — — 2 25 25 — — Securitized stranded costs 50 — — — 50 — — 50 Removal costs 564 — — — 564 158 97 309 DC PLUG charge 159 — — — 159 159 — — Deferred storm costs 41 — — — 41 9 4 28 Other 303 110 24 17 162 79 28 13 Total regulatory assets 9,427 1,600 541 575 2,769 881 290 426 Less: current portion 1,190 293 81 177 457 238 59 40 Total noncurrent regulatory assets $ 8,237 $ 1,307 $ 460 $ 398 $ 2,312 $ 643 $ 231 $ 386 December 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Deferred income taxes $ 5,228 $ 2,394 $ — $ 1,132 $ 1,702 $ 798 $ 510 $ 394 Nuclear decommissioning 2,606 2,217 389 — — — — — Removal costs 1,547 1,368 — 52 127 20 107 — Electric Energy and Natural Gas Costs 294 137 132 6 19 — 18 1 Other 528 227 75 79 100 11 30 25 Total regulatory liabilities 10,203 6,343 596 — 1,269 1,948 829 665 420 Less: current portion 644 293 175 77 84 7 59 18 Total noncurrent regulatory liabilities $ 9,559 $ 6,050 $ 421 $ 1,192 $ 1,864 $ 822 $ 606 $ 402 Descriptions of the regulatory assets and liabilities included in the tables above are summarized below, including their recovery and amortization periods. Line Item Description End Date of Remaining Recovery/Refund Period Return Pension and Other Postretirement Benefits Primarily reflects the Utility Registrants' portion of deferred costs, including unamortized actuarial losses (gains) and prior service costs (credits), associated with Exelon's pension and other postretirement benefit plans, which are recovered through customer rates once amortized through net periodic benefit cost. Also, includes the Utility Registrants' non–service cost components capitalized in Property, plant and equipment, net on their Consolidated Balance Sheets. The deferred costs are amortized over the plan participants' average remaining service periods subject to applicable pension and other postretirement cost recognition policies. See Note 14 – Retirement Benefits for additional information. The capitalized non–service cost components are amortized over the lives of the underlying assets. No Pension and Other Postretirement Benefits - Merger Related The deferred costs are amortized over the plan participants' average remaining service periods subject to applicable pension and other postretirement cost recognition policies. See Note 14 – Retirement Benefits for additional information. The capitalized non–service cost components are amortized over the lives of the underlying assets. Legacy Constellation - 2038 Legacy PHI - 2032 No Line Item Description End Date of Remaining Recovery/Refund Period Return Deferred Income Taxes Deferred income taxes that are recoverable or refundable through customer rates, primarily associated with accelerated depreciation, the equity component of AFUDC, and the effects of income tax rate changes, including those resulting from the TCJA. These amounts include transmission-related regulatory liabilities that require FERC approval separate from the transmission formula rate. See Transmission-Related Income Tax Regulatory Assets section above for additional information. Over the period in which the related deferred income taxes reverse, which is generally based on the expected life of the underlying assets. For TCJA, generally refunded over the remaining depreciable life of the underlying assets, except in certain jurisdictions where the commissions have approved a shorter refund period for certain assets not subject to IRS normalization rules. No AMI Programs - Deployment Costs Installation costs of new smart meters, including implementation costs at Pepco and DPL of dynamic pricing for energy usage resulting from smart meters. BGE - 2026 Pepco - 2027 DPL - 2030 Yes AMI Programs - Legacy Meters Early retirement costs of legacy meters. ComEd - 2028 PECO - 2020 BGE - 2026 Pepco - 2027 DPL - 2030 ComEd, Pepco (District of Columbia), DPL (Delaware) - Yes PECO, BGE, Pepco (Maryland), DPL (Maryland) - No Electric distribution formula rate annual reconciliations Under-recoveries related to electric distribution service costs recoverable through ComEd's performance-based formula rate, which is updated annually with rates effective on January 1 st . 2021 Yes Electric distribution formula rate significant one-time events Under-recoveries of electric distribution service costs related to ComEd's significant one-time events (e.g., storm costs), which are recovered over 5 years from date of the event. 2023 Yes Energy Efficiency Costs ComEd's costs recovered through the energy efficiency formula rate tariff and the reconciliation of the difference of the revenue requirement in effect for the prior year and the revenue requirement based on actual prior year costs. Deferred energy efficiency costs are recovered over the weighted average useful life of the related energy measure. 2029 Yes Line Item Description End Date of Remaining Recovery/Refund Period Return Fair Value of Long-Term Debt Represents the difference between the carrying value and fair value of long-term debt of PHI and BGE of $523 million and $127 million, respectively, as of December 30, 2019 and $569 million and $133 million, respectively, as of December 30, 2018, as of the PHI and Constellation merger dates. BGE - 2043 PHI - 2045 No Fair Value of PHI’s Unamortized Energy Contracts Represents the regulatory assets recorded at Exelon and PHI offsetting the fair value adjustment related to Pepco's, DPL's and ACE's electricity and natural gas energy supply contracts recorded at PHI as of the PHI merger date. 2036 No Asset Retirement Obligations Future legally required removal costs associated with existing asset retirement obligations. Over the life of the related assets. Yes, once the removal activities have been performed. MGP Remediation Costs Environmental remediation costs for MGP sites. Over the expected remediation period. See Note 18 - Commitments and Contingencies for additional information. ComEd, PECO - No Renewable Energy Represents the change in fair value of ComEd‘s 20-year floating-to-fixed long-term renewable energy swap contracts. 2032 No Electric Energy and Natural Gas Costs Under (over) recoveries related to energy and gas supply related costs recoverable (refundable) under approved rate riders. 2025 DPL (Delaware), ACE - Yes ComEd, PECO, BGE, Pepco, DPL (Maryland) - No Transmission formula rate annual reconciliations Under (over)-recoveries related to transmission service costs recoverable through the Utility Registrants’ FERC formula rates, which are updated annually with rates effective each June 1 st . 2021 Yes Energy efficiency and demand response programs Includes under (over)-recoveries of costs incurred related to energy efficiency programs and demand response programs and recoverable costs associated with customer direct load control and energy efficiency and conservation programs that are being recovered from customers. PECO - 2021 BGE - 2024 Pepco, DPL - 2034 BGE, Pepco, DPL - Yes PECO - Yes on ca

Revenue from Contracts with Cus

Revenue from Contracts with Customers Revenue from Contracts with Customers (All Registrants)	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer (All Registrants) [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. The performance obligations, revenue recognition and payment terms associated with these sources of revenue are further discussed in the table below. There are no significant financing components for these sources of revenue and no variable consideration for regulated electric and gas tariff sales and regulated transmission services unless noted below. Unless otherwise noted, for each of the significant revenue categories and related performance obligations described below, the Registrants have the right to consideration from the customer in an amount that corresponds directly with the value transferred to the customer for the performance completed to date. Therefore, the Registrant's generally recognize revenue in the amount for which they have the right to invoice the customer. As a result, there are generally no significant judgments used in determining or allocating the transaction price. Revenue Source Description Performance Obligation Timing of Revenue Recognition Payment Terms Competitive Power Sales (Exelon and Generation) Sales of power and other energy-related commodities to wholesale and retail customers across multiple geographic regions through its customer-facing business, Constellation. Various including the delivery of power (generally delivered over time) and other energy-related commodities such as capacity (generally delivered over time), ZECs, RECs or other ancillary services (generally delivered at a point in time). Concurrently as power is generated for bundled power sale contracts. (a) Within the month following delivery to the customer. Competitive Natural Gas Sales (Exelon and Generation) Sales of natural gas on a full requirement basis or for an agreed upon volume to commercial and residential customers. Delivery of natural gas to the customer. Over time as the natural gas is delivered and consumed by the customer. Within the month following delivery to the customer. Other Competitive Products and Services (Exelon and Generation) Sales of other energy-related products and services such as long-term construction and installation of energy efficiency assets and new power generating facilities, primarily to commercial and industrial customers. Construction and/or installation of the asset for the customer. Revenues, and associated costs, are recognized throughout the contract term using an input method to measure progress towards completion. (b) Within 30 or 45 days from the invoice date. Regulated Electric and Gas Tariff Sales (Exelon and the Utility Registrants) Sales of electricity and electricity distribution services (the Utility Registrants) and natural gas and gas distribution services (PECO, BGE and DPL) to residential, commercial, industrial and governmental customers through regulated tariff rates approved by state regulatory commissions. Delivery of electricity and/or natural gas. Over time (each day) as the electricity and/or natural gas is delivered to customers. Tariff sales are generally considered daily contracts as customers can discontinue service at any time. (c) Within the month following delivery of the electricity or natural gas to the customer. Regulated Transmission Services (Exelon and the Utility Registrants) The Utility Registrants provide open access to their transmission facilities to PJM, which directs and controls the operation of these transmission facilities and accordingly compensates the Utility Registrants pursuant to filed tariffs at cost-based rates approved by FERC. Various including (i) Network Integration Transmission Services (NITS), (ii) scheduling, system control and dispatch services, and (iii) access to the wholesale grid. Over time utilizing output methods to measure progress towards completion. (d) Paid weekly by PJM. __________ (a) Certain contracts may contain limits on the total amount of revenue Exelon and Generation are able to collect over the entire term of the contract. In such cases, Exelon and Generation estimate the total consideration expected to be received over the term of the contract net of the constraint and allocate the expected consideration to the performance obligations in the contract such that revenue is recognized ratably over the term of the entire contract as the performance obligations are satisfied. (b) The method recognizes revenue based on the various inputs used to satisfy the performance obligation, such as costs incurred and total labor hours expended. The total amount of revenue that will be recognized is based on the agreed upon contractually-stated amount. The average contract term for these projects is approximately 18 months. (c) Electric and natural gas utility customers have the choice to purchase electricity or natural gas from competitive electric generation and natural gas suppliers. While the Utility Registrants are required under state legislation to bill their customers for the supply and distribution of electricity and/or natural gas, they recognize revenue related only to the distribution services when customers purchase their electricity or natural gas from competitive suppliers. (d) Passage of time is used for NITS and access to the wholesale grid and MWHs of energy transported over the wholesale grid is used for scheduling, system control and dispatch services. Generation incurs incremental costs in order to execute certain retail power and gas sales contracts. These costs, which primarily relate to retail broker fees and sales commissions, are capitalized when incurred as contract acquisition costs and were immaterial as of December 31, 2019 and 2018. The Utility Registrants do not incur any material costs to obtain or fulfill contracts with customers. 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. The Generation contract liability related to the Illinois ZEC program includes certain amounts with ComEd that are eliminated in consolidation in Exelon’s Consolidated Statements of Operations and Consolidated Balance Sheets. 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 December 31, 2019 : Contract Assets Contract Liabilities Exelon Generation Exelon Generation Balance as of January 1, 2018 $ 283 $ 283 $ 35 $ 35 Consideration received or due (146 ) (146 ) 179 465 Revenues recognized 50 50 (187 ) (458 ) Balance at December 31, 2018 187 187 27 42 Consideration received or due (143 ) (143 ) 94 287 Revenues recognized 130 130 (88 ) (258 ) Balance at December 31, 2019 $ 174 $ 174 $ 33 $ 71 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 December 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 December 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. 2020 2021 2022 2023 2024 and thereafter Total Exelon $ 400 $ 141 $ 65 $ 45 $ 199 $ 850 Generation 501 196 80 45 199 1,021 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 Note 5 — Segment Information for the presentation of the Registrant's revenue disaggregation.

Segment Information (All Regist

Segment Information (All Registrants)	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
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 NYISO. • ERCOT represents operations within Electric Reliability Council of Texas. • Other Power Regions: • New England represents operations within ISO-NE. • South represents operations in the FRCC, MISO’s Southern Region, the remaining portions of the SERC not included within MISO or PJM. • West represents operations in the WECC, including 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 years ended December 31, 2019 , 2018 , and 2017 is as follows: Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon Operating revenues (c) : 2019 Competitive businesses electric revenues $ 16,285 $ — $ — $ — $ — $ — $ (1,165 ) $ 15,120 Competitive businesses natural gas revenues 2,148 — — — — — (1 ) 2,147 Competitive businesses other revenues 491 — — — — — (4 ) 487 Rate-regulated electric revenues — 5,747 2,490 2,379 4,626 — (47 ) 15,195 Rate-regulated natural gas revenues — — 610 727 167 — (15 ) 1,489 Shared service and other revenues — — — — 13 1,921 (1,934 ) — Total operating revenues $ 18,924 $ 5,747 $ 3,100 $ 3,106 $ 4,806 $ 1,921 $ (3,166 ) $ 34,438 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon 2018 Competitive businesses electric revenues $ 17,411 $ — $ — $ — $ — $ — $ (1,256 ) $ 16,155 Competitive businesses natural gas revenues 2,718 — — — — — (8 ) 2,710 Competitive businesses other revenues 308 — — — — — (5 ) 303 Rate-regulated electric revenues — 5,882 2,470 2,428 4,602 — (45 ) 15,337 Rate-regulated natural gas revenues — — 568 741 181 — (20 ) 1,470 Shared service and other revenues — — — — 15 1,948 (1,960 ) 3 Total operating revenues $ 20,437 $ 5,882 $ 3,038 $ 3,169 $ 4,798 $ 1,948 $ (3,294 ) $ 35,978 2017 Competitive businesses electric revenues $ 15,332 $ — $ — $ — $ — $ — $ (1,105 ) $ 14,227 Competitive businesses natural gas revenues 2,575 — — — — — — 2,575 Competitive businesses other revenues 593 — — — — — (1 ) 592 Rate-regulated electric revenues — 5,536 2,375 2,489 4,462 — (29 ) 14,833 Rate-regulated natural gas revenues — — 495 687 161 — (10 ) 1,333 Shared service and other revenues — — — — 49 1,831 (1,880 ) — Total operating revenues $ 18,500 $ 5,536 $ 2,870 $ 3,176 $ 4,672 $ 1,831 $ (3,025 ) $ 33,560 Intersegment revenues (d) : 2019 $ 1,172 $ 30 $ 6 $ 26 $ 14 $ 1,913 $ (3,159 ) $ 2 2018 1,269 27 8 29 15 1,942 (3,289 ) 1 2017 1,110 15 7 16 50 1,824 (3,020 ) 2 Depreciation and amortization: 2019 $ 1,535 $ 1,033 $ 333 $ 502 $ 754 $ 95 $ — $ 4,252 2018 1,797 940 301 483 740 92 — 4,353 2017 1,457 850 286 473 675 87 — 3,828 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon Operating expenses (c) : 2019 $ 17,628 $ 4,580 $ 2,388 $ 2,574 $ 4,084 $ 1,996 $ (3,154 ) $ 30,096 2018 19,510 4,741 2,452 2,696 4,156 1,929 (3,341 ) 32,143 2017 18,001 4,214 2,215 2,562 3,911 1,742 (3,026 ) 29,619 Interest expense, net: 2019 $ 429 $ 359 $ 136 $ 121 $ 263 $ 308 $ — $ 1,616 2018 432 347 129 106 261 279 — 1,554 2017 440 361 126 105 245 283 — 1,560 Income (loss) before income taxes: 2019 $ 1,917 $ 851 $ 593 $ 439 $ 514 $ (327 ) $ (2 ) $ 3,985 2018 365 832 466 387 425 (249 ) (1 ) 2,225 2017 1,455 984 538 525 571 (296 ) (2 ) 3,775 Income taxes: 2019 $ 516 $ 163 $ 65 $ 79 $ 38 $ (87 ) $ — $ 774 2018 (108 ) 168 6 74 33 (55 ) — 118 2017 (1,376 ) 417 104 218 217 294 — (126 ) Net income (loss): 2019 $ 1,217 $ 688 $ 528 $ 360 $ 477 $ (240 ) $ (2 ) $ 3,028 2018 443 664 460 313 393 (193 ) (1 ) 2,079 2017 2,798 567 434 307 355 (590 ) (2 ) 3,869 Capital expenditures: 2019 $ 1,845 $ 1,915 $ 939 $ 1,145 $ 1,355 $ 49 $ — $ 7,248 2018 2,242 2,126 849 959 1,375 43 — 7,594 2017 2,259 2,250 732 882 1,396 65 — 7,584 Total assets: 2019 $ 48,995 $ 32,765 $ 11,469 $ 10,634 $ 22,719 $ 8,484 $ (10,089 ) $ 124,977 2018 47,556 31,213 10,642 9,716 21,952 8,355 (9,800 ) 119,634 __________ (a) See Note 24 — Related Party Transactions for additional information on intersegment revenues. (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 23 — 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 authoritative 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 $ 2,260 $ 1,139 $ 1,240 $ — $ (13 ) $ 4,626 Rate-regulated natural gas revenues — 167 — — — 167 Shared service and other revenues — — — 396 (383 ) 13 Total operating revenues $ 2,260 $ 1,306 $ 1,240 $ 396 $ (396 ) $ 4,806 2018 Rate-regulated electric revenues $ 2,232 $ 1,151 $ 1,236 $ — $ (17 ) $ 4,602 Rate-regulated natural gas revenues — 181 — — — 181 Shared service and other revenues — — — 435 (420 ) 15 Total operating revenues $ 2,232 $ 1,332 $ 1,236 $ 435 $ (437 ) $ 4,798 2017 Rate-regulated electric revenues $ 2,151 $ 1,139 $ 1,186 $ — $ (14 ) $ 4,462 Rate-regulated natural gas revenues — 161 — — — 161 Shared service and other revenues — — — 52 (3 ) 49 Total operating revenues $ 2,151 $ 1,300 $ 1,186 $ 52 $ (17 ) $ 4,672 Intersegment revenues: 2019 $ 5 $ 7 $ 3 $ 396 $ (397 ) $ 14 2018 6 8 3 435 (437 ) 15 2017 6 8 2 53 (19 ) 50 Depreciation and amortization: 2019 $ 374 $ 184 $ 157 $ 39 $ — $ 754 2018 385 182 136 37 — $ 740 2017 321 167 146 42 (1 ) $ 675 Operating expenses: 2019 $ 1,899 $ 1,089 $ 1,089 $ 403 $ (396 ) $ 4,084 2018 1,919 1,143 1,087 442 (435 ) $ 4,156 2017 1,760 1,071 1,029 68 (17 ) $ 3,911 Interest expense, net: 2019 $ 133 $ 61 $ 58 $ 10 $ 1 $ 263 2018 128 58 64 11 — $ 261 2017 121 51 61 13 (1 ) $ 245 Income (loss) before income taxes: 2019 $ 259 $ 169 $ 99 $ 476 $ (489 ) $ 514 2018 216 142 87 388 (408 ) $ 425 2017 303 192 103 377 (404 ) $ 571 Income taxes: 2019 $ 16 $ 22 $ — $ (1 ) $ 1 $ 38 2018 11 22 12 (10 ) (2 ) $ 33 2017 105 71 26 15 — $ 217 Pepco DPL ACE Other (b) Intersegment PHI Net income (loss): 2019 $ 243 $ 147 $ 99 $ (26 ) $ 14 $ 477 2018 205 120 75 (22 ) 15 $ 393 2017 198 121 77 (91 ) 50 $ 355 Capital expenditures: 2019 $ 626 $ 348 $ 375 $ 6 $ — $ 1,355 2018 656 364 335 20 — $ 1,375 2017 628 428 312 28 — 1,396 Total assets: 2019 $ 8,661 $ 4,830 $ 3,933 $ 11,105 $ (5,810 ) $ 22,719 2018 8,267 4,588 3,699 10,819 (5,421 ) 21,952 __________ (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 23 — 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): 2019 Revenues from external customers (a) Contracts with customers Other (b) Total Intersegment Revenues Total Revenues Mid-Atlantic $ 5,053 $ 17 $ 5,070 $ 4 $ 5,074 Midwest 4,095 232 4,327 (34 ) 4,293 New York 1,571 25 1,596 — 1,596 ERCOT 768 229 997 16 1,013 Other Power Regions 3,687 608 4,295 (49 ) 4,246 Total Competitive Businesses Electric Revenues 15,174 1,111 16,285 (63 ) 16,222 Competitive Businesses Natural Gas Revenues 1,446 702 2,148 62 2,210 Competitive Businesses Other Revenues (c) 440 51 491 1 492 Total Generation Consolidated Operating Revenues 17,060 1,864 $ 18,924 $ — $ 18,924 2018 Revenues from external customers (a) Contracts with customers Other (b) Total Intersegment Revenues Total Revenues Mid-Atlantic $ 5,241 $ 233 $ 5,474 $ 13 $ 5,487 Midwest 4,527 190 4,717 (11 ) 4,706 New York 1,723 (36 ) 1,687 — 1,687 ERCOT 572 560 1,132 1 1,133 Other Power Regions 3,530 871 4,401 (66 ) 4,335 Total Competitive Businesses Electric Revenues 15,593 1,818 17,411 (63 ) 17,348 Competitive Businesses Natural Gas Revenues 1,524 1,194 2,718 62 2,780 Competitive Businesses Other Revenues (c) 510 (202 ) 308 1 309 Total Generation Consolidated Operating Revenues $ 17,627 $ 2,810 $ 20,437 $ — $ 20,437 2017 Revenues from external customers (a) Contracts with customers Other (b) Total Intersegment Revenues Total Revenues Mid-Atlantic $ 5,523 $ (8 ) $ 5,515 $ 25 $ 5,540 Midwest 3,923 283 4,206 (25 ) 4,181 New York 1,605 (38 ) 1,567 (17 ) 1,550 ERCOT 641 317 958 4 962 Other Power Regions 2,658 428 3,086 (35 ) 3,051 Total Competitive Businesses Electric Revenues 14,350 982 15,332 (48 ) 15,284 Competitive Businesses Natural Gas Revenues 1,658 917 2,575 53 2,628 Competitive Businesses Other Revenues (c) 744 (151 ) 593 (5 ) 588 Total Generation Consolidated Operating Revenues $ 16,752 $ 1,748 $ 18,500 $ — $ 18,500 __________ (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 a $38 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value in 2017 , unrealized mark-to-market losses of $4 million , $262 million , and $131 million in 2019 , 2018 , and 2017 , respectively, and elimination of intersegment revenues. Revenues net of purchased power and fuel expense (Generation): 2019 2018 2017 RNF from external (a) Intersegment Total RNF RNF from external (a) Intersegment RNF Total RNF RNF from external (a) Intersegment Total RNF Mid-Atlantic $ 2,637 $ 18 $ 2,655 $ 3,022 $ 51 $ 3,073 $ 3,105 $ 109 $ 3,214 Midwest 2,994 (32 ) 2,962 3,112 23 3,135 2,810 10 2,820 New York 1,081 13 1,094 1,112 10 1,122 1,007 1 1,008 ERCOT 338 (30 ) 308 501 (243 ) 258 575 (243 ) 332 Other Power Regions 694 (74 ) 620 883 (154 ) 729 1,014 (195 ) 819 Total Revenues net of purchased power and fuel for Reportable Segments $ 7,744 $ (105 ) $ 7,639 $ 8,630 $ (313 ) $ 8,317 $ 8,511 $ (318 ) $ 8,193 Other (b) 324 105 429 114 313 427 299 318 617 Total Generation Revenues net of purchased power and fuel expense $ 8,068 $ — $ 8,068 $ 8,744 $ — $ 8,744 $ 8,810 $ — $ 8,810 __________ (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 a $54 million decrease in RNF for the amortization of intangible assets and liabilities related to commodity contracts in 2017 , unrealized mark-to-market losses of $215 million , $319 million , and $175 million in 2019 , 2018 , and 2017 , respectively, accelerated nuclear fuel amortization associated with the announced early plant retirements as discussed in Note 6 - Early Plant Retirements of $13 million , $57 million and $12 million in 2019 , 2018 , and 2017 , respectively, and the elimination of intersegment RNF. Electric and Gas Revenue by Customer Class (Utility Registrants): 2019 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,916 $ 1,596 $ 1,326 $ 2,316 $ 1,012 $ 645 $ 659 Small commercial & industrial 1,463 404 254 505 149 186 170 Large commercial & industrial 540 219 436 1,112 833 99 180 Public authorities & electric railroads 47 29 27 61 34 14 13 Other (a) 888 249 321 650 227 204 218 Total rate-regulated electric revenues (b) 5,854 2,497 2,364 4,644 2,255 1,148 1,240 Rate-regulated natural gas revenues Residential — 409 474 96 — 96 — Small commercial & industrial — 169 77 44 — 45 — Large commercial & industrial — 1 132 5 — 5 — Transportation — 25 — 14 — 14 — Other (c) — 6 31 7 — 7 — Total rate-regulated natural gas revenues (d) — 610 714 166 — 167 — Total rate-regulated revenues from contracts with customers 5,854 3,107 3,078 4,810 2,255 1,315 1,240 Other revenues Revenues from alternative revenue programs (133 ) (21 ) 12 (14 ) (3 ) (11 ) — Other rate-regulated electric revenues (e) 26 13 12 10 8 2 — Other rate-regulated natural gas revenues (e) — 1 4 — — — — Total other revenues (107 ) (7 ) 28 (4 ) 5 (9 ) — Total rate-regulated revenues for reportable segments $ 5,747 $ 3,100 $ 3,106 $ 4,806 $ 2,260 $ 1,306 $ 1,240 2018 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,942 $ 1,566 $ 1,382 $ 2,351 $ 1,021 $ 669 $ 661 Small commercial & industrial 1,487 404 257 488 140 186 162 Large commercial & industrial 538 223 429 1,124 846 100 178 Public authorities & electric railroads 47 28 28 58 32 14 12 Other (a) 867 243 327 593 193 175 227 Total rate-regulated electric revenues (b) 5,881 2,464 2,423 4,614 2,232 1,144 1,240 Rate-regulated natural gas revenues Residential — 395 491 99 — 99 — Small commercial & industrial — 143 77 44 — 44 — Large commercial & industrial — 1 124 8 — 8 — Transportation — 23 — 16 — 16 — Other (c) — 6 63 13 — 13 — Total rate-regulated natural gas revenues (d) — 568 755 180 — 180 — Total rate-regulated revenues from contracts with customers 5,881 3,032 3,178 4,794 2,232 1,324 1,240 Other revenues Revenues from alternative revenue programs (29 ) (7 ) (26 ) (7 ) (7 ) 4 (4 ) Other rate-regulated electric revenues (e) 30 12 13 10 7 3 — Other rate-regulated natural gas revenues (e) — 1 4 1 — 1 — Total other revenues 1 6 (9 ) 4 — 8 (4 ) Total rate-regulated revenues for reportable segments $ 5,882 $ 3,038 $ 3,169 $ 4,798 $ 2,232 $ 1,332 $ 1,236 2017 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,715 $ 1,505 $ 1,365 $ 2,246 $ 964 $ 663 $ 619 Small commercial & industrial 1,363 401 254 490 137 187 166 Large commercial & industrial 455 223 427 1,086 794 103 189 Public authorities & electric railroads 44 30 31 60 33 14 13 Other (a) 886 204 299 541 199 163 191 Total rate-regulated electric revenues (b) 5,463 2,363 2,376 4,423 2,127 1,130 1,178 Rate-regulated natural gas revenues Residential — 331 437 90 — 90 — Small commercial & industrial — 131 75 38 — 38 — Large commercial & industrial — 1 119 8 — 8 — Transportation — 23 — 15 — 15 — Other (c) — 8 28 9 — 9 — Total rate-regulated natural gas revenues (d) — 494 659 160 — 160 — Total rate-regulated revenues from contracts with customers 5,463 2,857 3,035 4,583 2,127 1,290 1,178 Other revenues Revenues from alternative revenue programs 43 — 124 33 19 6 8 Other rate-regulated electric revenues (e) 30 12 13 8 5 3 — Other rate-regulated natural gas revenues (e) — 1 4 1 — 1 — Other revenues (f) — — — 47 — — — Total other revenues 73 13 141 89 24 10 8 Total rate-regulated revenues for reportable segments $ 5,536 $ 2,870 $ 3,176 $ 4,672 $ 2,151 $ 1,300 $ 1,186 __________ (a) Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue. (b) Includes operating revenues from affiliates of $ 30 million , $5 million , $8 million , $14 million , $5 million , $7 million and $3 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2019 , $27 million , $7 million , $8 million , $15 million , $6 million , $8 million and $3 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, in 2018 , and $15 million , $6 million , $5 million , $3 million , $6 million , $8 million and $2 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2017 . (c) Includes revenues from off-system natural gas sales. (d) Includes operating revenues from affiliates of $1 million and $18 million at PECO and BGE, respectively, in 2019 , $1 million and $21 million at PECO and BGE, respectively, in 2018 , and $1 million and $11 million at PECO and BGE, respectively, in 2017 . (e) Includes late payment charge revenues. (f) Includes operating revenues from affiliates of $47 million at PHI in 2017 .

Early Plant Retirements (Exelon

Early Plant Retirements (Exelon, Generation)	12 Months Ended
	Dec. 31, 2019
Implications of Potential Early Plant Retirements [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 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. In addition, FERC’s December 19, 2019 order on the MOPR in PJM may undermine the continued effectiveness of the Illinois ZES and the New Jersey ZEC program unless Illinois and New Jersey implement an FRR mechanism under which the Generation plants in these states would be removed from PJM’s capacity auction. See Note 3 — Regulatory Matters for additional information on the Illinois ZES, New Jersey ZEC program, New York CES and FERC's December 19, 2019 order. 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, Generation announced that it would permanently cease generation operations at TMI. On September 20, 2019, Generation permanently ceased generation operations at TMI. On February 2, 2018, Generation announced that it would permanently cease generation operations at the Oyster Creek nuclear plant at the end of its current operating cycle and permanently ceased generation operations on September 17, 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. The total annual impact of these charges by year are summarized in the table below. Income statement expense (pre-tax) 2019 (a) 2018 (b) 2017 (c) Depreciation and Amortization Accelerated depreciation $ 216 $ 539 $ 250 Accelerated nuclear fuel amortization 13 57 12 Operating and Maintenance (d) (53 ) 32 77 Total $ 176 $ 628 $ 339 _________ (a) Reflects incremental charges for TMI from January 1, 2019 through September 20, 2019. (b) Reflects incremental charges for TMI in 2018 and Oyster Creek from February 2, 2018 through September 17, 2018. (c) Reflects incremental charges for TMI from May 30, 2017 through December 31, 2017. (d) In 2019, primarily reflects the net impacts associated with the remeasurements of the TMI ARO in the first and third quarters. In 2018 and 2017, primarily reflects materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments associated with the early retirement decisions for TMI and Oyster Creek. Excludes the charges in the third quarter of 2018 and second quarter of 2019 for the ARO remeasurement due to the sale of Oyster Creek. See Note 2 — Mergers, Acquisitions and Dispositions and Note 9 — Asset Retirement Obligations for additional information. 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 Mystic Units 8 and 9 absent regulatory reforms on June 1, 2022, at the end of the then-current capacity commitment for Mystic Units 7 and 8. Mystic Unit 9 was then 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 compensation, 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 on March 1, 2019. In the December 20, 2018 order, FERC also directed a paper hearing on ROE using a new methodology. On January 22, 2019, Exelon and several other parties filed requests for rehearing of certain findings in the order. 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. The Inventoried Energy Program went into effect on August 5, 2019. On October 7, 2019, requests for rehearing were denied and several parties have appealed to the D.C. Circuit Court. FERC ordered ISO-NE to file long-term, market-based fuel security rules by October 15, 2019; FERC has granted an extension to April 15, 2020. The following table provides the balance sheet amounts as of December 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 the failure to adopt long-term solutions for reliability and fuel security. December 31, 2019 Asset Balances Materials and supplies inventory $ 31 Fuel inventory 11 Property, plant and equipment, net 902 Liability Balances Asset retirement obligation (3 ) To ensure the continued reliable supply of fuel to Mystic Units 8 and 9 while they remain operating, on October 1, 2018, Generation acquired the Everett Marine Terminal in Massachusetts for a purchase price of $81 million , with the majority of the fair value allocated to Property, plant and equipment and no goodwill recorded. Generation also settled its existing long-term gas supply agreement, resulting in a pre-tax gain of $75 million , which is included within Purchased power and fuel expense in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. See Note 11 — Asset Impairments for impairment assessment considerations on the New England Asset Group.

Property, Plant and Equipment (

Property, Plant and Equipment (All Registrants)	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment (All Registrants)	Property, Plant and Equipment (All Registrants) The following tables present a summary of property, plant and equipment by asset category as of December 31, 2019 and 2018 : Asset Category Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 Electric—transmission and distribution $ 56,809 $ — $ 27,566 $ 8,957 $ 8,326 $ 13,809 $ 9,734 $ 4,464 $ 4,207 Electric—generation 29,839 29,839 — — — — — — — Gas—transportation and distribution 6,147 — — 2,899 2,999 525 — 690 — Common—electric and gas 1,907 — — 877 991 146 — 160 — Nuclear fuel (a) 5,656 5,656 — — — — — — — Construction work in progress 3,055 702 662 250 483 921 628 125 166 Other property, plant and equipment (b) 799 13 47 27 25 108 64 21 27 Total property, plant and equipment 104,212 36,210 28,275 13,010 12,824 15,509 10,426 5,460 4,400 Less: accumulated depreciation (c) 23,979 12,017 5,168 3,718 3,834 1,213 3,517 1,425 1,210 Property, plant and equipment, net $ 80,233 $ 24,193 $ 23,107 $ 9,292 $ 8,990 $ 14,296 $ 6,909 $ 4,035 $ 3,190 December 31, 2018 Electric—transmission and distribution $ 53,090 $ — $ 25,991 $ 8,359 $ 7,951 $ 12,664 $ 9,217 $ 4,195 $ 3,866 Electric—generation 29,170 29,170 — — — — — — — Gas—transportation and distribution 5,530 — — 2,694 2,630 486 — 651 — Common—electric and gas 1,627 — — 756 860 126 — 136 — Nuclear fuel (a) 5,957 5,957 — — — — — — — Construction work in progress 3,377 997 705 343 410 912 536 151 209 Other property, plant and equipment (b) 858 63 46 19 25 99 61 17 28 Total property, plant and equipment 99,609 36,187 26,742 12,171 11,876 14,287 9,814 5,150 4,103 Less: accumulated depreciation (c) 22,902 12,206 4,684 3,561 3,633 841 3,354 1,329 1,137 Property, plant and equipment, net $ 76,707 $ 23,981 $ 22,058 $ 8,610 $ 8,243 $ 13,446 $ 6,460 $ 3,821 $ 2,966 __________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,025 million and $1,004 million at December 31, 2019 and 2018 , respectively. (b) Primarily composed of land and non-utility property. (c) Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $2,867 million and $2,969 million as of December 31, 2019 and 2018 , respectively. The following table presents the average service life for each asset category in number of years: Average Service Life (years) Asset Category Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Electric - transmission and distribution 5-80 N/A 5-80 5-65 5-75 5-75 5-75 5-70 5-65 Electric - generation 1-56 1-56 N/A N/A N/A N/A N/A N/A N/A Gas - transportation and distribution 5-80 N/A N/A 5-70 5-80 5-75 N/A 5-75 N/A Common - electric and gas 4-75 N/A N/A 5-50 4-50 5-75 N/A 5-75 N/A Nuclear fuel 1-8 1-8 N/A N/A N/A N/A N/A N/A N/A Other property, plant and equipment 1-50 1-10 34-50 50 20-50 3-50 33-50 8-50 13-15 Depreciation provisions are based on the estimated useful lives of the stations, which reflect the first renewal of the operating licenses for all of Generation's operating nuclear generating stations except for Clinton and Peach Bottom. Clinton depreciation provisions are based on an estimated useful life through 2027, which is the last year of the Illinois ZES. Peach Bottom depreciation provisions are based on estimated useful life of 2053 and 2054 for Unit 2 and Unit 3, respectively, which reflects the anticipated second renewal of its operating licenses. Beginning in 2017, TMI and Oyster Creek depreciation provisions were based on their 2019 expected shutdown dates. Beginning February 2018, Oyster Creek depreciation provisions were based on its announced shutdown date of September 2018. See Note 3 — Regulatory Matters for additional information regarding license renewals and the Illinois ZECs and Note 6 — Early Plant Retirements for additional information on the impacts of early plant retirements. The following table presents the annual depreciation rates for each asset category. Nuclear fuel amortization is charged to fuel expense using the unit-of-production method and not included in the below table. Annual Depreciation Rates Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 Electric—transmission and distribution 2.80 % N/A 2.99 % 2.36 % 2.60 % 2.77 % 2.47 % 2.86 % 2.94 % Electric—generation 4.35 % 4.35 % N/A N/A N/A N/A N/A N/A N/A Gas—transportation and distribution 2.04 % N/A N/A 1.89 % 2.30 % 1.55 % N/A 1.55 % N/A Common—electric and gas 7.37 % N/A N/A 6.06 % 8.30 % 8.25 % N/A 6.24 % N/A December 31, 2018 Electric—transmission and distribution 2.73 % N/A 2.95 % 2.35 % 2.61 % 2.61 % 2.40 % 2.77 % 2.45 % Electric—generation 5.37 % 5.37 % N/A N/A N/A N/A N/A N/A N/A Gas—transportation and distribution 2.07 % N/A N/A 1.90 % 2.36 % 1.59 % N/A 1.59 % N/A Common—electric and gas 6.98 % N/A N/A 5.44 % 8.50 % 6.30 % N/A 3.70 % N/A December 31, 2017 Electric—transmission and distribution 2.75 % N/A 2.99 % 2.37 % 2.58 % 2.63 % 2.35 % 2.75 % 2.46 % Electric—generation 4.36 % 4.36 % N/A N/A N/A N/A N/A N/A N/A Gas—transportation and distribution 2.10 % N/A N/A 1.89 % 2.33 % 2.07 % N/A 2.07 % N/A Common—electric and gas 7.05 % N/A N/A 5.47 % 8.64 % 6.50 % N/A 4.14 % N/A Capitalized Interest and AFUDC (All Registrants) The following table summarizes capitalized interest and credits to AFUDC by year: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 Capitalized interest $ 24 $ 24 $ — $ — $ — $ — $ — $ — $ — AFUDC debt and equity 132 — 32 17 29 54 39 6 9 December 31, 2018 Capitalized interest $ 31 $ 31 $ — $ — $ — $ — $ — $ — $ — AFUDC debt and equity 109 — 30 12 24 44 34 4 4 December 31, 2017 Capitalized interest $ 63 $ 63 $ — $ — $ — $ — $ — $ — $ — AFUDC debt and equity 108 — 20 12 22 54 34 10 9 See Note 1 — Significant Accounting Policies for additional information regarding property, plant and equipment policies. See Note 16 — Debt and Credit Agreements for additional information regarding Exelon’s, ComEd’s and PECO’s property, plant and equipment subject to mortgage liens.

Jointly Owned Electric Utility

Jointly Owned Electric Utility Plant (Exelon, Generation, PECO, DPL and ACE)	12 Months Ended
	Dec. 31, 2019
Public Utilities, Property, Plant and Equipment [Abstract]
Jointly Owned Electric Utility Plant (Exelon, Generation, PECO, DPL and ACE)	Jointly Owned Electric Utility Plant (Exelon, Generation, PECO, DPL and ACE) Exelon's, Generation's, PECO's, DPL's and ACE's material undivided ownership interests in jointly owned electric plants and transmission facilities at December 31, 2019 and 2018 were as follows: Nuclear Generation Transmission Quad Cities Peach Bottom Salem Nine Mile Point Unit 2 NJ/DE (a) Operator Generation Generation PSEG Generation PSEG/DPL Ownership interest 75.00 % 50.00 % 42.59 % 82.00 % various Exelon’s share at December 31, 2019: Plant in service $ 1,161 $ 1,466 $ 663 $ 951 $ 102 Accumulated depreciation 627 571 249 156 53 Construction work in progress 13 21 53 27 — Exelon’s share at December 31, 2018: Plant in service $ 1,131 $ 1,451 $ 648 $ 910 $ 103 Accumulated depreciation 587 523 227 126 53 Construction work in progress 13 15 44 56 — __________ (a) PECO, DPL and ACE own a 42.55% , 1% and 13.9% share, respectively in 151.3 miles of 500 kV lines located in New Jersey and of the Salem generating plant substation. PECO, DPL and ACE also own a 42.55% , 7.45% and 7.45% share, respectively, in 2.5 miles of 500 kV line located over the Delaware River. ACE also has a 21.78% share in a 500 kV New Freedom Switching substation. Exelon’s, Generation’s, PECO's, DPL's and ACE's undivided ownership interests are financed with their funds and all operations are accounted for as if such participating interests were wholly owned facilities. Exelon’s, Generation’s, PECO's, DPL's and ACE's share of direct expenses of the jointly owned plants are included in Purchased power and fuel and Operating and maintenance expenses in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income and in Operating and maintenance expenses in PECO's, PHI's, DPL's and ACE's Consolidated Statements of Operations and Comprehensive Income.

Asset Retirement Obligations (A

Asset Retirement Obligations (All Registrants)	12 Months Ended
	Dec. 31, 2019
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations (All Registrants)	Asset Retirement Obligations (All Registrants) 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. Generation began decommissioning the TMI nuclear plant upon permanently ceasing operations in 2019. See below section for decommissioning of Zion Station. The financial statement impact for changes in the ARO, on an individual unit basis, due to the changes in and timing of estimated cash flows generally result in a corresponding change in the unit’s ARC within Property, plant and equipment on Exelon’s and Generation’s Consolidated Balance Sheets. If the ARO decreases for a Non-Regulatory Agreement unit without any remaining ARC, the corresponding change is recorded as decrease in Operating and maintenance expense within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. The following table provides a rollforward of the nuclear decommissioning ARO reflected in Exelon’s and Generation’s Consolidated Balance Sheets, from January 1, 2018 to December 31, 2019 : Nuclear decommissioning ARO at January 1, 2018 $ 9,662 Accretion expense 478 Net decrease due to changes in, and timing of, estimated future cash flows (77 ) Costs incurred related to decommissioning plants (58 ) Nuclear decommissioning ARO at December 31, 2018 (a) (b) 10,005 Net increase due to changes in, and timing of, estimated future cash flows 864 Sale of Oyster Creek (755 ) Accretion Expense 479 Costs incurred related to decommissioning plants (89 ) Nuclear decommissioning ARO at December 31, 2019 (a) $ 10,504 __________ (a) Includes $112 million and $22 million as the current portion of the ARO at December 31, 2019 and 2018 , respectively, which is included in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets. (b) Includes $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 December 31, 2018. See Note 2 — Mergers, Acquisitions and Dispositions for additional information. The net $864 million increase in the ARO during 2019 for changes in the amounts and timing of estimated decommissioning cash flows was driven by multiple adjustments throughout the year, some with offsetting impacts. These adjustments primarily include: • An increase of approximately $780 million for changes in the assumed retirement timing probabilities for sites including certain economically challenged nuclear plants and the extension of Peach Bottom’s operating life; and • An increase of approximately $490 million for other impacts that included updated cost escalation rates, primarily for labor, equipment and materials, and current discount rates; partially offset by • Lower estimated costs to decommission TMI, Nine Mile Point, Ginna, Braidwood, Byron and LaSalle nuclear units of approximately $410 million resulting from the completion of updated cost studies. The 2019 ARO updates resulted in a decrease of $150 million in Operating and maintenance expense for the year ended December 31, 2019 within Exelon and Generation's Consolidated Statements of Operations and Comprehensive Income. See Note 6 — Early Plant Retirements for additional information regarding TMI and economically challenged nuclear plants and Note 3 - Regulatory Matters regarding the Peach Bottom second license renewal. The net $77 million decrease in the ARO during 2018 for changes in the amounts and timing of estimated decommissioning cash flows was driven by multiple adjustments throughout the year, some with offsetting impacts. These adjustments primarily include: • A decrease of approximately $205 million primarily due to lower estimated costs for the construction of interim spent fuel storage at TMI and a net decrease in estimated costs to decommission Calvert Cliffs, FitzPatrick, Limerick, and Salem nuclear units resulting from the completion of updated cost studies. There was also a decrease due to changes in decommissioning scenarios and their probabilities. These decreases were partially offset by • An increase of approximately $115 million for the impact of the early retirement and the announced pending sale of Oyster Creek which closed on July 1, 2019; and • An increase of approximately $120 million for estimated cost escalation rates, primarily for labor, energy and waste burial costs. See Note 2 — Mergers, Acquisitions and Dispositions and Note 6 — Early Plant Retirements for additional information regarding Oyster Creek. NDT Funds NDT funds have been established for each generation station unit to satisfy Generation’s nuclear decommissioning obligations. Generally, NDT funds established for a particular unit may not be used to fund the decommissioning obligations of any other unit. The NDT funds associated with Generation's nuclear units have been funded with amounts collected from the previous owners and their respective utility customers. PECO is authorized to collect funds, in revenues, for decommissioning the former PECO nuclear plants through regulated rates, and these collections are scheduled through the operating lives of the former PECO plants. The amounts collected from PECO customers are remitted to Generation and deposited into the NDT funds for the unit for which funds are collected. Every five years, PECO files a rate adjustment with the PAPUC that reflects PECO’s calculations of the estimated amount needed to decommission each of the former PECO units based on updated fund balances and estimated decommissioning costs. The rate adjustment is used to determine the amount collectible from PECO customers. On March 31, 2017, PECO filed its Nuclear Decommissioning Cost Adjustment with the PAPUC proposing an annual recovery from customers of approximately $4 million . This amount reflects a decrease from the previously approved annual collection of approximately $24 million primarily due to the removal of the collections for Limerick Units 1 and 2 as a result of the NRC approving the extension of the operating licenses for an additional 20 years. On August 8, 2017, the PAPUC approved the filing and the new rates became effective January 1, 2018. Any shortfall of funds necessary for decommissioning, determined for each generating station unit, is ultimately required to be funded by Generation, with the exception of a shortfall for the current decommissioning activities at Zion Station, where certain decommissioning activities have been transferred to a third-party (see Zion Station Decommissioning below) and the CENG units, where any shortfall is required to be funded by both Generation and EDF. Generation, through PECO, has recourse to collect additional amounts from PECO customers related to a shortfall of NDT funds for the former PECO units, subject to certain limitations and thresholds, as prescribed by an order from the PAPUC. Generally, PECO, and likewise Generation will not be allowed to collect amounts associated with the first $50 million of any shortfall of trust funds compared to decommissioning costs, as well as 5% of any additional shortfalls, on an aggregate basis for all former PECO units. The initial $50 million and up to 5% of any additional shortfalls would be borne by Generation. No recourse exists to collect additional amounts from utility customers for any of Generation's other nuclear units. With respect to the former ComEd and PECO units, any funds remaining in the NDTs after all decommissioning has been completed are required to be refunded to ComEd’s or PECO’s customers, subject to certain limitations that allow sharing of excess funds with Generation related to the former PECO units. With respect to Generation's other nuclear units, Generation retains any funds remaining after decommissioning. However, in connection with CENG's acquisition of the Nine Mile Point and Ginna plants and settlements with certain regulatory agencies, CENG is subject to certain conditions pertaining to NDT funds that, if met, could possibly result in obligations to make payments to certain third parties (clawbacks). For Nine Mile Point and Ginna, the clawback provisions are triggered only in the event that the required decommissioning activities are discontinued or not started or completed in a timely manner. In the event that the clawback provisions are triggered for Nine Mile Point, then, depending upon the triggering event, an amount equal to 50% of the total amount withdrawn from the funds for non-decommissioning activities or 50% of any excess funds in the trust funds above the amounts required for decommissioning (including spent fuel management and decommissioning) is to be paid to the Nine Mile Point sellers. In the event that the clawback provisions are triggered for Ginna, then an amount equal to any estimated cost savings realized by not completing any of the required decommissioning activities is to be paid to the Ginna sellers. Generation expects to comply with applicable regulations and timely commence and complete all required decommissioning activities. At December 31, 2019 and 2018 , Exelon and Generation had NDT funds totaling $13,353 million and $12,695 million , respectively. The NDT funds included $890 million at December 31, 2018, related to Oyster Creek NDT funds which were classified as Assets held for sale in Exelon's and Generation's Consolidated Balance Sheets. See Note 2 — Mergers, Acquisitions and Dispositions for additional information. The NDT funds include $163 million and $144 million for the current portion of the NDT at December 31, 2019 and 2018 , respectively, which are included in Other current assets in Exelon's and Generation's Consolidated Balance Sheets. See Note 23 — Supplemental Financial Information for additional information on activities of the NDT funds. Accounting Implications of the Regulatory Agreements with ComEd and PECO Based on the regulatory agreements with the ICC and PAPUC that dictate Generation’s obligations related to the shortfall or excess of NDT funds necessary for decommissioning the former ComEd units on a unit-by-unit basis and the former PECO units in total, decommissioning-related activities net of applicable taxes, including realized and unrealized gains and losses on the NDT funds and accretion of the decommissioning obligation, are generally offset within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. For the former ComEd units, decommissioning-related activities are generally offset within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income as long as the NDT funds are expected to exceed the total estimated decommissioning obligation. For the former PECO units, decommissioning-related activities are generally offset within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income regardless of whether the NDT funds are expected to exceed or fall short of the total estimated decommissioning obligation. The offset of decommissioning-related activities within the Consolidated Statement of Operations and Comprehensive Income results in an equal adjustment to the noncurrent payables to affiliates at Generation. ComEd and PECO have recorded an equal noncurrent affiliate receivable from Generation and corresponding regulatory liability. Should the expected value of the NDT fund for any former ComEd unit fall below the amount of the expected decommissioning obligation for that unit, the accounting to offset decommissioning-related activities in the Consolidated Statement of Operations and Comprehensive Income for that unit would be discontinued, the decommissioning-related activities would be recognized in the Consolidated Statements of Operations and Comprehensive Income and the adverse impact to Exelon’s and Generation’s financial statements could be material. As of December 31, 2019 , the NDT funds of each of the former ComEd units, except for Zion (see Zion Station Decommissioning below), are expected to exceed the related decommissioning obligation for each of the units. For the purposes of making this determination, the decommissioning obligation referred to is different, as described below, from the calculation used in the NRC minimum funding obligation filings based on NRC guidelines. Any changes to the PECO regulatory agreements could impact Exelon’s and Generation’s ability to offset decommissioning-related activities within the Consolidated Statement of Operations and Comprehensive Income, and the impact to Exelon’s and Generation’s financial statements could be material. The decommissioning-related activities related to the Non-Regulatory Agreement Units are reflected in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. See Note 3 — Regulatory Matters and Note 24 — Related Party Transactions for additional information regarding regulatory liabilities at ComEd and PECO and intercompany balances between Generation, ComEd and PECO reflecting the obligation to refund to customers any decommissioning-related assets in excess of the related decommissioning obligations. Zion Station Decommissioning In 2010, Generation completed an Asset Sale Agreement (ASA) under which ZionSolutions assumed responsibility for decommissioning Zion Station and Generation transferred to ZionSolutions substantially all the Zion Station’s assets, including the related NDT funds. To reduce the risk of default by ZionSolutions, EnergySolutions has provided a $25 million letter of credit to be used to fund decommissioning costs in the event the NDT assets are insufficient. EnergySolutions and its parent company have also provided a performance guarantee. Following ZionSolutions' completion of its contractual obligations and transfer of the NRC license to Generation, Generation will store the SNF at Zion Station until it is transferred to the DOE for ultimate disposal, and will complete all remaining decommissioning activities associated with the SNF dry storage facility. Generation had retained its obligation for the SNF as well as certain NDT assets to fund its obligation to maintain the SNF at Zion Station until transfer to the DOE and to complete all remaining decommissioning activities for the SNF storage facility. Any shortage of funds necessary to maintain the SNF and decommission the SNF storage facility is ultimately required to be funded by Generation. Any Zion Station NDT funds remaining after the completion of all decommissioning activities will be returned to ComEd customers in accordance with the applicable orders. NRC Minimum Funding Requirements NRC regulations require that licensees of nuclear generating facilities demonstrate reasonable assurance that funds will be available in specified minimum amounts to decommission the facility at the end of its life. The estimated decommissioning obligations as calculated using the NRC methodology differ from the ARO recorded in Generation’s and Exelon’s Consolidated Balance Sheets primarily due to differences in the type of costs included in the estimates, the basis for estimating such costs, and assumptions regarding the decommissioning alternatives to be used, potential license renewals, decommissioning cost escalation, and the growth rate in the NDT funds. Under NRC regulations, if the minimum funding requirements calculated under the NRC methodology are less than the future value of the NDT funds, also calculated under the NRC methodology, then the NRC requires either further funding or other financial guarantees. Key assumptions used in the minimum funding calculation using the NRC methodology at December 31, 2019 include: (1) consideration of costs only for the removal of radiological contamination at each unit; (2) the option on a unit-by-unit basis to use generic, non-site specific cost estimates; (3) consideration of only one decommissioning scenario for each unit; (4) the plants cease operation at the end of their current license lives (with no assumed license renewals for those units that have not already received renewals); (5) the assumption of current nominal dollar cost estimates that are neither escalated through the anticipated period of decommissioning, nor discounted using the CARFR; and (6) assumed annual after-tax returns on the NDT funds of 2% ( 3% for the former PECO units, as specified by the PAPUC). In contrast, the key criteria and assumptions used by Generation to determine the ARO and to forecast the target growth in the NDT funds at December 31, 2019 include: (1) the use of site specific cost estimates that are updated at least once every five years; (2) the inclusion in the ARO estimate of all legally unavoidable costs required to decommission the unit (e.g., radiological decommissioning and full site restoration for certain units, on-site spent fuel maintenance and storage subsequent to ceasing operations and until DOE acceptance, and disposal of certain low-level radioactive waste); (3) the consideration of multiple scenarios where decommissioning and site restoration activities, as applicable, are completed under possible scenarios ranging from 10 to 70 years after the cessation of plant operations; (4) the consideration of multiple end of life scenarios; (5) the measurement of the obligation at the present value of the future estimated costs and an annual average accretion of the ARO of approximately 5% through a period of approximately 30 years after the end of the extended lives of the units; and (6) an estimated targeted annual pre-tax return on the NDT funds of 5.4% to 6.5% (as compared to a historical 5-year annual average pre-tax return of approximately 6.7% ). Generation is required to provide to the NRC a biennial report by unit (annually for units that have been retired or are within five years of the current approved license life), based on values as of December 31, addressing Generation’s ability to meet the NRC minimum funding levels. Depending on the value of the trust funds, Generation may be required to take steps, such as providing financial guarantees through letters of credit or parent company guarantees or making additional contributions to the trusts, which could be significant, to ensure that the trusts are adequately funded and that NRC minimum funding requirements are met. As a result, Exelon’s and Generation’s cash flows and financial positions may be significantly adversely affected. 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 NDT Funds section above for additional information. Generation will file its next annual decommissioning funding status report with the NRC by March 31, 2020 for shutdown reactors, reactors within five years of shutdown except for Zion Station which is included in a separate report to the NRC submitted by EnergySolutions (see Zion Station Decommissioning above). This report will reflect the status of decommissioning funding assurance as of December 31, 2019 and will include an update for the retirement of TMI in 2019. A shortfall at any unit could necessitate that Exelon post a parental guarantee for Generation's share of the funding assurance. However, the amount of any required guarantee will ultimately depend on the decommissioning approach adopted, the associated level of costs, and the decommissioning trust fund investment performance going forward. As the future values of trust funds change due to market conditions, the NRC minimum funding status of Generation’s units will change. In addition, if changes occur to the regulatory agreement with the PAPUC that currently allows amounts to be collected from PECO customers for decommissioning the former PECO units, the NRC minimum funding status of those plants could change at subsequent NRC filing dates. Non-Nuclear Asset Retirement Obligations (All Registrants) Generation has AROs for plant closure costs associated with its fossil and renewable generating facilities, including asbestos abatement, removal of certain storage tanks, restoring leased land to the condition it was in prior to construction of renewable generating stations and other decommissioning-related activities. The Utility Registrants have AROs primarily associated with the abatement and disposal of equipment and buildings contaminated with asbestos and PCBs. See Note 1 — Significant Accounting Policies for additional information on the Registrants’ accounting policy for AROs. The following table provides a rollforward of the non-nuclear AROs reflected in the Registrants’ Consolidated Balance Sheets from January 1, 2018 to December 31, 2019 : Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Non-nuclear AROs at January 1, 2018 $ 384 $ 197 $ 113 $ 27 $ 24 $ 16 $ 3 $ 10 $ 3 Net increase due to changes in, and timing of, estimated future cash flows (a) 80 35 7 — 2 36 34 1 1 Accretion expense (b) 16 10 4 1 1 — — — — Asset divestitures (3 ) (3 ) — — — — — — — Payments (6 ) (1 ) (3 ) — (2 ) — — — — Non-nuclear AROs at December 31, 2018 471 238 121 28 25 52 37 11 4 Net (decrease) increase due to changes in, and timing of, estimated future cash flows 17 7 8 — (2 ) 4 3 1 — Development projects 2 2 — — — — — — — Accretion expense (b) 16 12 1 1 1 1 1 — — Asset divestitures (42 ) (42 ) — — — — — — — Payments (4 ) (1 ) (1 ) (1 ) (1 ) — — — — Non-nuclear AROs at December 31, 2019 $ 460 $ 216 $ 129 $ 28 $ 23 $ 57 $ 41 $ 12 $ 4 __________ (a) In 2018, Pepco recorded an increase of $22 million in Operating and maintenance expense primarily related to asbestos identified at its Buzzard Point property as part of an annual ARO study. Buzzard Point is a waterfront property in the District of Columbia occupied by an active substation and former Pepco operated steam plant building, which Pepco retired and closed in 1981. (b) For ComEd and PECO, the majority of the accretion is recorded as an increase to a regulatory asset due to the associated regulatory treatment.

Leases (All Registrants)

Leases (All Registrants)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Lessee, Operating Leases [Text Block]	Lessee The Registrants have operating leases for which they are the lessees. The following tables outline the significant types of operating lease 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 1-86 1-36 1-5 1-14 1-86 1-12 1-12 1-12 1-6 Options to extend the term 3-30 3-30 5 N/A N/A 3-30 5 3-30 N/A Options to terminate within 1-13 1 3 N/A 2 N/A N/A N/A N/A The components of lease costs for the year ended December 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating lease costs $ 320 $ 222 $ 3 $ 1 $ 33 $ 48 $ 12 $ 14 $ 7 Variable lease costs 300 282 2 — 2 6 2 2 1 Short-term lease costs 19 19 — — — — — — — Total lease costs (a) $ 639 $ 523 $ 5 $ 1 $ 35 $ 54 $ 14 $ 16 $ 8 __________ (a) Excludes $51 million , $44 million , $7 million and $7 million of sublease income recorded at Exelon, Generation, PHI and DPL. The following table presents the Registrants' rental expense under the prior lease accounting guidance for the years ended December 31, 2018 and 2017 : Exelon Generation (a) ComEd PECO BGE PHI Pepco DPL ACE 2018 $ 670 $ 558 $ 7 $ 10 $ 35 $ 48 $ 10 $ 13 $ 8 2017 709 578 9 9 32 63 11 16 14 __________ (a) Includes contingent operating lease payments associated with contracted generation agreements that are not included in the minimum future operating lease payments above. Payments made under Generation's contracted generation lease agreements totaled $493 million and $508 million during 2018 and 2017, respectively. The following table provides additional information regarding the presentation of operating ROU assets and lease liabilities within the Registrants’ Consolidated Balance Sheets as of December 31, 2019 : Exelon (a) Generation (a) ComEd PECO BGE PHI Pepco DPL ACE Operating lease ROU assets Other deferred debits and other assets $ 1,305 $ 895 $ 9 $ 2 $ 77 $ 273 $ 56 $ 63 $ 18 Operating lease liabilities Other current liabilities 225 157 3 — 32 31 6 9 4 Other deferred credits and other liabilities 1,307 925 8 1 50 254 51 65 14 Total operating lease liabilities $ 1,532 $ 1,082 $ 11 $ 1 $ 82 $ 285 $ 57 $ 74 $ 18 __________ (a) Exelon's and Generation's operating ROU assets and lease liabilities include $515 million and $664 million , respectively, related to contracted generation. The weighted average remaining lease terms, in years, and discount rates for operating leases as of December 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Remaining lease term 10.1 10.6 4.6 4.4 5.4 9.0 9.8 9.7 4.7 Discount rate 4.6 % 4.8 % 3.0 % 3.2 % 3.6 % 4.2 % 4.0 % 4.0 % 3.6 % Future minimum lease payments for operating leases as of December 31, 2019 were as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2020 $ 287 $ 203 $ 3 $ — $ 34 $ 42 $ 8 $ 11 $ 5 2021 243 162 4 1 31 41 8 11 4 2022 177 113 2 — 16 38 8 10 4 2023 145 100 1 — 1 37 7 9 3 2024 140 97 1 — — 35 5 9 2 Remaining years 976 741 1 — 18 153 34 41 2 Total 1,968 1,416 12 1 100 346 70 91 20 Interest 436 334 1 — 18 61 13 17 2 Total operating lease liabilities $ 1,532 $ 1,082 $ 11 $ 1 $ 82 $ 285 $ 57 $ 74 $ 18 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 year ended December 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating cash flows from operating leases $ 287 $ 206 $ 3 $ — $ 33 $ 37 $ 9 $ 6 $ 5 ROU assets obtained in exchange for lease obligations for the year ended December 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating leases $ 52 $ 14 $ 6 $ — $ 2 $ (3 ) $ (1 ) $ (2 ) $ (1 )
Lessor, Operating Leases [Text Block]	Lessor 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 1-83 1-32 1-17 1-83 23 1-13 1-6 12-13 1-2 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 year ended December 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating lease income $ 54 $ 47 $ — $ — $ — $ 5 $ — $ 4 $ — Variable lease income $ 261 $ 258 $ — $ — $ — $ 3 $ — $ 3 $ — Future minimum lease payments to be recovered under operating leases as of December 31, 2019 were as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2020 $ 51 $ 46 $ — $ — $ — $ 4 $ — $ 3 $ — 2021 51 45 — — — 4 1 3 — 2022 50 45 — — — 4 — 3 — 2023 49 44 — — — 5 — 4 — 2024 48 44 — — — 4 — 4 — Remaining years 265 226 1 3 1 34 — 34 — Total $ 514 $ 450 $ 1 $ 3 $ 1 $ 55 $ 1 $ 51 $ —

Asset Impairments (Exelon, Gene

Asset Impairments (Exelon, Generation and PHI)	12 Months Ended
	Dec. 31, 2019
Impairment or Disposal of Tangible Assets Disclosure [Abstract]
Asset Impairments (Exelon, Generation and PHI)	Asset Impairments (Exelon, Generation and PHI) The Registrants evaluate the carrying value of long-lived assets or asset groups for recoverability whenever events or changes in circumstances indicate that the carrying value of those assets may not be recoverable. Indicators of impairment may include a deteriorating business climate, including, but not limited to, declines in energy prices, condition of the asset, specific regulatory disallowance, or plans to dispose of a long-lived asset significantly before the end of its useful life. The Registrants determine if long-lived assets or asset groups are impaired by comparing the undiscounted expected future cash flows to the carrying value. When the undiscounted cash flow analysis indicates a long-lived asset or asset group is not recoverable, the amount of the impairment loss is determined by measuring the excess of the carrying amount of the long-lived asset or asset group over its fair value. 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. A variation in the assumptions used could lead to a different conclusion regarding the recoverability of an asset or asset group and, thus, could potentially result in material future impairments of the Registrant's long-lived assets. Equity Method Investments in Certain Distributed Energy Companies (Exelon and Generation) In the third quarter of 2019, Generation’s equity method investments in certain distributed energy companies were fully impaired due to an other-than-temporary decline in market conditions and underperforming projects. Exelon and Generation recorded a pre-tax impairment charge of $164 million in Equity in losses of unconsolidated affiliates and an offsetting pre-tax $96 million in Net income attributable to noncontrolling interests in their Consolidated Statements of Operations and Comprehensive Income. As a result, Generation accelerated the amortization of investment tax credits associated with these companies and Exelon and Generation recorded a benefit of $46 million in Income taxes. The impairment charge and the accelerated amortization of investment tax credits resulted in a net $15 million decrease to Exelon’s and Generation’s earnings. See Note 22 — Variable Interest Entities for additional information. Antelope Valley Solar Facility (Exelon and Generation) Generation’s Antelope Valley, a 242 MW solar facility in Lancaster, CA, sells all of its output to PG&E through a PPA. As of December 31, 2019 , Generation had approximately $725 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 ba nkruptcy 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 $1,893 million of additional net long-lived assets as of December 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 16 — Debt and Credit Agreements for additional information on the PG&E bankruptcy. New England Asset Group (Exelon and Generation) During the first quarter of 2018, Mystic Unit 9 did not clear in the ISO-NE capacity auction for the 2021 - 2022 planning year. On March 29, 2018, Generation notified ISO-NE of the early retirement of its Mystic Generating Station's Units 7, 8, 9 and the Mystic Jet Unit (Mystic Generating Station assets) absent regulatory reforms. These events suggested that the carrying value of its New England asset group may be impaired. Generation completed a comprehensive review of the estimated undiscounted future cash flows of the New England asset group and no impairment charge was required. Further developments such as the failure of ISO-NE to adopt long-term solutions for reliability and fuel security could potentially result in material future impairments of the New England asset group. See Note 6 — Early Plant Retirements for additional information. District of Columbia Sponsorship (Exelon and PHI) In the third quarter of 2015, PHI entered into a sponsorship agreement with the District of Columbia for future sponsorship rights associated with public property within the District of Columbia, which Exelon and PHI had recorded as a finite-lived intangible asset as of December 31, 2016. The specific sponsorship rights were to be determined through future negotiations. In the fourth quarter of 2017, based upon the lack of available sponsorship opportunities at that time, the asset was written off and a pre-tax impairment charge of $25 million was recorded within Operating and maintenance expense in Exelon’s and PHI's Consolidated Statements of Operations and Comprehensive Income. ExGen Texas Power (Exelon and Generation) On May 2, 2017, EGTP entered into a consent agreement with its lenders to initiate the sale of the assets of its wholly owned subsidiaries. As a result, Exelon and Generation classified certain of EGTP's assets and liabilities as held for sale at their respective fair values less costs to sell and recorded a pre-tax impairment charge in 2017 of $460 million within Operating and maintenance expense in their Consolidated Statements of Operations and Comprehensive Income. On November 7, 2017, EGTP and its wholly owned subsidiaries filed voluntary petitions for relief under Chapter 11 of Title 11 of the United States Code in the United States Bankruptcy Court for the District of Delaware and, as a result, Exelon and Generation deconsolidated EGTP's assets and liabilities from their consolidated financial statements. See Note 2 — Mergers, Acquisitions and Dispositions for additional information.

Intangible Assets (Exelon, Gene

Intangible Assets (Exelon, Generation, ComEd, PHI, Pepco, DPL, and ACE)	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets (All Registrants)	Intangible Assets (Exelon, Generation, ComEd, PHI, Pepco, DPL and ACE) Goodwill The following table presents the gross amount of goodwill, accumulated impairment loss and carrying amount of goodwill of Exelon, ComEd and PHI as of December 31, 2019 and 2018 . There were no additions, impairments or measurement period adjustments during the years ended December 31, 2019 and 2018 . Gross amount Accumulated impairment loss Carrying amount Exelon $ 8,660 $ 1,983 $ 6,677 ComEd (a) 4,608 1,983 2,625 PHI (b) 4,005 — 4,005 __________ (a) Reflects goodwill recorded in 2000 from the PECO/Unicom merger (predecessor parent company of ComEd). (b) Reflects goodwill recorded in 2016 from the PHI merger. Goodwill is not amortized, but is subject to an assessment for impairment at least annually, or more frequently if events occur or circumstances change that would more likely than not reduce the fair value of ComEd's and PHI's reporting units below their carrying amounts. A reporting unit is an operating segment or one level below an operating segment (known as a component) and is the level at which goodwill is tested for impairment. A component of an operating segment is a reporting unit if the component constitutes a business for which discrete financial information is available and its operating results are regularly reviewed by segment management. ComEd has a single operating segment. PHI's operating segments are Pepco, DPL and ACE. See Note 5 — Segment Information for additional information. There is no level below these operating segments for which operating results are regularly reviewed by segment management. Therefore, the ComEd, Pepco, DPL and ACE operating segments are also considered reporting units for goodwill impairment testing purposes. Exelon's and ComEd's $2.6 billion of goodwill has been assigned entirely to the ComEd reporting unit, while Exelon's and PHI's $4.0 billion of goodwill has been assigned to the Pepco, DPL and ACE reporting units in the amounts of $2.1 billion , $1.4 billion and $0.5 billion , respectively. Entities assessing goodwill for impairment have the option of first performing a qualitative assessment to determine whether a quantitative assessment is necessary. As part of the qualitative assessments, Exelon, ComEd and PHI evaluate, among other things, management's best estimate of projected operating and capital cash flows for their businesses, outcomes of recent regulatory proceedings, changes in certain market conditions, including the discount rate and regulated utility peer EBITDA multiples, and the passing margin from their last quantitative assessments performed. If an entity bypasses the qualitative assessment, a quantitative two-step, fair value-based test is performed. The first step compares the fair value of the reporting unit to its carrying amount, including goodwill. If the carrying amount of the reporting unit exceeds its fair value, the second step is performed. The second step requires an allocation of fair value to the individual assets and liabilities using purchase price allocation authoritative guidance in order to determine the implied fair value of goodwill. Application of the goodwill impairment test requires management judgment, including the identification of reporting units and determining the fair value of the reporting unit, which management estimates using a weighted combination of a discounted cash flow analysis and a market multiples analysis. Significant assumptions used in these fair value analyses include discount and growth rates, utility sector market performance and transactions, projected operating and capital cash flows for ComEd's, Pepco's, DPL's and ACE's businesses and the fair value of debt. In applying the second step, if needed, management must estimate the fair value of specific assets and liabilities of the reporting unit. 2019 and 2018 Goodwill Impairment Assessment. ComEd and PHI qualitatively determined that it was more likely than not that the fair values of their reporting units exceeded their carrying values and, therefore, did not perform quantitative assessments as of November 1, 2019 and 2018 for ComEd and as of November 1, 2019 for PHI. The last quantitative assessments performed were as of November 1, 2016 for ComEd and November 1, 2018 for PHI. PHI performed a quantitative test for its 2018 annual goodwill impairment assessment as of November 1, 2018. The first step of the test comparing the estimated fair values of the Pepco, DPL and ACE reporting units to their carrying values, including goodwill, indicated no impairments of goodwill; therefore, no second step was required. While the annual assessments indicated no impairments, certain assumptions used to estimate reporting unit fair values are highly sensitive to changes. Adverse regulatory actions or changes in significant assumptions could potentially result in future impairments of Exelon's, ComEd's and PHI’s goodwill, which could be material. Based on the results of the last quantitative goodwill test performed, the estimated fair values of the ComEd, Pepco, DPL and ACE reporting units would have needed to decrease by more than 30% , 30% , 20% and 30% , respectively, for ComEd and PHI to fail the first step of their respective impairment tests. Other Intangible Assets and Liabilities Exelon’s, Generation’s, ComEd’s and PHI's other intangible assets and liabilities, included in Unamortized energy contract assets and liabilities and Other deferred debits and other assets in their Consolidated Balance Sheets, consisted of the following as of December 31, 2019 and 2018 . The intangible assets and liabilities shown below are amortized on a straight line basis, except for unamortized energy contracts which are amortized in relation to the expected realization of the underlying cash flows: December 31, 2019 December 31, 2018 Gross Accumulated Amortization Net Gross Accumulated Amortization Net Generation Unamortized Energy Contracts 1,967 (1,612 ) 355 1,957 (1,588 ) 369 Customer Relationships 343 (190 ) 153 325 (162 ) 163 Trade Name 243 (193 ) 50 243 (171 ) 72 ComEd Chicago Settlement Agreements 162 (155 ) 7 162 (148 ) 14 PHI Unamortized Energy Contracts (1,515 ) 1,073 (442 ) (1,515 ) 954 (561 ) Exelon Corporate Software License 95 (44 ) 51 95 (34 ) 61 Exelon $ 1,295 $ (1,121 ) $ 174 $ 1,267 $ (1,149 ) $ 118 The following table summarizes the amortization expense related to intangible assets and liabilities for each of the years ended December 31, 2019 , 2018 and 2017 : For the Years Ended December 31, Exelon (a)(b) Generation (a) ComEd PHI (b) 2019 $ (28 ) $ 74 $ 7 $ (119 ) 2018 (109 ) 63 7 (188 ) 2017 (237 ) 83 7 (336 ) __________ (a) At Exelon and Generation, amortization of unamortized energy contracts totaling $21 million , $14 million and $35 million for the years ended December 31, 2019 , 2018 and 2017 , respectively, was recorded in Operating revenues or Purchased power and fuel expense in their Consolidated Statements of Operations and Comprehensive Income. (b) At Exelon and PHI, amortization of the unamortized energy contract fair value adjustment amounts and the corresponding offsetting regulatory asset and liability amounts are amortized through Purchased power and fuel expense in their Consolidated Statements of Operations and Comprehensive Income. The following table summarizes the estimated future amortization expense related to intangible assets and liabilities as of December 31, 2019 : For the Years Ending December 31, Exelon Generation ComEd PHI 2020 $ (13 ) $ 85 $ 7 $ (115 ) 2021 2 84 — (92 ) 2022 (21 ) 58 — (89 ) 2023 (18 ) 53 — (81 ) 2024 22 50 — (38 ) Renewable Energy Credits (Exelon and Generation) Exelon’s and Generation’s RECs are included in Other current assets and Other deferred debits and other assets in the Consolidated Balance Sheets. Purchased RECs are recorded at cost on the date they are purchased. The cost of RECs purchased on a stand-alone basis is based on the transaction price, while the cost of RECs acquired through PPAs represents the difference between the total contract price and the market price of energy at contract inception. Generally, revenue for RECs that are sold to a counterparty under a contract that specifically identifies a power plant is recognized at a point in time when the power is produced. This includes both bundled and unbundled REC sales. Otherwise, the revenue is recognized upon physical transfer of the REC to the customer. The following table presents the current and noncurrent Renewable Energy Credits as of December 31, 2019 and 2018 : As of December 31, 2019 As of December 31, 2018 Exelon Generation Exelon Generation Current REC's 345 336 279 270 Noncurrent REC's 86 86 52 52

Income Taxes (All Registrants)

Income Taxes (All Registrants)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes (All Registrants)	Income Taxes (All Registrants) Components of Income Tax Expense or Benefit Income tax expense (benefit) from continuing operations is comprised of the following components: For the Year Ended December 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Included in operations: Federal Current $ 85 $ 147 $ 59 $ 45 $ (51 ) $ 43 $ 16 $ 29 $ (3 ) Deferred 489 346 15 20 95 (34 ) (6 ) (21 ) (6 ) Investment tax credit amortization (72 ) (69 ) (2 ) — — (1 ) — — — State Current 5 10 (5 ) — — 3 — — — Deferred 267 82 96 — 35 27 6 14 9 Total $ 774 $ 516 $ 163 $ 65 $ 79 $ 38 $ 16 $ 22 $ — For the Year Ended December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Included in operations: Federal Current $ 226 $ 337 $ (63 ) $ 11 $ (5 ) $ (4 ) $ 28 $ (3 ) $ (14 ) Deferred (99 ) (347 ) 145 10 47 23 (22 ) 13 18 Investment tax credit amortization (24 ) (21 ) (2 ) — — (1 ) — — — State Current (1 ) 6 (29 ) 1 — 7 — — — Deferred 16 (83 ) 117 (16 ) 32 8 5 12 8 Total $ 118 $ (108 ) $ 168 $ 6 $ 74 $ 33 $ 11 $ 22 $ 12 For the Year Ended December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Included in operations: Federal Current $ 194 $ 584 $ (191 ) $ 71 $ 74 $ (60 ) $ (20 ) $ (24 ) $ (12 ) Deferred (470 ) (2,005 ) 523 28 101 251 115 82 34 Investment tax credit amortization (25 ) (21 ) (2 ) — (1 ) (1 ) — — — State Current 14 65 (49 ) 14 (5 ) (4 ) (2 ) — — Deferred 161 1 136 (9 ) 49 31 12 13 4 Total $ (126 ) $ (1,376 ) $ 417 $ 104 $ 218 $ 217 $ 105 $ 71 $ 26 Rate Reconciliation The effective income tax rate from continuing operations varies from the U.S. federal statutory rate principally due to the following: For the Year Ended December 31, 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 5.4 3.8 8.5 — 6.4 4.7 2.0 6.8 7.0 Qualified NDT fund income 5.9 12.3 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.5 ) (3.0 ) (0.2 ) — (0.1 ) (0.2 ) (0.1 ) (0.2 ) (0.3 ) Plant basis differences (1.4 ) — — (7.2 ) (1.2 ) (1.2 ) (1.8 ) (0.4 ) (0.7 ) Production tax credits and other credits (3.1 ) (4.8 ) (1.2 ) — (1.3 ) (0.2 ) (0.1 ) — (0.1 ) Noncontrolling interests (0.6 ) (1.2 ) — — — — — — — Excess deferred tax amortization (5.5 ) — (9.7 ) (2.8 ) (6.8 ) (17.5 ) (15.1 ) (14.2 ) (27.0 ) Other (0.8 ) (1.2 ) 0.8 — — 0.8 0.3 — 0.1 Effective income tax rate 19.4 % 26.9 % 19.2 % 11.0 % 18.0 % 7.4 % 6.2 % 13.0 % — % For the Year Ended December 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 0.5 (16.6 ) 8.3 (2.6 ) 6.6 2.9 2.0 6.7 7.4 Qualified NDT fund income (1.9 ) (11.8 ) — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.2 ) (6.5 ) (0.2 ) (0.1 ) (0.1 ) (0.2 ) (0.1 ) (0.3 ) (0.4 ) Plant basis differences (3.5 ) — (0.2 ) (14.1 ) (1.3 ) (1.6 ) (2.8 ) (0.3 ) (0.5 ) Production tax credits and other credits (2.2 ) (13.5 ) — — — — — — — Noncontrolling interests (1.0 ) (6.1 ) — — — — — — — Excess deferred tax amortization (8.3 ) — (9.1 ) (3.2 ) (8.0 ) (14.8 ) (15.3 ) (12.0 ) (14.9 ) Tax Cuts and Jobs Act of 2017 0.9 2.7 (0.1 ) — — 0.1 — — — Other 1.0 1.3 0.5 0.3 0.9 0.4 0.3 0.4 1.2 Effective income tax rate 5.3 % (29.5 )% 20.2 % 1.3 % 19.1 % 7.8 % 5.1 % 15.5 % 13.8 % For the Year Ended December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 2.2 2.9 5.7 0.6 5.4 4.8 3.1 5.4 5.6 Qualified NDT fund income 3.8 9.9 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.9 ) (2.1 ) (0.2 ) (0.1 ) (0.1 ) (0.2 ) (0.1 ) (0.2 ) (0.4 ) Plant basis differences (a) (1.7 ) — 0.3 (13.8 ) 0.1 1.1 (0.4 ) 2.0 3.6 Production tax credits and other credits (1.8 ) (4.7 ) — — — — — — — Like-kind exchange (1.2 ) — 1.3 — — — — — — Merger expenses (3.6 ) (1.2 ) — — — (9.6 ) (6.4 ) (7.8 ) (19.8 ) FitzPatrick bargain purchase gain (2.2 ) (5.6 ) — — — — — — — Tax Cuts and Jobs Act of 2017 (b) (33.1 ) (128.3 ) 0.1 (2.3 ) 0.9 6.4 2.8 2.5 1.6 Other 0.2 (0.5 ) 0.2 (0.1 ) 0.2 0.5 0.7 0.1 (0.4 ) Effective income tax rate (3.3 )% (94.6 )% 42.4 % 19.3 % 41.5 % 38.0 % 34.7 % 37.0 % 25.2 % __________ (a) Includes the charges related to the transmission-related income tax regulatory asset for Exelon, ComEd, BGE, PHI, Pepco, DPL and ACE of $ 35 million , $ 3 million , $ 5 million , $ 27 million , $ 14 million , $ 6 million and $ 7 million , respectively. See Note 3 - Regulatory Matters for additional information. (b) As a result of TCJA, Generation recorded a net decrease to income tax expense, while the Utility Registrants recorded corresponding regulatory liabilities or assets to the extent such amounts are probable of settlement or recovery through customer rates and an adjustment to income tax expense for all other amounts. Tax Differences and Carryforwards The tax effects of temporary differences and carryforwards, which give rise to significant portions of the deferred tax assets (liabilities), as of December 31, 2019 and 2018 are presented below: As of December 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Plant basis differences $ (13,413 ) $ (2,814 ) $ (4,197 ) $ (1,978 ) $ (1,578 ) $ (2,681 ) $ (1,204 ) $ (753 ) $ (687 ) Accrual based contracts 61 (43 ) — — — 104 — — — Derivatives and other financial instruments 165 88 84 — — 2 — — — Deferred pension and postretirement obligation 1,504 (220 ) (270 ) (28 ) (28 ) (89 ) (75 ) (42 ) (10 ) Nuclear decommissioning activities (503 ) (503 ) — — — — — — — Deferred debt refinancing costs 183 20 (7 ) — (3 ) 142 (3 ) (2 ) (1 ) Regulatory assets and liabilities (884 ) — 183 (169 ) 157 (10 ) 55 88 77 Tax loss carryforward 240 55 — 25 49 93 13 44 31 Tax credit carryforward 892 897 — — — — — — — Investment in partnerships (830 ) (808 ) — — — — — — — Other, net 926 236 196 70 10 181 85 12 16 Deferred income tax liabilities (net) $ (11,659 ) $ (3,092 ) $ (4,011 ) $ (2,080 ) $ (1,393 ) $ (2,258 ) $ (1,129 ) $ (653 ) $ (574 ) Unamortized investment tax credits (668 ) (648 ) (10 ) (1 ) (3 ) (7 ) (2 ) (2 ) (3 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (12,327 ) $ (3,740 ) $ (4,021 ) $ (2,081 ) $ (1,396 ) $ (2,265 ) $ (1,131 ) $ (655 ) $ (577 ) As of December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Plant basis differences $ (12,533 ) $ (2,495 ) $ (4,059 ) $ (1,862 ) $ (1,399 ) $ (2,577 ) $ (1,148 ) $ (743 ) $ (645 ) Accrual based contracts 117 (44 ) — — — 161 — — — Derivatives and other financial instruments 89 35 69 — — 3 — — — Deferred pension and postretirement obligation 1,435 (188 ) (255 ) (26 ) (26 ) (102 ) (78 ) (46 ) (14 ) Nuclear decommissioning activities (351 ) (351 ) — — — — — — — Deferred debt refinancing costs 234 23 (7 ) — (3 ) 187 (4 ) (2 ) (1 ) Regulatory assets and liabilities (740 ) — 300 (129 ) 172 (81 ) 67 96 83 Tax loss carryforward 237 78 — 18 25 96 12 52 26 Tax credit carryforward 811 816 — — — — — — — Investment in partnerships (797 ) (775 ) — — — — — — — Other, net 934 239 151 67 12 196 98 17 19 Deferred income tax liabilities (net) $ (10,564 ) $ (2,662 ) $ (3,801 ) $ (1,932 ) $ (1,219 ) $ (2,117 ) $ (1,053 ) $ (626 ) $ (532 ) Unamortized investment tax credits (724 ) (700 ) (12 ) (1 ) (3 ) (8 ) (2 ) (2 ) (3 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (11,288 ) $ (3,362 ) $ (3,813 ) $ (1,933 ) $ (1,222 ) $ (2,125 ) $ (1,055 ) $ (628 ) $ (535 ) The following table provides Exelon’s, Generation’s, PECO’s, BGE’s, PHI’s, Pepco’s, DPL’s and ACE’s carryforwards, which are presented on a post-apportioned basis, and any corresponding valuation allowances as of December 31, 2019 . ComEd does not have net operating losses or credit carryforwards for the year ended December 31, 2019 . Exelon Generation PECO BGE PHI Pepco DPL ACE Federal Federal general business credits carryforwards (a) $ 891 $ 897 $ — $ — $ — $ — $ — $ — State State net operating losses 3,986 1,142 312 762 1,360 202 654 438 Deferred taxes on state tax attributes (net) 264 78 25 50 93 13 44 31 Valuation allowance on state tax attributes 26 24 — 1 — — — — Year in which net operating loss or credit carryforwards will begin to expire 2025 2029 2031 2026 2028 2028 2030 2031 __________ (a) Exelon's and Generation's federal general business credit carryforwards will begin expiring in 2034 . Tabular Reconciliation of Unrecognized Tax Benefits The following table presents changes in unrecognized tax benefits, by Registrant. Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Balance at January 1, 2017 $ 916 $ 490 $ (12 ) $ — $ 120 $ 172 $ 80 $ 37 $ 22 Increases based on tax positions prior to 2017 28 — 14 — — 14 — — 14 Decreases based on tax positions prior to 2017 (a) (196 ) (17 ) — — — (61 ) (21 ) (16 ) (22 ) Decrease from settlements with taxing authorities (5 ) (5 ) — — — — — — — Balance at December 31, 2017 743 468 2 — 120 125 59 21 14 Change to positions that only affect timing 15 15 — — — — — — — Increases based on tax positions prior to 2018 30 21 — — — 8 7 1 — Decreases based on tax positions prior to 2018 (b) (251 ) (36 ) — — (120 ) (88 ) (66 ) (22 ) — Decrease from settlements with taxing authorities (53 ) (53 ) — — — — — — — Decreases from expiration of statute of limitations (7 ) (7 ) — — — — — — — Balance at December 31, 2018 477 408 2 — — 45 — — 14 Change to positions that only affect timing 26 12 3 1 4 3 2 1 — Increases based on tax positions related to 2019 2 1 — — — — — — — Increases based on tax positions prior to 2019 34 19 3 2 3 — — — — Decreases based on tax positions prior to 2019 (3 ) (3 ) — — — — — — — Decrease from settlements with taxing authorities (29 ) 4 (2 ) — — — — — — Balance at December 31, 2019 $ 507 $ 441 $ 6 $ 3 $ 7 $ 48 $ 2 $ 1 $ 14 __________ (a) Exelon established a liability for an uncertain tax position associated with the tax deductibility of certain merger commitments incurred by Exelon in connection with the acquisitions of Constellation and PHI. In 2017, as a part of its examination of Exelon's return, the IRS National Office issued guidance concurring with Exelon's position that the merger commitments were deductible. As a result, Exelon, Generation, PHI, Pepco, DPL, and ACE decreased their liability for unrecognized tax benefits by $146 million , $19 million , $59 million , $21 million , $16 million and $22 million , respectively, resulting in a benefit to Income taxes on Exelon's, Generation's, PHI's, Pepco's, DPL's, and ACE's Consolidated Statements of Operations and Comprehensive Income and corresponding decreases in their effective tax rates. (b) Exelon, Generation, BGE, PHI, Pepco, and DPL decreased their unrecognized state tax benefits primarily due to the receipt of favorable guidance with respect to the deductibility of certain depreciable fixed assets. The recognition of the tax benefits related to BGE, PHI, Pepco, and DPL was offset by corresponding regulatory liabilities and that portion had no immediate impact to their effective tax rate. Like-Kind Exchange 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. Recognition of unrecognized tax benefits The following table presents Exelon's, Generation's and PHI's unrecognized tax benefits that, if recognized, would decrease the effective tax rate. ComEd's, PECO's, BGE's, Pepco's, DPL's and ACE's amounts are not material. Exelon Generation PHI (a) December 31, 2019 $ 462 $ 429 $ 32 December 31, 2018 463 408 31 December 31, 2017 523 461 32 __________ (a) PHI has $ 21 million of unrecognized state tax benefits that, if recognized, $ 14 million would be in the form of a net operating loss carryforward, which is expected to require a full valuation allowance based on present circumstances. The following table presents Exelon's, BGE's, PHI's, Pepco's, DPL's and ACE’s unrecognized tax benefits that, if recognized, may be included in future base rates and that portion would have no impact to the effective tax rate. ComEd's and PECO's amounts are not material. Exelon BGE PHI Pepco DPL ACE December 31, 2019 $ 19 $ 1 $ 14 $ — $ — $ 14 December 31, 2018 14 — 14 — — 14 December 31, 2017 214 120 94 59 21 14 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 The following table represents Exelon's, Generation's and ACE's 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, refund claims, and the outcomes of pending court cases as of December 31, 2019 . ComEd's, PECO's, BGE's, PHI's, Pepco's and DPL's amounts are not material. Exelon (a) Generation (a) ACE (b) $ 425 $ 411 $ 14 __________ (a) Exelon and Generation have $ 411 million that, if recognized, would decrease the effective tax rate. (b) The unrecognized tax benefit related to ACE, if recognized, may be included in future base rates and that portion would have no impact to the effective tax rate. Total amounts of interest and penalties recognized The following table represents the net interest and penalties receivable (payable) related to tax positions reflected in Exelon's Consolidated Balance Sheets. Generation's and the Utility Registrants' amounts are not material. Net interest and penalties receivable as of Exelon December 31, 2019 $ 318 December 31, 2018 219 The Registrants did not record material interest and penalty expense related to tax positions reflected in their Consolidated Balance Sheets. Interest expense and penalty expense are recorded in Interest expense, net and Other, net, respectively, in Other income and deductions in the Registrants' Consolidated Statements of Operations and Comprehensive Income. Description of tax years open to assessment by major jurisdiction Major Jurisdiction Open Years Registrants Impacted Federal consolidated income tax returns 2002-2018 All Registrants PHI Holdings and subsidiaries consolidated federal income tax returns 2016 Exelon, Generation, PHI, Pepco, DPL, ACE Delaware separate corporate income tax returns Same as federal DPL District of Columbia combined corporate income tax returns 2016-2018 Exelon, PHI, Pepco Illinois unitary corporate income tax returns 2010-2018 Exelon, Generation, ComEd Maryland separate company corporate net income tax returns Same as federal BGE, Pepco, DPL New Jersey separate corporate income tax returns 2013-2018 Exelon, Generation New Jersey separate corporate income tax returns 2014-2018 ACE New York combined corporate income tax returns 2010-March 2012 Exelon, Generation New York combined corporate income tax returns 2011-2018 Exelon, Generation Pennsylvania separate corporate income tax returns 2011-2018 Exelon, Generation Pennsylvania separate corporate income tax returns 2016-2018 PECO Other Tax Matters Federal Income Tax Law Changes On December 22, 2017, President Trump signed the TCJA into law. Pursuant to the enactment of the TCJA, the Registrants remeasured their existing deferred income tax balances as of December 31, 2017 to reflect the decrease in the corporate income tax rate from 35% to 21% , which resulted in a material decrease to their net deferred income tax liability balances as shown in the table below. Generation recorded a corresponding net decrease to income tax expense, while the Utility Registrants recorded corresponding regulatory liabilities or assets to the extent such amounts are probable of settlement or recovery through customer rates and an adjustment to income tax expense for all other amounts. The one-time impacts recorded by the Registrants to remeasure their deferred income tax balances at the 21% corporate federal income tax rate as of December 31, 2017 are presented below: Exelon (b) Generation ComEd PECO (c) BGE PHI Pepco DPL ACE Net Decrease to Deferred Income Tax Liability Balances $8,624 $1,895 $2,819 $1,407 $1,120 $1,944 $968 $540 $456 Net Increase to Regulatory Liabilities Recorded (a) 7,315 N/A 2,818 1,394 1,124 1,979 976 545 458 Net Deferred Income Tax Benefit/(Expense) Recorded $1,309 $1,895 $1 $13 $(4) $(35) $(8) $(5) $(2) __________ (a) Reflects the net regulatory liabilities recorded on a pre-tax basis before taking into consideration the income tax benefits associated with the ultimate settlement with customers. (b) Amounts do not sum across due to deferred tax adjustments recorded at the Exelon Corporation parent company, primarily related to certain employee compensation plans. (c) Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remained in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. State Income Tax Law Changes Illinois - On June 5, 2019, the Governor of Illinois signed a tax bill which would increase the Illinois corporate income tax rate from 9.50% to 10.49% effective for tax years beginning on or after January 1, 2021. The tax rate is contingent upon ratification of state constitutional amendments in November 2020. The effect of the rate change will be recognized in the period in which the new legislation is enacted. Exelon, Generation and ComEd do not expect a material impact to their financial statements as a result of the rate change. In 2017, Exelon reviewed and updated its marginal state income tax rates based on 2016 state apportionment rates. In addition, Exelon, Generation and ComEd recorded the impacts of Illinois’ statutory rate change, which increased the total corporate income tax rate from 7.75% to 9.50% effective July 1, 2017. The following table provides the one-time impact of the rate changes in 2017 for Exelon, Generation and ComEd: Exelon Generation ComEd Increase to Deferred Income Taxes $ 250 $ 20 $ 270 Increase in Regulatory Assets 270 — 270 (Decrease)/Increase to Income Tax Expense (20 ) 20 — Long-Term Marginal State Income Tax Rate (All Registrants) Quarterly, Exelon reviews and updates its marginal state income tax rates for changes in state apportionment. The Registrants remeasure their existing deferred income tax balances to reflect the changes in marginal rates, which results in either an increase or decrease to their net deferred income tax liability balances. Utility Registrants record corresponding regulatory liabilities or assets to the extent such amounts are probable of settlement or recovery through customer rates and an adjustment to income tax expense for all other amounts. December 31, 2019 Exelon Generation PHI DPL Increase to Deferred Income Tax Liability $ 23 $ 9 $ — $ — Increase to Income Tax Expense, Net of Federal Taxes 23 9 — — December 31, 2018 Decrease to Deferred Income Tax Liability $ 50 $ 53 $ 4 $ 2 Decrease to Income Tax Expense, Net of Federal Taxes 50 53 3 — There were no material adjustments to income tax expense in 2017 as a result of changes in state apportionment. Allocation of Tax Benefits (All Registrants) Generation and the Utility Registrants are all party to an agreement with Exelon and other subsidiaries of Exelon that provides for the allocation of consolidated tax liabilities and benefits (Tax Sharing Agreement). The Tax Sharing Agreement provides that each party is allocated an amount of tax similar to that which would be owed had the party been separately subject to tax. In addition, any net benefit attributable to Exelon is reallocated to the other Registrants. That allocation is treated as a contribution to the capital of the party receiving the benefit. The following table presents the allocation of federal tax benefits from Exelon under the Tax Sharing Agreement. Generation ComEd PECO BGE PHI Pepco DPL December 31, 2019 (a) $ 41 $ — $ 14 $ 3 $ 7 $ 6 $ 1 December 31, 2018 (b) 155 1 48 26 2 — — December 31, 2017 (c) 102 — 16 10 7 — — __________ (a) ACE did not record an allocation of federal tax benefits from Exelon under the Tax Sharing Agreement as a result of a tax net operating loss. (b) Pepco, DPL and ACE did not record an allocation of federal tax benefits from Exelon under the Tax Sharing Agreement as a result of a tax net operating loss. (c) ComEd, Pepco, DPL and ACE did not record an allocation of federal tax benefits from Exelon under the Tax Sharing Agreement as a result of a tax net operating loss. Research and Development Activities In the fourth quarter 2019, Exelon and Generation recognized additional tax benefits related to certain research and development activities that qualify for federal and state tax incentives for the 2010 through 2018 tax years, which resulted in an increase to Exelon’s and Generation’s net income of $ 108 million and $ 75 million , respectively, for the year ended December 31, 2019, reflecting a decrease to Exelon’s and Generation’s Income tax expense of $ 97 million and $ 66 million , respectively.

Retirement Benefits (All Regist

Retirement Benefits (All Registrants)	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Retirement Benefits (All Registrants)	Retirement Benefits (All Registrants) Exelon sponsors defined benefit pension plans and OPEB 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, non-craft, 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, non-craft, 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 did not change the benefits offered to the plan participants and, thus, had no impact on Exelon's pension obligation. However, beginning in 2019, actuarial losses and gains related to the CBPP and ECRP are amortized over participants’ average remaining service period of the merged ECRP rather than each individual plan. The table below shows the pension and OPEB plans in which employees of each operating company participated at December 31, 2019 : Operating Company (e) Name of Plan: Generation ComEd PECO BGE PHI Pepco DPL ACE Qualified Pension Plans: Exelon Corporation Retirement Program (a) X X X X X X X X Exelon Corporation Pension Plan for Bargaining Unit Employees (a) X X Exelon New England Union Employees Pension Plan (a) X Exelon Employee Pension Plan for Clinton, TMI and Oyster Creek (a) X X X X X Pension Plan of Constellation Energy Group, Inc. (b) X X X X X X X Pension Plan of Constellation Energy Nuclear Group, LLC (c) X X X X Nine Mile Point Pension Plan (c) X Constellation Mystic Power, LLC Union Employees Pension Plan Including Plan A and Plan B (b) X Pepco Holdings LLC Retirement Plan (d) X X X X X X X X Non-Qualified Pension Plans: Exelon Corporation Supplemental Pension Benefit Plan and 2000 Excess Benefit Plan (a) X X X X Exelon Corporation Supplemental Management Retirement Plan (a) X X X X X X X Constellation Energy Group, Inc. Senior Executive Supplemental Plan (b) X X Constellation Energy Group, Inc. Supplemental Pension Plan (b) X X Constellation Energy Group, Inc. Benefits Restoration Plan (b) X X X X Constellation Energy Nuclear Plan, LLC Executive Retirement Plan (c) X X Constellation Energy Nuclear Plan, LLC Benefits Restoration Plan (c) X Baltimore Gas & Electric Company Executive Benefit Plan (b) X X Baltimore Gas & Electric Company Manager Benefit Plan (b) X X X Pepco Holdings LLC 2011 Supplemental Executive Retirement Plan (d) X X X X Conectiv Supplemental Executive Retirement Plan (d) X X X X Pepco Holdings LLC Combined Executive Retirement Plan (d) X X Atlantic City Electric Director Retirement Plan (d) X Operating Company (e) Name of Plan: Generation ComEd PECO BGE PHI Pepco DPL ACE OPEB Plans: PECO Energy Company Retiree Medical Plan (a) X X X X X X X X Exelon Corporation Health Care Program (a) X X X X X X X Exelon Corporation Employees’ Life Insurance Plan (a) X X X X Exelon Corporation Health Reimbursement Arrangement Plan (a) X X X X Constellation Energy Group, Inc. Retiree Medical Plan (b) X X X X X X Constellation Energy Group, Inc. Retiree Dental Plan (b) X X Constellation Energy Group, Inc. Employee Life Insurance Plan and Family Life Insurance Plan (b) X X X X X X Constellation Mystic Power, LLC Post-Employment Medical Account Savings Plan (b) X Exelon New England Union Post-Employment Medical Savings Account Plan (a) X Retiree Medical Plan of Constellation Energy Nuclear Group LLC (c) X X X Retiree Dental Plan of Constellation Energy Nuclear Group LLC (c) X X X Nine Mile Point Nuclear Station, LLC Medical Care and Prescription Drug Plan for Retired Employees (c) X Pepco Holdings LLC Welfare Plan for Retirees (d) X X X X X X X X __________ (a) These plans are collectively referred to as the legacy Exelon plans. (b) These plans are collectively referred to as the legacy Constellation Energy Group (CEG) Plans. (c) These plans are collectively referred to as the legacy CENG plans. (d) These plans are collectively referred to as the legacy PHI plans. (e) Employees generally remain in their legacy benefit plans when transferring between operating companies. Exelon’s traditional and cash balance pension plans are intended to be tax-qualified defined benefit plans. Exelon has elected that the trusts underlying these plans be treated as qualified trusts under the IRC. If certain conditions are met, Exelon can deduct payments made to the qualified trusts, subject to certain IRC limitations. Benefit Obligations, Plan Assets and Funded Status 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 following tables provide a rollforward of the changes in the benefit obligations and plan assets of Exelon for the most recent two years for all plans combined: Pension Benefits OPEB 2019 2018 2019 2018 Change in benefit obligation: Net benefit obligation at beginning of year $ 20,692 $ 22,337 $ 4,369 $ 4,856 Service cost 357 405 93 112 Interest cost 883 802 188 175 Plan participants’ contributions — — 44 45 Actuarial (gain) loss (a) 2,322 (1,561 ) 250 (540 ) Plan amendments 68 (4 ) — — Curtailments (3 ) — — — Settlements (35 ) (48 ) (4 ) (4 ) Contractual termination benefits 1 — — — Gross benefits paid (1,417 ) (1,239 ) (282 ) (275 ) Net benefit obligation at end of year $ 22,868 $ 20,692 $ 4,658 $ 4,369 Pension Benefits OPEB 2019 2018 2019 2018 Change in plan assets: Fair value of net plan assets at beginning of year $ 16,678 $ 18,573 $ 2,408 $ 2,732 Actual return on plan assets 3,008 (945 ) 324 (136 ) Employer contributions 356 337 51 46 Plan participants’ contributions — — 44 45 Gross benefits paid (1,417 ) (1,239 ) (282 ) (275 ) Settlements (35 ) (48 ) (4 ) (4 ) Fair value of net plan assets at end of year $ 18,590 $ 16,678 $ 2,541 $ 2,408 __________ (a) The pension actuarial loss in 2019 primarily reflects a decrease in the discount rate. The OPEB actuarial loss in 2019 primarily reflects a decrease in the discount rate. The pension actuarial gain in 2018 primarily reflects an increase in the discount rate. The OPEB actuarial gain in 2018 primarily reflects an increase in the discount rate and favorable health care claims experience. Exelon presents its benefit obligations and plan assets net on its balance sheet within the following line items: Pension Benefits OPEB 2019 2018 2019 2018 Other current liabilities $ 31 $ 26 $ 41 $ 33 Pension obligations 4,247 3,988 — — Non-pension postretirement benefit obligations — — 2,076 1,928 Unfunded status (net benefit obligation less plan assets) $ 4,278 $ 4,014 $ 2,117 $ 1,961 The following table provides the accumulated benefit obligation (ABO) and fair value of plan assets for all pension plans with an ABO in excess of plan assets. Information for pension and OPEB plans with projected benefit obligations (PBO) and accumulated postretirement benefit obligation (APBO), respectively, in excess of plan assets has been disclosed in the Obligations and Plan Assets table above as all pension and OPEB plans are underfunded. ABO in excess of plan assets Exelon 2019 2018 Accumulated benefit obligation 21,727 19,656 Fair value of net plan assets 18,590 16,678 Components of Net Periodic Benefit Costs The majority of the 2019 pension benefit cost for the 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 OPEB 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 tables present the components of Exelon’s net periodic benefit costs, prior to capitalization, for the years ended December 31, 2019 , 2018 and 2017 . Pension Benefits OPEB 2019 2018 2017 (a) 2019 2018 2017 (a) Components of net periodic benefit cost: Service cost $ 357 $ 405 $ 387 $ 93 $ 112 $ 106 Interest cost 883 802 842 188 175 182 Expected return on assets (1,225 ) (1,252 ) (1,196 ) (153 ) (173 ) (162 ) Amortization of: Prior service cost (credit) — 2 1 (179 ) (186 ) (188 ) Actuarial loss 414 629 607 45 66 61 Settlement and other charges 17 3 3 1 1 — Contractual termination benefits 1 — — — — — Net periodic benefit cost $ 447 $ 589 $ 644 $ (5 ) $ (5 ) $ (1 ) __________ (a) FitzPatrick net benefit costs are included for the period after acquisition. Cost Allocation to Exelon Subsidiaries All Registrants account for their participation in Exelon’s pension and OPEB plans by applying multi-employer accounting. Exelon allocates costs related to its pension and OPEB plans to its subsidiaries based on both active and retired employee participation in each plan. The amounts below represent the Registrants’ allocated pension and OPEB costs. As a result of new pension guidance effective on January 1, 2018, certain balances have been reclassified on Exelon’s Consolidated Statements of Operations and Comprehensive Income for the year ended December 31, 2017. For Exelon, the service cost component is included in Operating and maintenance expense and Property, plant and equipment, net, while the non–service cost components are included in Other, net and Regulatory assets for the years ended December 31, 2019 and December 31, 2018 and in Other, net and Property, plant and equipment, net, for the year ended December 31, 2017. For Generation and the Utility Registrants, the service cost and non–service cost components are included in Operating and maintenance expense and Property, plant and equipment, net on their consolidated financial statements. For the Years Ended December 31, Exelon Generation (a) ComEd PECO BGE PHI Pepco DPL ACE 2019 $ 442 $ 135 $ 96 $ 12 $ 61 $ 95 $ 25 $ 15 $ 16 2018 583 204 177 18 60 67 15 6 12 2017 643 227 176 29 64 94 25 13 13 __________ (a) FitzPatrick net benefit costs are included for the period after acquisition. Components of AOCI and Regulatory Assets Exelon recognizes the overfunded or underfunded status of defined benefit pension and OPEB plans as an asset or liability on its balance sheet, with offsetting entries to AOCI and regulatory assets (liabilities). A portion of current year actuarial gains and losses and prior service costs (credits) is capitalized within Exelon’s Consolidated Balance Sheets to reflect the expected regulatory recovery of these amounts, which would otherwise be recorded to AOCI. The following tables provide the components of AOCI and regulatory assets (liabilities) for Exelon for the years ended December 31, 2019 , 2018 and 2017 for all plans combined. Pension Benefits OPEB 2019 2018 2017 2019 2018 2017 Changes in plan assets and benefit obligations recognized in AOCI and regulatory assets (liabilities): Current year actuarial (gain) loss $ 538 $ 635 $ (222 ) $ 80 $ (232 ) $ 166 Amortization of actuarial loss (414 ) (629 ) (607 ) (45 ) (66 ) (61 ) Current year prior service cost (credit) 68 (4 ) 9 — — — Amortization of prior service (cost) credit — (2 ) (1 ) 179 186 188 Curtailments (3 ) — — — — — Settlements (17 ) (3 ) (3 ) (1 ) — — Total recognized in AOCI and regulatory assets (liabilities) $ 172 $ (3 ) $ (824 ) $ 213 $ (112 ) $ 293 Total recognized in AOCI $ 169 $ 3 $ (401 ) $ 107 $ (55 ) $ 168 Total recognized in regulatory assets (liabilities) $ 3 $ (6 ) $ (423 ) $ 106 $ (57 ) $ 125 The following table provides the components of gross accumulated other comprehensive loss and regulatory assets (liabilities) for Exelon that have not been recognized as components of periodic benefit cost at December 31, 2019 and 2018 , respectively, for all plans combined: Pension Benefits OPEB 2019 2018 2019 2018 Prior service (credit) cost $ 39 $ (29 ) $ (158 ) $ (337 ) Actuarial loss 7,662 7,558 565 531 Total $ 7,701 $ 7,529 $ 407 $ 194 Total included in AOCI $ 4,068 $ 3,899 $ 177 $ 70 Total included in regulatory assets (liabilities) $ 3,633 $ 3,630 $ 230 $ 124 Average Remaining Service Period For pension benefits, Exelon amortizes its unrecognized prior service costs and certain actuarial gains and losses, as applicable, based on participants’ average remaining service periods. For OPEB, Exelon amortizes its unrecognized prior service costs over participants’ average remaining service period to benefit eligibility age and amortizes certain actuarial gains and losses over participants’ average remaining service period to expected retirement. The resulting average remaining service periods for pension and OPEB were as follows: 2019 2018 2017 Pension plans 11.7 12.0 11.8 OPEB plans: Benefit Eligibility Age 8.7 8.8 8.8 Expected Retirement 9.3 9.5 9.6 Assumptions The measurement of the plan obligations and costs of providing benefits under Exelon’s defined benefit and other postretirement plans involves various factors, including the development of valuation assumptions and inputs and accounting policy elections. The measurement of benefit obligations and costs is impacted by several assumptions and inputs, as shown below, among other factors. When developing the required assumptions, Exelon considers historical information as well as future expectations. Expected Rate of Return. In selecting the EROA, Exelon considers historical economic indicators (including inflation and GDP growth) that impact asset returns, as well as expectations regarding future long-term capital market performance, weighted by Exelon’s target asset class allocations. Mortality . The mortality assumption is composed of a base table that represents the current expectation of life expectancy of the population adjusted by an improvement scale that attempts to anticipate future improvements in life expectancy. For the year ended December 31, 2018, Exelon’s mortality assumption was supported by an actuarial experience study of Exelon's plan participants and utilized the IRS's RP–2000 base table projected to 2012 with improvement scale AA and projected thereafter with generational improvement scale BB two-dimensional adjusted to a 0.75% long-term rate reached in 2027. For the year ended December 31, 2019, Exelon's mortality assumption utilizes the Society of Actuaries' 2019 base table (Pri-2012) and MP- 2019 improvement scale adjusted to a 0.75% long-term rate reached in 2035. For Exelon, the following assumptions were used to determine the benefit obligations for the plans at December 31, 2019 and 2018 . Assumptions used to determine year-end benefit obligations are the assumptions used to estimate the subsequent year’s net periodic benefit costs. Pension Benefits OPEB 2019 2018 2019 2018 Discount rate 3.34 % (a) 4.31 % (a) 3.31 % (a) 4.30 % (a) Investment Crediting Rate 3.82 % (b) 4.46 % (b) N/A N/A Rate of compensation increase (c) (c) (c) (c) Mortality table Pri-2012 table with MP- 2019 improvement scale (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) Pri-2012 table with MP- 2019 improvement scale (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) Health care cost trend on covered charges N/A N/A 5.00% with 5.00% with __________ (a) The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and OPEB obligations. Certain benefit plans used individual rates, which range from 3.02% - 3.44% and 3.27% - 3.4% for pension and OPEB plans, respectively, as of December 31, 2019 and 4.13% - 4.36% and 4.27% - 4.38% for pension and OPEB plans, respectively, as of December 31, 2018 . (b) The investment crediting rate above represents a weighted average rate. (c) 3.25% through 2019 and 3.75% thereafter. The following assumptions were used to determine the net periodic benefit cost for Exelon for the years ended December 31, 2019 , 2018 and 2017 : Pension Benefits Other Postretirement Benefits Exelon 2019 2018 2017 2019 2018 2017 Discount rate 4.31 % (a) 3.62 % (a) 4.04 % (a) 4.30 % (a) 3.61 % (a) 4.04 % (a) Investment Crediting Rate 4.46 % (b) 4.00 % (b) 4.46 % (b) N/A N/A N/A Expected return on plan assets 7.00 % (c) 7.00 % (c) 7.00 % (c) 6.67 % (c) 6.60 % (c) 6.58 % (c) Rate of compensation increase (d) (d) (e) (d) (d) (e) Mortality table RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) Health care cost trend on covered charges N/A N/A N/A 5.00% 5.00% 5.50% __________ (a) The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and OPEB costs. Certain benefit plans used individual rates, which range from 4.13% - 4.36% and 4.27% - 4.38% for pension and OPEB plans, respectively, for the year ended December 31, 2019 ; 3.49% - 3.65% and 3.57% - 3.68% for pension and OPEB plans; respectively, for the year ended December 31, 2018 ; and 3.66% - 4.11% and 4.00% - 4.17% for pension and OPEB plans, respectively, for the year ended December 31, 2017 . (b) The investment crediting rate above represents a weighted average rate. (c) Not applicable to pension and other postretirement benefit plans that do not have plan assets. (d) 3.25% through 2019 and 3.75% thereafter. (e) The legacy Exelon, CEG and CENG pension and other postretirement plans used a rate of compensation increase of 3.25% through 2019 and 3.75% thereafter, while the legacy PHI pension and OPEB plans used a weighted-average rate of compensation increase of 5% for all periods. Contributions Exelon allocates contributions related to its legacy Exelon pension and OPEB plans to its subsidiaries based on accounting cost. For legacy CEG, CENG, FitzPatrick, and PHI plans, pension and OPEB contributions are allocated to the subsidiaries based on employee participation (both active and retired). The following tables provide contributions to the pension and OPEB plans: Pension Benefits OPEB 2019 (a) 2018 (a) 2017 (a) 2019 2018 2017 Exelon $ 356 $ 337 $ 341 $ 51 $ 46 $ 64 Generation 160 128 137 15 11 11 ComEd 72 38 36 5 4 5 PECO 27 28 24 1 — — BGE 34 40 39 14 14 14 PHI 10 62 67 15 12 32 Pepco 2 6 62 12 11 10 DPL 1 — — — — 2 ACE — 6 — 1 — 20 __________ (a) Exelon's and Generation's pension contributions include $21 million related to the legacy CENG plans that was funded by CENG as provided in an Employee Matters Agreement (EMA) between Exelon and CENG for the year ended December 31, 2017 . There were no pension contributions for the years ended December 31, 2019 and 2018 . Management considers various factors when making pension funding decisions, including actuarially determined minimum contribution requirements under ERISA, contributions required to avoid benefit restrictions and at-risk status as defined by the Pension Protection Act of 2006 (the Act), management of the pension obligation and regulatory implications. The Act requires the attainment of certain funding levels to avoid benefit restrictions (such as an inability to pay lump sums or to accrue benefits prospectively), and at-risk status (which triggers higher minimum contribution requirements and participant notification). The projected contributions below reflect a funding strategy to make levelized annual contributions with the objective of achieving 100% funded status on an ABO basis over time. This level funding strategy helps minimize volatility of future period required pension contributions. Based on this funding strategy and current market conditions, which are subject to change, Exelon’s estimated annual qualified pension contributions will be approximately $500 million beginning in 2020. Unlike the qualified pension plans, Exelon’s non-qualified pension plans are not funded, given that they are not subject to statutory minimum contribution requirements. While other postretirement plans are also not subject to statutory minimum contribution requirements, Exelon does fund certain of its plans. For Exelon's funded OPEB plans, contributions generally equal accounting costs, however, Exelon’s management has historically considered several factors in determining the level of contributions to its OPEB plans, including liabilities management, levels of benefit claims paid and regulatory implications (amounts deemed prudent to meet regulatory expectations and best assure continued rate recovery). The amounts below include benefit payments related to unfunded plans. The following table provides all registrants' planned contributions to the qualified pension plans, planned benefit payments to non-qualified pension plans, and planned contributions to other postretirement plans in 2020 : Qualified Pension Plans Non-Qualified Pension Plans OPEB Exelon $ 505 $ 36 $ 42 Generation 227 14 16 ComEd 141 2 3 PECO 17 1 — BGE 56 2 16 PHI 22 9 7 Pepco — 2 7 DPL — 1 — ACE 2 — — Estimated Future Benefit Payments Estimated future benefit payments to participants in all of the pension plans and postretirement benefit plans at December 31, 2019 were: Pension Benefits OPEB 2020 $ 1,227 $ 258 2021 1,252 263 2022 1,295 267 2023 1,310 270 2024 1,324 275 2025 through 2029 6,770 1,402 Total estimated future benefit payments through 2029 $ 13,178 $ 2,735 Plan Assets Investment Strategy. On a regular basis, Exelon evaluates its investment strategy to ensure that plan assets will be sufficient to pay plan benefits when due. As part of this ongoing evaluation, Exelon may make changes to its targeted asset allocation and investment strategy. Exelon has developed and implemented a liability hedging investment strategy for its qualified pension plans that has reduced the volatility of its pension assets relative to its pension liabilities. Exelon is likely to continue to gradually increase the liability hedging portfolio as the funded status of its plans improves. The overall objective is to achieve attractive risk-adjusted returns that will balance the liquidity requirements of the plans’ liabilities while striving to minimize the risk of significant losses. Trust assets for Exelon’s other postretirement plans are managed in a diversified investment strategy that prioritizes maximizing liquidity and returns while minimizing asset volatility. Actual asset returns have an impact on the costs reported for the Exelon-sponsored pension and OPEB plans. The actual asset returns across Exelon’s pension and OPEB plans for the year ended December 31, 2019 were 18.80% and 14.40% , respectively, compared to an expected long-term return assumption of 7.00% and 6.67% , respectively. Exelon used an EROA of 7.00% and 6.69% to estimate its 2020 pension and OPEB costs, respectively. Exelon’s pension and OPEB plan target asset allocations at December 31, 2019 and 2018 were as follows: December 31, 2019 December 31, 2018 Asset Category Pension Benefits OPEB Pension Benefits OPEB Equity securities 33 % 46 % 35 % 47 % Fixed income securities 44 % 32 % 37 % 28 % Alternative investments (a) 23 % 22 % 28 % 25 % Total 100 % 100 % 100 % 100 % __________ (a) Alternative investments include private equity, hedge funds, real estate, and private credit. Concentrations of Credit Risk. Exelon evaluated its pension and OPEB plans’ asset portfolios for the existence of significant concentrations of credit risk as of December 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 December 31, 2019 , there were no significant concentrations (defined as greater than 10% of plan assets) of risk in Exelon’s pension and OPEB plan assets. Fair Value Measurements The following tables present pension and OPEB plan assets measured and recorded at fair value in Exelon's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy at December 31, 2019 and 2018 : December 31, 2019 (a) Level 1 Level 2 Level 3 Not subject to leveling Total Pension plan assets Cash equivalents $ 258 $ — $ — $ — $ 258 Equities (b) 3,616 — 5 2,589 6,210 Fixed income: U.S. Treasury and agencies 1,294 280 — — 1,574 State and municipal debt — 56 — — 56 Corporate debt — 4,342 245 — 4,587 Other (b) — 461 — 851 1,312 Fixed income subtotal 1,294 5,139 245 851 7,529 Private equity — — — 1,391 1,391 Hedge funds — — — 1,126 1,126 Real estate — — — 1,030 1,030 Private credit — — 237 929 1,166 Pension plan assets subtotal $ 5,168 $ 5,139 $ 487 $ 7,916 $ 18,710 December 31, 2019 (a) Level 1 Level 2 Level 3 Not subject to leveling Total OPEB plan assets Cash equivalents $ 39 $ — $ — $ — $ 39 Equities 473 3 — 719 1,195 Fixed income: U.S. Treasury and agencies 17 64 — — 81 State and municipal debt — 107 — — 107 Corporate debt — 49 — — 49 Other 258 78 — 201 537 Fixed income subtotal 275 298 — 201 774 Hedge funds — — — 293 293 Real estate — — — 109 109 Private credit — — — 131 131 OPEB plan assets subtotal $ 787 $ 301 $ — $ 1,453 $ 2,541 Total pension and OPEB plan assets (c) $ 5,955 $ 5,440 $ 487 $ 9,369 $ 21,251 December 31, 2018 (a) Level 1 Level 2 Level 3 Not subject to leveling Total Pension plan assets Cash equivalents $ 350 $ — $ — $ — $ 350 Equities (b) 3,364 — 2 1,980 5,346 Fixed income: U.S. Treasury and agencies 996 173 — — 1,169 State and municipal debt — 59 — — 59 Corporate debt — 3,716 216 — 3,932 Other (b) — 329 — 613 942 Fixed income subtotal 996 4,277 216 613 6,102 Private equity — — — 1,219 1,219 Hedge funds — — — 1,608 1,608 Real estate — — — 1,029 1,029 Private credit — — 268 798 1,066 Pension plan assets subtotal $ 4,710 $ 4,277 $ 486 $ 7,247 $ 16,720 December 31, 2018 (a) Level 1 Level 2 Level 3 Not subject to leveling Total OPEB plan assets Cash equivalents $ 22 $ — $ — $ — $ 22 Equities 537 2 — 508 1,047 Fixed income: U.S. Treasury and agencies 11 56 — — 67 State and municipal debt — 126 — — 126 Corporate debt — 48 — — 48 Other 183 72 — 170 425 Fixed income subtotal 194 302 — 170 666 Hedge funds — — — 411 411 Real estate — — — 132 132 Private credit — — — 132 132 OPEB plan assets subtotal $ 753 $ 304 $ — $ 1,353 $ 2,410 Total pension and OPEB plan assets (c) $ 5,463 $ 4,581 $ 486 $ 8,600 $ 19,130 __________ (a) See Note 17 — Fair Value of Financial Assets and Liabilities for a description of levels within the fair value hierarchy. (b) Includes derivative instruments of $2 million and less than $1 million , which have a total notional amount of $6,668 million and $5,991 million at December 31, 2019 and 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 the company’s exposure to credit or market loss. (c) Excludes net liabilities of $120 million and $44 million at December 31, 2019 and 2018 , respectively, which are required to reconcile to the fair value of net plan assets. These items consist primarily of receivables or payables related to pending securities sales and purchases, interest and dividends receivable. The following table presents the reconciliation of Level 3 assets and liabilities for Exelon measured at fair value for pension and OPEB plans for the years ended December 31, 2019 and 2018 : Fixed Income Equities Private Credit Total Pension Assets Balance as of January 1, 2019 $ 216 $ 2 $ 268 $ 486 Actual return on plan assets: Relating to assets still held at the 28 3 28 59 Relating to assets sold during the period (7 ) — — (7 ) Purchases, sales and settlements: Purchases 26 — 41 67 Sales (4 ) — — (4 ) Settlements (a) (2 ) — (100 ) (102 ) Transfers out of Level 3 (12 ) — — (12 ) Balance as of December 31, 2019 $ 245 $ 5 $ 237 $ 487 Fixed income Equities Private Credit Total Pension Assets Balance as of January 1, 2018 $ 232 $ 2 $ 224 $ 458 Actual return on plan assets: Relating to assets still held at the reporting date (14 ) — 9 (5 ) Relating to assets sold during the period (1 ) — — (1 ) Purchases, sales and settlements: Purchases 19 — 35 54 Sales (8 ) — — (8 ) Settlements (a) (12 ) — — (12 ) Balance as of December 31, 2018 $ 216 $ 2 $ 268 $ 486 __________ (a) Represents cash settlements only. There were no significant transfers between Level 1 and Level 2 during the year ended December 31, 2019 for the pension and OPEB plan assets. Valuation Techniques Used to Determine Fair Value The techniques used to fair value the pension and OPEB assets invested in cash equivalents, equities, fixed income, derivatives, private equity, real estate, and private credit investments are the same as the valuation techniques for these types of investments in NDTFs. See Cash Equivalents and NDT Fund Investments in Note 17 - Fair Value of Financial Assets and Liabilities for further information. Pension and OPEB assets also include investments in hedge funds. Hedge fund investments include those seeking to maximize absolute returns using a broad range of strategies to enhance returns and provide additional diversification. The fair value of hedge funds is determined using NAV or its equivalent as a practical expedient, and therefore, hedge funds are not classified within the fair value hierarchy. Exelon has the ability to redeem these investments at NAV or its equivalent subject to certain restrictions which may include a lock-up period or a gate. Defined Contribution Savings Plan (All Registrants) 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 matching contributions to the savings plan for the years ended December 31, 2019 , 2018 and 2017 : For the Year Ended December 31, Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2019 $ 161 $ 73 $ 35 $ 11 $ 12 13 $ 3 $ 3 $ 2 2018 179 86 37 9 12 13 3 2 2 2017 128 55 31 10 10 13 3 2 2

Derivative Financial Instrument

Derivative Financial Instruments (All Registrants)	12 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial 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. 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 NPNS, cash flow hedges and fair value hedges. All derivative economic hedges related to commodities, referred to as economic hedges, are recorded at fair value through earnings at Generation and are offset by a corresponding regulatory asset or liability at ComEd. For all NPNS derivative instruments, accounts receivable or accounts payable are recorded when derivative settles and revenue or expense is recognized in earnings as the underlying physical commodity is sold or consumed. Authoritative guidance 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 Sheets. 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. In the tables below that present fair value balances, 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 columns. Generation’s and ComEd’s use of cash collateral is generally unrestricted unless Generation or ComEd are downgraded below investment grade. Cash collateral held by PECO, BGE, Pepco, DPL and ACE must be deposited in an unaffiliated major U.S. commercial bank or foreign bank with a U.S. branch office that meet certain qualifications. Commodity Price Risk (All Registrants) 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. Generation. 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. 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. 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 and are subject to limits established by Exelon’s RMC. Utility Registrants. The Utility Registrants procure electric and natural gas supply through a competitive procurement process approved by each of the respective state utility commissions. The Utility Registrants’ hedging programs are intended to reduce exposure to energy and natural gas price volatility and have no direct earnings impact as the costs are fully recovered from customers through regulatory-approved recovery mechanisms. The following table provides a summary of the Utility Registrants’ primary derivative hedging instruments, listed by commodity and accounting treatment. Registrant Commodity Accounting Treatment Hedging instrument ComEd Electricity NPNS Fixed price contracts based on all requirements in the IPA procurement plans. Electricity Changes in fair value of economic hedge recorded to an offsetting regulatory asset or liability (a) 20-year floating-to-fixed energy swap contracts beginning June 2012 based on the renewable energy resource procurement requirements in the Illinois Settlement Legislation of approximately 1.3 million MWhs per year. PECO (b) Gas NPNS Fixed price contracts to cover about 20% of planned natural gas purchases in support of projected firm sales. BGE Electricity NPNS Fixed price contracts for all SOS requirements through full requirements contracts. Gas NPNS Fixed price contracts for between 10-20% of forecasted system supply requirements for flowing (i.e., non-storage) gas for the November through March period. Pepco Electricity NPNS Fixed price contracts for all SOS requirements through full requirements contracts. DPL Electricity NPNS Fixed price contracts for all SOS requirements through full requirements contracts. Gas NPNS Fixed price contracts through full requirements contracts. Changes in fair value of economic hedge recorded to an offsetting regulatory asset or liability (c) Exchange traded future contracts for 50% of estimated monthly purchase requirements each month, including purchases for storage injections. ACE Electricity NPNS Fixed price contracts for all BGS requirements through full requirements contracts. _________ (a) See Note 3 - Regulatory Matters for additional information. (b) As part of its hedging program, PECO enters into electric supply procurement contracts that do not meet the definition of a derivative instrument. (c) The fair value of the DPL economic hedge is not material as of December 31, 2019 and 2018 and is not presented in the fair value tables below. The following table provides a summary of the derivative fair value balances recorded by Exelon, Generation and ComEd as of December 31, 2019 and 2018 : Exelon Generation ComEd December 31, 2019 Total Derivatives Economic Hedges Proprietary Trading Collateral (a)(b) Netting (a) Subtotal Economic Hedges Mark-to-market derivative assets (current assets) $ 675 $ 3,506 $ 72 $ 287 $ (3,190 ) $ 675 $ — Mark-to-market derivative assets (noncurrent assets) 508 1,238 25 122 (877 ) 508 — Total mark-to-market derivative assets 1,183 4,744 97 409 (4,067 ) 1,183 — Mark-to-market derivative liabilities (current liabilities) (236 ) (3,713 ) (38 ) 357 3,190 (204 ) (32 ) Mark-to-market derivative liabilities (noncurrent liabilities) (380 ) (1,140 ) (11 ) 163 877 (111 ) (269 ) Total mark-to-market derivative liabilities (616 ) (4,853 ) (49 ) 520 4,067 (315 ) (301 ) Total mark-to-market derivative net assets (liabilities) $ 567 $ (109 ) $ 48 $ 929 $ — $ 868 $ (301 ) December 31, 2018 Mark-to-market derivative assets (current assets) $ 801 $ 3,505 $ 105 $ 121 $ (2,930 ) $ 801 $ — Mark-to-market derivative assets (noncurrent assets) 445 1,266 41 51 (913 ) 445 — Total mark-to-market derivative assets 1,246 4,771 146 172 (3,843 ) 1,246 — Mark-to-market derivative liabilities (current liabilities) (473 ) (3,429 ) (74 ) 125 2,931 (447 ) (26 ) Mark-to-market derivative liabilities (noncurrent liabilities) (474 ) (1,203 ) (20 ) 60 912 (251 ) (223 ) Total mark-to-market derivative liabilities (947 ) (4,632 ) (94 ) 185 3,843 (698 ) (249 ) Total mark-to-market derivative net assets (liabilities) $ 299 $ 139 $ 52 $ 357 $ — $ 548 $ (249 ) _________ (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 amounts are immaterial and not reflected in the table above. (b) Of the collateral posted/(received), $511 million and $(94) million represents variation margin on the exchanges at December 31, 2019 and 2018 , respectively. Economic Hedges (Commodity Price Risk) Generation. For the years ended December 31, 2019 , 2018 and 2017 , 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 line in the Consolidated Statements of Cash Flows. 2019 2018 2017 Income Statement Location Gain (Loss) Operating revenues $ — $ (270 ) $ (126 ) Purchased power and fuel (204 ) (47 ) (43 ) Total Exelon and Generation $ (204 ) $ (317 ) $ (169 ) In general, increases and decreases in forward market prices have a positive and negative impact, respectively, on Generation’s owned and contracted generation positions that have not been hedged. Generation hedges commodity price risk on a ratable basis over three-year periods. As of December 31, 2019 , the percentage of expected generation hedged for the Mid-Atlantic, Midwest, New York and ERCOT reportable segments is 91% - 94% and 61% - 64% for 2020 and 2021 , respectively. 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. 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 and are included in the Net fair value changes related to derivatives line in the Consolidated Statements of Cash Flows. For the years ended December 31, 2019 , 2018 and 2017 , net pre-tax commodity mark-to-market gains (losses) for Exelon and Generation were not material. The Utility Registrants do not execute derivatives for proprietary trading purposes. 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 $1,269 million and $1,420 million at December 31, 2019 and 2018 , respectively, for Exelon and $569 million and $620 million at December 31, 2019 and 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 $231 million and $268 million at December 31, 2019 and 2018 , respectively. The mark-to-market derivative assets and liabilities as of December 31, 2019 and 2018 and the mark-to-market gains (losses) for the years ended December 31, 2019 , 2018 and 2017 were not material for Exelon and Generation. Credit Risk (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. Generation. 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 payables and receivables, net of collateral and instruments that are subject to master netting agreements, as of December 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. Rating as of December 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 $ 877 $ 20 $ 857 — $ — Non-investment grade 79 63 16 No external ratings Internally rated — investment grade 218 — 218 Internally rated — non-investment grade 139 23 116 Total $ 1,313 $ 106 $ 1,207 — $ — Net Credit Exposure by Type of Counterparty As of Financial institutions $ 9 Investor-owned utilities, marketers, power producers 930 Energy cooperatives and municipalities 235 Other 33 Total $ 1,207 __________ (a) As of December 31, 2019 , credit collateral held from counterparties where Generation had credit exposure included $25 million of cash and $81 million of letters of credit. The credit collateral does not include non-liquid collateral. Utility Registrants. The Utility Registrants have contracts to procure electric and natural gas supply that provide suppliers with a certain amount of unsecured credit. If the exposure on the supply contract exceeds the amount of unsecured credit, the suppliers may be required to post collateral. The net credit exposure is mitigated primarily by the ability to recover procurement costs through customer rates. As of December 31, 2019 , the Utility Registrants’ counterparty credit risk with suppliers was immaterial. Credit-Risk-Related Contingent Features (All Registrants) Generation. 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: As of December 31, Credit-Risk Related Contingent Features 2019 2018 Gross fair value of derivative contracts containing this feature (a) $ (956 ) $ (1,723 ) Offsetting fair value of in-the-money contracts under master netting arrangements (b) 649 1,105 Net fair value of derivative contracts containing this feature (c) $ (307 ) $ (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. As of December 31, 2019 and 2018 , Exelon and Generation posted or held the following amounts of cash collateral and letters of credit on derivative contracts with external counterparties, after giving consideration to offsetting derivative and non-derivative positions under master netting agreements. As of December 31, 2019 2018 Cash collateral posted $ 982 $ 418 Letters of credit posted 264 367 Cash collateral held 103 47 Letters of credit held 112 44 Additional collateral required in the event of a credit downgrade below investment grade 1,509 2,104 Generation entered into supply forward contracts with certain utilities, including PECO and BGE, with one-sided collateral postings only from Generation. If market prices fall below the benchmark price levels in these contracts, the utilities are not required to post collateral. However, when market prices rise above the benchmark price levels, counterparty suppliers, including Generation, are required to post collateral once certain unsecured credit limits are exceeded. Utility Registrants The Utility Registrants’ electric supply procurement contracts do not contain provisions that would require them to post collateral. PECO’s, BGE’s, and DPL’s natural gas procurement contracts contain provisions that could require PECO, BGE, and DPL to post collateral in the form of cash or credit support, which vary by contract and counterparty, with thresholds contingent upon PECO’s, BGE, and DPL’s credit rating. As of December 31, 2019 , PECO, BGE, and DPL were not required to post collateral for any of these agreements. If PECO, BGE or DPL lost their investment grade credit rating as of December 31, 2019 , they could have been required to post incremental collateral to its counterparties of $44 million , $50 million , and $11 million , respectively.

Debt and Credit Agreements (All

Debt and Credit Agreements (All Registrants)	12 Months Ended
	Dec. 31, 2019
Line of Credit Facility [Line Items]
Schedule Of Credit Agreement Covenants [Table Text Block]	Bilateral Credit Agreements The following table reflects the bilateral credit agreements at December 31, 2019 : Registrant Date Initiated Latest Amendment Date Maturity Date (a) Amount Generation (b) October 26, 2012 October 24, 2019 October 24, 2020 $ 200 Generation (c) January 11, 2013 January 4, 2019 March 1, 2021 100 Generation (c) January 5, 2016 January 4, 2019 April 5, 2021 150 Generation (c) February 21, 2019 N/A March 31, 2021 100 Generation (c) October 25, 2019 N/A N/A 200 Generation (c) October 25, 2019 N/A N/A 100 Generation (c) November 20, 2019 N/A N/A 300 Generation (c) November 21, 2019 N/A November 21, 2020 150 Generation (c) November 21, 2019 N/A November 21, 2021 100 __________ (a) Credit facilities that do not contain a maturity date are specific to the agreements set within each contract. In some instances, credit facilities are automatically renewed based on the contingency standards set within the specific agreement. (b) Bilateral credit facility relates to CENG, which is incorporated within Generation, and supports the issuance of letters of credit and funding for working capital and does not back Generation's commercial paper program. (c) Bilateral credit agreements solely support the issuance of letters of credit and do not back Generation's commercial paper program.
Debt and Credit Agreements (All Registrants)	Debt and Credit Agreements (All Registrants) Short-Term Borrowings Exelon Corporate, ComEd and BGE meet their short-term liquidity requirements primarily through the issuance of commercial paper. Generation and PECO meet their short-term liquidity requirements primarily through the issuance of commercial paper and borrowings from the Exelon intercompany money pool. Pepco, DPL, and ACE meet their short-term liquidity requirements primarily through the issuance of commercial paper and borrowings from the PHI intercompany money pool. P HI 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 supported by the revolving credit agreements and bilateral credit agreements at December 31, 2019 and 2018 : Maximum Program Size at December 31, Outstanding Commercial Paper at December 31, Average Interest Rate on Commercial Paper Borrowings for the Year Ended December 31, Commercial Paper Issuer 2019 (a)(b)(c) 2018 (a)(b)(c) 2019 2018 2019 2018 Exelon (d) $ 9,000 $ 9,000 $ 870 $ 89 2.25 % 2.15 % Generation 5,300 5,300 320 — 1.84 % 1.96 % ComEd 1,000 1,000 130 — 2.38 % 2.14 % PECO 600 600 — — 2.39 % 2.24 % BGE 600 600 76 35 2.46 % 2.18 % PHI 900 900 208 54 N/A N/A Pepco 300 300 82 40 2.56 % 2.24 % DPL 300 300 56 — 2.02 % 2.07 % ACE 300 300 70 14 2.43 % 2.21 % __________ (a) Excludes $1,400 million and $545 million in bilateral credit facilities at December 31, 2019 and 2018 , respectively, and $159 million in credit facilities for project finance at December 31, 2019 and 2018 , respectively. These credit facilities do not back Generation's commercial paper program. (b) At December 31, 2019 , excludes $142 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $44 million , $33 million , $33 million , $8 million , $8 million , $8 million and $8 million , respectively. These facilities expire on October 9, 2020. These facilities are solely utilized to issue letters of credit. At December 31, 2018 , excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million , $33 million , $34 million , $5 million , $5 million , $5 million , and $5 million , respectively. (c) Pepco, DPL and ACE's revolving credit facility has the ability to flex to $500 million , $500 million , and $350 million , respectively. The borrowing capacity may be increased or decreased during the term of the facility, except that (i) the sum of the borrowing capacity must equal the total amount of the facility, and (ii) the aggregate amount of credit used at any given time by each of Pepco, DPL or ACE may not exceed $900 million or the maximum amount of short-term debt the company is permitted to have outstanding by its regulatory authorities. The total number of the borrowing reallocations may not exceed eight per year during the term of the facility. (d) Includes revolving credit agreement at Exelon Corporate with a maximum program size of $600 million at both December 31, 2019 and 2018 , respectively. Exelon Corporate had $136 million of outstanding commercial paper at December 31, 2019 and no outstanding commercial paper at the end of 2018 . In order to maintain their respective commercial paper programs in the amounts indicated above, each Registrant must have credit facilities in place, at least equal to the amount of its commercial paper program. A registrant does not issue commercial paper in an aggregate amount exceeding the then available capacity under its credit facility. At December 31, 2019 , the Registrants had the following aggregate bank commitments, credit facility borrowings and available capacity under their respective credit facilities: Available Capacity at December 31, 2019 Borrower Facility Type Aggregate Bank (a) Facility Draws Outstanding Letters of Credit Actual To Support Additional Commercial (b) Exelon (b) Syndicated Revolver / Bilaterals / Project Finance $ 10,559 $ — $ 1,443 $ 9,116 $ 7,353 Generation Syndicated Revolver 5,300 — 769 4,531 4,211 Generation Bilaterals 1,400 — 545 855 — Generation Project Finance 159 — 120 39 — ComEd Syndicated Revolver 1,000 — 2 998 868 PECO Syndicated Revolver 600 — — 600 600 BGE Syndicated Revolver 600 — — 600 524 PHI Syndicated Revolver 900 — — 900 692 Pepco Syndicated Revolver 300 — — 300 218 DPL Syndicated Revolver 300 — — 300 244 ACE Syndicated Revolver 300 — — 300 230 __________ (a) Excludes $142 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $44 million , $33 million , $33 million , $8 million , $8 million , $8 million and $8 million , respectively. These facilities expire on October 9, 2020. These facilities are solely utilized to issue letters of credit. As of December 31, 2019 , letters of credit issued under these facilities totaled $5 million , $5 million , $2 million for Generation, ComEd, and BGE, respectively. (b) Includes $600 million aggregate bank commitment related to Exelon Corporate. Exelon Corporate had $6 million and $9 million outstanding letters of credit at December 31, 2019 and 2018 , respectively. Exelon Corporate had $458 million in available capacity to support additional commercial paper at December 31, 2019 . The following tables present the short-term borrowings activity for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE during 2019 and 2018 . December 31, 2019 Exelon (a) Generation ComEd PECO BGE PHI Pepco DPL ACE Average borrowings $ 472 $ 13 $ 236 $ — $ 103 N/A $ 45 $ 21 $ 51 Maximum borrowings outstanding 890 357 465 21 298 N/A 144 125 180 Average interest rates, computed on a daily basis 2.25 % 1.84 % 2.38 % 2.39 % 2.46 % N/A 2.56 % 2.02 % 2.43 % Average interest rates, at December 31 2.25 % 1.84 % 2.38 % 2.39 % 2.46 % N/A 2.56 % 2.02 % 2.43 % December 31, 2018 Exelon (a) Generation ComEd PECO BGE PHI Pepco DPL ACE Average borrowings $ 531 $ 37 $ 154 $ 68 $ 65 N/A $ 22 $ 87 $ 95 Maximum borrowings outstanding 1,237 583 520 350 239 N/A 90 245 210 Average interest rates, computed on a daily basis 2.21 % 1.96 % 2.14 % 2.24 % 2.18 % N/A 2.24 % 2.07 % 2.21 % Average interest rates, at December 31 2.15 % 1.96 % 2.14 % 2.24 % 2.18 % N/A 2.24 % 2.07 % 2.21 % __________ (a) Includes $3 million and $4 million average borrowings related to Exelon Corporate at December 31, 2019 and 2018 , respectively. Exelon Corporate had $144 million and $95 million maximum borrowings outstanding at December 31, 2019 and 2018 , with 1.92% and 1.93% average interest rates computed on a daily basis for 2019 and 2018, and 1.92% and 1.93% average interest rates at December 31, 2019 and 2018 , respectively. 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. Revolving Credit Agreements On May 26, 2016, Exelon Corporate, Generation, ComEd, PECO and BGE entered into amendments to each of their respective syndicated revolving credit facilities, which extended the maturity of each of the facilities to May 26, 2021. Exelon Corporate also increased the size of its facility from $500 million to $600 million . On May 26, 2016, PHI, Pepco, DPL and ACE entered into an amendment to their Second Amended and Restated Credit Agreement dated as of August 1, 2011, which (i) extended the maturity date of the facility to May 26, 2021, (ii) removed PHI as a borrower under the facility, (iii) decreased the size of the facility from $1.5 billion to $900 million and (iv) aligned its financial covenant from debt to capitalization leverage ratio to interest coverage ratio. On May 26, 2018, each of the Registrants' respective syndicated revolving credit facilities had their maturity dates extended to May 26, 2023. Bilateral Credit Agreements The following table reflects the bilateral credit agreements at December 31, 2019 : Registrant Date Initiated Latest Amendment Date Maturity Date (a) Amount Generation (b) October 26, 2012 October 24, 2019 October 24, 2020 $ 200 Generation (c) January 11, 2013 January 4, 2019 March 1, 2021 100 Generation (c) January 5, 2016 January 4, 2019 April 5, 2021 150 Generation (c) February 21, 2019 N/A March 31, 2021 100 Generation (c) October 25, 2019 N/A N/A 200 Generation (c) October 25, 2019 N/A N/A 100 Generation (c) November 20, 2019 N/A N/A 300 Generation (c) November 21, 2019 N/A November 21, 2020 150 Generation (c) November 21, 2019 N/A November 21, 2021 100 __________ (a) Credit facilities that do not contain a maturity date are specific to the agreements set within each contract. In some instances, credit facilities are automatically renewed based on the contingency standards set within the specific agreement. (b) Bilateral credit facility relates to CENG, which is incorporated within Generation, and supports the issuance of letters of credit and funding for working capital and does not back Generation's commercial paper program. (c) Bilateral credit agreements solely support the issuance of letters of credit and do not back Generation's commercial paper program. Borrowings under Exelon Corporate’s, Generation’s, ComEd’s, PECO’s, BGE's, Pepco's, DPL's and ACE's revolving credit agreements bear interest at a rate based upon either the prime rate or a LIBOR-based rate, plus an adder based upon the particular Registrant’s credit rating. The adders for the prime based borrowings and LIBOR-based borrowings are presented in the following table: Exelon Generation ComEd PECO BGE Pepco DPL ACE Prime based borrowings 27.5 27.5 7.5 — — 7.5 7.5 7.5 LIBOR-based borrowings 127.5 127.5 107.5 90.0 100.0 107.5 107.5 107.5 If any registrant loses its investment grade rating, the maximum adders for prime rate borrowings and LIBOR-based rate borrowings would be 65 basis points and 165 basis points. The credit agreements also require the borrower to pay a facility fee based upon the aggregate commitments. The fee varies depending upon the respective credit ratings of the borrower. Variable Rate Demand Bonds DPL has outstanding obligations in respect of Variable Rate Demand Bonds (VRDB). VRDBs are subject to repayment on the demand of the holders and, for this reason, are accounted for as short-term debt in accordance with GAAP. However, these bonds may be converted to a fixed-rate, fixed-term option to establish a maturity which corresponds to the date of final maturity of the bonds. On this basis, PHI views VRDBs as a source of long-term financing. As of both December 31, 2019 and December 31, 2018 , $79 million in variable rate demand bonds issued by DPL were outstanding and are included in the Long-term debt due within one year in Exelon's, PHI's and DPL's Consolidated Balance Sheet. Long-Term Debt The following tables present the outstanding long-term debt at the Registrants as of December 31, 2019 and 2018 : Exelon Maturity Date December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 1.70 % - 7.90 % 2020 - 2049 $ 17,486 $ 16,496 Senior unsecured notes 2.45 % - 7.60 % 2020 - 2046 10,685 11,285 Unsecured notes 2.40 % - 6.35 % 2021 - 2049 3,300 2,900 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 412 435 Nuclear fuel procurement contracts 3.15 % 2020 3 39 Notes payable and other 2.53 % - 7.99 % 2020 - 2053 154 188 Junior subordinated notes 3.50 % 2022 1,150 1,150 Long-term software licensing agreement 3.95 % 2024 55 73 Unsecured Tax-Exempt Bonds (b) 1.63 % - 5.40 % 2022 - 2031 222 112 Medium-Terms Notes (unsecured) 7.61 % - 7.72 % 2027 10 22 Transition bonds 5.55 % 2023 40 59 Loan Agreement 2.00 % 2023 50 50 Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,182 1,253 Variable rates 3.18 % - 4.91 % 2020 - 2024 811 849 Total long-term debt 35,560 34,911 Unamortized debt discount and premium, net (72 ) (66 ) Unamortized debt issuance costs (214 ) (216 ) Fair value adjustment 765 795 Long-term debt due within one year (4,710 ) (1,349 ) Long-term debt $ 31,329 $ 34,075 Long-term debt to financing trusts (c) Subordinated debentures to ComEd Financing III 6.35 % 2033 $ 206 $ 206 Subordinated debentures to PECO Trust III 6.75 % - 7.38 % 2028 81 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Total long-term debt to financing trusts 390 390 Unamortized debt issuance costs — — Long-term debt to financing trusts $ 390 $ 390 __________ (a) Substantially all of ComEd’s assets other than expressly excepted property and substantially all of PECO’s, Pepco's, DPL's and ACE's assets are subject to the liens of their respective mortgage indentures. (b) Bond amount totaling $110 million was previously disclosed within the first mortgage bonds line item, as it was classified as a secured tax-exempt bond. In 2019, the callable bond was reissued as an unsecured tax-exempt bond, and is presented as such within this section. (c) Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets. Generation Maturity Date December 31, Rates 2019 2018 Long-term debt Senior unsecured notes 2.95 % - 7.60 % 2020 - 2042 $ 5,420 $ 6,019 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 412 435 Nuclear fuel procurement contracts 3.15 % 2020 3 39 Notes payable and other 2.53 % - 4.26 % 2020 - 2028 115 164 Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,182 1,253 Variable rates 3.18 % - 4.91 % 2020 - 2024 811 849 Total long-term debt 7,943 8,759 Unamortized debt discount and premium, net (5 ) (6 ) Unamortized debt issuance costs (42 ) (51 ) Fair value adjustment 78 91 Long-term debt due within one year (3,182 ) (906 ) Long-term debt $ 4,792 $ 7,887 ComEd Maturity Date December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 2.55 % - 6.45 % 2020 - 2049 $ 8,578 $ 8,179 Notes payable and other 7.49 % 2053 8 8 Total long-term debt 8,586 8,187 Unamortized debt discount and premium, net (27 ) (23 ) Unamortized debt issuance costs (68 ) (63 ) Long-term debt due within one year (500 ) (300 ) Long-term debt $ 7,991 $ 7,801 Long-term debt to financing trust (b) Subordinated debentures to ComEd Financing III 6.35 % 2033 $ 206 $ 206 Total long-term debt to financing trusts 206 206 Unamortized debt issuance costs (1 ) (1 ) Long-term debt to financing trusts $ 205 $ 205 __________ (a) Substantially all of ComEd’s assets, other than expressly excepted property, are subject to the lien of its mortgage indenture. (b) Amount owed to this financing trust is recorded as Long-term debt to financing trust within ComEd’s Consolidated Balance Sheets. PECO Maturity Date December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 1.70 % - 5.95 % 2021 - 2049 $ 3,400 $ 3,075 Loan Agreement 2.00 % 2023 50 50 Total long-term debt 3,450 3,125 Unamortized debt discount and premium, net (21 ) (18 ) Unamortized debt issuance costs (24 ) (23 ) Long-term debt $ 3,405 $ 3,084 Long-term debt to financing trusts (b) Subordinated debentures to PECO Trust III 6.75 % - 7.38 % 2028 $ 81 $ 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Long-term debt to financing trusts $ 184 $ 184 __________ (a) Substantially all of PECO’s assets are subject to the lien of its mortgage indenture. (b) Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets. BGE Maturity Date December 31, Rates 2019 2018 Long-term debt Unsecured notes 2.40 % - 6.35 % 2021 - 2049 $ 3,300 $ 2,900 Total long-term debt 3,300 2,900 Unamortized debt discount and premium, net (9 ) (6 ) Unamortized debt issuance costs (21 ) (18 ) Long-term debt $ 3,270 $ 2,876 PHI Maturity December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 1.76 % - 7.90 % 2021 - 2049 $ 5,508 $ 5,242 Senior unsecured notes 7.45 % 2032 185 185 Unsecured Tax-Exempt Bonds (b) 1.63 % - 5.40 % 2022 - 2031 222 112 Medium-terms notes (unsecured) 7.61 % - 7.72 % 2027 10 22 Transition bonds (c) 5.55 % 2023 40 59 Notes payable and other 3.54 % - 7.99 % 2021 - 2027 30 16 Total long-term debt 5,995 5,636 Unamortized debt discount and premium, net 4 4 Unamortized debt issuance costs (19 ) (14 ) Fair value adjustment 583 633 Long-term debt due within one year (103 ) (125 ) Long-term debt $ 6,460 $ 6,134 _________ (a) Substantially all of Pepco's, DPL's, and ACE's assets are subject to the lien of its respective mortgage indenture. (b) Bond amount totaling $110 million was previously disclosed within the first mortgage bonds line item, as it was classified as a secured tax-exempt bond. In 2019, the callable bond was reissued as an unsecured tax-exempt bond, and is presented as such within this section. (c) Transition bonds are recorded as part of Long-term debt within ACE's Consolidated Balance Sheets. Pepco Maturity December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 3.05 % - 7.90 % 2022 - 2048 $ 2,775 $ 2,735 Unsecured Tax-Exempt Bonds (b) 1.70 % 2022 110 — Notes payable and other 3.54 % - 7.99 % 2021 - 2027 12 16 Total long-term debt 2,897 2,751 Unamortized debt discount and premium, net 2 2 Unamortized debt issuance costs (35 ) (34 ) Long-term debt due within one year (2 ) (15 ) Long-term debt $ 2,862 $ 2,704 __________ (a) Substantially all of Pepco's assets are subject to the lien of its respective mortgage indenture. (b) Bond amount totaling $110 million was previously disclosed within the first mortgage bonds line item, as it was classified as a secured tax-exempt bond. In 2019, the callable bond was reissued as an unsecured tax-exempt bond, and is presented as such within this section. DPL Maturity December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 1.76 % - 4.27 % 2023 - 2049 $ 1,446 $ 1,370 Unsecured Tax-Exempt Bonds 1.63 % - 5.40 % 2024 - 2031 112 112 Medium-terms notes (unsecured) 7.61 % - 7.72 % 2027 10 22 Other 3.54 % 2027 10 — Total long-term debt 1,578 1,504 Unamortized debt discount and premium, net 1 2 Unamortized debt issuance costs (12 ) (12 ) Long-term debt due within one year (80 ) (91 ) Long-term debt $ 1,487 $ 1,403 __________ (a) Substantially all of DPL's assets are subject to the lien of its respective mortgage indenture. ACE Maturity December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 3.38 % - 6.80 % 2021 - 2049 $ 1,287 $ 1,137 Transition bonds (b) 5.55 % 2023 40 59 Other 3.54 % 2027 8 — Total long-term debt $ 1,335 $ 1,196 Unamortized debt discount and premium, net (1 ) (1 ) Unamortized debt issuance costs (7 ) (7 ) Long-term debt due within one year (20 ) (18 ) Long-term debt $ 1,307 $ 1,170 __________ (a) Substantially all of ACE's assets are subject to the lien of its respective mortgage indenture. (b) Maturities of ACE's Transition Bonds outstanding at December 31, 2019 are $19 million in 2020 and $21 million in 2021. Long-term debt maturities at Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE in the periods 2020 through 2024 and thereafter are as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2020 $ 4,710 $ 3,182 $ 500 $ — $ — $ 103 $ 2 $ 80 $ 20 2021 1,517 2 350 300 300 265 2 2 261 2022 3,088 1,024 — 350 250 314 311 2 1 2023 855 1 — 50 300 504 1 502 1 2024 1,596 792 250 — — 553 401 1 151 Thereafter 24,184 (a) 2,942 7,691 (b) 2,934 (c) 2,450 4,256 2,180 991 901 Total $ 35,950 $ 7,943 $ 8,791 $ 3,634 $ 3,300 $ 5,995 $ 2,897 $ 1,578 $ 1,335 __________ (a) Includes $390 million due to ComEd and PECO financing trusts. (b) Includes $206 million due to ComEd financing trust. (c) Includes $184 million due to PECO financing trusts. Debt Covenants As of December 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, in which approximately $2.8 billion of generating assets have been pledged as collateral at December 31, 2019 . 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. If a specific project financing entity does not maintain compliance with its specific nonrecourse debt financing covenants, there could be a requirement to accelerate repayment of the associated debt or other borrowings earlier than the stated maturity dates. In these instances, if such repayment was not satisfied, the lenders or security holders would generally have rights to foreclose against the project-specific assets and related collateral. The potential requirement to satisfy its associated debt or other borrowings earlier than otherwise anticipated could lead to impairments due to a higher likelihood of disposing of the respective project-specific assets significantly before the end of their useful lives. 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. Interest rates on the loan were fixed upon each advance at a spread of 37.5 basis points above U.S. Treasuries of comparable maturity. The advances were completed as of December 31, 2015 and the outstanding loan balance will bear interest at an average blended interest rate of 2.82% . As of December 31, 2019 , approximately $485 million was outstanding. In addition, Generation has issued letters of credit to support its equity investment in the project. As of December 31, 2019 , Generation had $38 million in letters of credit outstanding related to the project. 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 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 in the first quarter of 2019 and continues to be classified as current as of December 31, 2019 . Further, distributions from Antelope Valley to EGR IV are currently suspended. Continental Wind. In September 2013, Continental Wind, LLC (Continental Wind), an indirect subsidiary of Exelon and Generation, completed the issuance and sale of $613 million senior secured notes. Continental Wind owns and operates a portfolio of wind farms in Idaho, Kansas, Michigan, Oregon, New Mexico and Texas with a total net capacity of 667 MW. The net proceeds were distributed to Generation for its general business purposes. The notes are scheduled to mature on February 28, 2033. The notes bear interest at a fixed rate of 6.00% with interest payable semi-annually. As of December 31, 2019 , $447 million was outstanding. In addition, Continental Wind entered into a $131 million letter of credit facility and $10 million working capital revolver facility. Continental Wind has issued letters of credit to satisfy certain of its credit support and security obligations. As of December 31, 2019 , the Continental Wind letter of credit facility had $115 million in letters of credit outstanding related to the project. In 2017, Generation’s interests in Continental Wind were contributed to EGRP. Refer to Note 22 - Variable Interest Entities for additional information on EGRP. Renewable Power Generation. In March 2016, RPG, an indirect subsidiary of Exelon and Generation, issued $150 million aggregate principal amount of a nonrecourse senior secured notes. The net proceeds were distributed to Generation for paydown of long term debt obligations at Sacramento PV Energy and Constellation Solar Horizons and for general business purposes. The loan is scheduled to mature on March 31, 2035. The term loan bears interest at a fixed rate of 4.11% payable semi-annually. As of December 31, 2019 , $106 million was outstanding. In 2017, Generation’s interests in Renewable Power Generation were contributed to EGRP. Refer to Note 22 - Variable Interest Entities for additional information on EGRP. SolGen. In September 2016, SolGen, LLC (SolGen), an indirect subsidiary of Exelon and Generation, issued $150 million aggregate principal amount of a nonrecourse senior secured notes. The net proceeds were distributed to Generation for general business purposes. The loan is scheduled to mature on September 30, 2036. The term loan bears interest at a fixed rate of 3.93% payable semi-annually. As of December 31, 2019 , $131 million was outstanding. In 2017, Generation’s interests in SolGen were also contributed to and are pledged as collateral for the EGR IV financing structure referenced below. 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 net proceeds of $785 million , after the initial funding of $50 million for debt service and liquidity reserves as well as deductions for original discount and estimated costs, fees and expenses incurred in connection with the execution and delivery of the credit facility agreement, were distributed to Generation for general corporate purposes. The $50 million of debt service and liquidity reserves was treated as restricted cash in Exelon’s and Generation’s Consolidated Balance Sheets and Consolidated Statements of Cash Flows. The loan is scheduled to mature on November 28, 2024. The term loan bears interest at a variable rate equal to LIBOR + 3% , subject to a 1% LIBOR floor with interest payable quarterly. As of December 31, 2019 , $796 million was outstanding. In addition to the financing, EGR IV entered into interest rate swaps with an initial notional amount of $636 million at an interest rate of 2.32% to manage a portion of the interest rate exposure in connection with the financing. 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 22 - Variable Interest Entities for additional information on EGRP.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities (All Registrants)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities (All Registrants)	Fair Value of Financial Assets and Liabilities (All Registrants) Exelon measure and records fair value measurements in accordance with the hierarchy as defined by GAAP . 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. Fair Value of Financial Liabilities Recorded at the Carrying Amount The following tables present the carrying amounts and fair values of the Registrants’ short-term liabilities, long-term debt, SNF obligation, and trust preferred securities (long-term debt to financing trusts or junior subordinated debentures) as of December 31, 2019 and 2018 . The Registrants have no financial liabilities classified as Level 1. The carrying amounts of the Registrants’ short-term liabilities as presented on their Consolidated Balance Sheets are representative of their fair value (Level 2) because of the short-term nature of these instruments. December 31, 2019 December 31, 2018 Carrying Amount Fair Value Carrying Amount Fair Value Level 2 Level 3 Total Level 2 Level 3 Total Long-Term Debt, including amounts due within one year (a) Exelon $ 36,039 $ 37,453 $ 2,580 $ 40,033 $ 35,424 $ 33,711 $ 2,158 $ 35,869 Generation 7,974 7,304 1,366 8,670 8,793 7,467 1,443 8,910 ComEd 8,491 9,848 — 9,848 8,101 8,390 — 8,390 PECO 3,405 3,868 50 3,918 3,084 3,157 50 3,207 BGE 3,270 3,649 — 3,649 2,876 2,950 — 2,950 PHI 6,563 5,902 1,164 7,066 6,259 5,436 665 6,101 Pepco 2,864 3,198 388 3,586 2,719 2,901 196 3,097 DPL 1,567 1,408 311 1,719 1,494 1,303 193 1,496 ACE 1,327 1,026 464 1,490 1,188 987 275 1,262 Long-Term Debt to Financing Trusts (a) Exelon $ 390 $ — $ 428 $ 428 $ 390 $ — $ 400 $ 400 ComEd 205 — 227 227 205 — 209 209 PECO 184 — 201 201 184 — 191 191 SNF Obligation Exelon $ 1,199 $ 1,055 $ — $ 1,055 $ 1,171 $ 949 $ — $ 949 Generation 1,199 1,055 — 1,055 1,171 949 — 949 ________ (a) Includes unamortized debt issuance costs which are not fair valued. Refer to Note 16 — Debt and Credit Agreements for each Registrants’ unamortized debt issuance costs . Exelon uses the following methods and assumptions to estimate fair value of financial liabilities recorded at carrying cost: Type Level Registrants Valuation Long-term debt, including amounts due within one year Taxable Debt Securities 2 All The fair value is determined by a valuation model that is based on a conventional discounted cash flow methodology and utilizes assumptions of current market pricing curves. Exelon obtains credit spreads based on trades of existing Exelon debt securities as well as other issuers in the utility sector with similar credit ratings. The yields are then converted into discount rates of various tenors that are used for discounting the respective cash flows of the same tenor for each bond or note. Variable Rate Financing Debt 2 Exelon, Generation, DPL Debt rates are reset on a regular basis and the carrying value approximates fair value. Taxable Private Placement Debt Securities 3 Exelon, Pepco, DPL, ACE Rates are obtained similar to the process for taxable debt securities. Due to low trading volume and qualitative factors such as market conditions, low volume of investors and investor demand, these debt securities are Level 3. Government Backed Fixed Rate Project Financing Debt 3 Exelon, Generation The fair value is similar to the process for taxable debt securities. Due to the lack of market trading data on similar debt, the discount rates are derived based on the original loan interest rate spread to the applicable U.S. Treasury rate as well as a current market curve derived from government-backed securities. Non-Government Backed Fixed Rate Nonrecourse Debt 3 Exelon, Generation, Pepco Fair value is based on market and quoted prices for its own and other nonrecourse debt with similar risk profiles. Given the low trading volume in the nonrecourse debt market, the price quotes used to determine fair value will reflect certain qualitative factors, such as market conditions, investor demand, new developments that might significantly impact the project cash flows or off-taker credit, and other circumstances related to the project Long Term Debt to Financing Trusts 3 Exelon, ComEd, PECO Fair value is based on publicly traded securities issued by the financing trusts. Due to low trading volume of these securities and qualitative factors, such as market conditions, investor demand, and circumstances related to each issue, this debt is classified as Level 3. SNF Obligation 2 Exelon, Generation The carrying amount is derived from a contract with the DOE to provide for disposal of SNF from Generation’s nuclear generating stations. When determining the fair value of the obligation, the future carrying amount of the SNF obligation is calculated by compounding the current book value of the SNF obligation at the 13-week U.S. Treasury rate. The compounded obligation amount is discounted back to present value using Generation’s discount rate, which is calculated using the same methodology as described above for the taxable debt securities, and an estimated maturity date of 2030. Recurring Fair Value Measurements The following tables present assets and liabilities measured and recorded at fair value in the Registrants' Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2019 and 2018 : Exelon Generation As of December 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) $ 639 $ — $ — $ — $ 639 $ 214 $ — $ — $ — $ 214 NDT fund investments Cash equivalents (b) 365 87 — — 452 365 87 — — 452 Equities 3,353 1,753 — 1,388 6,494 3,353 1,753 — 1,388 6,494 Fixed income Corporate debt — 1,469 257 — 1,726 — 1,469 257 — 1,726 U.S. Treasury and agencies 1,808 131 — — 1,939 1,808 131 — — 1,939 Foreign governments — 42 — — 42 — 42 — — 42 State and municipal debt — 90 — — 90 — 90 — — 90 Other (c) — 33 — 953 986 — 33 — 953 986 Fixed income subtotal 1,808 1,765 257 953 4,783 1,808 1,765 257 953 4,783 Private credit — — 254 508 762 — — 254 508 762 Private equity — — — 402 402 — — — 402 402 Real estate — — — 607 607 — — — 607 607 NDT fund investments subtotal (d) 5,526 3,605 511 3,858 13,500 5,526 3,605 511 3,858 13,500 Rabbi trust investments Cash equivalents 50 — — — 50 4 — — — 4 Mutual funds 81 — — — 81 25 — — — 25 Fixed income — 12 — — 12 — — — — — Life insurance contracts — 78 41 — 119 — 25 — — 25 Rabbi trust investments subtotal 131 90 41 — 262 29 25 — — 54 Commodity derivative assets Economic hedges 768 2,491 1,485 — 4,744 768 2,491 1,485 — 4,744 Proprietary trading — 37 60 — 97 — 37 60 — 97 Effect of netting and allocation of (e)(f) (908 ) (2,162 ) (588 ) — (3,658 ) (908 ) (2,162 ) (588 ) — (3,658 ) Commodity derivative assets subtotal (140 ) 366 957 — 1,183 (140 ) 366 957 — 1,183 Total assets 6,156 4,061 1,509 3,858 15,584 5,629 3,996 1,468 3,858 14,951 Exelon Generation As of December 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 (1,071 ) (2,855 ) (1,228 ) — (5,154 ) (1,071 ) (2,855 ) (927 ) — (4,853 ) Proprietary trading — (34 ) (15 ) — (49 ) — (34 ) (15 ) — (49 ) Effect of netting and allocation of (e)(f) 1,071 2,714 802 — 4,587 1,071 2,714 802 — 4,587 Commodity derivative liabilities subtotal — (175 ) (441 ) — (616 ) — (175 ) (140 ) — (315 ) Deferred compensation obligation — (147 ) — — (147 ) — (41 ) — — (41 ) Total liabilities — (322 ) (441 ) — (763 ) — (216 ) (140 ) — (356 ) Total net assets $ 6,156 $ 3,739 $ 1,068 $ 3,858 $ 14,821 $ 5,629 $ 3,780 $ 1,328 $ 3,858 $ 14,595 Exelon Generation 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) $ 1,243 $ — $ — $ — $ 1,243 $ 581 $ — $ — $ — $ 581 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 Private credit — — 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 Exelon Generation 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 Rabbi trust investments Cash equivalents 48 — — — 48 5 — — — 5 Mutual funds 72 — — — 72 24 — — — 24 Fixed income — 15 — — 15 — — — — — Life insurance contracts — 70 38 — 108 — 22 — — 22 Rabbi trust investments subtotal 120 85 38 — 243 29 22 — — 51 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 (e)(f) (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 Total assets 6,573 4,155 1,396 3,433 15,557 5,820 4,092 1,358 3,433 14,703 Liabilities Commodity derivative liabilities Economic hedges (642 ) (2,963 ) (1,276 ) — (4,881 ) (642 ) (2,963 ) (1,027 ) — (4,632 ) Proprietary trading — (73 ) (21 ) — (94 ) — (73 ) (21 ) — (94 ) Effect of netting and allocation of (e)(f) 639 2,581 808 — 4,028 639 2,581 808 — 4,028 Commodity derivative liabilities subtotal (3 ) (455 ) (489 ) — (947 ) (3 ) (455 ) (240 ) — (698 ) Deferred compensation obligation — (137 ) — — (137 ) — (35 ) — — (35 ) Total liabilities (3 ) (592 ) (489 ) — (1,084 ) (3 ) (490 ) (240 ) — (733 ) Total net assets $ 6,570 $ 3,563 $ 907 $ 3,433 $ 14,473 $ 5,817 $ 3,602 $ 1,118 $ 3,433 $ 13,970 __________ (a) Exelon excludes cash of $373 million and $458 million at December 31, 2019 and 2018 , respectively, and restricted cash of $110 million and $80 million at December 31, 2019 and 2018 , respectively, and includes long-term restricted cash of $177 million and $185 million at December 31, 2019 and 2018 , respectively, which is reported in Other deferred debits in the Consolidated Balance Sheets. Generation excludes cash of $177 million and $283 million at December 31, 2019 and 2018 , respectively and restricted cash of $58 million and $39 million at December 31, 2019 and 2018 , respectively. (b) Includes $90 million and $50 million of cash received from outstanding repurchase agreements at December 31, 2019 and 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 $2 million and $44 million , which have a total notional amount of $724 million and $1,432 million at December 31, 2019 and 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 the company's exposure to credit or market loss. (d) Excludes net liabilities of $147 million and $130 million at December 31, 2019 and 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) Collateral posted/(received) from counterparties totaled $163 million , $551 million and $214 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2019 . Collateral posted/(received) from 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 . (f) Of the collateral posted/(received), $511 million and $(94) million represents variation margin on the exchanges as of December 31, 2019 and 2018 , respectively. As of December 31, 2019 , Generation has outstanding commitments to invest in fixed income, private credit, private equity and real estate investments of approximately $85 million , $166 million , $375 million and $427 million , respectively. These commitments will be funded by Generation’s existing NDT funds. Exelon and Generation hold investments without readily determinable fair values with carrying amounts of $69 million as of December 31, 2019 . Changes were immaterial in fair value, cumulative adjustments and impairments for the year ended December 31, 2019 . ComEd PECO BGE As of December 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) $ 280 $ — $ — $ 280 $ 15 $ — $ — $ 15 $ — $ — $ — $ — Rabbi trust investments Mutual funds — — — — 8 — — 8 8 — — 8 Life insurance contracts — — — — — 11 — 11 — — — — Rabbi trust investments subtotal — — — — 8 11 — 19 8 — — 8 Total assets 280 — — 280 23 11 — 34 8 — — 8 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (9 ) — (9 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (b) — — (301 ) (301 ) — — — — — — — — Total liabilities — (8 ) (301 ) (309 ) — (9 ) — (9 ) — (5 ) — (5 ) Total net assets (liabilities) $ 280 $ (8 ) $ (301 ) $ (29 ) $ 23 $ 2 $ — $ 25 $ 8 $ (5 ) $ — $ 3 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 — — — — 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 (b) — — (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 $90 million and $93 million at December 31, 2019 and 2018 and restricted cash of $33 million and $28 million at December 31, 2019 and 2018 , respectively, and includes long-term restricted cash of $163 million and $166 million at December 31, 2019 and 2018 , respectively which is reported in Other deferred debits in the Consolidated Balance Sheets. PECO excludes cash of $12 million and $24 million at December 31, 2019 and 2018 , respectively. BGE excludes cash of $24 million and $7 million at December 31, 2019 and 2018 , respectively, and restricted cash of $1 million and $2 million at December 31, 2019 and 2018 , respectively. (b) The Level 3 balance consists of the current and noncurrent liability of $32 million and $269 million , respectively, at December 31, 2019 , and $26 million and $223 million , respectively, at December 31, 2018 , related to floating-to-fixed energy swap contracts with unaffiliated suppliers. As of December 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) $ 124 $ — $ — $ 124 $ 147 $ — $ — $ 147 Rabbi trust investments Cash equivalents 44 — — 44 42 — — 42 Mutual Funds 14 — — 14 13 — — 13 Fixed income — 12 — 12 — 15 — 15 Life insurance contracts — 24 41 65 — 22 38 60 Rabbi trust investments subtotal (b) 58 36 41 135 55 37 38 130 Total assets 182 36 41 259 202 37 38 277 Liabilities Deferred compensation obligation — (19 ) — (19 ) — (21 ) — (21 ) Total liabilities — (19 ) — (19 ) — (21 ) — (21 ) Total net assets $ 182 $ 17 $ 41 $ 240 $ 202 $ 16 $ 38 $ 256 Pepco DPL ACE As of December 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) $ 34 $ — $ — $ 34 $ — $ — $ — $ — $ 16 $ — $ — $ 16 Rabbi trust investments Cash equivalents 43 — — 43 — — — — — — — — Fixed income — 2 — 2 — — — — — — — — Life insurance contracts — 24 41 65 — — — — — — — — Rabbi trust investments subtotal 43 26 41 110 — — — — — — — — Total assets 77 26 41 144 — — — — 16 — — 16 Liabilities Deferred compensation obligation — (2 ) — (2 ) — — — — — — — — Total liabilities — (2 ) — (2 ) — — — — — — — — Total net assets $ 77 $ 24 $ 41 $ 142 $ — $ — $ — $ — $ 16 $ — $ — $ 16 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 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 $ 79 $ 24 $ 37 $ 140 $ 16 $ (1 ) $ — $ 15 $ 23 $ — $ — $ 23 __________ (a) PHI excludes cash of $57 million and $39 million at December 31, 2019 and 2018 , respectively, and includes long term restricted cash of $14 million and $19 million at December 31, 2019 and 2018 , respectively, which is reported in Other deferred debits in the Consolidated Balance Sheets. Pepco excludes cash of $29 million and $15 million at December 31, 2019 and 2018 , respectively. DPL excludes cash of $13 million and $8 million at December 31, 2019 and 2018 , respectively. ACE excludes cash of $12 million and $7 million at December 31, 2019 and 2018 , respectively, and includes long-term restricted cash of $14 million and $19 million at December 31, 2019 and 2018 , respectively, which is reported in Other deferred debits in the Consolidated Balance Sheets. The following tables present the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis during the years ended December 31, 2019 and 2018 : Exelon Generation ComEd PHI and Pepco For the year ended December 31, 2019 Total NDT Fund Investments Mark-to-Market Total Generation Mark-to-Market Derivatives Life Insurance Contracts Eliminated in Consolidation Balance as of January 1, 2019 $ 907 $ 543 $ 575 $ 1,118 $ (249 ) $ 38 $ — Total realized / unrealized gains (losses) Included in net income (23 ) 5 (31 ) (a) (26 ) — 3 — Included in noncurrent payables to affiliates — 34 — 34 — — (34 ) Included in regulatory assets/liabilities (18 ) — — — (52 ) (b) — 34 Change in collateral 138 — 138 138 — — — Purchases, sales, issuances and settlements Purchases 176 44 132 176 — — — Sales (23 ) (21 ) (2 ) (23 ) — — — Settlements (89 ) (94 ) 5 (89 ) — — — Transfers into Level 3 5 — 5 (c) 5 — — — Transfers out of Level 3 (5 ) — (5 ) (c) (5 ) — — — Balance as of December 31, 2019 $ 1,068 $ 511 $ 817 $ 1,328 $ (301 ) $ 41 $ — The amount of total gains (losses) included in income attributed to the change in unrealized (losses) gains related to assets and liabilities held as of December 31, 2019 $ 359 $ 5 $ 351 $ 356 $ — $ 3 $ — Exelon Generation ComEd PHI and Pepco For the year ended December 31, 2018 Total NDT Fund Investments Mark-to-Market Derivatives Total Generation Mark-to-Market Derivatives Life Insurance Contracts Eliminated in Consolidation Balance as of January 1, 2018 $ 966 $ 648 $ 552 $ 1,200 $ (256 ) $ 22 $ — Total realized / unrealized gains (losses) Included in net income (101 ) — (105 ) (a) (105 ) — 4 — Included in noncurrent payables to affiliates — (1 ) — (1 ) — — 1 Included in regulatory assets/liabilities 6 — — — 7 (b) — (1 ) Change in collateral (5 ) — (5 ) (5 ) — — — Purchases, sales, issuances and settlements Purchases 226 36 190 226 — — — Sales (4 ) — (4 ) (4 ) — — — Settlements (123 ) (140 ) 5 (135 ) — 12 — Transfers into Level 3 (22 ) — (22 ) (c) (22 ) — — — Transfers out of Level 3 (36 ) — (36 ) (c) (36 ) — — — Balance as of December 31, 2018 $ 907 $ 543 $ 575 $ 1,118 $ (249 ) $ 38 $ — The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held as of December 31, 2018 $ 160 $ (5 ) $ 165 $ 160 $ — $ — $ — __________ (a) Includes a reduction for the reclassification of $377 million and $265 million of realized gains due to the settlement of derivative contracts for the years ended December 31, 2019 and 2018 , respectively. (b) Includes $78 million of decreases in fair value and an increase for realized losses due to settlements of $26 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2019 . Includes $24 million of decreases in fair value and an increase for realized losses due to settlements of $17 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2018 . (c) 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 years ended December 31, 2019 and 2018 : Exelon Generation PHI and Pepco Operating Purchased Operating and Maintenance Other, net Operating Purchased Other, net Operating and Total gains (losses) included in net income for the year ended December 31, 2019 $ 219 $ (245 ) $ 3 $ 5 $ 219 $ (245 ) $ 5 $ 3 Change in the unrealized gains (losses) relating to assets and liabilities held for the year ended December 31, 2019 546 (195 ) 3 5 546 (195 ) 5 3 Exelon Generation PHI and Pepco Operating Purchased Operating and Maintenance Other, net Operating Purchased Other, net Operating and Total (losses) gains included in net income for the year ended December 31, 2018 $ (7 ) $ (93 ) $ 4 $ 3 $ (7 ) $ (93 ) $ 3 $ 4 Change in the unrealized gains (losses) relating to assets and liabilities held for the year ended December 31, 2018 144 21 — (2 ) 144 21 (2 ) — Valuation Techniques Used to Determine Fair Value Cash Equivalents (All Registrants). Investments with original maturities of three months or less when purchased, including mutual and money market funds, are considered cash equivalents. The fair values are based on observable market prices and, therefore, are included in the recurring fair value measurements hierarchy as Level 1. 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, including private credit, private equity and real estate. 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. Equities. These investments consist of individually held equity securities, equity mutual funds and equity commingled funds in domestic and foreign markets. 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 Exelon and Generation are able to independently corroborate. Equity securities held individually, including real estate investment trusts, rights and warrants, are primarily traded on exchanges that contain only actively traded securities due to the volume trading requirements imposed by these exchanges. The equity securities that are held directly by the trust funds are valued based on quoted prices in active markets and categorized as 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. Certain private placement equity securities are categorized as Level 3 because they are not publicly traded and are priced using significant unobservable inputs. Equity commingled funds and mutual funds are maintained by investment companies, and fund investments are held in accordance with a stated set of fund objectives. 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 equity commingled funds and mutual funds which are not publicly quoted, the fund administrators value the funds using the NAV per fund share, derived from the quoted prices in active markets of the underlying securities and are not classified within the fair value hierarchy. These investments typically can be redeemed monthly or more frequently, with 30 or less days of notice and without further restrictions. Fixed income. For fixed income securities, which consist primarily of corporate debt securities, U.S. government securities, foreign government securities, municipal bonds, asset and mortgage-backed securities, commingled funds, mutual funds and derivative instruments, the trustees obtain multiple prices from pricing vendors 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. Exelon and Generation have obtained an understanding of how these prices are derived, including the nature and observability of the inputs used in deriving such prices. Additionally, Exelon and Generation selectively corroborate the fair values of securities by comparison to other market-based price sources. Investments in U.S. Treasury securities have been categorized as Level 1 because they trade in highly-liquid and transparent markets. Certain private placement fixed income securities have been categorized as Level 3 because they are priced using certain significant unobservable inputs and are typically illiquid. The remaining fixed income securities, including certain other fixed income investments, are based on evaluated prices that reflect observable market information, such as actual trade information of similar securities, adjusted for observable differences and are categorized as Level 2. Other fixed income investments primarily consist of fixed income commingled funds and mutual funds, which are maintained by investment companies and hold fund investments in accordance with a stated set of fund objectives. 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 fixed income commingled funds and mutual funds which are not publicly quoted, the fund administrators value the funds using the NAV per fund share, derived from the quoted prices in active markets of the underlying securities and are not classified within the fair value hierarchy. These investments typically can be redeemed monthly or more frequently, with 30 or less days of notice and without further restrictions. Derivative instruments. These instruments, consisting primarily of futures and 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. Private credit. Private credit investments primarily consist of investments in private debt strategies. These investments are generally less liquid assets with an underlying term of 3 to 5 years and are intended to be held to maturity. The fair value of these investments is determined by the fund manager or administrator and include unobservable inputs such as cost, operating results, and discounted cash flows. Private credit investments held directly by Exelon and Generation are categorized as Level 3 because they are based largely on inputs that are unobservable and utilize complex valuation models. Private credit fund investments with multiple investors are not classified within the fair value hierarchy because their fair value is determined using NAV or its equivalent as a practical expedient. Private equity. These investments include those in limited partnerships that invest in operating companies that are not publicly traded on a stock exchange such as leveraged buyouts, growth capital, venture capital, distressed investments and investments in natural resources. Private equity valuations are reported by the fund manager and are based on the valuation of the underlying investments, which include unobservable inputs such as cost, operating results, discounted future cash flows and market based comparable data. The fair value of private equity investments is determined using NAV or its equivalent as a practical expedient, and therefore, these investments are not classified within the fair value hierarchy. Real estate. These investments are funds with a direct investment in pools of real estate properties. These funds are valued by investment managers on a periodic basis using pricing models that use independent appraisals from sources with professional qualifications. These valuation inputs are not highly observable. The fair value of real estate investments is determined using NAV or its equivalent as a practical expedient, and therefore, these investments are not classified within the fair value hierarchy. Generation evaluated its NDT portfolios for the existence of significant concentrations of credit risk as of December 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 December 31, 2019 , there were no significant concentrations (generally defined as greater than 10 percent) of risk in Generation's NDT assets. See Note 9 — Asset Retirement Obligations for additional information on the NDT fund investments. See Note 14 — Retirement Benefits for the valuation techniques used for hedge fund investments. Rabbi Trust Investments (Exelon, Generation, PECO, BGE, PHI, Pepco, DPL and ACE). 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. Money market funds and mutual funds are publicly quoted and have been categorized as Level 1 given the clear observ

Commitments and Contingencies (

Commitments and Contingencies (All Registrants)	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies (All Registrants)	Commitments and Contingencies (All Registrants) Commitments PHI Merger Commitments (Exelon, PHI, Pepco, DPL and ACE). Approval of the PHI Merger in Delaware, New Jersey, Maryland and the District of Columbia was conditioned upon Exelon and PHI agreeing to certain commitments. The following amounts represent total commitment costs that have been recorded since the acquisition date and the total remaining obligations for Exelon, PHI, Pepco, DPL and ACE as of December 31, 2019 : Description Exelon PHI Pepco DPL ACE Total commitments $ 513 $ 320 $ 120 $ 89 $ 111 Remaining commitments (a) $ 101 $ 79 $ 65 $ 8 $ 6 _________ (a) Remaining commitments extend through 2026 and include rate credits, energy efficiency programs and delivery system modernization. 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, are recognized as incurred and recorded in Exelon's and Generation's financial statements. As of December 31, 2019 , 27 MWs of new generation were developed and Exelon and Generation have incurred costs of $120 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. Commercial Commitments (All Registrants). The Registrant s' commercial commitments as of December 31, 2019 , representing commitments potentially triggered by future events, were as follows: Expiration within Exelon Total 2020 2021 2022 2023 2024 2025 and beyond Letters of credit $ 1,455 $ 1,314 $ 141 $ — $ — $ — $ — Surety bonds (a) 855 809 46 — — — — Financing trust guarantees 378 — — — — — 378 Guaranteed lease residual values (b) 26 2 2 4 3 6 10 Total commercial commitments $ 2,714 $ 2,125 $ 189 $ 4 $ 3 $ 6 $ 388 Generation Letters of credit $ 1,440 $ 1,302 $ 138 $ — $ — $ — $ — Surety bonds (a) 670 662 8 — — — — Total commercial commitments $ 2,110 $ 1,964 $ 146 $ — $ — $ — $ — ComEd Letters of credit $ 7 $ 7 $ — $ — $ — $ — $ — Surety bonds (a) 50 48 2 — — — — Financing trust guarantees 200 — — — — — 200 Total commercial commitments $ 257 $ 55 $ 2 $ — $ — $ — $ 200 PECO Surety bonds (a) $ 9 $ 9 $ — $ — $ — $ — $ — Financing trust guarantees 178 — — — — — 178 Total commercial commitments $ 187 $ 9 $ — $ — $ — $ — $ 178 BGE Letters of credit $ 2 $ 2 $ — $ — $ — $ — $ — Surety bonds (a) 3 3 — — — — — Total commercial commitments $ 5 $ 5 $ — $ — $ — $ — $ — PHI Surety bonds (a) $ 21 $ 21 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 26 2 2 4 3 6 10 Total commercial commitments $ 47 $ 23 $ 2 $ 4 $ 3 $ 6 $ 10 Pepco Surety bonds (a) $ 14 $ 14 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 9 — — 1 1 2 5 Total commercial commitments $ 23 $ 14 $ — $ 1 $ 1 $ 2 $ 5 DPL Surety bonds (a) $ 4 $ 4 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 11 1 1 2 1 3 3 Total commercial commitments $ 15 $ 5 $ 1 $ 2 $ 1 $ 3 $ 3 ACE Surety bonds (a) $ 3 $ 3 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 7 1 1 1 1 1 2 Total commercial commitments $ 10 $ 4 $ 1 $ 1 $ 1 $ 1 $ 2 _________ (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 lease term associated with these assets ranges from 1 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $69 million guaranteed by Exelon and PHI, of which $23 million , $29 million and $18 million is guaranteed by Pepco, DPL and ACE, respectively. 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 to limit the liability of nuclear reactor owners for such claims from any single incident. As of December 31, 2019 , the current liability limit per incident is $13.9 billion and is subject to change to account for the effects of inflation and changes in the number of licensed reactors 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 $13.5 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 $2.9 billion , however any amounts payable under this secondary layer would be capped at $434 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 $13.9 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 22 — Variable Interest Entities for additional information on Generation’s operations relating to CENG. Generation is required each year to report to the NRC the current levels and sources of property insurance that demonstrates Generation possesses sufficient financial resources to stabilize and decontaminate a reactor and reactor station site in the event of an accident. The property insurance maintained for each facility is currently provided through insurance policies purchased from NEIL, an industry mutual insurance company of which Generation is a member. NEIL may declare distributions to its members as a result of favorable operating experience. In recent years, NEIL has made distributions to its members, but Generation cannot predict the level of future distributions or if they will continue at all. Generation's portion of the annual distribution declared by NEIL is estimated to be $136 million for 2019 , and was $58 million and $60 million for 2018 and 2017 , respectively. In addition, in March 2018, NEIL declared a supplemental distribution. Generation's portion of the supplemental distribution declared by NEIL was $31 million . The distributions were recorded as a reduction to Operating and maintenance expense within Exelon and Generation’s Consolidated Statements of Operations and Comprehensive Income. Premiums paid to NEIL by its members are 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 $334 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 statements. Spent Nuclear Fuel Obligation (Exelon and Generation) Under the NWPA, the DOE is responsible for the development of a geologic repository for and the disposal of SNF and high-level radioactive waste. As required by the NWPA, Generation is a party to contracts with the DOE (Standard Contracts) to provide for disposal of SNF from Generation’s nuclear generating stations. In accordance with the NWPA and the Standard Contracts, Generation historically had paid the DOE one mill ( $0.001 ) per kWh of net nuclear generation for the cost of SNF disposal. Due to the lack of a viable disposal program, the DOE reduced the SNF disposal fee to zero in May 2014. Until a new fee structure is in effect, Exelon and Generation will not accrue any further costs related to SNF disposal fees. This fee may be adjusted prospectively to ensure full cost recovery. Generation currently assumes the DOE will begin accepting SNF in 2030 and uses that date for purposes of estimating the nuclear decommissioning asset retirement obligations. The SNF acceptance date assumption is based on management’s estimates of the amount of time required for DOE to select a site location and develop the necessary infrastructure for long-term SNF storage. The NWPA and the Standard Contracts required the DOE to begin taking possession of SNF generated by nuclear generating units by no later than January 31, 1998. The DOE, however, failed to meet that deadline and its performance is expected to be delayed significantly. In August 2004, Generation and the DOJ, in close consultation with the DOE, reached a settlement under which the government agreed to reimburse Generation, subject to certain damage limitations based on the extent of the government’s breach, for costs associated with storage of SNF at Generation’s nuclear stations pending the DOE’s fulfillment of its obligations. Generation’s settlement agreement does not include FitzPatrick and FitzPatrick does not currently have a settlement agreement in place. Calvert Cliffs, Ginna and Nine Mile Point each have separate settlement agreements in place with the DOE which were extended during 2017 to provide for the reimbursement of SNF storage costs through December 31, 2019. Generation expects the terms for each of the settlement agreements to be extended during 2020 for another three years to cover SNF storage costs through December 31, 2022. Generation submits annual reimbursement requests to the DOE for costs associated with the storage of SNF. In all cases, reimbursement requests are made only after costs are incurred and only for costs resulting from DOE delays in accepting the SNF. Under the settlement agreements, Generation has received cumulative cash reimbursements for costs incurred as follows: Total Net (a) Cumulative cash reimbursements $ 1,288 $ 1,113 __________ (a) Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Creek. As of December 31, 2019 and 2018 , the amount of SNF storage costs for which reimbursement has been or will be requested from the DOE under the DOE settlement agreements is as follows: December 31, 2019 December 31, 2018 DOE receivable - current (a) $ 249 $ 124 DOE receivable - noncurrent (b) 30 15 Amounts owed to co-owners (a)(c) (37 ) (17 ) __________ (a) Recorded in Accounts receivable, other. (b) Recorded in Deferred debits and other assets, other. (c) Non-CENG amounts owed to co-owners are recorded in Accounts receivable, other. CENG amounts owed to co-owners are recorded in Accounts payable. Represents amounts owed to the co-owners of Peach Bottom, Quad Cities, and Nine Mile Point Unit 2 generating facilities. The Standard Contracts with the DOE also required the payment to the DOE of a one-time fee applicable to nuclear generation through April 6, 1983. The below table outlines the SNF liability recorded at Exelon and Generation as of December 31, 2019 and 2018 : December 31, 2019 December 31, 2018 Former ComEd units (a) $ 1,075 $ 1,052 Fitzpatrick (b) 124 119 Total SNF Obligation $ 1,199 $ 1,171 __________ (a) ComEd previously elected to defer payment of the one-time fee of $277 million for its units (which are now part of Generation), with interest to the date of payment, until just prior to the first delivery of SNF to the DOE. The unfunded liabilities for SNF disposal costs, including the one-time fee, were transferred to Generation as part of Exelon’s 2001 corporate restructuring. (b) A prior owner of FitzPatrick elected to defer payment of the one-time fee of $34 million , with interest to the date of payment, for the FitzPatrick unit. As part of the FitzPatrick acquisition on March 31, 2017, Generation assumed a SNF liability for the DOE one-time fee obligation with interest related to FitzPatrick along with an offsetting asset, included in Other deferred debits and other assets, for the contractual right to reimbursement from NYPA, a prior owner of FitzPatrick, for amounts paid for the FitzPatrick DOE one-time fee obligation . Interest for Exelon's and Generation's SNF liabilities accrues at the 13-week Treasury Rate. The 13-week Treasury Rate in effect for calculation of the interest accrual at December 31, 2019 was 1.551% for the deferred amount transferred from ComEd and 1.879% for the deferred FitzPatrick amount. The following table summarizes sites for which Exelon and Generation do not have an outstanding SNF Obligation: Description Sites Fees have been paid Former PECO units, Clinton and Calvert Cliffs Outstanding SNF Obligation remains with former owners Nine Mile Point, Ginna and TMI 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 on the Registrants' financial statements. MGP Sites (Exelon and the Utility Registrants). 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 21 sites 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 2025. • PECO has 8 sites 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 4 sites that currently require some level of remediation and/or ongoing activity. BGE expects the majority of the remediation at these sites to continue through at least 2021. • DPL has 1 site that is currently 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. 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 December 31, 2019 and 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: December 31, 2019 December 31, 2018 Total environmental Portion of total related to Total environmental Portion of total related to Exelon $ 478 $ 320 $ 496 $ 356 Generation 105 — 108 — ComEd 304 303 329 327 PECO 19 17 27 25 BGE 2 — 5 4 PHI 48 — 27 — Pepco 46 — 25 — DPL 1 — 1 — ACE 1 — 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 have entered into a Consent Agreement to perform the Remedial Design, which is expected to be completed in the 2020 - 2021 time frame. In March 2019 the PRPs received Special Notice Letters from the EPA to perform the Remedial Action work. On October 8, 2019, Generation provided a non-binding good faith offer to conduct, or finance, a portion of the remedy, subject to certain conditions. The total estimated cost of the remedy, taking into account the current EPA technical requirements and the total costs expected to be incurred collectively 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 Remedial Investigation (RI)/Feasibility Study (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 February 2020 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. 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, which was deactivated in June 2012. 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 RI/FS for the Benning Road site and an approximately 10 to 15-acre portion of the adjacent Anacostia River. Since 2013, Pepco and Pepco Energy Services (now Generation, pursuant to Exelon's 2016 acquisition of PHI) have been performing RI work and have submitted multiple draft RI reports to the DOEE. In September 2019, Pepco and Generation issued a draft “final” RI report which DOEE approved and on October 4, 2019 released this document for review and comment by the public. The 45 day comment period ended on November 18, 2019 and a public meeting was held by Pepco on November 2, 2019. Pepco and Generation will proceed to develop a FS to evaluate possible remedial alternatives for submission to DOEE. The Court has established a schedule for completion of the FS, and approval by the DOEE, by September 16, 2021. DOEE will then prepare a Proposed Plan and issue a Record of Decision identifying any further response actions determined to be necessary, after considering public comment on the Proposed Plan. 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 Road site RI/FS being performed by Pepco and Generation, DOEE and the National Park Service have been conducting a separate RI/FS focused on the entire tidal reach of the Anacostia River extending from just north of the Maryland-District of Columbia boundary line to the confluence of the Anacostia and Potomac Rivers. 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 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 Road site RI/FS. In addition, the District of Columbia Council directed DOEE to form an official advisory committee made up of members of federal, state and local environmental regulators, community and environmental groups and various academic and technical experts to provide guidance and support to DOEE as the project progressed. This group, called the Anacostia Leadership Council, has met regularly since it was formed. Pepco has participated in the Consultative Working Group. In April 2018, DOEE released a draft RI report for public review and comment. Pepco submitted written comments to the draft RI and participated in a public hearing. Pepco has determined that it is probable that costs for remediation will be incurred and recorded a liability in the third quarter 2019 for management’s best estimate of its share of those costs based on DOEE’s stated position following a series of meetings attended by representatives from the Anacostia Leadership Council and the Consultative Working Group. On December 27, 2019, DOEE released a Focused Feasibility Study (FFS) and a Proposed Plan (PP) for review and comment by the public which will be the basis for the Interim ROD, which is expected to be completed in September 2020. The FFS and PP are consistent with the DOEE’s stated position to follow an adaptive management approach which will allow several identified “hot spots” in the river to be addressed first while continuing to conduct studies and to monitor the river to evaluate improvements and determine potential future remediation plans. The adaptive management process chosen by DOEE is less intrusive, provides more long term environmental certainty, is less costly, and allows for site specific remediation plans already underway, including the plan for the Benning Road site to proceed to conclusion. The comment period ends on March 2, 2020 and a public meeting will be held on January 23, 2021. Pepco concluded that incremental exposure remains reasonably possible, however management cannot reasonably estimate a range of loss beyond the amounts recorded, which are included in the table above. 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 Natural Resource Damage Trustees, who are defined by CERCLA as the responsible parties for the restoration or compensation for any loss of those resources from the environmental contaminants at the site. If natural resources cannot be restored, then compensation for the injury can be sought from the responsible parties. 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, Pepco cannot reasonably estimate the range of loss. Litigation and Regulatory Matters Asbestos Personal Injury Claims (Ex

Severance (All Registrants)

Severance (All Registrants)	12 Months Ended
	Dec. 31, 2019
Restructuring and Related Activities [Abstract]
Severance (All Registrants)	<div style="font-family:Times New Roman;font-size:10pt;"><div style="line-height:120%;padding-bottom:12px;padding-top:12px;text-align:justify;font-size:9pt;"><font style="font-family:Arial;font-size:9pt;color:#231f20;">The Registrants have an ongoing severance plan under which, in general, the longer an employee worked prior to termination the greater the amount of severance benefits. The Registrants record a liability and expense or regulatory asset for severance once terminations are probable of occurrence and the related severance benefits can be reasonably estimated. For severance benefits that are incremental to its ongoing severance plan (“one-time termination benefits”), the Registrants measure the obligation and record the expense at fair value at the communication date if there are no future service requirements, or, if future service is required to receive the termination benefit, ratably over the required service period.</font></div><div style="line-height:120%;padding-bottom:12px;padding-top:12px;text-align:justify;font-size:9pt;"><font style="font-family:Arial;font-size:9pt;font-weight:bold;">Severance Liability</font></div><div style="line-height:120%;padding-bottom:12px;padding-top:12px;text-align:justify;font-size:10pt;"><font style="font-family:Arial;font-size:9pt;">Amounts included in the table below represent the severance liability recorded for employees of each Registrant. Exelon's severance liability includes amounts related to BSC that are billed through intercompany allocations</font><font style="font-family:Arial;font-size:10pt;">.</font></div><div style="line-height:120%;text-align:center;font-size:10pt;"><div style="padding-left:0px;text-indent:0px;line-height:normal;padding-top:10px;"><table cellpadding="0" cellspacing="0" style="font-family:Times New Roman;font-size:10pt;margin-left:auto;margin-right:auto;width:100%;border-collapse:collapse;text-align:left;"><tr><td colspan="18" rowspan="1"></td></tr><tr><td style="width:23%;" rowspan="1" colspan="1"></td><td style="width:9%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:11%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td></tr><tr><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:left;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;text-decoration:underline;">Severance Liability</font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">Exelon</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">Generation</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">ComEd</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">PECO</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">BGE</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">PHI</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">Pepco</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">DPL</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">ACE</font></div></td></tr></table></div></div><div style="line-height:120%;text-align:justify;font-size:10pt;"><font style="font-family:Arial;font-size:10pt;">__________</font></div><table cellpadding="0" cellspacing="0" style="padding-top:0px;padding-bottom:0px;font-family:Times New Roman; font-size:10pt;"><tr><td style="width:24px;" rowspan="1" colspan="1"></td><td rowspan="1" colspan="1"></td></tr><tr><td style="vertical-align:top" rowspan="1" colspan="1"><div style="line-height:120%;font-size:8pt;padding-left:0px;"><font style="font-family:Arial;font-size:8pt;">(a)</font></div></td><td style="vertical-align:top;" rowspan="1" colspan="1"><div style="line-height:120%;text-align:justify;font-size:8pt;"><font style="font-family:Arial;font-size:8pt;">Includes salary continuance and health and welfare severance benefits.</font></div></td></tr></table></div>

Shareholders' Equity (Exelon an

Shareholders' Equity (Exelon and Utility Registrants)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Shareholders' Equity (Exelon and Utility Registrants) [Text Block]	Shareholders' Equity (Exelon and Utility Registrants) ComEd Common Stock Warrants The following table presents warrants outstanding to purchase ComEd common stock and shares of common stock reserved for the conversion of warrants. The warrants entitle the holders to convert such warrants into common stock of ComEd at a conversion rate of one share of common stock for three warrants. December 31, 2019 2018 Warrants outstanding 60,228 60,285 Common Stock reserved for conversion 20,076 20,095 Equity Securities Offering In June 2014, Exelon issued $1.15 billion of junior subordinated notes in the form of 23 million equity units. In June 2017, Exelon settled the forward equity purchase contract on these equity units through issuance of 33 million shares of common stock from treasury stock, which triggered full dilution in the EPS calculation. Previously, the equity units were included in the calculation of diluted EPS using the treasury stock method. Share Repurchases There currently is no Exelon Board of Director authority to repurchase shares. Any previous shares repurchased are held as treasury shares, at cost, unless cancelled or reissued at the discretion of Exelon’s management. Preferred and Preference Securities The following table presents the Registrants' shares of preferred securities authorized, none of which are outstanding as of December 31, 2019 and 2018 : Preferred Securities Authorized Exelon 100,000,000 ComEd 850,000 PECO 15,000,000 BGE 1,000,000 Pepco 6,000,000 ACE (a) 2,799,979 __________ (a) Includes 799,979 shares of cumulative preferred stock and 2,000,000 of no-par preferred stock as of December 31, 2019 and 2018 , respectively. The following table presents ComEd's, BGE's and ACE's preference securities authorized, none of which are outstanding as of December 31, 2019 and 2018 : Preference Securities Authorized ComEd - Cumulative preference securities 6,810,451 BGE (a) 6,500,000 ACE 3,000,000 __________ (a) Includes 4,600,000 shares of unclassified preference securities and 1,900,000 shares of previously redeemed preference securities as of December 31, 2019 and 2018

Stock-Based Compensation Plans

Stock-Based Compensation Plans Stock-Based Compensation Plans (All Registrants)	12 Months Ended
	Dec. 31, 2019
Common Stock [Abstract]
Stock-Based Compensation Plans	Stock-Based Compensation Plans (All Registrants) Stock-Based Compensation Plans Exelon grants stock-based awards through its LTIP, which primarily includes performance share awards, restricted stock units and stock options. At December 31, 2019 , there were approximately 12 million shares authorized for issuance under the LTIP. For the years ended December 31, 2019 , 2018 and 2017 , exercised and distributed stock-based awards were primarily issued from authorized but unissued common stock shares. The Registrants grant cash awards. The following table does not include expense related to these plans as they are not considered stock-based compensation plans under the applicable authoritative guidance . The following table presents the stock-based compensation expense included in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. The Utility Registrants' stock-based compensation expense for the years ended December 31, 2019 , 2018 and 2017 was not material. Exelon Year Ended December 31, Components of Stock-Based Compensation Expense 2019 2018 2017 Total stock-based compensation expense included in operating and maintenance expense $ 77 $ 208 $ 191 Income tax benefit (20 ) (54 ) (74 ) Total after-tax stock-based compensation expense $ 57 $ 154 $ 117 Generation Components of Stock-Based Compensation Expense Total stock-based compensation expense included in operating and maintenance expense $ 37 $ 77 $ 88 Income tax benefit (10 ) (20 ) (34 ) Total after-tax stock-based compensation expense $ 27 $ 57 $ 54 Exelon receives a tax deduction based on the intrinsic value of the award on the exercise date for stock options and the distribution date for performance share awards and restricted stock units. For each award, throughout the requisite service period, Exelon recognizes the tax benefit related to compensation costs. The following table presents information regarding Exelon’s realized tax benefit when distributed: Year Ended December 31, 2019 2018 2017 Performance share awards $ 41 $ 16 $ 29 Restricted stock units 24 28 35 Performance Share Awards Performance share awards are granted under the LTIP. The performance share awards are settled 50% in common stock and 50% in cash at the end of the three-year performance period, except for awards granted to vice presidents and higher officers that are settled 100% in cash if certain ownership requirements are satisfied. The common stock portion of the performance share awards is considered an equity award and is valued based on Exelon's stock price on the grant date. The cash portion of the performance share awards is considered a liability award which is remeasured each reporting period based on Exelon’s current stock price. As the value of the common stock and cash portions of the awards are based on Exelon’s stock price during the performance period, coupled with changes in the total shareholder return modifier and expected payout of the award, the compensation costs are subject to volatility until payout is established. For nonretirement-eligible employees, stock-based compensation costs are recognized over the vesting period of three years using the straight-line method. For performance share awards granted to retirement-eligible employees, the value of the performance shares is recognized ratably over the vesting period, which is the year of grant. Exelon processes forfeitures as they occur for employees who do not complete the requisite service period. The following table summarizes Exelon’s nonvested performance share awards activity: Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2018 (a) 3,403,228 $ 33.13 Granted 1,089,903 47.37 Change in performance (799,618 ) 40.85 Vested (1,610,146 ) 28.90 Forfeited (25,249 ) 45.03 Undistributed vested awards (b) (348,363 ) 48.82 Nonvested at December 31, 2019 (a) 1,709,755 $ 39.21 __________ (a) Excludes 2,017,870 and 3,586,259 of performance share awards issued to retirement-eligible employees as of December 31, 2019 and 2018 , respectively, as they are fully vested. (b) Represents performance share awards that vested but were not distributed to retirement-eligible employees during 2019 . The following table summarizes the weighted average grant date fair value and the total fair value of performance share awards granted and settled. Year Ended December 31, 2019 (a) 2018 2017 Weighted average grant date fair value (per share) $ 47.37 $ 38.15 $ 35.00 Total fair value of performance shares settled 158 61 72 Total fair value of performance shares settled in cash 131 49 56 __________ (a) As of December 31, 2019 , $17 million of total unrecognized compensation costs related to nonvested performance shares are expected to be recognized over the remaining weighted-average period of 1.6 years . Restricted Stock Units Restricted stock units are granted under the LTIP with the majority being settled in a specific number of shares of common stock after the service condition has been met. The corresponding cost of services is measured based on the grant date fair value of the restricted stock unit issued. The value of the restricted stock units is expensed over the requisite service period using the straight-line method. The requisite service period for restricted stock units is generally three to five years . However, certain restricted stock unit awards become fully vested upon the employee reaching retirement-eligibility. The value of the restricted stock units granted to retirement-eligible employees is either recognized immediately upon the date of grant or through the date at which the employee reaches retirement eligibility. Exelon processes forfeitures as they occur for employees who do not complete the requisite service period. The following table summarizes Exelon’s nonvested restricted stock unit activity: Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2018 (a) 2,293,341 $ 35.06 Granted 902,857 45.65 Vested (1,232,704 ) 32.83 Forfeited (33,603 ) 39.01 Undistributed vested awards (b) (431,178 ) 44.75 Nonvested at December 31, 2019 (a) 1,498,713 $ 40.35 __________ (a) Excludes 863,196 and 1,131,487 of restricted stock units issued to retirement-eligible employees as of December 31, 2019 and 2018 , respectively, as they are fully vested. (b) Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2019 . The following table summarizes the weighted average grant date fair value and the total fair value of restricted stock units granted and vested. Year Ended December 31, 2019 (a) 2018 2017 Weighted average grant date fair value (per share) $ 45.65 $ 38.60 $ 34.98 Total fair value of restricted stock units vested 92 106 88 __________ (a) As of December 31, 2019 , $28 million of total unrecognized compensation costs related to nonvested restricted stock units are expected to be recognized over the remaining weighted-average period of 2.8 years . Stock Options Non-qualified stock options to purchase shares of Exelon’s common stock were granted through 2012 under the LTIP. The exercise price of the stock options is equal to the fair market value of the underlying stock on the date of option grant. Stock options will expire no later than ten years from the date of grant. At December 31, 2019 all stock options were vested and there were no unrecognized compensation costs. The following table presents information with respect to stock option activity: Shares Weighted Average Exercise Price (per share) Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value Balance of shares outstanding at December 31, 2018 4,027,652 $ 43.95 2.90 $ 14 Options exercised (1,388,165 ) 42.25 Options expired (750,442 ) 55.96 Balance of shares outstanding at December 31, 2019 1,889,045 $ 40.43 1.56 $ 10 Exercisable at December 31, 2019 (a) 1,889,045 $ 40.43 1.56 $ 10 __________ (a) Includes stock options issued to retirement eligible employees. The following table summarizes additional information regarding stock options exercised: Year Ended December 31, 2019 2018 2017 Intrinsic value (a) $ 9 $ 12 $ 15 Cash received for exercise price 59 56 107 __________ (a) The difference between the market value on the date of exercise and the option exercise price.

Changes in Accumulated Other Co

Changes in Accumulated Other Comprehensive Income (Exelon)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Changes in Accumulated Other Comprehensive Income (Exelon)	Changes in Accumulated Other Comprehensive Income (Exelon) The following tables present changes in Exelon's AOCI, net of tax, by component: Gains and Unrealized Pension and (a) Foreign AOCI of Investments (b) Total Balance at December 31, 2016 $ (17 ) $ 4 $ (2,610 ) $ (30 ) $ (7 ) $ (2,660 ) OCI before reclassifications (1 ) 6 11 7 6 29 Amounts reclassified from AOCI 4 — 140 — — 144 Net current-period OCI 3 6 151 7 6 173 Impact of adoption of Reclassification of Certain Tax Effects from AOCI (c) — — (539 ) — — (539 ) Balance at December 31, 2017 $ (14 ) $ 10 $ (2,998 ) $ (23 ) $ (1 ) $ (3,026 ) OCI before reclassifications 11 — (143 ) (10 ) 1 (141 ) Amounts reclassified from AOCI 1 — 181 — — 182 Net current-period OCI 12 — 38 (10 ) 1 41 Impact of adoption of Recognition and Measurement of Financial Assets and Financial Liabilities standard (d) — (10 ) — — — (10 ) Balance at December 31, 2018 $ (2 ) $ — $ (2,960 ) $ (33 ) $ — $ (2,995 ) OCI before reclassifications — — (289 ) 6 (2 ) (285 ) Amounts reclassified from AOCI — — 84 — 2 86 Net current-period OCI — — (205 ) 6 — (199 ) Balance at December 31, 2019 $ (2 ) $ — $ (3,165 ) $ (27 ) $ — $ (3,194 ) __________ (a) This AOCI component is included in the computation of net periodic pension and OPEB cost. See Note 14 — Retirement Benefits for additional information. See Exelon's Statements of Operations and Comprehensive Income for individual components of AOCI. (b) All amounts are net of noncontrolling interests. (c) 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. (d) Exelon prospectively adopted the new standard Recognition and Measurement of Financial Assets and Financial 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 for Exelon. The amounts reclassified related to Rabbi Trusts. The following table presents income tax benefit (expense) allocated to each component of Exelon's other comprehensive income (loss): For the Year Ended December 31, 2019 2018 2017 Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 23 $ 24 $ 36 Actuarial loss reclassified to periodic benefit cost (52 ) (86 ) (128 ) Pension and non-pension postretirement benefit plans valuation adjustment 100 50 13

Variable Interest Entities (Exe

Variable Interest Entities (Exelon, Generation, PHI, and ACE)	12 Months Ended
	Dec. 31, 2019
Variable Interest Entity [Abstract]
Variable Interest Entity Disclosure [Text Block]	Variable Interest Entities (Exelon, Generation, PHI and ACE) At December 31, 2019 and 2018 , Exelon, Generation, PHI and ACE collectively consolidated several VIEs or VIE groups for which the applicable Registrant was the primary beneficiary (see Consolidated VIEs below) and had significant interests in several 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 VIEs below). Consolidated and unconsolidated VIEs are aggregated to the extent that the entities have similar risk profiles. Consolidated VIEs The table below shows the carrying amounts and classification of the consolidated VIEs’ assets and liabilities included in the consolidated financial statements of Exelon, Generation, PHI and ACE as of December 31, 2019 and 2018 . The assets, except as noted in the footnotes to the table below, can only be used to settle obligations of the VIEs. The liabilities, except as noted in the footnotes to the table below, are such that creditors, or beneficiaries, do not have recourse to the general credit of Exelon, Generation, PHI and ACE. December 31, 2019 December 31, 2018 Exelon (a) Generation PHI (a) ACE Exelon Generation PHI ACE Cash and cash equivalents $ 163 $ 163 $ — $ — $ 414 $ 414 $ — $ — Restricted cash and cash equivalents 88 85 3 3 66 62 4 4 Accounts receivable, net Customer 151 151 — — 146 146 — — Other 39 39 — — 23 23 — — Unamortized energy contract asset (b) 23 23 — — 25 25 — — Inventories, net Materials and supplies 227 227 — — 212 212 — — Other current assets 32 31 1 — 52 49 3 — Total current assets 723 719 4 3 938 931 7 4 Property, plant and equipment, net (c) 6,022 6,022 — — 6,188 6,188 — — Nuclear decommissioning trust funds 2,741 2,741 — — 2,351 2,351 — — Unamortized energy contract asset (b) 250 250 — — 274 274 — — Other noncurrent assets 89 73 16 14 258 232 26 19 Total noncurrent assets 9,102 9,086 16 14 9,071 9,045 26 19 Total assets $ 9,825 $ 9,805 $ 20 $ 17 $ 10,009 $ 9,976 $ 33 $ 23 Long-term debt due within one year $ 544 $ 523 $ 21 $ 20 $ 87 $ 66 $ 21 $ 18 Accounts payable 106 106 — — 96 96 — — Accrued expenses 70 70 — — 73 72 1 1 Unamortized energy contract liabilities 8 8 — — 15 15 — — Other current liabilities 3 3 — — 3 3 — — Total current liabilities 731 710 21 20 274 252 22 19 Long-term debt 527 504 23 21 1,072 1,025 47 40 Asset retirement obligations (d) 2,128 2,128 — — 2,165 2,165 — — Unamortized energy contract liabilities 1 1 — — 1 1 — — Other noncurrent liabilities 89 89 — — 42 42 — — Total noncurrent liabilities 2,745 2,722 23 21 3,280 3,233 47 40 Total liabilities $ 3,476 $ 3,432 $ 44 $ 41 $ 3,554 $ 3,485 $ 69 $ 59 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. (b) These are unrestricted assets to Exelon and Generation. (c) Exelon's and Generation's balances include unrestricted assets of $ 20 million and $ 43 million as of December 31, 2019 and 2018 , respectively. (d) Exelon's and Generation's balances include liabilities with recourse of $ 3 million and $ 5 million as of December 31, 2019 and 2018 , respectively. As of December 31, 2019 and 2018 , Exelon's and Generation's consolidated VIEs consist of: Consolidated VIE or VIE groups: Reason entity is a VIE: Reason Generation is primary beneficiary: CENG - A joint venture between Generation and EDF. Generation has a 50.01% equity ownership in CENG. See additional discussion below. Disproportionate relationship between equity interest and operational control as a result of the Nuclear Operating Services Agreement (NOSA) described further below. Generation conducts the operational activities. EGRP - A collection of wind and solar project entities. Generation has a 51% equity ownership in EGRP. See additional discussion below. Similar structure to a limited partnership and the limited partners do not have kick out rights with respect to the general partner. Generation conducts the operational activities. Blue Stem Wind - A Tax Equity structure which is consolidated by EGRP. Generation is a minority interest holder. Similar structure to a limited partnership and the limited partners do not have kick out rights with respect to the general partner. Generation conducts the operational activities. Antelope Valley - A solar generating facility, which is 100% owned by Generation. Antelope Valley sells all of its output to PG&E through a PPA. The PPA contract absorbs variability through a performance guarantee. Generation conducts all activities. Equity investment in distributed energy company - Generation has a 31% equity ownership. This distributed energy company has an interest in an unconsolidated VIE. (See Unconsolidated VIEs disclosure below). Generation fully impaired this investment in the third quarter of 2019. See note 11- Asset Impairments for additional information. Similar structure to a limited partnership and the limited partners do not have kick out rights with respect to the general partner. Generation conducts the operational activities. CENG - On April 1, 2014, Generation, CENG, and subsidiaries of CENG executed the NOSA pursuant to which Generation conducts all activities associated with the operations of the CENG fleet and provides corporate and administrative services to CENG and the CENG fleet for the remaining life of the CENG nuclear plants as if they were a part of the Generation nuclear fleet, subject to the CENG member rights of EDF. See Note 2 — Mergers, Acquisitions and Dispositions for additional information. Exelon and Generation, where indicated, provide the following support to CENG: • Generation provided a $400 million loan to CENG. The remaining balance was fully paid 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 18 — Commitments and Contingencies for more details), • 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. EGRP - EGRP is a collection of wind and solar project entities and some of these project entities are VIEs that are consolidated by EGRP. Generation owns a number of limited liability companies that build, own, and operate solar and wind power facilities some of which are owned by EGRP. While Generation or EGRP owns 100% of the solar entities and 100% of the majority of the wind entities, it has been determined that certain of the solar and wind entities are VIEs because the entities require additional subordinated financial support in the form of a parental guarantee of debt, loans from the customers in order to obtain the necessary funds for construction of the solar facilities, or the customers absorb price variability from the entities through the fixed price power and/or REC purchase agreements. Generation is the primary beneficiary of these solar and wind entities that qualify as VIEs because Generation controls the design, construction, and operation of the facilities. Generation provides operating and capital funding to the solar and wind entities for ongoing construction, operations and maintenance and there is limited recourse related to Generation related to certain solar and wind entities. In 2017, Generation’s interests in EGRP were contributed to and are pledged for the ExGen Renewables IV non-recourse debt project financing structure. Refer to Note 16 — Debt and Credit Agreements for additional information on ExGen Renewables IV. As of December 31, 2019 and 2018 , Exelon's, PHI's and ACE's consolidated VIE consists of: Consolidated VIEs: Reason entity is a VIE: Reason ACE is the primary beneficiary: ACE Transition Funding - 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. 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. ACE’s equity investment is a variable interest as, by design, it absorbs any initial variability of ACETF. The bondholders also have a variable interest for the investment made to purchase the transition bonds. ACE controls the servicing activities. Unconsolidated VIEs 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. As of December 31, 2019 and 2018 , Exelon and Generation had significant unconsolidated variable interests in several VIEs for which Exelon or Generation, as applicable, was not the primary beneficiary. These interests include certain equity method investments and certain commercial agreements. The following table presents summary information about Exelon and Generation’s significant unconsolidated VIE entities: December 31, 2019 December 31, 2018 Commercial Agreement VIEs Equity Investment VIEs Total Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 636 $ 443 $ 1,079 $ 597 $ 472 $ 1,069 Total liabilities (a) 33 227 260 37 222 259 Exelon's ownership interest in VIE (a) — 191 191 — 223 223 Other ownership interests in VIE (a) 604 25 629 560 27 587 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — — — — 223 223 __________ (a) These items represent amounts on 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. As of December 31, 2019 and 2018 , Exelon's and Generation's unconsolidated VIEs consist of: Unconsolidated VIE groups: Reason entity is a VIE: Reason Generation is not the primary beneficiary: Equity investments in distributed energy companies - 1) Generation has a 90% equity ownership in a distributed energy company. 2) Generation, via a consolidated VIE, has a 90% equity ownership in a distributed energy company (See Consolidated VIEs disclosure above). Generation fully impaired this investment in the third quarter of 2019. See note 11- Asset Impairments for additional information. Similar structures to a limited partnership and the limited partners do not have kick out rights with respect to the general partner. Generation does not conduct the operational activities. Energy Purchase and Sale agreements - Generation has several energy purchase and sale agreements with generating facilities. PPA contracts that absorb variability through fixed pricing. Generation does not conduct the operational activities.

Supplemental Financial Informat

Supplemental Financial Information (All Registrants)	12 Months Ended
	Dec. 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 material items recorded in the Registrants' Consolidated Statements of Operations and Comprehensive Income. Taxes other than income taxes Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE For the year ended December 31, 2019 Utility (a) $ 881 $ 112 $ 242 $ 132 $ 90 $ 304 $ 286 $ 18 $ — Property 595 274 29 17 153 122 85 34 2 Payroll 232 115 27 15 17 24 7 4 2 For the year ended December 31, 2018 Utility (a) $ 919 $ 114 $ 243 $ 131 $ 94 $ 337 $ 316 $ 21 $ — Property 557 273 30 15 143 94 58 32 3 Payroll 247 130 27 16 17 24 5 3 2 For the year ended December 31, 2017 Utility (a) $ 898 $ 126 $ 240 $ 125 $ 89 $ 318 $ 300 $ 18 $ — Property 545 269 28 14 132 101 62 32 3 Payroll 230 121 26 15 15 26 6 4 2 __________ (a) Generation’s utility tax represents gross receipts tax related to its retail operations and the Utility Registrants’ utility taxes represents municipal and state utility taxes and gross receipts taxes related to their operating revenues. Other, Net Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE For the year ended December 31, 2019 Decommissioning-related activities: Net realized income on NDT funds (a) Regulatory agreement units $ 297 $ 297 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 363 363 — — — — — — — Net unrealized gains on NDT funds Regulatory agreement units 795 795 — — — — — — — Non-regulatory agreement units 411 411 — — — — — — — Regulatory offset to NDT fund-related activities (b) (876 ) (876 ) — — — — — — — Decommissioning-related activities 990 990 — — — — — — — AFUDC—Equity 85 — 17 13 21 34 25 4 5 Non-service net periodic benefit cost 13 — — — — — — — — For the year ended December 31, 2018 Decommissioning-related activities: Net realized income on NDT funds (a) Regulatory agreement units $ 506 $ 506 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 302 302 — — — — — — — Net unrealized losses on NDT funds Regulatory agreement units (715 ) (715 ) — — — — — — — Non-regulatory agreement units (483 ) (483 ) — — — — — — — Regulatory offset to NDT fund-related activities (b) 171 171 — — — — — — — Decommissioning-related activities (219 ) (219 ) — — — — — — — AFUDC—Equity 69 — 19 7 18 25 22 2 1 Non-service net periodic benefit cost (47 ) — — — — — — — — For the year ended December 31, 2017 Decommissioning-related activities: Net realized income on NDT funds (a) Regulatory agreement units $ 488 $ 488 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 209 209 — — — — — — — Net unrealized gains on NDT funds Regulatory agreement units 455 455 — — — — — — — Non-regulatory agreement units 521 521 — — — — — — — Regulatory offset to NDT fund-related activities (b) (724 ) (724 ) — — — — — — — Decommissioning-related activities 949 949 — — — — — — — AFUDC—Equity 73 — 12 9 16 36 23 7 6 Non-service net periodic benefit cost (109 ) — — — — — — — — __________ (a) Realized income includes interest, dividends and realized gains and losses on sales of NDT fund investments. (b) Includes the elimination of decommissioning-related activities for the Regulatory Agreement Units, including the elimination of income taxes related to all NDT fund activity for those units. See Note 9 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. Supplemental Cash Flow Information The following tables provide additional information about material items recorded in the Registrants' Consolidated Statements of Cash Flows. Depreciation, amortization and accretion Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE For the year ended December 31, 2019 Property, plant and equipment $ 3,665 $ 1,485 $ 886 $ 303 $ 359 $ 547 $ 239 $ 146 $ 123 Amortization of regulatory assets 528 — 147 30 143 207 135 38 34 Amortization of intangible assets, net 59 50 — — — — — — — Amortization of energy contract assets and liabilities (a) 21 21 — — — — — — — Nuclear fuel (b) 1,016 1,016 — — — — — — — ARO accretion (c) 491 491 — — — — — — — Total depreciation, amortization and accretion $ 5,780 $ 3,063 $ 1,033 $ 333 $ 502 $ 754 $ 374 $ 184 $ 157 For the year ended December 31, 2018 Property, plant and equipment $ 3,740 $ 1,748 $ 820 $ 274 $ 335 $ 480 $ 218 $ 131 $ 94 Amortization of regulatory assets 555 — 120 27 148 260 167 51 42 Amortization of intangible assets, net 58 49 — — — — — — — Amortization of energy contract assets and liabilities (a) 14 14 — — — — — — — Nuclear fuel (b) 1,115 1,115 — — — — — — — ARO accretion (c) 489 489 — — — — — — — Total depreciation, amortization and accretion $ 5,971 $ 3,415 $ 940 $ 301 $ 483 $ 740 $ 385 $ 182 $ 136 For the year ended December 31, 2017 Property, plant and equipment $ 3,293 $ 1,409 $ 777 $ 261 $ 312 $ 457 $ 203 $ 124 $ 89 Amortization of regulatory assets 478 — 73 25 161 218 118 43 57 Amortization of intangible assets, net 57 48 — — — — — — — Amortization of energy contract assets and liabilities (a) 35 35 — — — — — — — Nuclear fuel (b) 1,096 1,096 — — — — — — — ARO accretion (c) 468 468 — — — — — — — Total depreciation, amortization and accretion $ 5,427 $ 3,056 $ 850 $ 286 $ 473 $ 675 $ 321 $ 167 $ 146 __________ (a) Included in Operating revenues or Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (b) Included in Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (c) Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Cash paid (refunded) during the year: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE For the year ended December 31, 2019 Interest (net of amount capitalized) $ 1,470 $ 373 $ 343 $ 129 $ 106 $ 255 $ 130 $ 59 $ 55 Income taxes (net of refunds) 265 (44 ) (42 ) 82 17 29 7 19 (5 ) For the year ended December 31, 2018 Interest (net of amount capitalized) $ 1,421 $ 369 $ 332 $ 125 $ 94 $ 250 $ 123 $ 56 $ 61 Income taxes (net of refunds) 95 746 (153 ) (2 ) 14 (32 ) 41 (6 ) (12 ) For the year ended December 31, 2017 Interest (net of amount capitalized) $ 2,430 $ 391 $ 307 $ 103 $ 96 $ 236 $ 114 $ 49 $ 59 Income taxes (net of refunds) 540 337 83 47 (2 ) (144 ) (104 ) (49 ) (2 ) Other non-cash operating activities: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE For the year ended December 31, 2019 Pension and non-pension postretirement benefit costs $ 438 $ 135 $ 96 $ 12 $ 61 $ 95 $ 25 $ 15 $ 16 Provision for uncollectible accounts 120 31 33 31 8 17 7 4 5 Other decommissioning-related activity (a) (506 ) (506 ) — — — — — — — Energy-related options (b) 22 22 — — — — — — — Amortization of rate stabilization deferral (4 ) — — — — (4 ) (4 ) — — Discrete impacts from EIMA and FEJA (d) 128 — 128 — — — — — — Long-term incentive plan 10 — — — — — — — — Amortization of operating ROU asset 244 172 3 — 30 33 8 8 4 Change in environmental liabilities 23 — — — — 23 23 — — For the year ended December 31, 2018 Pension and non-pension postretirement benefit costs $ 583 $ 204 $ 177 $ 18 $ 59 $ 67 $ 15 $ 6 $ 12 Provision for uncollectible accounts 159 48 40 33 10 28 11 6 11 Other decommissioning-related activity (a) (2 ) (2 ) — — — — — — — Energy-related options (b) 10 10 — — — — — — — Amortization of rate stabilization deferral 21 — — — — 21 21 — — Asset retirement costs 20 — — — — 20 22 (1 ) (1 ) Discrete impacts from EIMA and FEJA (d) 28 — 28 — — — — — — Long-term incentive plan 140 — — — — — — — — For the year ended December 31, 2017 Pension and non-pension postretirement benefit costs $ 643 $ 227 $ 176 $ 29 $ 62 $ 94 $ 25 $ 13 $ 13 Provision for uncollectible accounts 125 38 34 26 8 19 8 3 8 Other decommissioning-related activity (a) (313 ) (313 ) — — — — — — — Energy-related options (b) 7 7 — — — — — — — Amortization of rate stabilization deferral (3 ) — — — 7 (10 ) (10 ) — — Discrete impacts from EIMA and FEJA (d) (52 ) — (52 ) — — — — — — Vacation accrual adjustment (e) (68 ) (35 ) (12 ) — — (8 ) (8 ) — — Long-term incentive plan 109 — — — — — — — — Change in environmental liabilities 44 44 — — — — — — — __________ (a) Includes the elimination of decommissioning-related activities 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 9 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) See Note 2 - Mergers, Acquisitions and Dispositions for additional information. (d) Reflects the change in ComEd's distribution and energy efficiency formula rates . See Note 3 — Regulatory Matters for additional information. (e) On December 1, 2017, Exelon adopted a single, standard vacation accrual policy for all non-represented, non-craft (represented and craft policies remained unchanged) employees effective January 1, 2018. To reflect the new policy, Exelon recorded a one-time, $68 million pre-tax credit to expense to reverse 2018 vacation cost originally accrued throughout 2017 that was accrued ratably during 2018. 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. Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 Cash and cash equivalents $ 587 $ 303 $ 90 $ 21 $ 24 $ 131 $ 30 $ 13 $ 12 Restricted cash 358 146 150 6 1 36 33 — 2 Restricted cash included in other long-term assets 177 — 163 — — 14 — — 14 Total cash, cash equivalents and restricted cash $ 1,122 $ 449 $ 403 $ 27 $ 25 $ 181 $ 63 $ 13 $ 28 December 31, 2018 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 December 31, 2017 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 December 31, 2016 Cash and cash equivalents $ 635 $ 290 $ 56 $ 63 $ 23 $ 170 $ 9 $ 46 $ 101 Restricted cash 253 158 2 4 24 43 33 — 9 Restricted cash included in other long-term assets 26 — — — 3 23 — — 23 Total cash, cash equivalents and restricted cash $ 914 $ 448 $ 58 $ 67 $ 50 $ 236 $ 42 $ 46 $ 133 Supplemental Balance Sheet Information The following tables provide additional information about material items recorded in the Registrants' Consolidated Balance Sheets. Unbilled customer revenues (a) Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 $ 1,535 $ 807 $ 218 $ 146 $ 170 $ 194 $ 100 $ 61 $ 33 December 31, 2018 1,656 965 223 114 168 186 97 59 30 __________ (a) Unbilled customer revenues are classified in customer accounts receivables, net in Exelon's and the Utility Registrants' Consolidated Balance Sheets. Investments Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 Equity method investments: Other equity method investments $ 92 $ 71 $ 6 $ 8 $ — $ — $ — $ — $ — Other investments: Employee benefit trusts and investments (a) 262 54 — 19 7 135 110 — — Equity investments without readily determinable fair values 69 69 — — — — — — — Other available for sale debt security investments 41 41 — — — — — — — Total investments $ 464 $ 235 $ 6 $ 27 $ 7 $ 135 $ 110 $ — $ — December 31, 2018 Equity method investments: Distributed energy companies $ 180 $ 180 $ — $ — $ — $ — $ — $ — $ — Other equity method investments 87 71 6 8 — — — — — Total equity method investments 267 251 6 8 — — — — — Other investments: Employee benefit trusts and investments (a) 244 49 — 17 5 130 105 — — Equity investments without readily determinable fair values 72 72 — — — — — — — Other available for sale debt security investments 40 40 — — — — — — — Other 2 2 — — — — — — — Total investments $ 625 $ 414 $ 6 $ 25 $ 5 $ 130 $ 105 $ — $ — __________ (a) The Registrants’ debt and equity security investments are recorded at fair market value. Accrued expenses Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 Compensation-related accruals (a) $ 1,052 $ 422 $ 171 $ 58 $ 78 $ 101 $ 28 $ 19 $ 15 Taxes accrued 414 222 83 3 26 117 90 14 8 Interest accrued 337 65 110 37 46 49 23 8 12 December 31, 2018 Compensation-related accruals (a) $ 1,191 $ 479 $ 187 $ 49 $ 68 $ 99 $ 29 $ 19 $ 12 Taxes accrued 412 226 71 28 46 74 58 4 5 Interest accrued 334 77 105 33 39 50 25 8 12 __________ (a) Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits.

Related Party Transactions (All

Related Party Transactions (All Registrants)	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Related-Party Transactions (All Registrants)	Related Party Transactions (All Registrants) Operating revenues from affiliates Generation The following table presents Generation’s Operating revenues from affiliates, which are primarily recorded as Purchased power from affiliates and an immaterial amount recorded as Operating and maintenance expense from affiliates at the Utility Registrants: For the Years Ended December 31, 2019 2018 2017 Operating revenues from affiliates: ComEd (a)(b) $ 369 $ 523 $ 121 PECO (c) 158 128 138 BGE (d) 289 260 388 PHI 353 355 463 Pepco (e) 264 206 255 DPL (f) 70 120 179 ACE (g) 19 29 29 Other 3 2 5 Total operating revenues from affiliates (Generation) $ 1,172 $ 1,268 $ 1,115 __________ (a) Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs and ZECs to ComEd. (b) For 2019 , ComEd’s Purchased power from Generation of $376 million is recorded as Operating revenues from ComEd of $369 million and Purchased power and fuel from ComEd of $7 million at Generation. For 2018 , ComEd’s Purchased power from Generation of $529 million is recorded as Operating revenues from ComEd of $523 million and Purchased power and fuel from ComEd of $6 million at Generation. (c) Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has a ten-year agreement with PECO to sell solar AECs. (d) Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. (e) Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC. (f) Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs. (g) Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process. PHI PHI’s Operating revenues from affiliates are primarily with BSC for services that PHISCO provides to BSC. Operating and maintenance expense from affiliates The Registrants receive a variety of corporate support services from BSC. Pepco, DPL and ACE also receive corporate support services from PHISCO. See Note 1 - Significant Accounting Policies for additional information regarding BSC and PHISCO. The following table presents the service company costs allocated to the Registrants: Operating and maintenance from affiliates Operating and maintenance Capitalized costs For the years ended December 31, For the years ended December 31, For the years ended December 31, 2019 2018 2017 2017 2019 2018 2017 Exelon BSC $ 516 $ 448 $ 330 PHISCO 72 79 — Generation BSC $ 570 $ 652 $ 689 $ — 66 67 98 ComEd BSC 263 265 270 — 148 135 118 PECO BSC 149 146 146 — 88 64 59 BGE BSC 157 157 152 — 126 79 54 PHI BSC 139 147 145 — 88 102 — PHISCO (a) — — — — 72 79 — Pepco BSC 85 89 53 — 38 40 — PHISCO (a) 124 137 5 219 33 32 — PES (b) — — — 29 — — — DPL BSC 52 51 31 — 25 28 — PHISCO (a) 100 111 — 165 20 25 — PES (b) — — — 9 — — — ACE BSC 42 42 25 — 19 20 — PHISCO (a) 90 98 — 135 19 21 — __________ (a) Due to the PHI entities' system conversion to Exelon's accounting systems on January 1, 2018, corporate support services received from PHISCO are reported in Operating and maintenance from affiliates and in Capitalized costs beginning in 2018. (b) PES performed underground transmission, distribution construction and maintenance services, including services that are treated as capital costs, for Pepco and DPL. Current Receivables from/Payables to affiliates The following tables present current receivables from affiliates and current payables to affiliates: December 31, 2019 Receivables from affiliates: Payables to affiliates: Generation Comed PECO BGE ACE BSC PHISCO Other Total Generation $ 27 $ — $ — $ — $ 67 $ — $ 23 $ 117 ComEd $ 78 (a) — — — 54 — 8 140 PECO 27 — — — 25 — 3 55 BGE 28 — — — 34 — 4 66 PHI — — — — — 4 — 10 14 Pepco 34 — — — — 16 15 1 66 DPL 7 — — — 3 10 11 1 32 ACE 7 — — — 7 10 1 25 Other 9 1 1 1 1 — — 13 Total $ 190 $ 28 $ 1 $ 1 $ 4 $ 217 $ 36 $ 51 $ 528 December 31, 2018 Receivables from affiliates: Payables to affiliates: Generation Comed BGE Pepco ACE BSC PHISCO Other Total Generation $ 19 $ — $ — $ — $ 95 $ — $ 25 $ 139 ComEd $ 69 (a) — — — 56 — 8 133 PECO 30 — — — — 26 — 3 59 BGE 24 — — — 38 — 3 65 PHI — — — — — 3 — 9 12 Pepco 28 — — — 19 14 1 62 DPL 7 — — 1 1 11 12 1 33 ACE 5 — — — 8 13 2 28 Other 10 1 1 — — — — 12 Total $ 173 $ 20 $ 1 $ 1 $ 1 $ 256 $ 39 $ 52 $ 543 __________ (a) At December 31, 2019 and 2018, Generation also had a contract liability with ComEd for $37 million and $14 million , respectively, that was included in Other liabilities on Generation’s Consolidated Balance Sheets. At December 31, 2019 and 2018, ComEd had a Current Payable to Generation of $41 million and $55 million , respectively, on its Consolidated Balance Sheets, which consisted of Generation’s Current Receivable from ComEd, partially offset by Generation’s contract liability with ComEd. Borrowings from Exelon/PHI intercompany money pool To provide an additional short-term borrowing option that will generally be more favorable to the borrowing participants than the cost of external financing both Exelon and PHI operate an intercompany money pool. Generation, ComEd, PECO, and PHI Corporate participate in the Exelon money pool. Pepco, DPL and ACE participate in the PHI intercompany money pool. Noncurrent Receivables from/Payables to affiliates Generation has long-term payables to ComEd and PECO as a result of the nuclear decommissioning contractual construct whereby, to the extent NDT funds are greater than the underlying ARO at the end of decommissioning, such amounts are due back to ComEd and PECO, as applicable, for payment to their respective customers. See Note 9 — Asset Retirement Obligations for additional information. The following table presents noncurrent receivables from affiliates at ComEd and PECO which are recorded as noncurrent payables to affiliates at Generation: December 31, 2019 2018 ComEd $ 2,622 $ 2,217 PECO 480 389 Other 1 — Total: $ 3,103 $ 2,606 Long-term debt to financing trusts The following table presents Long-term debt to financing trusts: As of December 31, 2019 2018 Exelon ComEd PECO Exelon ComEd PECO ComEd Financing III $ 206 $ 205 $ — $ 206 $ 205 $ — PECO Trust III 81 — 81 81 — 81 PECO Trust IV 103 — 103 103 — 103 Total $ 390 $ 205 $ 184 $ 390 $ 205 $ 184 Long-term debt to affiliates In connection with the debt obligations assumed by Exelon as part of the Constellation merger, Exelon and subsidiaries of Generation (former Constellation subsidiaries) assumed intercompany loan agreements that mirror the terms and amounts of the third-party debt obligations of Exelon, resulting in intercompany notes payable included in Long-term debt to affiliates in Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate.

Quarterly Data (Unaudited) (All

Quarterly Data (Unaudited) (All Registrants)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Data [Abstract]
Quarterly Data (Unaudited) (All Registrants)	Quarterly Data (Unaudited) (All Registrants) Exelon The data shown below, which may not equal the total for the year due to the effects of rounding and dilution, includes all adjustments that Exelon considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 9,477 $ 9,691 $ 1,218 $ 1,099 $ 907 $ 583 June 30 7,689 8,074 841 940 484 537 September 30 8,929 9,401 1,353 1,144 772 731 December 31 (a) 8,343 8,812 962 706 773 152 Net Income Net Income 2019 2018 2019 2018 Quarter ended: March 31 $ 0.93 $ 0.60 $ 0.93 $ 0.60 June 30 0.50 0.56 0.50 0.55 September 30 0.79 0.76 0.79 0.75 December 31 0.79 0.16 0.79 0.16 __________ (a) Operating revenues, Operating income and Net income attributable to common shareholders for the quarter ended December 31, 2019 include a $6 million reduction related to a correction for Pepco’s decoupling mechanism for the 2019 interim periods. See Note 1 — Significant Accounting Policies for additional information. Generation The data shown below includes all adjustments that Generation considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income (Loss) 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 5,296 $ 5,512 $ 333 $ 347 $ 363 $ 136 June 30 4,210 4,579 147 282 108 178 September 30 4,774 5,278 482 311 257 234 December 31 4,644 5,069 362 35 397 (178 ) ComEd The data shown below includes all adjustments that ComEd considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 1,408 $ 1,512 $ 276 $ 292 $ 157 $ 165 June 30 1,351 1,398 311 288 186 164 September 30 1,583 1,598 328 323 200 193 December 31 1,405 1,373 255 242 144 141 PECO The data shown below includes all adjustments that PECO considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 900 $ 866 $ 222 $ 142 $ 168 $ 113 June 30 655 653 145 127 102 96 September 30 778 757 183 154 140 126 December 31 766 765 162 165 118 124 BGE The data shown below includes all adjustments that BGE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 976 $ 977 $ 220 $ 177 $ 160 $ 128 June 30 649 662 80 85 45 51 September 30 703 731 91 103 55 63 December 31 779 799 142 109 99 71 PHI The data shown below includes all adjustments that PHI considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 1,228 $ 1,249 $ 175 $ 124 $ 117 $ 63 June 30 1,091 1,074 165 151 106 82 September 30 1,380 1,359 256 243 189 185 December 31 (a) 1,107 1,115 128 124 65 62 __________ (a) Operating revenues, Operating income and Net income attributable to common shareholders for the quarter ended December 31, 2019 include a $6 million reduction related to a correction for Pepco’s decoupling mechanism for the 2019 interim periods. See Note 1 — Significant Accounting Policies for additional information. Pepco The data shown below includes all adjustments that Pepco considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 575 $ 555 $ 84 $ 54 $ 55 $ 29 June 30 531 521 93 83 64 52 September 30 642 626 127 110 98 87 December 31 (a) 513 529 57 63 26 36 _________ (a) Operating revenues, Operating income and Net income attributable to common shareholders for the quarter ended December 31, 2019 include a $6 million reduction related to a correction for Pepco’s decoupling mechanism for the 2019 interim periods. See Note 1 — Significant Accounting Policies for additional information. DPL The data shown below includes all adjustments that DPL considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 380 $ 384 $ 72 $ 49 $ 53 $ 31 June 30 287 289 44 42 30 26 September 30 319 328 51 51 33 33 December 31 319 331 50 48 31 30 ACE The data shown below includes all adjustments that ACE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income (Loss) 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 273 $ 310 $ 21 $ 23 $ 10 $ 7 June 30 274 265 28 25 14 8 September 30 419 406 79 84 63 61 December 31 274 254 23 14 12 (1 )

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Valuation and Qualifying Accounts	Exelon Corporation and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2019 Allowance for uncollectible accounts (a) $ 319 $ 119 $ 26 (c) $ 170 (e) $ 294 Deferred tax valuation allowance 35 — (9 ) — 26 Reserve for obsolete materials 156 6 — (d) 7 155 For the year ended December 31, 2018 Allowance for uncollectible accounts (a) $ 322 $ 159 $ 35 (c) $ 197 (e) $ 319 Deferred tax valuation allowance 37 — 5 7 35 Reserve for obsolete materials 174 25 (31 ) 12 156 For the year ended December 31, 2017 Allowance for uncollectible accounts (a) $ 334 $ 126 $ 27 (b)(c) $ 165 (e) $ 322 Deferred tax valuation allowance 20 — 17 (b) — 37 Reserve for obsolete materials 113 56 10 (b) 5 174 __________ (a) Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $9 million , $13 million , and $15 million for the years ended December 31, 2019 , 2018 and 2017 , respectively. (b) Primarily represents the addition of PHI's results as of March 23, 2016 , the date of the merger. (c) Includes charges for late payments and non-service receivables. (d) Primarily reflects the reclassification of assets as held for sale. (e) Write-off of individual accounts receivable. Exelon Generation Company, LLC and Subsidiary Companies (2) Generation (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 11, 2020 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2019, 2018 and 2017 Consolidated Statements of Cash Flows for the Years Ended December 31, 2019, 2018 and 2017 Consolidated Balance Sheets at December 31, 2019 and 2018 Consolidated Statements of Changes in Equity for the Years Ended December 31, 2019, 2018 and 2017 Notes to Consolidated Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2019, 2018 and 2017 Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Exelon Generation Company, LLC and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2019 Allowance for uncollectible accounts $ 104 $ 27 $ (11 ) $ 39 $ 81 Deferred tax valuation allowance 26 — (2 ) — 24 Reserve for obsolete materials 145 — — 2 143 For the year ended December 31, 2018 Allowance for uncollectible accounts $ 114 $ 44 $ 4 $ 58 $ 104 Deferred tax valuation allowance 23 — 3 — 26 Reserve for obsolete materials 166 20 (32 ) (a) 9 145 For the year ended December 31, 2017 Allowance for uncollectible accounts $ 91 $ 34 $ — $ 11 $ 114 Deferred tax valuation allowance 9 — 14 — 23 Reserve for obsolete materials 106 51 9 — 166 __________ (a) Primarily reflects the reclassification of assets as held for sale. Commonwealth Edison Company and Subsidiary Companies (3) ComEd (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 11, 2020 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2019, 2018 and 2017 Consolidated Statements of Cash Flows for the Years Ended December 31, 2019, 2018 and 2017 Consolidated Balance Sheets at December 31, 2019 and 2018 Consolidated Statements of Changes in Shareholders’ Equity for the Years Ended December 31, 2019, 2018 and 2017 Notes to Consolidated Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2019, 2018 and 2017 Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Commonwealth Edison Company and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2019 Allowance for uncollectible accounts $ 81 $ 35 $ 20 (a) $ 57 (b) $ 79 Reserve for obsolete materials 6 6 — 5 7 For the year ended December 31, 2018 Allowance for uncollectible accounts $ 73 $ 44 $ 23 (a) $ 59 (b) $ 81 Reserve for obsolete materials 5 3 1 3 6 For the year ended December 31, 2017 Allowance for uncollectible accounts $ 70 $ 39 $ 20 (a) $ 56 (b) $ 73 Reserve for obsolete materials 4 3 1 3 5 __________ (a) Primarily charges for late payments and non-service receivables. (b) Write-off of individual accounts receivable. PECO Energy Company and Subsidiary Companies (4) PECO (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 11, 2020 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2019, 2018 and 2017 Consolidated Statements of Cash Flows for the Years Ended December 31, 2019, 2018 and 2017 Consolidated Balance Sheets at December 31, 2019 and 2018 Consolidated Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2019, 2018 and 2017 Notes to Consolidated Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2019, 2018 and 2017 Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto PECO Energy Company and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2019 Allowance for uncollectible accounts (a) $ 61 $ 31 $ 3 (b) $ 33 (c) $ 62 Reserve for obsolete materials 2 — — — 2 For the year ended December 31, 2018 Allowance for uncollectible accounts (a) $ 56 $ 33 $ 3 (b) $ 31 (c) $ 61 Reserve for obsolete materials 2 — — — 2 For the year ended December 31, 2017 Allowance for uncollectible accounts (a) $ 61 $ 26 $ 4 (b) $ 35 (c) $ 56 Reserve for obsolete materials 2 — — — 2 __________ (a) Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $9 million , $13 million , and $15 million for the years ended December 31, 2019 , 2018 , and 2017 , respectively. (b) Primarily charges for late payments. (c) Write-off of individual accounts receivable. Baltimore Gas and Electric Company and Subsidiary Companies (5) BGE (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 11, 2020 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2019, 2018 and 2017 Consolidated Statements of Cash Flows for the Years Ended December 31, 2019, 2018 and 2017 Consolidated Balance Sheets at December 31, 2019 and 2018 Consolidated Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2019, 2018 and 2017 Notes to Consolidated Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2019, 2018 and 2017 Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Baltimore Gas and Electric Company and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2019 Allowance for uncollectible accounts $ 20 $ 8 $ 7 $ 18 (a) $ 17 Deferred tax valuation allowance 1 — — — 1 Reserve for obsolete materials 1 — — — 1 For the year ended December 31, 2018 Allowance for uncollectible accounts $ 24 $ 10 $ (2 ) $ 12 (a) $ 20 Deferred tax valuation allowance 1 — — — 1 Reserve for obsolete materials — 1 — — 1 For the year ended December 31, 2017 Allowance for uncollectible accounts $ 32 $ 8 $ (3 ) $ 13 (a) $ 24 Deferred tax valuation allowance 1 — — — 1 Reserve for obsolete materials — — — — — __________ (a) Write-off of individual accounts receivable. Pepco Holdings LLC and Subsidiary Companies (6) PHI (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 11, 2020 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2019, 2018 and 2017 Consolidated Statements of Cash Flows for the Years Ended December 31, 2019, 2018 and 2017 Consolidated Balance Sheets at December 31, 2019 and 2018 Consolidated Statements of Changes in Equity for the Years Ended December 31, 2019, 2018 and 2017 Notes to Consolidated Financial Statements (ii) Financial Statement Schedule: Schedule II – Valuation and Qualifying Accounts for the Years Ended December 31, 2019, 2018 and 2017 Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Pepco Holdings LLC and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Charged to Charged Deductions Balance at (in millions) For the Year Ended December 31, 2019 Allowance for uncollectible accounts $ 53 $ 17 $ 7 (a) $ 24 (b) $ 53 Deferred tax valuation allowance 8 — (8 ) — — Reserve for obsolete materials 2 1 — — 3 For the Year Ended December 31, 2018 Allowance for uncollectible accounts $ 55 $ 28 $ 7 (a) $ 37 (b) $ 53 Deferred tax valuation allowance 13 — 2 7 8 Reserve for obsolete materials 2 — — — 2 For the Year Ended December 31, 2017 Allowance for uncollectible accounts $ 80 $ 19 $ 6 (a) $ 50 (b) $ 55 Deferred tax valuation allowance 10 — 3 — 13 Reserve for obsolete materials 2 2 — 2 2 __________ (a) Primarily charges for late payments. (b) Write-off of individual accounts receivable. Potomac Electric Power Company (7) Pepco (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 11, 2020 of PricewaterhouseCoopers LLP Statements of Operations and Comprehensive Income for the Years Ended December 31, 2019, 2018 and 2017 Statements of Cash Flows for the Years Ended December 31, 2019, 2018 and 2017 Balance Sheets at December 31, 2019 and 2018 Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2019, 2018 and 2017 Notes to Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2019, 2018 and 2017 Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Potomac Electric Power Company Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Charged to Charged Deductions Balance at (in millions) For the year ended December 31, 2019 Allowance for uncollectible accounts $ 21 $ 7 $ 2 (a) $ 10 (b) $ 20 Reserve for obsolete materials 1 — — — 1 For the year ended December 31, 2018 Allowance for uncollectible accounts $ 21 $ 11 $ 3 (a) $ 14 (b) $ 21 Reserve for obsolete materials 1 — — — 1 For the year ended December 31, 2017 Allowance for uncollectible accounts $ 29 $ 8 $ 2 (a) $ 18 (b) $ 21 Reserve for obsolete materials 1 1 — 1 1 __________ (a) Primarily charges for late payments. (b) Write-off of individual accounts receivable. Delmarva Power & Light Company (8) DPL (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 11, 2020 of PricewaterhouseCoopers LLP Statements of Operations and Comprehensive Income for the Years Ended December 31, 2019, 2018 and 2017 Statements of Cash Flows for the Years Ended December 31, 2019, 2018 and 2017 Balance Sheets at December 31, 2019 and 2018 Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2019, 2018 and 2017 Notes to Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2019, 2018 and 2017 Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Delmarva Power & Light Company Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Charged to Charged Deductions Balance at (in millions) For the year ended December 31, 2019 Allowance for uncollectible accounts $ 13 $ 4 $ 3 (a) $ 5 (b) $ 15 Reserve for obsolete materials — — — — — For the year ended December 31, 2018 Allowance for uncollectible accounts $ 16 $ 6 $ 2 (a) $ 11 (b) $ 13 Reserve for obsolete materials — — — — — For the year ended December 31, 2017 Allowance for uncollectible accounts $ 24 $ 3 $ 2 (a) $ 13 (b) $ 16 Reserve for obsolete materials — 1 — 1 — __________ (a) Primarily charges for late payments. (b) Write-off of individual accounts receivable. Atlantic City Electric Company and Subsidiary Company (9) ACE (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 11, 2020 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2019, 2018 and 2017 Consolidated Statements of Cash Flows for the Years Ended December 31, 2019, 2018 and 2017 Consolidated Balance Sheets at December 31, 2019 and 2018 Consolidated Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2019, 2018 and 2017 Notes to Consolidated Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2019, 2018 and 2017 Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Atlantic City Electric Company and Subsidiary Company Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Charged to Charged Deductions Balance at (in millions) For the year ended December 31, 2019 Allowance for uncollectible accounts $ 19 $ 5 $ 2 (a) $ 8 (b) $ 18 Reserve for obsolete materials 1 — — — 1 For the year ended December 31, 2018 Allowance for uncollectible accounts $ 18 $ 11 $ 2 (a) $ 12 (b) $ 19 Reserve for obsolete materials 1 — — — 1 For the year ended December 31, 2017 Allowance for uncollectible accounts $ 27 $ 8 $ 2 (a) $ 19 (b) $ 18 Reserve for obsolete materials 1 — — — 1 __________ (a) Primarily charges for late payments. (b) Write-off of individual accounts receivable.

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Description of Business (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) This is a combined annual report of all Registrants. The Notes to the Consolidated Financial Statements apply to the Registrants as indicated above in the Index to Combined Notes to Consolidated Financial Statements and parenthetically next to each corresponding disclosure. When appropriate, the Registrants are named specifically for their related activities and disclosures. Each of the Registrant’s Consolidated Financial Statements includes the accounts of its subsidiaries. All intercompany transactions have been eliminated. 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. Exelon owns 100% of Generation, PECO, BGE and PHI and more than 99% of ComEd. PHI owns 100% of Pepco, DPL and ACE. Generation owns 100% of its significant consolidated subsidiaries, either directly or indirectly, except for certain consolidated VIEs, including CENG and EGRP, of which Generation holds a 50.01% and 51% interest, respectively. The remaining interests in these consolidated VIEs are included in noncontrolling interests on Exelon’s and Generation’s Consolidated Balance Sheets. See Note 22 — Variable Interest Entities for additional information of Exelon’s and Generation’s consolidated VIEs. The Registrants consolidate the accounts of entities in which a Registrant has a controlling financial interest, after the elimination of intercompany transactions. Where the Registrants do not have a controlling financial interest in an entity, proportionate consolidation, equity method accounting or accounting for investments in equity securities without readily determinable fair value is applied. The Registrants apply proportionate consolidation when they have an undivided interest in an asset and are proportionately liable for their share of each liability associated with the asset. The Registrants proportionately consolidate their undivided ownership interests in jointly owned electric plants and transmission facilities. Under proportionate consolidation, the Registrants separately record their proportionate share of the assets, liabilities, revenues and expenses related to the undivided interest in the asset. The Registrants apply equity method accounting when they have significant influence over an investee through an ownership in common stock, which generally approximates a 20% to 50% voting interest. The Registrants apply equity method accounting to certain investments and joint ventures, including certain financing trusts of ComEd and PECO. Under equity method accounting, the Registrants report their interest in the entity as an investment and the Registrants’ percentage share of the earnings from the entity as single line items in their financial statements. The Registrants use accounting for investments in equity securities without readily determinable fair values if they lack significant influence, which generally results when they hold less than 20% of the common stock of an entity. Under accounting for investments in equity securities without readily determinable fair values, the Registrants report their investments at cost adjusted for changes from observable transactions for identical or similar investments of the same issuer, less impairment. Changes in measurement are reported in earnings. The accompanying consolidated financial statements have been prepared in accordance with GAAP for annual financial statements and in accordance with the instructions to Form 10-K and Regulation S-X promulgated by the SEC.
Use Of Estimates (All Registrants)	Use of Estimates (All Registrants) The preparation of financial statements of each of the Registrants in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Areas in which significant estimates have been made include, but are not limited to, the accounting for nuclear decommissioning costs and other AROs, pension and OPEB, the application of purchase accounting, inventory reserves, allowance for uncollectible accounts, goodwill and asset impairments, derivative instruments, unamortized energy contracts, fixed asset depreciation, environmental costs and other loss contingencies, taxes and unbilled energy revenues. Actual results could differ from those estimates.
Accounting for the Effects of Regulation (Exelon, ComEd, PECO and BGE)	Accounting for the Effects of Regulation (Exelon and the Utility Registrants) For their regulated electric and gas operations, Exelon and the Utility Registrants reflect the effects of cost-based rate regulation in their financial statements, which is required for entities with regulated operations that meet the following criteria: 1) rates are established or approved by a third-party regulator; (2) rates are designed to recover the entities’ cost of providing services or products; and (3) there is a reasonable expectation that rates designed to recover costs can be charged to and collected from customers. Exelon and the Utility Registrants account for their regulated operations in accordance with regulatory and legislative guidance from the regulatory authorities having jurisdiction, principally the ICC, PAPUC, MDPSC, DCPSC, DPSC and NJBPU, under state public utility laws and the FERC under various Federal laws. Regulatory assets and liabilities are amortized and the related expense or revenue is recognized in the Consolidated Statements of Operations consistent with the recovery or refund included in customer rates. Exelon's regulatory assets and liabilities as of the balance sheet date are probable of being recovered or settled in future rates. If a separable portion of the Registrants' business was no longer able to meet the criteria discussed above, the affected entities would be required to eliminate from their consolidated financial statements the effects of regulation for that portion, which could have a material impact on their financial statements. See Note 3 — Regulatory Matters for additional information. With the exception of income tax-related regulatory assets and liabilities, Exelon and the Utility Registrants classify regulatory assets and liabilities with a recovery or settlement period greater than one year as both current and non-current in their Consolidated Balance Sheets, with the current portion representing the amount expected to be recovered from or settled to customers over the next twelve-month period as of the balance sheet date. Income tax-related regulatory assets and liabilities are classified entirely as non-current in Exelon's and the Utility Registrants’ Consolidated Balance Sheets to align with the classification of the related deferred income tax balances. Exelon and the Utility Registrants treat the impacts of a final rate order received after the balance sheet date but prior to the issuance of the financial statements as a non-recognized subsequent event, as the receipt of a final rate order is a separate and distinct event that has future impacts on the parties affected by the order.
Revenues (All Registrants)	Revenues (All Registrants) Operating Revenues. The Registrants’ operating revenues generally consist of revenues from contracts with customers involving the sale and delivery of energy commodities and related products and services, utility revenues from ARP, and realized and unrealized revenues recognized under mark-to-market energy commodity derivative contracts. The Registrants recognize revenue from contracts with customers to depict the transfer of goods or services to customers in 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 natural gas tariff sales, distribution and transmission services. At the end of each month, the Registrants accrue an estimate for the unbilled amount of energy delivered or services provided to customers. ComEd records ARP revenue for its best estimate of the electric distribution, energy efficiency, and transmission revenue impacts resulting from future changes in rates that ComEd believes are probable of approval by the ICC and FERC in accordance with its formula rate mechanisms. BGE, Pepco and DPL record ARP revenue for their best estimate of the electric and natural gas distribution revenue impacts resulting from future changes in rates that they believe are probable of approval by the MDPSC and/or DCPSC in accordance with their revenue decoupling mechanisms. PECO, BGE, Pepco, DPL and ACE record ARP revenue for their best estimate of the transmission revenue impacts resulting from future changes in rates that they believe are probable of approval by FERC in accordance with their formula rate mechanisms. See Note 3 — Regulatory Matters for additional information. Option Contracts, Swaps and Commodity Derivatives. Certain option contracts and swap arrangements that meet the definition of derivative instruments are recorded at fair value with subsequent changes in fair value recognized as revenue or expense. The classification of revenue or expense is based on the intent of the transaction. To the extent a Utility Registrant receives full cost recovery for energy procurement and related costs from retail customers, it records the fair value of its energy swap contracts with unaffiliated suppliers as well as an offsetting regulatory asset or liability in its Consolidated Balance Sheets. See Note 3 — Regulatory Matters and Note 15 — Derivative Financial Instruments for additional information.
Revenue, Transaction Price Measurement, Tax Exclusion [Policy Text Block]	Taxes Directly Imposed on Revenue-Producing Transactions. The Registrants collect certain taxes from customers such as sales and gross receipts taxes, along with other taxes, surcharges and fees, that are levied by state or local governments on the sale or distribution of gas and electricity. Some of these taxes are imposed on the customer, but paid by the Registrants, while others are imposed on the Registrants. Where these taxes are imposed on the customer, such as sales taxes, they are reported on a net basis with no impact to the Consolidated Statements of Operations and Comprehensive Income. However, where these taxes are imposed on the Registrants, such as gross receipts taxes or other surcharges or fees, they are reported on a gross basis. Accordingly, revenues are recognized for the taxes collected from customers along with an offsetting expense. Se e Note 23 — Supplemental Financial Information for Generation’s, ComEd’s, PECO’s, BGE’s, Pepco's, DPL's and ACE's utility taxes that are presented on a gross basis.
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 for most asset classes, 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 generally do 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.
Income Taxes (All Registrants)	Income Taxes (All Registrants) Deferred Federal and state income taxes are recorded on significant temporary differences between the book and tax basis of assets and liabilities and for tax benefits carried forward. Investment tax credits have been deferred in the Registrants’ Consolidated Balance Sheets and are recognized in book income over the life of the related property. The Registrants account for uncertain income tax positions using a benefit recognition model with a two-step approach; a more-likely-than-not recognition criterion; and a measurement approach that measures the position as the largest amount of tax benefit that is greater than 50% likely of being realized upon ultimate settlement. If it is not more-likely-than-not that the benefit of the tax position will be sustained on its technical merits, no benefit is recorded. Uncertain tax positions that relate only to timing of when an item is included on a tax return are considered to have met the recognition threshold. The Registrants recognize accrued interest related to unrecognized tax benefits in Interest expense or Other income and deductions (interest income) and recognize penalties related to unrecognized tax benefits in Other, net in their Consolidated Statements of Operations and Comprehensive Income.
Cash and Cash Equivalents (All Registrants)	Cash and Cash Equivalents (All Registrants) The Registrants consider investments purchased with an original maturity of three months or less to be cash equivalents. Restricted Cash and Cash Equivalents (All Registrants) Restricted cash and cash equivalents represent funds that are restricted to satisfy designated current liabilities. As of December 31, 2019 and 2018 , the Registrants' restricted cash and cash equivalents primarily represented the following items: Registrant Description Exelon Payment of medical, dental, vision and long-term disability benefits, in addition to the items listed for Generation and the Utility Registrants. Generation Project-specific nonrecourse financing structures for debt service and financing of operations of the underlying entities. ComEd Collateral held from suppliers associated with energy and REC procurement contracts, any over-recovered RPS costs and alternative compliance payments received from RES pursuant to FEJA and costs for the remediation of an MGP site. PECO Proceeds from the sales of assets that were subject to PECO’s mortgage indenture. BGE Proceeds from the loan program for the completion of certain energy efficiency measures and collateral held from energy suppliers. PHI Payment of merger commitments, collateral held from its energy suppliers associated with procurement contracts and repayment of transition bonds. Pepco Payment of merger commitments and collateral held from energy suppliers. DPL Collateral held from energy suppliers. ACE Repayment of transition bonds and collateral held from energy suppliers. Restricted cash and cash equivalents not available to satisfy current liabilities are classified as noncurrent assets. As of December 31, 2019 and 2018 , the Registrants' noncurrent restricted cash and cash equivalents primarily represented ComEd’s over-recovered RPS costs and alternative compliance payments received from RES pursuant to FEJA and costs for the remediation of an MGP site, and ACE’s repayment of transition bonds.
Allowance for Uncollectible Accounts (All Registrants)	Allowance for Uncollectible Accounts (All Registrants)
Variable Interest Entities (All Registrants)	Variable Interest Entities (Exelon, Generation, PHI and ACE) Exelon accounts for its investments in and arrangements with VIEs based on the following specific requirements: • requires an entity to qualitatively assess whether it should consolidate a VIE based on whether the entity has a controlling financial interest, • requires an ongoing reconsideration of this assessment instead of only upon certain triggering events, and • requires the entity that consolidates a VIE (the primary beneficiary) to disclose (1) the assets of the consolidated VIE, if they can be used to only settle specific obligations of the consolidated VIE, and (2) the liabilities of a consolidated VIE for which creditors do not have recourse to the general credit of the primary beneficiary.
Inventories (All Registrants)	Inventories (All Registrants) Inventory is recorded at the lower of weighted average cost or net realizable value. Provisions are recorded for excess and obsolete inventory. Fossil fuel, materials and supplies, and emissions allowances are generally included in inventory when purchased. Fossil fuel and emissions allowances are expensed to purchased power and fuel expense when used or sold. Materials and supplies generally includes transmission, distribution and generating plant materials and are expensed to operating and maintenance or capitalized to property, plant and equipment, as appropriate, when installed or used.
Marketable Securities (All Registrants)	Debt and Equity Security Investments (Exelon and Generation ) Debt Security Investments. Debt securities are reported at fair value and classified as available-for-sale securities. Unrealized gains and losses, net of tax, are reported in OCI. Equity Security Investments without Readily Determinable Fair Values. Exelon has certain equity securities without readily determinable fair values. Exelon has elected to use the practicability exception to measure these investments, defined as cost adjusted for changes from observable transactions for identical or similar investments of the same issuer, less impairment. Changes in measurement are reported in earnings. Equity Security Investments with Readily Determinable Fair Values.
Property Plant And Equipment (All Registrants)	Property, Plant and Equipment (All Registrants) Property, plant and equipment is recorded at original cost. Original cost includes construction-related direct labor and material costs. The Utility Registrants also include indirect construction costs including labor and related costs of departments associated with supporting construction activities. When appropriate, original cost also includes capitalized interest for Generation, Exelon Corporate and PHI and AFUDC for regulated property at the Utility Registrants. The cost of repairs and maintenance, including planned major maintenance activities and minor replacements of property, is charged to Operating and maintenance expense as incurred. Third parties reimburse the Utility Registrants for all or a portion of expenditures for certain capital projects. Such contributions in aid of construction costs (CIAC) are recorded as a reduction to Property, plant and equipment, net. DOE SGIG and other funds reimbursed to the Utility Registrants have been accounted for as CIAC. For Generation, upon retirement, the cost of property is generally charged to accumulated depreciation in accordance with the composite and group methods of depreciation. Upon replacement of an asset, the costs to remove the asset, net of salvage, are capitalized to gross plant when incurred as part of the cost of the newly-installed asset and recorded to depreciation expense over the life of the new asset. Removal costs, net of salvage, incurred for property that will not be replaced is charged to Operating and maintenance expense as incurred. For the Utility Registrants, upon retirement, the cost of property, net of salvage, is charged to accumulated depreciation consistent with the composite and group methods of depreciation. Depreciation expense at ComEd, BGE, Pepco, DPL and ACE includes the estimated cost of dismantling and removing plant from service upon retirement. Actual incurred removal costs are applied against a related regulatory liability or recorded to a regulatory asset if in excess of previously collected removal costs. PECO’s removal costs are capitalized to accumulated depreciation when incurred, and recorded to depreciation expense over the life of the new asset constructed consistent with PECO’s regulatory recovery method. Capitalized Software. Certain costs, such as design, coding, and testing incurred during the application development stage of software projects that are internally developed or purchased for operational use are capitalized within Property, plant and equipment. Similar costs incurred for cloud-based solutions treated as service arrangements are capitalized within Other Current Assets and Deferred Debits and Other Assets. Such capitalized amounts are amortized ratably over the expected lives of the projects when they become operational, generally not to exceed five years. Certain other capitalized software costs are being amortized over longer lives based on the expected life or pursuant to prescribed regulatory requirements. Capitalized Interest and AFUDC. During construction, Exelon and Generation capitalize the costs of debt funds used to finance non-regulated construction projects. Capitalization of debt funds is recorded as a charge to construction work in progress and as a non-cash credit to interest expense. AFUDC is the cost, during the period of construction, of debt and equity funds used to finance construction projects for regulated operations. AFUDC is recorded to construction work in progress and as a non-cash credit to an allowance that is included in interest expense for debt-related funds and other income and deductions for equity-related funds. The rates used for capitalizing AFUDC are computed under a method prescribed by regulatory authorities.
Nuclear Fuel (Exelon and Generation)	Nuclear Fuel (Exelon and Generation)
Nuclear Outage Costs (Exelon and Generation)	Nuclear Outage Costs (Exelon and Generation) Costs associated with nuclear outages, including planned major maintenance activities, are expensed to Operating and maintenance expense or capitalized to Property, plant and equipment (based on the nature of the activities) in the period incurred.
Depreciation, Depletion, and Amortization (All Registrants)	Depreciation and Amortization (All Registrants) Except for the amortization of nuclear fuel, depreciation is generally recorded over the estimated service lives of property, plant and equipment on a straight-line basis using the group, composite or unitary methods of depreciation. The group approach is typically for groups of similar assets that have approximately the same useful lives and the composite approach is used for dissimilar assets that have different lives. Under both methods, a reporting entity depreciates the assets over the average life of the assets in the group. The Utility Registrants' depreciation expense includes the estimated cost of dismantling and removing plant from service upon retirement, which is consistent with each utility's regulatory recovery method. The estimated service lives for the Registrants are based on a combination of depreciation studies, historical retirements, site licenses and management estimates of operating costs and expected future energy market conditions. See Note 6 — Early Plant Retirements for additional information on the impacts of expected and potential early plant retirements. See Note 7 — Property, Plant and Equipment for additional information regarding depreciation. Amortization of regulatory assets and liabilities are recorded over the recovery or refund period specified in the related legislation or regulatory order or agreement. When the recovery or refund period is less than one year, amortization is recorded to the line item in which the deferred cost or income would have originally been recorded in the Utility Registrants’ Consolidated Statements of Operations and Comprehensive Income. Amortization of ComEd’s electric distribution and energy efficiency formula rate regulatory assets and the Utility Registrants' transmission formula rate regulatory assets is recorded to Operating revenues. Amortization of income tax related regulatory assets and liabilities is generally recorded to Income tax expense. With the exception of the regulatory assets and liabilities discussed above, when the recovery period is more than one year, the amortization is generally recorded to Depreciation and amortization in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
Asset Retirement Obligations (All Registrants)	Asset Retirement Obligations (All Registrants)
Guarantees (All Registrants)	Guarantees (All Registrants) The Registrants recognize, at the inception of a guarantee, a liability for the fair market value of the obligations they have undertaken by issuing the guarantee, including the ongoing obligation to perform over the term of the guarantee in the event that the specified triggering events or conditions occur.
Asset Impairments (All Registrants)	Asset Impairments Long-Lived Assets (All Registrants). The Registrants regularly monitor and evaluate the carrying value of long-lived assets and asset groups for recoverability whenever events or changes in circumstances indicate that the carrying value of those assets may not be recoverable. Indicators of impairment may include a deteriorating business climate, including, but not limited to, declines in energy prices, condition of the asset, specific regulatory disallowance, or plans to dispose of a long-lived asset significantly before the end of its useful life. The Registrants determine if long-lived assets and asset groups are impaired by comparing the undiscounted expected future cash flows to the carrying value. When the undiscounted cash flow analysis indicates a long-lived asset or asset group is not recoverable, the amount of the impairment loss is determined by measuring the excess of the carrying amount of the long-lived asset or asset group over its fair value. See Note 11 — Asset Impairments for additional information. Goodwill (Exelon, ComEd and PHI). Goodwill represents the excess of the purchase price paid over the estimated fair value of the net assets acquired and liabilities assumed in the acquisition of a business. Goodwill is not amortized, but is tested for impairment at least annually or on an interim basis if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying value. See Note 12 — Intangible Assets for additional information. Equity Method Investments (Exelon and Generation). Exelon and Generation regularly monitor and evaluate equity method investments to determine whether they are impaired. An impairment is recorded when the investment has experienced a decline in value that is other-than-temporary in nature. Additionally, if the entity in which Generation holds an investment recognizes an impairment loss, Exelon and Generation would record their proportionate share of that impairment loss and evaluate the investment for an other-than-temporary decline in value. Debt Security Investments (Exelon and Generation). Declines in the fair value of debt security investments below the cost basis are reviewed to determine if such decline is other-than-temporary. If the decline is determined to be other-than-temporary, the amount of the impairment loss is included in earnings. Equity Security Investments (Exelon and Generation). Equity investments with readily determinable fair values are measured and recorded at fair value with any changes in fair value recorded through earnings. Investments in equity securities without readily determinable fair values are qualitatively assessed for impairment each reporting period. If it is determined that the equity security is impaired on the basis of the qualitative assessment, an impairment loss will be recognized in earnings to the amount by which the security’s carrying amount exceeds its fair value.
Derivatives Financial Instruments (All Registrants)	Derivative Financial Instruments (All Registrants) All derivatives are recognized on the balance sheet at their fair value unless they qualify for certain exceptions, including the NPNS. For derivatives intended to serve as economic hedges, changes in fair value are recognized in earnings each period. Amounts classified in earnings are included in Operating revenue, Purchased power and fuel, Interest expense or Other, net in the Consolidated Statements of Operations and Comprehensive Income based on the activity the transaction is economically hedging. While the majority of the derivatives serve as economic hedges, there are also derivatives entered into for proprietary trading purposes, subject to Exelon’s Risk Management Policy, and changes in the fair value of those derivatives are recorded in revenue in the Consolidated Statements of Operations and Comprehensive Income. At the Utility Registrants, changes in fair value may be recorded as a regulatory asset or liability if there is an ability to recover or return the associated costs. Cash inflows and outflows related to derivative instruments are included as a component of operating, investing or financing cash flows in the Consolidated Statements of Cash Flows, depending on the nature of each transaction. On July 1, 2018, Exelon and Generation de-designated its fair value and cash flow hedges. See Note 3 — Regulatory Matters and Note 15 — Derivative Financial Instruments for additional information.
Retirement Benefits (All Registrants)	Retirement Benefits (All Registrants) Exelon sponsors defined benefit pension plans and OPEB plans for essentially all employees.
New Accounting Pronouncements, Policy [Policy Text Block]	New Accounting Standards Adopted in 2019: In 2019, the Registrants adopted the following new authoritative accounting guidance issued by the FASB. Cloud Computing Arrangements (Issued August 2018) . Aligns the requirements for capitalizing costs incurred to implement a cloud computing arrangement with the internal-use software guidance. As a result, certain implementation costs incurred in a cloud computing arrangement that are currently expensed as incurred will be deferred and amortized over the non-cancellable term of the arrangement plus any reasonably certain renewal periods. The standard was effective January 1, 2020 and can be applied using either a prospective or retrospective transition approach. A retrospective approach requires a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Registrants early adopted this standard using a prospective approach as of January 1, 2019. The new guidance did not have a material impact on the Registrants' financial statements. Leases (Issued February 2016). 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) carry forward 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 resulted in the Registrants recording ROU assets and lease liabilities for operating leases in their 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 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, excluding 2019 expense and payment activity. See Note 10 — Leases for additional information. New Accounting Standards Adopted as of January 1, 2020: The following new authoritative accounting guidance issued by the FASB was adopted as of January 1, 2020 and will be reflected by the Registrants in their consolidated financial statements beginning in the first quarter of 2020. 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 its current estimate of credit losses expected to be incurred over the life of the financial instrument based on historical experience, current conditions and reasonable and supportable forecasts. The standard was effective January 1, 2020 and requires a modified retrospective transition approach through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. This standard is primarily applicable to Generation's and the Utility Registrants' trade accounts receivables balances. The guidance did not have a significant impact on the Registrants' consolidated financial statements. 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. The standard was effective January 1, 2020 and must be applied on a prospective basis. Exelon, Generation, ComEd, PHI and DPL will apply the new guidance for their goodwill impairment assessments in 2020 and do not expect the updated guidance to have a material impact to their financial statements.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Regulated Operations [Abstract]
Public Utilities Distribution Rate Cases [Table Text Block]	Completed Distribution Base Rate Case Proceedings Registrant/Jurisdiction Filing Date Requested Revenue Requirement (Decrease) Increase Approved Revenue Requirement (Decrease) Increase Approved ROE Approval Date Rate Effective Date ComEd - Illinois (Electric) (a) April 16, 2018 $ (23 ) $ (24 ) 8.69 % December 4, 2018 January 1, 2019 ComEd - Illinois (Electric) (a) April 8, 2019 (6 ) (17 ) 8.91 % December 4, 2019 January 1, 2020 PECO - Pennsylvania (Electric) March 29, 2018 82 25 N/A (b) December 20, 2018 January 1, 2019 BGE - Maryland June 8, 2018 (amended October 12, 2018) 61 43 9.8 % January 4, 2019 January 4, 2019 BGE - Maryland (Electric) May 24, 2019 (amended December 17, 2019) 74 18 9.7 % (d) December 17, 2019 December 17, 2019 BGE - Maryland (Natural Gas) May 24, 2019 (amended December 17, 2019) 59 45 9.75 % (d) December 17, 2019 December 17, 2019 ACE - New Jersey (Electric) August 21, 2018 (amended November 19, 2018) 122 (c) 70 (c) 9.6 % March 13, 2019 April 1, 2019 Pepco - Maryland (Electric) January 15, 2019 (amended May 16, 2019) 27 10 9.6 % August 12, 2019 August 13, 2019 __________ (a) Pursuant to EIMA and FEJA, ComEd’s electric distribution rates are established through a performance-based formula, which sunsets at the end of 2022. ComEd is required to file an annual update to its electric distribution formula rate on or before May 1 st , with resulting rates effective in January of the following year. ComEd’s annual electric distribution formula rate update is based on prior year actual costs and current year projected capital additions (initial year revenue requirement). The update also reconciles any differences between the revenue requirement in effect for the prior year and actual costs incurred from the year (annual reconciliation). ComEd’s 2018 approved revenue requirement above reflects a decrease of $58 million for the initial year revenue requirement for 2018 and an increase of $34 million related to the annual reconciliation for 2017. The revenue requirement for 2018 and the annual reconciliation for 2017 provides for a weighted average debt and equity return on distribution rate base of 6.52% inclusive of an allowed ROE of 8.69% , reflecting the average rate on 30-year treasury notes plus 580 basis points. ComEd’s 2019 approved revenue requirement above reflects an increase of $51 million for the initial year revenue requirement for 2019 and a decrease of $68 million related to the annual reconciliation for 2018. The revenue requirement for 2019 and the annual reconciliation for 2018 provides for a weighted average debt and equity return on distribution rate base of 6.51% inclusive of an allowed ROE of 8.91% , reflecting the average rate on 30-year treasury notes plus 580 basis points. See table below for ComEd's regulatory assets associated with its electric distribution formula rate. During the first quarter of 2018, ComEd revised its electric distribution formula rate to implement revenue decoupling provisions provided for under FEJA. As a result of this revision, ComEd’s electric distribution formula rate revenues are not impacted by abnormal weather, usage per customer or numbers of customers. ComEd began reflecting the impacts of this change in its Operating revenues and electric distribution formula rate regulatory asset in the first quarter of 2017. (b) The PECO rate case proceeding was resolved through a settlement agreement, which did not specify an approved ROE. (c) Requested and approved increases are before New Jersey sales and use tax. (d) ROEs in approved settlement are for the purpose of calculating AFUDC and carrying charges. Pending Distribution Base Rate Case Proceedings Registrant/Jurisdiction Filing Date Requested Revenue Requirement Increase Requested ROE Expected Approval Timing Pepco - District of Columbia (Electric) (a) May 30, 2019 (amended September 16, 2019) $ 160 10.3 % Fourth quarter of 2020 DPL - Maryland (Electric) December 5, 2019 19 10.3 % Third quarter of 2020 _________ (a) Reflects a three-year cumulative multi-year plan and total requested revenue requirement increases of $84 million , $40 million and $36 million for years 2020, 2021, and 2022, respectively, to recover capital investments made in 2018 and 2019 and planned capital investments from 2020 to 2022.
Public Utilities Transmission Rate Filings [Table Text Block]	For 2019 , the following total increases/(decreases) were included in ComEd’s, BGE’s, Pepco's, DPL's and ACE's electric transmission formula rate filings: Registrant Initial Revenue Requirement Increase/(Decrease) Annual Reconciliation (Decrease)/Increase Total Revenue Requirement Increase/(Decrease) Allowed Return on Rate Base (c) Allowed ROE (d) ComEd (a) $ 21 $ (16 ) $ 5 8.21 % 11.50 % BGE (a) (10 ) (23 ) (19 ) (b) 7.35 % 10.50 % Pepco 15 11 26 7.75 % 10.50 % DPL 17 (1 ) 16 7.14 % 10.50 % ACE 11 (2 ) 9 7.79 % 10.50 % __________ (a) The time period for any formal challenges to the annual transmission formula rate update filings expired with no formal challenges submitted (b) The change in BGE's transmission revenue requirement includes a FERC approved dedicated facilities charge of $14 million to recover the costs of providing transmission service to specifically designated load by BGE. (c) Represents the weighted average debt and equity return on transmission rate bases. (d) As part of the FERC-approved settlement of ComEd’s 2007 transmission rate case, the rate of return on common equity is 11.50% , inclusive of a 50 -basis-point incentive adder for being a member of a RTO, and the common equity component of the ratio used to calculate the weighted average debt and equity return for the transmission formula rate is currently capped at 55% . As part of the FERC-approved settlement of the ROE complaint against BGE, Pepco, DPL and ACE, the rate of return on common equity is 10.50% , inclusive of a 50 -basis-point incentive adder for being a member of a RTO.
Public Utilities Energy Efficiency Revenue [Table Text Block]	During 2019, the ICC approved the following total increases in ComEd's requested energy efficiency revenue requirement: Filing Date Requested Revenue Requirement Increase Approved Revenue Requirement Increase Approved ROE Approval Date Rate Effective Date May 23, 2019 $ 51 $ 50 (a) 8.91 % November 26, 2019 January 1, 2020 _________ (a) ComEd’s 2020 approved revenue requirement above reflects an increase of $53 million for the initial year revenue requirement for 2020 and a decrease of $3 million related to the annual reconciliation for 2018. The revenue requirement for 2020 provides for a weighted average debt and equity return on the energy efficiency regulatory asset and rate base of 6.51% inclusive of an allowed ROE of 8.91% , reflecting the average rate on 30-year treasury notes plus 580 basis points. See table below for ComEd's regulatory assets associated with its energy efficiency formula rate.
Public Utilities Transmission Rate Order [Table Text Block]	The Utility Registrants recorded the following payables to/receivables from PJM and related regulatory assets/liabilities in 2018 and have been refunding or recovering these amounts through electric distribution customer rates. Generation recorded a $41 million net payable to PJM and a pre-tax charge within Purchased power and fuel expense in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. PJM Receivable PJM Payable Regulatory Asset Regulatory Liability Exelon $ 220 $ 176 $ 136 $ 221 Generation (a) — 41 — — ComEd 122 — — 122 PECO 85 — — 85 BGE — 51 51 — PHI 13 84 85 14 Pepco — 84 84 — DPL 10 — — 10 ACE 3 — 1 4 __________ (a) Does not include an offsetting receivable from New Jersey Utilities of $16 million as of December 31, 2018.
Schedule of Regulatory Assets	The following tables provide information about the regulatory assets and liabilities of Exelon, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE as of December 31, 2019 and December 31, 2018 : December 31, 2019 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits $ 2,784 $ — $ — $ — $ — $ — $ — $ — Pension and other postretirement benefits - Merger related 1,138 — — — — — — — Deferred income taxes 528 — 518 — 10 10 — — AMI programs - Deployment costs 207 — — 129 78 43 35 — AMI programs - Legacy Meters 276 113 12 45 106 79 27 — Electric distribution formula rate annual reconciliations 34 34 — — — — — — Electric distribution formula rate significant one-time events 66 66 — — — — — — Energy efficiency costs 746 746 — — — — — — Fair value of long-term debt 650 — — — 523 — — — Fair value of PHI's unamortized energy contracts 443 — — — 443 — — — Asset retirement obligations 127 85 23 16 3 2 — 1 MGP remediation costs 302 287 11 4 — — — — Renewable energy 301 301 — — — — — — Electric Energy and Natural Gas Costs 110 — 6 36 68 43 5 20 Transmission formula rate annual reconciliations 11 — — 1 10 1 2 7 Energy efficiency and demand response programs 572 — — 303 269 196 73 — Merger integration costs 32 — — 2 30 15 8 7 Under-recovered revenue decoupling 37 — — 8 29 29 — — Securitized stranded costs 37 — — — 37 — — 37 Removal costs 641 — — 67 574 152 100 324 DC PLUG charge 126 — — — 126 126 — — Other 337 129 25 26 167 76 24 29 Total regulatory assets 9,505 1,761 595 637 2,473 772 274 425 Less: current portion 1,170 281 41 183 412 188 52 57 Total noncurrent regulatory assets $ 8,335 $ 1,480 $ 554 $ 454 $ 2,061 $ 584 $ 222 $ 368	December 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits $ 2,553 $ — $ — $ — $ — $ — $ — $ — Pension and other postretirement benefits - Merger related 1,266 — — — — — — — Deferred income taxes 414 — 404 — 10 10 — — AMI programs - Deployment costs 234 — — 145 89 50 39 — AMI programs - Legacy Meters 328 136 24 48 120 90 30 — Electric distribution formula rate annual reconciliations 158 158 — — — — — — Electric distribution formula rate significant one-time events 81 81 — — — — — — Energy efficiency costs 472 472 — — — — — — Fair value of long-term debt 702 — — — 569 — — — Fair value of PHI's unamortized energy contracts 561 — — — 561 — — — Asset retirement obligations 118 79 22 16 1 1 — — MGP remediation costs 326 309 17 — — — — — Renewable energy 249 249 — — — — — — Electric Energy and Natural Gas Costs 193 — 49 51 93 84 — 9 Transmission formula rate annual reconciliations 41 6 — 4 31 10 14 7 Energy efficiency and demand response programs 545 — 1 289 255 188 67 — Merger integration costs 42 — — 3 39 18 11 10 Under-recovered revenue decoupling 27 — — 2 25 25 — — Securitized stranded costs 50 — — — 50 — — 50 Removal costs 564 — — — 564 158 97 309 DC PLUG charge 159 — — — 159 159 — — Deferred storm costs 41 — — — 41 9 4 28 Other 303 110 24 17 162 79 28 13 Total regulatory assets 9,427 1,600 541 575 2,769 881 290 426 Less: current portion 1,190 293 81 177 457 238 59 40 Total noncurrent regulatory assets $ 8,237 $ 1,307 $ 460 $ 398 $ 2,312 $ 643 $ 231 $ 386
Schedule of Regulatory Liabilities	December 31, 2019 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Deferred income taxes $ 4,944 $ 2,297 $ — $ 1,089 $ 1,558 $ 725 $ 477 $ 356 Nuclear decommissioning 3,102 2,622 480 — — — — — Removal costs 1,621 1,435 — 58 128 20 108 — Electric Energy and Natural Gas Costs 109 45 56 — 8 — 8 — Transmission formula rate annual reconciliations 34 6 28 — — — — — Other 582 337 37 81 83 9 18 26 Total regulatory liabilities 10,392 6,742 601 1,228 1,777 754 611 382 Less: current portion 406 200 91 33 70 8 37 25 Total noncurrent regulatory liabilities $ 9,986 $ 6,542 $ 510 $ 1,195 $ 1,707 $ 746 $ 574 $ 357	December 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Deferred income taxes $ 5,228 $ 2,394 $ — $ 1,132 $ 1,702 $ 798 $ 510 $ 394 Nuclear decommissioning 2,606 2,217 389 — — — — — Removal costs 1,547 1,368 — 52 127 20 107 — Electric Energy and Natural Gas Costs 294 137 132 6 19 — 18 1 Other 528 227 75 79 100 11 30 25 Total regulatory liabilities 10,203 6,343 596 — 1,269 1,948 829 665 420 Less: current portion 644 293 175 77 84 7 59 18 Total noncurrent regulatory liabilities $ 9,559 $ 6,050 $ 421 $ 1,192 $ 1,864 $ 822 $ 606 $ 402
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 December 31, 2019 $ 63 $ 3 $ — $ 53 $ 7 $ 4 $ 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.

Revenue from Contracts with C_2

Revenue from Contracts with Customers Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer (All Registrants) [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 December 31, 2019 : Contract Assets Contract Liabilities Exelon Generation Exelon Generation Balance as of January 1, 2018 $ 283 $ 283 $ 35 $ 35 Consideration received or due (146 ) (146 ) 179 465 Revenues recognized 50 50 (187 ) (458 ) Balance at December 31, 2018 187 187 27 42 Consideration received or due (143 ) (143 ) 94 287 Revenues recognized 130 130 (88 ) (258 ) Balance at December 31, 2019 $ 174 $ 174 $ 33 $ 71
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]	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. 2020 2021 2022 2023 2024 and thereafter Total Exelon $ 400 $ 141 $ 65 $ 45 $ 199 $ 850 Generation 501 196 80 45 199 1,021

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 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 years ended December 31, 2019 , 2018 , and 2017 is as follows: Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon Operating revenues (c) : 2019 Competitive businesses electric revenues $ 16,285 $ — $ — $ — $ — $ — $ (1,165 ) $ 15,120 Competitive businesses natural gas revenues 2,148 — — — — — (1 ) 2,147 Competitive businesses other revenues 491 — — — — — (4 ) 487 Rate-regulated electric revenues — 5,747 2,490 2,379 4,626 — (47 ) 15,195 Rate-regulated natural gas revenues — — 610 727 167 — (15 ) 1,489 Shared service and other revenues — — — — 13 1,921 (1,934 ) — Total operating revenues $ 18,924 $ 5,747 $ 3,100 $ 3,106 $ 4,806 $ 1,921 $ (3,166 ) $ 34,438 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon 2018 Competitive businesses electric revenues $ 17,411 $ — $ — $ — $ — $ — $ (1,256 ) $ 16,155 Competitive businesses natural gas revenues 2,718 — — — — — (8 ) 2,710 Competitive businesses other revenues 308 — — — — — (5 ) 303 Rate-regulated electric revenues — 5,882 2,470 2,428 4,602 — (45 ) 15,337 Rate-regulated natural gas revenues — — 568 741 181 — (20 ) 1,470 Shared service and other revenues — — — — 15 1,948 (1,960 ) 3 Total operating revenues $ 20,437 $ 5,882 $ 3,038 $ 3,169 $ 4,798 $ 1,948 $ (3,294 ) $ 35,978 2017 Competitive businesses electric revenues $ 15,332 $ — $ — $ — $ — $ — $ (1,105 ) $ 14,227 Competitive businesses natural gas revenues 2,575 — — — — — — 2,575 Competitive businesses other revenues 593 — — — — — (1 ) 592 Rate-regulated electric revenues — 5,536 2,375 2,489 4,462 — (29 ) 14,833 Rate-regulated natural gas revenues — — 495 687 161 — (10 ) 1,333 Shared service and other revenues — — — — 49 1,831 (1,880 ) — Total operating revenues $ 18,500 $ 5,536 $ 2,870 $ 3,176 $ 4,672 $ 1,831 $ (3,025 ) $ 33,560 Intersegment revenues (d) : 2019 $ 1,172 $ 30 $ 6 $ 26 $ 14 $ 1,913 $ (3,159 ) $ 2 2018 1,269 27 8 29 15 1,942 (3,289 ) 1 2017 1,110 15 7 16 50 1,824 (3,020 ) 2 Depreciation and amortization: 2019 $ 1,535 $ 1,033 $ 333 $ 502 $ 754 $ 95 $ — $ 4,252 2018 1,797 940 301 483 740 92 — 4,353 2017 1,457 850 286 473 675 87 — 3,828 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon Operating expenses (c) : 2019 $ 17,628 $ 4,580 $ 2,388 $ 2,574 $ 4,084 $ 1,996 $ (3,154 ) $ 30,096 2018 19,510 4,741 2,452 2,696 4,156 1,929 (3,341 ) 32,143 2017 18,001 4,214 2,215 2,562 3,911 1,742 (3,026 ) 29,619 Interest expense, net: 2019 $ 429 $ 359 $ 136 $ 121 $ 263 $ 308 $ — $ 1,616 2018 432 347 129 106 261 279 — 1,554 2017 440 361 126 105 245 283 — 1,560 Income (loss) before income taxes: 2019 $ 1,917 $ 851 $ 593 $ 439 $ 514 $ (327 ) $ (2 ) $ 3,985 2018 365 832 466 387 425 (249 ) (1 ) 2,225 2017 1,455 984 538 525 571 (296 ) (2 ) 3,775 Income taxes: 2019 $ 516 $ 163 $ 65 $ 79 $ 38 $ (87 ) $ — $ 774 2018 (108 ) 168 6 74 33 (55 ) — 118 2017 (1,376 ) 417 104 218 217 294 — (126 ) Net income (loss): 2019 $ 1,217 $ 688 $ 528 $ 360 $ 477 $ (240 ) $ (2 ) $ 3,028 2018 443 664 460 313 393 (193 ) (1 ) 2,079 2017 2,798 567 434 307 355 (590 ) (2 ) 3,869 Capital expenditures: 2019 $ 1,845 $ 1,915 $ 939 $ 1,145 $ 1,355 $ 49 $ — $ 7,248 2018 2,242 2,126 849 959 1,375 43 — 7,594 2017 2,259 2,250 732 882 1,396 65 — 7,584 Total assets: 2019 $ 48,995 $ 32,765 $ 11,469 $ 10,634 $ 22,719 $ 8,484 $ (10,089 ) $ 124,977 2018 47,556 31,213 10,642 9,716 21,952 8,355 (9,800 ) 119,634 __________ (a) See Note 24 — Related Party Transactions for additional information on intersegment revenues. (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 23 — 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 authoritative 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 $ 2,260 $ 1,139 $ 1,240 $ — $ (13 ) $ 4,626 Rate-regulated natural gas revenues — 167 — — — 167 Shared service and other revenues — — — 396 (383 ) 13 Total operating revenues $ 2,260 $ 1,306 $ 1,240 $ 396 $ (396 ) $ 4,806 2018 Rate-regulated electric revenues $ 2,232 $ 1,151 $ 1,236 $ — $ (17 ) $ 4,602 Rate-regulated natural gas revenues — 181 — — — 181 Shared service and other revenues — — — 435 (420 ) 15 Total operating revenues $ 2,232 $ 1,332 $ 1,236 $ 435 $ (437 ) $ 4,798 2017 Rate-regulated electric revenues $ 2,151 $ 1,139 $ 1,186 $ — $ (14 ) $ 4,462 Rate-regulated natural gas revenues — 161 — — — 161 Shared service and other revenues — — — 52 (3 ) 49 Total operating revenues $ 2,151 $ 1,300 $ 1,186 $ 52 $ (17 ) $ 4,672 Intersegment revenues: 2019 $ 5 $ 7 $ 3 $ 396 $ (397 ) $ 14 2018 6 8 3 435 (437 ) 15 2017 6 8 2 53 (19 ) 50 Depreciation and amortization: 2019 $ 374 $ 184 $ 157 $ 39 $ — $ 754 2018 385 182 136 37 — $ 740 2017 321 167 146 42 (1 ) $ 675 Operating expenses: 2019 $ 1,899 $ 1,089 $ 1,089 $ 403 $ (396 ) $ 4,084 2018 1,919 1,143 1,087 442 (435 ) $ 4,156 2017 1,760 1,071 1,029 68 (17 ) $ 3,911 Interest expense, net: 2019 $ 133 $ 61 $ 58 $ 10 $ 1 $ 263 2018 128 58 64 11 — $ 261 2017 121 51 61 13 (1 ) $ 245 Income (loss) before income taxes: 2019 $ 259 $ 169 $ 99 $ 476 $ (489 ) $ 514 2018 216 142 87 388 (408 ) $ 425 2017 303 192 103 377 (404 ) $ 571 Income taxes: 2019 $ 16 $ 22 $ — $ (1 ) $ 1 $ 38 2018 11 22 12 (10 ) (2 ) $ 33 2017 105 71 26 15 — $ 217 Pepco DPL ACE Other (b) Intersegment PHI Net income (loss): 2019 $ 243 $ 147 $ 99 $ (26 ) $ 14 $ 477 2018 205 120 75 (22 ) 15 $ 393 2017 198 121 77 (91 ) 50 $ 355 Capital expenditures: 2019 $ 626 $ 348 $ 375 $ 6 $ — $ 1,355 2018 656 364 335 20 — $ 1,375 2017 628 428 312 28 — 1,396 Total assets: 2019 $ 8,661 $ 4,830 $ 3,933 $ 11,105 $ (5,810 ) $ 22,719 2018 8,267 4,588 3,699 10,819 (5,421 ) 21,952 __________ (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 23 — 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.
Analysis and reconciliation of reportable segment revenues for Generation	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): 2019 Revenues from external customers (a) Contracts with customers Other (b) Total Intersegment Revenues Total Revenues Mid-Atlantic $ 5,053 $ 17 $ 5,070 $ 4 $ 5,074 Midwest 4,095 232 4,327 (34 ) 4,293 New York 1,571 25 1,596 — 1,596 ERCOT 768 229 997 16 1,013 Other Power Regions 3,687 608 4,295 (49 ) 4,246 Total Competitive Businesses Electric Revenues 15,174 1,111 16,285 (63 ) 16,222 Competitive Businesses Natural Gas Revenues 1,446 702 2,148 62 2,210 Competitive Businesses Other Revenues (c) 440 51 491 1 492 Total Generation Consolidated Operating Revenues 17,060 1,864 $ 18,924 $ — $ 18,924 2018 Revenues from external customers (a) Contracts with customers Other (b) Total Intersegment Revenues Total Revenues Mid-Atlantic $ 5,241 $ 233 $ 5,474 $ 13 $ 5,487 Midwest 4,527 190 4,717 (11 ) 4,706 New York 1,723 (36 ) 1,687 — 1,687 ERCOT 572 560 1,132 1 1,133 Other Power Regions 3,530 871 4,401 (66 ) 4,335 Total Competitive Businesses Electric Revenues 15,593 1,818 17,411 (63 ) 17,348 Competitive Businesses Natural Gas Revenues 1,524 1,194 2,718 62 2,780 Competitive Businesses Other Revenues (c) 510 (202 ) 308 1 309 Total Generation Consolidated Operating Revenues $ 17,627 $ 2,810 $ 20,437 $ — $ 20,437 2017 Revenues from external customers (a) Contracts with customers Other (b) Total Intersegment Revenues Total Revenues Mid-Atlantic $ 5,523 $ (8 ) $ 5,515 $ 25 $ 5,540 Midwest 3,923 283 4,206 (25 ) 4,181 New York 1,605 (38 ) 1,567 (17 ) 1,550 ERCOT 641 317 958 4 962 Other Power Regions 2,658 428 3,086 (35 ) 3,051 Total Competitive Businesses Electric Revenues 14,350 982 15,332 (48 ) 15,284 Competitive Businesses Natural Gas Revenues 1,658 917 2,575 53 2,628 Competitive Businesses Other Revenues (c) 744 (151 ) 593 (5 ) 588 Total Generation Consolidated Operating Revenues $ 16,752 $ 1,748 $ 18,500 $ — $ 18,500 __________ (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 a $38 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value in 2017 , unrealized mark-to-market losses of $4 million , $262 million , and $131 million in 2019 , 2018 , and 2017 , respectively, and elimination of intersegment revenues. Revenues net of purchased power and fuel expense (Generation): 2019 2018 2017 RNF from external (a) Intersegment Total RNF RNF from external (a) Intersegment RNF Total RNF RNF from external (a) Intersegment Total RNF Mid-Atlantic $ 2,637 $ 18 $ 2,655 $ 3,022 $ 51 $ 3,073 $ 3,105 $ 109 $ 3,214 Midwest 2,994 (32 ) 2,962 3,112 23 3,135 2,810 10 2,820 New York 1,081 13 1,094 1,112 10 1,122 1,007 1 1,008 ERCOT 338 (30 ) 308 501 (243 ) 258 575 (243 ) 332 Other Power Regions 694 (74 ) 620 883 (154 ) 729 1,014 (195 ) 819 Total Revenues net of purchased power and fuel for Reportable Segments $ 7,744 $ (105 ) $ 7,639 $ 8,630 $ (313 ) $ 8,317 $ 8,511 $ (318 ) $ 8,193 Other (b) 324 105 429 114 313 427 299 318 617 Total Generation Revenues net of purchased power and fuel expense $ 8,068 $ — $ 8,068 $ 8,744 $ — $ 8,744 $ 8,810 $ — $ 8,810 __________ (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 a $54 million decrease in RNF for the amortization of intangible assets and liabilities related to commodity contracts in 2017 , unrealized mark-to-market losses of $215 million , $319 million , and $175 million in 2019 , 2018 , and 2017 , respectively, accelerated nuclear fuel amortization associated with the announced early plant retirements as discussed in Note 6 - Early Plant Retirements of $13 million , $57 million and $12 million in 2019 , 2018 , and 2017 , respectively, and the elimination of intersegment RNF.
Schedule of Revenue by Major Customers by Reporting Segments [Table Text Block]	Electric and Gas Revenue by Customer Class (Utility Registrants): 2019 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,916 $ 1,596 $ 1,326 $ 2,316 $ 1,012 $ 645 $ 659 Small commercial & industrial 1,463 404 254 505 149 186 170 Large commercial & industrial 540 219 436 1,112 833 99 180 Public authorities & electric railroads 47 29 27 61 34 14 13 Other (a) 888 249 321 650 227 204 218 Total rate-regulated electric revenues (b) 5,854 2,497 2,364 4,644 2,255 1,148 1,240 Rate-regulated natural gas revenues Residential — 409 474 96 — 96 — Small commercial & industrial — 169 77 44 — 45 — Large commercial & industrial — 1 132 5 — 5 — Transportation — 25 — 14 — 14 — Other (c) — 6 31 7 — 7 — Total rate-regulated natural gas revenues (d) — 610 714 166 — 167 — Total rate-regulated revenues from contracts with customers 5,854 3,107 3,078 4,810 2,255 1,315 1,240 Other revenues Revenues from alternative revenue programs (133 ) (21 ) 12 (14 ) (3 ) (11 ) — Other rate-regulated electric revenues (e) 26 13 12 10 8 2 — Other rate-regulated natural gas revenues (e) — 1 4 — — — — Total other revenues (107 ) (7 ) 28 (4 ) 5 (9 ) — Total rate-regulated revenues for reportable segments $ 5,747 $ 3,100 $ 3,106 $ 4,806 $ 2,260 $ 1,306 $ 1,240 2018 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,942 $ 1,566 $ 1,382 $ 2,351 $ 1,021 $ 669 $ 661 Small commercial & industrial 1,487 404 257 488 140 186 162 Large commercial & industrial 538 223 429 1,124 846 100 178 Public authorities & electric railroads 47 28 28 58 32 14 12 Other (a) 867 243 327 593 193 175 227 Total rate-regulated electric revenues (b) 5,881 2,464 2,423 4,614 2,232 1,144 1,240 Rate-regulated natural gas revenues Residential — 395 491 99 — 99 — Small commercial & industrial — 143 77 44 — 44 — Large commercial & industrial — 1 124 8 — 8 — Transportation — 23 — 16 — 16 — Other (c) — 6 63 13 — 13 — Total rate-regulated natural gas revenues (d) — 568 755 180 — 180 — Total rate-regulated revenues from contracts with customers 5,881 3,032 3,178 4,794 2,232 1,324 1,240 Other revenues Revenues from alternative revenue programs (29 ) (7 ) (26 ) (7 ) (7 ) 4 (4 ) Other rate-regulated electric revenues (e) 30 12 13 10 7 3 — Other rate-regulated natural gas revenues (e) — 1 4 1 — 1 — Total other revenues 1 6 (9 ) 4 — 8 (4 ) Total rate-regulated revenues for reportable segments $ 5,882 $ 3,038 $ 3,169 $ 4,798 $ 2,232 $ 1,332 $ 1,236 2017 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,715 $ 1,505 $ 1,365 $ 2,246 $ 964 $ 663 $ 619 Small commercial & industrial 1,363 401 254 490 137 187 166 Large commercial & industrial 455 223 427 1,086 794 103 189 Public authorities & electric railroads 44 30 31 60 33 14 13 Other (a) 886 204 299 541 199 163 191 Total rate-regulated electric revenues (b) 5,463 2,363 2,376 4,423 2,127 1,130 1,178 Rate-regulated natural gas revenues Residential — 331 437 90 — 90 — Small commercial & industrial — 131 75 38 — 38 — Large commercial & industrial — 1 119 8 — 8 — Transportation — 23 — 15 — 15 — Other (c) — 8 28 9 — 9 — Total rate-regulated natural gas revenues (d) — 494 659 160 — 160 — Total rate-regulated revenues from contracts with customers 5,463 2,857 3,035 4,583 2,127 1,290 1,178 Other revenues Revenues from alternative revenue programs 43 — 124 33 19 6 8 Other rate-regulated electric revenues (e) 30 12 13 8 5 3 — Other rate-regulated natural gas revenues (e) — 1 4 1 — 1 — Other revenues (f) — — — 47 — — — Total other revenues 73 13 141 89 24 10 8 Total rate-regulated revenues for reportable segments $ 5,536 $ 2,870 $ 3,176 $ 4,672 $ 2,151 $ 1,300 $ 1,186 __________ (a) Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue. (b) Includes operating revenues from affiliates of $ 30 million , $5 million , $8 million , $14 million , $5 million , $7 million and $3 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2019 , $27 million , $7 million , $8 million , $15 million , $6 million , $8 million and $3 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, in 2018 , and $15 million , $6 million , $5 million , $3 million , $6 million , $8 million and $2 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2017 . (c) Includes revenues from off-system natural gas sales. (d) Includes operating revenues from affiliates of $1 million and $18 million at PECO and BGE, respectively, in 2019 , $1 million and $21 million at PECO and BGE, respectively, in 2018 , and $1 million and $11 million at PECO and BGE, respectively, in 2017 . (e) Includes late payment charge revenues. (f) Includes operating revenues from affiliates of $47 million at PHI in 2017 .

Early Plant Retirements (Tables

Early Plant Retirements (Tables)	12 Months Ended
	Dec. 31, 2019
Implications of Potential Early Plant Retirements [Abstract]
Restructuring and Related Costs [Table Text Block]	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. The total annual impact of these charges by year are summarized in the table below. Income statement expense (pre-tax) 2019 (a) 2018 (b) 2017 (c) Depreciation and Amortization Accelerated depreciation $ 216 $ 539 $ 250 Accelerated nuclear fuel amortization 13 57 12 Operating and Maintenance (d) (53 ) 32 77 Total $ 176 $ 628 $ 339 _________ (a) Reflects incremental charges for TMI from January 1, 2019 through September 20, 2019. (b) Reflects incremental charges for TMI in 2018 and Oyster Creek from February 2, 2018 through September 17, 2018. (c) Reflects incremental charges for TMI from May 30, 2017 through December 31, 2017. (d) In 2019, primarily reflects the net impacts associated with the remeasurements of the TMI ARO in the first and third quarters. In 2018 and 2017, primarily reflects materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments associated with the early retirement decisions for TMI and Oyster Creek. Excludes the charges in the third quarter of 2018 and second quarter of 2019 for the ARO remeasurement due to the sale of Oyster Creek. See Note 2 — Mergers, Acquisitions and Dispositions and Note 9 — Asset Retirement Obligations for additional information.
Implications of Potential Early Plant Retirement on Balance Sheet [Table Text Block]	The following table provides the balance sheet amounts as of December 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 the failure to adopt long-term solutions for reliability and fuel security. December 31, 2019 Asset Balances Materials and supplies inventory $ 31 Fuel inventory 11 Property, plant and equipment, net 902 Liability Balances Asset retirement obligation (3 )

Property, Plant and Equipment_2

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The following tables present a summary of property, plant and equipment by asset category as of December 31, 2019 and 2018 : Asset Category Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 Electric—transmission and distribution $ 56,809 $ — $ 27,566 $ 8,957 $ 8,326 $ 13,809 $ 9,734 $ 4,464 $ 4,207 Electric—generation 29,839 29,839 — — — — — — — Gas—transportation and distribution 6,147 — — 2,899 2,999 525 — 690 — Common—electric and gas 1,907 — — 877 991 146 — 160 — Nuclear fuel (a) 5,656 5,656 — — — — — — — Construction work in progress 3,055 702 662 250 483 921 628 125 166 Other property, plant and equipment (b) 799 13 47 27 25 108 64 21 27 Total property, plant and equipment 104,212 36,210 28,275 13,010 12,824 15,509 10,426 5,460 4,400 Less: accumulated depreciation (c) 23,979 12,017 5,168 3,718 3,834 1,213 3,517 1,425 1,210 Property, plant and equipment, net $ 80,233 $ 24,193 $ 23,107 $ 9,292 $ 8,990 $ 14,296 $ 6,909 $ 4,035 $ 3,190 December 31, 2018 Electric—transmission and distribution $ 53,090 $ — $ 25,991 $ 8,359 $ 7,951 $ 12,664 $ 9,217 $ 4,195 $ 3,866 Electric—generation 29,170 29,170 — — — — — — — Gas—transportation and distribution 5,530 — — 2,694 2,630 486 — 651 — Common—electric and gas 1,627 — — 756 860 126 — 136 — Nuclear fuel (a) 5,957 5,957 — — — — — — — Construction work in progress 3,377 997 705 343 410 912 536 151 209 Other property, plant and equipment (b) 858 63 46 19 25 99 61 17 28 Total property, plant and equipment 99,609 36,187 26,742 12,171 11,876 14,287 9,814 5,150 4,103 Less: accumulated depreciation (c) 22,902 12,206 4,684 3,561 3,633 841 3,354 1,329 1,137 Property, plant and equipment, net $ 76,707 $ 23,981 $ 22,058 $ 8,610 $ 8,243 $ 13,446 $ 6,460 $ 3,821 $ 2,966 __________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,025 million and $1,004 million at December 31, 2019 and 2018 , respectively. (b) Primarily composed of land and non-utility property. (c) Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $2,867 million and $2,969 million as of December 31, 2019 and 2018 , respectively. The following table presents the average service life for each asset category in number of years: Average Service Life (years) Asset Category Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Electric - transmission and distribution 5-80 N/A 5-80 5-65 5-75 5-75 5-75 5-70 5-65 Electric - generation 1-56 1-56 N/A N/A N/A N/A N/A N/A N/A Gas - transportation and distribution 5-80 N/A N/A 5-70 5-80 5-75 N/A 5-75 N/A Common - electric and gas 4-75 N/A N/A 5-50 4-50 5-75 N/A 5-75 N/A Nuclear fuel 1-8 1-8 N/A N/A N/A N/A N/A N/A N/A Other property, plant and equipment 1-50 1-10 34-50 50 20-50 3-50 33-50 8-50 13-15
Property Plant And Equipment Average Service Life Percentage By Asset Category Table	The following table presents the annual depreciation rates for each asset category. Nuclear fuel amortization is charged to fuel expense using the unit-of-production method and not included in the below table. Annual Depreciation Rates Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 Electric—transmission and distribution 2.80 % N/A 2.99 % 2.36 % 2.60 % 2.77 % 2.47 % 2.86 % 2.94 % Electric—generation 4.35 % 4.35 % N/A N/A N/A N/A N/A N/A N/A Gas—transportation and distribution 2.04 % N/A N/A 1.89 % 2.30 % 1.55 % N/A 1.55 % N/A Common—electric and gas 7.37 % N/A N/A 6.06 % 8.30 % 8.25 % N/A 6.24 % N/A December 31, 2018 Electric—transmission and distribution 2.73 % N/A 2.95 % 2.35 % 2.61 % 2.61 % 2.40 % 2.77 % 2.45 % Electric—generation 5.37 % 5.37 % N/A N/A N/A N/A N/A N/A N/A Gas—transportation and distribution 2.07 % N/A N/A 1.90 % 2.36 % 1.59 % N/A 1.59 % N/A Common—electric and gas 6.98 % N/A N/A 5.44 % 8.50 % 6.30 % N/A 3.70 % N/A December 31, 2017 Electric—transmission and distribution 2.75 % N/A 2.99 % 2.37 % 2.58 % 2.63 % 2.35 % 2.75 % 2.46 % Electric—generation 4.36 % 4.36 % N/A N/A N/A N/A N/A N/A N/A Gas—transportation and distribution 2.10 % N/A N/A 1.89 % 2.33 % 2.07 % N/A 2.07 % N/A Common—electric and gas 7.05 % N/A N/A 5.47 % 8.64 % 6.50 % N/A 4.14 % N/A
Schedule Of Capitalized Interest And AFUDC	The following table summarizes capitalized interest and credits to AFUDC by year: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 Capitalized interest $ 24 $ 24 $ — $ — $ — $ — $ — $ — $ — AFUDC debt and equity 132 — 32 17 29 54 39 6 9 December 31, 2018 Capitalized interest $ 31 $ 31 $ — $ — $ — $ — $ — $ — $ — AFUDC debt and equity 109 — 30 12 24 44 34 4 4 December 31, 2017 Capitalized interest $ 63 $ 63 $ — $ — $ — $ — $ — $ — $ — AFUDC debt and equity 108 — 20 12 22 54 34 10 9

Jointly Owned Electric Utilit_2

Jointly Owned Electric Utility Plant (Tables)	12 Months Ended
	Dec. 31, 2019
Public Utilities, Property, Plant and Equipment [Abstract]
Schedule of Jointly Owned Utility Plants	Exelon's, Generation's, PECO's, DPL's and ACE's material undivided ownership interests in jointly owned electric plants and transmission facilities at December 31, 2019 and 2018 were as follows: Nuclear Generation Transmission Quad Cities Peach Bottom Salem Nine Mile Point Unit 2 NJ/DE (a) Operator Generation Generation PSEG Generation PSEG/DPL Ownership interest 75.00 % 50.00 % 42.59 % 82.00 % various Exelon’s share at December 31, 2019: Plant in service $ 1,161 $ 1,466 $ 663 $ 951 $ 102 Accumulated depreciation 627 571 249 156 53 Construction work in progress 13 21 53 27 — Exelon’s share at December 31, 2018: Plant in service $ 1,131 $ 1,451 $ 648 $ 910 $ 103 Accumulated depreciation 587 523 227 126 53 Construction work in progress 13 15 44 56 — __________ (a) PECO, DPL and ACE own a 42.55% , 1% and 13.9% share, respectively in 151.3 miles of 500 kV lines located in New Jersey and of the Salem generating plant substation. PECO, DPL and ACE also own a 42.55% , 7.45% and 7.45% share, respectively, in 2.5 miles of 500 kV line located over the Delaware River. ACE also has a 21.78% share in a 500 kV New Freedom Switching substation.

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2019
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligation Rollforward	The following table provides a rollforward of the nuclear decommissioning ARO reflected in Exelon’s and Generation’s Consolidated Balance Sheets, from January 1, 2018 to December 31, 2019 : Nuclear decommissioning ARO at January 1, 2018 $ 9,662 Accretion expense 478 Net decrease due to changes in, and timing of, estimated future cash flows (77 ) Costs incurred related to decommissioning plants (58 ) Nuclear decommissioning ARO at December 31, 2018 (a) (b) 10,005 Net increase due to changes in, and timing of, estimated future cash flows 864 Sale of Oyster Creek (755 ) Accretion Expense 479 Costs incurred related to decommissioning plants (89 ) Nuclear decommissioning ARO at December 31, 2019 (a) $ 10,504 __________ (a) Includes $112 million and $22 million as the current portion of the ARO at December 31, 2019 and 2018 , respectively, which is included in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets. (b) Includes $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 December 31, 2018. See Note 2 — Mergers, Acquisitions and Dispositions for additional information. The following table provides a rollforward of the non-nuclear AROs reflected in the Registrants’ Consolidated Balance Sheets from January 1, 2018 to December 31, 2019 : Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Non-nuclear AROs at January 1, 2018 $ 384 $ 197 $ 113 $ 27 $ 24 $ 16 $ 3 $ 10 $ 3 Net increase due to changes in, and timing of, estimated future cash flows (a) 80 35 7 — 2 36 34 1 1 Accretion expense (b) 16 10 4 1 1 — — — — Asset divestitures (3 ) (3 ) — — — — — — — Payments (6 ) (1 ) (3 ) — (2 ) — — — — Non-nuclear AROs at December 31, 2018 471 238 121 28 25 52 37 11 4 Net (decrease) increase due to changes in, and timing of, estimated future cash flows 17 7 8 — (2 ) 4 3 1 — Development projects 2 2 — — — — — — — Accretion expense (b) 16 12 1 1 1 1 1 — — Asset divestitures (42 ) (42 ) — — — — — — — Payments (4 ) (1 ) (1 ) (1 ) (1 ) — — — — Non-nuclear AROs at December 31, 2019 $ 460 $ 216 $ 129 $ 28 $ 23 $ 57 $ 41 $ 12 $ 4 __________ (a) In 2018, Pepco recorded an increase of $22 million in Operating and maintenance expense primarily related to asbestos identified at its Buzzard Point property as part of an annual ARO study. Buzzard Point is a waterfront property in the District of Columbia occupied by an active substation and former Pepco operated steam plant building, which Pepco retired and closed in 1981. (b) For ComEd and PECO, the majority of the accretion is recorded as an increase to a regulatory asset due to the associated regulatory treatment.

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Components of Lease Cost [Table Text Block]	ROU assets obtained in exchange for lease obligations for the year ended December 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating leases $ 52 $ 14 $ 6 $ — $ 2 $ (3 ) $ (1 ) $ (2 ) $ (1 ) The weighted average remaining lease terms, in years, and discount rates for operating leases as of December 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Remaining lease term 10.1 10.6 4.6 4.4 5.4 9.0 9.8 9.7 4.7 Discount rate 4.6 % 4.8 % 3.0 % 3.2 % 3.6 % 4.2 % 4.0 % 4.0 % 3.6 % The components of lease costs for the year ended December 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating lease costs $ 320 $ 222 $ 3 $ 1 $ 33 $ 48 $ 12 $ 14 $ 7 Variable lease costs 300 282 2 — 2 6 2 2 1 Short-term lease costs 19 19 — — — — — — — Total lease costs (a) $ 639 $ 523 $ 5 $ 1 $ 35 $ 54 $ 14 $ 16 $ 8 __________ (a) Excludes $51 million , $44 million , $7 million and $7 million of sublease income recorded at Exelon, Generation, PHI and DPL.
Schedule of Rent Expense [Table Text Block]	The following table presents the Registrants' rental expense under the prior lease accounting guidance for the years ended December 31, 2018 and 2017 : Exelon Generation (a) ComEd PECO BGE PHI Pepco DPL ACE 2018 $ 670 $ 558 $ 7 $ 10 $ 35 $ 48 $ 10 $ 13 $ 8 2017 709 578 9 9 32 63 11 16 14
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 ROU assets and lease liabilities within the Registrants’ Consolidated Balance Sheets as of December 31, 2019 : Exelon (a) Generation (a) ComEd PECO BGE PHI Pepco DPL ACE Operating lease ROU assets Other deferred debits and other assets $ 1,305 $ 895 $ 9 $ 2 $ 77 $ 273 $ 56 $ 63 $ 18 Operating lease liabilities Other current liabilities 225 157 3 — 32 31 6 9 4 Other deferred credits and other liabilities 1,307 925 8 1 50 254 51 65 14 Total operating lease liabilities $ 1,532 $ 1,082 $ 11 $ 1 $ 82 $ 285 $ 57 $ 74 $ 18 __________ (a) Exelon's and Generation's operating ROU assets and lease liabilities include $515 million and $664 million , respectively, related to contracted generation.
Lessee, Operating Lease, Liability, Maturity [Table Text Block]	Future minimum lease payments for operating leases as of December 31, 2019 were as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2020 $ 287 $ 203 $ 3 $ — $ 34 $ 42 $ 8 $ 11 $ 5 2021 243 162 4 1 31 41 8 11 4 2022 177 113 2 — 16 38 8 10 4 2023 145 100 1 — 1 37 7 9 3 2024 140 97 1 — — 35 5 9 2 Remaining years 976 741 1 — 18 153 34 41 2 Total 1,968 1,416 12 1 100 346 70 91 20 Interest 436 334 1 — 18 61 13 17 2 Total operating lease liabilities $ 1,532 $ 1,082 $ 11 $ 1 $ 82 $ 285 $ 57 $ 74 $ 18
Schedule of Future Minimum Rental 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 year ended December 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating cash flows from operating leases $ 287 $ 206 $ 3 $ — $ 33 $ 37 $ 9 $ 6 $ 5
Components of Operating Lease Income [Table Text Block]	The components of lease income for the year ended December 31, 2019 were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating lease income $ 54 $ 47 $ — $ — $ — $ 5 $ — $ 4 $ — Variable lease income $ 261 $ 258 $ — $ — $ — $ 3 $ — $ 3 $ —
Lessor, Operating Lease, Payments to be Received, Maturity [Table Text Block]	Future minimum lease payments to be recovered under operating leases as of December 31, 2019 were as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2020 $ 51 $ 46 $ — $ — $ — $ 4 $ — $ 3 $ — 2021 51 45 — — — 4 1 3 — 2022 50 45 — — — 4 — 3 — 2023 49 44 — — — 5 — 4 — 2024 48 44 — — — 4 — 4 — Remaining years 265 226 1 3 1 34 — 34 — Total $ 514 $ 450 $ 1 $ 3 $ 1 $ 55 $ 1 $ 51 $ —

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Schedule Of Goodwill	The following table presents the gross amount of goodwill, accumulated impairment loss and carrying amount of goodwill of Exelon, ComEd and PHI as of December 31, 2019 and 2018 . There were no additions, impairments or measurement period adjustments during the years ended December 31, 2019 and 2018 . Gross amount Accumulated impairment loss Carrying amount Exelon $ 8,660 $ 1,983 $ 6,677 ComEd (a) 4,608 1,983 2,625 PHI (b) 4,005 — 4,005 __________ (a) Reflects goodwill recorded in 2000 from the PECO/Unicom merger (predecessor parent company of ComEd). (b) Reflects goodwill recorded in 2016 from the PHI merger.
Schedule of Finite-Lived Intangible Assets	Exelon’s, Generation’s, ComEd’s and PHI's other intangible assets and liabilities, included in Unamortized energy contract assets and liabilities and Other deferred debits and other assets in their Consolidated Balance Sheets, consisted of the following as of December 31, 2019 and 2018 . The intangible assets and liabilities shown below are amortized on a straight line basis, except for unamortized energy contracts which are amortized in relation to the expected realization of the underlying cash flows: December 31, 2019 December 31, 2018 Gross Accumulated Amortization Net Gross Accumulated Amortization Net Generation Unamortized Energy Contracts 1,967 (1,612 ) 355 1,957 (1,588 ) 369 Customer Relationships 343 (190 ) 153 325 (162 ) 163 Trade Name 243 (193 ) 50 243 (171 ) 72 ComEd Chicago Settlement Agreements 162 (155 ) 7 162 (148 ) 14 PHI Unamortized Energy Contracts (1,515 ) 1,073 (442 ) (1,515 ) 954 (561 ) Exelon Corporate Software License 95 (44 ) 51 95 (34 ) 61 Exelon $ 1,295 $ (1,121 ) $ 174 $ 1,267 $ (1,149 ) $ 118
Schedule Of Finite-Lived Intangible Assets Amortization Expense	The following table summarizes the amortization expense related to intangible assets and liabilities for each of the years ended December 31, 2019 , 2018 and 2017 : For the Years Ended December 31, Exelon (a)(b) Generation (a) ComEd PHI (b) 2019 $ (28 ) $ 74 $ 7 $ (119 ) 2018 (109 ) 63 7 (188 ) 2017 (237 ) 83 7 (336 ) __________ (a) At Exelon and Generation, amortization of unamortized energy contracts totaling $21 million , $14 million and $35 million for the years ended December 31, 2019 , 2018 and 2017 , respectively, was recorded in Operating revenues or Purchased power and fuel expense in their Consolidated Statements of Operations and Comprehensive Income. (b) At Exelon and PHI, amortization of the unamortized energy contract fair value adjustment amounts and the corresponding offsetting regulatory asset and liability amounts are amortized through Purchased power and fuel expense in their Consolidated Statements of Operations and Comprehensive Income.
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	The following table summarizes the estimated future amortization expense related to intangible assets and liabilities as of December 31, 2019 : For the Years Ending December 31, Exelon Generation ComEd PHI 2020 $ (13 ) $ 85 $ 7 $ (115 ) 2021 2 84 — (92 ) 2022 (21 ) 58 — (89 ) 2023 (18 ) 53 — (81 ) 2024 22 50 — (38 )
Schedule of Alternative or Renewable Energy Credits [Table Text Block]	The following table presents the current and noncurrent Renewable Energy Credits as of December 31, 2019 and 2018 : As of December 31, 2019 As of December 31, 2018 Exelon Generation Exelon Generation Current REC's 345 336 279 270 Noncurrent REC's 86 86 52 52

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Schedule of Components of Income Tax Expense (Benefit)	Income tax expense (benefit) from continuing operations is comprised of the following components: For the Year Ended December 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Included in operations: Federal Current $ 85 $ 147 $ 59 $ 45 $ (51 ) $ 43 $ 16 $ 29 $ (3 ) Deferred 489 346 15 20 95 (34 ) (6 ) (21 ) (6 ) Investment tax credit amortization (72 ) (69 ) (2 ) — — (1 ) — — — State Current 5 10 (5 ) — — 3 — — — Deferred 267 82 96 — 35 27 6 14 9 Total $ 774 $ 516 $ 163 $ 65 $ 79 $ 38 $ 16 $ 22 $ — For the Year Ended December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Included in operations: Federal Current $ 226 $ 337 $ (63 ) $ 11 $ (5 ) $ (4 ) $ 28 $ (3 ) $ (14 ) Deferred (99 ) (347 ) 145 10 47 23 (22 ) 13 18 Investment tax credit amortization (24 ) (21 ) (2 ) — — (1 ) — — — State Current (1 ) 6 (29 ) 1 — 7 — — — Deferred 16 (83 ) 117 (16 ) 32 8 5 12 8 Total $ 118 $ (108 ) $ 168 $ 6 $ 74 $ 33 $ 11 $ 22 $ 12 For the Year Ended December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Included in operations: Federal Current $ 194 $ 584 $ (191 ) $ 71 $ 74 $ (60 ) $ (20 ) $ (24 ) $ (12 ) Deferred (470 ) (2,005 ) 523 28 101 251 115 82 34 Investment tax credit amortization (25 ) (21 ) (2 ) — (1 ) (1 ) — — — State Current 14 65 (49 ) 14 (5 ) (4 ) (2 ) — — Deferred 161 1 136 (9 ) 49 31 12 13 4 Total $ (126 ) $ (1,376 ) $ 417 $ 104 $ 218 $ 217 $ 105 $ 71 $ 26
Effective Income Tax Rate Reconciliation	The effective income tax rate from continuing operations varies from the U.S. federal statutory rate principally due to the following: For the Year Ended December 31, 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 5.4 3.8 8.5 — 6.4 4.7 2.0 6.8 7.0 Qualified NDT fund income 5.9 12.3 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.5 ) (3.0 ) (0.2 ) — (0.1 ) (0.2 ) (0.1 ) (0.2 ) (0.3 ) Plant basis differences (1.4 ) — — (7.2 ) (1.2 ) (1.2 ) (1.8 ) (0.4 ) (0.7 ) Production tax credits and other credits (3.1 ) (4.8 ) (1.2 ) — (1.3 ) (0.2 ) (0.1 ) — (0.1 ) Noncontrolling interests (0.6 ) (1.2 ) — — — — — — — Excess deferred tax amortization (5.5 ) — (9.7 ) (2.8 ) (6.8 ) (17.5 ) (15.1 ) (14.2 ) (27.0 ) Other (0.8 ) (1.2 ) 0.8 — — 0.8 0.3 — 0.1 Effective income tax rate 19.4 % 26.9 % 19.2 % 11.0 % 18.0 % 7.4 % 6.2 % 13.0 % — % For the Year Ended December 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 0.5 (16.6 ) 8.3 (2.6 ) 6.6 2.9 2.0 6.7 7.4 Qualified NDT fund income (1.9 ) (11.8 ) — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.2 ) (6.5 ) (0.2 ) (0.1 ) (0.1 ) (0.2 ) (0.1 ) (0.3 ) (0.4 ) Plant basis differences (3.5 ) — (0.2 ) (14.1 ) (1.3 ) (1.6 ) (2.8 ) (0.3 ) (0.5 ) Production tax credits and other credits (2.2 ) (13.5 ) — — — — — — — Noncontrolling interests (1.0 ) (6.1 ) — — — — — — — Excess deferred tax amortization (8.3 ) — (9.1 ) (3.2 ) (8.0 ) (14.8 ) (15.3 ) (12.0 ) (14.9 ) Tax Cuts and Jobs Act of 2017 0.9 2.7 (0.1 ) — — 0.1 — — — Other 1.0 1.3 0.5 0.3 0.9 0.4 0.3 0.4 1.2 Effective income tax rate 5.3 % (29.5 )% 20.2 % 1.3 % 19.1 % 7.8 % 5.1 % 15.5 % 13.8 % For the Year Ended December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 2.2 2.9 5.7 0.6 5.4 4.8 3.1 5.4 5.6 Qualified NDT fund income 3.8 9.9 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.9 ) (2.1 ) (0.2 ) (0.1 ) (0.1 ) (0.2 ) (0.1 ) (0.2 ) (0.4 ) Plant basis differences (a) (1.7 ) — 0.3 (13.8 ) 0.1 1.1 (0.4 ) 2.0 3.6 Production tax credits and other credits (1.8 ) (4.7 ) — — — — — — — Like-kind exchange (1.2 ) — 1.3 — — — — — — Merger expenses (3.6 ) (1.2 ) — — — (9.6 ) (6.4 ) (7.8 ) (19.8 ) FitzPatrick bargain purchase gain (2.2 ) (5.6 ) — — — — — — — Tax Cuts and Jobs Act of 2017 (b) (33.1 ) (128.3 ) 0.1 (2.3 ) 0.9 6.4 2.8 2.5 1.6 Other 0.2 (0.5 ) 0.2 (0.1 ) 0.2 0.5 0.7 0.1 (0.4 ) Effective income tax rate (3.3 )% (94.6 )% 42.4 % 19.3 % 41.5 % 38.0 % 34.7 % 37.0 % 25.2 % __________ (a) Includes the charges related to the transmission-related income tax regulatory asset for Exelon, ComEd, BGE, PHI, Pepco, DPL and ACE of $ 35 million , $ 3 million , $ 5 million , $ 27 million , $ 14 million , $ 6 million and $ 7 million , respectively. See Note 3 - Regulatory Matters for additional information. (b) As a result of TCJA, Generation recorded a net decrease to income tax expense, while the Utility Registrants recorded corresponding regulatory liabilities or assets to the extent such amounts are probable of settlement or recovery through customer rates and an adjustment to income tax expense for all other amounts.
Tax Effects of Temporary Differences	The tax effects of temporary differences and carryforwards, which give rise to significant portions of the deferred tax assets (liabilities), as of December 31, 2019 and 2018 are presented below: As of December 31, 2019 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Plant basis differences $ (13,413 ) $ (2,814 ) $ (4,197 ) $ (1,978 ) $ (1,578 ) $ (2,681 ) $ (1,204 ) $ (753 ) $ (687 ) Accrual based contracts 61 (43 ) — — — 104 — — — Derivatives and other financial instruments 165 88 84 — — 2 — — — Deferred pension and postretirement obligation 1,504 (220 ) (270 ) (28 ) (28 ) (89 ) (75 ) (42 ) (10 ) Nuclear decommissioning activities (503 ) (503 ) — — — — — — — Deferred debt refinancing costs 183 20 (7 ) — (3 ) 142 (3 ) (2 ) (1 ) Regulatory assets and liabilities (884 ) — 183 (169 ) 157 (10 ) 55 88 77 Tax loss carryforward 240 55 — 25 49 93 13 44 31 Tax credit carryforward 892 897 — — — — — — — Investment in partnerships (830 ) (808 ) — — — — — — — Other, net 926 236 196 70 10 181 85 12 16 Deferred income tax liabilities (net) $ (11,659 ) $ (3,092 ) $ (4,011 ) $ (2,080 ) $ (1,393 ) $ (2,258 ) $ (1,129 ) $ (653 ) $ (574 ) Unamortized investment tax credits (668 ) (648 ) (10 ) (1 ) (3 ) (7 ) (2 ) (2 ) (3 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (12,327 ) $ (3,740 ) $ (4,021 ) $ (2,081 ) $ (1,396 ) $ (2,265 ) $ (1,131 ) $ (655 ) $ (577 ) As of December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Plant basis differences $ (12,533 ) $ (2,495 ) $ (4,059 ) $ (1,862 ) $ (1,399 ) $ (2,577 ) $ (1,148 ) $ (743 ) $ (645 ) Accrual based contracts 117 (44 ) — — — 161 — — — Derivatives and other financial instruments 89 35 69 — — 3 — — — Deferred pension and postretirement obligation 1,435 (188 ) (255 ) (26 ) (26 ) (102 ) (78 ) (46 ) (14 ) Nuclear decommissioning activities (351 ) (351 ) — — — — — — — Deferred debt refinancing costs 234 23 (7 ) — (3 ) 187 (4 ) (2 ) (1 ) Regulatory assets and liabilities (740 ) — 300 (129 ) 172 (81 ) 67 96 83 Tax loss carryforward 237 78 — 18 25 96 12 52 26 Tax credit carryforward 811 816 — — — — — — — Investment in partnerships (797 ) (775 ) — — — — — — — Other, net 934 239 151 67 12 196 98 17 19 Deferred income tax liabilities (net) $ (10,564 ) $ (2,662 ) $ (3,801 ) $ (1,932 ) $ (1,219 ) $ (2,117 ) $ (1,053 ) $ (626 ) $ (532 ) Unamortized investment tax credits (724 ) (700 ) (12 ) (1 ) (3 ) (8 ) (2 ) (2 ) (3 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (11,288 ) $ (3,362 ) $ (3,813 ) $ (1,933 ) $ (1,222 ) $ (2,125 ) $ (1,055 ) $ (628 ) $ (535 )
Summary of Loss Carryforwards	The following table provides Exelon’s, Generation’s, PECO’s, BGE’s, PHI’s, Pepco’s, DPL’s and ACE’s carryforwards, which are presented on a post-apportioned basis, and any corresponding valuation allowances as of December 31, 2019 . ComEd does not have net operating losses or credit carryforwards for the year ended December 31, 2019 . Exelon Generation PECO BGE PHI Pepco DPL ACE Federal Federal general business credits carryforwards (a) $ 891 $ 897 $ — $ — $ — $ — $ — $ — State State net operating losses 3,986 1,142 312 762 1,360 202 654 438 Deferred taxes on state tax attributes (net) 264 78 25 50 93 13 44 31 Valuation allowance on state tax attributes 26 24 — 1 — — — — Year in which net operating loss or credit carryforwards will begin to expire 2025 2029 2031 2026 2028 2028 2030 2031 __________ (a) Exelon's and Generation's federal general business credit carryforwards will begin expiring in 2034 .
Reconciliation of Unrecognized Tax Benefits Excluding Amounts Pertaining to Examined Tax Returns Roll Forward	Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Balance at January 1, 2017 $ 916 $ 490 $ (12 ) $ — $ 120 $ 172 $ 80 $ 37 $ 22 Increases based on tax positions prior to 2017 28 — 14 — — 14 — — 14 Decreases based on tax positions prior to 2017 (a) (196 ) (17 ) — — — (61 ) (21 ) (16 ) (22 ) Decrease from settlements with taxing authorities (5 ) (5 ) — — — — — — — Balance at December 31, 2017 743 468 2 — 120 125 59 21 14 Change to positions that only affect timing 15 15 — — — — — — — Increases based on tax positions prior to 2018 30 21 — — — 8 7 1 — Decreases based on tax positions prior to 2018 (b) (251 ) (36 ) — — (120 ) (88 ) (66 ) (22 ) — Decrease from settlements with taxing authorities (53 ) (53 ) — — — — — — — Decreases from expiration of statute of limitations (7 ) (7 ) — — — — — — — Balance at December 31, 2018 477 408 2 — — 45 — — 14 Change to positions that only affect timing 26 12 3 1 4 3 2 1 — Increases based on tax positions related to 2019 2 1 — — — — — — — Increases based on tax positions prior to 2019 34 19 3 2 3 — — — — Decreases based on tax positions prior to 2019 (3 ) (3 ) — — — — — — — Decrease from settlements with taxing authorities (29 ) 4 (2 ) — — — — — — Balance at December 31, 2019 $ 507 $ 441 $ 6 $ 3 $ 7 $ 48 $ 2 $ 1 $ 14 __________ (a) Exelon established a liability for an uncertain tax position associated with the tax deductibility of certain merger commitments incurred by Exelon in connection with the acquisitions of Constellation and PHI. In 2017, as a part of its examination of Exelon's return, the IRS National Office issued guidance concurring with Exelon's position that the merger commitments were deductible. As a result, Exelon, Generation, PHI, Pepco, DPL, and ACE decreased their liability for unrecognized tax benefits by $146 million , $19 million , $59 million , $21 million , $16 million and $22 million , respectively, resulting in a benefit to Income taxes on Exelon's, Generation's, PHI's, Pepco's, DPL's, and ACE's Consolidated Statements of Operations and Comprehensive Income and corresponding decreases in their effective tax rates. (b) Exelon, Generation, BGE, PHI, Pepco, and DPL decreased their unrecognized state tax benefits primarily due to the receipt of favorable guidance with respect to the deductibility of certain depreciable fixed assets. The recognition of the tax benefits related to BGE, PHI, Pepco, and DPL was offset by corresponding regulatory liabilities and that portion had no immediate impact to their effective tax rate.
Summary of Positions for which Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Table Text Block]	The following table presents Exelon's, Generation's and PHI's unrecognized tax benefits that, if recognized, would decrease the effective tax rate. ComEd's, PECO's, BGE's, Pepco's, DPL's and ACE's amounts are not material. Exelon Generation PHI (a) December 31, 2019 $ 462 $ 429 $ 32 December 31, 2018 463 408 31 December 31, 2017 523 461 32 __________ (a) PHI has $ 21 million of unrecognized state tax benefits that, if recognized, $ 14 million would be in the form of a net operating loss carryforward, which is expected to require a full valuation allowance based on present circumstances. The following table presents Exelon's, BGE's, PHI's, Pepco's, DPL's and ACE’s unrecognized tax benefits that, if recognized, may be included in future base rates and that portion would have no impact to the effective tax rate. ComEd's and PECO's amounts are not material. Exelon BGE PHI Pepco DPL ACE December 31, 2019 $ 19 $ 1 $ 14 $ — $ — $ 14 December 31, 2018 14 — 14 — — 14 December 31, 2017 214 120 94 59 21 14 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 The following table represents Exelon's, Generation's and ACE's 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, refund claims, and the outcomes of pending court cases as of December 31, 2019 . ComEd's, PECO's, BGE's, PHI's, Pepco's and DPL's amounts are not material. Exelon (a) Generation (a) ACE (b) $ 425 $ 411 $ 14 __________ (a) Exelon and Generation have $ 411 million that, if recognized, would decrease the effective tax rate. (b) The unrecognized tax benefit related to ACE, if recognized, may be included in future base rates and that portion would have no impact to the effective tax rate. Total amounts of interest and penalties recognized The following table represents the net interest and penalties receivable (payable) related to tax positions reflected in Exelon's Consolidated Balance Sheets. Generation's and the Utility Registrants' amounts are not material. Net interest and penalties receivable as of Exelon December 31, 2019 $ 318 December 31, 2018 219
Schedule of Remeasurement Of Deferred Income Taxes Due to Tax Reform [Table Text Block]	The one-time impacts recorded by the Registrants to remeasure their deferred income tax balances at the 21% corporate federal income tax rate as of December 31, 2017 are presented below: Exelon (b) Generation ComEd PECO (c) BGE PHI Pepco DPL ACE Net Decrease to Deferred Income Tax Liability Balances $8,624 $1,895 $2,819 $1,407 $1,120 $1,944 $968 $540 $456 Net Increase to Regulatory Liabilities Recorded (a) 7,315 N/A 2,818 1,394 1,124 1,979 976 545 458 Net Deferred Income Tax Benefit/(Expense) Recorded $1,309 $1,895 $1 $13 $(4) $(35) $(8) $(5) $(2) __________ (a) Reflects the net regulatory liabilities recorded on a pre-tax basis before taking into consideration the income tax benefits associated with the ultimate settlement with customers. (b) Amounts do not sum across due to deferred tax adjustments recorded at the Exelon Corporation parent company, primarily related to certain employee compensation plans. (c) Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remained in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA.
State Income Tax Law Changes [Table Text Block]	The following table provides the one-time impact of the rate changes in 2017 for Exelon, Generation and ComEd: Exelon Generation ComEd Increase to Deferred Income Taxes $ 250 $ 20 $ 270 Increase in Regulatory Assets 270 — 270 (Decrease)/Increase to Income Tax Expense (20 ) 20 —
Long-Term Marginal State Income Tax Rate [Table Text Block]	Quarterly, Exelon reviews and updates its marginal state income tax rates for changes in state apportionment. The Registrants remeasure their existing deferred income tax balances to reflect the changes in marginal rates, which results in either an increase or decrease to their net deferred income tax liability balances. Utility Registrants record corresponding regulatory liabilities or assets to the extent such amounts are probable of settlement or recovery through customer rates and an adjustment to income tax expense for all other amounts. December 31, 2019 Exelon Generation PHI DPL Increase to Deferred Income Tax Liability $ 23 $ 9 $ — $ — Increase to Income Tax Expense, Net of Federal Taxes 23 9 — — December 31, 2018 Decrease to Deferred Income Tax Liability $ 50 $ 53 $ 4 $ 2 Decrease to Income Tax Expense, Net of Federal Taxes 50 53 3 —
Allocation of Federal Tax Benefit Under Tax Sharing Agreement [Table Text Block] [Table Text Block]	The following table presents the allocation of federal tax benefits from Exelon under the Tax Sharing Agreement. Generation ComEd PECO BGE PHI Pepco DPL December 31, 2019 (a) $ 41 $ — $ 14 $ 3 $ 7 $ 6 $ 1 December 31, 2018 (b) 155 1 48 26 2 — — December 31, 2017 (c) 102 — 16 10 7 — — __________ (a) ACE did not record an allocation of federal tax benefits from Exelon under the Tax Sharing Agreement as a result of a tax net operating loss. (b) Pepco, DPL and ACE did not record an allocation of federal tax benefits from Exelon under the Tax Sharing Agreement as a result of a tax net operating loss. (c) ComEd, Pepco, DPL and ACE did not record an allocation of federal tax benefits from Exelon under the Tax Sharing Agreement as a result of a tax net operating loss.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Defined Benefit Plan Change In Benefit Obligation RollForward	The following tables provide a rollforward of the changes in the benefit obligations and plan assets of Exelon for the most recent two years for all plans combined: Pension Benefits OPEB 2019 2018 2019 2018 Change in benefit obligation: Net benefit obligation at beginning of year $ 20,692 $ 22,337 $ 4,369 $ 4,856 Service cost 357 405 93 112 Interest cost 883 802 188 175 Plan participants’ contributions — — 44 45 Actuarial (gain) loss (a) 2,322 (1,561 ) 250 (540 ) Plan amendments 68 (4 ) — — Curtailments (3 ) — — — Settlements (35 ) (48 ) (4 ) (4 ) Contractual termination benefits 1 — — — Gross benefits paid (1,417 ) (1,239 ) (282 ) (275 ) Net benefit obligation at end of year $ 22,868 $ 20,692 $ 4,658 $ 4,369 Pension Benefits OPEB 2019 2018 2019 2018 Change in plan assets: Fair value of net plan assets at beginning of year $ 16,678 $ 18,573 $ 2,408 $ 2,732 Actual return on plan assets 3,008 (945 ) 324 (136 ) Employer contributions 356 337 51 46 Plan participants’ contributions — — 44 45 Gross benefits paid (1,417 ) (1,239 ) (282 ) (275 ) Settlements (35 ) (48 ) (4 ) (4 ) Fair value of net plan assets at end of year $ 18,590 $ 16,678 $ 2,541 $ 2,408 __________ (a) The pension actuarial loss in 2019 primarily reflects a decrease in the discount rate. The OPEB actuarial loss in 2019 primarily reflects a decrease in the discount rate. The pension actuarial gain in 2018 primarily reflects an increase in the discount rate. The OPEB actuarial gain in 2018 primarily reflects an increase in the discount rate and favorable health care claims experience.
Schedule of Amounts Recognized in Balance Sheet	Exelon presents its benefit obligations and plan assets net on its balance sheet within the following line items: Pension Benefits OPEB 2019 2018 2019 2018 Other current liabilities $ 31 $ 26 $ 41 $ 33 Pension obligations 4,247 3,988 — — Non-pension postretirement benefit obligations — — 2,076 1,928 Unfunded status (net benefit obligation less plan assets) $ 4,278 $ 4,014 $ 2,117 $ 1,961
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Table Text Block]	The following table provides the accumulated benefit obligation (ABO) and fair value of plan assets for all pension plans with an ABO in excess of plan assets. Information for pension and OPEB plans with projected benefit obligations (PBO) and accumulated postretirement benefit obligation (APBO), respectively, in excess of plan assets has been disclosed in the Obligations and Plan Assets table above as all pension and OPEB plans are underfunded. ABO in excess of plan assets Exelon 2019 2018 Accumulated benefit obligation 21,727 19,656 Fair value of net plan assets 18,590 16,678
Schedule of Defined Benefit Plans Disclosures	The following tables present the components of Exelon’s net periodic benefit costs, prior to capitalization, for the years ended December 31, 2019 , 2018 and 2017 . Pension Benefits OPEB 2019 2018 2017 (a) 2019 2018 2017 (a) Components of net periodic benefit cost: Service cost $ 357 $ 405 $ 387 $ 93 $ 112 $ 106 Interest cost 883 802 842 188 175 182 Expected return on assets (1,225 ) (1,252 ) (1,196 ) (153 ) (173 ) (162 ) Amortization of: Prior service cost (credit) — 2 1 (179 ) (186 ) (188 ) Actuarial loss 414 629 607 45 66 61 Settlement and other charges 17 3 3 1 1 — Contractual termination benefits 1 — — — — — Net periodic benefit cost $ 447 $ 589 $ 644 $ (5 ) $ (5 ) $ (1 ) __________ (a) FitzPatrick net benefit costs are included for the period after acquisition.
Schedule Of Pension And Other Postretirement Benefit Costs [Table Text Block]	The amounts below represent the Registrants’ allocated pension and OPEB costs. As a result of new pension guidance effective on January 1, 2018, certain balances have been reclassified on Exelon’s Consolidated Statements of Operations and Comprehensive Income for the year ended December 31, 2017. For Exelon, the service cost component is included in Operating and maintenance expense and Property, plant and equipment, net, while the non–service cost components are included in Other, net and Regulatory assets for the years ended December 31, 2019 and December 31, 2018 and in Other, net and Property, plant and equipment, net, for the year ended December 31, 2017. For Generation and the Utility Registrants, the service cost and non–service cost components are included in Operating and maintenance expense and Property, plant and equipment, net on their consolidated financial statements. For the Years Ended December 31, Exelon Generation (a) ComEd PECO BGE PHI Pepco DPL ACE 2019 $ 442 $ 135 $ 96 $ 12 $ 61 $ 95 $ 25 $ 15 $ 16 2018 583 204 177 18 60 67 15 6 12 2017 643 227 176 29 64 94 25 13 13 __________ (a) FitzPatrick net benefit costs are included for the period after acquisition.
Changes In Plan Assets And Benefit Obligations Recognized In OCI And Regulatory Assets	The following tables provide the components of AOCI and regulatory assets (liabilities) for Exelon for the years ended December 31, 2019 , 2018 and 2017 for all plans combined. Pension Benefits OPEB 2019 2018 2017 2019 2018 2017 Changes in plan assets and benefit obligations recognized in AOCI and regulatory assets (liabilities): Current year actuarial (gain) loss $ 538 $ 635 $ (222 ) $ 80 $ (232 ) $ 166 Amortization of actuarial loss (414 ) (629 ) (607 ) (45 ) (66 ) (61 ) Current year prior service cost (credit) 68 (4 ) 9 — — — Amortization of prior service (cost) credit — (2 ) (1 ) 179 186 188 Curtailments (3 ) — — — — — Settlements (17 ) (3 ) (3 ) (1 ) — — Total recognized in AOCI and regulatory assets (liabilities) $ 172 $ (3 ) $ (824 ) $ 213 $ (112 ) $ 293 Total recognized in AOCI $ 169 $ 3 $ (401 ) $ 107 $ (55 ) $ 168 Total recognized in regulatory assets (liabilities) $ 3 $ (6 ) $ (423 ) $ 106 $ (57 ) $ 125 The following table provides the components of gross accumulated other comprehensive loss and regulatory assets (liabilities) for Exelon that have not been recognized as components of periodic benefit cost at December 31, 2019 and 2018 , respectively, for all plans combined: Pension Benefits OPEB 2019 2018 2019 2018 Prior service (credit) cost $ 39 $ (29 ) $ (158 ) $ (337 ) Actuarial loss 7,662 7,558 565 531 Total $ 7,701 $ 7,529 $ 407 $ 194 Total included in AOCI $ 4,068 $ 3,899 $ 177 $ 70 Total included in regulatory assets (liabilities) $ 3,633 $ 3,630 $ 230 $ 124
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Benefit Obligation [Table Text Block]	For Exelon, the following assumptions were used to determine the benefit obligations for the plans at December 31, 2019 and 2018 . Assumptions used to determine year-end benefit obligations are the assumptions used to estimate the subsequent year’s net periodic benefit costs. Pension Benefits OPEB 2019 2018 2019 2018 Discount rate 3.34 % (a) 4.31 % (a) 3.31 % (a) 4.30 % (a) Investment Crediting Rate 3.82 % (b) 4.46 % (b) N/A N/A Rate of compensation increase (c) (c) (c) (c) Mortality table Pri-2012 table with MP- 2019 improvement scale (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) Pri-2012 table with MP- 2019 improvement scale (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) Health care cost trend on covered charges N/A N/A 5.00% with 5.00% with __________ (a) The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and OPEB obligations. Certain benefit plans used individual rates, which range from 3.02% - 3.44% and 3.27% - 3.4% for pension and OPEB plans, respectively, as of December 31, 2019 and 4.13% - 4.36% and 4.27% - 4.38% for pension and OPEB plans, respectively, as of December 31, 2018 . (b) The investment crediting rate above represents a weighted average rate. (c) 3.25% through 2019 and 3.75% thereafter.
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Net Periodic Benefit Cost [Table Text Block]	The following assumptions were used to determine the net periodic benefit cost for Exelon for the years ended December 31, 2019 , 2018 and 2017 : Pension Benefits Other Postretirement Benefits Exelon 2019 2018 2017 2019 2018 2017 Discount rate 4.31 % (a) 3.62 % (a) 4.04 % (a) 4.30 % (a) 3.61 % (a) 4.04 % (a) Investment Crediting Rate 4.46 % (b) 4.00 % (b) 4.46 % (b) N/A N/A N/A Expected return on plan assets 7.00 % (c) 7.00 % (c) 7.00 % (c) 6.67 % (c) 6.60 % (c) 6.58 % (c) Rate of compensation increase (d) (d) (e) (d) (d) (e) Mortality table RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) Health care cost trend on covered charges N/A N/A N/A 5.00% 5.00% 5.50% __________ (a) The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and OPEB costs. Certain benefit plans used individual rates, which range from 4.13% - 4.36% and 4.27% - 4.38% for pension and OPEB plans, respectively, for the year ended December 31, 2019 ; 3.49% - 3.65% and 3.57% - 3.68% for pension and OPEB plans; respectively, for the year ended December 31, 2018 ; and 3.66% - 4.11% and 4.00% - 4.17% for pension and OPEB plans, respectively, for the year ended December 31, 2017 . (b) The investment crediting rate above represents a weighted average rate. (c) Not applicable to pension and other postretirement benefit plans that do not have plan assets. (d) 3.25% through 2019 and 3.75% thereafter. (e) The legacy Exelon, CEG and CENG pension and other postretirement plans used a rate of compensation increase of 3.25% through 2019 and 3.75% thereafter, while the legacy PHI pension and OPEB plans used a weighted-average rate of compensation increase of 5% for all periods.
Pension And Other Postretirement Benefit Contributions [Table Text Block]	The following table provides all registrants' planned contributions to the qualified pension plans, planned benefit payments to non-qualified pension plans, and planned contributions to other postretirement plans in 2020 : Qualified Pension Plans Non-Qualified Pension Plans OPEB Exelon $ 505 $ 36 $ 42 Generation 227 14 16 ComEd 141 2 3 PECO 17 1 — BGE 56 2 16 PHI 22 9 7 Pepco — 2 7 DPL — 1 — ACE 2 — — Exelon allocates contributions related to its legacy Exelon pension and OPEB plans to its subsidiaries based on accounting cost. For legacy CEG, CENG, FitzPatrick, and PHI plans, pension and OPEB contributions are allocated to the subsidiaries based on employee participation (both active and retired). The following tables provide contributions to the pension and OPEB plans: Pension Benefits OPEB 2019 (a) 2018 (a) 2017 (a) 2019 2018 2017 Exelon $ 356 $ 337 $ 341 $ 51 $ 46 $ 64 Generation 160 128 137 15 11 11 ComEd 72 38 36 5 4 5 PECO 27 28 24 1 — — BGE 34 40 39 14 14 14 PHI 10 62 67 15 12 32 Pepco 2 6 62 12 11 10 DPL 1 — — — — 2 ACE — 6 — 1 — 20 __________ (a) Exelon's and Generation's pension contributions include $21 million related to the legacy CENG plans that was funded by CENG as provided in an Employee Matters Agreement (EMA) between Exelon and CENG for the year ended December 31, 2017 . There were no pension contributions for the years ended December 31, 2019 and 2018 .
Schedule of Expected Benefit Payments [Table Text Block]	Estimated future benefit payments to participants in all of the pension plans and postretirement benefit plans at December 31, 2019 were: Pension Benefits OPEB 2020 $ 1,227 $ 258 2021 1,252 263 2022 1,295 267 2023 1,310 270 2024 1,324 275 2025 through 2029 6,770 1,402 Total estimated future benefit payments through 2029 $ 13,178 $ 2,735
Defined Benefit Plan Weighted Average Asset Allocations And Target Allocations [Table Text Block]	Exelon’s pension and OPEB plan target asset allocations at December 31, 2019 and 2018 were as follows: December 31, 2019 December 31, 2018 Asset Category Pension Benefits OPEB Pension Benefits OPEB Equity securities 33 % 46 % 35 % 47 % Fixed income securities 44 % 32 % 37 % 28 % Alternative investments (a) 23 % 22 % 28 % 25 % Total 100 % 100 % 100 % 100 % __________ (a) Alternative investments include private equity, hedge funds, real estate, and private credit.
Defined Benefit Plan Fair Value Of Plan Assets [Text Block]	The following tables present pension and OPEB plan assets measured and recorded at fair value in Exelon's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy at December 31, 2019 and 2018 : December 31, 2019 (a) Level 1 Level 2 Level 3 Not subject to leveling Total Pension plan assets Cash equivalents $ 258 $ — $ — $ — $ 258 Equities (b) 3,616 — 5 2,589 6,210 Fixed income: U.S. Treasury and agencies 1,294 280 — — 1,574 State and municipal debt — 56 — — 56 Corporate debt — 4,342 245 — 4,587 Other (b) — 461 — 851 1,312 Fixed income subtotal 1,294 5,139 245 851 7,529 Private equity — — — 1,391 1,391 Hedge funds — — — 1,126 1,126 Real estate — — — 1,030 1,030 Private credit — — 237 929 1,166 Pension plan assets subtotal $ 5,168 $ 5,139 $ 487 $ 7,916 $ 18,710 December 31, 2019 (a) Level 1 Level 2 Level 3 Not subject to leveling Total OPEB plan assets Cash equivalents $ 39 $ — $ — $ — $ 39 Equities 473 3 — 719 1,195 Fixed income: U.S. Treasury and agencies 17 64 — — 81 State and municipal debt — 107 — — 107 Corporate debt — 49 — — 49 Other 258 78 — 201 537 Fixed income subtotal 275 298 — 201 774 Hedge funds — — — 293 293 Real estate — — — 109 109 Private credit — — — 131 131 OPEB plan assets subtotal $ 787 $ 301 $ — $ 1,453 $ 2,541 Total pension and OPEB plan assets (c) $ 5,955 $ 5,440 $ 487 $ 9,369 $ 21,251 December 31, 2018 (a) Level 1 Level 2 Level 3 Not subject to leveling Total Pension plan assets Cash equivalents $ 350 $ — $ — $ — $ 350 Equities (b) 3,364 — 2 1,980 5,346 Fixed income: U.S. Treasury and agencies 996 173 — — 1,169 State and municipal debt — 59 — — 59 Corporate debt — 3,716 216 — 3,932 Other (b) — 329 — 613 942 Fixed income subtotal 996 4,277 216 613 6,102 Private equity — — — 1,219 1,219 Hedge funds — — — 1,608 1,608 Real estate — — — 1,029 1,029 Private credit — — 268 798 1,066 Pension plan assets subtotal $ 4,710 $ 4,277 $ 486 $ 7,247 $ 16,720 December 31, 2018 (a) Level 1 Level 2 Level 3 Not subject to leveling Total OPEB plan assets Cash equivalents $ 22 $ — $ — $ — $ 22 Equities 537 2 — 508 1,047 Fixed income: U.S. Treasury and agencies 11 56 — — 67 State and municipal debt — 126 — — 126 Corporate debt — 48 — — 48 Other 183 72 — 170 425 Fixed income subtotal 194 302 — 170 666 Hedge funds — — — 411 411 Real estate — — — 132 132 Private credit — — — 132 132 OPEB plan assets subtotal $ 753 $ 304 $ — $ 1,353 $ 2,410 Total pension and OPEB plan assets (c) $ 5,463 $ 4,581 $ 486 $ 8,600 $ 19,130 __________ (a) See Note 17 — Fair Value of Financial Assets and Liabilities for a description of levels within the fair value hierarchy. (b) Includes derivative instruments of $2 million and less than $1 million , which have a total notional amount of $6,668 million and $5,991 million at December 31, 2019 and 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 the company’s exposure to credit or market loss. (c) Excludes net liabilities of $120 million and $44 million at December 31, 2019 and 2018
Schedule of Changes in Fair Value of Plan Assets [Table Text Block]	The following table presents the reconciliation of Level 3 assets and liabilities for Exelon measured at fair value for pension and OPEB plans for the years ended December 31, 2019 and 2018 : Fixed Income Equities Private Credit Total Pension Assets Balance as of January 1, 2019 $ 216 $ 2 $ 268 $ 486 Actual return on plan assets: Relating to assets still held at the 28 3 28 59 Relating to assets sold during the period (7 ) — — (7 ) Purchases, sales and settlements: Purchases 26 — 41 67 Sales (4 ) — — (4 ) Settlements (a) (2 ) — (100 ) (102 ) Transfers out of Level 3 (12 ) — — (12 ) Balance as of December 31, 2019 $ 245 $ 5 $ 237 $ 487 Fixed income Equities Private Credit Total Pension Assets Balance as of January 1, 2018 $ 232 $ 2 $ 224 $ 458 Actual return on plan assets: Relating to assets still held at the reporting date (14 ) — 9 (5 ) Relating to assets sold during the period (1 ) — — (1 ) Purchases, sales and settlements: Purchases 19 — 35 54 Sales (8 ) — — (8 ) Settlements (a) (12 ) — — (12 ) Balance as of December 31, 2018 $ 216 $ 2 $ 268 $ 486 __________ (a) Represents cash settlements only.
Schedule Of Defined Contributions [Table Text Block]	The following table presents matching contributions to the savings plan for the years ended December 31, 2019 , 2018 and 2017 : For the Year Ended December 31, Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2019 $ 161 $ 73 $ 35 $ 11 $ 12 13 $ 3 $ 3 $ 2 2018 179 86 37 9 12 13 3 2 2 2017 128 55 31 10 10 13 3 2 2

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of the derivative fair value	The following table provides a summary of the derivative fair value balances recorded by Exelon, Generation and ComEd as of December 31, 2019 and 2018 : Exelon Generation ComEd December 31, 2019 Total Derivatives Economic Hedges Proprietary Trading Collateral (a)(b) Netting (a) Subtotal Economic Hedges Mark-to-market derivative assets (current assets) $ 675 $ 3,506 $ 72 $ 287 $ (3,190 ) $ 675 $ — Mark-to-market derivative assets (noncurrent assets) 508 1,238 25 122 (877 ) 508 — Total mark-to-market derivative assets 1,183 4,744 97 409 (4,067 ) 1,183 — Mark-to-market derivative liabilities (current liabilities) (236 ) (3,713 ) (38 ) 357 3,190 (204 ) (32 ) Mark-to-market derivative liabilities (noncurrent liabilities) (380 ) (1,140 ) (11 ) 163 877 (111 ) (269 ) Total mark-to-market derivative liabilities (616 ) (4,853 ) (49 ) 520 4,067 (315 ) (301 ) Total mark-to-market derivative net assets (liabilities) $ 567 $ (109 ) $ 48 $ 929 $ — $ 868 $ (301 ) December 31, 2018 Mark-to-market derivative assets (current assets) $ 801 $ 3,505 $ 105 $ 121 $ (2,930 ) $ 801 $ — Mark-to-market derivative assets (noncurrent assets) 445 1,266 41 51 (913 ) 445 — Total mark-to-market derivative assets 1,246 4,771 146 172 (3,843 ) 1,246 — Mark-to-market derivative liabilities (current liabilities) (473 ) (3,429 ) (74 ) 125 2,931 (447 ) (26 ) Mark-to-market derivative liabilities (noncurrent liabilities) (474 ) (1,203 ) (20 ) 60 912 (251 ) (223 ) Total mark-to-market derivative liabilities (947 ) (4,632 ) (94 ) 185 3,843 (698 ) (249 ) Total mark-to-market derivative net assets (liabilities) $ 299 $ 139 $ 52 $ 357 $ — $ 548 $ (249 ) _________ (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 amounts are immaterial and not reflected in the table above. (b) Of the collateral posted/(received), $511 million and $(94) million represents variation margin on the exchanges at December 31, 2019 and 2018 , respectively.
Economic Hedges (Commodity Price Risk)	For the years ended December 31, 2019 , 2018 and 2017 , 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 line in the Consolidated Statements of Cash Flows. 2019 2018 2017 Income Statement Location Gain (Loss) Operating revenues $ — $ (270 ) $ (126 ) Purchased power and fuel (204 ) (47 ) (43 ) Total Exelon and Generation $ (204 ) $ (317 ) $ (169 )
Disclosure of Credit Derivatives [Table Text Block]	The following tables provide information on Generation’s credit exposure for all derivative instruments, NPNS and payables and receivables, net of collateral and instruments that are subject to master netting agreements, as of December 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. Rating as of December 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 $ 877 $ 20 $ 857 — $ — Non-investment grade 79 63 16 No external ratings Internally rated — investment grade 218 — 218 Internally rated — non-investment grade 139 23 116 Total $ 1,313 $ 106 $ 1,207 — $ — Net Credit Exposure by Type of Counterparty As of Financial institutions $ 9 Investor-owned utilities, marketers, power producers 930 Energy cooperatives and municipalities 235 Other 33 Total $ 1,207 __________ (a) As of December 31, 2019 , credit collateral held from counterparties where Generation had credit exposure included $25 million of cash and $81 million of letters of credit. The credit collateral does not include non-liquid collateral.
Fair Value of Derivatives with Credit- Risk Related Contingent Features [Table Text Block] [Table Text Block]	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: As of December 31, Credit-Risk Related Contingent Features 2019 2018 Gross fair value of derivative contracts containing this feature (a) $ (956 ) $ (1,723 ) Offsetting fair value of in-the-money contracts under master netting arrangements (b) 649 1,105 Net fair value of derivative contracts containing this feature (c) $ (307 ) $ (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.
Cash Collateral and Letters of Credit on Derivative Contracts [Table Text Block]	As of December 31, 2019 and 2018 , Exelon and Generation posted or held the following amounts of cash collateral and letters of credit on derivative contracts with external counterparties, after giving consideration to offsetting derivative and non-derivative positions under master netting agreements. As of December 31, 2019 2018 Cash collateral posted $ 982 $ 418 Letters of credit posted 264 367 Cash collateral held 103 47 Letters of credit held 112 44 Additional collateral required in the event of a credit downgrade below investment grade 1,509 2,104

Debt and Credit Agreements (Tab

Debt and Credit Agreements (Tables)	12 Months Ended
	Dec. 31, 2019
Short-term Debt [Line Items]
Schedule of Line of Credit Facilities [Table Text Block]	Borrowings under Exelon Corporate’s, Generation’s, ComEd’s, PECO’s, BGE's, Pepco's, DPL's and ACE's revolving credit agreements bear interest at a rate based upon either the prime rate or a LIBOR-based rate, plus an adder based upon the particular Registrant’s credit rating. The adders for the prime based borrowings and LIBOR-based borrowings are presented in the following table: Exelon Generation ComEd PECO BGE Pepco DPL ACE Prime based borrowings 27.5 27.5 7.5 — — 7.5 7.5 7.5 LIBOR-based borrowings 127.5 127.5 107.5 90.0 100.0 107.5 107.5 107.5
Schedule of Maturities of Long-term Debt	Long-term debt maturities at Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE in the periods 2020 through 2024 and thereafter are as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2020 $ 4,710 $ 3,182 $ 500 $ — $ — $ 103 $ 2 $ 80 $ 20 2021 1,517 2 350 300 300 265 2 2 261 2022 3,088 1,024 — 350 250 314 311 2 1 2023 855 1 — 50 300 504 1 502 1 2024 1,596 792 250 — — 553 401 1 151 Thereafter 24,184 (a) 2,942 7,691 (b) 2,934 (c) 2,450 4,256 2,180 991 901 Total $ 35,950 $ 7,943 $ 8,791 $ 3,634 $ 3,300 $ 5,995 $ 2,897 $ 1,578 $ 1,335 __________ (a) Includes $390 million due to ComEd and PECO financing trusts. (b) Includes $206 million due to ComEd financing trust. (c) Includes $184 million due to PECO financing trusts. Debt Covenants
Schedule of Long-term Debt Instruments	Long-Term Debt The following tables present the outstanding long-term debt at the Registrants as of December 31, 2019 and 2018 : Exelon Maturity Date December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 1.70 % - 7.90 % 2020 - 2049 $ 17,486 $ 16,496 Senior unsecured notes 2.45 % - 7.60 % 2020 - 2046 10,685 11,285 Unsecured notes 2.40 % - 6.35 % 2021 - 2049 3,300 2,900 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 412 435 Nuclear fuel procurement contracts 3.15 % 2020 3 39 Notes payable and other 2.53 % - 7.99 % 2020 - 2053 154 188 Junior subordinated notes 3.50 % 2022 1,150 1,150 Long-term software licensing agreement 3.95 % 2024 55 73 Unsecured Tax-Exempt Bonds (b) 1.63 % - 5.40 % 2022 - 2031 222 112 Medium-Terms Notes (unsecured) 7.61 % - 7.72 % 2027 10 22 Transition bonds 5.55 % 2023 40 59 Loan Agreement 2.00 % 2023 50 50 Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,182 1,253 Variable rates 3.18 % - 4.91 % 2020 - 2024 811 849 Total long-term debt 35,560 34,911 Unamortized debt discount and premium, net (72 ) (66 ) Unamortized debt issuance costs (214 ) (216 ) Fair value adjustment 765 795 Long-term debt due within one year (4,710 ) (1,349 ) Long-term debt $ 31,329 $ 34,075 Long-term debt to financing trusts (c) Subordinated debentures to ComEd Financing III 6.35 % 2033 $ 206 $ 206 Subordinated debentures to PECO Trust III 6.75 % - 7.38 % 2028 81 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Total long-term debt to financing trusts 390 390 Unamortized debt issuance costs — — Long-term debt to financing trusts $ 390 $ 390 __________ (a) Substantially all of ComEd’s assets other than expressly excepted property and substantially all of PECO’s, Pepco's, DPL's and ACE's assets are subject to the liens of their respective mortgage indentures. (b) Bond amount totaling $110 million was previously disclosed within the first mortgage bonds line item, as it was classified as a secured tax-exempt bond. In 2019, the callable bond was reissued as an unsecured tax-exempt bond, and is presented as such within this section. (c) Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets. Generation Maturity Date December 31, Rates 2019 2018 Long-term debt Senior unsecured notes 2.95 % - 7.60 % 2020 - 2042 $ 5,420 $ 6,019 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 412 435 Nuclear fuel procurement contracts 3.15 % 2020 3 39 Notes payable and other 2.53 % - 4.26 % 2020 - 2028 115 164 Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,182 1,253 Variable rates 3.18 % - 4.91 % 2020 - 2024 811 849 Total long-term debt 7,943 8,759 Unamortized debt discount and premium, net (5 ) (6 ) Unamortized debt issuance costs (42 ) (51 ) Fair value adjustment 78 91 Long-term debt due within one year (3,182 ) (906 ) Long-term debt $ 4,792 $ 7,887 ComEd Maturity Date December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 2.55 % - 6.45 % 2020 - 2049 $ 8,578 $ 8,179 Notes payable and other 7.49 % 2053 8 8 Total long-term debt 8,586 8,187 Unamortized debt discount and premium, net (27 ) (23 ) Unamortized debt issuance costs (68 ) (63 ) Long-term debt due within one year (500 ) (300 ) Long-term debt $ 7,991 $ 7,801 Long-term debt to financing trust (b) Subordinated debentures to ComEd Financing III 6.35 % 2033 $ 206 $ 206 Total long-term debt to financing trusts 206 206 Unamortized debt issuance costs (1 ) (1 ) Long-term debt to financing trusts $ 205 $ 205 __________ (a) Substantially all of ComEd’s assets, other than expressly excepted property, are subject to the lien of its mortgage indenture. (b) Amount owed to this financing trust is recorded as Long-term debt to financing trust within ComEd’s Consolidated Balance Sheets. PECO Maturity Date December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 1.70 % - 5.95 % 2021 - 2049 $ 3,400 $ 3,075 Loan Agreement 2.00 % 2023 50 50 Total long-term debt 3,450 3,125 Unamortized debt discount and premium, net (21 ) (18 ) Unamortized debt issuance costs (24 ) (23 ) Long-term debt $ 3,405 $ 3,084 Long-term debt to financing trusts (b) Subordinated debentures to PECO Trust III 6.75 % - 7.38 % 2028 $ 81 $ 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Long-term debt to financing trusts $ 184 $ 184 __________ (a) Substantially all of PECO’s assets are subject to the lien of its mortgage indenture. (b) Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets. BGE Maturity Date December 31, Rates 2019 2018 Long-term debt Unsecured notes 2.40 % - 6.35 % 2021 - 2049 $ 3,300 $ 2,900 Total long-term debt 3,300 2,900 Unamortized debt discount and premium, net (9 ) (6 ) Unamortized debt issuance costs (21 ) (18 ) Long-term debt $ 3,270 $ 2,876 PHI Maturity December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 1.76 % - 7.90 % 2021 - 2049 $ 5,508 $ 5,242 Senior unsecured notes 7.45 % 2032 185 185 Unsecured Tax-Exempt Bonds (b) 1.63 % - 5.40 % 2022 - 2031 222 112 Medium-terms notes (unsecured) 7.61 % - 7.72 % 2027 10 22 Transition bonds (c) 5.55 % 2023 40 59 Notes payable and other 3.54 % - 7.99 % 2021 - 2027 30 16 Total long-term debt 5,995 5,636 Unamortized debt discount and premium, net 4 4 Unamortized debt issuance costs (19 ) (14 ) Fair value adjustment 583 633 Long-term debt due within one year (103 ) (125 ) Long-term debt $ 6,460 $ 6,134 _________ (a) Substantially all of Pepco's, DPL's, and ACE's assets are subject to the lien of its respective mortgage indenture. (b) Bond amount totaling $110 million was previously disclosed within the first mortgage bonds line item, as it was classified as a secured tax-exempt bond. In 2019, the callable bond was reissued as an unsecured tax-exempt bond, and is presented as such within this section. (c) Transition bonds are recorded as part of Long-term debt within ACE's Consolidated Balance Sheets. Pepco Maturity December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 3.05 % - 7.90 % 2022 - 2048 $ 2,775 $ 2,735 Unsecured Tax-Exempt Bonds (b) 1.70 % 2022 110 — Notes payable and other 3.54 % - 7.99 % 2021 - 2027 12 16 Total long-term debt 2,897 2,751 Unamortized debt discount and premium, net 2 2 Unamortized debt issuance costs (35 ) (34 ) Long-term debt due within one year (2 ) (15 ) Long-term debt $ 2,862 $ 2,704 __________ (a) Substantially all of Pepco's assets are subject to the lien of its respective mortgage indenture. (b) Bond amount totaling $110 million was previously disclosed within the first mortgage bonds line item, as it was classified as a secured tax-exempt bond. In 2019, the callable bond was reissued as an unsecured tax-exempt bond, and is presented as such within this section. DPL Maturity December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 1.76 % - 4.27 % 2023 - 2049 $ 1,446 $ 1,370 Unsecured Tax-Exempt Bonds 1.63 % - 5.40 % 2024 - 2031 112 112 Medium-terms notes (unsecured) 7.61 % - 7.72 % 2027 10 22 Other 3.54 % 2027 10 — Total long-term debt 1,578 1,504 Unamortized debt discount and premium, net 1 2 Unamortized debt issuance costs (12 ) (12 ) Long-term debt due within one year (80 ) (91 ) Long-term debt $ 1,487 $ 1,403 __________ (a) Substantially all of DPL's assets are subject to the lien of its respective mortgage indenture. ACE Maturity December 31, Rates 2019 2018 Long-term debt First mortgage bonds (a) 3.38 % - 6.80 % 2021 - 2049 $ 1,287 $ 1,137 Transition bonds (b) 5.55 % 2023 40 59 Other 3.54 % 2027 8 — Total long-term debt $ 1,335 $ 1,196 Unamortized debt discount and premium, net (1 ) (1 ) Unamortized debt issuance costs (7 ) (7 ) Long-term debt due within one year (20 ) (18 ) Long-term debt $ 1,307 $ 1,170 __________ (a) Substantially all of ACE's assets are subject to the lien of its respective mortgage indenture. (b) Maturities of ACE's Transition Bonds outstanding at December 31, 2019 are $19 million in 2020 and $21 million in 2021.
Schedule of Short-term Debt	The following tables present the short-term borrowings activity for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE during 2019 and 2018 . December 31, 2019 Exelon (a) Generation ComEd PECO BGE PHI Pepco DPL ACE Average borrowings $ 472 $ 13 $ 236 $ — $ 103 N/A $ 45 $ 21 $ 51 Maximum borrowings outstanding 890 357 465 21 298 N/A 144 125 180 Average interest rates, computed on a daily basis 2.25 % 1.84 % 2.38 % 2.39 % 2.46 % N/A 2.56 % 2.02 % 2.43 % Average interest rates, at December 31 2.25 % 1.84 % 2.38 % 2.39 % 2.46 % N/A 2.56 % 2.02 % 2.43 % December 31, 2018 Exelon (a) Generation ComEd PECO BGE PHI Pepco DPL ACE Average borrowings $ 531 $ 37 $ 154 $ 68 $ 65 N/A $ 22 $ 87 $ 95 Maximum borrowings outstanding 1,237 583 520 350 239 N/A 90 245 210 Average interest rates, computed on a daily basis 2.21 % 1.96 % 2.14 % 2.24 % 2.18 % N/A 2.24 % 2.07 % 2.21 % Average interest rates, at December 31 2.15 % 1.96 % 2.14 % 2.24 % 2.18 % N/A 2.24 % 2.07 % 2.21 % __________ (a) Includes $3 million and $4 million average borrowings related to Exelon Corporate at December 31, 2019 and 2018 , respectively. Exelon Corporate had $144 million and $95 million maximum borrowings outstanding at December 31, 2019 and 2018 , with 1.92% and 1.93% average interest rates computed on a daily basis for 2019 and 2018, and 1.92% and 1.93% average interest rates at December 31, 2019 and 2018 , respectively.
Commercial Paper [Member]
Short-term Debt [Line Items]
Schedule of Line of Credit Facilities [Table Text Block]	The following table reflects the Registrants' commercial paper programs supported by the revolving credit agreements and bilateral credit agreements at December 31, 2019 and 2018 : Maximum Program Size at December 31, Outstanding Commercial Paper at December 31, Average Interest Rate on Commercial Paper Borrowings for the Year Ended December 31, Commercial Paper Issuer 2019 (a)(b)(c) 2018 (a)(b)(c) 2019 2018 2019 2018 Exelon (d) $ 9,000 $ 9,000 $ 870 $ 89 2.25 % 2.15 % Generation 5,300 5,300 320 — 1.84 % 1.96 % ComEd 1,000 1,000 130 — 2.38 % 2.14 % PECO 600 600 — — 2.39 % 2.24 % BGE 600 600 76 35 2.46 % 2.18 % PHI 900 900 208 54 N/A N/A Pepco 300 300 82 40 2.56 % 2.24 % DPL 300 300 56 — 2.02 % 2.07 % ACE 300 300 70 14 2.43 % 2.21 % __________ (a) Excludes $1,400 million and $545 million in bilateral credit facilities at December 31, 2019 and 2018 , respectively, and $159 million in credit facilities for project finance at December 31, 2019 and 2018 , respectively. These credit facilities do not back Generation's commercial paper program. (b) At December 31, 2019 , excludes $142 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $44 million , $33 million , $33 million , $8 million , $8 million , $8 million and $8 million , respectively. These facilities expire on October 9, 2020. These facilities are solely utilized to issue letters of credit. At December 31, 2018 , excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million , $33 million , $34 million , $5 million , $5 million , $5 million , and $5 million , respectively. (c) Pepco, DPL and ACE's revolving credit facility has the ability to flex to $500 million , $500 million , and $350 million , respectively. The borrowing capacity may be increased or decreased during the term of the facility, except that (i) the sum of the borrowing capacity must equal the total amount of the facility, and (ii) the aggregate amount of credit used at any given time by each of Pepco, DPL or ACE may not exceed $900 million or the maximum amount of short-term debt the company is permitted to have outstanding by its regulatory authorities. The total number of the borrowing reallocations may not exceed eight per year during the term of the facility. (d) Includes revolving credit agreement at Exelon Corporate with a maximum program size of $600 million at both December 31, 2019 and 2018 , respectively. Exelon Corporate had $136 million of outstanding commercial paper at December 31, 2019 and no outstanding commercial paper at the end of 2018 .
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Schedule of Line of Credit Facilities [Table Text Block]	At December 31, 2019 , the Registrants had the following aggregate bank commitments, credit facility borrowings and available capacity under their respective credit facilities: Available Capacity at December 31, 2019 Borrower Facility Type Aggregate Bank (a) Facility Draws Outstanding Letters of Credit Actual To Support Additional Commercial (b) Exelon (b) Syndicated Revolver / Bilaterals / Project Finance $ 10,559 $ — $ 1,443 $ 9,116 $ 7,353 Generation Syndicated Revolver 5,300 — 769 4,531 4,211 Generation Bilaterals 1,400 — 545 855 — Generation Project Finance 159 — 120 39 — ComEd Syndicated Revolver 1,000 — 2 998 868 PECO Syndicated Revolver 600 — — 600 600 BGE Syndicated Revolver 600 — — 600 524 PHI Syndicated Revolver 900 — — 900 692 Pepco Syndicated Revolver 300 — — 300 218 DPL Syndicated Revolver 300 — — 300 244 ACE Syndicated Revolver 300 — — 300 230 __________ (a) Excludes $142 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $44 million , $33 million , $33 million , $8 million , $8 million , $8 million and $8 million , respectively. These facilities expire on October 9, 2020. These facilities are solely utilized to issue letters of credit. As of December 31, 2019 , letters of credit issued under these facilities totaled $5 million , $5 million , $2 million for Generation, ComEd, and BGE, respectively. (b) Includes $600 million aggregate bank commitment related to Exelon Corporate. Exelon Corporate had $6 million and $9 million outstanding letters of credit at December 31, 2019 and 2018 , respectively. Exelon Corporate had $458 million in available capacity to support additional commercial paper at December 31, 2019 .

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of financial liabilities recorded at the carrying amount	The following tables present the carrying amounts and fair values of the Registrants’ short-term liabilities, long-term debt, SNF obligation, and trust preferred securities (long-term debt to financing trusts or junior subordinated debentures) as of December 31, 2019 and 2018 . The Registrants have no financial liabilities classified as Level 1. The carrying amounts of the Registrants’ short-term liabilities as presented on their Consolidated Balance Sheets are representative of their fair value (Level 2) because of the short-term nature of these instruments. December 31, 2019 December 31, 2018 Carrying Amount Fair Value Carrying Amount Fair Value Level 2 Level 3 Total Level 2 Level 3 Total Long-Term Debt, including amounts due within one year (a) Exelon $ 36,039 $ 37,453 $ 2,580 $ 40,033 $ 35,424 $ 33,711 $ 2,158 $ 35,869 Generation 7,974 7,304 1,366 8,670 8,793 7,467 1,443 8,910 ComEd 8,491 9,848 — 9,848 8,101 8,390 — 8,390 PECO 3,405 3,868 50 3,918 3,084 3,157 50 3,207 BGE 3,270 3,649 — 3,649 2,876 2,950 — 2,950 PHI 6,563 5,902 1,164 7,066 6,259 5,436 665 6,101 Pepco 2,864 3,198 388 3,586 2,719 2,901 196 3,097 DPL 1,567 1,408 311 1,719 1,494 1,303 193 1,496 ACE 1,327 1,026 464 1,490 1,188 987 275 1,262 Long-Term Debt to Financing Trusts (a) Exelon $ 390 $ — $ 428 $ 428 $ 390 $ — $ 400 $ 400 ComEd 205 — 227 227 205 — 209 209 PECO 184 — 201 201 184 — 191 191 SNF Obligation Exelon $ 1,199 $ 1,055 $ — $ 1,055 $ 1,171 $ 949 $ — $ 949 Generation 1,199 1,055 — 1,055 1,171 949 — 949 ________ (a) Includes unamortized debt issuance costs which are not fair valued. Refer to Note 16 — Debt and Credit Agreements for each Registrants’ unamortized debt issuance costs .
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 the Registrants' Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2019 and 2018 : Exelon Generation As of December 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) $ 639 $ — $ — $ — $ 639 $ 214 $ — $ — $ — $ 214 NDT fund investments Cash equivalents (b) 365 87 — — 452 365 87 — — 452 Equities 3,353 1,753 — 1,388 6,494 3,353 1,753 — 1,388 6,494 Fixed income Corporate debt — 1,469 257 — 1,726 — 1,469 257 — 1,726 U.S. Treasury and agencies 1,808 131 — — 1,939 1,808 131 — — 1,939 Foreign governments — 42 — — 42 — 42 — — 42 State and municipal debt — 90 — — 90 — 90 — — 90 Other (c) — 33 — 953 986 — 33 — 953 986 Fixed income subtotal 1,808 1,765 257 953 4,783 1,808 1,765 257 953 4,783 Private credit — — 254 508 762 — — 254 508 762 Private equity — — — 402 402 — — — 402 402 Real estate — — — 607 607 — — — 607 607 NDT fund investments subtotal (d) 5,526 3,605 511 3,858 13,500 5,526 3,605 511 3,858 13,500 Rabbi trust investments Cash equivalents 50 — — — 50 4 — — — 4 Mutual funds 81 — — — 81 25 — — — 25 Fixed income — 12 — — 12 — — — — — Life insurance contracts — 78 41 — 119 — 25 — — 25 Rabbi trust investments subtotal 131 90 41 — 262 29 25 — — 54 Commodity derivative assets Economic hedges 768 2,491 1,485 — 4,744 768 2,491 1,485 — 4,744 Proprietary trading — 37 60 — 97 — 37 60 — 97 Effect of netting and allocation of (e)(f) (908 ) (2,162 ) (588 ) — (3,658 ) (908 ) (2,162 ) (588 ) — (3,658 ) Commodity derivative assets subtotal (140 ) 366 957 — 1,183 (140 ) 366 957 — 1,183 Total assets 6,156 4,061 1,509 3,858 15,584 5,629 3,996 1,468 3,858 14,951 Exelon Generation As of December 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 (1,071 ) (2,855 ) (1,228 ) — (5,154 ) (1,071 ) (2,855 ) (927 ) — (4,853 ) Proprietary trading — (34 ) (15 ) — (49 ) — (34 ) (15 ) — (49 ) Effect of netting and allocation of (e)(f) 1,071 2,714 802 — 4,587 1,071 2,714 802 — 4,587 Commodity derivative liabilities subtotal — (175 ) (441 ) — (616 ) — (175 ) (140 ) — (315 ) Deferred compensation obligation — (147 ) — — (147 ) — (41 ) — — (41 ) Total liabilities — (322 ) (441 ) — (763 ) — (216 ) (140 ) — (356 ) Total net assets $ 6,156 $ 3,739 $ 1,068 $ 3,858 $ 14,821 $ 5,629 $ 3,780 $ 1,328 $ 3,858 $ 14,595 Exelon Generation 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) $ 1,243 $ — $ — $ — $ 1,243 $ 581 $ — $ — $ — $ 581 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 Private credit — — 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 Exelon Generation 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 Rabbi trust investments Cash equivalents 48 — — — 48 5 — — — 5 Mutual funds 72 — — — 72 24 — — — 24 Fixed income — 15 — — 15 — — — — — Life insurance contracts — 70 38 — 108 — 22 — — 22 Rabbi trust investments subtotal 120 85 38 — 243 29 22 — — 51 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 (e)(f) (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 Total assets 6,573 4,155 1,396 3,433 15,557 5,820 4,092 1,358 3,433 14,703 Liabilities Commodity derivative liabilities Economic hedges (642 ) (2,963 ) (1,276 ) — (4,881 ) (642 ) (2,963 ) (1,027 ) — (4,632 ) Proprietary trading — (73 ) (21 ) — (94 ) — (73 ) (21 ) — (94 ) Effect of netting and allocation of (e)(f) 639 2,581 808 — 4,028 639 2,581 808 — 4,028 Commodity derivative liabilities subtotal (3 ) (455 ) (489 ) — (947 ) (3 ) (455 ) (240 ) — (698 ) Deferred compensation obligation — (137 ) — — (137 ) — (35 ) — — (35 ) Total liabilities (3 ) (592 ) (489 ) — (1,084 ) (3 ) (490 ) (240 ) — (733 ) Total net assets $ 6,570 $ 3,563 $ 907 $ 3,433 $ 14,473 $ 5,817 $ 3,602 $ 1,118 $ 3,433 $ 13,970 __________ (a) Exelon excludes cash of $373 million and $458 million at December 31, 2019 and 2018 , respectively, and restricted cash of $110 million and $80 million at December 31, 2019 and 2018 , respectively, and includes long-term restricted cash of $177 million and $185 million at December 31, 2019 and 2018 , respectively, which is reported in Other deferred debits in the Consolidated Balance Sheets. Generation excludes cash of $177 million and $283 million at December 31, 2019 and 2018 , respectively and restricted cash of $58 million and $39 million at December 31, 2019 and 2018 , respectively. (b) Includes $90 million and $50 million of cash received from outstanding repurchase agreements at December 31, 2019 and 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 $2 million and $44 million , which have a total notional amount of $724 million and $1,432 million at December 31, 2019 and 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 the company's exposure to credit or market loss. (d) Excludes net liabilities of $147 million and $130 million at December 31, 2019 and 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) Collateral posted/(received) from counterparties totaled $163 million , $551 million and $214 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2019 . Collateral posted/(received) from 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 . (f) Of the collateral posted/(received), $511 million and $(94) million represents variation margin on the exchanges as of December 31, 2019 and 2018 , respectively. As of December 31, 2019 , Generation has outstanding commitments to invest in fixed income, private credit, private equity and real estate investments of approximately $85 million , $166 million , $375 million and $427 million , respectively. These commitments will be funded by Generation’s existing NDT funds. Exelon and Generation hold investments without readily determinable fair values with carrying amounts of $69 million as of December 31, 2019 . Changes were immaterial in fair value, cumulative adjustments and impairments for the year ended December 31, 2019 . ComEd PECO BGE As of December 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) $ 280 $ — $ — $ 280 $ 15 $ — $ — $ 15 $ — $ — $ — $ — Rabbi trust investments Mutual funds — — — — 8 — — 8 8 — — 8 Life insurance contracts — — — — — 11 — 11 — — — — Rabbi trust investments subtotal — — — — 8 11 — 19 8 — — 8 Total assets 280 — — 280 23 11 — 34 8 — — 8 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (9 ) — (9 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (b) — — (301 ) (301 ) — — — — — — — — Total liabilities — (8 ) (301 ) (309 ) — (9 ) — (9 ) — (5 ) — (5 ) Total net assets (liabilities) $ 280 $ (8 ) $ (301 ) $ (29 ) $ 23 $ 2 $ — $ 25 $ 8 $ (5 ) $ — $ 3 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 — — — — 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 (b) — — (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 $90 million and $93 million at December 31, 2019 and 2018 and restricted cash of $33 million and $28 million at December 31, 2019 and 2018 , respectively, and includes long-term restricted cash of $163 million and $166 million at December 31, 2019 and 2018 , respectively which is reported in Other deferred debits in the Consolidated Balance Sheets. PECO excludes cash of $12 million and $24 million at December 31, 2019 and 2018 , respectively. BGE excludes cash of $24 million and $7 million at December 31, 2019 and 2018 , respectively, and restricted cash of $1 million and $2 million at December 31, 2019 and 2018 , respectively. (b) The Level 3 balance consists of the current and noncurrent liability of $32 million and $269 million , respectively, at December 31, 2019 , and $26 million and $223 million , respectively, at December 31, 2018 , related to floating-to-fixed energy swap contracts with unaffiliated suppliers. As of December 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) $ 124 $ — $ — $ 124 $ 147 $ — $ — $ 147 Rabbi trust investments Cash equivalents 44 — — 44 42 — — 42 Mutual Funds 14 — — 14 13 — — 13 Fixed income — 12 — 12 — 15 — 15 Life insurance contracts — 24 41 65 — 22 38 60 Rabbi trust investments subtotal (b) 58 36 41 135 55 37 38 130 Total assets 182 36 41 259 202 37 38 277 Liabilities Deferred compensation obligation — (19 ) — (19 ) — (21 ) — (21 ) Total liabilities — (19 ) — (19 ) — (21 ) — (21 ) Total net assets $ 182 $ 17 $ 41 $ 240 $ 202 $ 16 $ 38 $ 256 Pepco DPL ACE As of December 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) $ 34 $ — $ — $ 34 $ — $ — $ — $ — $ 16 $ — $ — $ 16 Rabbi trust investments Cash equivalents 43 — — 43 — — — — — — — — Fixed income — 2 — 2 — — — — — — — — Life insurance contracts — 24 41 65 — — — — — — — — Rabbi trust investments subtotal 43 26 41 110 — — — — — — — — Total assets 77 26 41 144 — — — — 16 — — 16 Liabilities Deferred compensation obligation — (2 ) — (2 ) — — — — — — — — Total liabilities — (2 ) — (2 ) — — — — — — — — Total net assets $ 77 $ 24 $ 41 $ 142 $ — $ — $ — $ — $ 16 $ — $ — $ 16 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 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 $ 79 $ 24 $ 37 $ 140 $ 16 $ (1 ) $ — $ 15 $ 23 $ — $ — $ 23 __________ (a) PHI excludes cash of $57 million and $39 million at December 31, 2019 and 2018 , respectively, and includes long term restricted cash of $14 million and $19 million at December 31, 2019 and 2018 , respectively, which is reported in Other deferred debits in the Consolidated Balance Sheets. Pepco excludes cash of $29 million and $15 million at December 31, 2019 and 2018 , respectively. DPL excludes cash of $13 million and $8 million at December 31, 2019 and 2018 , respectively. ACE excludes cash of $12 million and $7 million at December 31, 2019 and 2018 , respectively, and includes long-term restricted cash of $14 million and $19 million at December 31, 2019 and 2018 , respectively, which is reported in Other deferred debits in the Consolidated Balance Sheets.
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]	The following tables present assets and liabilities measured and recorded at fair value in the Registrants' Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2019 and 2018 : Exelon Generation As of December 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) $ 639 $ — $ — $ — $ 639 $ 214 $ — $ — $ — $ 214 NDT fund investments Cash equivalents (b) 365 87 — — 452 365 87 — — 452 Equities 3,353 1,753 — 1,388 6,494 3,353 1,753 — 1,388 6,494 Fixed income Corporate debt — 1,469 257 — 1,726 — 1,469 257 — 1,726 U.S. Treasury and agencies 1,808 131 — — 1,939 1,808 131 — — 1,939 Foreign governments — 42 — — 42 — 42 — — 42 State and municipal debt — 90 — — 90 — 90 — — 90 Other (c) — 33 — 953 986 — 33 — 953 986 Fixed income subtotal 1,808 1,765 257 953 4,783 1,808 1,765 257 953 4,783 Private credit — — 254 508 762 — — 254 508 762 Private equity — — — 402 402 — — — 402 402 Real estate — — — 607 607 — — — 607 607 NDT fund investments subtotal (d) 5,526 3,605 511 3,858 13,500 5,526 3,605 511 3,858 13,500 Rabbi trust investments Cash equivalents 50 — — — 50 4 — — — 4 Mutual funds 81 — — — 81 25 — — — 25 Fixed income — 12 — — 12 — — — — — Life insurance contracts — 78 41 — 119 — 25 — — 25 Rabbi trust investments subtotal 131 90 41 — 262 29 25 — — 54 Commodity derivative assets Economic hedges 768 2,491 1,485 — 4,744 768 2,491 1,485 — 4,744 Proprietary trading — 37 60 — 97 — 37 60 — 97 Effect of netting and allocation of (e)(f) (908 ) (2,162 ) (588 ) — (3,658 ) (908 ) (2,162 ) (588 ) — (3,658 ) Commodity derivative assets subtotal (140 ) 366 957 — 1,183 (140 ) 366 957 — 1,183 Total assets 6,156 4,061 1,509 3,858 15,584 5,629 3,996 1,468 3,858 14,951 Exelon Generation As of December 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 (1,071 ) (2,855 ) (1,228 ) — (5,154 ) (1,071 ) (2,855 ) (927 ) — (4,853 ) Proprietary trading — (34 ) (15 ) — (49 ) — (34 ) (15 ) — (49 ) Effect of netting and allocation of (e)(f) 1,071 2,714 802 — 4,587 1,071 2,714 802 — 4,587 Commodity derivative liabilities subtotal — (175 ) (441 ) — (616 ) — (175 ) (140 ) — (315 ) Deferred compensation obligation — (147 ) — — (147 ) — (41 ) — — (41 ) Total liabilities — (322 ) (441 ) — (763 ) — (216 ) (140 ) — (356 ) Total net assets $ 6,156 $ 3,739 $ 1,068 $ 3,858 $ 14,821 $ 5,629 $ 3,780 $ 1,328 $ 3,858 $ 14,595 Exelon Generation 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) $ 1,243 $ — $ — $ — $ 1,243 $ 581 $ — $ — $ — $ 581 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 Private credit — — 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 Exelon Generation 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 Rabbi trust investments Cash equivalents 48 — — — 48 5 — — — 5 Mutual funds 72 — — — 72 24 — — — 24 Fixed income — 15 — — 15 — — — — — Life insurance contracts — 70 38 — 108 — 22 — — 22 Rabbi trust investments subtotal 120 85 38 — 243 29 22 — — 51 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 (e)(f) (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 Total assets 6,573 4,155 1,396 3,433 15,557 5,820 4,092 1,358 3,433 14,703 Liabilities Commodity derivative liabilities Economic hedges (642 ) (2,963 ) (1,276 ) — (4,881 ) (642 ) (2,963 ) (1,027 ) — (4,632 ) Proprietary trading — (73 ) (21 ) — (94 ) — (73 ) (21 ) — (94 ) Effect of netting and allocation of (e)(f) 639 2,581 808 — 4,028 639 2,581 808 — 4,028 Commodity derivative liabilities subtotal (3 ) (455 ) (489 ) — (947 ) (3 ) (455 ) (240 ) — (698 ) Deferred compensation obligation — (137 ) — — (137 ) — (35 ) — — (35 ) Total liabilities (3 ) (592 ) (489 ) — (1,084 ) (3 ) (490 ) (240 ) — (733 ) Total net assets $ 6,570 $ 3,563 $ 907 $ 3,433 $ 14,473 $ 5,817 $ 3,602 $ 1,118 $ 3,433 $ 13,970 __________ (a) Exelon excludes cash of $373 million and $458 million at December 31, 2019 and 2018 , respectively, and restricted cash of $110 million and $80 million at December 31, 2019 and 2018 , respectively, and includes long-term restricted cash of $177 million and $185 million at December 31, 2019 and 2018 , respectively, which is reported in Other deferred debits in the Consolidated Balance Sheets. Generation excludes cash of $177 million and $283 million at December 31, 2019 and 2018 , respectively and restricted cash of $58 million and $39 million at December 31, 2019 and 2018 , respectively. (b) Includes $90 million and $50 million of cash received from outstanding repurchase agreements at December 31, 2019 and 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 $2 million and $44 million , which have a total notional amount of $724 million and $1,432 million at December 31, 2019 and 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 the company's exposure to credit or market loss. (d) Excludes net liabilities of $147 million and $130 million at December 31, 2019 and 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) Collateral posted/(received) from counterparties totaled $163 million , $551 million and $214 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2019 . Collateral posted/(received) from 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 . (f) Of the collateral posted/(received), $511 million and $(94) million represents variation margin on the exchanges as of December 31, 2019 and 2018 , respectively. As of December 31, 2019 , Generation has outstanding commitments to invest in fixed income, private credit, private equity and real estate investments of approximately $85 million , $166 million , $375 million and $427 million , respectively. These commitments will be funded by Generation’s existing NDT funds. Exelon and Generation hold investments without readily determinable fair values with carrying amounts of $69 million as of December 31, 2019 . Changes were immaterial in fair value, cumulative adjustments and impairments for the year ended December 31, 2019 . ComEd PECO BGE As of December 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) $ 280 $ — $ — $ 280 $ 15 $ — $ — $ 15 $ — $ — $ — $ — Rabbi trust investments Mutual funds — — — — 8 — — 8 8 — — 8 Life insurance contracts — — — — — 11 — 11 — — — — Rabbi trust investments subtotal — — — — 8 11 — 19 8 — — 8 Total assets 280 — — 280 23 11 — 34 8 — — 8 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (9 ) — (9 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (b) — — (301 ) (301 ) — — — — — — — — Total liabilities — (8 ) (301 ) (309 ) — (9 ) — (9 ) — (5 ) — (5 ) Total net assets (liabilities) $ 280 $ (8 ) $ (301 ) $ (29 ) $ 23 $ 2 $ — $ 25 $ 8 $ (5 ) $ — $ 3 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 — — — — 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 (b) — — (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 $90 million and $93 million at December 31, 2019 and 2018 and restricted cash of $33 million and $28 million at December 31, 2019 and 2018 , respectively, and includes long-term restricted cash of $163 million and $166 million at December 31, 2019 and 2018 , respectively which is reported in Other deferred debits in the Consolidated Balance Sheets. PECO excludes cash of $12 million and $24 million at December 31, 2019 and 2018 , respectively. BGE excludes cash of $24 million and $7 million at December 31, 2019 and 2018 , respectively, and restricted cash of $1 million and $2 million at December 31, 2019 and 2018 , respectively. (b) The Level 3 balance consists of the current and noncurrent liability of $32 million and $269 million , respectively, at December 31, 2019 , and $26 million and $223 million , respectively, at December 31, 2018 , related to floating-to-fixed energy swap contracts with unaffiliated suppliers. As of December 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) $ 124 $ — $ — $ 124 $ 147 $ — $ — $ 147 Rabbi trust investments Cash equivalents 44 — — 44 42 — — 42 Mutual Funds 14 — — 14 13 — — 13 Fixed income — 12 — 12 — 15 — 15 Life insurance contracts — 24 41 65 — 22 38 60 Rabbi trust investments subtotal (b) 58 36 41 135 55 37 38 130 Total assets 182 36 41 259 202 37 38 277 Liabilities Deferred compensation obligation — (19 ) — (19 ) — (21 ) — (21 ) Total liabilities — (19 ) — (19 ) — (21 ) — (21 ) Total net assets $ 182 $ 17 $ 41 $ 240 $ 202 $ 16 $ 38 $ 256 Pepco DPL ACE As of December 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) $ 34 $ — $ — $ 34 $ — $ — $ — $ — $ 16 $ — $ — $ 16 Rabbi trust investments Cash equivalents 43 — — 43 — — — — — — — — Fixed income — 2 — 2 — — — — — — — — Life insurance contracts — 24 41 65 — — — — — — — — Rabbi trust investments subtotal 43 26 41 110 — — — — — — — — Total assets 77 26 41 144 — — — — 16 — — 16 Liabilities Deferred compensation obligation — (2 ) — (2 ) — — — — — — — — Total liabilities — (2 ) — (2 ) — — — — — — — — Total net assets $ 77 $ 24 $ 41 $ 142 $ — $ — $ — $ — $ 16 $ — $ — $ 16 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 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 $ 79 $ 24 $ 37 $ 140 $ 16 $ (1 ) $ — $ 15 $ 23 $ — $ — $ 23 __________ (a) PHI excludes cash of $57 million and $39 million at December 31, 2019 and 2018 , respectively, and includes long term restricted cash of $14 million and $19 million at December 31, 2019 and 2018 , respectively, which is reported in Other deferred debits in the Consolidated Balance Sheets. Pepco excludes cash of $29 million and $15 million at December 31, 2019 and 2018 , respectively. DPL excludes cash of $13 million and $8 million at December 31, 2019 and 2018 , respectively. ACE excludes cash of $12 million and $7 million at December 31, 2019 and 2018 , respectively, and includes long-term restricted cash of $14 million and $19 million at December 31, 2019 and 2018 , respectively, which is reported in Other deferred debits in the Consolidated Balance Sheets.
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Text Block]	The following tables present the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis during the years ended December 31, 2019 and 2018 : Exelon Generation ComEd PHI and Pepco For the year ended December 31, 2019 Total NDT Fund Investments Mark-to-Market Total Generation Mark-to-Market Derivatives Life Insurance Contracts Eliminated in Consolidation Balance as of January 1, 2019 $ 907 $ 543 $ 575 $ 1,118 $ (249 ) $ 38 $ — Total realized / unrealized gains (losses) Included in net income (23 ) 5 (31 ) (a) (26 ) — 3 — Included in noncurrent payables to affiliates — 34 — 34 — — (34 ) Included in regulatory assets/liabilities (18 ) — — — (52 ) (b) — 34 Change in collateral 138 — 138 138 — — — Purchases, sales, issuances and settlements Purchases 176 44 132 176 — — — Sales (23 ) (21 ) (2 ) (23 ) — — — Settlements (89 ) (94 ) 5 (89 ) — — — Transfers into Level 3 5 — 5 (c) 5 — — — Transfers out of Level 3 (5 ) — (5 ) (c) (5 ) — — — Balance as of December 31, 2019 $ 1,068 $ 511 $ 817 $ 1,328 $ (301 ) $ 41 $ — The amount of total gains (losses) included in income attributed to the change in unrealized (losses) gains related to assets and liabilities held as of December 31, 2019 $ 359 $ 5 $ 351 $ 356 $ — $ 3 $ — Exelon Generation ComEd PHI and Pepco For the year ended December 31, 2018 Total NDT Fund Investments Mark-to-Market Derivatives Total Generation Mark-to-Market Derivatives Life Insurance Contracts Eliminated in Consolidation Balance as of January 1, 2018 $ 966 $ 648 $ 552 $ 1,200 $ (256 ) $ 22 $ — Total realized / unrealized gains (losses) Included in net income (101 ) — (105 ) (a) (105 ) — 4 — Included in noncurrent payables to affiliates — (1 ) — (1 ) — — 1 Included in regulatory assets/liabilities 6 — — — 7 (b) — (1 ) Change in collateral (5 ) — (5 ) (5 ) — — — Purchases, sales, issuances and settlements Purchases 226 36 190 226 — — — Sales (4 ) — (4 ) (4 ) — — — Settlements (123 ) (140 ) 5 (135 ) — 12 — Transfers into Level 3 (22 ) — (22 ) (c) (22 ) — — — Transfers out of Level 3 (36 ) — (36 ) (c) (36 ) — — — Balance as of December 31, 2018 $ 907 $ 543 $ 575 $ 1,118 $ (249 ) $ 38 $ — The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held as of December 31, 2018 $ 160 $ (5 ) $ 165 $ 160 $ — $ — $ — __________ (a) Includes a reduction for the reclassification of $377 million and $265 million of realized gains due to the settlement of derivative contracts for the years ended December 31, 2019 and 2018 , respectively. (b) Includes $78 million of decreases in fair value and an increase for realized losses due to settlements of $26 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2019 . Includes $24 million of decreases in fair value and an increase for realized losses due to settlements of $17 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2018 . (c) 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 years ended December 31, 2019 and 2018 : Exelon Generation PHI and Pepco Operating Purchased Operating and Maintenance Other, net Operating Purchased Other, net Operating and Total gains (losses) included in net income for the year ended December 31, 2019 $ 219 $ (245 ) $ 3 $ 5 $ 219 $ (245 ) $ 5 $ 3 Change in the unrealized gains (losses) relating to assets and liabilities held for the year ended December 31, 2019 546 (195 ) 3 5 546 (195 ) 5 3 Exelon Generation PHI and Pepco Operating Purchased Operating and Maintenance Other, net Operating Purchased Other, net Operating and Total (losses) gains included in net income for the year ended December 31, 2018 $ (7 ) $ (93 ) $ 4 $ 3 $ (7 ) $ (93 ) $ 3 $ 4 Change in the unrealized gains (losses) relating to assets and liabilities held for the year ended December 31, 2018 144 21 — (2 ) 144 21 (2 ) —
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques [Table Text Block]	The following table presents the significant inputs to the forward curve used to value these positions: Type of trade Fair Value at December 31, 2019 Fair Value at December 31, 2018 Valuation Unobservable 2019 Range 2018 Range Mark-to-market derivatives—Economic hedges (Exelon and Generation) (a)(b) $ 558 $ 443 Discounted Forward power price $9 - $180 $12 - $174 Forward gas price $0.83 - $10.72 $0.78 - $12.38 Option Model Volatility percentage 8% - 236% 10% - 277% Mark-to-market derivatives—Proprietary trading (Exelon and Generation) (a)(b) $ 45 $ 56 Discounted Forward power price $25 - $180 $14 - $174 Mark-to-market derivatives (Exelon and ComEd) $ (301 ) $ (249 ) Discounted Forward heat rate (c) 9X - 10X 10X - 11X Marketability reserve 3% - 7% 4% - 8% Renewable factor 91% - 123% 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 $214 million and $76 million as of December 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.

Commitments and Contingencies_2

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Environmental Loss Contingency Tables [Abstract]
PHI Merger Commitments [Table Text Block]	The following amounts represent total commitment costs that have been recorded since the acquisition date and the total remaining obligations for Exelon, PHI, Pepco, DPL and ACE as of December 31, 2019 : Description Exelon PHI Pepco DPL ACE Total commitments $ 513 $ 320 $ 120 $ 89 $ 111 Remaining commitments (a) $ 101 $ 79 $ 65 $ 8 $ 6 _________ (a) Remaining commitments extend through 2026 and include rate credits, energy efficiency programs and delivery system modernization.
Other Commitments [Table Text Block]	The Registrant s' commercial commitments as of December 31, 2019 , representing commitments potentially triggered by future events, were as follows: Expiration within Exelon Total 2020 2021 2022 2023 2024 2025 and beyond Letters of credit $ 1,455 $ 1,314 $ 141 $ — $ — $ — $ — Surety bonds (a) 855 809 46 — — — — Financing trust guarantees 378 — — — — — 378 Guaranteed lease residual values (b) 26 2 2 4 3 6 10 Total commercial commitments $ 2,714 $ 2,125 $ 189 $ 4 $ 3 $ 6 $ 388 Generation Letters of credit $ 1,440 $ 1,302 $ 138 $ — $ — $ — $ — Surety bonds (a) 670 662 8 — — — — Total commercial commitments $ 2,110 $ 1,964 $ 146 $ — $ — $ — $ — ComEd Letters of credit $ 7 $ 7 $ — $ — $ — $ — $ — Surety bonds (a) 50 48 2 — — — — Financing trust guarantees 200 — — — — — 200 Total commercial commitments $ 257 $ 55 $ 2 $ — $ — $ — $ 200 PECO Surety bonds (a) $ 9 $ 9 $ — $ — $ — $ — $ — Financing trust guarantees 178 — — — — — 178 Total commercial commitments $ 187 $ 9 $ — $ — $ — $ — $ 178 BGE Letters of credit $ 2 $ 2 $ — $ — $ — $ — $ — Surety bonds (a) 3 3 — — — — — Total commercial commitments $ 5 $ 5 $ — $ — $ — $ — $ — PHI Surety bonds (a) $ 21 $ 21 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 26 2 2 4 3 6 10 Total commercial commitments $ 47 $ 23 $ 2 $ 4 $ 3 $ 6 $ 10 Pepco Surety bonds (a) $ 14 $ 14 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 9 — — 1 1 2 5 Total commercial commitments $ 23 $ 14 $ — $ 1 $ 1 $ 2 $ 5 DPL Surety bonds (a) $ 4 $ 4 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 11 1 1 2 1 3 3 Total commercial commitments $ 15 $ 5 $ 1 $ 2 $ 1 $ 3 $ 3 ACE Surety bonds (a) $ 3 $ 3 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 7 1 1 1 1 1 2 Total commercial commitments $ 10 $ 4 $ 1 $ 1 $ 1 $ 1 $ 2 _________ (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 lease term associated with these assets ranges from 1 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $69 million guaranteed by Exelon and PHI, of which $23 million , $29 million and $18 million is guaranteed by Pepco, DPL and ACE, respectively. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote.
Schedule of Government Settlement Agreements [Table Text Block]	Under the settlement agreements, Generation has received cumulative cash reimbursements for costs incurred as follows: Total Net (a) Cumulative cash reimbursements $ 1,288 $ 1,113 __________ (a) Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Creek. As of December 31, 2019 and 2018 , the amount of SNF storage costs for which reimbursement has been or will be requested from the DOE under the DOE settlement agreements is as follows: December 31, 2019 December 31, 2018 DOE receivable - current (a) $ 249 $ 124 DOE receivable - noncurrent (b) 30 15 Amounts owed to co-owners (a)(c) (37 ) (17 ) __________ (a) Recorded in Accounts receivable, other. (b) Recorded in Deferred debits and other assets, other. (c)
Spent Nuclear Fuel Obligation [Table Text Block]	The below table outlines the SNF liability recorded at Exelon and Generation as of December 31, 2019 and 2018 : December 31, 2019 December 31, 2018 Former ComEd units (a) $ 1,075 $ 1,052 Fitzpatrick (b) 124 119 Total SNF Obligation $ 1,199 $ 1,171 __________ (a) ComEd previously elected to defer payment of the one-time fee of $277 million for its units (which are now part of Generation), with interest to the date of payment, until just prior to the first delivery of SNF to the DOE. The unfunded liabilities for SNF disposal costs, including the one-time fee, were transferred to Generation as part of Exelon’s 2001 corporate restructuring. (b) A prior owner of FitzPatrick elected to defer payment of the one-time fee of $34 million , with interest to the date of payment, for the FitzPatrick unit. As part of the FitzPatrick acquisition on March 31, 2017, Generation assumed a SNF liability for the DOE one-time fee obligation with interest related to FitzPatrick along with an offsetting asset, included in Other deferred debits and other assets, for the contractual right to reimbursement from NYPA, a prior owner of FitzPatrick, for amounts paid for the FitzPatrick DOE one-time fee obligation .
Accrued environmental liabilities	As of December 31, 2019 and 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: December 31, 2019 December 31, 2018 Total environmental Portion of total related to Total environmental Portion of total related to Exelon $ 478 $ 320 $ 496 $ 356 Generation 105 — 108 — ComEd 304 303 329 327 PECO 19 17 27 25 BGE 2 — 5 4 PHI 48 — 27 — Pepco 46 — 25 — DPL 1 — 1 — ACE 1 — 1 —

Severance (Tables)

Severance (Tables)	12 Months Ended
	Dec. 31, 2019
Restructuring and Related Activities [Abstract]
Severance	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. The total annual impact of these charges by year are summarized in the table below. Income statement expense (pre-tax) 2019 (a) 2018 (b) 2017 (c) Depreciation and Amortization Accelerated depreciation $ 216 $ 539 $ 250 Accelerated nuclear fuel amortization 13 57 12 Operating and Maintenance (d) (53 ) 32 77 Total $ 176 $ 628 $ 339 _________ (a) Reflects incremental charges for TMI from January 1, 2019 through September 20, 2019. (b) Reflects incremental charges for TMI in 2018 and Oyster Creek from February 2, 2018 through September 17, 2018. (c) Reflects incremental charges for TMI from May 30, 2017 through December 31, 2017. (d) In 2019, primarily reflects the net impacts associated with the remeasurements of the TMI ARO in the first and third quarters. In 2018 and 2017, primarily reflects materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments associated with the early retirement decisions for TMI and Oyster Creek. Excludes the charges in the third quarter of 2018 and second quarter of 2019 for the ARO remeasurement due to the sale of Oyster Creek. See Note 2 — Mergers, Acquisitions and Dispositions and Note 9 — Asset Retirement Obligations for additional information.
Severance Liability	<div style="font-family:Times New Roman;font-size:10pt;"><div style="line-height:120%;padding-bottom:12px;padding-top:12px;text-align:justify;font-size:10pt;"><font style="font-family:Arial;font-size:9pt;">Amounts included in the table below represent the severance liability recorded for employees of each Registrant. Exelon's severance liability includes amounts related to BSC that are billed through intercompany allocations</font><font style="font-family:Arial;font-size:10pt;">.</font></div><div style="line-height:120%;text-align:center;font-size:10pt;"><div style="padding-left:0px;text-indent:0px;line-height:normal;padding-top:10px;"><table cellpadding="0" cellspacing="0" style="font-family:Times New Roman;font-size:10pt;margin-left:auto;margin-right:auto;width:100%;border-collapse:collapse;text-align:left;"><tr><td colspan="18" rowspan="1"></td></tr><tr><td style="width:23%;" rowspan="1" colspan="1"></td><td style="width:9%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:11%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:7%;" rowspan="1" colspan="1"></td></tr><tr><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:left;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;text-decoration:underline;">Severance Liability</font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">Exelon</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">Generation</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">ComEd</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">PECO</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">BGE</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">PHI</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">Pepco</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">DPL</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:bottom;border-bottom:1px solid #000000;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:center;font-size:7pt;"><font style="font-family:Arial;font-size:7pt;font-weight:bold;">ACE</font></div></td></tr></table></div></div><div style="line-height:120%;text-align:justify;font-size:10pt;"><font style="font-family:Arial;font-size:10pt;">__________</font></div><table cellpadding="0" cellspacing="0" style="padding-top:0px;padding-bottom:0px;font-family:Times New Roman; font-size:10pt;"><tr><td style="width:24px;" rowspan="1" colspan="1"></td><td rowspan="1" colspan="1"></td></tr><tr><td style="vertical-align:top" rowspan="1" colspan="1"><div style="line-height:120%;font-size:8pt;padding-left:0px;"><font style="font-family:Arial;font-size:8pt;">(a)</font></div></td><td style="vertical-align:top;" rowspan="1" colspan="1"><div style="line-height:120%;text-align:justify;font-size:8pt;"><font style="font-family:Arial;font-size:8pt;">Includes salary continuance and health and welfare severance benefits. </font></div></td></tr></table></div>

Shareholder Equity (Tables)

Shareholder Equity (Tables)	12 Months Ended
	Dec. 31, 2019
Shareholder [Abstract]
Common Stock Warrants [Table Text Block]	The following table presents warrants outstanding to purchase ComEd common stock and shares of common stock reserved for the conversion of warrants. The warrants entitle the holders to convert such warrants into common stock of ComEd at a conversion rate of one share of common stock for three warrants. December 31, 2019 2018 Warrants outstanding 60,228 60,285 Common Stock reserved for conversion 20,076 20,095
Preferred Stock [Table Text Block]	The following table presents the Registrants' shares of preferred securities authorized, none of which are outstanding as of December 31, 2019 and 2018 : Preferred Securities Authorized Exelon 100,000,000 ComEd 850,000 PECO 15,000,000 BGE 1,000,000 Pepco 6,000,000 ACE (a) 2,799,979 __________ (a) Includes 799,979 shares of cumulative preferred stock and 2,000,000 of no-par preferred stock as of December 31, 2019 and 2018 , respectively.
Preference Securities [Table Text Block]	The following table presents ComEd's, BGE's and ACE's preference securities authorized, none of which are outstanding as of December 31, 2019 and 2018 : Preference Securities Authorized ComEd - Cumulative preference securities 6,810,451 BGE (a) 6,500,000 ACE 3,000,000 __________ (a) Includes 4,600,000 shares of unclassified preference securities and 1,900,000 shares of previously redeemed preference securities as of December 31, 2019 and 2018

Stock-Based Compensation Plan_2

Stock-Based Compensation Plans Stock-Based Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2019
Common Stock [Abstract]
Share-based Payment Arrangement, Cost by Plan [Table Text Block]	The following table presents the stock-based compensation expense included in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. The Utility Registrants' stock-based compensation expense for the years ended December 31, 2019 , 2018 and 2017 was not material. Exelon Year Ended December 31, Components of Stock-Based Compensation Expense 2019 2018 2017 Total stock-based compensation expense included in operating and maintenance expense $ 77 $ 208 $ 191 Income tax benefit (20 ) (54 ) (74 ) Total after-tax stock-based compensation expense $ 57 $ 154 $ 117 Generation Components of Stock-Based Compensation Expense Total stock-based compensation expense included in operating and maintenance expense $ 37 $ 77 $ 88 Income tax benefit (10 ) (20 ) (34 ) Total after-tax stock-based compensation expense $ 27 $ 57 $ 54
Stock Based Compensation Tax Benefit	The following table presents information regarding Exelon’s realized tax benefit when distributed: Year Ended December 31, 2019 2018 2017 Performance share awards $ 41 $ 16 $ 29 Restricted stock units 24 28 35
Schedule of Nonvested Performance-based Units Activity	The following table summarizes Exelon’s nonvested performance share awards activity: Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2018 (a) 3,403,228 $ 33.13 Granted 1,089,903 47.37 Change in performance (799,618 ) 40.85 Vested (1,610,146 ) 28.90 Forfeited (25,249 ) 45.03 Undistributed vested awards (b) (348,363 ) 48.82 Nonvested at December 31, 2019 (a) 1,709,755 $ 39.21 __________ (a) Excludes 2,017,870 and 3,586,259 of performance share awards issued to retirement-eligible employees as of December 31, 2019 and 2018 , respectively, as they are fully vested. (b) Represents performance share awards that vested but were not distributed to retirement-eligible employees during 2019 . The following table summarizes the weighted average grant date fair value and the total fair value of performance share awards granted and settled. Year Ended December 31, 2019 (a) 2018 2017 Weighted average grant date fair value (per share) $ 47.37 $ 38.15 $ 35.00 Total fair value of performance shares settled 158 61 72 Total fair value of performance shares settled in cash 131 49 56 __________ (a) As of December 31, 2019 , $17 million of total unrecognized compensation costs related to nonvested performance shares are expected to be recognized over the remaining weighted-average period of 1.6 years .
Schedule of Nonvested Restricted Stock Units Activity	The following table summarizes Exelon’s nonvested restricted stock unit activity: Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2018 (a) 2,293,341 $ 35.06 Granted 902,857 45.65 Vested (1,232,704 ) 32.83 Forfeited (33,603 ) 39.01 Undistributed vested awards (b) (431,178 ) 44.75 Nonvested at December 31, 2019 (a) 1,498,713 $ 40.35 __________ (a) Excludes 863,196 and 1,131,487 of restricted stock units issued to retirement-eligible employees as of December 31, 2019 and 2018 , respectively, as they are fully vested. (b) Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2019 . The following table summarizes the weighted average grant date fair value and the total fair value of restricted stock units granted and vested. Year Ended December 31, 2019 (a) 2018 2017 Weighted average grant date fair value (per share) $ 45.65 $ 38.60 $ 34.98 Total fair value of restricted stock units vested 92 106 88 __________ (a) As of December 31, 2019 , $28 million of total unrecognized compensation costs related to nonvested restricted stock units are expected to be recognized over the remaining weighted-average period of 2.8 years .
Schedule of Share-based Compensation, Stock Options, Activity	The following table presents information with respect to stock option activity: Shares Weighted Average Exercise Price (per share) Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value Balance of shares outstanding at December 31, 2018 4,027,652 $ 43.95 2.90 $ 14 Options exercised (1,388,165 ) 42.25 Options expired (750,442 ) 55.96 Balance of shares outstanding at December 31, 2019 1,889,045 $ 40.43 1.56 $ 10 Exercisable at December 31, 2019 (a) 1,889,045 $ 40.43 1.56 $ 10 __________ (a) Includes stock options issued to retirement eligible employees.
Stock Options Exercised	The following table summarizes additional information regarding stock options exercised: Year Ended December 31, 2019 2018 2017 Intrinsic value (a) $ 9 $ 12 $ 15 Cash received for exercise price 59 56 107 __________ (a) The difference between the market value on the date of exercise and the option exercise price.

Changes in Accumulated Other _2

Changes in Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Schedule Of Changes In Accumulated Other Comprehensive Income (Loss)	The following tables present changes in Exelon's AOCI, net of tax, by component: Gains and Unrealized Pension and (a) Foreign AOCI of Investments (b) Total Balance at December 31, 2016 $ (17 ) $ 4 $ (2,610 ) $ (30 ) $ (7 ) $ (2,660 ) OCI before reclassifications (1 ) 6 11 7 6 29 Amounts reclassified from AOCI 4 — 140 — — 144 Net current-period OCI 3 6 151 7 6 173 Impact of adoption of Reclassification of Certain Tax Effects from AOCI (c) — — (539 ) — — (539 ) Balance at December 31, 2017 $ (14 ) $ 10 $ (2,998 ) $ (23 ) $ (1 ) $ (3,026 ) OCI before reclassifications 11 — (143 ) (10 ) 1 (141 ) Amounts reclassified from AOCI 1 — 181 — — 182 Net current-period OCI 12 — 38 (10 ) 1 41 Impact of adoption of Recognition and Measurement of Financial Assets and Financial Liabilities standard (d) — (10 ) — — — (10 ) Balance at December 31, 2018 $ (2 ) $ — $ (2,960 ) $ (33 ) $ — $ (2,995 ) OCI before reclassifications — — (289 ) 6 (2 ) (285 ) Amounts reclassified from AOCI — — 84 — 2 86 Net current-period OCI — — (205 ) 6 — (199 ) Balance at December 31, 2019 $ (2 ) $ — $ (3,165 ) $ (27 ) $ — $ (3,194 ) __________ (a) This AOCI component is included in the computation of net periodic pension and OPEB cost. See Note 14 — Retirement Benefits for additional information. See Exelon's Statements of Operations and Comprehensive Income for individual components of AOCI. (b) All amounts are net of noncontrolling interests. (c) 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. (d) Exelon prospectively adopted the new standard Recognition and Measurement of Financial Assets and Financial 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 for Exelon. The amounts reclassified related to Rabbi Trusts.
Schedule of Income Taxes Allocated to Other Comprehensive Income (Loss) Components	The following table presents income tax benefit (expense) allocated to each component of Exelon's other comprehensive income (loss): For the Year Ended December 31, 2019 2018 2017 Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 23 $ 24 $ 36 Actuarial loss reclassified to periodic benefit cost (52 ) (86 ) (128 ) Pension and non-pension postretirement benefit plans valuation adjustment 100 50 13

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	12 Months Ended
	Dec. 31, 2019
Variable Interest Entity [Abstract]
Assets and Liabilities of Variable Interest Entity [Table Text Block]	The table below shows the carrying amounts and classification of the consolidated VIEs’ assets and liabilities included in the consolidated financial statements of Exelon, Generation, PHI and ACE as of December 31, 2019 and 2018 . The assets, except as noted in the footnotes to the table below, can only be used to settle obligations of the VIEs. The liabilities, except as noted in the footnotes to the table below, are such that creditors, or beneficiaries, do not have recourse to the general credit of Exelon, Generation, PHI and ACE. December 31, 2019 December 31, 2018 Exelon (a) Generation PHI (a) ACE Exelon Generation PHI ACE Cash and cash equivalents $ 163 $ 163 $ — $ — $ 414 $ 414 $ — $ — Restricted cash and cash equivalents 88 85 3 3 66 62 4 4 Accounts receivable, net Customer 151 151 — — 146 146 — — Other 39 39 — — 23 23 — — Unamortized energy contract asset (b) 23 23 — — 25 25 — — Inventories, net Materials and supplies 227 227 — — 212 212 — — Other current assets 32 31 1 — 52 49 3 — Total current assets 723 719 4 3 938 931 7 4 Property, plant and equipment, net (c) 6,022 6,022 — — 6,188 6,188 — — Nuclear decommissioning trust funds 2,741 2,741 — — 2,351 2,351 — — Unamortized energy contract asset (b) 250 250 — — 274 274 — — Other noncurrent assets 89 73 16 14 258 232 26 19 Total noncurrent assets 9,102 9,086 16 14 9,071 9,045 26 19 Total assets $ 9,825 $ 9,805 $ 20 $ 17 $ 10,009 $ 9,976 $ 33 $ 23 Long-term debt due within one year $ 544 $ 523 $ 21 $ 20 $ 87 $ 66 $ 21 $ 18 Accounts payable 106 106 — — 96 96 — — Accrued expenses 70 70 — — 73 72 1 1 Unamortized energy contract liabilities 8 8 — — 15 15 — — Other current liabilities 3 3 — — 3 3 — — Total current liabilities 731 710 21 20 274 252 22 19 Long-term debt 527 504 23 21 1,072 1,025 47 40 Asset retirement obligations (d) 2,128 2,128 — — 2,165 2,165 — — Unamortized energy contract liabilities 1 1 — — 1 1 — — Other noncurrent liabilities 89 89 — — 42 42 — — Total noncurrent liabilities 2,745 2,722 23 21 3,280 3,233 47 40 Total liabilities $ 3,476 $ 3,432 $ 44 $ 41 $ 3,554 $ 3,485 $ 69 $ 59 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. (b) These are unrestricted assets to Exelon and Generation. (c) Exelon's and Generation's balances include unrestricted assets of $ 20 million and $ 43 million as of December 31, 2019 and 2018 , respectively. (d) Exelon's and Generation's balances include liabilities with recourse of $ 3 million and $ 5 million as of December 31, 2019 and 2018 , respectively.
Schedule of Variable Interest Entities	The following table presents summary information about Exelon and Generation’s significant unconsolidated VIE entities: December 31, 2019 December 31, 2018 Commercial Agreement VIEs Equity Investment VIEs Total Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 636 $ 443 $ 1,079 $ 597 $ 472 $ 1,069 Total liabilities (a) 33 227 260 37 222 259 Exelon's ownership interest in VIE (a) — 191 191 — 223 223 Other ownership interests in VIE (a) 604 25 629 560 27 587 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — — — — 223 223 __________ (a) These items represent amounts on 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.

Supplemental Financial Inform_2

Supplemental Financial Information (Tables)	12 Months Ended
	Dec. 31, 2019
Supplemental Financial Information [Abstract]
Schedule Of Taxes Excluding Income And Excise Taxes [Table Text Block]	The following tables provide additional information about material items recorded in the Registrants' Consolidated Statements of Operations and Comprehensive Income. Taxes other than income taxes Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE For the year ended December 31, 2019 Utility (a) $ 881 $ 112 $ 242 $ 132 $ 90 $ 304 $ 286 $ 18 $ — Property 595 274 29 17 153 122 85 34 2 Payroll 232 115 27 15 17 24 7 4 2 For the year ended December 31, 2018 Utility (a) $ 919 $ 114 $ 243 $ 131 $ 94 $ 337 $ 316 $ 21 $ — Property 557 273 30 15 143 94 58 32 3 Payroll 247 130 27 16 17 24 5 3 2 For the year ended December 31, 2017 Utility (a) $ 898 $ 126 $ 240 $ 125 $ 89 $ 318 $ 300 $ 18 $ — Property 545 269 28 14 132 101 62 32 3 Payroll 230 121 26 15 15 26 6 4 2 __________ (a) Generation’s utility tax represents gross receipts tax related to its retail operations and the Utility Registrants’ utility taxes represents municipal and state utility taxes and gross receipts taxes related to their operating revenues.
Schedule of Other Nonoperating Income, by Component [Table Text Block]	Other, Net Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE For the year ended December 31, 2019 Decommissioning-related activities: Net realized income on NDT funds (a) Regulatory agreement units $ 297 $ 297 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 363 363 — — — — — — — Net unrealized gains on NDT funds Regulatory agreement units 795 795 — — — — — — — Non-regulatory agreement units 411 411 — — — — — — — Regulatory offset to NDT fund-related activities (b) (876 ) (876 ) — — — — — — — Decommissioning-related activities 990 990 — — — — — — — AFUDC—Equity 85 — 17 13 21 34 25 4 5 Non-service net periodic benefit cost 13 — — — — — — — — For the year ended December 31, 2018 Decommissioning-related activities: Net realized income on NDT funds (a) Regulatory agreement units $ 506 $ 506 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 302 302 — — — — — — — Net unrealized losses on NDT funds Regulatory agreement units (715 ) (715 ) — — — — — — — Non-regulatory agreement units (483 ) (483 ) — — — — — — — Regulatory offset to NDT fund-related activities (b) 171 171 — — — — — — — Decommissioning-related activities (219 ) (219 ) — — — — — — — AFUDC—Equity 69 — 19 7 18 25 22 2 1 Non-service net periodic benefit cost (47 ) — — — — — — — — For the year ended December 31, 2017 Decommissioning-related activities: Net realized income on NDT funds (a) Regulatory agreement units $ 488 $ 488 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 209 209 — — — — — — — Net unrealized gains on NDT funds Regulatory agreement units 455 455 — — — — — — — Non-regulatory agreement units 521 521 — — — — — — — Regulatory offset to NDT fund-related activities (b) (724 ) (724 ) — — — — — — — Decommissioning-related activities 949 949 — — — — — — — AFUDC—Equity 73 — 12 9 16 36 23 7 6 Non-service net periodic benefit cost (109 ) — — — — — — — — __________ (a) Realized income includes interest, dividends and realized gains and losses on sales of NDT fund investments. (b) Includes the elimination of decommissioning-related activities for the Regulatory Agreement Units, including the elimination of income taxes related to all NDT fund activity for those units. See Note 9 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.
Cash Flow Supplemental Disclosures	The following tables provide additional information about material items recorded in the Registrants' Consolidated Statements of Cash Flows. Depreciation, amortization and accretion Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE For the year ended December 31, 2019 Property, plant and equipment $ 3,665 $ 1,485 $ 886 $ 303 $ 359 $ 547 $ 239 $ 146 $ 123 Amortization of regulatory assets 528 — 147 30 143 207 135 38 34 Amortization of intangible assets, net 59 50 — — — — — — — Amortization of energy contract assets and liabilities (a) 21 21 — — — — — — — Nuclear fuel (b) 1,016 1,016 — — — — — — — ARO accretion (c) 491 491 — — — — — — — Total depreciation, amortization and accretion $ 5,780 $ 3,063 $ 1,033 $ 333 $ 502 $ 754 $ 374 $ 184 $ 157 For the year ended December 31, 2018 Property, plant and equipment $ 3,740 $ 1,748 $ 820 $ 274 $ 335 $ 480 $ 218 $ 131 $ 94 Amortization of regulatory assets 555 — 120 27 148 260 167 51 42 Amortization of intangible assets, net 58 49 — — — — — — — Amortization of energy contract assets and liabilities (a) 14 14 — — — — — — — Nuclear fuel (b) 1,115 1,115 — — — — — — — ARO accretion (c) 489 489 — — — — — — — Total depreciation, amortization and accretion $ 5,971 $ 3,415 $ 940 $ 301 $ 483 $ 740 $ 385 $ 182 $ 136 For the year ended December 31, 2017 Property, plant and equipment $ 3,293 $ 1,409 $ 777 $ 261 $ 312 $ 457 $ 203 $ 124 $ 89 Amortization of regulatory assets 478 — 73 25 161 218 118 43 57 Amortization of intangible assets, net 57 48 — — — — — — — Amortization of energy contract assets and liabilities (a) 35 35 — — — — — — — Nuclear fuel (b) 1,096 1,096 — — — — — — — ARO accretion (c) 468 468 — — — — — — — Total depreciation, amortization and accretion $ 5,427 $ 3,056 $ 850 $ 286 $ 473 $ 675 $ 321 $ 167 $ 146 __________ (a) Included in Operating revenues or Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (b) Included in Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (c) Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Cash paid (refunded) during the year: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE For the year ended December 31, 2019 Interest (net of amount capitalized) $ 1,470 $ 373 $ 343 $ 129 $ 106 $ 255 $ 130 $ 59 $ 55 Income taxes (net of refunds) 265 (44 ) (42 ) 82 17 29 7 19 (5 ) For the year ended December 31, 2018 Interest (net of amount capitalized) $ 1,421 $ 369 $ 332 $ 125 $ 94 $ 250 $ 123 $ 56 $ 61 Income taxes (net of refunds) 95 746 (153 ) (2 ) 14 (32 ) 41 (6 ) (12 ) For the year ended December 31, 2017 Interest (net of amount capitalized) $ 2,430 $ 391 $ 307 $ 103 $ 96 $ 236 $ 114 $ 49 $ 59 Income taxes (net of refunds) 540 337 83 47 (2 ) (144 ) (104 ) (49 ) (2 ) Other non-cash operating activities: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE For the year ended December 31, 2019 Pension and non-pension postretirement benefit costs $ 438 $ 135 $ 96 $ 12 $ 61 $ 95 $ 25 $ 15 $ 16 Provision for uncollectible accounts 120 31 33 31 8 17 7 4 5 Other decommissioning-related activity (a) (506 ) (506 ) — — — — — — — Energy-related options (b) 22 22 — — — — — — — Amortization of rate stabilization deferral (4 ) — — — — (4 ) (4 ) — — Discrete impacts from EIMA and FEJA (d) 128 — 128 — — — — — — Long-term incentive plan 10 — — — — — — — — Amortization of operating ROU asset 244 172 3 — 30 33 8 8 4 Change in environmental liabilities 23 — — — — 23 23 — — For the year ended December 31, 2018 Pension and non-pension postretirement benefit costs $ 583 $ 204 $ 177 $ 18 $ 59 $ 67 $ 15 $ 6 $ 12 Provision for uncollectible accounts 159 48 40 33 10 28 11 6 11 Other decommissioning-related activity (a) (2 ) (2 ) — — — — — — — Energy-related options (b) 10 10 — — — — — — — Amortization of rate stabilization deferral 21 — — — — 21 21 — — Asset retirement costs 20 — — — — 20 22 (1 ) (1 ) Discrete impacts from EIMA and FEJA (d) 28 — 28 — — — — — — Long-term incentive plan 140 — — — — — — — — For the year ended December 31, 2017 Pension and non-pension postretirement benefit costs $ 643 $ 227 $ 176 $ 29 $ 62 $ 94 $ 25 $ 13 $ 13 Provision for uncollectible accounts 125 38 34 26 8 19 8 3 8 Other decommissioning-related activity (a) (313 ) (313 ) — — — — — — — Energy-related options (b) 7 7 — — — — — — — Amortization of rate stabilization deferral (3 ) — — — 7 (10 ) (10 ) — — Discrete impacts from EIMA and FEJA (d) (52 ) — (52 ) — — — — — — Vacation accrual adjustment (e) (68 ) (35 ) (12 ) — — (8 ) (8 ) — — Long-term incentive plan 109 — — — — — — — — Change in environmental liabilities 44 44 — — — — — — — __________ (a) Includes the elimination of decommissioning-related activities 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 9 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) See Note 2 - Mergers, Acquisitions and Dispositions for additional information. (d) Reflects the change in ComEd's distribution and energy efficiency formula rates . See Note 3 — Regulatory Matters for additional information. (e) On December 1, 2017, Exelon adopted a single, standard vacation accrual policy for all non-represented, non-craft (represented and craft policies remained unchanged) employees effective January 1, 2018. To reflect the new policy, Exelon recorded a one-time, $68 million pre-tax credit to expense to reverse 2018 vacation cost originally accrued throughout 2017 that was accrued ratably during 2018. 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. Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 Cash and cash equivalents $ 587 $ 303 $ 90 $ 21 $ 24 $ 131 $ 30 $ 13 $ 12 Restricted cash 358 146 150 6 1 36 33 — 2 Restricted cash included in other long-term assets 177 — 163 — — 14 — — 14 Total cash, cash equivalents and restricted cash $ 1,122 $ 449 $ 403 $ 27 $ 25 $ 181 $ 63 $ 13 $ 28 December 31, 2018 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 December 31, 2017 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 December 31, 2016 Cash and cash equivalents $ 635 $ 290 $ 56 $ 63 $ 23 $ 170 $ 9 $ 46 $ 101 Restricted cash 253 158 2 4 24 43 33 — 9 Restricted cash included in other long-term assets 26 — — — 3 23 — — 23 Total cash, cash equivalents and restricted cash $ 914 $ 448 $ 58 $ 67 $ 50 $ 236 $ 42 $ 46 $ 133
Supplemental Balance Sheet Disclosures [Text Block]	The following tables provide additional information about material items recorded in the Registrants' Consolidated Balance Sheets. Unbilled customer revenues (a) Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 $ 1,535 $ 807 $ 218 $ 146 $ 170 $ 194 $ 100 $ 61 $ 33 December 31, 2018 1,656 965 223 114 168 186 97 59 30 __________ (a) Unbilled customer revenues are classified in customer accounts receivables, net in Exelon's and the Utility Registrants' Consolidated Balance Sheets. Investments Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 Equity method investments: Other equity method investments $ 92 $ 71 $ 6 $ 8 $ — $ — $ — $ — $ — Other investments: Employee benefit trusts and investments (a) 262 54 — 19 7 135 110 — — Equity investments without readily determinable fair values 69 69 — — — — — — — Other available for sale debt security investments 41 41 — — — — — — — Total investments $ 464 $ 235 $ 6 $ 27 $ 7 $ 135 $ 110 $ — $ — December 31, 2018 Equity method investments: Distributed energy companies $ 180 $ 180 $ — $ — $ — $ — $ — $ — $ — Other equity method investments 87 71 6 8 — — — — — Total equity method investments 267 251 6 8 — — — — — Other investments: Employee benefit trusts and investments (a) 244 49 — 17 5 130 105 — — Equity investments without readily determinable fair values 72 72 — — — — — — — Other available for sale debt security investments 40 40 — — — — — — — Other 2 2 — — — — — — — Total investments $ 625 $ 414 $ 6 $ 25 $ 5 $ 130 $ 105 $ — $ — __________ (a) The Registrants’ debt and equity security investments are recorded at fair market value. Accrued expenses Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2019 Compensation-related accruals (a) $ 1,052 $ 422 $ 171 $ 58 $ 78 $ 101 $ 28 $ 19 $ 15 Taxes accrued 414 222 83 3 26 117 90 14 8 Interest accrued 337 65 110 37 46 49 23 8 12 December 31, 2018 Compensation-related accruals (a) $ 1,191 $ 479 $ 187 $ 49 $ 68 $ 99 $ 29 $ 19 $ 12 Taxes accrued 412 226 71 28 46 74 58 4 5 Interest accrued 334 77 105 33 39 50 25 8 12 __________ (a) Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits.

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Schedule of Related Party Transactions [Table Text Block]	The following table presents Generation’s Operating revenues from affiliates, which are primarily recorded as Purchased power from affiliates and an immaterial amount recorded as Operating and maintenance expense from affiliates at the Utility Registrants: For the Years Ended December 31, 2019 2018 2017 Operating revenues from affiliates: ComEd (a)(b) $ 369 $ 523 $ 121 PECO (c) 158 128 138 BGE (d) 289 260 388 PHI 353 355 463 Pepco (e) 264 206 255 DPL (f) 70 120 179 ACE (g) 19 29 29 Other 3 2 5 Total operating revenues from affiliates (Generation) $ 1,172 $ 1,268 $ 1,115 __________ (a) Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs and ZECs to ComEd. (b) For 2019 , ComEd’s Purchased power from Generation of $376 million is recorded as Operating revenues from ComEd of $369 million and Purchased power and fuel from ComEd of $7 million at Generation. For 2018 , ComEd’s Purchased power from Generation of $529 million is recorded as Operating revenues from ComEd of $523 million and Purchased power and fuel from ComEd of $6 million at Generation. (c) Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has a ten-year agreement with PECO to sell solar AECs. (d) Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. (e) Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC. (f) Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs. (g) Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process.
Related Party Transactions - BSC and PHISCO Service Companies [Table Text Block]	The following table presents the service company costs allocated to the Registrants: Operating and maintenance from affiliates Operating and maintenance Capitalized costs For the years ended December 31, For the years ended December 31, For the years ended December 31, 2019 2018 2017 2017 2019 2018 2017 Exelon BSC $ 516 $ 448 $ 330 PHISCO 72 79 — Generation BSC $ 570 $ 652 $ 689 $ — 66 67 98 ComEd BSC 263 265 270 — 148 135 118 PECO BSC 149 146 146 — 88 64 59 BGE BSC 157 157 152 — 126 79 54 PHI BSC 139 147 145 — 88 102 — PHISCO (a) — — — — 72 79 — Pepco BSC 85 89 53 — 38 40 — PHISCO (a) 124 137 5 219 33 32 — PES (b) — — — 29 — — — DPL BSC 52 51 31 — 25 28 — PHISCO (a) 100 111 — 165 20 25 — PES (b) — — — 9 — — — ACE BSC 42 42 25 — 19 20 — PHISCO (a) 90 98 — 135 19 21 — __________ (a) Due to the PHI entities' system conversion to Exelon's accounting systems on January 1, 2018, corporate support services received from PHISCO are reported in Operating and maintenance from affiliates and in Capitalized costs beginning in 2018. (b) PES performed underground transmission, distribution construction and maintenance services, including services that are treated as capital costs, for Pepco and DPL.
Related Party Transactions - Current Receivables From/Payables To Affiliates [Table Text Block]	The following tables present current receivables from affiliates and current payables to affiliates: December 31, 2019 Receivables from affiliates: Payables to affiliates: Generation Comed PECO BGE ACE BSC PHISCO Other Total Generation $ 27 $ — $ — $ — $ 67 $ — $ 23 $ 117 ComEd $ 78 (a) — — — 54 — 8 140 PECO 27 — — — 25 — 3 55 BGE 28 — — — 34 — 4 66 PHI — — — — — 4 — 10 14 Pepco 34 — — — — 16 15 1 66 DPL 7 — — — 3 10 11 1 32 ACE 7 — — — 7 10 1 25 Other 9 1 1 1 1 — — 13 Total $ 190 $ 28 $ 1 $ 1 $ 4 $ 217 $ 36 $ 51 $ 528 December 31, 2018 Receivables from affiliates: Payables to affiliates: Generation Comed BGE Pepco ACE BSC PHISCO Other Total Generation $ 19 $ — $ — $ — $ 95 $ — $ 25 $ 139 ComEd $ 69 (a) — — — 56 — 8 133 PECO 30 — — — — 26 — 3 59 BGE 24 — — — 38 — 3 65 PHI — — — — — 3 — 9 12 Pepco 28 — — — 19 14 1 62 DPL 7 — — 1 1 11 12 1 33 ACE 5 — — — 8 13 2 28 Other 10 1 1 — — — — 12 Total $ 173 $ 20 $ 1 $ 1 $ 1 $ 256 $ 39 $ 52 $ 543 __________ (a) At December 31, 2019 and 2018, Generation also had a contract liability with ComEd for $37 million and $14 million , respectively, that was included in Other liabilities on Generation’s Consolidated Balance Sheets. At December 31, 2019 and 2018, ComEd had a Current Payable to Generation of $41 million and $55 million , respectively, on its Consolidated Balance Sheets, which consisted of Generation’s Current Receivable from ComEd, partially offset by Generation’s contract liability with ComEd.
Related Party Transactions - Noncurrent Receivables from/Payables to affiliates [Table Text Block]	The following table presents noncurrent receivables from affiliates at ComEd and PECO which are recorded as noncurrent payables to affiliates at Generation: December 31, 2019 2018 ComEd $ 2,622 $ 2,217 PECO 480 389 Other 1 — Total: $ 3,103 $ 2,606
Related Party Transactions - Long Term Debt to Financing Trusts [Table Text Block]	The following table presents Long-term debt to financing trusts: As of December 31, 2019 2018 Exelon ComEd PECO Exelon ComEd PECO ComEd Financing III $ 206 $ 205 $ — $ 206 $ 205 $ — PECO Trust III 81 — 81 81 — 81 PECO Trust IV 103 — 103 103 — 103 Total $ 390 $ 205 $ 184 $ 390 $ 205 $ 184

Quarterly Data (Unaudited) (Tab

Quarterly Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Selected Quarterly Financial Information [Line Items]
Quarterly Financial Information	The data shown below, which may not equal the total for the year due to the effects of rounding and dilution, includes all adjustments that Exelon considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 9,477 $ 9,691 $ 1,218 $ 1,099 $ 907 $ 583 June 30 7,689 8,074 841 940 484 537 September 30 8,929 9,401 1,353 1,144 772 731 December 31 (a) 8,343 8,812 962 706 773 152 Net Income Net Income 2019 2018 2019 2018 Quarter ended: March 31 $ 0.93 $ 0.60 $ 0.93 $ 0.60 June 30 0.50 0.56 0.50 0.55 September 30 0.79 0.76 0.79 0.75 December 31 0.79 0.16 0.79 0.16 __________ (a) Operating revenues, Operating income and Net income attributable to common shareholders for the quarter ended December 31, 2019 include a $6 million reduction related to a correction for Pepco’s decoupling mechanism for the 2019 interim periods. See Note 1 — Significant Accounting Policies for additional information.
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Quarterly Financial Information	The data shown below includes all adjustments that Generation considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income (Loss) 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 5,296 $ 5,512 $ 333 $ 347 $ 363 $ 136 June 30 4,210 4,579 147 282 108 178 September 30 4,774 5,278 482 311 257 234 December 31 4,644 5,069 362 35 397 (178 )
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Quarterly Financial Information	The data shown below includes all adjustments that ComEd considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 1,408 $ 1,512 $ 276 $ 292 $ 157 $ 165 June 30 1,351 1,398 311 288 186 164 September 30 1,583 1,598 328 323 200 193 December 31 1,405 1,373 255 242 144 141
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Quarterly Financial Information	The data shown below includes all adjustments that PECO considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 900 $ 866 $ 222 $ 142 $ 168 $ 113 June 30 655 653 145 127 102 96 September 30 778 757 183 154 140 126 December 31 766 765 162 165 118 124
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Quarterly Financial Information	The data shown below includes all adjustments that BGE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 976 $ 977 $ 220 $ 177 $ 160 $ 128 June 30 649 662 80 85 45 51 September 30 703 731 91 103 55 63 December 31 779 799 142 109 99 71
Pepco Holdings LLC [Member]
Selected Quarterly Financial Information [Line Items]
Quarterly Financial Information	PHI The data shown below includes all adjustments that PHI considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 1,228 $ 1,249 $ 175 $ 124 $ 117 $ 63 June 30 1,091 1,074 165 151 106 82 September 30 1,380 1,359 256 243 189 185 December 31 (a) 1,107 1,115 128 124 65 62 __________ (a) Operating revenues, Operating income and Net income attributable to common shareholders for the quarter ended December 31, 2019 include a $6 million reduction related to a correction for Pepco’s decoupling mechanism for the 2019 interim periods. See Note 1 — Significant Accounting Policies for additional information.
Potomac Electric Power Company [Member]
Selected Quarterly Financial Information [Line Items]
Quarterly Financial Information	The data shown below includes all adjustments that Pepco considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 575 $ 555 $ 84 $ 54 $ 55 $ 29 June 30 531 521 93 83 64 52 September 30 642 626 127 110 98 87 December 31 (a) 513 529 57 63 26 36 _________ (a) Operating revenues, Operating income and Net income attributable to common shareholders for the quarter ended December 31, 2019 include a $6 million reduction related to a correction for Pepco’s decoupling mechanism for the 2019 interim periods. See Note 1 — Significant Accounting Policies for additional information.
Delmarva Power & Light Company [Member]
Selected Quarterly Financial Information [Line Items]
Quarterly Financial Information	The data shown below includes all adjustments that DPL considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 380 $ 384 $ 72 $ 49 $ 53 $ 31 June 30 287 289 44 42 30 26 September 30 319 328 51 51 33 33 December 31 319 331 50 48 31 30
Atlantic City Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Quarterly Financial Information	The data shown below includes all adjustments that ACE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income (Loss) 2019 2018 2019 2018 2019 2018 Quarter ended: March 31 $ 273 $ 310 $ 21 $ 23 $ 10 $ 7 June 30 274 265 28 25 14 8 September 30 419 406 79 84 63 61 December 31 274 254 23 14 12 (1 )

Significant Accounting Polici_3

Significant Accounting Policies - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2017
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	100.00%
Minimum expectation of tax position to be realized	50.00%
Restatement Adjustment [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Impact of Prior Period Adjustment on Opening Retained Earnings, Net of Tax				$ 11
Impact of Prior Period Adjustment on Opening Regulatory Assets				18
Impact of Prior Period Adjustment on Deferred Income Taxes and Unamortized Investment Tax Credits				7
Prior Period Adjustment of Operating Revenues		$ 7	$ 7
Impact of Prior Period Adjustment on Prior Year Income, Net of Tax		$ 5	$ 7
Impact of Prior Period Adjustment on Earnings Per Share, Basic		$ 0.01	$ 0.01
Impact of Prior Period Adjustment on Earnings Per Share, Diluted		$ 0	$ 0.01
Restatement Adjustment [Member] | Pepco Holdings LLC [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Impact of Prior Period Adjustment on Opening Retained Earnings, Net of Tax				11
Impact of Prior Period Adjustment on Opening Regulatory Assets				18
Impact of Prior Period Adjustment on Deferred Income Taxes and Unamortized Investment Tax Credits				7
Prior Period Adjustment of Operating Revenues		$ 7	$ 7
Impact of Prior Period Adjustment on Prior Year Income, Net of Tax		5	7
Restatement Adjustment [Member] | Potomac Electric Power Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Impact of Prior Period Adjustment on Opening Retained Earnings, Net of Tax				11
Impact of Prior Period Adjustment on Opening Regulatory Assets				18
Impact of Prior Period Adjustment on Deferred Income Taxes and Unamortized Investment Tax Credits				$ 7
Prior Period Adjustment of Operating Revenues		7	7
Impact of Prior Period Adjustment on Prior Year Income, Net of Tax		$ 5	$ 7
Commonwealth Edison Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	99.00%
CENG [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	50.01%
ExGen Renewables [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	51.00%
Minimum [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	20.00%
Maximum [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	50.00%

Mergers, Acquisitions and Dis_2

Mergers, Acquisitions and Dispositions - Acquisitions Narrative (Details) - USD ($) $ in Millions	Apr. 04, 2018	Mar. 31, 2017	Apr. 01, 2014	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross				$ 41	$ 154	$ 208
Business Combination, Bargain Purchase, Gain Recognized, Amount				0	0	233
Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		$ 289
Business Combination, Consideration Transferred, Other		179
Business Combination, Bargain Purchase, Gain Recognized, Amount						233
Business Combination, Integration Related Costs						57
Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		110
Handley [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	$ 62
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross				41	154	208
Business Combination, Bargain Purchase, Gain Recognized, Amount				$ 0	$ 0	233
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		289
Business Combination, Consideration Transferred, Other		179
Business Combination, Bargain Purchase, Gain Recognized, Amount						233
Business Combination, Integration Related Costs						$ 57
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		$ 110
Exelon Generation Co L L C [Member] | Handley [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	$ 62
CENG [Member]
Business Acquisition [Line Items]
Ownership Percentage Of Consolidated Variable Interest Entities				50.01%
Payments of Capital Distribution			$ 400
Due from Affiliates			400	$ 571
CENG Preferred Distribution Return				8.50%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners				49.99%
CENG [Member] | Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Ownership Percentage Of Consolidated Variable Interest Entities				50.01%
Payments of Capital Distribution			400
Due from Affiliates			$ 400	$ 571
CENG Preferred Distribution Return				8.50%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners				49.99%
Nine Mile Point [Member]
Business Acquisition [Line Items]
Ownership Percentage Of Consolidated Variable Interest Entities				82.00%
Nine Mile Point [Member] | Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Ownership Percentage Of Consolidated Variable Interest Entities				82.00%

Mergers, Acquisitions and Dis_3

Mergers, Acquisitions and Dispositions - Dispositions Narrative (Details) $ in Millions	Feb. 28, 2018USD ($)	Nov. 07, 2017USD ($)	Jun. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Dec. 31, 2019USD ($)GW	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Business Dispositions [Line Items]
Disposal Group, Including Discontinued Operation, Assets, Current						$ 0	$ 904
Disposal Group, Including Discontinued Operation, Liabilities, Current						0	777
Asset Retirement Obligation, Revision of Estimate							20
Impairment of Long-Lived Assets Held-for-use						201	50	$ 573
Deconsolidation, Gain (Loss), Amount						0	0	213
Operating Expense [Member]
Business Dispositions [Line Items]
Asset Retirement Obligation, Revision of Estimate						(150)
ExGen Texas Power [Member]
Business Dispositions [Line Items]
Deconsolidation, Gain (Loss), Amount		$ 213
Oyster Creek [Member]
Business Dispositions [Line Items]
Disposal Group, Including Discontinued Operation, Assets, Current							897
Disposal Group, Including Discontinued Operation, Liabilities, Current							777
Oyster Creek [Member] | Operating Expense [Member]
Business Dispositions [Line Items]
Asset Retirement Obligation, Revision of Estimate			$ 9	$ 84
Electrical Contracting Business [Member]
Business Dispositions [Line Items]
Proceeds from Divestiture of Businesses	$ 87
Exelon Generation Co L L C [Member]
Business Dispositions [Line Items]
Disposal Group, Including Discontinued Operation, Assets, Current						0	904
Disposal Group, Including Discontinued Operation, Liabilities, Current						0	777
Asset Retirement Obligation, Revision of Estimate							0
Impairment of Long-Lived Assets Held-for-use						201	50	510
Deconsolidation, Gain (Loss), Amount						0	0	$ 213
Exelon Generation Co L L C [Member] | Operating Expense [Member]
Business Dispositions [Line Items]
Asset Retirement Obligation, Revision of Estimate						$ (150)
Exelon Generation Co L L C [Member] | ExGen Texas Power [Member]
Business Dispositions [Line Items]
Impairment of Long-Lived Assets Held-for-use					$ 460
Generating Capacity | GW						3.4
Deconsolidation, Gain (Loss), Amount		$ 213
Exelon Generation Co L L C [Member] | Oyster Creek [Member]
Business Dispositions [Line Items]
Disposal Group, Including Discontinued Operation, Assets, Current							897
Disposal Group, Including Discontinued Operation, Liabilities, Current							$ 777
Exelon Generation Co L L C [Member] | Oyster Creek [Member] | Operating Expense [Member]
Business Dispositions [Line Items]
Asset Retirement Obligation, Revision of Estimate			$ 9	$ 84
Exelon Generation Co L L C [Member] | Electrical Contracting Business [Member]
Business Dispositions [Line Items]
Proceeds from Divestiture of Businesses	$ 87

Regulatory Matters- Narrative (

Regulatory Matters- Narrative (Details)	Dec. 05, 2019USD ($)	Nov. 26, 2019USD ($)	May 23, 2019	Jun. 27, 2017USD ($)	Apr. 30, 2016USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Sep. 30, 2017USD ($)	Mar. 31, 2013USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2024USD ($)	Jun. 30, 2023USD ($)	Dec. 31, 2022USD ($)	Dec. 31, 2023USD ($)	Jul. 10, 2023USD ($)	Jul. 21, 2017USD ($)
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities						$ 10,392,000,000				$ 10,203,000,000								$ 10,392,000,000	$ 10,203,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets										35,000,000									35,000,000
Regulatory Assets						9,505,000,000				9,427,000,000								9,505,000,000	9,427,000,000
Payments to Acquire Property, Plant, and Equipment														$ 4,000,000	$ 24,000,000
Accounts Payable, Current						3,560,000,000				3,800,000,000								3,560,000,000	3,800,000,000
Revenues						8,343,000,000	$ 8,929,000,000	$ 7,689,000,000	$ 9,477,000,000	8,812,000,000	$ 9,401,000,000	$ 8,074,000,000	$ 9,691,000,000					34,438,000,000	35,978,000,000	$ 33,558,000,000
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Equity Capital Structure, Percentage	7.62%
Public Utilities, Requested Equity Capital Structure, Percentage	10.35%			11.00%
Additional basis points for RTO membership incentive	50			50
Regulatory Liabilities						601,000,000				596,000,000								601,000,000	596,000,000
Annual Reconciliation Increase (Decrease)																		8,000,000	(6,000,000)
Regulatory Assets						595,000,000				541,000,000								595,000,000	541,000,000
Payments to Acquire Property, Plant, and Equipment	$ 14,000,000			$ 22,000,000
Accounts Payable, Current						387,000,000				370,000,000								387,000,000	370,000,000
Revenues						766,000,000	778,000,000	655,000,000	900,000,000	765,000,000	757,000,000	653,000,000	866,000,000					$ 3,100,000,000	3,038,000,000	2,870,000,000
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Equity Capital Structure, Percentage																		8.21%
Public Utilities, Requested Equity Capital Structure, Percentage			6.51%
Additional basis points for RTO membership incentive																		50
Regulatory Liabilities						6,742,000,000				6,343,000,000								$ 6,742,000,000	6,343,000,000
Annual Reconciliation Increase (Decrease)																		(16,000,000)
Amount of Impairment to Carrying Amount of Regulatory Assets										3,000,000									3,000,000
Regulatory Assets						1,761,000,000				1,600,000,000								1,761,000,000	1,600,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount																		21,000,000
Payments to Acquire Property, Plant, and Equipment		$ 50,000,000																53,000,000	(3,000,000)
Accounts Payable, Current						527,000,000				607,000,000								527,000,000	607,000,000
Purchase Obligation																										$ 170,000,000
Revenues						1,405,000,000	1,583,000,000	1,351,000,000	1,408,000,000	1,373,000,000	1,598,000,000	1,398,000,000	1,512,000,000					$ 5,747,000,000	5,882,000,000	5,536,000,000
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Equity Capital Structure, Percentage																		7.35%
Additional basis points for RTO membership incentive																		50
Regulatory Liabilities						1,228,000,000				1,269,000,000								$ 1,228,000,000	1,269,000,000
Annual Reconciliation Increase (Decrease)																		(23,000,000)
Amount of Impairment to Carrying Amount of Regulatory Assets										5,000,000									5,000,000
Regulatory Assets						637,000,000				575,000,000								637,000,000	575,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount																		(10,000,000)
Accounts Payable, Current						243,000,000				295,000,000								243,000,000	295,000,000
Revenues						779,000,000	703,000,000	649,000,000	976,000,000	799,000,000	731,000,000	662,000,000	977,000,000					3,106,000,000	3,169,000,000	3,176,000,000
Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities						1,777,000,000				1,948,000,000								1,777,000,000	1,948,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets										27,000,000									27,000,000
Regulatory Assets						2,473,000,000				2,769,000,000								2,473,000,000	2,769,000,000
Accounts Payable, Current						462,000,000				496,000,000								462,000,000	496,000,000
Revenues						1,107,000,000	1,380,000,000	1,091,000,000	1,228,000,000	1,115,000,000	1,359,000,000	1,074,000,000	1,249,000,000					$ 4,806,000,000	4,798,000,000	4,672,000,000
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Equity Capital Structure, Percentage																		7.75%
Additional basis points for RTO membership incentive																		50
Regulatory Liabilities						754,000,000				829,000,000								$ 754,000,000	829,000,000
Annual Reconciliation Increase (Decrease)																		11,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets										14,000,000									14,000,000
Regulatory Assets						772,000,000				881,000,000								772,000,000	881,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount																		15,000,000
Accounts Payable, Current						195,000,000				214,000,000								195,000,000	214,000,000
Revenues						513,000,000	642,000,000	531,000,000	575,000,000	529,000,000	626,000,000	521,000,000	555,000,000					$ 2,260,000,000	2,232,000,000	2,151,000,000
Delmarva Power & Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Equity Capital Structure, Percentage																		7.14%
Additional basis points for RTO membership incentive																		50
Regulatory Liabilities						611,000,000				665,000,000								$ 611,000,000	665,000,000
Annual Reconciliation Increase (Decrease)																		(1,000,000)
Amount of Impairment to Carrying Amount of Regulatory Assets										6,000,000									6,000,000
Regulatory Assets						274,000,000				290,000,000								274,000,000	290,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount																		17,000,000
Accounts Payable, Current						112,000,000				111,000,000								112,000,000	111,000,000
Revenues						319,000,000	319,000,000	287,000,000	380,000,000	331,000,000	328,000,000	289,000,000	384,000,000					$ 1,306,000,000	1,332,000,000	1,300,000,000
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Equity Capital Structure, Percentage																		7.79%
Additional basis points for RTO membership incentive																		50
Regulatory Liabilities						382,000,000				420,000,000								$ 382,000,000	420,000,000
Annual Reconciliation Increase (Decrease)																		(2,000,000)
Amount of Impairment to Carrying Amount of Regulatory Assets										7,000,000									7,000,000
Regulatory Assets						425,000,000				426,000,000								425,000,000	426,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount																		11,000,000
Accounts Payable, Current						144,000,000				154,000,000								144,000,000	154,000,000
Revenues						274,000,000	419,000,000	274,000,000	273,000,000	254,000,000	406,000,000	265,000,000	310,000,000					1,240,000,000	1,236,000,000	1,186,000,000
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment														$ 4,000,000	$ 24,000,000
Accounts Payable, Current						1,692,000,000				1,847,000,000								1,692,000,000	1,847,000,000
Revenues						4,644,000,000	$ 4,774,000,000	$ 4,210,000,000	$ 5,296,000,000	5,069,000,000	$ 5,278,000,000	$ 4,579,000,000	$ 5,512,000,000					18,924,000,000	20,437,000,000	18,500,000,000
Under/Over Recovered Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						11,000,000				41,000,000								11,000,000	41,000,000
Under/Over Recovered Transmission Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities						28,000,000												28,000,000
Regulatory Assets						0				0								0	0
Under/Over Recovered Transmission Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						0				6,000,000								0	6,000,000
Under/Over Recovered Transmission Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						1,000,000				4,000,000								1,000,000	4,000,000
Under/Over Recovered Transmission Costs [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						10,000,000				31,000,000								10,000,000	31,000,000
Under/Over Recovered Transmission Costs [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						1,000,000				10,000,000								1,000,000	10,000,000
Under/Over Recovered Transmission Costs [Member] | Delmarva Power & Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						2,000,000				14,000,000								2,000,000	14,000,000
Under/Over Recovered Transmission Costs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						7,000,000				7,000,000								7,000,000	7,000,000
MergerIntegrationCostsToBeRecoveredInMarylandServiceTerritory [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						6,000,000				9,000,000								6,000,000	9,000,000
MergerIntegrationCostsToBeRecoveredInDCServiceTerritory [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						9,000,000				9,000,000								9,000,000	9,000,000
Difference between Carrying Value and Fair Value [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						127,000,000				133,000,000								127,000,000	133,000,000
Difference between Carrying Value and Fair Value [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						523,000,000				569,000,000								523,000,000	569,000,000
DC PLUG Charge [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						126,000,000				159,000,000								126,000,000	159,000,000
DC PLUG Charge [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						0				0								0	0
DC PLUG Charge [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						0				0								0	0
DC PLUG Charge [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						0				0								0	0
DC PLUG Charge [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						126,000,000				159,000,000								126,000,000	159,000,000
DC PLUG Charge [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						126,000,000				159,000,000								126,000,000	159,000,000
DC PLUG Charge [Member] | Delmarva Power & Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						0				0								0	0
DC PLUG Charge [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						0				0								0	0
AMI Expenses [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						32,000,000				10,000,000								32,000,000	10,000,000
Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						276,000,000				328,000,000								276,000,000	328,000,000
Advanced Metering Infrastructure Legacy Meter Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						12,000,000				24,000,000								12,000,000	24,000,000
Advanced Metering Infrastructure Legacy Meter Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						113,000,000				136,000,000								113,000,000	136,000,000
Advanced Metering Infrastructure Legacy Meter Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						45,000,000				48,000,000								45,000,000	48,000,000
Advanced Metering Infrastructure Legacy Meter Costs [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						106,000,000				120,000,000								106,000,000	120,000,000
Advanced Metering Infrastructure Legacy Meter Costs [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						79,000,000				90,000,000								79,000,000	90,000,000
Advanced Metering Infrastructure Legacy Meter Costs [Member] | Delmarva Power & Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						27,000,000				30,000,000								27,000,000	30,000,000
Advanced Metering Infrastructure Legacy Meter Costs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets						0				0								0	0
Maximum [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation						14,000,000												14,000,000
Minimum [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation						11,000,000												11,000,000
One-Time Revenue Adjustment [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets						79,000,000												79,000,000
One-Time Revenue Adjustment [Member] | Maximum [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets						51,000,000												51,000,000
One-Time Revenue Adjustment [Member] | Maximum [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets						17,000,000												17,000,000
One-Time Revenue Adjustment [Member] | Maximum [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets						11,000,000												11,000,000
One-Time Revenue Adjustment [Member] | Maximum [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets						4,000,000												4,000,000
One-Time Revenue Adjustment [Member] | Maximum [Member] | Delmarva Power & Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets						5,000,000												5,000,000
One-Time Revenue Adjustment [Member] | Maximum [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets						2,000,000												2,000,000
PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current										176,000,000									176,000,000
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current										0									0
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current										0									0
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current										51,000,000									51,000,000
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current										84,000,000									84,000,000
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current										84,000,000									84,000,000
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current										0									0
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current										0									0
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current										$ 41,000,000									41,000,000
Illinois Utilities [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation																										$ 235,000,000
Energy Commodities and Service [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax																		17,754,000,000	19,168,000,000	17,394,000,000
Energy Commodities and Service [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax																		17,752,000,000	19,169,000,000	$ 17,385,000,000
Zero Emission Standard [Member] | Energy Commodities and Service [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax																$ 150,000,000
Clean Energy Legislation [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Competitive businesses other revenues																		53,000,000
One-Time Revenue Adjustment [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenues					$ 101,000,000
Conowingo [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Environmental Costs Recognized, Capitalized						$ 42,000,000												$ 42,000,000
Nuclear Plant [Member] | Salem [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Ownership interest						42.59%												42.59%
Forecast [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Proposed Capital Expenditure																								$ 732,000,000
Payments to Acquire Property, Plant, and Equipment																								$ 200,000,000
Forecast [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Proposed Capital Expenditure																	$ 30,000,000				$ 67,000,000				$ 500,000,000
Forecast [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Proposed Capital Expenditure																							$ 338,000,000
Payments to Acquire Property, Plant, and Equipment																						$ 96,000,000
Forecast [Member] | DC PLUG Charge [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Proposed Capital Expenditure																									250,000,000
DISTRICT OF COLUMBIA | Forecast [Member] | DC PLUG Charge [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Proposed Capital Expenditure																									$ 250,000,000
ILLINOIS | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
exc_ZECChargeperMWh																			$ 16.50
NEW JERSEY | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
exc_ZECChargeperMWh																		$ 10
NEW YORK | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
exc_ZECChargeperMWh																		$ 17.48
CENG [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners						49.99%												49.99%
CENG [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners						49.99%												49.99%

Regulatory Matters - Schedule o

Regulatory Matters - Schedule of Completed Rate Cases (Details) $ in Millions	Dec. 17, 2019USD ($)	Dec. 05, 2019USD ($)	Dec. 04, 2019USD ($)	Nov. 26, 2019USD ($)	Aug. 12, 2019USD ($)	May 23, 2019USD ($)	May 16, 2019USD ($)	Apr. 08, 2019USD ($)	Mar. 13, 2019USD ($)	Jan. 04, 2019USD ($)	Dec. 20, 2018USD ($)	Dec. 04, 2018USD ($)	Nov. 19, 2018USD ($)	Oct. 12, 2018USD ($)	Apr. 16, 2018USD ($)	Mar. 29, 2018USD ($)	Jun. 27, 2017USD ($)	Sep. 30, 2017USD ($)	Mar. 31, 2013USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount																		$ 4	$ 24
Commonwealth Edison Co [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																				$ 21
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount						$ 51														5
Public Utilities, Approved Rate Increase (Decrease), Amount				$ 50																$ 53	$ (3)
Public Utilities, Approved Return on Equity, Percentage				8.91%																11.50%
Basis points for ComEd's Revenue Requirement						580
Public Utilities, Approved Equity Capital Structure, Percentage																				8.21%
Commonwealth Edison Co [Member] | Electric Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount								$ (6)							$ (23)
Public Utilities, Approved Rate Increase (Decrease), Amount			$ (17)									$ (24)									$ (68)	$ 34
Public Utilities, Approved Return on Equity, Percentage			8.91%									8.69%
Basis points for ComEd's Revenue Requirement																				580	580
Public Utilities, Approved Equity Capital Structure, Percentage																				6.51%	6.52%
Public Utilities, Interim Rate Increase (Decrease), Amount																				$ 51	$ (58)
PECO Energy Co [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 14															$ 22
Public Utilities, Approved Equity Capital Structure, Percentage		7.62%
PECO Energy Co [Member] | Electric Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																$ 82
Public Utilities, Approved Rate Increase (Decrease), Amount											$ 25
Baltimore Gas and Electric Company [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																				(10)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																				$ (19)
Public Utilities, Approved Return on Equity, Percentage																				10.50%
Public Utilities, Approved Equity Capital Structure, Percentage																				7.35%
Baltimore Gas and Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 59
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 45
Public Utilities, Approved Return on Equity, Percentage	9.75%
Baltimore Gas and Electric Company [Member] | Gas Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 74													$ 61
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 18									$ 43
Public Utilities, Approved Return on Equity, Percentage	9.70%									9.80%
Atlantic City Electric Company [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																				$ 11
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																				$ 9
Public Utilities, Approved Return on Equity, Percentage																				10.50%
Public Utilities, Approved Equity Capital Structure, Percentage																				7.79%
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount													$ 122
Public Utilities, Approved Rate Increase (Decrease), Amount									$ 70
Public Utilities, Approved Return on Equity, Percentage									9.60%
Potomac Electric Power Company [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																				$ 15
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																				$ 26
Public Utilities, Approved Return on Equity, Percentage																				10.50%
Public Utilities, Approved Equity Capital Structure, Percentage																				7.75%
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount							$ 27
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 10
Public Utilities, Approved Return on Equity, Percentage					9.60%

Regulatory Matters - Schedule_2

Regulatory Matters - Schedule of Pending Rate Cases (Details) - USD ($) $ in Millions	Dec. 05, 2019	Sep. 16, 2019	May 16, 2019	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Potomac Electric Power Company [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount							$ 26
Public Utilities, Requested Rate Increase (Decrease), Amount							15
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 27
Delmarva Power & Light Company [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount							16
Public Utilities, Requested Rate Increase (Decrease), Amount							$ 17
Delmarva Power & Light Company [Member] | Electric Distribution [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 19
Public Utilities, Requested Return on Equity, Percentage	10.30%
DISTRICT OF COLUMBIA | Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount		$ 160
Public Utilities, Requested Return on Equity, Percentage		10.30%
Forecast [Member] | DISTRICT OF COLUMBIA | Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 36	$ 40	$ 84

Regulatory Matters - Annual Ele

Regulatory Matters - Annual Electric Transmission Filings (Details) $ in Millions	Dec. 05, 2019USD ($)	Nov. 26, 2019USD ($)	May 23, 2019USD ($)	Jun. 27, 2017USD ($)	Sep. 30, 2017USD ($)	Mar. 31, 2013USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 4	$ 24
Commonwealth Edison Co [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 50					$ 53	$ (3)
Public Utilities, Requested Rate Increase (Decrease), Amount							21
Annual Reconciliation Increase (Decrease)							(16)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 51				$ 5
Public Utilities, Approved Equity Capital Structure, Percentage							8.21%
Public Utilities, Approved Return on Equity, Percentage		8.91%					11.50%
Additional basis points for RTO membership incentive							50
Cap on Equity Component of Rate of Return on Common Equity in Federal Energy Regulatory Committee Complaint							55.00%
PECO Energy Co [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 14			$ 22
Annual Reconciliation Increase (Decrease)							$ 8	$ (6)
Public Utilities, Approved Equity Capital Structure, Percentage	7.62%
Additional basis points for RTO membership incentive	50			50
Baltimore Gas and Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount							(10)
Annual Reconciliation Increase (Decrease)							(23)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount							$ (19)
Public Utilities, Approved Equity Capital Structure, Percentage							7.35%
Public Utilities, Approved Return on Equity, Percentage							10.50%
Additional basis points for RTO membership incentive							50
Potomac Electric Power Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount							$ 15
Annual Reconciliation Increase (Decrease)							11
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount							$ 26
Public Utilities, Approved Equity Capital Structure, Percentage							7.75%
Public Utilities, Approved Return on Equity, Percentage							10.50%
Additional basis points for RTO membership incentive							50
Delmarva Power & Light Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount							$ 17
Annual Reconciliation Increase (Decrease)							(1)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount							$ 16
Public Utilities, Approved Equity Capital Structure, Percentage							7.14%
Public Utilities, Approved Return on Equity, Percentage							10.50%
Additional basis points for RTO membership incentive							50
Atlantic City Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount							$ 11
Annual Reconciliation Increase (Decrease)							(2)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount							$ 9
Public Utilities, Approved Equity Capital Structure, Percentage							7.79%
Public Utilities, Approved Return on Equity, Percentage							10.50%
Additional basis points for RTO membership incentive							50
Electric Transmission [Member] | Baltimore Gas and Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount							$ 14

Regulatory Matters - Energy Eff

Regulatory Matters - Energy Efficiency Formula Rate (Details) $ in Millions	Dec. 04, 2019USD ($)	Nov. 26, 2019USD ($)	May 23, 2019USD ($)	Dec. 04, 2018USD ($)	Sep. 30, 2017USD ($)	Mar. 31, 2013USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Schedule of Energy Efficiency Formula Rate Updates [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 4	$ 24
Commonwealth Edison Co [Member]
Schedule of Energy Efficiency Formula Rate Updates [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 50					$ 53	$ (3)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 51				$ 5
Public Utilities, Requested Equity Capital Structure, Percentage			6.51%
Public Utilities, Approved Return on Equity, Percentage		8.91%					11.50%
Basis points for ComEd's Revenue Requirement			580
Electric Distribution [Member] | Commonwealth Edison Co [Member]
Schedule of Energy Efficiency Formula Rate Updates [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ (17)			$ (24)				$ (68)	$ 34
Public Utilities, Approved Return on Equity, Percentage	8.91%			8.69%
Basis points for ComEd's Revenue Requirement							580	580

Regulatory Matters - Estimated

Regulatory Matters - Estimated Commitments related to PJM Agreements (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Other Commitments [Line Items]
Other Receivables	$ 1,583	$ 1,256
Accounts Payable, Current	3,560	3,800
Regulatory Assets	9,505	9,427
Regulatory Liabilities	10,392	10,203
Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Receivables	619	562
Accounts Payable, Current	1,692	1,847
Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Other Receivables	286	320
Accounts Payable, Current	527	607
Regulatory Assets	1,761	1,600
Regulatory Liabilities	6,742	6,343
PECO Energy Co [Member]
Other Commitments [Line Items]
Other Receivables	138	151
Accounts Payable, Current	387	370
Regulatory Assets	595	541
Regulatory Liabilities	601	596
Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Receivables	147	90
Accounts Payable, Current	243	295
Regulatory Assets	637	575
Regulatory Liabilities	1,228	1,269
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Receivables	174	177
Accounts Payable, Current	462	496
Regulatory Assets	2,473	2,769
Regulatory Liabilities	1,777	1,948
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Receivables	91	81
Accounts Payable, Current	195	214
Regulatory Assets	772	881
Regulatory Liabilities	754	829
Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Other Receivables	38	46
Accounts Payable, Current	112	111
Regulatory Assets	274	290
Regulatory Liabilities	611	665
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Receivables	48	55
Accounts Payable, Current	144	154
Regulatory Assets	425	426
Regulatory Liabilities	$ 382	420
PJM Transmission Rate Design Settlement [Member]
Other Commitments [Line Items]
Other Receivables		220
Accounts Payable, Current		176
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Receivables		0
Accounts Payable, Current		41
Accounts Receivable, before Allowance for Credit Loss, Current		16
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Other Receivables		122
Accounts Payable, Current		0
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Other Receivables		85
Accounts Payable, Current		0
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Receivables		0
Accounts Payable, Current		51
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Receivables		13
Accounts Payable, Current		84
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Receivables		0
Accounts Payable, Current		84
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Other Receivables		10
Accounts Payable, Current		0
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Receivables		3
Accounts Payable, Current		0
PJM Transmission Rate Design Settlement [Member]
Other Commitments [Line Items]
Regulatory Assets		136
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Regulatory Assets		0
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Regulatory Assets		0
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Regulatory Assets		0
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Regulatory Assets		51
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Regulatory Assets		85
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Regulatory Assets		84
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Regulatory Assets		0
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Regulatory Assets		1
PJM Transmission Rate Design Settlement [Member]
Other Commitments [Line Items]
Regulatory Liabilities		221
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Regulatory Liabilities		0
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Regulatory Liabilities		122
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Regulatory Liabilities		85
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Regulatory Liabilities		0
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Regulatory Liabilities		14
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Regulatory Liabilities		0
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Regulatory Liabilities		10
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Regulatory Liabilities		$ 4

Regulatory Matters - Schedule_3

Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Regulatory Assets [Line Items]
Regulatory Assets	$ 9,505	$ 9,427
Current regulatory assets	1,170	1,190
Noncurrent regulatory assets	8,335	8,237
Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	2,784	2,553
Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	1,138	1,266
Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	528	414
Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	207	234
Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	276	328
Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	34	158
Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	66	81
Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	746	472
Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	650	702
Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	443	561
Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	127	118
MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	302	326
Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	301	249
Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	110	193
Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	11	41
Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	572	545
Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	32	42
Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	37	27
Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	37	50
Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	641	564
DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	126	159
Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		41
Other
Regulatory Assets [Line Items]
Regulatory Assets	337	303
Commonwealth Edison Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets	1,761	1,600
Current regulatory assets	281	293
Noncurrent regulatory assets	1,480	1,307
Commonwealth Edison Co [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	113	136
Commonwealth Edison Co [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	34	158
Commonwealth Edison Co [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	66	81
Commonwealth Edison Co [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	746	472
Commonwealth Edison Co [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	85	79
Commonwealth Edison Co [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	287	309
Commonwealth Edison Co [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	301	249
Commonwealth Edison Co [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	6
Commonwealth Edison Co [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	129	110
PECO Energy Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets	595	541
Current regulatory assets	41	81
Noncurrent regulatory assets	554	460
PECO Energy Co [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	518	404
PECO Energy Co [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	12	24
PECO Energy Co [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	23	22
PECO Energy Co [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	11	17
PECO Energy Co [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	6	49
PECO Energy Co [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	0	1
PECO Energy Co [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	25	24
Baltimore Gas and Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets	637	575
Current regulatory assets	183	177
Noncurrent regulatory assets	454	398
Baltimore Gas and Electric Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	129	145
Baltimore Gas and Electric Company [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	45	48
Baltimore Gas and Electric Company [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	16	16
Baltimore Gas and Electric Company [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	4	0
Baltimore Gas and Electric Company [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	36	51
Baltimore Gas and Electric Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	1	4
Baltimore Gas and Electric Company [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	303	289
Baltimore Gas and Electric Company [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	2	3
Baltimore Gas and Electric Company [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	8	2
Baltimore Gas and Electric Company [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	67	0
Baltimore Gas and Electric Company [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
Baltimore Gas and Electric Company [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	26	17
Pepco Holdings LLC [Member]
Regulatory Assets [Line Items]
Regulatory Assets	2,473	2,769
Current regulatory assets	412	457
Noncurrent regulatory assets	2,061	2,312
Pepco Holdings LLC [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	10	10
Pepco Holdings LLC [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	78	89
Pepco Holdings LLC [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	106	120
Pepco Holdings LLC [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	523	569
Pepco Holdings LLC [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	443	561
Pepco Holdings LLC [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	3	1
Pepco Holdings LLC [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	68	93
Pepco Holdings LLC [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	10	31
Pepco Holdings LLC [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	269	255
Pepco Holdings LLC [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	30	39
Pepco Holdings LLC [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	29	25
Pepco Holdings LLC [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	37	50
Pepco Holdings LLC [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	574	564
Pepco Holdings LLC [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	126	159
Pepco Holdings LLC [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		41
Pepco Holdings LLC [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	167	162
Potomac Electric Power Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets	772	881
Current regulatory assets	188	238
Noncurrent regulatory assets	584	643
Potomac Electric Power Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	10	10
Potomac Electric Power Company [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	43	50
Potomac Electric Power Company [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	79	90
Potomac Electric Power Company [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	2	1
Potomac Electric Power Company [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	43	84
Potomac Electric Power Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	1	10
Potomac Electric Power Company [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	196	188
Potomac Electric Power Company [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	15	18
Potomac Electric Power Company [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	29	25
Potomac Electric Power Company [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	152	158
Potomac Electric Power Company [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	126	159
Potomac Electric Power Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9
Potomac Electric Power Company [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	76	79
Delmarva Power & Light Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets	274	290
Current regulatory assets	52	59
Noncurrent regulatory assets	222	231
Delmarva Power & Light Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	35	39
Delmarva Power & Light Company [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	27	30
Delmarva Power & Light Company [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	5	0
Delmarva Power & Light Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	2	14
Delmarva Power & Light Company [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	73	67
Delmarva Power & Light Company [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	8	11
Delmarva Power & Light Company [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	100	97
Delmarva Power & Light Company [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		4
Delmarva Power & Light Company [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	24	28
Atlantic City Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets	425	426
Current regulatory assets	57	40
Noncurrent regulatory assets	368	386
Atlantic City Electric Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	1	0
Atlantic City Electric Company [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	20	9
Atlantic City Electric Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	7	7
Atlantic City Electric Company [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	7	10
Atlantic City Electric Company [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	37	50
Atlantic City Electric Company [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	324	309
Atlantic City Electric Company [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		28
Atlantic City Electric Company [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	$ 29	$ 13

Regulatory Matters - Schedule_4

Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 10,392	$ 10,203
Regulatory Liability, Current	406	644
Noncurrent regulatory liabilities	9,986	9,559
Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	4,944	5,228
Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3,102	2,606
Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,621	1,547
Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	109	294
Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	34
Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	582	528
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6,742	6,343
Regulatory Liability, Current	200	293
Noncurrent regulatory liabilities	6,542	6,050
Commonwealth Edison Co [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,297	2,394
Commonwealth Edison Co [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,622	2,217
Commonwealth Edison Co [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,435	1,368
Commonwealth Edison Co [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	45	137
Commonwealth Edison Co [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6
Commonwealth Edison Co [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	337	227
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	601	596
Regulatory Liability, Current	91	175
Noncurrent regulatory liabilities	510	421
PECO Energy Co [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	480	389
PECO Energy Co [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	56	132
PECO Energy Co [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	28
PECO Energy Co [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	37	75
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,228	1,269
Regulatory Liability, Current	33	77
Noncurrent regulatory liabilities	1,195	1,192
Baltimore Gas and Electric Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,089	1,132
Baltimore Gas and Electric Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	58	52
Baltimore Gas and Electric Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	6
Baltimore Gas and Electric Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Baltimore Gas and Electric Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	81	79
Pepco Holdings LLC [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,777	1,948
Regulatory Liability, Current	70	84
Noncurrent regulatory liabilities	1,707	1,864
Pepco Holdings LLC [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,558	1,702
Pepco Holdings LLC [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	128	127
Pepco Holdings LLC [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	8	19
Pepco Holdings LLC [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Pepco Holdings LLC [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	83	100
Potomac Electric Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	754	829
Regulatory Liability, Current	8	7
Noncurrent regulatory liabilities	746	822
Potomac Electric Power Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	725	798
Potomac Electric Power Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	20	20
Potomac Electric Power Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Potomac Electric Power Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	9	11
Delmarva Power & Light Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	611	665
Regulatory Liability, Current	37	59
Noncurrent regulatory liabilities	574	606
Delmarva Power & Light Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	477	510
Delmarva Power & Light Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power & Light Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	108	107
Delmarva Power & Light Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	8	18
Delmarva Power & Light Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Delmarva Power & Light Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	18	30
Atlantic City Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	382	420
Regulatory Liability, Current	25	18
Noncurrent regulatory liabilities	357	402
Atlantic City Electric Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	356	394
Atlantic City Electric Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	1
Atlantic City Electric Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Atlantic City Electric Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 26	$ 25

Regulatory Matters - Capitalize

Regulatory Matters - Capitalized Ratemaking Amounts Not Recognized (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	$ 63	$ 65
Commonwealth Edison Co [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	3	8
PECO Energy Co [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	0	0
Baltimore Gas and Electric Company [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	53	49
Pepco Holdings LLC [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	7	8
Potomac Electric Power Company [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	4	5
Delmarva Power & Light Company [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	3	3
Atlantic City Electric Company [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	$ 0	$ 0

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Contract Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018
Change in Contract with Customer, Asset and Liability [Abstract]
Contract with Customer, Asset, Net, Current	$ 174	$ 187	$ 283
Contract with Customer, Asset, Reclassified to Receivable	(143)	(146)
Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	130	50
Contract with Customer, Liability, Current	33	27	35
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Modification of Contract	94	179
Contract with Customer, Liability, Revenue Recognized	(88)	(187)
Exelon Generation Co L L C [Member]
Change in Contract with Customer, Asset and Liability [Abstract]
Contract with Customer, Asset, Net, Current	174	187	283
Contract with Customer, Asset, Reclassified to Receivable	(143)	(146)
Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	130	50
Contract with Customer, Liability, Current	71	42	$ 35
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Modification of Contract	287	465
Contract with Customer, Liability, Revenue Recognized	$ (258)	$ (458)

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Performance Obligations (Details) $ in Millions	Dec. 31, 2019USD ($)
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, Amount	$ 400
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, Amount	501
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, Amount	141
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, Amount	196
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, Amount	65
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, Amount	80
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, Amount	45
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, Amount	45
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	199
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01 | Exelon Generation Co L L C [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	199
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, Amount	850
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, Amount	$ 1,021

Segment Information - Narrative

Segment Information - Narrative (Details)	12 Months Ended
	Dec. 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								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues		$ 8,343	$ 8,929	$ 7,689	$ 9,477	$ 8,812	$ 9,401	$ 8,074	$ 9,691	$ 34,438	$ 35,978	$ 33,558
Depreciation and amortization										4,252	4,353	3,828
Operating Expenses										30,096	32,143	29,619
Interest expense, net										1,616	1,554	1,560
Income (loss) before income taxes										3,985	2,225	3,775
Income taxes										774	118	(126)
Net income (loss)										3,028	2,079	3,869
Capital expenditures										7,248	7,594	7,584
Assets	[1]	124,977				119,634				124,977	119,634
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues		1,107	1,380	1,091	1,228	1,115	1,359	1,074	1,249	4,806	4,798	4,672
Operating revenues from affiliates										14	15	50
Income (loss) before income taxes										514	425	571
Income taxes										38	33	217
Net income (loss)		65	189	106	117	62	185	82	63	477	393	355
Capital expenditures										1,355	1,375	1,396
Assets		22,719				21,952				22,719	21,952
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues		4,644	$ 4,774	$ 4,210	$ 5,296	5,069	$ 5,278	$ 4,579	$ 5,512	18,924	20,437	18,500
Operating revenues from affiliates										1,172	1,268	1,115
Income (loss) before income taxes										1,917	365	1,455
Income taxes										516	(108)	(1,376)
Net income (loss)										1,217	443	2,798
Capital expenditures										1,845	2,242	2,259
Assets	[2]	48,995				47,556				48,995	47,556
Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues										487	303	592
Revenues										34,438	35,978	33,560
Net income (loss)										3,028	2,079	3,869
Assets		124,977				119,634				124,977	119,634
Operating Segments [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										(14)	(7)	33
Revenues												47
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues										(4)	(5)	(1)
Revenues										(3,166)	(3,294)	(3,025)
Operating revenues from affiliates										2	1	2
Depreciation and amortization										0	0	0
Operating Expenses										(3,154)	(3,341)	(3,026)
Interest expense, net										0	0	0
Income (loss) before income taxes										(2)	(1)	(2)
Income taxes										0	0	0
Net income (loss)										(2)	(1)	(2)
Capital expenditures										0	0	0
Assets		(10,089)				(9,800)				(10,089)	(9,800)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues										(396)	(437)	(17)
Operating revenues from affiliates										(397)	(437)	(19)
Depreciation and amortization										0	0	(1)
Operating Expenses										(396)	(435)	(17)
Interest expense, net										1	0	(1)
Income (loss) before income taxes										(489)	(408)	(404)
Income taxes										1	(2)	0
Net income (loss)										14	15	50
Capital expenditures										0	0	0
Assets		(5,810)				(5,421)				(5,810)	(5,421)
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues										491	308	593
Revenues										18,924	20,437	18,500
Depreciation and amortization										1,535	1,797	1,457
Operating Expenses										17,628	19,510	18,001
Interest expense, net										429	432	440
Income (loss) before income taxes										1,917	365	1,455
Income taxes										516	(108)	(1,376)
Net income (loss)										1,217	443	2,798
Capital expenditures										1,845	2,242	2,259
Assets		48,995				47,556				48,995	47,556
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										1,172	1,269	1,110
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues										0	0	0
Revenues										5,747	5,882	5,536
Depreciation and amortization										1,033	940	850
Operating Expenses										4,580	4,741	4,214
Interest expense, net										359	347	361
Income (loss) before income taxes										851	832	984
Income taxes										163	168	417
Net income (loss)										688	664	567
Capital expenditures										1,915	2,126	2,250
Assets		32,765				31,213				32,765	31,213
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										30	27	15
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues										0	0	0
Revenues										3,100	3,038	2,870
Depreciation and amortization										333	301	286
Operating Expenses										2,388	2,452	2,215
Interest expense, net										136	129	126
Income (loss) before income taxes										593	466	538
Income taxes										65	6	104
Net income (loss)										528	460	434
Capital expenditures										939	849	732
Assets		11,469				10,642				11,469	10,642
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										6	8	7
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues										0	0	0
Revenues										3,106	3,169	3,176
Depreciation and amortization										502	483	473
Operating Expenses										2,574	2,696	2,562
Interest expense, net										121	106	105
Income (loss) before income taxes										439	387	525
Income taxes										79	74	218
Net income (loss)										360	313	307
Capital expenditures										1,145	959	882
Assets		10,634				9,716				10,634	9,716
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										26	29	16
Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues										0	0	0
Revenues										4,806	4,798	4,672
Depreciation and amortization										754	740	675
Operating Expenses										4,084	4,156	3,911
Interest expense, net										263	261	245
Income (loss) before income taxes										514	425	571
Income taxes										38	33	217
Net income (loss)										477	393	355
Capital expenditures										1,355	1,375	1,396
Assets		22,719				21,952				22,719	21,952
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										14	15	50
Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues										2,260	2,232	2,151
Depreciation and amortization										374	385	321
Operating Expenses										1,899	1,919	1,760
Interest expense, net										133	128	121
Income (loss) before income taxes										259	216	303
Income taxes										16	11	105
Net income (loss)										243	205	198
Capital expenditures										626	656	628
Assets		8,661				8,267				8,661	8,267
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										5	6	6
Delmarva Power & Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues										1,306	1,332	1,300
Depreciation and amortization										184	182	167
Operating Expenses										1,089	1,143	1,071
Interest expense, net										61	58	51
Income (loss) before income taxes										169	142	192
Income taxes										22	22	71
Net income (loss)										147	120	121
Capital expenditures										348	364	428
Assets		4,830				4,588				4,830	4,588
Delmarva Power & Light Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										7	8	8
Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues										1,240	1,236	1,186
Depreciation and amortization										157	136	146
Operating Expenses										1,089	1,087	1,029
Interest expense, net										58	64	61
Income (loss) before income taxes										99	87	103
Income taxes										0	12	26
Net income (loss)										99	75	77
Capital expenditures										375	335	312
Assets		3,933				3,699				3,933	3,699
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										3	3	2
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses other revenues										0	0	0
Revenues										1,921	1,948	1,831
Depreciation and amortization										95	92	87
Operating Expenses										1,996	1,929	1,742
Interest expense, net										308	279	283
Income (loss) before income taxes										(327)	(249)	(296)
Income taxes										(87)	(55)	294
Net income (loss)										(240)	(193)	(590)
Capital expenditures										49	43	65
Assets		8,484				8,355				8,484	8,355
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues										396	435	52
Depreciation and amortization										39	37	42
Operating Expenses										403	442	68
Interest expense, net										10	11	13
Income (loss) before income taxes										476	388	377
Income taxes										(1)	(10)	15
Net income (loss)										(26)	(22)	(91)
Capital expenditures										6	20	28
Assets		$ 11,105				$ 10,819				11,105	10,819
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										1,913	1,942	1,824
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										396	435	53
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues										5,074	5,487	5,540
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues										5,070	5,474	5,515
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										4	13	25
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues										4,293	4,706	4,181
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues										4,327	4,717	4,206
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(34)	(11)	(25)
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(3,159)	(3,289)	(3,020)
Electricity, Generation [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										15,120	16,155	14,227
Electricity, Generation [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										(1,165)	(1,256)	(1,105)
Electricity, Generation [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										16,285	17,411	15,332
Electricity, Generation [Member] | Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Electricity, Generation [Member] | PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Electricity, Generation [Member] | Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Electricity, Generation [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Electricity, Generation [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										167	181	161
Natural Gas, US Regulated [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										1,489	1,470	1,333
Natural Gas, US Regulated [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										(15)	(20)	(10)
Natural Gas, US Regulated [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Natural Gas, US Regulated [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Natural Gas, US Regulated [Member] | Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Natural Gas, US Regulated [Member] | PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										610	568	495
Natural Gas, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										727	741	687
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										167	181	161
Natural Gas, US Regulated [Member] | Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Natural Gas, US Regulated [Member] | Delmarva Power & Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										167	181	161
Natural Gas, US Regulated [Member] | Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Natural Gas, US Regulated [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Natural Gas, US Regulated [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Service, Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	3	0
Service, Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										(1,934)	(1,960)	(1,880)
Service, Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										(383)	(420)	(3)
Service, Other [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Service, Other [Member] | Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Service, Other [Member] | PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Service, Other [Member] | Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Service, Other [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										13	15	49
Service, Other [Member] | Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Service, Other [Member] | Delmarva Power & Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Service, Other [Member] | Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Service, Other [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										1,921	1,948	1,831
Service, Other [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										396	435	52
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										4,639	4,609	4,428
Electricity, US Regulated [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										15,195	15,337	14,833
Electricity, US Regulated [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										(47)	(45)	(29)
Electricity, US Regulated [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										(13)	(17)	(14)
Electricity, US Regulated [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Electricity, US Regulated [Member] | Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										5,747	5,882	5,536
Electricity, US Regulated [Member] | PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										2,490	2,470	2,375
Electricity, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										2,379	2,428	2,489
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										4,626	4,602	4,462
Electricity, US Regulated [Member] | Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										2,260	2,232	2,151
Electricity, US Regulated [Member] | Delmarva Power & Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										1,139	1,151	1,139
Electricity, US Regulated [Member] | Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										1,240	1,236	1,186
Electricity, US Regulated [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Electricity, US Regulated [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Oil and Gas, Purchased [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										2,147	2,710	2,575
Oil and Gas, Purchased [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										(1)	(8)	0
Oil and Gas, Purchased [Member] | Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										2,148	2,718	2,575
Oil and Gas, Purchased [Member] | Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Oil and Gas, Purchased [Member] | PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Oil and Gas, Purchased [Member] | Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Oil and Gas, Purchased [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										0	0	0
Oil and Gas, Purchased [Member] | Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Including Assessed Tax										$ 0	$ 0	$ 0
[1]	Exelon’s consolidated assets include $9,532 million and $9,667 million at December 31, 2019 and 2018 , respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,473 million and $3,548 million at December 31, 2019 and 2018 , respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 22 – Variable Interest Entities for additional information.
[2]	Generation’s consolidated assets include $9,512 million and $9,634 million at December 31, 2019 and 2018 , respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,429 million and $3,480 million at December 31, 2019 and 2018 , respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 22 – Variable Interest Entities for additional information.

Segment Information - Generatio

Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 8,343	$ 8,929	$ 7,689	$ 9,477	$ 8,812	$ 9,401	$ 8,074	$ 9,691	$ 34,438	$ 35,978	$ 33,558
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues									5,074	5,487	5,540
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues									4,293	4,706	4,181
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues									1,596	1,687	1,550
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues									1,013	1,133	962
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues									4,246	4,335	3,051
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues									16,222	17,348	15,284
Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues									2,210	2,780	2,628
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues									492	309	588
Unrealized Gain (Loss) on Securities									(4)	(262)	(131)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues									18,924	20,437	18,500
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues									34,438	35,978	33,560
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues									5,070	5,474	5,515
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues									4,327	4,717	4,206
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues									1,596	1,687	1,567
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues									997	1,132	958
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues									4,295	4,401	3,086
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues									16,285	17,411	15,332
Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues									2,148	2,718	2,575
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Amortization of intangible assets related to commodity contracts											38
Unrealized Gain (Loss) on Securities									(215)	(319)	(175)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues									18,924	20,437	18,500
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues									(3,166)	(3,294)	(3,025)
Revenue from Related Parties									2	1	2
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									4	13	25
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									(34)	(11)	(25)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									0	0	(17)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									16	1	4
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									(49)	(66)	(35)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									(63)	(63)	(48)
Intersegment Eliminations [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									62	62	53
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									1	1	(5)
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									0	0	0
Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues									491	308	593
Contracts with Customers [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues									5,053	5,241	5,523
Contracts with Customers [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues									4,095	4,527	3,923
Contracts with Customers [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues									1,571	1,723	1,605
Contracts with Customers [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues									768	572	641
Contracts with Customers [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues									3,687	3,530	2,658
Contracts with Customers [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues									15,174	15,593	14,350
Contracts with Customers [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues									1,446	1,524	1,658
Contracts with Customers [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues									17,060	17,627	16,752
Contracts with Customers [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues									440	510	744
Other [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues									17	233	(8)
Other [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues									232	190	283
Other [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues									25	(36)	(38)
Other [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues									229	560	317
Other [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues									608	871	428
Other [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues									1,111	1,818	982
Other [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues									702	1,194	917
Other [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues									1,864	2,810	1,748
Other [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues									$ 51	$ (202)	$ (151)

Segment Information - Generat_2

Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	$ 2,655	$ 3,073	$ 3,214
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	2,962	3,135	2,820
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	1,094	1,122	1,008
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	308	258	332
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	620	729	819
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	7,639	8,317	8,193
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	429	427	617
Unrealized Gain (Loss) on Securities	(4)	(262)	(131)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	8,068	8,744	8,810
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
RNF from external customers	2,637	3,022	3,105
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
RNF from external customers	2,994	3,112	2,810
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
RNF from external customers	1,081	1,112	1,007
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
RNF from external customers	338	501	575
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
RNF from external customers	694	883	1,014
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
RNF from external customers	7,744	8,630	8,511
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	324	114	299
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel			(54)
Unrealized Gain (Loss) on Securities	(215)	(319)	(175)
Nuclear Fuel Amortization	13	57	12
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
RNF from external customers	8,068	8,744	8,810
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	18	51	109
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(32)	23	10
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	13	10	1
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(30)	(243)	(243)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(74)	(154)	(195)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(105)	(313)	(318)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	105	313	318
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	$ 0	$ 0	$ 0

Segment Information - Electric

Segment Information - Electric and Gas Revenue by Customer Class (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue, Major Customer [Line Items]
Revenues	$ 8,343	$ 8,929	$ 7,689	$ 9,477	$ 8,812	$ 9,401	$ 8,074	$ 9,691	$ 34,438	$ 35,978	$ 33,558
Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues									34,438	35,978	33,560
Operating Segments [Member] | Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Revenues									4,806	4,798	4,672
Commonwealth Edison Co [Member]
Revenue, Major Customer [Line Items]
Revenues	1,405	1,583	1,351	1,408	1,373	1,598	1,398	1,512	5,747	5,882	5,536
Revenue from Related Parties									30	27	15
Commonwealth Edison Co [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									(133)	(29)	43
Revenues											0
Commonwealth Edison Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues									5,854	5,881	5,463
Commonwealth Edison Co [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues									(107)	1	73
PECO Energy Co [Member]
Revenue, Major Customer [Line Items]
Revenues	766	778	655	900	765	757	653	866	3,100	3,038	2,870
Revenue from Related Parties									6	8	7
PECO Energy Co [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									(21)	(7)	0
Revenues											0
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Revenue from Related Parties									5	7	6
PECO Energy Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues									3,107	3,032	2,857
PECO Energy Co [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues									(7)	6	13
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Revenue from Related Parties									1	1	1
Baltimore Gas and Electric Company [Member]
Revenue, Major Customer [Line Items]
Revenues	779	703	649	976	799	731	662	977	3,106	3,169	3,176
Revenue from Related Parties									26	29	16
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									12	(26)	124
Revenues											0
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Revenue from Related Parties									8	8	5
Baltimore Gas and Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues									3,078	3,178	3,035
Baltimore Gas and Electric Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues									28	(9)	141
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Revenue from Related Parties									18	21	11
Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Revenues	1,107	1,380	1,091	1,228	1,115	1,359	1,074	1,249	4,806	4,798	4,672
Revenue from Related Parties									14	15	50
Pepco Holdings LLC [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									(14)	(7)	33
Revenues											47
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Revenue from Related Parties										15	3
Pepco Holdings LLC [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues									4,810	4,794	4,583
Pepco Holdings LLC [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues									(4)	4	89
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Revenue from Related Parties										47
Potomac Electric Power Company [Member]
Revenue, Major Customer [Line Items]
Revenues	513	642	531	575	529	626	521	555	2,260	2,232	2,151
Revenue from Related Parties									5	6	6
Potomac Electric Power Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									(3)	(7)	19
Revenues											0
Potomac Electric Power Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues									2,255	2,232	2,127
Potomac Electric Power Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues									5	0	24
Delmarva Power & Light Company [Member]
Revenue, Major Customer [Line Items]
Revenues	319	319	287	380	331	328	289	384	1,306	1,332	1,300
Revenue from Related Parties									7	8	8
Delmarva Power & Light Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									(11)	4	6
Revenues											0
Delmarva Power & Light Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues									1,315	1,324	1,290
Delmarva Power & Light Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues									(9)	8	10
Atlantic City Electric Company [Member]
Revenue, Major Customer [Line Items]
Revenues	$ 274	$ 419	$ 274	$ 273	$ 254	$ 406	$ 265	$ 310	1,240	1,236	1,186
Revenue from Related Parties									3	3	2
Atlantic City Electric Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	(4)	8
Revenues											0
Atlantic City Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues									1,240	1,240	1,178
Atlantic City Electric Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues									0	(4)	8
Electricity, US Regulated [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									15,195	15,337	14,833
Electricity, US Regulated [Member] | Operating Segments [Member] | Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									4,626	4,602	4,462
Electricity, US Regulated [Member] | Commonwealth Edison Co [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									5,850	5,884	5,478
Electricity, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									5,854	5,881	5,463
Electricity, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									2,916	2,942	2,715
Electricity, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1,463	1,487	1,363
Electricity, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									540	538	455
Electricity, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									47	47	44
Electricity, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									888	867	886
Electricity, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									26	30	30
Electricity, US Regulated [Member] | PECO Energy Co [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									2,505	2,469	2,369
Electricity, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									2,497	2,464	2,363
Electricity, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1,596	1,566	1,505
Electricity, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									404	404	401
Electricity, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									219	223	223
Electricity, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									29	28	30
Electricity, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									249	243	204
Electricity, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									13	12	12
Electricity, US Regulated [Member] | Baltimore Gas and Electric Company [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									2,368	2,428	2,384
Electricity, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									2,364	2,423	2,376
Electricity, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1,326	1,382	1,365
Electricity, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									254	257	254
Electricity, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									436	429	427
Electricity, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									27	28	31
Electricity, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									321	327	299
Electricity, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									12	13	13
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									4,639	4,609	4,428
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									4,644	4,614	4,423
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									2,316	2,351	2,246
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									505	488	490
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1,112	1,124	1,086
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									61	58	60
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									650	593	541
Electricity, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									10	10	8
Electricity, US Regulated [Member] | Potomac Electric Power Company [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									2,258	2,233	2,126
Electricity, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									2,255	2,232	2,127
Electricity, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1,012	1,021	964
Electricity, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									149	140	137
Electricity, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									833	846	794
Electricity, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									34	32	33
Electricity, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									227	193	199
Electricity, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									8	7	5
Electricity, US Regulated [Member] | Delmarva Power & Light Company [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1,143	1,139	1,125
Electricity, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1,148	1,144	1,130
Electricity, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									645	669	663
Electricity, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									186	186	187
Electricity, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									99	100	103
Electricity, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									14	14	14
Electricity, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									204	175	163
Electricity, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									2	3	3
Electricity, US Regulated [Member] | Atlantic City Electric Company [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1,237	1,237	1,176
Electricity, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1,240	1,240	1,178
Electricity, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									659	661	619
Electricity, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									170	162	166
Electricity, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									180	178	189
Electricity, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									13	12	13
Electricity, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									218	227	191
Electricity, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1,489	1,470	1,333
Natural Gas, US Regulated [Member] | Operating Segments [Member] | Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									167	181	161
Natural Gas, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | PECO Energy Co [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									610	568	494
Natural Gas, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									610	568	494
Natural Gas, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									409	395	331
Natural Gas, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									169	143	131
Natural Gas, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1	1	1
Natural Gas, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									25	23	23
Natural Gas, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									6	6	8
Natural Gas, US Regulated [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1	1	1
Natural Gas, US Regulated [Member] | Baltimore Gas and Electric Company [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									700	738	652
Natural Gas, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									714	755	659
Natural Gas, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									474	491	437
Natural Gas, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									77	77	75
Natural Gas, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									132	124	119
Natural Gas, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									31	63	28
Natural Gas, US Regulated [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									4	4	4
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									167	181	161
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									166	180	160
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									96	99	90
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									44	44	38
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									5	8	8
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									14	16	15
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									7	13	9
Natural Gas, US Regulated [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	1	1
Natural Gas, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Delmarva Power & Light Company [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									167	181	161
Natural Gas, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									167	180	160
Natural Gas, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									96	99	90
Natural Gas, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									45	44	38
Natural Gas, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									5	8	8
Natural Gas, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									14	16	15
Natural Gas, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									7	13	9
Natural Gas, US Regulated [Member] | Delmarva Power & Light Company [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	1	1
Natural Gas, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0	0
Natural Gas, US Regulated [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									$ 0	$ 0	$ 0

Early Plant Retirements - Narra

Early Plant Retirements - Narrative (Details) - USD ($) $ in Millions	Oct. 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Payments to Acquire Businesses, Gross		$ 41	$ 154	$ 208
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Payments to Acquire Businesses, Gross		$ 41	$ 154	$ 208
Exelon Generation Co L L C [Member] | Salem [Member] | Nuclear Plant [Member]
Property, Plant and Equipment [Line Items]
Ownership interest		42.59%
Everett Marine Terminal [Member]
Property, Plant and Equipment [Line Items]
Payments to Acquire Businesses, Gross	$ 81
Business Combination, Separately Recognized Transactions, Net Gains and Losses	75
Everett Marine Terminal [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Payments to Acquire Businesses, Gross	81
Business Combination, Separately Recognized Transactions, Net Gains and Losses	$ 75

Early Plant Retirements - Preta

Early Plant Retirements - Pretax Expense (Details) - Facility Closing [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Three Mile Island [Member]
Accelerated depreciation	$ 216		$ 250
Accelerated nuclear fuel amortization	13		12
Operating and maintenance	(53)		77
Restructuring and Related Cost, Incurred Cost	176		339
Three Mile Island [Member] | Exelon Generation Co L L C [Member]
Accelerated depreciation	216		250
Accelerated nuclear fuel amortization	13		12
Operating and maintenance	(53)		77
Restructuring and Related Cost, Incurred Cost	$ 176		$ 339
TMI, Oyster Creek [Member]
Accelerated depreciation		$ 539
Accelerated nuclear fuel amortization		57
Operating and maintenance		32
Restructuring and Related Cost, Incurred Cost		628
TMI, Oyster Creek [Member] | Exelon Generation Co L L C [Member]
Accelerated depreciation		539
Accelerated nuclear fuel amortization		57
Operating and maintenance		32
Restructuring and Related Cost, Incurred Cost		$ 628

Early Plant Retirements - Impli

Early Plant Retirements - Implications of Potential Early Plant Retirement on Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Implications of Potential Early Plant Retirement [Line Items]
Fuel inventory	$ 312	$ 334
Property, plant and equipment, net	80,233	76,707
Mystic Generating Station [Member] | Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies inventory	31
Fuel inventory	11
Property, plant and equipment, net	902
Asset retirement obligation	(3)
Exelon Generation Co L L C [Member]
Implications of Potential Early Plant Retirement [Line Items]
Property, plant and equipment, net	24,193	$ 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	31
Fuel inventory	11
Property, plant and equipment, net	902
Asset retirement obligation	$ (3)

Property, Plant and Equipment -

Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 104,212	$ 99,609
Less: accumulated depreciation	23,979	22,902
Property, plant and equipment, net	80,233	76,707
Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 56,809	53,090
Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	80 years
Electric—generation
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 29,839	29,170
Electric—generation | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	1 year
Electric—generation | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	56 years
Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 6,147	5,530
Gas Distribution Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Gas Distribution Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	80 years
Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 1,907	1,627
Common—electric and gas | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	4 years
Common—electric and gas | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	75 years
Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 5,656	5,957
Nuclear Fuel [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	1 year
Nuclear Fuel [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	8 years
Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 3,055	3,377
Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 799	858
Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	1 year
Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	50 years
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 36,210	36,187
Less: accumulated depreciation	12,017	12,206
Property, plant and equipment, net	24,193	23,981
Nuclear fuel - work in progress	1,025	1,004
Exelon Generation Co L L C [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	0
Exelon Generation Co L L C [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 29,839	29,170
Exelon Generation Co L L C [Member] | Electric—generation | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	1 year
Exelon Generation Co L L C [Member] | Electric—generation | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	56 years
Exelon Generation Co L L C [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	0
Exelon Generation Co L L C [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	0
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	5,656	5,957
Less: accumulated depreciation	$ 2,867	2,969
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	1 year
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	8 years
Exelon Generation Co L L C [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 702	997
Exelon Generation Co L L C [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 13	63
Exelon Generation Co L L C [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	1 year
Exelon Generation Co L L C [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	10 years
Commonwealth Edison Co [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 28,275	26,742
Less: accumulated depreciation	5,168	4,684
Property, plant and equipment, net	23,107	22,058
Commonwealth Edison Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 27,566	25,991
Commonwealth Edison Co [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Commonwealth Edison Co [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	80 years
Commonwealth Edison Co [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	0
Commonwealth Edison Co [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	0
Commonwealth Edison Co [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	0
Commonwealth Edison Co [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	0
Commonwealth Edison Co [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	662	705
Commonwealth Edison Co [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 47	46
Commonwealth Edison Co [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	34 years
Commonwealth Edison Co [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	50 years
PECO Energy Co [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 13,010	12,171
Less: accumulated depreciation	3,718	3,561
Property, plant and equipment, net	9,292	8,610
PECO Energy Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 8,957	8,359
PECO Energy Co [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
PECO Energy Co [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	65 years
PECO Energy Co [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	0
PECO Energy Co [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 2,899	2,694
PECO Energy Co [Member] | Gas Distribution Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
PECO Energy Co [Member] | Gas Distribution Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	70 years
PECO Energy Co [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 877	756
PECO Energy Co [Member] | Common—electric and gas | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
PECO Energy Co [Member] | Common—electric and gas | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	50 years
PECO Energy Co [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	0
PECO Energy Co [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	250	343
PECO Energy Co [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 27	19
Average Service Life (years)	50 years
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 12,824	11,876
Less: accumulated depreciation	3,834	3,633
Property, plant and equipment, net	8,990	8,243
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 8,326	7,951
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	75 years
Baltimore Gas and Electric Company [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	0
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 2,999	2,630
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	80 years
Baltimore Gas and Electric Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 991	860
Baltimore Gas and Electric Company [Member] | Common—electric and gas | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	4 years
Baltimore Gas and Electric Company [Member] | Common—electric and gas | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	50 years
Baltimore Gas and Electric Company [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	0
Baltimore Gas and Electric Company [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	483	410
Baltimore Gas and Electric Company [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 25	25
Baltimore Gas and Electric Company [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	20 years
Baltimore Gas and Electric Company [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	50 years
Pepco Holdings LLC [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 15,509	14,287
Less: accumulated depreciation	1,213	841
Property, plant and equipment, net	14,296	13,446
Pepco Holdings LLC [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 13,809	12,664
Pepco Holdings LLC [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Pepco Holdings LLC [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	75 years
Pepco Holdings LLC [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	0
Pepco Holdings LLC [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 525	486
Pepco Holdings LLC [Member] | Gas Distribution Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Pepco Holdings LLC [Member] | Gas Distribution Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	75 years
Pepco Holdings LLC [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 146	126
Pepco Holdings LLC [Member] | Common—electric and gas | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Pepco Holdings LLC [Member] | Common—electric and gas | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	75 years
Pepco Holdings LLC [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	0
Pepco Holdings LLC [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	921	912
Pepco Holdings LLC [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 108	99
Pepco Holdings LLC [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	3 years
Pepco Holdings LLC [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	50 years
Potomac Electric Power Company [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 10,426	9,814
Less: accumulated depreciation	3,517	3,354
Property, plant and equipment, net	6,909	6,460
Potomac Electric Power Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 9,734	9,217
Potomac Electric Power Company [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Potomac Electric Power Company [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	75 years
Potomac Electric Power Company [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	0
Potomac Electric Power Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	0
Potomac Electric Power Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	0
Potomac Electric Power Company [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	0
Potomac Electric Power Company [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	628	536
Potomac Electric Power Company [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 64	61
Potomac Electric Power Company [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	33 years
Potomac Electric Power Company [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	50 years
Delmarva Power & Light Company [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 5,460	5,150
Less: accumulated depreciation	1,425	1,329
Property, plant and equipment, net	4,035	3,821
Delmarva Power & Light Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 4,464	4,195
Delmarva Power & Light Company [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Delmarva Power & Light Company [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	70 years
Delmarva Power & Light Company [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	0
Delmarva Power & Light Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 690	651
Delmarva Power & Light Company [Member] | Gas Distribution Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Delmarva Power & Light Company [Member] | Gas Distribution Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	75 years
Delmarva Power & Light Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 160	136
Delmarva Power & Light Company [Member] | Common—electric and gas | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Delmarva Power & Light Company [Member] | Common—electric and gas | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	75 years
Delmarva Power & Light Company [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	0
Delmarva Power & Light Company [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	125	151
Delmarva Power & Light Company [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 21	17
Delmarva Power & Light Company [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	8 years
Delmarva Power & Light Company [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	50 years
Atlantic City Electric Company [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 4,400	4,103
Less: accumulated depreciation	1,210	1,137
Property, plant and equipment, net	3,190	2,966
Atlantic City Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 4,207	3,866
Atlantic City Electric Company [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	5 years
Atlantic City Electric Company [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	65 years
Atlantic City Electric Company [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 0	0
Atlantic City Electric Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	0
Atlantic City Electric Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	0
Atlantic City Electric Company [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	0	0
Atlantic City Electric Company [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	166	209
Atlantic City Electric Company [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 27	$ 28
Atlantic City Electric Company [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	13 years
Atlantic City Electric Company [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)	15 years

Property, Plant and Equipment_3

Property, Plant and Equipment - Annual Depreciation Provisions as Percentage of Average Service Life (Details)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.80%	2.73%	2.75%
Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	4.35%	5.37%	4.36%
Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.04%	2.07%	2.10%
Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	7.37%	6.98%	7.05%
Exelon Generation Co L L C [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	4.35%	5.37%	4.36%
Commonwealth Edison Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.99%	2.95%	2.99%
PECO Energy Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.36%	2.35%	2.37%
PECO Energy Co [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.89%	1.90%	1.89%
PECO Energy Co [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	6.06%	5.44%	5.47%
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.60%	2.61%	2.58%
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.30%	2.36%	2.33%
Baltimore Gas and Electric Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	8.30%	8.50%	8.64%
Pepco Holdings LLC [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.77%	2.61%	2.63%
Pepco Holdings LLC [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.55%	1.59%	2.07%
Pepco Holdings LLC [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	8.25%	6.30%	6.50%
Potomac Electric Power Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.47%	2.40%	2.35%
Delmarva Power & Light Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.86%	2.77%	2.75%
Delmarva Power & Light Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.55%	1.59%	2.07%
Delmarva Power & Light Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	6.24%	3.70%	4.14%
Atlantic City Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.94%	2.45%	2.46%

Property, Plant and Equipment_4

Property, Plant and Equipment - Summary of Capitalized Interest and AFUDC (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	$ 24	$ 31	$ 63
Allowance for Funds Used During Construction, Capitalized Interest	132	109	108
Exelon Generation Co L L C [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	24	31	63
Allowance for Funds Used During Construction, Capitalized Interest	0	0	0
Commonwealth Edison Co [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	32	30	20
PECO Energy Co [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	17	12	12
Baltimore Gas and Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	29	24	22
Pepco Holdings LLC [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	54	44	54
Potomac Electric Power Company [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	39	34	34
Delmarva Power & Light Company [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	6	4	10
Atlantic City Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Capitalized	0	0	0
Allowance for Funds Used During Construction, Capitalized Interest	$ 9	$ 4	$ 9

Jointly Owned Electric Utilit_3

Jointly Owned Electric Utility Plant - Ownership Interests in Jointly Owned Electric Plants and Transmission Facilities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)Vmi	Dec. 31, 2018USD ($)
Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Miles of transmission voltage lines | mi	151.3
Transmission line capacity | V	500
Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Miles of transmission voltage lines | mi	2.5
Transmission line capacity | V	500
New Freedom Switching [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Transmission line capacity | V	500
Electric Transmission [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant	$ 102	$ 103
Accumulated depreciation	53	53
Construction work in progress	$ 0	0
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Quad Cities [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	75.00%
Plant	$ 1,161	1,131
Accumulated depreciation	627	587
Construction work in progress	$ 13	13
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Peach Bottom [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	50.00%
Plant	$ 1,466	1,451
Accumulated depreciation	571	523
Construction work in progress	$ 21	15
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	42.59%
Plant	$ 663	648
Accumulated depreciation	249	227
Construction work in progress	$ 53	44
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Nine Mile Point [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	82.00%
Plant	$ 951	910
Accumulated depreciation	156	126
Construction work in progress	$ 27	$ 56
PECO Energy Co [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	42.55%
PECO Energy Co [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	42.55%
Delmarva Power & Light Company [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	1.00%
Delmarva Power & Light Company [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	7.45%
Atlantic City Electric Company [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	13.90%
Atlantic City Electric Company [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	7.45%
Atlantic City Electric Company [Member] | New Freedom Switching [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	21.78%

Asset Retirement Obligations -

Asset Retirement Obligations - Narrative (Details) - USD ($) $ in Millions	Dec. 05, 2019	Jun. 27, 2017	Sep. 30, 2017	Mar. 31, 2013	Dec. 31, 2019	Dec. 31, 2018
Asset Retirement Obligations [Line Items]
Increase (Decrease) in ARO Due to Change in Retirement Timing Probabilities					$ 780
Increase (Decrease) in ARO for Other Impacts					490	$ 120
Increase (Decrease) in ARO for Impacts of Revised Decommissioning Cost Estimates						(205)
Asset Retirement Obligation, Revision of Estimate						20
Public Utilities, Approved Rate Increase (Decrease), Amount			$ 4	$ 24
Shortfall of decommissioning funds with recourse					$ 50
Percent of additional decommissioning shortfall with recourse					5.00%
Nuclear decommissioning trust funds					$ 13,190	11,661
Disposal Group, Including Discontinued Operation, Assets, Current					0	904
Line of credit facility, maximum borrowing capacity					$ 25
Estimated annual after tax return on nuclear decommissioning funds					2.00%
Historical five-year annual average after-tax return on NDT funds					6.70%
Annual average accretion of the ARO					5.00%
Minimum [Member]
Asset Retirement Obligations [Line Items]
Estimated annual after tax return on nuclear decommissioning funds					5.40%
Maximum [Member]
Asset Retirement Obligations [Line Items]
Estimated annual after tax return on nuclear decommissioning funds					6.50%
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Increase (Decrease) in ARO Due to Change in Retirement Timing Probabilities					$ 780
Increase (Decrease) in ARO for Other Impacts					490	120
Increase (Decrease) in ARO for Impacts of Revised Decommissioning Cost Estimates						(205)
Asset Retirement Obligation, Revision of Estimate						0
Public Utilities, Approved Rate Increase (Decrease), Amount			$ 4	$ 24
Shortfall of decommissioning funds with recourse					$ 50
Percent of additional decommissioning shortfall with recourse					5.00%
Nuclear decommissioning trust funds					$ 13,190	11,661
Disposal Group, Including Discontinued Operation, Assets, Current					0	904
Line of credit facility, maximum borrowing capacity					$ 25
Estimated annual after tax return on nuclear decommissioning funds					2.00%
Historical five-year annual average after-tax return on NDT funds					6.70%
Annual average accretion of the ARO					5.00%
Number Of Years Used In Present Value Measurement					30 years
Exelon Generation Co L L C [Member] | Minimum [Member]
Asset Retirement Obligations [Line Items]
Estimated annual after tax return on nuclear decommissioning funds					5.40%
Number Of Years Used In Present Value Measurement					10 years
Exelon Generation Co L L C [Member] | Maximum [Member]
Asset Retirement Obligations [Line Items]
Estimated annual after tax return on nuclear decommissioning funds					6.50%
Number Of Years Used In Present Value Measurement					70 years
PECO Energy Co [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Revision of Estimate						0
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 14	$ 22
Estimated annual after tax return on nuclear decommissioning funds					3.00%
Nuclear decommissioning
Asset Retirement Obligations [Line Items]
Net increase/decrease due to changes in, and timing of, estimated future cash flows					$ 864	(77)
Increase (Decrease) in ARO for Impacts of Revised Decommissioning Cost Estimates					(410)
Nuclear decommissioning | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Net increase/decrease due to changes in, and timing of, estimated future cash flows					864	(77)
Increase (Decrease) in ARO for Impacts of Revised Decommissioning Cost Estimates					$ (410)
Oyster Creek [Member]
Asset Retirement Obligations [Line Items]
Increase (Decrease) in ARO Due to Early Retirement						115
Oyster Creek [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Increase (Decrease) in ARO Due to Early Retirement						115
Nine Mile Point [Member]
Asset Retirement Obligations [Line Items]
Percent of additional decommissioning shortfall with recourse					50.00%
Nine Mile Point [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Percent of additional decommissioning shortfall with recourse					50.00%
Assets, Total [Member]
Asset Retirement Obligations [Line Items]
Nuclear decommissioning trust funds					$ 13,353	12,695
Assets, Total [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Nuclear decommissioning trust funds					13,353	12,695
Nuclear Decommissioning Trust Fund Investments [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Lessee, Operating Lease, Renewal Term			20 years
Nuclear Decommissioning Trust Fund Investments [Member] | Oyster Creek [Member]
Asset Retirement Obligations [Line Items]
Disposal Group, Including Discontinued Operation, Assets, Current						890
Nuclear Decommissioning Trust Fund Investments [Member] | Oyster Creek [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Disposal Group, Including Discontinued Operation, Assets, Current						890
Other Current Assets [Member]
Asset Retirement Obligations [Line Items]
Nuclear decommissioning trust funds					163	144
Other Current Assets [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Nuclear decommissioning trust funds					163	$ 144
Operating Expense [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Revision of Estimate					(150)
Operating Expense [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Revision of Estimate					$ (150)

Asset Retirement Obligations _2

Asset Retirement Obligations - Nuclear Decommissioning Asset Retirement Obligation Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense	$ 491	$ 489	$ 468
Disposal Group, Including Discontinued Operation, Liabilities, Current	0	777
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense	491	489	468
Disposal Group, Including Discontinued Operation, Liabilities, Current	0	777
Nuclear decommissioning
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	10,005	9,662
Accretion expense	479	478
Net increase/decrease due to changes in, and timing of, estimated future cash flows	864	(77)
Sale of Oyster Creek	(755)
Cost incurred related to decommissioning plants	(89)	(58)
ARO ending balance	10,504	10,005	9,662
Asset Retirement Obligation, Current	112	22
Nuclear decommissioning | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	10,005	9,662
Accretion expense	479	478
Net increase/decrease due to changes in, and timing of, estimated future cash flows	864	(77)
Sale of Oyster Creek	(755)
Cost incurred related to decommissioning plants	(89)	(58)
ARO ending balance	10,504	10,005	$ 9,662
Asset Retirement Obligation, Current	$ 112	22
Nuclear Decommissioning Asset Retirement Obligation [Member] | Oyster Creek [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Disposal Group, Including Discontinued Operation, Liabilities, Current		772
Nuclear Decommissioning Asset Retirement Obligation [Member] | Oyster Creek [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Disposal Group, Including Discontinued Operation, Liabilities, Current		$ 772

Asset Retirement Obligations _3

Asset Retirement Obligations - Non-Nuclear Asset Retirement Obligations Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate		$ 20
Accretion expense	$ 491	489	$ 468
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate		0
Accretion expense	491	489	468
Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate		0
Accretion expense	0	0	0
PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate		0
Accretion expense	0	0	0
Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate		0
Accretion expense	0	0	0
Pepco Holdings LLC [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate		20
Accretion expense	0	0	0
Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate		22
Accretion expense	0	0	0
Delmarva Power & Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate		(1)
Accretion expense	0	0	0
Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate		(1)
Accretion expense	0	0	0
Nuclear Decommissioning [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	10,005	9,662
Accretion expense	479	478
Asset divestitures	755
Payments	(89)	(58)
ARO ending balance	10,504	10,005	9,662
Nuclear Decommissioning [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	10,005	9,662
Accretion expense	479	478
Asset divestitures	755
Payments	(89)	(58)
ARO ending balance	10,504	10,005	9,662
Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	471	384
Asset Retirement Obligation, Revision of Estimate	17	80
Development Projects	2
Accretion expense	16	16
Asset divestitures	(42)	(3)
Payments	(4)	(6)
ARO ending balance	460	471	384
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	238	197
Asset Retirement Obligation, Revision of Estimate	7	35
Development Projects	2
Accretion expense	12	10
Asset divestitures	(42)	(3)
Payments	(1)	(1)
ARO ending balance	216	238	197
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	121	113
Asset Retirement Obligation, Revision of Estimate	8	7
Development Projects	0
Accretion expense	1	4
Asset divestitures	0	0
Payments	(1)	(3)
ARO ending balance	129	121	113
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	28	27
Asset Retirement Obligation, Revision of Estimate	0	0
Development Projects	0
Accretion expense	1	1
Asset divestitures	0	0
Payments	(1)	0
ARO ending balance	28	28	27
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	25	24
Asset Retirement Obligation, Revision of Estimate	(2)	2
Development Projects	0
Accretion expense	1	1
Asset divestitures	0	0
Payments	(1)	(2)
ARO ending balance	23	25	24
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Pepco Holdings LLC [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	52	16
Asset Retirement Obligation, Revision of Estimate	4	36
Development Projects	0
Accretion expense	1	0
Asset divestitures	0	0
Payments	0	0
ARO ending balance	57	52	16
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	37	3
Asset Retirement Obligation, Revision of Estimate	3	34
Development Projects	0
Accretion expense	1	0
Asset divestitures	0	0
Payments	0	0
ARO ending balance	41	37	3
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Delmarva Power & Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	11	10
Asset Retirement Obligation, Revision of Estimate	1	1
Development Projects	0
Accretion expense	0	0
Asset divestitures	0	0
Payments	0	0
ARO ending balance	12	11	10
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	4	3
Asset Retirement Obligation, Revision of Estimate	0	1
Development Projects	0
Accretion expense	0	0
Asset divestitures	0	0
Payments	0	0
ARO ending balance	4	4	$ 3
Operating Expense [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate	(150)
Operating Expense [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate	$ (150)
Operating Expense [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate		$ 22

Lessee - Narrative (Details)

Lessee - Narrative (Details)	12 Months Ended
	Dec. 31, 2019
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
Option to terminate within, Lessee, Operating Lease	1 years
Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	86 years
Options to extend the term, Lessee, Operating Lease	30 years
Option to terminate within, Lessee, Operating Lease	13 years
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
Option to terminate within, Lessee, Operating Lease	1 years
Exelon Generation Co L L C [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	36 years
Options to extend the term, Lessee, Operating Lease	30 years
Option to terminate within, Lessee, Operating Lease	1 years
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	5 years
Option to terminate within, Lessee, Operating Lease	3 years
Commonwealth Edison Co [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	5 years
Options to extend the term, Lessee, Operating Lease	5 years
Option to terminate within, Lessee, Operating Lease	3 years
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	14 years
Baltimore Gas and Electric Company [Member] | Minimum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	1 year
Option to terminate within, Lessee, Operating Lease	2 years
Baltimore Gas and Electric Company [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	86 years
Option to terminate within, Lessee, Operating Lease	2 years
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	12 years
Options to extend the term, Lessee, Operating Lease	30 years
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	12 years
Options to extend the term, Lessee, Operating Lease	5 years
Delmarva Power & 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 & Light Company [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Remaining lease terms, Lessee, Operating Lease	12 years
Options to extend the term, Lessee, Operating Lease	30 years
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	6 years
Contracted Generation [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Contracted Generation [Member] | Exelon Generation Co L L C [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Real Estate [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Real Estate [Member] | Exelon Generation Co L L C [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Real Estate [Member] | Commonwealth Edison Co [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Real Estate [Member] | PECO Energy Co [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Real Estate [Member] | Baltimore Gas and Electric Company [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Real Estate [Member] | Pepco Holdings LLC [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Real Estate [Member] | Potomac Electric Power Company [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Real Estate [Member] | Delmarva Power & Light Company [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Real Estate [Member] | Atlantic City Electric Company [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Vehicles & Equipment [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Vehicles & Equipment [Member] | Exelon Generation Co L L C [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Vehicles & Equipment [Member] | Commonwealth Edison Co [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Vehicles & Equipment [Member] | PECO Energy Co [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Vehicles & Equipment [Member] | Baltimore Gas and Electric Company [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Vehicles & Equipment [Member] | Pepco Holdings LLC [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Vehicles & Equipment [Member] | Potomac Electric Power Company [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Vehicles & Equipment [Member] | Delmarva Power & Light Company [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●
Vehicles & Equipment [Member] | Atlantic City Electric Company [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Description	●

Lessee - Components of Lease Co

Lessee - Components of Lease Cost (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	$ 320
Variable Lease, Cost	300
Short-term Lease, Cost	19
Total Lease Cost	639
Sublease Income	$ 51
Operating Lease, Weighted Average Remaining Lease Term	10 years 1 month 6 days
Operating Lease, Weighted Average Discount Rate, Percent	4.60%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 52
Exelon Generation Co L L C [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	222
Variable Lease, Cost	282
Short-term Lease, Cost	19
Total Lease Cost	523
Sublease Income	$ 44
Operating Lease, Weighted Average Remaining Lease Term	10 years 7 months 6 days
Operating Lease, Weighted Average Discount Rate, Percent	4.80%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 14
Commonwealth Edison Co [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	3
Variable Lease, Cost	2
Short-term Lease, Cost	0
Total Lease Cost	$ 5
Operating Lease, Weighted Average Remaining Lease Term	4 years 7 months 6 days
Operating Lease, Weighted Average Discount Rate, Percent	3.00%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 6
PECO Energy 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	4 years 4 months 24 days
Operating Lease, Weighted Average Discount Rate, Percent	3.20%
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	33
Variable Lease, Cost	2
Short-term Lease, Cost	0
Total Lease Cost	$ 35
Operating Lease, Weighted Average Remaining Lease Term	5 years 4 months 24 days
Operating Lease, Weighted Average Discount Rate, Percent	3.60%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 2
Pepco Holdings LLC [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	48
Variable Lease, Cost	6
Short-term Lease, Cost	0
Total Lease Cost	54
Sublease Income	$ 7
Operating Lease, Weighted Average Remaining Lease Term	9 years
Operating Lease, Weighted Average Discount Rate, Percent	4.20%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ (3)
Potomac Electric Power Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	12
Variable Lease, Cost	2
Short-term Lease, Cost	0
Total Lease Cost	$ 14
Operating Lease, Weighted Average Remaining Lease Term	9 years 9 months 18 days
Operating Lease, Weighted Average Discount Rate, Percent	4.00%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ (1)
Delmarva Power & Light Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	14
Variable Lease, Cost	2
Short-term Lease, Cost	0
Total Lease Cost	16
Sublease Income	$ 7
Operating Lease, Weighted Average Remaining Lease Term	9 years 8 months 12 days
Operating Lease, Weighted Average Discount Rate, Percent	4.00%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ (2)
Atlantic City Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	7
Variable Lease, Cost	1
Short-term Lease, Cost	0
Total Lease Cost	$ 8
Operating Lease, Weighted Average Remaining Lease Term	4 years 8 months 12 days
Operating Lease, Weighted Average Discount Rate, Percent	3.60%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ (1)

Lessee - Schedule of Rent Expen

Lessee - Schedule of Rent Expense Under Prior Lease Guidance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Operating Lease, Liability			$ 1,532
Operating Leases, Rent Expense	$ 670	$ 709
Exelon Generation Co L L C [Member]
Operating Lease, Liability			1,082
Operating Leases, Rent Expense	558	578
Commonwealth Edison Co [Member]
Operating Lease, Liability			11
Operating Leases, Rent Expense	7	9
PECO Energy Co [Member]
Operating Lease, Liability			1
Operating Leases, Rent Expense	10	9
Baltimore Gas and Electric Company [Member]
Operating Lease, Liability			82
Operating Leases, Rent Expense	35	32
Pepco Holdings LLC [Member]
Operating Lease, Liability			285
Operating Leases, Rent Expense	48	63
Potomac Electric Power Company [Member]
Operating Lease, Liability			57
Operating Leases, Rent Expense	10	11
Delmarva Power & Light Company [Member]
Operating Lease, Liability			74
Operating Leases, Rent Expense	13	16
Atlantic City Electric Company [Member]
Operating Lease, Liability			18
Operating Leases, Rent Expense	8	14
Long-term Contract for Purchase of Electric Power [Member]
Operating Lease, Liability			664
Long-term Contract for Purchase of Electric Power [Member] | Exelon Generation Co L L C [Member]
Operating Lease, Liability	$ 493	$ 508	$ 664

Lessee - Supplemental Balance S

Lessee - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	$ 3,197	$ 1,575
Other current liabilities	1,331	1,035
Other deferred credits and other liabilities	3,064	2,130
Total operating lease liabilities	1,532
Long-term Contract for Purchase of Electric Power [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	515
Total operating lease liabilities	664
Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	1,960	755
Other current liabilities	517	279
Other deferred credits and other liabilities	1,415	610
Total operating lease liabilities	1,082
Exelon Generation Co L L C [Member] | Long-term Contract for Purchase of Electric Power [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	515
Total operating lease liabilities	664	493	$ 508
Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	347	395
Other current liabilities	122	96
Other deferred credits and other liabilities	635	630
Total operating lease liabilities	11
PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	29	27
Other current liabilities	19	24
Other deferred credits and other liabilities	74	76
Total operating lease liabilities	1
Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	86	5
Other current liabilities	63	27
Other deferred credits and other liabilities	116	73
Total operating lease liabilities	82
Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	323	60
Other current liabilities	131	123
Other deferred credits and other liabilities	577	369
Total operating lease liabilities	285
Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	66	15
Other current liabilities	22	42
Other deferred credits and other liabilities	297	275
Total operating lease liabilities	57
Delmarva Power & Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	69	6
Other current liabilities	15	7
Other deferred credits and other liabilities	104	50
Total operating lease liabilities	74
Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	53	40
Other current liabilities	9	4
Other deferred credits and other liabilities	39	$ 27
Total operating lease liabilities	18
Other deferred debits and other assets [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	1,305
Other deferred debits and other assets [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	895
Other deferred debits and other assets [Member] | Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	9
Other deferred debits and other assets [Member] | PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	2
Other deferred debits and other assets [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	77
Other deferred debits and other assets [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	273
Other deferred debits and other assets [Member] | Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	56
Other deferred debits and other assets [Member] | Delmarva Power & Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	63
Other deferred debits and other assets [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other Assets, Noncurrent	18
Other Current Liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	225
Other Current Liabilities [Member] | Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	157
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	0
Other Current Liabilities [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	32
Other Current Liabilities [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	31
Other Current Liabilities [Member] | Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	6
Other Current Liabilities [Member] | Delmarva Power & Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	9
Other Current Liabilities [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other current liabilities	4
Other deferred credits and other liabilities [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	1,307
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	925
Other deferred credits and other liabilities [Member] | Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	8
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	50
Other deferred credits and other liabilities [Member] | Pepco Holdings LLC [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	254
Other deferred credits and other liabilities [Member] | Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	51
Other deferred credits and other liabilities [Member] | Delmarva Power & Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	65
Other deferred credits and other liabilities [Member] | Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Other deferred credits and other liabilities	$ 14

Lessee - Lessee Future Minimum

Lessee - Lessee Future Minimum Operating Lease Maturity Payments (Details) $ in Millions	Dec. 31, 2019USD ($)
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	$ 287
2021	243
2022	177
2023	145
2024	140
Remaining years	976
Lessee, Operating Lease, Liability, Payments, Due	1,968
Interest	436
Operating Lease, Liability	1,532
Exelon Generation Co L L C [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	203
2021	162
2022	113
2023	100
2024	97
Remaining years	741
Lessee, Operating Lease, Liability, Payments, Due	1,416
Interest	334
Operating Lease, Liability	1,082
Commonwealth Edison Co [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	3
2021	4
2022	2
2023	1
2024	1
Remaining years	1
Lessee, Operating Lease, Liability, Payments, Due	12
Interest	1
Operating Lease, Liability	11
PECO Energy Co [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	0
2021	1
2022	0
2023	0
2024	0
Remaining years	0
Lessee, Operating Lease, Liability, Payments, Due	1
Interest	0
Operating Lease, Liability	1
Baltimore Gas and Electric Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	34
2021	31
2022	16
2023	1
2024	0
Remaining years	18
Lessee, Operating Lease, Liability, Payments, Due	100
Interest	18
Operating Lease, Liability	82
Pepco Holdings LLC [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	42
2021	41
2022	38
2023	37
2024	35
Remaining years	153
Lessee, Operating Lease, Liability, Payments, Due	346
Interest	61
Operating Lease, Liability	285
Potomac Electric Power Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	8
2021	8
2022	8
2023	7
2024	5
Remaining years	34
Lessee, Operating Lease, Liability, Payments, Due	70
Interest	13
Operating Lease, Liability	57
Delmarva Power & Light Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	11
2021	11
2022	10
2023	9
2024	9
Remaining years	41
Lessee, Operating Lease, Liability, Payments, Due	91
Interest	17
Operating Lease, Liability	74
Atlantic City Electric Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	5
2021	4
2022	4
2023	3
2024	2
Remaining years	2
Lessee, Operating Lease, Liability, Payments, Due	20
Interest	2
Operating Lease, Liability	$ 18

Lessee - 2018 Schedule of Minim

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
2020	149
2021	143
2022	126
2023	97
Remaining Years	723
Total Minimum Future Lease Payments	1,378
Exelon Generation Co L L C [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	33
2020	46
2021	46
2022	47
2023	46
Remaining Years	545
Total Minimum Future Lease Payments	763
Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	7
2020	5
2021	4
2022	4
2023	3
Remaining Years	0
Total Minimum Future Lease Payments	23
PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	5
2020	5
2021	5
2022	5
2023	5
Remaining Years	0
Total Minimum Future Lease Payments	25
Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	35
2020	35
2021	33
2022	18
2023	3
Remaining Years	19
Total Minimum Future Lease Payments	143
Pepco Holdings LLC [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	48
2020	46
2021	43
2022	42
2023	39
Remaining Years	159
Total Minimum Future Lease Payments	377
Potomac Electric Power Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	11
2020	10
2021	9
2022	8
2023	8
Remaining Years	40
Total Minimum Future Lease Payments	86
Delmarva Power & Light Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	14
2020	13
2021	12
2022	12
2023	10
Remaining Years	35
Total Minimum Future Lease Payments	96
Atlantic City Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	7
2020	6
2021	5
2022	5
2023	4
Remaining Years	5
Total Minimum Future Lease Payments	32
Real Estate Leases and Railroad Licenses [Member] | Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total Minimum Future Lease Payments	3
Real Estate Leases and Railroad Licenses [Member] | PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total Minimum Future Lease Payments	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 Lease Payments	1
Real Estate Leases and Railroad Licenses [Member] | Delmarva Power & Light Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total Minimum Future Lease Payments	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

Lessee - Supplemental Cash Flow

Lessee - Supplemental Cash Flow Information Related to Leases (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	$ 287
Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	206
Commonwealth Edison Co [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	3
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	33
Pepco Holdings LLC [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	37
Potomac Electric Power Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	9
Delmarva Power & Light Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	6
Atlantic City Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Operating cash flows from operating leases	$ 5

Lessor - Narrative (Details)

Lessor - Narrative (Details)	12 Months Ended
	Dec. 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	83 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	32 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	17 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	83 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	23 years
Baltimore Gas and Electric Company [Member] | Maximum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	23 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	13 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	1 year
Potomac Electric Power Company [Member] | Maximum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	6 years
Delmarva Power & Light Company [Member] | Minimum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	12 years
Delmarva Power & Light Company [Member] | Maximum [Member]
Lessor, Lease, Description [Line Items]
Remaining lease terms, Lessor, Operating Lease	13 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	2 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 & 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	●

Lessor - Components of Operatin

Lessor - Components of Operating Lease Income (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	$ 54
Variable Lease Income	261
Exelon Generation Co L L C [Member]
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	47
Variable Lease Income	258
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	5
Variable Lease Income	3
Potomac Electric Power Company [Member]
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	0
Variable Lease Income	0
Delmarva Power & Light Company [Member]
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	4
Variable Lease Income	3
Atlantic City Electric Company [Member]
Schedule of Operating Lease, Lease Income [Line Items]
Operating Lease Income	0
Variable Lease Income	$ 0

Lessor - Operating Lease, Payme

Lessor - Operating Lease, Payments, Fiscal Year Maturity (Details) $ in Millions	Dec. 31, 2019USD ($)
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	$ 51
2020	51
2021	50
2022	49
2023	48
Remaining years	265
Total Lessor, Operating Lease, Payments to be Received	514
Exelon Generation Co L L C [Member]
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	46
2020	45
2021	45
2022	44
2023	44
Remaining years	226
Total Lessor, Operating Lease, Payments to be Received	450
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	5
2023	4
Remaining years	34
Total Lessor, Operating Lease, Payments to be Received	55
Potomac Electric Power Company [Member]
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	0
2020	1
2021	0
2022	0
2023	0
Remaining years	0
Total Lessor, Operating Lease, Payments to be Received	1
Delmarva Power & Light Company [Member]
Schedule of Lessor, Operating Lease, Payments to be Received, Maturity [Line Items]
2019	3
2020	3
2021	3
2022	4
2023	4
Remaining years	34
Total Lessor, Operating Lease, Payments to be Received	51
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

Asset Impairments - Narrative (

Asset Impairments - Narrative (Details) $ in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2019USD ($)	Dec. 31, 2017USD ($)	Jun. 30, 2017USD ($)	Dec. 31, 2019USD ($)MW	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Property, Plant and Equipment [Line Items]
Deferred Income Taxes and Tax Credits				$ 681	$ (108)	$ (362)
Impairment of Intangible Assets, Finite-lived		$ 25
Impairment of Long-Lived Assets Held-for-use				201	50	573
Certain Distributed Energy Companies [Member]
Property, Plant and Equipment [Line Items]
Equity Method Investment, Other than Temporary Impairment	$ 164
Net income (loss) attributable to noncontrolling interests	96
Deferred Income Taxes and Tax Credits	(46)
Income (Loss) from Equity Method Investments	(15)
Antelope Valley [Member]
Property, Plant and Equipment [Line Items]
Net Assets				725
Impairment of Long-Lived Assets Held-for-use				0
ExGen Renewables IV, LLC [Member]
Property, Plant and Equipment [Line Items]
Net Assets				1,893
Electricity Generation Plant, Non-Nuclear [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets to be Disposed of			$ 460
Pepco Holdings LLC [Member]
Property, Plant and Equipment [Line Items]
Deferred Income Taxes and Tax Credits				(7)	30	252
Impairment of Intangible Assets, Finite-lived		$ 25
Impairment of Long-Lived Assets Held-for-use				0	0	52
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Net income (loss) attributable to noncontrolling interests				92	73	88
Deferred Income Taxes and Tax Credits				361	(451)	(2,023)
Impairment of Long-Lived Assets Held-for-use				$ 201	$ 50	$ 510
Exelon Generation Co L L C [Member] | Certain Distributed Energy Companies [Member]
Property, Plant and Equipment [Line Items]
Equity Method Investment, Other than Temporary Impairment	164
Net income (loss) attributable to noncontrolling interests	96
Deferred Income Taxes and Tax Credits	(46)
Income (Loss) from Equity Method Investments	$ (15)
Exelon Generation Co L L C [Member] | Antelope Valley [Member]
Property, Plant and Equipment [Line Items]
Capacity Of Facility Of Company Owned Solar Distribution Generation Facilities | MW				242
Net Assets				$ 725
Impairment of Long-Lived Assets Held-for-use				0
Exelon Generation Co L L C [Member] | ExGen Renewables IV, LLC [Member]
Property, Plant and Equipment [Line Items]
Net Assets				$ 1,893
Exelon Generation Co L L C [Member] | Electricity Generation Plant, Non-Nuclear [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets to be Disposed of			$ 460

Intangible Assets - Narrative (

Intangible Assets - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Nov. 01, 2018	Mar. 24, 2016
Goodwill [Line Items]
Goodwill	$ 6,677	$ 6,677
Commonwealth Edison Co [Member]
Goodwill [Line Items]
Goodwill	2,625	2,625
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount			30.00%
Pepco Holdings LLC [Member]
Goodwill [Line Items]
Goodwill	4,005	4,005
Potomac Electric Power Company [Member]
Goodwill [Line Items]
Goodwill				$ 2,100
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount			30.00%
Delmarva Power & Light Company [Member]
Goodwill [Line Items]
Goodwill	$ 8	$ 8		1,400
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount			20.00%
Atlantic City Electric Company [Member]
Goodwill [Line Items]
Goodwill				$ 500
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount			30.00%

Intangible Assets - Schedule of

Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill, Gross	$ 8,660	$ 8,660
Accumulated Impairment Loss	1,983	1,983
Carrying amount	6,677	6,677
Commonwealth Edison Co [Member]
Goodwill [Line Items]
Goodwill, Gross	4,608	4,608
Accumulated Impairment Loss	1,983	1,983
Carrying amount	2,625	2,625
Pepco Holdings LLC [Member]
Goodwill [Line Items]
Goodwill, Gross	4,005	4,005
Accumulated Impairment Loss	0	0
Carrying amount	$ 4,005	$ 4,005

Intangible Assets - Schedule _2

Intangible Assets - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross	$ 1,295	$ 1,267
Accumulated Amortization	(1,121)	(1,149)
Net	174	118
Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	1,967	1,957
Accumulated Amortization	(1,612)	(1,588)
Net	355	369
Exelon Generation Co L L C [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	343	325
Accumulated Amortization	(190)	(162)
Net	153	163
Exelon Generation Co L L C [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	243	243
Accumulated Amortization	(193)	(171)
Net	50	72
Commonwealth Edison Co [Member] | Intangible Asset Nineteen Ninety Nine Chicago Settlement Agreement [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	162	162
Accumulated Amortization	(155)	(148)
Net	7	14
Pepco Holdings LLC [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	(1,515)	(1,515)
Accumulated Amortization	1,073	954
Net	(442)	(561)
Business Services Company [Member] | Licensing Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	95	95
Accumulated Amortization	(44)	(34)
Net	$ 51	$ 61

Intangible Assets Intangible As

Intangible Assets Intangible Assets - Summary of Amortization Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	$ (28)	$ (109)	$ (237)
Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	74	63	83
Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	7	7	7
Pepco Holdings LLC [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	(119)	(188)	(336)
Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Power Contracts Emission Credits	21	14	35
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Power Contracts Emission Credits	$ 21	$ 14	$ 35

Intangible Assets Intangible _2

Intangible Assets Intangible Assets - Schedule of Finite-Lived Intangible Assets, Future Amortization Expense (Details) $ in Millions	Dec. 31, 2019USD ($)
Finite-Lived Intangible Assets [Line Items]
2020	$ (13)
2021	2
2022	(21)
2023	(18)
2024	22
Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
2020	85
2021	84
2022	58
2023	53
2024	50
Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
2020	7
2021	0
2022	0
2023	0
2024	0
Pepco Holdings LLC [Member]
Finite-Lived Intangible Assets [Line Items]
2020	(115)
2021	(92)
2022	(89)
2023	(81)
2024	$ (38)

Intangible Assets - Renewable a

Intangible Assets - Renewable and Alternative Energy Credits (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	$ 345	$ 279
Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	86	52
Exelon Generation Co L L C [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	336	270
Exelon Generation Co L L C [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	$ 86	$ 52

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Millions	Jun. 05, 2019	Jul. 01, 2017	Jun. 30, 2017	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2019
Income Taxes [Line Items]
Income Tax Credits and Adjustments					$ 108
Current Federal, State and Local, Tax Expense (Benefit)					$ 97
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					19.40%	5.30%	(3.30%)
Like kind exchange [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible								$ 33
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Income Tax Credits and Adjustments					$ 75
Current Federal, State and Local, Tax Expense (Benefit)					$ 66
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					26.90%	(29.50%)	(94.60%)
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					19.20%	20.20%	42.40%
Commonwealth Edison Co [Member] | Like kind exchange [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible								$ 2
PECO Energy Co [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					11.00%	1.30%	19.30%
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					0.00%	13.80%	25.20%
Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					13.00%	15.50%	37.00%
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					6.20%	5.10%	34.70%
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					7.40%	7.80%	38.00%
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					18.00%	19.10%	41.50%
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes					$ (23)	$ 50	$ 0
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes					(9)	53	0
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes							0
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes							0
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes							0
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes					0	0	0
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes							0
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible					14
Increase (Decrease) in Income Taxes					0	$ 3	0
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes							$ 0
ILLINOIS
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, Percent	10.49%	9.50%	7.75%	9.50%
Tax Year 2019 [Member] | State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible					$ 21

Income Taxes - Components of In

Income Taxes - Components of Income Tax Expense (Benefit) from Continuing Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Income taxes	$ 774	$ 118	$ (126)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Income taxes	516	(108)	(1,376)
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Income taxes	163	168	417
PECO Energy Co [Member]
Income Taxes [Line Items]
Income taxes	65	6	104
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Income taxes	79	74	218
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Income taxes	38	33	217
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Income taxes	16	11	105
Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Income taxes	22	22	71
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Income taxes	0	12	26
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Current	85	226	194
Deferred	489	(99)	(470)
Investment Tax Credit	(72)	(24)	(25)
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current	147	337	584
Deferred	346	(347)	(2,005)
Investment Tax Credit	(69)	(21)	(21)
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current	59	(63)	(191)
Deferred	15	145	523
Investment Tax Credit	(2)	(2)	(2)
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Current	45	11	71
Deferred	20	10	28
Investment Tax Credit	0	0	0
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current	(51)	(5)	74
Deferred	95	47	101
Investment Tax Credit	0	0	(1)
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Current	43	(4)	(60)
Deferred	(34)	23	251
Investment Tax Credit	(1)	(1)	(1)
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Current	16	28	(20)
Deferred	(6)	(22)	115
Investment Tax Credit	0	0	0
Internal Revenue Service (IRS) [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Current	29	(3)	(24)
Deferred	(21)	13	82
Investment Tax Credit	0	0	0
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Current	(3)	(14)	(12)
Deferred	(6)	18	34
Investment Tax Credit	0	0	0
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Current	5	(1)	14
Deferred	267	16	161
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current	10	6	65
Deferred	82	(83)	1
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current	(5)	(29)	(49)
Deferred	96	117	136
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Current	0	1	14
Deferred	0	(16)	(9)
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current	0	0	(5)
Deferred	35	32	49
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Current	3	7	(4)
Deferred	27	8	31
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Current	0	0	(2)
Deferred	6	5	12
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Current	0	0	0
Deferred	14	12	13
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Current	0	0	0
Deferred	$ 9	$ 8	$ 4

Income Taxes - Reconciliation t

Income Taxes - Reconciliation to Effective Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	35.00%
State income taxes, net of Federal income tax benefit	5.40%	0.50%	2.20%
Qualified nuclear decommissioning trust fund income	5.90%	(1.90%)	3.80%
Amortization of investment tax credit, including deferred taxes on basis difference	(1.50%)	(1.20%)	(0.90%)
Plant basis differences	(1.40%)	(3.50%)	(1.70%)
Production tax credits and other credits	(3.10%)	(2.20%)	(1.80%)
Noncontrolling interests	(0.60%)	(1.00%)
Excess deferred tax amortization	(5.50%)	(8.30%)
Like-king exchange			(1.20%)
Merger expenses			(3.60%)
FitzPatrick bargain purchase gain			(2.20%)
Tax Cuts and Jobs Act of 2017		0.90%	(33.10%)
Other	(0.80%)	1.00%	0.20%
Effective income tax rate	19.40%	5.30%	(3.30%)
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 35
Exelon Generation Co L L C [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	35.00%
State income taxes, net of Federal income tax benefit	3.80%	(16.60%)	2.90%
Qualified nuclear decommissioning trust fund income	12.30%	(11.80%)	9.90%
Amortization of investment tax credit, including deferred taxes on basis difference	(3.00%)	(6.50%)	(2.10%)
Plant basis differences	0.00%	0.00%	0.00%
Production tax credits and other credits	(4.80%)	(13.50%)	(4.70%)
Noncontrolling interests	(1.20%)	(6.10%)
Excess deferred tax amortization	0.00%	0.00%
Like-king exchange			0.00%
Merger expenses			(1.20%)
FitzPatrick bargain purchase gain			(5.60%)
Tax Cuts and Jobs Act of 2017		2.70%	(128.30%)
Other	(1.20%)	1.30%	(0.50%)
Effective income tax rate	26.90%	(29.50%)	(94.60%)
Commonwealth Edison Co [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	35.00%
State income taxes, net of Federal income tax benefit	8.50%	8.30%	5.70%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)	(0.20%)
Plant basis differences	0.00%	(0.20%)	0.30%
Production tax credits and other credits	(1.20%)	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(9.70%)	(9.10%)
Like-king exchange			1.30%
Merger expenses			0.00%
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		(0.10%)	0.10%
Other	0.80%	0.50%	0.20%
Effective income tax rate	19.20%	20.20%	42.40%
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 3
PECO Energy Co [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	35.00%
State income taxes, net of Federal income tax benefit	0.00%	(2.60%)	0.60%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	(0.10%)	(0.10%)
Plant basis differences	(7.20%)	(14.10%)	(13.80%)
Production tax credits and other credits	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(2.80%)	(3.20%)
Like-king exchange			0.00%
Merger expenses			0.00%
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		0.00%	(2.30%)
Other	0.00%	0.30%	(0.10%)
Effective income tax rate	11.00%	1.30%	19.30%
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	35.00%
State income taxes, net of Federal income tax benefit	6.40%	6.60%	5.40%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)	(0.10%)
Plant basis differences	(1.20%)	(1.30%)	0.10%
Production tax credits and other credits	(1.30%)	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(6.80%)	(8.00%)
Like-king exchange			0.00%
Merger expenses			0.00%
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		0.00%	0.90%
Other	0.00%	0.90%	0.20%
Effective income tax rate	18.00%	19.10%	41.50%
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 5
Pepco Holdings LLC [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	35.00%
State income taxes, net of Federal income tax benefit	4.70%	2.90%	4.80%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)	(0.20%)
Plant basis differences	(1.20%)	(1.60%)	1.10%
Production tax credits and other credits	(0.20%)	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(17.50%)	(14.80%)
Like-king exchange			0.00%
Merger expenses			(9.60%)
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		0.10%	6.40%
Other	0.80%	0.40%	0.50%
Effective income tax rate	7.40%	7.80%	38.00%
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 27
Potomac Electric Power Company [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	35.00%
State income taxes, net of Federal income tax benefit	2.00%	2.00%	3.10%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)	(0.10%)
Plant basis differences	(1.80%)	(2.80%)	(0.40%)
Production tax credits and other credits	(0.10%)	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(15.10%)	(15.30%)
Like-king exchange			0.00%
Merger expenses			(6.40%)
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		0.00%	2.80%
Other	0.30%	0.30%	0.70%
Effective income tax rate	6.20%	5.10%	34.70%
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 14
Delmarva Power & Light Company [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	35.00%
State income taxes, net of Federal income tax benefit	6.80%	6.70%	5.40%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.30%)	(0.20%)
Plant basis differences	(0.40%)	(0.30%)	2.00%
Production tax credits and other credits	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(14.20%)	(12.00%)
Like-king exchange			0.00%
Merger expenses			(7.80%)
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		0.00%	2.50%
Other	0.00%	0.40%	0.10%
Effective income tax rate	13.00%	15.50%	37.00%
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 6
Atlantic City Electric Company [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	35.00%
State income taxes, net of Federal income tax benefit	7.00%	7.40%	5.60%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.30%)	(0.40%)	(0.40%)
Plant basis differences	(0.70%)	(0.50%)	3.60%
Production tax credits and other credits	(0.10%)	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(27.00%)	(14.90%)
Like-king exchange			0.00%
Merger expenses			(19.80%)
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		0.00%	1.60%
Other	0.10%	1.20%	(0.40%)
Effective income tax rate	0.00%	13.80%	25.20%
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 7

Income Taxes - Tax Effects of T

Income Taxes - Tax Effects of Temporary Differences and Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Plant basis differences	$ (13,413)	$ (12,533)
Deferred Tax Liabilities, Other Finite-Lived Assets	61	117
Derivatives and other financial instruments	165	89
Deferred pension and postretirement obligation	1,504	1,435
Deferred Tax Liabilities, Investments	(503)	(351)
Deferred debt refinancing costs	183	234
Deferred Tax Liabilities, Regulatory Assets and Liabilities	(884)	(740)
Tax loss carryforward	240	237
Tax credit carryforward	892	811
Investment in partnerships	(830)	(797)
Other, net	926	934
Deferred income tax liabilities (net)	(11,659)	(10,564)
Unamortized investment tax credits	(668)	(724)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(12,327)	(11,288)
Income Tax Expense (Benefit)	774	118	$ (126)
Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(2,814)	(2,495)
Deferred Tax Liabilities, Other Finite-Lived Assets	(43)	(44)
Derivatives and other financial instruments	88	35
Deferred pension and postretirement obligation	(220)	(188)
Deferred Tax Liabilities, Investments	(503)	(351)
Deferred debt refinancing costs	20	23
Deferred Tax Liabilities, Regulatory Assets and Liabilities	0	0
Tax loss carryforward	55	78
Tax credit carryforward	897	816
Investment in partnerships	(808)	(775)
Other, net	236	239
Deferred income tax liabilities (net)	(3,092)	(2,662)
Unamortized investment tax credits	(648)	(700)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(3,740)	(3,362)
Income Tax Expense (Benefit)	516	(108)	(1,376)
Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(4,197)	(4,059)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	84	69
Deferred pension and postretirement obligation	(270)	(255)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(7)	(7)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	183	300
Tax loss carryforward	0	0
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	196	151
Deferred income tax liabilities (net)	(4,011)	(3,801)
Unamortized investment tax credits	(10)	(12)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(4,021)	(3,813)
Income Tax Expense (Benefit)	163	168	417
PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,978)	(1,862)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(28)	(26)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	0	0
Deferred Tax Liabilities, Regulatory Assets and Liabilities	(169)	(129)
Tax loss carryforward	25	18
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	70	67
Deferred income tax liabilities (net)	(2,080)	(1,932)
Unamortized investment tax credits	(1)	(1)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(2,081)	(1,933)
Income Tax Expense (Benefit)	65	6	104
Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,578)	(1,399)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(28)	(26)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(3)	(3)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	157	172
Tax loss carryforward	49	25
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	10	12
Deferred income tax liabilities (net)	(1,393)	(1,219)
Unamortized investment tax credits	(3)	(3)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(1,396)	(1,222)
Income Tax Expense (Benefit)	79	74	218
Pepco Holdings LLC [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(2,681)	(2,577)
Deferred Tax Liabilities, Other Finite-Lived Assets	104	161
Derivatives and other financial instruments	2	3
Deferred pension and postretirement obligation	(89)	(102)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	142	187
Deferred Tax Liabilities, Regulatory Assets and Liabilities	(10)	(81)
Tax loss carryforward	93	96
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	181	196
Deferred income tax liabilities (net)	(2,258)	(2,117)
Unamortized investment tax credits	(7)	(8)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(2,265)	(2,125)
Income Tax Expense (Benefit)	38	33	217
Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,204)	(1,148)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(75)	(78)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(3)	(4)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	55	67
Tax loss carryforward	13	12
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	85	98
Deferred income tax liabilities (net)	(1,129)	(1,053)
Unamortized investment tax credits	(2)	(2)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(1,131)	(1,055)
Income Tax Expense (Benefit)	16	11	105
Delmarva Power & Light Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(753)	(743)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(42)	(46)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(2)	(2)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	88	96
Tax loss carryforward	44	52
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	12	17
Deferred income tax liabilities (net)	(653)	(626)
Unamortized investment tax credits	(2)	(2)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(655)	(628)
Income Tax Expense (Benefit)	22	22	71
Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(687)	(645)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(10)	(14)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(1)	(1)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	77	83
Tax loss carryforward	31	26
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	16	19
Deferred income tax liabilities (net)	(574)	(532)
Unamortized investment tax credits	(3)	(3)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(577)	(535)
Income Tax Expense (Benefit)	$ 0	12	$ 26
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Deferred Income Taxes		8,624
Increase (Decrease) in Regulatory Liabilities		7,315
Income Tax Expense (Benefit)		1,309
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Deferred Income Taxes		1,895
Income Tax Expense (Benefit)		1,895
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Deferred Income Taxes		2,819
Increase (Decrease) in Regulatory Liabilities		2,818
Income Tax Expense (Benefit)		1
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Deferred Income Taxes		1,407
Increase (Decrease) in Regulatory Liabilities		1,394
Income Tax Expense (Benefit)		13
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Deferred Income Taxes		1,120
Increase (Decrease) in Regulatory Liabilities		1,124
Income Tax Expense (Benefit)		(4)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Pepco Holdings LLC [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Deferred Income Taxes		1,944
Increase (Decrease) in Regulatory Liabilities		1,979
Income Tax Expense (Benefit)		(35)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Deferred Income Taxes		968
Increase (Decrease) in Regulatory Liabilities		976
Income Tax Expense (Benefit)		(8)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Delmarva Power & Light Company [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Deferred Income Taxes		540
Increase (Decrease) in Regulatory Liabilities		545
Income Tax Expense (Benefit)		(5)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Deferred Income Taxes		456
Increase (Decrease) in Regulatory Liabilities		458
Income Tax Expense (Benefit)		$ (2)

Income Taxes - Schedule of Carr

Income Taxes - Schedule of Carryforwards and Corresponding Valuation Allowances (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards(a)	$ 0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2034
Federal general business credits carryforwards(a)	$ 891
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards(a)	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards(a)	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Pepco Holdings LLC [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards(a)	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards(a)	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Delmarva Power & Light Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards(a)	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards(a)	$ 0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2034
Federal general business credits carryforwards(a)	$ 897
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	3,986
Deferred taxes on state tax attributes (net)	264
Valuation allowance on state tax attributes	$ 26
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2025
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 0
Deferred taxes on state tax attributes (net)	0
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	312
Deferred taxes on state tax attributes (net)	25
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2031
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 762
Deferred taxes on state tax attributes (net)	50
Valuation allowance on state tax attributes	$ 1
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2026
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 1,360
Deferred taxes on state tax attributes (net)	93
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2028
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 202
Deferred taxes on state tax attributes (net)	13
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2028
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 654
Deferred taxes on state tax attributes (net)	44
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2030
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 438
Deferred taxes on state tax attributes (net)	31
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2031
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 1,142
Deferred taxes on state tax attributes (net)	78
Valuation allowance on state tax attributes	$ 24
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2029

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning Balance	$ 477	$ 743	$ 916
Increases based on tax positions prior to current year	34	30	28
Unrecognized Tax Benefits, Period Increase (Decrease)	26	15
Increases based on tax positions related to current year	2
Decreases based on tax positions prior to current year	3	251	196
Decrease from settlements with taxing authorities	(29)	(53)	(5)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		(7)
Unrecognized tax benefits - Ending Balance	507	477	743
Exelon Generation Co L L C [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning Balance	408	468	490
Increases based on tax positions prior to current year	19	21	0
Unrecognized Tax Benefits, Period Increase (Decrease)	12	15
Increases based on tax positions related to current year	1
Decreases based on tax positions prior to current year	3	36	17
Decrease from settlements with taxing authorities	4	(53)	(5)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		(7)
Unrecognized tax benefits - Ending Balance	441	408	468
Commonwealth Edison Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning Balance	2	2	(12)
Increases based on tax positions prior to current year	3	0	14
Unrecognized Tax Benefits, Period Increase (Decrease)	3	0
Increases based on tax positions related to current year	0
Decreases based on tax positions prior to current year	0	0	0
Decrease from settlements with taxing authorities	(2)	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		0
Unrecognized tax benefits - Ending Balance	6	2	2
PECO Energy Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning Balance	0	0	0
Increases based on tax positions prior to current year	2	0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	1	0
Increases based on tax positions related to current year	0
Decreases based on tax positions prior to current year	0	0	0
Decrease from settlements with taxing authorities	0	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		0
Unrecognized tax benefits - Ending Balance	3	0	0
Baltimore Gas and Electric Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning Balance	0	120	120
Increases based on tax positions prior to current year	3	0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	4	0
Increases based on tax positions related to current year	0
Decreases based on tax positions prior to current year	0	120	0
Decrease from settlements with taxing authorities	0	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		0
Unrecognized tax benefits - Ending Balance	7	0	120
Pepco Holdings LLC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning Balance	45	125	172
Increases based on tax positions prior to current year	0	8	14
Unrecognized Tax Benefits, Period Increase (Decrease)	3	0
Increases based on tax positions related to current year	0
Decreases based on tax positions prior to current year	0	88	61
Decrease from settlements with taxing authorities	0	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		0
Unrecognized tax benefits - Ending Balance	48	45	125
Potomac Electric Power Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning Balance	0	59	80
Increases based on tax positions prior to current year	0	7	0
Unrecognized Tax Benefits, Period Increase (Decrease)	2	0
Increases based on tax positions related to current year	0
Decreases based on tax positions prior to current year	0	66	21
Decrease from settlements with taxing authorities	0	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		0
Unrecognized tax benefits - Ending Balance	2	0	59
Delmarva Power & Light Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning Balance	0	21	37
Increases based on tax positions prior to current year	0	1	0
Unrecognized Tax Benefits, Period Increase (Decrease)	1	0
Increases based on tax positions related to current year	0
Decreases based on tax positions prior to current year	0	22	16
Decrease from settlements with taxing authorities	0	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		0
Unrecognized tax benefits - Ending Balance	1	0	21
Atlantic City Electric Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning Balance	14	14	22
Increases based on tax positions prior to current year	0	0	14
Unrecognized Tax Benefits, Period Increase (Decrease)	0	0
Increases based on tax positions related to current year	0
Decreases based on tax positions prior to current year	0	0	22
Decrease from settlements with taxing authorities	0	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		0
Unrecognized tax benefits - Ending Balance	14	$ 14	14
Internal Revenue Service (IRS) [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			146
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			19
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			59
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			21
Internal Revenue Service (IRS) [Member] | Delmarva Power & Light Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			16
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			$ 22
State and Local Jurisdiction [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	425
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	411
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 14

Income Taxes - Recognition of U

Income Taxes - Recognition of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 462	$ 463	$ 523
Exelon Generation Co L L C [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	429	408	461
Commonwealth Edison Co [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	0	0
PECO Energy Co [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	0	0
Baltimore Gas and Electric Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	1	0	0
Pepco Holdings LLC [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	32	31	32
Potomac Electric Power Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	0	0
Delmarva Power & Light Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	0	0
Atlantic City Electric Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	$ 0	$ 0
State and Local Jurisdiction [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	411
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	14
Tax Year 2019 [Member] | State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 21

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits That Effect Future Base Rates (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	$ 19	$ 14	$ 214
Commonwealth Edison Co [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	0	0	0
PECO Energy Co [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	0	0	0
Baltimore Gas and Electric Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	1	0	120
Pepco Holdings LLC [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	14	14	94
Potomac Electric Power Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	0	0	59
Delmarva Power & Light Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	0	0	21
Atlantic City Electric Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible	$ 14	$ 14	$ 14

Income Taxes - Settlements of I

Income Taxes - Settlements of Income Tax Audits, Refund Claims, and Litigation (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 462	$ 463	$ 523
State and Local Jurisdiction [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	425
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	411
Exelon Generation Co LLC Affiliate [Member] | State and Local Jurisdiction [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	411
Exelon Generation Co L L C [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	429	408	461
Exelon Generation Co L L C [Member] | State and Local Jurisdiction [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	411
Commonwealth Edison Co [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	0	0
Commonwealth Edison Co [Member] | State and Local Jurisdiction [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
PECO Energy Co [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	0	0
PECO Energy Co [Member] | State and Local Jurisdiction [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
Baltimore Gas and Electric Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	1	0	0
Baltimore Gas and Electric Company [Member] | State and Local Jurisdiction [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
Pepco Holdings LLC [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	32	31	32
Pepco Holdings LLC [Member] | State and Local Jurisdiction [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
Potomac Electric Power Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	0	0
Potomac Electric Power Company [Member] | State and Local Jurisdiction [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
Delmarva Power & Light Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	0	0
Delmarva Power & Light Company [Member] | State and Local Jurisdiction [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
Atlantic City Electric Company [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	$ 0	$ 0
Atlantic City Electric Company [Member] | State and Local Jurisdiction [Member]
Recognition of Unrecognized Tax Benefits [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 14

Income Taxes - Summary of Inter

Income Taxes - Summary of Interest Receivable (Payable) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	$ 318	$ 219
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	$ 0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
PECO Energy Co [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	$ 0	$ 0	$ 0

Income Taxes - Remeasurement of

Income Taxes - Remeasurement of Deferred Income Tax Balances - Federal (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Income Tax Expense (Benefit)	$ 774	$ 118	$ (126)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	516	(108)	(1,376)
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	163	168	417
PECO Energy Co [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	65	6	104
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	79	74	218
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	38	33	217
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	16	11	105
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	22	22	71
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	$ 0	12	$ 26
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		8,624
Increase (Decrease) in Regulatory Liabilities		7,315
Income Tax Expense (Benefit)		1,309
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		1,895
Income Tax Expense (Benefit)		1,895
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		2,819
Increase (Decrease) in Regulatory Liabilities		2,818
Income Tax Expense (Benefit)		1
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		1,407
Increase (Decrease) in Regulatory Liabilities		1,394
Income Tax Expense (Benefit)		13
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		1,120
Increase (Decrease) in Regulatory Liabilities		1,124
Income Tax Expense (Benefit)		(4)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		1,944
Increase (Decrease) in Regulatory Liabilities		1,979
Income Tax Expense (Benefit)		(35)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		968
Increase (Decrease) in Regulatory Liabilities		976
Income Tax Expense (Benefit)		(8)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		540
Increase (Decrease) in Regulatory Liabilities		545
Income Tax Expense (Benefit)		(5)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		456
Increase (Decrease) in Regulatory Liabilities		458
Income Tax Expense (Benefit)		$ (2)

Income Taxes - Remeasurement _2

Income Taxes - Remeasurement of Deferred Income Tax Balances - State (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Income Tax Expense (Benefit)	$ 774	$ 118	$ (126)
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes	23	(50)	0
ILLINOIS | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes			250
Increase (Decrease) in Other Regulatory Assets			270
Income Tax Expense (Benefit)			(20)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	516	(108)	(1,376)
Exelon Generation Co L L C [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes	9	(53)	0
Exelon Generation Co L L C [Member] | ILLINOIS
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes			20
Increase (Decrease) in Other Regulatory Assets			0
Income Tax Expense (Benefit)			20
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	$ 163	$ 168	417
Commonwealth Edison Co [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes			0
Commonwealth Edison Co [Member] | ILLINOIS
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes			270
Increase (Decrease) in Other Regulatory Assets			270
Income Tax Expense (Benefit)			$ 0

Income Taxes - Long-Term Margin

Income Taxes - Long-Term Marginal State Income Tax Rate (Details) - State and Local Jurisdiction [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes	$ 23	$ (50)	$ 0
Increase (Decrease) in Income Taxes	23	(50)	0
Exelon Generation Co L L C [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes	9	(53)	0
Increase (Decrease) in Income Taxes	9	(53)	0
Commonwealth Edison Co [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes			0
Increase (Decrease) in Income Taxes			0
PECO Energy Co [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes			0
Increase (Decrease) in Income Taxes			0
Baltimore Gas and Electric Company [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes			0
Increase (Decrease) in Income Taxes			0
Pepco Holdings LLC [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes	0	(4)	0
Increase (Decrease) in Income Taxes	0	(3)	0
Potomac Electric Power Company [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes			0
Increase (Decrease) in Income Taxes			0
Delmarva Power & Light Company [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes	0	(2)	0
Increase (Decrease) in Income Taxes	$ 0	$ 0	0
Atlantic City Electric Company [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes			0
Increase (Decrease) in Income Taxes			$ 0

Income Taxes - Allocation of Ta

Income Taxes - Allocation of Tax Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	$ 41	$ 155	$ 102
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	0	1	0
PECO Energy Co [Member]
Income Taxes [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	14	48	16
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	3	26	10
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	7	2	7
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	6	0	0
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	1	0	0
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	$ 0	$ 0	$ 0

Retirement Benefits- Narrative

Retirement Benefits- Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Increase (Decrease) in Obligation, Pension Benefits	$ 75
Benefit obligation increase (decrease) reflecting actual census data	36
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax	39
Regulatory asset increase (decrease) due to updated valuation adjustment	53
Defined benefit plan, amounts recognized In regulatory liabilities, before tax	$ 5
Defined Contribution Plan, Employer Discretionary Contribution Amount		$ 161	$ 179	$ 128
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount		0
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory asset increase (decrease) due to updated valuation adjustment		$ 3	$ (6)	$ (423)
Expected return on plan assets		7.00%	7.00%	7.00%
Mortality Rate		0.75%	0.75%
Discount rate		4.31%	3.62%	4.04%
Defined Contribution Plan, Employer Discretionary Contribution Amount		$ 500
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory asset increase (decrease) due to updated valuation adjustment		$ 106	$ (57)	$ 125
Expected return on plan assets		6.67%	6.60%	6.58%
Mortality Rate		0.75%	0.75%
Discount rate		4.30%	3.61%	4.04%
Change in Assumptions for Defined Benefit Plans [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets		7.00%
Discount rate		4.31%
Change in Assumptions for Defined Benefit Plans [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets		6.67%
Discount rate		4.30%
Assets [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate		18.80%
Assets [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate		14.40%
Subsequent Event [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets		7.00%
Subsequent Event [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets		6.69%

Retirement Benefits - Summary o

Retirement Benefits - Summary of Changes in Benefit Obligations and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Net benefit obligation at beginning of year	$ 20,692	$ 22,337
Service cost	357	405	$ 387
Interest cost	883	802	842
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	0	0
Actuarial (gain) loss(a)	2,322	(1,561)
Plan amendments	68	(4)
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment	(3)	0
Settlements	(35)	(48)
Defined Benefit Plan, Benefit Obligation, Special and Contractual Termination Benefits	1	0
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(1,417)	(1,239)
Net benefit obligation at end of year	22,868	20,692	22,337
Fair value of net plan assets at beginning of year	16,678	18,573
Actual return on plan assets	3,008	(945)
Employer contributions	356	337
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	0	0
Defined Benefit Plan, Plan Assets, Benefits Paid	(1,417)	(1,239)
Defined Benefit Plan, Plan Assets, Amount	18,590	16,678	18,573
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Net benefit obligation at beginning of year	4,369	4,856
Service cost	93	112	106
Interest cost	188	175	182
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	44	45
Actuarial (gain) loss(a)	250	(540)
Plan amendments	0	0
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment	0	0
Settlements	(4)	(4)
Defined Benefit Plan, Benefit Obligation, Special and Contractual Termination Benefits	0	0
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(282)	(275)
Net benefit obligation at end of year	4,658	4,369	4,856
Fair value of net plan assets at beginning of year	2,408	2,732
Actual return on plan assets	324	(136)
Employer contributions	51	46
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	44	45
Defined Benefit Plan, Plan Assets, Benefits Paid	(282)	(275)
Defined Benefit Plan, Plan Assets, Amount	$ 2,541	$ 2,408	$ 2,732

Retirement Benefits - Balance S

Retirement Benefits - Balance Sheet locations of Benefit Obligations and Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities	$ 31	$ 26
Pension obligations	4,247	3,988
Non-pension postretirement benefit obligations	0	0
Unfunded status (net benefit obligation less plan assets)	4,278	4,014
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities	41	33
Pension obligations	0	0
Non-pension postretirement benefit obligations	2,076	1,928
Unfunded status (net benefit obligation less plan assets)	$ 2,117	$ 1,961

Retirement Benefits- Projected

Retirement Benefits- Projected Benefit Obligations and Accumulated Benefit Obligations in Excess of Plan Assets (Details) - Accumulated Benefit Obligation In Excess Of Plan Assets [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 21,727	$ 19,656
Fair value of net plan assets	$ 18,590	$ 16,678

Retirement Benefits - Component

Retirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 13	$ (47)	$ (109)
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	357	405	387
Interest cost	883	802	842
Expected return on assets	(1,225)	(1,252)	(1,196)
Prior service cost (credit)	0	2	1
Actuarial loss	414	629	607
Settlement and other charges	17	3	3
Contractual Termination Benefits	1	0	0
Net periodic benefit cost	447	589	644
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	93	112	106
Interest cost	188	175	182
Expected return on assets	(153)	(173)	(162)
Prior service cost (credit)	(179)	(186)	(188)
Actuarial loss	45	66	61
Settlement and other charges	1	1	0
Contractual Termination Benefits	0	0	0
Net periodic benefit cost	$ (5)	$ (5)	$ (1)

Retirement Benefits - Allocated

Retirement Benefits - Allocated Portion of Pension and Postretirement Benefit Plan Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense	$ 442	$ 583	$ 643
Exelon Generation Co L L C [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense	135	204	227
Commonwealth Edison Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense	96	177	176
PECO Energy Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense	12	18	29
Baltimore Gas and Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense	61	60	64
Pepco Holdings LLC [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense	95	67	94
Potomac Electric Power Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense	25	15	25
Delmarva Power & Light Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense	15	6	13
Atlantic City Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense	$ 16	$ 12	$ 13

Retirement Benefits - Compone_2

Retirement Benefits - Components of Accumulated Other Comprehensive Income and Regulatory Assets (Liabilities) related to Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, amounts recognized in regulatory assets, before tax	$ 53
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial (gain) loss		$ 538	$ 635	$ (222)
Amortization of actuarial loss		(414)	(629)	(607)
Current year prior service cost (credit)		68	(4)	9
Amortization of prior service (cost) credit		0	(2)	(1)
Curtailments		(3)	0	0
Settlements		(17)	(3)	(3)
Total recognized in AOCI and regulatory assets (liabilities)		172	(3)	(824)
Defined benefit plan, amounts recognized in OCI, before tax		169	3	(401)
Defined benefit plan, amounts recognized in regulatory assets, before tax		3	(6)	(423)
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial (gain) loss		80	(232)	166
Amortization of actuarial loss		(45)	(66)	(61)
Current year prior service cost (credit)		0	0	0
Amortization of prior service (cost) credit		179	186	188
Curtailments		0	0	0
Settlements		(1)	0	0
Total recognized in AOCI and regulatory assets (liabilities)		213	(112)	293
Defined benefit plan, amounts recognized in OCI, before tax		107	(55)	168
Defined benefit plan, amounts recognized in regulatory assets, before tax		$ 106	$ (57)	$ 125

Retirement Benefits - Gross Acc

Retirement Benefits - Gross Accumulated Other Comprehensive Loss and Regulatory Assets (Liabilities) not Recognized as Components of Periodic Benefit Cost (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (credit) cost	$ 39	$ (29)
Actuarial loss	7,662	7,558
Total	7,701	7,529
Benefits included in accumulated other comprehensive income	4,068	3,899
Benefits included in regulatory assets	3,633	3,630
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (credit) cost	(158)	(337)
Actuarial loss	565	531
Total	407	194
Benefits included in accumulated other comprehensive income	177	70
Benefits included in regulatory assets	$ 230	$ 124

Retirement Benefits - Assumptio

Retirement Benefits - Assumptions Used in Calculations (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CENG Legacy Benefit Plans [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes	4.13%	3.49%	3.66%
CENG Legacy Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes	4.36%	3.65%	4.11%
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate - Obligation	3.34%	4.31%
Benefit Obligation Investment Crediting Rate	3.82%	4.46%
Discount rate - Net Periodic Benefit Costs	4.31%	3.62%	4.04%
Net Periodic Benefit Cost Investment Crediting Rate	4.46%	4.00%	4.46%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	7.00%	7.00%	7.00%
Pension Plan, Defined Benefit [Member] | CENG Legacy Benefit Plans [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes	3.02%	4.13%
Pension Plan, Defined Benefit [Member] | CENG Legacy Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes	3.44%	4.36%
Pension Plan, Defined Benefit [Member] | Period One [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.25%
Pension Plan, Defined Benefit [Member] | Period Two [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.75%
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Rate of compensation increase		5.00%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate - Obligation	3.31%	4.30%
Health care cost trend rate	5.00%	5.00%	5.50%
Ultimate health care cost trend rate	5.00%	5.00%	5.00%
Discount rate - Net Periodic Benefit Costs	4.30%	3.61%	4.04%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	6.67%	6.60%	6.58%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes	4.27%	3.57%	4.00%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes	4.38%	3.68%	4.17%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | CENG Legacy Benefit Plans [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes	3.27%	4.27%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | CENG Legacy Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes	3.40%	4.38%

Retirement Benefits - Contribut

Retirement Benefits - Contributions made to Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	$ 408	$ 383	$ 405
Expected qualified pension plan contributions	505
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	36
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	42
Constellation Legacy Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	0	0	21
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	175	139	148
Expected qualified pension plan contributions	227
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	14
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	16
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	77	42	41
Expected qualified pension plan contributions	141
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	2
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	3
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	28	28	24
Expected qualified pension plan contributions	17
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	1
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	0
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	48	54	53
Expected qualified pension plan contributions	56
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	2
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	16
Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	25	74	99
Expected qualified pension plan contributions	22
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	9
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	7
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	14	17	72
Expected qualified pension plan contributions	0
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	2
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	7
Delmarva Power & Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	1	0	2
Expected qualified pension plan contributions	0
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	1
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	0
Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	1	6	20
Expected qualified pension plan contributions	2
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	0
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	0
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	356	337	341
Pension Plan, Defined Benefit [Member] | Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	160	128	137
Pension Plan, Defined Benefit [Member] | Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	72	38	36
Pension Plan, Defined Benefit [Member] | PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	27	28	24
Pension Plan, Defined Benefit [Member] | Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	34	40	39
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	10	62	67
Pension Plan, Defined Benefit [Member] | Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	2	6	62
Pension Plan, Defined Benefit [Member] | Delmarva Power & Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	1	0	0
Pension Plan, Defined Benefit [Member] | Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	0	6	0
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	51	46	64
Other Postretirement Benefit Plan, Defined Benefit [Member] | Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	15	11	11
Other Postretirement Benefit Plan, Defined Benefit [Member] | Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	5	4	5
Other Postretirement Benefit Plan, Defined Benefit [Member] | PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	1	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	14	14	14
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	15	12	32
Other Postretirement Benefit Plan, Defined Benefit [Member] | Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	12	11	10
Other Postretirement Benefit Plan, Defined Benefit [Member] | Delmarva Power & Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	0	0	2
Other Postretirement Benefit Plan, Defined Benefit [Member] | Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	$ 1	$ 0	$ 20

Retirement Benefits - Estimated

Retirement Benefits - Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2019USD ($)
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2020	$ 1,227
2021	1,252
2022	1,295
2023	1,310
2024	1,324
2025 through 2029	6,770
Total estimated future benefit payments through 2029	13,178
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2020	258
2021	263
2022	267
2023	270
2024	275
2025 through 2029	1,402
Total estimated future benefit payments through 2029	$ 2,735

Retirement Benefits - Pension a

Retirement Benefits - Pension and Other Postretirement Benefit Plan Target Asset Allocations (Details)	Dec. 31, 2019	Dec. 31, 2018
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	100.00%	100.00%
Pension Plan, Defined Benefit [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	33.00%	35.00%
Pension Plan, Defined Benefit [Member] | Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	44.00%	37.00%
Pension Plan, Defined Benefit [Member] | Alternative Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	23.00%	28.00%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	100.00%	100.00%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	46.00%	47.00%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	32.00%	28.00%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Alternative Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	22.00%	25.00%

Retirement Benefits - Fair Valu

Retirement Benefits - Fair Value Measurements of Pension and Postretirement Benefit Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Derivative, Fair Value, Net	$ 2	$ 1
Derivative, Notional Amount	6,668	5,991
Net liabilities pending transactions excluded	120	44
Fair Value, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	21,251	19,130
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,955	5,463
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,440	4,581
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	487	486
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	18,590	16,678	$ 18,573
Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	487	486	458
Pension Plan, Defined Benefit [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	245	216	232
Pension Plan, Defined Benefit [Member] | Private Placement [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	237	268	224
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	18,710	16,720
Alternative Investment	7,916	7,247
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,168	4,710
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,139	4,277
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	487	486
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	258	350
Alternative Investment	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	258	350
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	6,210	5,346
Alternative Investment	2,589	1,980
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3,616	3,364
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5	2
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,574	1,169
Alternative Investment	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,294	996
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	280	173
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	56	59
Alternative Investment	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	56	59
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	4,587	3,932
Alternative Investment	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	4,342	3,716
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	245	216
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,312	942
Alternative Investment	851	613
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	461	329
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	7,529	6,102
Alternative Investment	851	613
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,294	996
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,139	4,277
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	245	216
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,391	1,219
Alternative Investment	1,391	1,219
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,126	1,608
Alternative Investment	1,126	1,608
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,030	1,029
Alternative Investment	1,030	1,029
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,166	1,066
Alternative Investment	929	798
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Pension Plan, Defined Benefit [Member] | Fair Value, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	237	268
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2,541	2,408	$ 2,732
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2,541	2,410
Alternative Investment	9,369	8,600
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	787	753
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	301	304
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Alternative Investment	1,453	1,353
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	39	22
Alternative Investment	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	39	22
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,195	1,047
Alternative Investment	719	508
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	473	537
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3	2
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	81	67
Alternative Investment	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	17	11
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	64	56
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	107	126
Alternative Investment	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	107	126
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	49	48
Alternative Investment	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	49	48
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	537	425
Alternative Investment	201	170
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	258	183
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	78	72
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	774	666
Alternative Investment	201	170
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	275	194
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	298	302
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	293	411
Alternative Investment	293	411
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	109	132
Alternative Investment	109	132
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	131	132
Alternative Investment	131	132
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefits Plan [Member] | Fair Value, Recurring [Member] | Private Placement [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0

Retirement Benefits - Reconcili

Retirement Benefits - Reconciliation of Level 3 Assets and Liabilities measured at Fair Value for Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	$ 16,678	$ 18,573
Defined Benefit Plan, Plan Assets, Amount	18,590	16,678
Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	486	458
Relating to assets still held at the reporting date	59	(5)
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	(7)	(1)
Defined Benefit Plan Purchases	67	54
Defined Benefit Plan Sales	(4)	(8)
Settlements	(102)	(12)
Transfers out of Level 3	(12)
Defined Benefit Plan, Plan Assets, Amount	487	486
Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	216	232
Relating to assets still held at the reporting date	28	(14)
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	(7)	(1)
Defined Benefit Plan Purchases	26	19
Defined Benefit Plan Sales	(4)	(8)
Settlements	(2)	(12)
Transfers out of Level 3	(12)
Defined Benefit Plan, Plan Assets, Amount	245	216
Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Security Individually Held [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	2	2
Relating to assets still held at the reporting date	3	0
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	0	0
Defined Benefit Plan Purchases	0	0
Defined Benefit Plan Sales	0	0
Settlements	0	0
Transfers out of Level 3	0
Defined Benefit Plan, Plan Assets, Amount	5	2
Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	268	224
Relating to assets still held at the reporting date	28	9
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	0	0
Defined Benefit Plan Purchases	41	35
Defined Benefit Plan Sales	0	0
Settlements	(100)	0
Transfers out of Level 3	0
Defined Benefit Plan, Plan Assets, Amount	237	268
Fair Value, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	19,130
Defined Benefit Plan, Plan Assets, Amount	21,251	19,130
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	486
Defined Benefit Plan, Plan Assets, Amount	487	486
Fair Value, Recurring [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	16,720
Defined Benefit Plan, Plan Assets, Amount	18,710	16,720
Fair Value, Recurring [Member] | Pension Plan, Defined Benefit [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	6,102
Defined Benefit Plan, Plan Assets, Amount	7,529	6,102
Fair Value, Recurring [Member] | Pension Plan, Defined Benefit [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	1,066
Defined Benefit Plan, Plan Assets, Amount	1,166	1,066
Fair Value, Recurring [Member] | Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	486
Defined Benefit Plan, Plan Assets, Amount	487	486
Fair Value, Recurring [Member] | Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	216
Defined Benefit Plan, Plan Assets, Amount	245	216
Fair Value, Recurring [Member] | Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	268
Defined Benefit Plan, Plan Assets, Amount	$ 237	$ 268

Retirement Benefits - Summary_2

Retirement Benefits - Summary of Defined Contribution Savings Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	$ 161	$ 179	$ 128
Exelon Generation Co L L C [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	73	86	55
Commonwealth Edison Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	35	37	31
PECO Energy Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	11	9	10
Baltimore Gas and Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	12	12	10
Pepco Holdings LLC [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	13	13	13
Potomac Electric Power Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	3	3	3
Delmarva Power & Light Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	3	2	2
Atlantic City Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	$ 2	$ 2	$ 2

Derivative Financial Instrume_3

Derivative Financial Instruments - Narrative (Details) MWh in Millions, $ in Millions	1 Months Ended	12 Months Ended
	Jun. 30, 2012MWh	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Derivative [Line Items]
Derivative, Notional Amount		$ 6,668	$ 5,991
Incremental collateral for loss of investment grade credit rating		1,509	2,104
Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		1,269	1,420
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating		1,509	2,104
Exelon Generation Co L L C [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		569	620
Exelon Generation Co L L C [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount		$ 231	$ 268
Exelon Generation Co L L C [Member] | Minimum [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months		91.00%
Expected generation hedged in year two		61.00%
Exelon Generation Co L L C [Member] | Maximum [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months		94.00%
Expected generation hedged in year two		64.00%
Commonwealth Edison Co [Member]
Derivative [Line Items]
Long-term Purchase Commitment, Minimum Energy Volume Required | MWh	1.3
PECO Energy Co [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating		$ 44
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating		50
Delmarva Power & Light Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating		$ 11

Derivative Financial Instrume_4

Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Mark-to-market derivative assets, current	$ 679	$ 804
Mark-to-market derivative assets, noncurrent	508	452
Mark-to-market derivative liabilities, current	(247)	(475)
Mark-to-market derivative liabilities, noncurrent	(393)	(479)
Total mark-to-market derivative net assets (liabilities)	2	1
Margin Deposit Assets	511	(94)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	675	804
Mark-to-market derivative assets, noncurrent	508	452
Mark-to-market derivative liabilities, current	(215)	(449)
Mark-to-market derivative liabilities, noncurrent	(123)	(252)
Margin Deposit Assets	511	94
Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities, current	(32)	(26)
Mark-to-market derivative liabilities, noncurrent	(269)	(223)
Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	675	801
Mark-to-market derivative assets, noncurrent	508	445
Total mark-to-market derivative assets	1,183	1,246
Mark-to-market derivative liabilities, current	(236)	(473)
Mark-to-market derivative liabilities, noncurrent	(380)	(474)
Total mark-to-market derivative liabilities	(616)	(947)
Total mark-to-market derivative net assets (liabilities)	567	299
Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	675	801
Mark-to-market derivative assets, noncurrent	508	445
Total mark-to-market derivative assets	1,183	1,246
Mark-to-market derivative liabilities, current	(204)	(447)
Mark-to-market derivative liabilities, noncurrent	(111)	(251)
Total mark-to-market derivative liabilities	(315)	(698)
Total mark-to-market derivative net assets (liabilities)	868	548
Commodity Contract [Member] | Collateral [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	287	121
Mark-to-market derivative assets, noncurrent	122	51
Total mark-to-market derivative assets	409	172
Mark-to-market derivative liabilities, current	357	125
Mark-to-market derivative liabilities, noncurrent	163	60
Total mark-to-market derivative liabilities	520	185
Total mark-to-market derivative net assets (liabilities)	929	357
Commodity Contract [Member] | Netting [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	(3,190)	(2,930)
Mark-to-market derivative assets, noncurrent	(877)	(913)
Total mark-to-market derivative assets	(4,067)	(3,843)
Mark-to-market derivative liabilities, current	3,190	2,931
Mark-to-market derivative liabilities, noncurrent	877	912
Total mark-to-market derivative liabilities	4,067	3,843
Total mark-to-market derivative net assets (liabilities)	0	0
Commodity Contract [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	3,506	3,505
Mark-to-market derivative assets, noncurrent	1,238	1,266
Total mark-to-market derivative assets	4,744	4,771
Mark-to-market derivative liabilities, current	(3,713)	(3,429)
Mark-to-market derivative liabilities, noncurrent	(1,140)	(1,203)
Total mark-to-market derivative liabilities	(4,853)	(4,632)
Total mark-to-market derivative net assets (liabilities)	(109)	139
Commodity Contract [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	0	0
Mark-to-market derivative assets, noncurrent	0	0
Total mark-to-market derivative assets	0	0
Mark-to-market derivative liabilities, current	(32)	(26)
Mark-to-market derivative liabilities, noncurrent	(269)	(223)
Total mark-to-market derivative liabilities	(301)	(249)
Total mark-to-market derivative net assets (liabilities)	(301)	(249)
Commodity Contract [Member] | Not Designated as Hedging Instrument, Trading [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	72	105
Mark-to-market derivative assets, noncurrent	25	41
Total mark-to-market derivative assets	97	146
Mark-to-market derivative liabilities, current	(38)	(74)
Mark-to-market derivative liabilities, noncurrent	(11)	(20)
Total mark-to-market derivative liabilities	(49)	(94)
Total mark-to-market derivative net assets (liabilities)	$ 48	$ 52

Derivative Financial Instrume_5

Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (222)	$ (294)	$ (151)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(228)	(307)	(167)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(204)	(317)	(169)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(204)	(317)	(169)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Operating Revenue [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	0	(270)	(126)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	0	(270)	(126)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Purchased Power And Fuel [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(204)	(47)	(43)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (204)	$ (47)	$ (43)

Derivative Financial Instrume_6

Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) $ in Millions	Dec. 31, 2019USD ($)
Derivative [Line Items]
Cash collateral held	$ 25
Letters of credit held	81
Total Exposure Before Credit Collateral [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade	877
Non-investment grade	79
Internally rated — investment grade	218
Internally rated — non-investment grade	139
Total	1,313
Credit Collateral [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade	20
Non-investment grade	63
Internally rated — investment grade	0
Internally rated — non-investment grade	23
Total	106
Net Exposure [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade	857
Non-investment grade	16
Internally rated — investment grade	218
Internally rated — non-investment grade	116
Total	1,207
Financial institutions	9
Investor-owned utilities, marketers, power producers	930
Energy cooperatives and municipalities	235
Other	33
Total	1,207
Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade	0
Total	0
Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade	0
Total	$ 0

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	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	$ (956)	$ (1,723)
Offsetting Fair Value of In-the-Money Contracts Under Master Netting Arrangements	649	1,105
Derivative liabilities, fair value	$ (307)	$ (618)

Derivative Financial Instrume_8

Derivative Financial Instruments - Summary of Cash Collateral and Letters of Credit (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Collateral, Right to Reclaim Cash	$ 982	$ 418
Derivative, Collateral, Right to Reclaim Securities	264	367
Derivative, Collateral, Obligation to Return Cash	103	47
Derivative, Collateral, Obligation to Return Securities	112	44
Incremental Collateral For Loss Of Investment Grade Credit Rating	1,509	2,104
Exelon Generation Co L L C [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Collateral, Right to Reclaim Cash	982	418
Derivative, Collateral, Right to Reclaim Securities	264	367
Derivative, Collateral, Obligation to Return Cash	103	47
Derivative, Collateral, Obligation to Return Securities	112	44
Incremental Collateral For Loss Of Investment Grade Credit Rating	$ 1,509	$ 2,104

Debt and Credit Agreements - Co

Debt and Credit Agreements - Commercial Paper Borrowings (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2016
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 25
Average Interest Rate on Commercial Paper Borrowings	2.25%	2.15%
Letters of Credit Outstanding, Amount	$ 1,443
Credit facility agreements with minority and community banks	142	$ 135
Line of Credit Facility, Remaining Borrowing Capacity	9,116
Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	9,000	9,000
Commercial Paper	$ 870	$ 89
Average Interest Rate on Commercial Paper Borrowings	2.25%	2.15%
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity			$ 500
Exelon Corporate [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	$ 6	$ 9
Exelon Corporate [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600
Exelon Corporate [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 25
Average Interest Rate on Commercial Paper Borrowings	1.84%	1.96%
Credit facility agreements with minority and community banks	$ 44	$ 49
Exelon Generation Co L L C [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	5,300	5,300
Commercial Paper	$ 320	$ 0
Average Interest Rate on Commercial Paper Borrowings	1.84%	1.96%
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	$ 1,400	$ 545
Exelon Generation Co L L C [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	159
Exelon Generation Co L L C [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	$ 5
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings	2.38%	2.14%
Letters of Credit Outstanding, Amount	$ 2
Credit facility agreements with minority and community banks	33	$ 33
Line of Credit Facility, Remaining Borrowing Capacity	998
Commonwealth Edison Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	1,000	1,000
Commercial Paper	$ 130	$ 0
Average Interest Rate on Commercial Paper Borrowings	2.38%	2.14%
Commonwealth Edison Co [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	$ 5
PECO Energy Co [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings	2.39%	2.24%
Letters of Credit Outstanding, Amount	$ 0
Credit facility agreements with minority and community banks	33	$ 34
Line of Credit Facility, Remaining Borrowing Capacity	600
PECO Energy Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600	600
Commercial Paper	$ 0	$ 0
Average Interest Rate on Commercial Paper Borrowings	2.39%	2.24%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings	2.46%	2.18%
Letters of Credit Outstanding, Amount	$ 0
Credit facility agreements with minority and community banks	8	$ 5
Line of Credit Facility, Remaining Borrowing Capacity	600
Baltimore Gas and Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600	600
Commercial Paper	$ 76	$ 35
Average Interest Rate on Commercial Paper Borrowings	2.46%	2.18%
Baltimore Gas and Electric Company [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	$ 2
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	0
Line of Credit Facility, Remaining Borrowing Capacity	900
Pepco Holdings LLC [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	900	$ 900
Commercial Paper	208	54
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 900	$ 1,500
Exelon Corporate [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings	1.92%	1.93%
Exelon Corporate [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 136
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings	2.56%	2.24%
Letters of Credit Outstanding, Amount	$ 0
Credit facility agreements with minority and community banks	8	$ 5
Line of Credit Facility, Remaining Borrowing Capacity	300
Potomac Electric Power Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	300	300
Commercial Paper	$ 82	$ 40
Average Interest Rate on Commercial Paper Borrowings	2.56%	2.24%
Line of Credit Facility, Remaining Borrowing Capacity	$ 500
Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings	2.02%	2.07%
Letters of Credit Outstanding, Amount	$ 0
Credit facility agreements with minority and community banks	8	$ 5
Line of Credit Facility, Remaining Borrowing Capacity	300
Delmarva Power & Light Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	300	300
Commercial Paper	$ 56	$ 0
Average Interest Rate on Commercial Paper Borrowings	2.02%	2.07%
Line of Credit Facility, Remaining Borrowing Capacity	$ 500
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings	2.43%	2.21%
Letters of Credit Outstanding, Amount	$ 0
Credit facility agreements with minority and community banks	8	$ 5
Line of Credit Facility, Remaining Borrowing Capacity	300
Atlantic City Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	300	300
Commercial Paper	$ 70	$ 14
Average Interest Rate on Commercial Paper Borrowings	2.43%	2.21%
Line of Credit Facility, Remaining Borrowing Capacity	$ 350
Maximum [Member] | Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 900

Debt and Credit Agreements - Su

Debt and Credit Agreements - Summary of Bank Commitments, Credit Facility Borrowings and Available Capacity (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2016
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 25
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	1,443
Actual available capacity	9,116
Credit facility agreements with minority and community banks	142	$ 135
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity			$ 500
Exelon Corporate [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	6	9
Exelon Corporate [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	25
To Support Additional Commercial Paper	4,211
Credit facility agreements with minority and community banks	44	49
Exelon Generation Co L L C [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	159
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	1,400	545
Exelon Generation Co L L C [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	5
Exelon Generation Co L L C [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Actual available capacity	855
To Support Additional Commercial Paper	0
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	2
Actual available capacity	998
To Support Additional Commercial Paper	868
Credit facility agreements with minority and community banks	33	33
Commonwealth Edison Co [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	5
PECO Energy Co [Member]
Short-term Debt [Line Items]
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	0
Actual available capacity	600
To Support Additional Commercial Paper	600
Credit facility agreements with minority and community banks	33	34
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	0
Actual available capacity	600
To Support Additional Commercial Paper	524
Credit facility agreements with minority and community banks	8	5
Baltimore Gas and Electric Company [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	2
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	0
Actual available capacity	300
To Support Additional Commercial Paper	218
Credit facility agreements with minority and community banks	8	5
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	0
Actual available capacity	900
To Support Additional Commercial Paper	692
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	900	1,500
Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	0
Actual available capacity	300
To Support Additional Commercial Paper	244
Credit facility agreements with minority and community banks	8	5
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	0
Actual available capacity	300
To Support Additional Commercial Paper	230
Credit facility agreements with minority and community banks	8	5
Line of Credit [Member] | Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	1,400
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	545
Line of Credit [Member] | Exelon Generation Co L L C [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	159
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	120
Actual available capacity	39
To Support Additional Commercial Paper	0
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	10,559
To Support Additional Commercial Paper	7,353
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600
To Support Additional Commercial Paper	458
Revolving Credit Facility [Member] | Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	5,300
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	769
Actual available capacity	4,531
Revolving Credit Facility [Member] | Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	1,000
Revolving Credit Facility [Member] | PECO Energy Co [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600
Revolving Credit Facility [Member] | Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600
Revolving Credit Facility [Member] | Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	300
Revolving Credit Facility [Member] | Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	900
Revolving Credit Facility [Member] | Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	300
Revolving Credit Facility [Member] | Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 300
Maximum [Member] | Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 900

Debt and Credit Agreements - _2

Debt and Credit Agreements - Summary of Short-term Borrowing Activities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Average borrowings	$ 472	$ 531
Maximum borrowings outstanding	$ 890	$ 1,237
Short-term Debt, Weighted Average Interest Rate, over Time	2.25%	2.21%
Average interest rates at year end	2.25%	2.15%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Average borrowings	$ 13	$ 37
Maximum borrowings outstanding	$ 357	$ 583
Short-term Debt, Weighted Average Interest Rate, over Time	1.84%	1.96%
Average interest rates at year end	1.84%	1.96%
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average borrowings	$ 236	$ 154
Maximum borrowings outstanding	$ 465	$ 520
Short-term Debt, Weighted Average Interest Rate, over Time	2.38%	2.14%
Average interest rates at year end	2.38%	2.14%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Average borrowings	$ 0	$ 68
Maximum borrowings outstanding	$ 21	$ 350
Short-term Debt, Weighted Average Interest Rate, over Time	2.39%	2.24%
Average interest rates at year end	2.39%	2.24%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 103	$ 65
Maximum borrowings outstanding	$ 298	$ 239
Short-term Debt, Weighted Average Interest Rate, over Time	2.46%	2.18%
Average interest rates at year end	2.46%	2.18%
Exelon Corporate [Member]
Short-term Debt [Line Items]
Average borrowings	$ 3	$ 4
Maximum borrowings outstanding	$ 144	$ 95
Short-term Debt, Weighted Average Interest Rate, over Time	1.92%	1.93%
Average interest rates at year end	1.92%	1.93%
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 45	$ 22
Maximum borrowings outstanding	$ 144	$ 90
Short-term Debt, Weighted Average Interest Rate, over Time	2.56%	2.24%
Average interest rates at year end	2.56%	2.24%
Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 21	$ 87
Maximum borrowings outstanding	$ 125	$ 245
Short-term Debt, Weighted Average Interest Rate, over Time	2.02%	2.07%
Average interest rates at year end	2.02%	2.07%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 51	$ 95
Maximum borrowings outstanding	$ 180	$ 210
Short-term Debt, Weighted Average Interest Rate, over Time	2.43%	2.21%
Average interest rates at year end	2.43%	2.21%
Commercial Paper [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 870	$ 89
Average interest rates at year end	2.25%	2.15%
Commercial Paper [Member] | Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 320	$ 0
Average interest rates at year end	1.84%	1.96%
Commercial Paper [Member] | Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 130	$ 0
Average interest rates at year end	2.38%	2.14%
Commercial Paper [Member] | PECO Energy Co [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 0	$ 0
Average interest rates at year end	2.39%	2.24%
Commercial Paper [Member] | Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 76	$ 35
Average interest rates at year end	2.46%	2.18%
Commercial Paper [Member] | Exelon Corporate [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 136
Commercial Paper [Member] | Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Commercial Paper	208	$ 54
Commercial Paper [Member] | Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 82	$ 40
Average interest rates at year end	2.56%	2.24%
Commercial Paper [Member] | Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 56	$ 0
Average interest rates at year end	2.02%	2.07%
Commercial Paper [Member] | Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 70	$ 14
Average interest rates at year end	2.43%	2.21%

Debt and Credit Agreements - _3

Debt and Credit Agreements - Summary of Credit Facility Thresholds (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2016
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 25
Line of Credit Facility, Current Borrowing Capacity	$ 142	$ 135
Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.275%
London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.275%
Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 25
Line of Credit Facility, Current Borrowing Capacity	$ 44	49
Exelon Generation Co L L C [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.275%
Exelon Generation Co L L C [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.275%
Commonwealth Edison Co [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 33	33
Commonwealth Edison Co [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.075%
Commonwealth Edison Co [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.075%
PECO Energy Co [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 33	34
PECO Energy Co [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.00%
PECO Energy Co [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.90%
Baltimore Gas and Electric Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 8	5
Baltimore Gas and Electric Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.00%
Baltimore Gas and Electric Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.00%
Potomac Electric Power Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 8	5
Potomac Electric Power Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.075%
Potomac Electric Power Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.075%
Delmarva Power & Light Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 8	5
Delmarva Power & Light Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.075%
Delmarva Power & Light Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.075%
Atlantic City Electric Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 8	5
Atlantic City Electric Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.075%
Atlantic City Electric Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.075%
Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,400
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	10,559
Revolving Credit Facility [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	5,300
Revolving Credit Facility [Member] | Commonwealth Edison Co [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,000
Revolving Credit Facility [Member] | PECO Energy Co [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600
Revolving Credit Facility [Member] | Baltimore Gas and Electric Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600
Revolving Credit Facility [Member] | Pepco Holdings LLC [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	900
Revolving Credit Facility [Member] | Potomac Electric Power Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	300
Revolving Credit Facility [Member] | Delmarva Power & Light Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	300
Revolving Credit Facility [Member] | Atlantic City Electric Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	300
Exelon Corporate [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 500
Revolving Credit Facility [Member] | Pepco Holdings LLC [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	900	$ 1,500
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600
BilateralOct2012 [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	200
BilateralJan2013 [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
BilateralJan2016 [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	150
BilateralFeb2019 [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
BilateralOct2019a [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	200
BilateralOct2019b [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
BilateralNov2019a [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	300
BilateralNov2019b [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	150
BilateralNov2019c [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 100

Debt and Credit Agreements - _4

Debt and Credit Agreements - Summary of Outstanding Long-term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 35,560	$ 34,911
Unamortized debt discount and premium, net	(72)	(66)
Unamortized Debt Issuance Expense	(214)	(216)
Fair value adjustment	765	795
Long-term debt due within one year	(4,710)	(1,349)
Long-term debt to financing trusts	390	390
Long-term debt	31,329	34,075
ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	206	206
PECO Trust III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	81	81
PECO Trust IV Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	103	103
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 17,486	16,496
Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.70%
Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.90%
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 10,685	11,285
Senior Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.45%
Senior Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.60%
Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 3,300	2,900
Unsecured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.40%
Unsecured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.35%
Pollution Control Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 412	435
Pollution Control Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.50%
Pollution Control Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.70%
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 3	39
Notes Payable to Banks [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.15%
Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 154	188
Unamortized Debt Issuance Expense	$ 0	0
Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.53%
Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.99%
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1,150	1,150
Junior Subordinated Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.50%
Software License Arrangement [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 55	73
Software License Arrangement [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.95%
Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 222	112
Tax-exempt Money Market Funds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.63%
Tax-exempt Money Market Funds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.40%
Medium-term Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 10	22
Medium-term Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.61%
Medium-term Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.72%
Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 40	59
Transition Bonds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.55%
Loans Payable [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 50	50
Loans Payable [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.00%
Non Recourse Fixed Rate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1,182	1,253
Non Recourse Fixed Rate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.29%
Non Recourse Fixed Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.00%
Non Recourse Variable Rate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 811	849
Non Recourse Variable Rate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.18%
Non Recourse Variable Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.91%
Long-term Debt [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 390	390
Long-term Debt [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 206	206
Long-term Debt [Member] | ComEd Financing III Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.35%
Long-term Debt [Member] | PECO Trust III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 81	81
Long-term Debt [Member] | PECO Trust III Affiliate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.75%
Long-term Debt [Member] | PECO Trust III Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.38%
Long-term Debt [Member] | PECO Trust IV Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 103	103
Long-term Debt [Member] | PECO Trust IV Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.75%
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 7,943	8,759
Unamortized debt discount and premium, net	(5)	(6)
Unamortized Debt Issuance Expense	(42)	(51)
Fair value adjustment	78	91
Long-term debt due within one year	(3,182)	(906)
Debt and Lease Obligation	4,792	7,887
Long-term debt	4,464	6,989
Exelon Generation Co L L C [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 5,420	6,019
Exelon Generation Co L L C [Member] | Senior Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.95%
Exelon Generation Co L L C [Member] | Senior Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.60%
Exelon Generation Co L L C [Member] | Pollution Control Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 412	435
Exelon Generation Co L L C [Member] | Pollution Control Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.50%
Exelon Generation Co L L C [Member] | Pollution Control Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.70%
Exelon Generation Co L L C [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 3	39
Exelon Generation Co L L C [Member] | Notes Payable to Banks [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.15%
Exelon Generation Co L L C [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 115	164
Exelon Generation Co L L C [Member] | Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.53%
Exelon Generation Co L L C [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.26%
Exelon Generation Co L L C [Member] | Non Recourse Fixed Rate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1,182	1,253
Exelon Generation Co L L C [Member] | Non Recourse Fixed Rate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.29%
Exelon Generation Co L L C [Member] | Non Recourse Fixed Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.00%
Exelon Generation Co L L C [Member] | Non Recourse Variable Rate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 811	849
Exelon Generation Co L L C [Member] | Non Recourse Variable Rate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.18%
Exelon Generation Co L L C [Member] | Non Recourse Variable Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.91%
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 8,586	8,187
Unamortized debt discount and premium, net	(27)	(23)
Unamortized Debt Issuance Expense	(68)	(63)
Long-term debt due within one year	(500)	(300)
Long-term debt to financing trusts	205	205
Debt and Lease Obligation	7,991	7,801
Long-term debt	7,991	7,801
Commonwealth Edison Co [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Expense	(1)	(1)
Long-term debt to financing trusts	205	205
Commonwealth Edison Co [Member] | PECO Trust III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	0	0
Commonwealth Edison Co [Member] | PECO Trust IV Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	0	0
Commonwealth Edison Co [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 8,578	8,179
Commonwealth Edison Co [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.55%
Commonwealth Edison Co [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.45%
Commonwealth Edison Co [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 8	8
Commonwealth Edison Co [Member] | Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage
Commonwealth Edison Co [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.49%
Commonwealth Edison Co [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 206	206
Commonwealth Edison Co [Member] | Long-term Debt [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 206	206
Commonwealth Edison Co [Member] | Long-term Debt [Member] | ComEd Financing III Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.35%
PECO Energy Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 3,450	3,125
Unamortized debt discount and premium, net	(21)	(18)
Unamortized Debt Issuance Expense	(24)	(23)
Long-term debt to financing trusts	184	184
Debt and Lease Obligation	3,405	3,084
Long-term debt	3,405	3,084
PECO Energy Co [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	0	0
PECO Energy Co [Member] | PECO Trust III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	81	81
PECO Energy Co [Member] | PECO Trust IV Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	103	103
PECO Energy Co [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 3,400	3,075
PECO Energy Co [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.70%
PECO Energy Co [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.95%
PECO Energy Co [Member] | Loans Payable [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 50	50
PECO Energy Co [Member] | Loans Payable [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.00%
PECO Energy Co [Member] | Long-term Debt [Member] | PECO Trust III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 81	81
PECO Energy Co [Member] | Long-term Debt [Member] | PECO Trust III Affiliate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.75%
PECO Energy Co [Member] | Long-term Debt [Member] | PECO Trust III Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.38%
PECO Energy Co [Member] | Long-term Debt [Member] | PECO Trust IV Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 103	103
PECO Energy Co [Member] | Long-term Debt [Member] | PECO Trust IV Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.75%
PECO Energy Co [Member] | Long-term Debt [Member] | PECO Financing Trusts [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 184
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	3,300	2,900
Unamortized debt discount and premium, net	(9)	(6)
Unamortized Debt Issuance Expense	(21)	(18)
Long-term debt	3,270	2,876
Long-term debt	3,270	2,876
Baltimore Gas and Electric Company [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 3,300	2,900
Baltimore Gas and Electric Company [Member] | Senior Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.40%
Baltimore Gas and Electric Company [Member] | Senior Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.35%
Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 5,995	5,636
Unamortized debt discount and premium, net	4	4
Unamortized Debt Issuance Expense	(19)	(14)
Fair value adjustment	583	633
Long-term debt due within one year	(103)	(125)
Long-term debt	6,460	6,134
Long-term debt	6,460	6,134
Pepco Holdings LLC [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 5,508	5,242
Pepco Holdings LLC [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.76%
Pepco Holdings LLC [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.90%
Pepco Holdings LLC [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 185	185
Pepco Holdings LLC [Member] | Unsecured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.45%
Pepco Holdings LLC [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 30	16
Pepco Holdings LLC [Member] | Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.54%
Pepco Holdings LLC [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.99%
Pepco Holdings LLC [Member] | Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 222	112
Pepco Holdings LLC [Member] | Tax-exempt Money Market Funds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.63%
Pepco Holdings LLC [Member] | Tax-exempt Money Market Funds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.40%
Pepco Holdings LLC [Member] | Medium-term Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 10	22
Pepco Holdings LLC [Member] | Medium-term Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.61%
Pepco Holdings LLC [Member] | Medium-term Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.72%
Pepco Holdings LLC [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 40	59
Pepco Holdings LLC [Member] | Transition Bonds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage
Pepco Holdings LLC [Member] | Transition Bonds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.55%
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 2,897	2,751
Unamortized debt discount and premium, net	2	2
Unamortized Debt Issuance Expense	(35)	(34)
Long-term debt due within one year	(2)	(15)
Long-term debt	2,862	2,704
Long-term debt	2,862	2,704
Potomac Electric Power Company [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 2,775	2,735
Potomac Electric Power Company [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.05%
Potomac Electric Power Company [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.90%
Potomac Electric Power Company [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 12	16
Potomac Electric Power Company [Member] | Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.54%
Potomac Electric Power Company [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.99%
Potomac Electric Power Company [Member] | Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 110	0
Potomac Electric Power Company [Member] | Tax-exempt Money Market Funds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.70%
Delmarva Power & Light Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1,578	1,504
Unamortized debt discount and premium, net	1	2
Unamortized Debt Issuance Expense	(12)	(12)
Long-term debt due within one year	(79)
Long-term debt due within one year	(80)	(91)
Long-term debt	1,487	1,403
Long-term debt	1,487	1,403
Delmarva Power & Light Company [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1,446	1,370
Delmarva Power & Light Company [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.76%
Delmarva Power & Light Company [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.27%
Delmarva Power & Light Company [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Finance Lease, Liability	$ 10	0
Delmarva Power & Light Company [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Lessee, Finance Lease, Discount Rate	3.54%
Delmarva Power & Light Company [Member] | Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 112	112
Delmarva Power & Light Company [Member] | Tax-exempt Money Market Funds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.63%
Delmarva Power & Light Company [Member] | Tax-exempt Money Market Funds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.40%
Delmarva Power & Light Company [Member] | Medium-term Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 10	22
Delmarva Power & Light Company [Member] | Medium-term Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.61%
Delmarva Power & Light Company [Member] | Medium-term Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.72%
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1,335	1,196
Unamortized debt discount and premium, net	(1)	(1)
Unamortized Debt Issuance Expense	(7)	(7)
Long-term debt due within one year	(20)	(18)
Long-term debt	1,307	1,170
Long-term debt	1,307	1,170
Atlantic City Electric Company [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1,287	1,137
Atlantic City Electric Company [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.38%
Atlantic City Electric Company [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.80%
Atlantic City Electric Company [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Finance Lease, Liability	$ 8	0
Atlantic City Electric Company [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Lessee, Finance Lease, Discount Rate	3.54%
Atlantic City Electric Company [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 40	59
Atlantic City Electric Company [Member] | Transition Bonds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.55%
Parent Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 7,039	7,039
Unamortized debt discount and premium, net	(7)	(7)
Unamortized Debt Issuance Expense	39	47
Long-term debt due within one year	(1,458)	0
Long-term debt	5,717	7,147
Parent Company [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 5,889	5,889
Parent Company [Member] | Senior Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.45%
Parent Company [Member] | Senior Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.60%
Parent Company [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1,150	$ 1,150
Parent Company [Member] | Junior Subordinated Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.50%

Debt and Credit Agreements - Sc

Debt and Credit Agreements - Schedule of Long-term Debt Maturities (Details) $ in Millions	Dec. 31, 2019USD ($)
Debt Instrument [Line Items]
2020	$ 4,710
2021	1,517
2022	3,088
2023	855
2024	1,596
Thereafter	24,184
Total	35,950
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
2020	3,182
2021	2
2022	1,024
2023	1
2024	792
Thereafter	2,942
Total	7,943
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
2020	500
2021	350
2022	0
2023	0
2024	250
Thereafter	7,691
Total	8,791
PECO Energy Co [Member]
Debt Instrument [Line Items]
2020	0
2021	300
2022	350
2023	50
2024	0
Thereafter	2,934
Total	3,634
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
2020	0
2021	300
2022	250
2023	300
2024	0
Thereafter	2,450
Total	3,300
Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
2020	103
2021	265
2022	314
2023	504
2024	553
Thereafter	4,256
Total	5,995
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
2020	2
2021	2
2022	311
2023	1
2024	401
Thereafter	2,180
Total	2,897
Delmarva Power & Light Company [Member]
Debt Instrument [Line Items]
2020	80
2021	2
2022	2
2023	502
2024	1
Thereafter	991
Total	1,578
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
2020	20
2021	261
2022	1
2023	1
2024	151
Thereafter	901
Total	1,335
Transition Bonds [Member] | Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
2020	19
2021	21
Exelon Corporate [Member]
Debt Instrument [Line Items]
2020	1,458
2021	300
2022	1,150
2023	0
2024	0
Thereafter	4,131
Total	$ 7,039

Debt and Credit Agreements - Na

Debt and Credit Agreements - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)MW	Dec. 31, 2018USD ($)	Mar. 31, 2016USD ($)
Debt Instrument [Line Items]
Outstanding letters of credit	$ 1,443
Collateral amount of debt	2,800
Long-term Line of Credit/Facility draws	0
Line of Credit Facility, Maximum Borrowing Capacity	25
Long-term debt	$ 35,950
Maximum [Member]
Debt Instrument [Line Items]
Basis points adders for prime-based borrowings	0.65%
Basis points adders for LIBOR-based borrowings	1.65%
Maximum [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	5.55%
Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	7.60%
Maximum [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	3.50%
Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	2.45%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 500
Exelon Corporate [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	$ 6	$ 9
Long-term debt	$ 7,039
Exelon Corporate [Member] | Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	7.60%
Exelon Corporate [Member] | Maximum [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	3.50%
Exelon Corporate [Member] | Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	2.45%
Exelon Corporate [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 600
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	25
Long-term debt	7,943
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | DOE Project Financing, 2.82% January 5, 2037 [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	38
Non-Recourse Debt	485
Long-term Line of Credit/Facility draws	$ 646
Debt, Weighted Average Interest Rate	2.82%
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | SolGen [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 150
Interest rate on long-term debt	3.93%
Non-Recourse Debt	$ 131
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Renewable Power Generation [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 150
Interest rate on long-term debt	4.11%
Non-Recourse Debt	$ 106
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Continetal Wind [Member]
Debt Instrument [Line Items]
Aggregate Bank Commitments Under Unsecured Revolving Credit Facilities	10
Outstanding letters of credit	115
Debt Instrument, Face Amount	$ 613
Interest rate on long-term debt	6.00%
Non-Recourse Debt	$ 447
Generation capacity of portfolio | MW	667
Line of Credit Facility, Maximum Borrowing Capacity	$ 131
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExGenRenewablesIVNov2024 [Member]
Debt Instrument [Line Items]
Non-Recourse Debt	796
Non-recourse debt, interest rate swap	$ 636
Non-recourse debt, hedge percentage	2.32%
Long-term debt	$ 850
Proceeds from Issuance of Debt	785
Proceeds from (Repayments of) Restricted Cash, Financing Activities	$ 50
Exelon Generation Co L L C [Member] | Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	7.60%
Exelon Generation Co L L C [Member] | Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	2.95%
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	$ 1,400	545
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	2
Long-term Line of Credit/Facility draws	0
Long-term debt	8,791
PECO Energy Co [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	0
Long-term Line of Credit/Facility draws	0
Long-term debt	3,634
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	0
Long-term Line of Credit/Facility draws	0
Long-term debt	$ 3,300
Baltimore Gas and Electric Company [Member] | Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	6.35%
Baltimore Gas and Electric Company [Member] | Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	2.40%
Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	$ 0
Long-term Line of Credit/Facility draws	0
Long-term debt	$ 5,995
Pepco Holdings LLC [Member] | Maximum [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	5.55%
Pepco Holdings LLC [Member] | Minimum [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 900	1,500
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 900
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	0
Long-term Line of Credit/Facility draws	0
Long-term debt	2,897
Delmarva Power & Light Company [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	0
Long-term Line of Credit/Facility draws	0
Long-term debt	1,578
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	0
Long-term Line of Credit/Facility draws	0
Long-term debt	$ 1,335
Atlantic City Electric Company [Member] | Maximum [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	5.55%
Corporate, Non-Segment [Member] | Exelon Corporate [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	$ 500
London Interbank Offered Rate (LIBOR) [Member] | ExGenRenewablesIVNov2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate During Period	3.00%
Debt Instrument, Interest Rate Terms	1.00%
London Interbank Offered Rate (LIBOR) [Member] | Corporate, Non-Segment [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate During Period	0.95%

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	$ 765	$ 795
Due to Affiliate, Noncurrent	390	390
Spent Nuclear Fuel Obligation, Noncurrent	1,199	1,171
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	40,033	35,869
Due to Affiliate, Noncurrent	428	400
Spent Nuclear Fuel Obligation, Noncurrent	1,055	949
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	0	0
Due to Affiliate, Noncurrent	0	0
Spent Nuclear Fuel Obligation, Noncurrent	0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	37,453	33,711
Due to Affiliate, Noncurrent	0	0
Spent Nuclear Fuel Obligation, Noncurrent	1,055	949
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	2,580	2,158
Due to Affiliate, Noncurrent	428	400
Spent Nuclear Fuel Obligation, Noncurrent	0	0
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	36,039	35,424
Due to Affiliate, Noncurrent	390	390
Spent Nuclear Fuel Obligation, Noncurrent	1,199	1,171
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	78	91
Spent Nuclear Fuel Obligation, Noncurrent	1,199	1,171
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	8,670	8,910
Spent Nuclear Fuel Obligation, Noncurrent	1,055	949
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	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]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	7,304	7,467
Spent Nuclear Fuel Obligation, Noncurrent	1,055	949
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	1,366	1,443
Spent Nuclear Fuel Obligation, Noncurrent	0	0
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	7,974	8,793
Spent Nuclear Fuel Obligation, Noncurrent	1,199	1,171
Commonwealth Edison Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to Affiliate, Noncurrent	205	205
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	9,848	8,390
Due to Affiliate, Noncurrent	227	209
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	0	0
Due to Affiliate, Noncurrent	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	9,848	8,390
Due to Affiliate, Noncurrent	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	0	0
Due to Affiliate, Noncurrent	227	209
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	8,491	8,101
Due to Affiliate, Noncurrent	205	205
PECO Energy Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to Affiliate, Noncurrent	184	184
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	3,918	3,207
Due to Affiliate, Noncurrent	201	191
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	0	0
Due to Affiliate, Noncurrent	0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	3,868	3,157
Due to Affiliate, Noncurrent	0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	50	50
Due to Affiliate, Noncurrent	201	191
PECO Energy Co [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	3,405	3,084
Due to Affiliate, Noncurrent	184	184
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	3,649	2,950
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	0	0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	3,649	2,950
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	0	0
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	3,270	2,876
Pepco Holdings LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	583	633
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	7,066	6,101
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	0	0
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	5,902	5,436
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	1,164	665
Pepco Holdings LLC [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	6,563	6,259
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	3,586	3,097
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	0	0
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	3,198	2,901
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	388	196
Potomac Electric Power Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	2,864	2,719
Delmarva Power & Light Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	1,719	1,496
Delmarva Power & Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	0	0
Delmarva Power & Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	1,408	1,303
Delmarva Power & Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	311	193
Delmarva Power & Light Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	1,567	1,494
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	1,490	1,262
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	0	0
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	1,026	987
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	464	275
Atlantic City Electric Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	$ 1,327	$ 1,188

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Fair Value Measurement of Assets and Liabilities, Recurring and Nonrecurring (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Current	$ (247)	$ (475)
Derivative Liability, Noncurrent	(393)	(479)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	2	44
Derivative Asset, Notional Amount	724	1,432
Margin Deposit Assets	511	(94)
Equity Securities without Readily Determinable Fair Value, Amount	69
Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	373	458
Restricted cash [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	110	80
Other assets
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	177	185
Nuclear Decommissioning Trust Fund Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair Value Net Assets Liabilities Excluded From Nuclear Decommissioning Trust Fund Investments	147	130
Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	639	1,243
Assets, Fair Value Disclosure	15,584	15,557
Deferred Compensation Liability, Current and Noncurrent	(147)	(137)
Financial Liabilities Fair Value Disclosure	(763)	(1,084)
Fair Value, Net Asset (Liability)	14,821	14,473
Fair Value, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(616)	(947)
Fair Value, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(5,154)	(4,881)
Fair Value, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(49)	(94)
Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	4,587	4,028
Fair Value, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	13,500	12,825
Fair Value, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	452	338
Fair Value, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	6,494	5,890
Fair Value, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	4,783	5,078
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,726	1,823
Fair Value, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,939	2,180
Fair Value, Recurring [Member] | Debt Security, Government, Non-US [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	42	50
Fair Value, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	90	149
Fair Value, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	986	876
Fair Value, Recurring [Member] | Private Credit [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	762	680
Fair Value, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	402	329
Fair Value, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	607	510
Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	262	243
Fair Value, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	50	48
Fair Value, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	81	72
Fair Value, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	12	15
Fair Value, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	119	108
Fair Value, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	1,183	1,246
Fair Value, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	4,744	4,771
Fair Value, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	97	146
Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	(3,658)	(3,671)
Fair Value, Inputs, Level 1 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Fair Value, Amount Offset Against Collateral, Net	163	57
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	639	1,243
Assets, Fair Value Disclosure	6,156	6,573
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	(3)
Fair Value, Net Asset (Liability)	6,156	6,570
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	0	(3)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(1,071)	(642)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	1,071	639
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	5,526	5,251
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	365	252
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	3,353	2,918
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,808	2,081
Fair Value, Inputs, Level 1 [Member] | Fair Value, 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, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,808	2,081
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Debt Security, Government, Non-US [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, 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, Recurring [Member] | Other Fixed Income [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, Recurring [Member] | Private Credit [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, 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, 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, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	131	120
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	50	48
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	81	72
Fair Value, Inputs, Level 1 [Member] | Fair Value, 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 1 [Member] | Fair Value, 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, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	(140)	(41)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	768	541
Fair Value, Inputs, Level 1 [Member] | Fair Value, 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, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	(908)	(582)
Fair Value, Inputs, Level 2 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Fair Value, Amount Offset Against Collateral, Net	551	224
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	4,061	4,155
Deferred Compensation Liability, Current and Noncurrent	(147)	(137)
Financial Liabilities Fair Value Disclosure	(322)	(592)
Fair Value, Net Asset (Liability)	3,739	3,563
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(175)	(455)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(2,855)	(2,963)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(34)	(73)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	2,714	2,581
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	3,605	3,598
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	87	86
Fair Value, Inputs, Level 2 [Member] | Fair Value, 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, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,765	1,921
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,469	1,593
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	131	99
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Debt Security, Government, Non-US [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	42	50
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	90	149
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	33	30
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Private Credit [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, 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, 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, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	90	85
Fair Value, Inputs, Level 2 [Member] | Fair Value, 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, Recurring [Member] | Mutual Fund [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, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	12	15
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	78	70
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	366	472
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	2,491	2,760
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	37	69
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	(2,162)	(2,357)
Fair Value, Inputs, Level 3 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Fair Value, Amount Offset Against Collateral, Net	214	76
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	1,509	1,396
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	(441)	(489)
Fair Value, Net Asset (Liability)	1,068	907
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(441)	(489)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(1,228)	(1,276)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(15)	(21)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	802	808
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	511	543
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Cash Equivalents NDT [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, Recurring [Member] | Equity 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, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	257	230
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	257	230
Fair Value, Inputs, Level 3 [Member] | Fair Value, 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, Recurring [Member] | Debt Security, Government, Non-US [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, 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, Recurring [Member] | Other Fixed Income [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, Recurring [Member] | Private Credit [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	254	313
Fair Value, Inputs, Level 3 [Member] | Fair Value, 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, 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, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	41	38
Fair Value, Inputs, Level 3 [Member] | Fair Value, 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, Recurring [Member] | Mutual Fund [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, 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 3 [Member] | Fair Value, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	41	38
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	957	815
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	1,485	1,470
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	60	77
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	(588)	(732)
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	3,858	3,433
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	3,858	3,433
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	3,858	3,433
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,388	1,381
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	953	846
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Debt Security, Government, Non-US [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	953	846
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Private Credit [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	508	367
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	402	329
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	607	510
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral [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, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Current	(215)	(449)
Derivative Liability, Noncurrent	(123)	(252)
Derivative liabilities, fair value	307	618
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	2	44
Derivative Asset, Notional Amount	724	1,432
Margin Deposit Assets	511	94
Equity Securities without Readily Determinable Fair Value, Amount	69
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 and Cash Equivalents, Fair Value Disclosure	177	283
Exelon Generation Co L L C [Member] | Restricted cash [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	58	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]
Fair Value Net Assets Liabilities Excluded From Nuclear Decommissioning Trust Fund Investments	147	130
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	214	581
Assets, Fair Value Disclosure	14,951	14,703
Deferred Compensation Liability, Current and Noncurrent	(41)	(35)
Financial Liabilities Fair Value Disclosure	(356)	(733)
Fair Value, Net Asset (Liability)	14,595	13,970
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(315)	(698)
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(4,853)	(4,632)
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(49)	(94)
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	4,587	4,028
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	13,500	12,825
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	452	338
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	6,494	5,890
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	4,783	5,078
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,726	1,823
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,939	2,180
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Debt Security, Government, Non-US [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	42	50
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	90	149
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	986	876
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Private Credit [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	762	680
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	402	329
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	607	510
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	54	51
Exelon Generation Co L L C [Member] | Fair Value, 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, Recurring [Member] | Mutual Fund [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, 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, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	25	22
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	1,183	1,246
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	4,744	4,771
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	97	146
Exelon Generation Co L L C [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	(3,658)	(3,671)
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]
Derivative, Fair Value, Amount Offset Against Collateral, Net	163	57
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	214	581
Assets, Fair Value Disclosure	5,629	5,820
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	(3)
Fair Value, Net Asset (Liability)	5,629	5,817
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	0	(3)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(1,071)	(642)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	1,071	639
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	5,526	5,251
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	365	252
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	3,353	2,918
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,808	2,081
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, 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, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,808	2,081
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Debt Security, Government, Non-US [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, 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, Recurring [Member] | Other Fixed Income [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, Recurring [Member] | Private Credit [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, 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, 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, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	29	29
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, 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, Recurring [Member] | Mutual Fund [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, 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] | Fair Value, 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, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	(140)	(41)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	768	541
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, 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, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	(908)	(582)
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]
Derivative, Fair Value, Amount Offset Against Collateral, Net	551	224
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	3,996	4,092
Deferred Compensation Liability, Current and Noncurrent	(41)	(35)
Financial Liabilities Fair Value Disclosure	(216)	(490)
Fair Value, Net Asset (Liability)	3,780	3,602
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(175)	(455)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(2,855)	(2,963)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(34)	(73)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	2,714	2,581
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	3,605	3,598
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	87	86
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, 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, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,765	1,921
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,469	1,593
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	131	99
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Debt Security, Government, Non-US [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	42	50
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	90	149
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	33	30
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Private Credit [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, 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, 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, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	25	22
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, 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, Recurring [Member] | Mutual Fund [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, 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] | Fair Value, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	25	22
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	366	472
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	2,491	2,760
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	37	69
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	(2,162)	(2,357)
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]
Derivative, Fair Value, Amount Offset Against Collateral, Net	214	76
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	1,468	1,358
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	(140)	(240)
Fair Value, Net Asset (Liability)	1,328	1,118
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(140)	(240)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(927)	(1,027)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	(15)	(21)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	802	808
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	511	543
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Cash Equivalents NDT [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, Recurring [Member] | Equity 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, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	257	230
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	257	230
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, 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, Recurring [Member] | Debt Security, Government, Non-US [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, 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, Recurring [Member] | Other Fixed Income [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, Recurring [Member] | Private Credit [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	254	313
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, 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, 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, Recurring [Member] | Rabbi Trust 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] | Fair Value, 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, Recurring [Member] | Mutual Fund [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, 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] | Fair Value, 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, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	957	815
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	1,485	1,470
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	60	77
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	(588)	(732)
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	3,858	3,433
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	3,858	3,433
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	0	0
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	0	0
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	0	0
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	0	0
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	3,858	3,433
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Cash Equivalents NDT [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 Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	1,388	1,381
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	953	846
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Debt Security, Government, Non-US [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 Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	953	846
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Private Credit [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	508	367
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	402	329
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	607	510
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Rabbi Trust 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 Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Mutual Fund [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 Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Commodity 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 Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	0	0
Exelon Generation Co L L C [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, 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 Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	0	0
Commonwealth Edison Co [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Current	(32)	(26)
Derivative Liability, Noncurrent	(269)	(223)
Commonwealth Edison Co [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	90	93
Commonwealth Edison Co [Member] | Restricted cash [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	33	28
Commonwealth Edison Co [Member] | Other assets
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	163	166
Commonwealth Edison Co [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	280	209
Assets, Fair Value Disclosure	280	209
Derivative Liability	(301)	(249)
Deferred Compensation Liability, Current and Noncurrent	(8)	(6)
Financial Liabilities Fair Value Disclosure	(309)	(255)
Fair Value, Net Asset (Liability)	(29)	(46)
Commonwealth Edison Co [Member] | Fair Value, Recurring [Member] | Rabbi Trust 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, Recurring [Member] | Mutual Fund [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, 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, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	280	209
Assets, Fair Value Disclosure	280	209
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	280	209
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Rabbi Trust 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, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Mutual Fund [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, 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, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	0	0
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	(8)	(6)
Financial Liabilities Fair Value Disclosure	(8)	(6)
Fair Value, Net Asset (Liability)	(8)	(6)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Rabbi Trust 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, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Mutual Fund [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, 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, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Current	(32)	(26)
Derivative Liability, Noncurrent	(269)	(223)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	0	0
Derivative Liability	(301)	(249)
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	(301)	(249)
Fair Value, Net Asset (Liability)	(301)	(249)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Rabbi Trust 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, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Mutual Fund [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, 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] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	12	24
PECO Energy Co [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	15	111
Assets, Fair Value Disclosure	34	128
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	(9)	(10)
Financial Liabilities Fair Value Disclosure	(9)	(10)
Fair Value, Net Asset (Liability)	25	118
PECO Energy Co [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	19	17
PECO Energy Co [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	8	7
PECO Energy Co [Member] | Fair Value, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	11	10
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	15	111
Assets, Fair Value Disclosure	23	118
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	23	118
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	8	7
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	8	7
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, 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, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	11	10
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	(9)	(10)
Financial Liabilities Fair Value Disclosure	(9)	(10)
Fair Value, Net Asset (Liability)	2	0
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	11	10
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Mutual Fund [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, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	11	10
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	0	0
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	0	0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [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, Recurring [Member] | Mutual Fund [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, 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] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	24	7
Baltimore Gas and Electric Company [Member] | Restricted cash [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	1	2
Baltimore Gas and Electric Company [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	4
Assets, Fair Value Disclosure	8	10
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	(5)	(5)
Financial Liabilities Fair Value Disclosure	(5)	(5)
Fair Value, Net Asset (Liability)	3	5
Baltimore Gas and Electric Company [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	8	6
Baltimore Gas and Electric Company [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	8	6
Baltimore Gas and Electric Company [Member] | Fair Value, 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, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	4
Assets, Fair Value Disclosure	8	10
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	8	10
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	8	6
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	8	6
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, 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, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	0	0
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	(5)	(5)
Financial Liabilities Fair Value Disclosure	(5)	(5)
Fair Value, Net Asset (Liability)	(5)	(5)
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [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, Recurring [Member] | Mutual Fund [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, 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, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	0	0
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [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, Recurring [Member] | Mutual Fund [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, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	0
Pepco Holdings LLC [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	57	39
Pepco Holdings LLC [Member] | Other assets
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	14	19
Pepco Holdings LLC [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	124	147
Assets, Fair Value Disclosure	259	277
Deferred Compensation Liability, Current and Noncurrent	(19)	(21)
Financial Liabilities Fair Value Disclosure	(19)	(21)
Fair Value, Net Asset (Liability)	240	256
Pepco Holdings LLC [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	135	130
Pepco Holdings LLC [Member] | Fair Value, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	44	42
Pepco Holdings LLC [Member] | Fair Value, Recurring [Member] | Mutual Fund [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, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	12	15
Pepco Holdings LLC [Member] | Fair Value, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	65	60
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	124	147
Assets, Fair Value Disclosure	182	202
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	182	202
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	58	55
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	44	42
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Mutual Fund [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, 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 1 [Member] | Fair Value, 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 2 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	36	37
Deferred Compensation Liability, Current and Noncurrent	(19)	(21)
Financial Liabilities Fair Value Disclosure	(19)	(21)
Fair Value, Net Asset (Liability)	17	16
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	36	37
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, 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, Recurring [Member] | Mutual Fund [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, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	12	15
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	24	22
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	41	38
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	41	38
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	41	38
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, 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, Recurring [Member] | Mutual Fund [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, 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 3 [Member] | Fair Value, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	41	38
Potomac Electric Power Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	29	15
Potomac Electric Power Company [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	34	38
Assets, Fair Value Disclosure	144	143
Deferred Compensation Liability, Current and Noncurrent	(2)	(3)
Financial Liabilities Fair Value Disclosure	(2)	(3)
Fair Value, Net Asset (Liability)	142	140
Potomac Electric Power Company [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	110	105
Potomac Electric Power Company [Member] | Fair Value, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	43	41
Potomac Electric Power Company [Member] | Fair Value, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	2	5
Potomac Electric Power Company [Member] | Fair Value, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	65	59
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	34	38
Assets, Fair Value Disclosure	77	79
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	77	79
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	43	41
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	43	41
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, 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 1 [Member] | Fair Value, 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 2 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	26	27
Deferred Compensation Liability, Current and Noncurrent	(2)	(3)
Financial Liabilities Fair Value Disclosure	(2)	(3)
Fair Value, Net Asset (Liability)	24	24
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	26	27
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, 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, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	2	5
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	24	22
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	41	37
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	41	37
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	41	37
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, 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, 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 3 [Member] | Fair Value, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	41	37
Delmarva Power & Light Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	13	8
Delmarva Power & Light Company [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	16
Assets, Fair Value Disclosure	0	16
Deferred Compensation Liability, Current and Noncurrent	0	(1)
Financial Liabilities Fair Value Disclosure	0	(1)
Fair Value, Net Asset (Liability)	0	15
Delmarva Power & Light Company [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	0	0
Delmarva Power & Light Company [Member] | Fair Value, 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 & Light Company [Member] | Fair Value, 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 & Light Company [Member] | Fair Value, 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 & Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	16
Assets, Fair Value Disclosure	0	16
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	0	16
Delmarva Power & Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	0	0
Delmarva Power & Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, 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 & Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, 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 & Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, 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 & Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	0	0
Deferred Compensation Liability, Current and Noncurrent	0	(1)
Financial Liabilities Fair Value Disclosure	0	(1)
Fair Value, Net Asset (Liability)	0	(1)
Delmarva Power & Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	0	0
Delmarva Power & Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, 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 & Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, 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 & Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, 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 & Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	0	0
Delmarva Power & Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	0	0
Delmarva Power & Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, 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 & Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, 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 & Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, 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] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	12	7
Atlantic City Electric Company [Member] | Other assets
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	14	19
Atlantic City Electric Company [Member] | Fair Value, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	16	23
Assets, Fair Value Disclosure	16	23
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	16	23
Atlantic City Electric Company [Member] | Fair Value, Recurring [Member] | Rabbi Trust 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, 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, 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, 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, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	16	23
Assets, Fair Value Disclosure	16	23
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	16	23
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Rabbi Trust 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, 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 1 [Member] | Fair Value, 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, 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, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Rabbi Trust 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, 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, 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, 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, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Net Asset (Liability)	0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | Rabbi Trust 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, 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, 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, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	0	0
Maturity Less than 30 Days [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash	90	50
Maturity Less than 30 Days [Member] | Exelon Generation Co L L C [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash	$ 90	$ 50

Fair Value of Financial Asset_5

Fair Value of Financial Assets and Liabilities - Fair Value Reconciliation of Level 3 Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Balance	$ 907	$ 966
Total realized / unrealized gains (losses)
Included in net income	(23)	(101)
Included in noncurrent payables to affiliates	0	0
Included in regulatory assets/liabilities	(18)	6
Change In Collateral	138	(5)
Purchases, sales, issuances and settlements
Purchases	176	226
Sales	(23)	(4)
Settlements	(89)	(123)
Transfers into Level 3	5	(22)
Transfers out of Level 3	(5)	(36)
Ending Balance	1,068	907
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	359	160
Fair Value, Inputs, Level 3 [Member] | Consolidation, Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Balance	0	0
Total realized / unrealized gains (losses)
Included in net income	0	0
Included in noncurrent payables to affiliates	(34)	1
Included in regulatory assets/liabilities	34	(1)
Change In Collateral	0	0
Purchases, sales, issuances and settlements
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	0	0
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	0	0
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 [Abstract]
Beginning Balance	38	22
Total realized / unrealized gains (losses)
Included in net income	(3)	(4)
Included in regulatory assets/liabilities	0	0
Change In Collateral	0	0
Purchases, sales, issuances and settlements
Purchases	0	0
Sales	0	0
Settlements	0	(12)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	41	38
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	3	0
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 [Abstract]
Beginning Balance	1,118	1,200
Total realized / unrealized gains (losses)
Included in net income	(26)	(105)
Included in noncurrent payables to affiliates	34	(1)
Included in regulatory assets/liabilities	0	0
Change In Collateral	138	(5)
Purchases, sales, issuances and settlements
Purchases	176	226
Sales	(23)	(4)
Settlements	(89)	(135)
Transfers into Level 3	5	(22)
Transfers out of Level 3	(5)	(36)
Ending Balance	1,328	1,118
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	356	160
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 [Abstract]
Beginning Balance	543	648
Total realized / unrealized gains (losses)
Included in net income	5	0
Included in noncurrent payables to affiliates	34	(1)
Included in regulatory assets/liabilities	0	0
Change In Collateral	0	0
Purchases, sales, issuances and settlements
Purchases	44	36
Sales	(21)	0
Settlements	(94)	(140)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	511	543
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	5	(5)
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 [Abstract]
Beginning Balance	575	552
Total realized / unrealized gains (losses)
Included in net income	(31)	(105)
Included in noncurrent payables to affiliates	0	0
Included in regulatory assets/liabilities	0	0
Change In Collateral	138	(5)
Purchases, sales, issuances and settlements
Purchases	132	190
Sales	(2)	(4)
Settlements	5	5
Transfers into Level 3	5	(22)
Transfers out of Level 3	(5)	(36)
Ending Balance	817	575
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	351	165
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	(377)	(265)
Commonwealth Edison Co [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Realized Investment Gains (Losses)	26	17
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member]
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)	(78)	(24)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Balance	(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/liabilities	(52)	7
Change In Collateral	0	0
Purchases, sales, issuances and settlements
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	(301)	(249)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	0	0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Balance	38	22
Total realized / unrealized gains (losses)
Included in net income	3	4
Included in noncurrent payables to affiliates	0	0
Included in regulatory assets/liabilities	0	0
Change In Collateral	0	0
Purchases, sales, issuances and settlements
Purchases	0	0
Sales	0	0
Settlements	0	12
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	41	38
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	$ 3	$ 0

Fair Value of Financial Asset_6

Fair Value of Financial Assets and Liabilities - Fair Value Assets and Liabilities Measure on Recurring Basis Gain Loss Included in Earnings (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	$ (23)	$ (101)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	359	160
Operating Revenue [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	(219)	7
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	546	144
Purchased Power And Fuel [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	245	93
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	(195)	21
Operating and Maintenance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	(3)	(4)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	3	0
Other, net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	(5)	(3)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	5	(2)
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	(26)	(105)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	356	160
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	(219)	7
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	546	144
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	245	93
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	(195)	21
Exelon Generation Co L L C [Member] | Other, net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	(5)	(3)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	5	(2)
Pepco Holdings LLC [Member] | Operating and Maintenance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	(3)	(4)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	3	0
Potomac Electric Power Company [Member] | Other, net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	(3)	(4)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	3	0
6311 Life Insurance [Member] | Pepco Holdings LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	(3)	(4)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	3	0
6311 Life Insurance [Member] | Potomac Electric Power Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in net income	3	4
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	$ 3	$ 0

Fair Value of Financial Asset_7

Fair Value of Financial Assets and Liabilities - Fair Value Inputs Assets Quantitative Information (Details)	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Collateral Posted	$ 214,000,000	$ 76,000,000
Fair Value, Inputs, Level 3 [Member] | Economic Hedges [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	558,000,000	443,000,000
Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value	$ (301,000,000)	$ (249,000,000)
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs Forward Heat Rate	900.00%	1000.00%
Derivative Asset (Liability) Net, Measurement Input	0.03	0.04
Fair Value Inputs [Abstract]
Forward power price assets	9	12
Forward gas price assets	0.83	0.78
Renewable factor	91.00%	86.00%
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs Forward Heat Rate	1000.00%	1100.00%
Derivative Asset (Liability) Net, Measurement Input	0.07	0.08
Fair Value Inputs [Abstract]
Forward power price assets	180	174
Forward gas price assets	10.72	12.38
Renewable factor	123.00%	120.00%
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.08	0.10
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	2.36	2.77
Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value	$ 45,000,000	$ 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	25	14
Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	180	174
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value	$ 307,000,000	$ 618,000,000
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Collateral Posted	214,000,000	76,000,000
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Economic Hedges [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	$ 558,000,000	$ 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	9	12
Forward gas price assets	0.83	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	180	174
Forward gas price assets	10.72	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, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.08	0.10
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	2.36	2.77
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value	$ 45,000,000	$ 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	25	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	180	174
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value	$ (301,000,000)	$ (249,000,000)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs Forward Heat Rate	900.00%	1000.00%
Derivative Asset (Liability) Net, Measurement Input	0.03	0.04
Fair Value Inputs [Abstract]
Renewable factor	91.00%	86.00%
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs Forward Heat Rate	1000.00%	1100.00%
Derivative Asset (Liability) Net, Measurement Input	0.07	0.08
Fair Value Inputs [Abstract]
Renewable factor	123.00%	120.00%

Fair Value of Financial Asset_8

Fair Value of Financial Assets and Liabilities - Narrative (Details)	Dec. 31, 2019USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward Power Basis	$ 2.22
Forward Gas Basis	0.54
Equity Securities without Readily Determinable Fair Value, Amount	69,000,000
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	85,000,000
Private Credit [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	166,000,000
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	375,000,000
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	427,000,000
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities without Readily Determinable Fair Value, Amount	$ 69,000,000

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details)	Mar. 23, 2016USD ($)MW	Dec. 31, 2022MW	Dec. 31, 2019USD ($)MGPSiteOpen_claimMW	Dec. 31, 2018USD ($)MW	Dec. 31, 2017USD ($)MW	Mar. 31, 2018USD ($)
Commitments and Contingencies [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted			$ 69,000,000
Other Commitment			2,714,000,000
Accrual for Environmental Loss Contingencies, Gross			478,000,000	$ 496,000,000
Environmental loss contingencies			83,000,000
Asbestos Liability Reserve				$ 79,000,000
West Lake [Member]
Commitments and Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross			280,000,000
Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Other Commitment			2,110,000,000
Nuclear financial protection pool value			450,000,000
Maximum recovery limit from a nuclear industry mutual insurance company in the event of multiple losses			13,500,000,000
Maximum annual assessment payment mandated by Price-Anderson Act for a nuclear incident			2,900,000,000
Mutual Insurance Total Retrospective Premium Obligation			334,000,000
Mutual Replacement Power Cost Insurance Maximum Retrospective Premium Obligation			3,200,000,000
Cost of spent nuclear fuel disposal per kWh of net nuclear generation			$ 0.001
Spent Nuclear Fuel Treasury Interest Rate			1.551%	1.879%
Accrual for Environmental Loss Contingencies, Gross			$ 105,000,000	$ 108,000,000
Environmental loss contingencies			83,000,000	79,000,000
Exelon Generation Co L L C [Member] | West Lake [Member]
Commitments and Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross			20,000,000
Environmental loss contingencies			90,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Nuclear insurance liability limit per incident			13,900,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Nuclear financial protection pool value			434,000,000
Exelon Generation Co L L C [Member] | Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Mutual Property Insurance Distribution To Members			136,000,000	58,000,000	$ 60,000,000	$ 31,000,000
Commonwealth Edison Co [Member]
Commitments and Contingencies [Line Items]
Other Commitment			$ 257,000,000
Sites under study/remediation | MGPSite			21
Accrual for Environmental Loss Contingencies, Gross			$ 304,000,000	329,000,000
PECO Energy Co [Member]
Commitments and Contingencies [Line Items]
Other Commitment			$ 187,000,000
Sites under study/remediation | MGPSite			8
Accrual for Environmental Loss Contingencies, Gross			$ 19,000,000	27,000,000
Baltimore Gas and Electric Company [Member]
Commitments and Contingencies [Line Items]
Other Commitment			$ 5,000,000
Sites under study/remediation | MGPSite			4
Accrual for Environmental Loss Contingencies, Gross			$ 2,000,000	5,000,000
Common Equity Tier One Capital Ratio			48.00%
Potomac Electric Power Company [Member]
Commitments and Contingencies [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted			$ 23,000,000
Other Commitment			23,000,000
Accrual for Environmental Loss Contingencies, Gross			$ 46,000,000	25,000,000
Common Equity Tier One Capital Ratio			48.00%
Delmarva Power & Light Company [Member]
Commitments and Contingencies [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted			$ 29,000,000
Other Commitment			$ 15,000,000
Total number of MGP sites | MGPSite			1
Accrual for Environmental Loss Contingencies, Gross			$ 1,000,000	1,000,000
Common Equity Tier One Capital Ratio			48.00%
Atlantic City Electric Company [Member]
Commitments and Contingencies [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted			$ 18,000,000
Other Commitment			10,000,000
Accrual for Environmental Loss Contingencies, Gross			$ 1,000,000	1,000,000
Common Equity Tier One Capital Ratio			48.00%
Atlantic City Electric Company [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Common Equity Tier One Capital Ratio			30.00%
Pepco Holdings LLC [Member]
Commitments and Contingencies [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted			$ 69,000,000
Other Commitment			47,000,000
Accrual for Environmental Loss Contingencies, Gross			48,000,000	$ 27,000,000
PEPCO Holdings Inc [Member]
Commitments and Contingencies [Line Items]
Other Commitment			513,000,000
PEPCO Holdings Inc [Member] | Potomac Electric Power Company [Member]
Commitments and Contingencies [Line Items]
Other Commitment			120,000,000
PEPCO Holdings Inc [Member] | Delmarva Power & Light Company [Member]
Commitments and Contingencies [Line Items]
Other Commitment			89,000,000
PEPCO Holdings Inc [Member] | Atlantic City Electric Company [Member]
Commitments and Contingencies [Line Items]
Other Commitment			111,000,000
PEPCO Holdings Inc [Member] | Pepco Holdings LLC [Member]
Commitments and Contingencies [Line Items]
Other Commitment			$ 320,000,000
PEPCO Holdings Inc [Member] | Other Solar Projects [Member]
Commitments and Contingencies [Line Items]
Business Acquisition, Expected New Generation Mwh | MW	37		27
Other Commitment	$ 127,000,000		$ 120,000,000
PEPCO Holdings Inc [Member] | Other Solar Projects [Member] | Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Other Commitment			120,000,000
PEPCO Holdings Inc [Member] | Wind Assets [Member]
Commitments and Contingencies [Line Items]
OtherNonFinancialCommitment1 | MW	100
PEPCO Holdings Inc [Member] | Wind Assets [Member] | Delmarva Power & Light Company [Member]
Commitments and Contingencies [Line Items]
Purchase Commitment | MW	120			40	40
Subsequent Event [Member] | PEPCO Holdings Inc [Member] | Wind Assets [Member] | Delmarva Power & Light Company [Member]
Commitments and Contingencies [Line Items]
Purchase Commitment | MW		40
Open Claims [Member] | Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Asbestos Liability Reserve			$ 26,000,000
Open Asbestos Liability Claims | Open_claim			263
Estimated Future Claims [Member] | Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Asbestos Liability Reserve			$ 57,000,000
Remaining Commitment [Member] | PEPCO Holdings Inc [Member]
Commitments and Contingencies [Line Items]
Other Commitment			101,000,000
Remaining Commitment [Member] | PEPCO Holdings Inc [Member] | Potomac Electric Power Company [Member]
Commitments and Contingencies [Line Items]
Other Commitment			65,000,000
Remaining Commitment [Member] | PEPCO Holdings Inc [Member] | Delmarva Power & Light Company [Member]
Commitments and Contingencies [Line Items]
Other Commitment			8,000,000
Remaining Commitment [Member] | PEPCO Holdings Inc [Member] | Atlantic City Electric Company [Member]
Commitments and Contingencies [Line Items]
Other Commitment			6,000,000
Remaining Commitment [Member] | PEPCO Holdings Inc [Member] | Pepco Holdings LLC [Member]
Commitments and Contingencies [Line Items]
Other Commitment			$ 79,000,000

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of PHI Merger Commitments (Details) $ in Millions	Dec. 31, 2019USD ($)
PHI Merger Commitments [Line Items]
Other Commitment	$ 2,714
PEPCO Holdings Inc [Member]
PHI Merger Commitments [Line Items]
Other Commitment	513
Pepco Holdings LLC [Member]
PHI Merger Commitments [Line Items]
Other Commitment	47
Pepco Holdings LLC [Member] | PEPCO Holdings Inc [Member]
PHI Merger Commitments [Line Items]
Other Commitment	320
Potomac Electric Power Company [Member]
PHI Merger Commitments [Line Items]
Other Commitment	23
Potomac Electric Power Company [Member] | PEPCO Holdings Inc [Member]
PHI Merger Commitments [Line Items]
Other Commitment	120
Delmarva Power & Light Company [Member]
PHI Merger Commitments [Line Items]
Other Commitment	15
Delmarva Power & Light Company [Member] | PEPCO Holdings Inc [Member]
PHI Merger Commitments [Line Items]
Other Commitment	89
Atlantic City Electric Company [Member]
PHI Merger Commitments [Line Items]
Other Commitment	10
Atlantic City Electric Company [Member] | PEPCO Holdings Inc [Member]
PHI Merger Commitments [Line Items]
Other Commitment	111
Remaining Commitment [Member] | PEPCO Holdings Inc [Member]
PHI Merger Commitments [Line Items]
Other Commitment	101
Remaining Commitment [Member] | Pepco Holdings LLC [Member] | PEPCO Holdings Inc [Member]
PHI Merger Commitments [Line Items]
Other Commitment	79
Remaining Commitment [Member] | Potomac Electric Power Company [Member] | PEPCO Holdings Inc [Member]
PHI Merger Commitments [Line Items]
Other Commitment	65
Remaining Commitment [Member] | Delmarva Power & Light Company [Member] | PEPCO Holdings Inc [Member]
PHI Merger Commitments [Line Items]
Other Commitment	8
Remaining Commitment [Member] | Atlantic City Electric Company [Member] | PEPCO Holdings Inc [Member]
PHI Merger Commitments [Line Items]
Other Commitment	$ 6

Commitments and Contingencies_4

Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Dec. 31, 2019USD ($)
Guarantor Obligations [Line Items]
Other Commitment	$ 2,714
Other Commitments, Due in Next Twelve Months	2,125
Other Commitment, Due in Second Year	189
Other Commitment, Due in Third Year	4
Other Commitment, Due in Fourth Year	3
Other Commitment, Due in Fifth Year	6
Other Commitment, Due after Fifth Year	388
Guarantee obligations maximum exposure	69
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Other Commitment	2,110
Other Commitments, Due in Next Twelve Months	1,964
Other Commitment, Due in Second Year	146
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Other Commitment	257
Other Commitments, Due in Next Twelve Months	55
Other Commitment, Due in Second Year	2
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	200
PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Other Commitment	187
Other Commitments, Due in Next Twelve Months	9
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	178
Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	5
Other Commitments, Due in Next Twelve Months	5
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Pepco Holdings LLC [Member]
Guarantor Obligations [Line Items]
Other Commitment	47
Other Commitments, Due in Next Twelve Months	23
Other Commitment, Due in Second Year	2
Other Commitment, Due in Third Year	4
Other Commitment, Due in Fourth Year	3
Other Commitment, Due in Fifth Year	6
Other Commitment, Due after Fifth Year	10
Guarantee obligations maximum exposure	69
Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	23
Other Commitments, Due in Next Twelve Months	14
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	1
Other Commitment, Due in Fourth Year	1
Other Commitment, Due in Fifth Year	2
Other Commitment, Due after Fifth Year	5
Guarantee obligations maximum exposure	23
Delmarva Power & Light Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	15
Other Commitments, Due in Next Twelve Months	5
Other Commitment, Due in Second Year	1
Other Commitment, Due in Third Year	2
Other Commitment, Due in Fourth Year	1
Other Commitment, Due in Fifth Year	3
Other Commitment, Due after Fifth Year	3
Guarantee obligations maximum exposure	29
Atlantic City Electric Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	10
Other Commitments, Due in Next Twelve Months	4
Other Commitment, Due in Second Year	1
Other Commitment, Due in Third Year	1
Other Commitment, Due in Fourth Year	1
Other Commitment, Due in Fifth Year	1
Other Commitment, Due after Fifth Year	2
Guarantee obligations maximum exposure	18
Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Other Commitment	1,455
Other Commitments, Due in Next Twelve Months	1,314
Other Commitment, Due in Second Year	141
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Financial Standby Letter of Credit [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Other Commitment	1,440
Other Commitments, Due in Next Twelve Months	1,302
Other Commitment, Due in Second Year	138
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Financial Standby Letter of Credit [Member] | Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Other Commitment	7
Other Commitments, Due in Next Twelve Months	7
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Financial Standby Letter of Credit [Member] | Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	2
Other Commitments, Due in Next Twelve Months	2
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Surety Bond [Member]
Guarantor Obligations [Line Items]
Other Commitment	855
Other Commitments, Due in Next Twelve Months	809
Other Commitment, Due in Second Year	46
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Surety Bond [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Other Commitment	670
Other Commitments, Due in Next Twelve Months	662
Other Commitment, Due in Second Year	8
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Surety Bond [Member] | Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Other Commitment	50
Other Commitments, Due in Next Twelve Months	48
Other Commitment, Due in Second Year	2
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Surety Bond [Member] | PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Other Commitment	9
Other Commitments, Due in Next Twelve Months	9
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Surety Bond [Member] | Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	3
Other Commitments, Due in Next Twelve Months	3
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Surety Bond [Member] | Pepco Holdings LLC [Member]
Guarantor Obligations [Line Items]
Other Commitment	21
Other Commitments, Due in Next Twelve Months	21
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Surety Bond [Member] | Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	14
Other Commitments, Due in Next Twelve Months	14
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Surety Bond [Member] | Delmarva Power & Light Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	4
Other Commitments, Due in Next Twelve Months	4
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Surety Bond [Member] | Atlantic City Electric Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	3
Other Commitments, Due in Next Twelve Months	3
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Other Commitment	378
Other Commitments, Due in Next Twelve Months	0
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	378
Guarantee of Indebtedness of Others [Member] | Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Other Commitment	200
Other Commitments, Due in Next Twelve Months	0
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	200
Guarantee of Indebtedness of Others [Member] | PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Other Commitment	178
Other Commitments, Due in Next Twelve Months	0
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	178
Guarantee Obligations [Member]
Guarantor Obligations [Line Items]
Other Commitment	26
Other Commitments, Due in Next Twelve Months	2
Other Commitment, Due in Second Year	2
Other Commitment, Due in Third Year	4
Other Commitment, Due in Fourth Year	3
Other Commitment, Due in Fifth Year	6
Other Commitment, Due after Fifth Year	10
Guarantee Obligations [Member] | Pepco Holdings LLC [Member]
Guarantor Obligations [Line Items]
Other Commitment	26
Other Commitments, Due in Next Twelve Months	2
Other Commitment, Due in Second Year	2
Other Commitment, Due in Third Year	4
Other Commitment, Due in Fourth Year	3
Other Commitment, Due in Fifth Year	6
Other Commitment, Due after Fifth Year	10
Guarantee Obligations [Member] | Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	9
Other Commitments, Due in Next Twelve Months	0
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	1
Other Commitment, Due in Fourth Year	1
Other Commitment, Due in Fifth Year	2
Other Commitment, Due after Fifth Year	5
Guarantee Obligations [Member] | Delmarva Power & Light Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	11
Other Commitments, Due in Next Twelve Months	1
Other Commitment, Due in Second Year	1
Other Commitment, Due in Third Year	2
Other Commitment, Due in Fourth Year	1
Other Commitment, Due in Fifth Year	3
Other Commitment, Due after Fifth Year	3
Guarantee Obligations [Member] | Atlantic City Electric Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	7
Other Commitments, Due in Next Twelve Months	1
Other Commitment, Due in Second Year	1
Other Commitment, Due in Third Year	1
Other Commitment, Due in Fourth Year	1
Other Commitment, Due in Fifth Year	1
Other Commitment, Due after Fifth Year	$ 2
Minimum [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	23 years
Minimum [Member] | Pepco Holdings LLC [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | Delmarva Power & Light Company [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	12 years
Minimum [Member] | Atlantic City Electric Company [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | Guarantee Obligations [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Maximum [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	83 years
Maximum [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	32 years
Maximum [Member] | Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	17 years
Maximum [Member] | PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	83 years
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	23 years
Maximum [Member] | Pepco Holdings LLC [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	13 years
Maximum [Member] | Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	6 years
Maximum [Member] | Delmarva Power & Light Company [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	13 years
Maximum [Member] | Atlantic City Electric Company [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	2 years
Maximum [Member] | Guarantee Obligations [Member]
Guarantor Obligations [Line Items]
Lessor, Operating Lease, Term of Contract	8 years

Commitments and Contingencies_5

Commitments and Contingencies - Settlement Agreements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Guarantor Obligations [Line Items]
Nontrade Receivables, Current	$ 249	$ 124
Nontrade Receivables, Noncurrent	30	15
Accounts Payable, Other, Current	(37)	$ (17)
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Spent Nuclear Fuel Storage Reimbursement	1,288
Spent Nuclear Fuel Storage Reimbursement Net Co Owners	$ 1,113

Commitments and Contingencies_6

Commitments and Contingencies - Schedule of Spent Nuclear Fuel Obligation (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	$ 1,199	$ 1,171
Spent Nuclear Fuel One Time Fee		34
Exelon Generation Co L L C [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	1,199	1,171
Spent Nuclear Fuel One Time Fee		277
Nuclear Plant [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	1,075	1,052
Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	1,075	1,052
Fitzpatrick [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	124	119
Fitzpatrick [Member] | Exelon Generation Co L L C [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	$ 124	$ 119

Commitments and Contingencies_7

Commitments and Contingencies - Schedule of Environmental Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 478	$ 496
Exelon Generation Co L L C [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	105	108
Commonwealth Edison Co [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	304	329
PECO Energy Co [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	19	27
Baltimore Gas and Electric Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	2	5
Pepco Holdings LLC [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	48	27
Potomac Electric Power Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	46	25
Delmarva Power & Light Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	1
Atlantic City Electric Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	1
Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	320	356
Accrual For MGP Investigation And Remediation [Member] | Exelon Generation Co L L C [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Commonwealth Edison Co [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	303	327
Accrual For MGP Investigation And Remediation [Member] | PECO Energy Co [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	17	25
Accrual For MGP Investigation And Remediation [Member] | Baltimore Gas and Electric Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	4
Accrual For MGP Investigation And Remediation [Member] | Pepco Holdings LLC [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Potomac Electric Power Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Delmarva Power & Light Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Atlantic City Electric Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 0	$ 0

Shareholders' Equity Shareholde

Shareholders' Equity Shareholder Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2017	Dec. 31, 2019	Jun. 30, 2014
Schedule of Capitalization, Equity [Line Items]
Stock Issued During Period, Shares, Treasury Stock Reissued	33,000,000
Stock Repurchase Program, Number of Shares Authorized to be Repurchased		0
Junior Subordinated Debt [Member]
Schedule of Capitalization, Equity [Line Items]
Junior Subordinated Notes			$ 1,150
Equity units issued			23,000,000

Shareholders' Equity Schedule o

Shareholders' Equity Schedule of Common Stock Warrants (Details) - Commonwealth Edison Co [Member] - shares	Dec. 31, 2019	Dec. 31, 2018
Class of Warrant or Right [Line Items]
Class of Warrant or Right, Outstanding	60,228	60,285
Common Stock [Member]
Class of Warrant or Right [Line Items]
Common Stock Shares Reserved For Warrant Conversion	20,076	20,095

Shareholders' Equity Schedule_2

Shareholders' Equity Schedule of Preferred Stock (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	100,000,000	100,000,000
Preferred Stock, Shares Outstanding	0	0
Preferred Stock [Member] | Commonwealth Edison Co [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	850,000	850,000
Preferred Stock, Shares Outstanding	0	0
Preferred Stock [Member] | PECO Energy Co [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	15,000,000	15,000,000
Preferred Stock, Shares Outstanding	0	0
Preferred Stock [Member] | Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	1,000,000	1,000,000
Preferred Stock, Shares Outstanding	0	0
Preferred Stock [Member] | Potomac Electric Power Company [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	6,000,000	6,000,000
Preferred Stock, Shares Outstanding	0	0
Preferred Stock [Member] | Atlantic City Electric Company [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	2,799,979	2,799,979
Preferred Stock, Shares Outstanding	0	0
Cumulative Preferred Stock [Member] | Atlantic City Electric Company [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	799,979	799,979
No-Par Preferred Stock [Member] | Atlantic City Electric Company [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	2,000,000	2,000,000

Shareholders' Equity Schedule_3

Shareholders' Equity Schedule of Preference Stock (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Commonwealth Edison Co [Member]
Class of Stock [Line Items]
Preference Stock, Shares Authorized	6,810,451	6,810,451
Preference Stock, Shares Outstanding	0	0
Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Preference Stock, Shares Authorized	6,500,000	6,500,000
Preference Stock, Shares Outstanding	0	0
Atlantic City Electric Company [Member]
Class of Stock [Line Items]
Preference Stock, Shares Authorized	3,000,000	3,000,000
Preference Stock, Shares Outstanding	0	0
Unclassified Preference Stock [Member] | Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Preference Stock, Shares Authorized	4,600,000	4,600,000
Preference Stock Redeemed [Member] | Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Preference Stock, Shares Authorized	1,900,000	1,900,000

Stock-Based Compensation Plan_3

Stock-Based Compensation Plans - Narrative (Details) shares in Millions	12 Months Ended
	Dec. 31, 2019shares
Performance Shares [Member]
Common Stock Narrative Information [Line Items]
Percentage to be settled as common stock	50.00%
Percentage to be settled as cash	50.00%
Percentage to be settled as cash if ownership requirements are met	100.00%
Minimum [Member] | Restricted Stock Units (RSUs) [Member]
Common Stock Narrative Information [Line Items]
Requisite service period	3 years
Maximum [Member] | Restricted Stock Units (RSUs) [Member]
Common Stock Narrative Information [Line Items]
Requisite service period	5 years
LTIP [Member]
Common Stock Narrative Information [Line Items]
Shares authorized	12

Stock-Based Compensation Plan_4

Stock-Based Compensation Plans - Schedule of Stock-based Compensation Expense (Details) - Share-based Payment Arrangement [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	$ 77	$ 208	$ 191
Share-based Payment Arrangement, Expense, Tax Benefit	(20)	(54)	(74)
Share-based Payment Arrangement, Expense, after Tax	57	154	117
Exelon Generation Co L L C [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	37	77	88
Share-based Payment Arrangement, Expense, Tax Benefit	(10)	(20)	(34)
Share-based Payment Arrangement, Expense, after Tax	$ 27	$ 57	$ 54

Stock-Based Compensation Plan_5

Stock-Based Compensation Plans - Components of Tax Benefits from Stock-based Compensation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Performance Shares [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit on stock compensation	$ 41	$ 16	$ 29
Restricted Stock Units (RSUs) [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit on stock compensation	$ 24	$ 28	$ 35

Stock-Based Compensation Plan_6

Stock-Based Compensation Plans - Summary of Nonvested Performance Share Awards Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount	$ 17
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance	3,403,228
Granted	1,089,903
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Period Increase (Decrease)	(799,618)
Vested	(1,610,146)
Forfeited	(25,249)
Undistributed vested awards	(348,363)
Ending Balance	1,709,755	3,403,228
Nonvested, Weighted Average Exercise Price (in usd per share)	$ 39.21	$ 33.13
Granted, Weighted Average Grant Date Fair Value (in usd per share)	47.37	$ 38.15	$ 35
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Change in Performance, Weighted Average Grant Date Fair Value	40.85
Vested, Weighted Average Exercise Price (in usd per share)	28.90
Forfeited, Weighted Average Exercise Price (in usd per share)	45.03
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	$ 48.82
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees	2,017,870	3,586,259
Fair Value Of Settled Performance Share Awards	$ 158	$ 61	$ 72
Performance Share Awards Obligations Settled In Cash	$ 131	$ 49	$ 56
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	1 year 7 months 6 days

Stock-Based Compensation Plan_7

Stock-Based Compensation Plans - Summary of Nonvested Restricted Stock Unit Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount	$ 17
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance	2,293,341
Granted	902,857
Vested	(1,232,704)
Forfeited	(33,603)
Undistributed vested awards	(431,178)
Ending Balance	1,498,713	2,293,341
Nonvested, Weighted Average Exercise Price (in usd per share)	$ 40.35	$ 35.06
Granted, Weighted Average Grant Date Fair Value (in usd per share)	45.65	$ 38.60	$ 34.98
Vested, Weighted Average Exercise Price (in usd per share)	32.83
Forfeited, Weighted Average Exercise Price (in usd per share)	39.01
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	$ 44.75
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees	863,196	1,131,487
Fair Value Of Settled Restricted Stock Units	$ 92	$ 106	$ 88
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount	$ 28
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	2 years 9 months 18 days
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance	3,403,228
Granted	1,089,903
Vested	(1,610,146)
Forfeited	(25,249)
Undistributed vested awards	(348,363)
Ending Balance	1,709,755	3,403,228
Nonvested, Weighted Average Exercise Price (in usd per share)	$ 39.21	$ 33.13
Granted, Weighted Average Grant Date Fair Value (in usd per share)	47.37	$ 38.15	$ 35
Vested, Weighted Average Exercise Price (in usd per share)	28.90
Forfeited, Weighted Average Exercise Price (in usd per share)	45.03
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	$ 48.82
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees	2,017,870	3,586,259
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	1 year 7 months 6 days

Stock-Based Compensation Plan_8

Stock-Based Compensation Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Aggregate value	$ 9	$ 12	$ 15
Cash received for exercise price	$ 59	$ 56	$ 107
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning Balance	4,027,652
Options exercised	(1,388,165)
Options expired	(750,442)
Ending Balance	1,889,045	4,027,652
Exercisable at December 31, 2019	1,889,045
Weighted Average Exercise Price (in usd per share)	$ 40.43	$ 43.95
Options Exercised, Weighted Average Exercise Price (in usd per share)	42.25
Options Expired, Weighted Average Exercise Price (in usd per share)	55.96
Shares Exercisable, Weighted Average Exercise Price (in usd per share)	$ 40.43
Shares Outstanding, Weighted Average Remaining Contractual Life	1 year 6 months 21 days	2 years 10 months 24 days
Shares Exercisable, Weighted Average Remaining Contractual Life	1 year 6 months 21 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 10	$ 14
Shares Exercisable, Aggregate Intrinsic Value	$ 10

Changes in Accumulated Other _3

Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ 33,047	$ 32,169	$ 27,629
Other comprehensive income (loss)	(198)	42	171
Ending Balance	34,573	33,047	32,169
Gains and (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(2)	(14)	(17)
OCI before reclassifications	0	11	(1)
Amounts reclassified from AOCI	0	1	4
Other comprehensive income (loss)	0	12	3
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings			0
Ending Balance	(2)	(2)	(14)
Gains and (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		0
Unrealized Gains and (Losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	0	10	4
OCI before reclassifications	0	0	6
Amounts reclassified from AOCI	0	0	0
Other comprehensive income (loss)	0	0	6
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings			0
Ending Balance	0	0	10
Unrealized Gains and (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		(10)
Pension and Non-Pension Postretirement Benefit Plan Items (a)
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(2,960)	(2,998)	(2,610)
OCI before reclassifications	(289)	(143)	11
Amounts reclassified from AOCI	84	181	140
Other comprehensive income (loss)	(205)	38	151
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings			(539)
Ending Balance	(3,165)	(2,960)	(2,998)
Pension and Non-Pension Postretirement Benefit Plan Items (a) | 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		0
Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(33)	(23)	(30)
OCI before reclassifications	6	(10)	7
Amounts reclassified from AOCI	0	0	0
Other comprehensive income (loss)	6	(10)	7
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings			0
Ending Balance	(27)	(33)	(23)
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		0
AOCI of Investments Unconsolidated Affiliates (b)
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	0	(1)	(7)
OCI before reclassifications	(2)	1	6
Amounts reclassified from AOCI	2	0	0
Other comprehensive income (loss)	0	1	6
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings			0
Ending Balance	0	0	(1)
AOCI of Investments Unconsolidated Affiliates (b) | 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		0
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(2,995)	(3,026)	(2,660)
OCI before reclassifications	(285)	(141)	29
Amounts reclassified from AOCI	86	182	144
Other comprehensive income (loss)	(199)	41	173
Ending Balance	$ (3,194)	(2,995)	$ (3,026)
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		$ (10)

Changes in Accumulated Other _4

Changes in Accumulated Other Comprehensive Income - Income Taxes Allocated to Other Comprehensive Income (Loss) Components (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Prior service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	$ 23	$ 24	$ 36
Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	(52)	(86)	(128)
Pension and Non-Pension Postretirement Benefit Plan Items (a)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	$ 100	$ 50	$ 13

Variable Interest Entities - Na

Variable Interest Entities - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Apr. 01, 2014
Variable Interest Entity [Line Items]
Guarantee obligations maximum exposure	$ 69
CENG [Member]
Variable Interest Entity [Line Items]
Ownership Percentage Of Consolidated Variable Interest Entities	50.01%
Due from Affiliates	$ 571	$ 400
Payment Guarantee [Member] | CENG [Member]
Variable Interest Entity [Line Items]
Guarantee obligations maximum exposure		245
Financial Guarantee [Member] | CENG [Member]
Variable Interest Entity [Line Items]
Guarantee obligations maximum exposure		165
Equity interest member [Member] | 2015 ESA Investco, LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	90.00%
Exelon Generation Co L L C [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	100.00%
Ownership Percentage Of Consolidated Variable Interest Entities	100.00%
Exelon Generation Co L L C [Member] | CENG [Member]
Variable Interest Entity [Line Items]
Parental guarantee provided	$ 688
Ownership Percentage Of Consolidated Variable Interest Entities	50.01%
Ownership interest	50.01%
Due from Affiliates	$ 571	$ 400
Exelon Generation Co L L C [Member] | Antelope Valley [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	100.00%
Exelon Generation Co L L C [Member] | Equity interest member [Member] | Bloom IV [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	90.00%
Exelon Generation Co L L C [Member] | Equity interest member [Member] | EGRP [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	51.00%
Exelon Generation Co L L C [Member] | Equity interest member [Member] | Bloom V [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	31.00%
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Guarantee obligations maximum exposure	$ 69
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Guarantee obligations maximum exposure	$ 18

Variable Interest Entities - As

Variable Interest Entities - Assets and Liabilities of VIEs which Creditors or Beneficiaries have No Recourse (Details) - USD ($) $ in Millions		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents		$ 587		$ 1,349		$ 898	$ 635
Restricted cash		358		247		207	253
Accounts Receivable, net
Customer		4,592		4,607
Other		1,583		1,256
Unamortized energy contract assets, current		47		48
Inventories, net
Materials and supplies		1,456		1,351
Other current assets		1,253		1,238
Total current assets		12,037		13,328
Property, plant and equipment, net		80,233		76,707
Nuclear decommissioning trust funds		13,190		11,661
Unamortized energy contract assets, noncurrent		336		372
Other Assets, Noncurrent		3,197		1,575
Total assets	[1]	124,977		119,634
Current liabilities
Long-term debt due within one year		4,710		1,349
Accounts payable		3,560		3,800
Accrued expenses		1,981		2,112
Unamortized energy contract liabilities		132		149
Other current liabilities		1,331		1,035
Total current liabilities		14,185		11,404
Long-term debt		31,329		34,075
Asset retirement obligations		10,846		9,679
Unamortized energy contract liabilities		338		463
Other Liabilities, Noncurrent		3,064		2,130
Total liabilities		90,404		86,587	[1]
Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents		163		414
Restricted cash		88		66
Accounts Receivable, net
Customer		151		146
Other		39		23
Unamortized energy contract assets, current		23		25
Inventories, net
Materials and supplies		227		212
Other current assets		32		52
Total current assets		723		938
Property, plant and equipment, net		6,022		6,188
Nuclear decommissioning trust funds		2,741		2,351
Unamortized energy contract assets, noncurrent		250		274
Other Assets, Noncurrent		89		258
Total noncurrent assets		9,102		9,071
Total assets		9,825		10,009
Current liabilities
Long-term debt due within one year		544		87
Accounts payable		106		96
Accrued expenses		70		73
Unamortized energy contract liabilities		8		15
Other current liabilities		3		3
Total current liabilities		731		274
Long-term debt		527		1,072
Asset retirement obligations		2,128		2,165
Unamortized energy contract liabilities		1		1
Other Liabilities, Noncurrent		89		42
Total noncurrent liabilities		2,745		3,280
Total liabilities		3,476		3,554
PP&E - unrestricted asset				43
Variable Interest Entity, Consolidated, Liabilities, Recourse		3		5
Exelon Generation Co L L C [Member]
Current assets
Cash and cash equivalents		303		750		416	290
Restricted cash		146		153		138	158
Accounts Receivable, net
Customer		2,893		2,941
Other		619		562
Unamortized energy contract assets, current		47		49
Inventories, net
Materials and supplies		1,026		963
Other current assets		941		883
Total current assets		7,076		8,433
Property, plant and equipment, net		24,193		23,981
Nuclear decommissioning trust funds		13,190		11,661
Unamortized energy contract assets, noncurrent		336		371
Other Assets, Noncurrent		1,960		755
Total assets	[2]	48,995		47,556
Current liabilities
Long-term debt due within one year		2,624		906
Accounts payable		1,692		1,847
Accrued expenses		786		898
Unamortized energy contract liabilities		17		31
Other current liabilities		517		279
Total current liabilities		7,289		5,769
Long-term debt		4,464		6,989
Asset retirement obligations		10,603		9,450
Unamortized energy contract liabilities		11		20
Other Liabilities, Noncurrent		1,415		610
Total liabilities	[2]	33,165		32,048
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents		163		414
Restricted cash		85		62
Accounts Receivable, net
Customer		151		146
Other		39		23
Unamortized energy contract assets, current		23		25
Inventories, net
Materials and supplies		227		212
Other current assets		31		49
Total current assets		719		931
Property, plant and equipment, net		6,022		6,188
Nuclear decommissioning trust funds		2,741		2,351
Unamortized energy contract assets, noncurrent		250		274
Other Assets, Noncurrent		73		232
Total noncurrent assets		9,086		9,045
Total assets		9,805		9,976
Current liabilities
Long-term debt due within one year		523		66
Accounts payable		106		96
Accrued expenses		70		72
Unamortized energy contract liabilities		8		15
Other current liabilities		3		3
Total current liabilities		710		252
Long-term debt		504		1,025
Asset retirement obligations		2,128		2,165
Unamortized energy contract liabilities		1		1
Other Liabilities, Noncurrent		89		42
Total noncurrent liabilities		2,722		3,233
Total liabilities		3,432		3,485
PP&E - unrestricted asset		20		43
Variable Interest Entity, Consolidated, Liabilities, Recourse		3		5
Pepco Holdings LLC [Member]
Current assets
Cash and cash equivalents		131		124		30	170
Restricted cash		36		43		42	43
Accounts Receivable, net
Customer		479		453
Other		174		177
Inventories, net
Materials and supplies		190		163
Other current assets		49		75
Total current assets		1,480		1,501
Property, plant and equipment, net		14,296		13,446
Other Assets, Noncurrent		323		60
Total assets		22,719		21,952
Current liabilities
Long-term debt due within one year		103		125
Accounts payable		462		496
Accrued expenses		296		256
Unamortized energy contract liabilities		115		119
Other current liabilities		131		123
Total current liabilities		1,612		1,592
Long-term debt		6,460		6,134
Asset retirement obligations		57		52
Unamortized energy contract liabilities		327		442
Other Liabilities, Noncurrent		577		369
Total liabilities		13,111	[3]	12,693
Pepco Holdings LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents		0		0
Restricted cash		3		4
Accounts Receivable, net
Customer		0		0
Other		0		0
Unamortized energy contract assets, current		0		0
Inventories, net
Materials and supplies		0		0
Other current assets		1		3
Total current assets		4		7
Property, plant and equipment, net		0		0
Nuclear decommissioning trust funds		0		0
Unamortized energy contract assets, noncurrent		0		0
Other Assets, Noncurrent		16		26
Total noncurrent assets		16		26
Total assets		20		33
Current liabilities
Long-term debt due within one year		21		21
Accounts payable		0		0
Accrued expenses		0		1
Unamortized energy contract liabilities		0		0
Other current liabilities		0		0
Total current liabilities		21		22
Long-term debt		23		47
Asset retirement obligations		0		0
Unamortized energy contract liabilities		0		0
Other Liabilities, Noncurrent		0		0
Total noncurrent liabilities		23		47
Total liabilities		44		69
Atlantic City Electric Company [Member]
Current assets
Cash and cash equivalents		12		7		2	101
Restricted cash		2		4		$ 6	$ 9
Accounts Receivable, net
Customer		108		95
Other		48		55
Inventories, net
Other current assets		5		5
Total current assets		270		240
Property, plant and equipment, net		3,190		2,966
Other Assets, Noncurrent		53		40
Total assets	[4]	3,933		3,699
Current liabilities
Long-term debt due within one year		20		18
Accounts payable		144		154
Accrued expenses		42		35
Other current liabilities		9		4
Total current liabilities		360		422
Long-term debt		1,307		1,170
Other Liabilities, Noncurrent		39		27
Total liabilities		2,657		2,573
Atlantic City Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents		0		0
Restricted cash		3		4
Accounts Receivable, net
Customer		0		0
Other		0		0
Unamortized energy contract assets, current		0		0
Inventories, net
Materials and supplies		0		0
Other current assets		0		0
Total current assets		3		4
Property, plant and equipment, net		0		0
Nuclear decommissioning trust funds		0		0
Unamortized energy contract assets, noncurrent		0		0
Other Assets, Noncurrent		14		19
Total noncurrent assets		14		19
Total assets		17		23
Current liabilities
Long-term debt due within one year		20		18
Accounts payable		0		0
Accrued expenses		0		1
Unamortized energy contract liabilities		0		0
Other current liabilities		0		0
Total current liabilities		20		19
Long-term debt		21		40
Asset retirement obligations		0		0
Unamortized energy contract liabilities		0		0
Other Liabilities, Noncurrent		0		0
Total noncurrent liabilities		21		40
Total liabilities		$ 41		$ 59
[1]	Exelon’s consolidated assets include $9,532 million and $9,667 million at December 31, 2019 and 2018 , respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,473 million and $3,548 million at December 31, 2019 and 2018 , respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 22 – Variable Interest Entities for additional information.
[2]	Generation’s consolidated assets include $9,512 million and $9,634 million at December 31, 2019 and 2018 , respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,429 million and $3,480 million at December 31, 2019 and 2018 , respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 22 – Variable Interest Entities for additional information.
[3]	PHI’s consolidated total assets include $20 million and $33 million at December 31, 2019 and 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 $44 million and $69 million at December 31, 2019 and 2018 , respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 22 - Variable Interest Entities for additional information.
[4]	ACE’s consolidated assets include $17 million and $23 million at December 31, 2019 and 2018 , respectively, of ACE’s consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated liabilities include $41 million and $59 million at December 31, 2019 and 2018 , respectively, of ACE’s consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 22 - Variable Interest Entities for additional information.

Variable Interest Entities - Su

Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Total assets	$ 1,079	$ 1,069
Total liabilities	260	259
Exelon's ownership interest in VIE	191	223
Other ownership interests in VIE	629	587
Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	0	223
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	636	597
Total liabilities	33	37
Exelon's ownership interest in VIE	0	0
Other ownership interests in VIE	604	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
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets	443	472
Total liabilities	227	222
Exelon's ownership interest in VIE	191	223
Other ownership interests in VIE	25	27
Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	0	223
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Total assets	1,079	1,069
Total liabilities	260	259
Exelon's ownership interest in VIE	191	223
Other ownership interests in VIE	629	587
Exelon Generation Co L L C [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	0	223
Exelon Generation Co L L C [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	636	597
Total liabilities	33	37
Exelon's ownership interest in VIE	0	0
Other ownership interests in VIE	604	560
Exelon Generation Co L L C [Member] | Commercial Agreement Variable Interest Entities [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	0	0
Exelon Generation Co L L C [Member] | Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets	443	472
Total liabilities	227	222
Exelon's ownership interest in VIE	191	223
Other ownership interests in VIE	25	27
Exelon Generation Co L L C [Member] | Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	$ 0	$ 223

Supplemental Financial Inform_3

Supplemental Financial Information - Summary of Taxes other than income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Statement of Operations Information [Line Items]
Utility	$ 881	$ 919	$ 898
Property	595	557	545
Payroll	232	247	230
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	112	114	126
Property	274	273	269
Payroll	115	130	121
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	242	243	240
Property	29	30	28
Payroll	27	27	26
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	132	131	125
Property	17	15	14
Payroll	15	16	15
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	90	94	89
Property	153	143	132
Payroll	17	17	15
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	304	337	318
Property	122	94	101
Payroll	24	24	26
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	286	316	300
Property	85	58	62
Payroll	7	5	6
Delmarva Power & Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	18	21	18
Property	34	32	32
Payroll	4	3	4
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	0	0	0
Property	2	3	3
Payroll	$ 2	$ 2	$ 2

Supplemental Financial Inform_4

Supplemental Financial Information - Summary of Other Income (Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	$ 297	$ 506	$ 488
Net realized income on NDT funds - Non-regulatory agreement units	363	302	209
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	795	(715)	455
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement	411	(483)	521
Regulatory offset to NDT fund-related activities	(876)	171	(724)
Total decommissioning-related activities	990	(219)	949
AFUDC—Equity	85	69	73
Non-service net periodic benefit cost	13	(47)	(109)
Exelon Generation Co L L C [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	297	506	488
Net realized income on NDT funds - Non-regulatory agreement units	363	302	209
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	795	(715)	455
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement	411	(483)	521
Regulatory offset to NDT fund-related activities	(876)	171	(724)
Total decommissioning-related activities	990	(219)	949
AFUDC—Equity	0	0	0
Commonwealth Edison Co [Member]
Decommissioning-Related Activities [Abstract]
AFUDC—Equity	17	19	12
PECO Energy Co [Member]
Decommissioning-Related Activities [Abstract]
AFUDC—Equity	13	7	9
Baltimore Gas and Electric Company [Member]
Decommissioning-Related Activities [Abstract]
AFUDC—Equity	21	18	16
Pepco Holdings LLC [Member]
Decommissioning-Related Activities [Abstract]
AFUDC—Equity	34	25	36
Potomac Electric Power Company [Member]
Decommissioning-Related Activities [Abstract]
AFUDC—Equity	25	22	23
Delmarva Power & Light Company [Member]
Decommissioning-Related Activities [Abstract]
AFUDC—Equity	4	2	7
Atlantic City Electric Company [Member]
Decommissioning-Related Activities [Abstract]
AFUDC—Equity	$ 5	$ 1	$ 6

Supplemental Financial Inform_5

Supplemental Financial Information - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Depreciation, amortization and accretion
Depreciation	$ 3,665	$ 3,740	$ 3,293
Amortization of Regulatory Asset	528	555	478
Amortization of Intangible Assets	(28)	(109)	(237)
Amortization of Nuclear Fuel Lease	1,016	1,115	1,096
Accretion expense	491	489	468
Total depreciation, amortization and accretion	5,780	5,971	5,427
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	1,470	1,421	2,430
Income taxes (net of refunds)	265	95	540
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	438	583	643
Provision for uncollectible accounts	120	159	125
Other decommissioning related-activity	(506)	(2)	(313)
Energy-related options	22	10	7
Amortization of rate stabilization deferral	(4)	21	(3)
Asset Retirement Obligation, Revision of Estimate		20
Discrete impacts from EIMA and FEJA	128	28	(52)
Vacation accrual adjustment		68	(68)
Long-term incentive plan	10	140	109
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	244
Change in environmental liabilities	23		44
Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Depreciation	1,485	1,748	1,409
Amortization of Regulatory Asset	0	0	0
Amortization of Intangible Assets	74	63	83
Amortization of Nuclear Fuel Lease	1,016	1,115	1,096
Accretion expense	491	489	468
Total depreciation, amortization and accretion	3,063	3,415	3,056
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	373	369	391
Income taxes (net of refunds)	(44)	746	337
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	135	204	227
Provision for uncollectible accounts	31	48	38
Other decommissioning related-activity	(506)	(2)	(313)
Energy-related options	22	10	7
Amortization of rate stabilization deferral	0	0	0
Asset Retirement Obligation, Revision of Estimate		0
Vacation accrual adjustment			(35)
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	172
Change in environmental liabilities	0		44
Commonwealth Edison Co [Member]
Depreciation, amortization and accretion
Depreciation	886	820	777
Amortization of Regulatory Asset	147	120	73
Amortization of Intangible Assets	7	7	7
Accretion expense	0	0	0
Total depreciation, amortization and accretion	1,033	940	850
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	343	332	307
Income taxes (net of refunds)	(42)	(153)	83
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	96	177	176
Provision for uncollectible accounts	33	40	34
Amortization of rate stabilization deferral	0	0	0
Asset Retirement Obligation, Revision of Estimate		0
Discrete impacts from EIMA and FEJA	128	28	(52)
Vacation accrual adjustment			(12)
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	3
Change in environmental liabilities	0		0
PECO Energy Co [Member]
Depreciation, amortization and accretion
Depreciation	303	274	261
Amortization of Regulatory Asset	30	27	25
Accretion expense	0	0	0
Total depreciation, amortization and accretion	333	301	286
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	129	125	103
Income taxes (net of refunds)	82	(2)	47
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	12	18	29
Provision for uncollectible accounts	31	33	26
Amortization of rate stabilization deferral	0	0	0
Asset Retirement Obligation, Revision of Estimate		0
Vacation accrual adjustment			0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	0
Change in environmental liabilities	0		0
Baltimore Gas and Electric Company [Member]
Depreciation, amortization and accretion
Depreciation	359	335	312
Amortization of Regulatory Asset	143	148	161
Accretion expense	0	0	0
Total depreciation, amortization and accretion	502	483	473
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	106	94	96
Income taxes (net of refunds)	17	14	(2)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	61	59	62
Provision for uncollectible accounts	8	10	8
Amortization of rate stabilization deferral	0	0	7
Asset Retirement Obligation, Revision of Estimate		0
Vacation accrual adjustment			0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	30
Change in environmental liabilities	0		0
Pepco Holdings LLC [Member]
Depreciation, amortization and accretion
Depreciation	547	480	457
Amortization of Regulatory Asset	207	260	218
Amortization of Intangible Assets	(119)	(188)	(336)
Accretion expense	0	0	0
Total depreciation, amortization and accretion	754	740	675
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	255	250	236
Income taxes (net of refunds)	29	(32)	(144)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	95	67	94
Provision for uncollectible accounts	17	28	19
Amortization of rate stabilization deferral	(4)	21	(10)
Asset Retirement Obligation, Revision of Estimate		20
Vacation accrual adjustment			(8)
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	33
Change in environmental liabilities	23		0
Potomac Electric Power Company [Member]
Depreciation, amortization and accretion
Depreciation	239	218	203
Amortization of Regulatory Asset	135	167	118
Accretion expense	0	0	0
Total depreciation, amortization and accretion	374	385	321
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	130	123	114
Income taxes (net of refunds)	7	41	(104)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	25	15	25
Provision for uncollectible accounts	7	11	8
Amortization of rate stabilization deferral	(4)	21	(10)
Asset Retirement Obligation, Revision of Estimate		22
Vacation accrual adjustment			(8)
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	8
Change in environmental liabilities	23		0
Delmarva Power & Light Company [Member]
Depreciation, amortization and accretion
Depreciation	146	131	124
Amortization of Regulatory Asset	38	51	43
Accretion expense	0	0	0
Total depreciation, amortization and accretion	184	182	167
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	59	56	49
Income taxes (net of refunds)	19	(6)	(49)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	15	6	13
Provision for uncollectible accounts	4	6	3
Amortization of rate stabilization deferral	0	0	0
Asset Retirement Obligation, Revision of Estimate		(1)
Vacation accrual adjustment			0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	8
Change in environmental liabilities	0		0
Atlantic City Electric Company [Member]
Depreciation, amortization and accretion
Depreciation	123	94	89
Amortization of Regulatory Asset	34	42	57
Accretion expense	0	0	0
Total depreciation, amortization and accretion	157	136	146
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	55	61	59
Income taxes (net of refunds)	(5)	(12)	(2)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	16	12	13
Provision for uncollectible accounts	5	11	8
Amortization of rate stabilization deferral	0	0	0
Asset Retirement Obligation, Revision of Estimate		(1)
Vacation accrual adjustment			0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	4
Change in environmental liabilities	0		0
Other Intangible Assets [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	59	58	57
Other Intangible Assets [Member] | Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	50	49	48
Other Intangible Assets [Member] | Commonwealth Edison Co [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	0	0	0
Other Intangible Assets [Member] | PECO Energy Co [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	0	0	0
Other Intangible Assets [Member] | Baltimore Gas and Electric Company [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	0	0	0
Other Intangible Assets [Member] | Pepco Holdings LLC [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	0	0	0
Other Intangible Assets [Member] | Potomac Electric Power Company [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	0	0	0
Other Intangible Assets [Member] | Delmarva Power & Light Company [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	0	0	0
Other Intangible Assets [Member] | Atlantic City Electric Company [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	0	0	0
Unamortized Energy Contracts [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	21	14	35
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	$ 21	$ 14	$ 35

Supplemental Financial Inform_6

Supplemental Financial Information - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 587	$ 1,349	$ 898	$ 635
Restricted cash	358	247	207	253
Restricted cash included in other long-term assets	177	185	85	26
Total cash, cash equivalents and restricted cash	1,122	1,781	1,190	914
Contracts Receivable [Abstract]
Unbilled customer revenues	1,535	1,656
Investments [Abstract]
Total equity method investments		267
Equity investments without readily determinable fair values	69	72
Other Investments		2
Total Investments	464	625
Accrued Expenses [Abstract]
Compensation-related accruals	1,052	1,191
Taxes accrued	414	412
Interest accrued	337	334
Distributed Energy Company [Member]
Investments [Abstract]
Equity Method Investments		180
Other Equity Method Investments
Investments [Abstract]
Equity Method Investments	92	87
Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	262	244
Other available for sale investments
Investments [Abstract]
Available for sale investments	41	40
Exelon Generation Co L L C [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	303	750	416	290
Restricted cash	146	153	138	158
Restricted cash included in other long-term assets	0	0	0	0
Total cash, cash equivalents and restricted cash	449	903	554	448
Contracts Receivable [Abstract]
Unbilled customer revenues	807	965
Investments [Abstract]
Total equity method investments		251
Equity investments without readily determinable fair values	69	72
Other Investments		2
Total Investments	235	414
Accrued Expenses [Abstract]
Compensation-related accruals	422	479
Taxes accrued	222	226
Interest accrued	65	77
Exelon Generation Co L L C [Member] | Distributed Energy Company [Member]
Investments [Abstract]
Equity Method Investments		180
Exelon Generation Co L L C [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments	71	71
Exelon Generation Co L L C [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	54	49
Exelon Generation Co L L C [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments	41	40
Commonwealth Edison Co [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	90	135	76	56
Restricted cash	150	29	5	2
Restricted cash included in other long-term assets	163	166	63	0
Total cash, cash equivalents and restricted cash	403	330	144	58
Contracts Receivable [Abstract]
Unbilled customer revenues	218	223
Investments [Abstract]
Total equity method investments		6
Equity investments without readily determinable fair values	0	0
Total Investments	6	6
Accrued Expenses [Abstract]
Compensation-related accruals	171	187
Taxes accrued	83	71
Interest accrued	110	105
Commonwealth Edison Co [Member] | Distributed Energy Company [Member]
Investments [Abstract]
Equity Method Investments		0
Commonwealth Edison Co [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments	6	6
Commonwealth Edison Co [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	0	0
Commonwealth Edison Co [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments	0	0
PECO Energy Co [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	21	130	271	63
Restricted cash	6	5	4	4
Restricted cash included in other long-term assets	0	0	0	0
Total cash, cash equivalents and restricted cash	27	135	275	67
Contracts Receivable [Abstract]
Unbilled customer revenues	146	114
Investments [Abstract]
Total equity method investments		8
Equity investments without readily determinable fair values	0	0
Total Investments	27	25
Accrued Expenses [Abstract]
Compensation-related accruals	58	49
Taxes accrued	3	28
Interest accrued	37	33
PECO Energy Co [Member] | Distributed Energy Company [Member]
Investments [Abstract]
Equity Method Investments		0
PECO Energy Co [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments	8	8
PECO Energy Co [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	19	17
PECO Energy Co [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments	0	0
Baltimore Gas and Electric Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	24	7	17	23
Restricted cash	1	6	1	24
Restricted cash included in other long-term assets	0	0	0	3
Total cash, cash equivalents and restricted cash	25	13	18	50
Contracts Receivable [Abstract]
Unbilled customer revenues	170	168
Investments [Abstract]
Total equity method investments		0
Equity investments without readily determinable fair values	0	0
Total Investments	7	5
Accrued Expenses [Abstract]
Compensation-related accruals	78	68
Taxes accrued	26	46
Interest accrued	46	39
Baltimore Gas and Electric Company [Member] | Distributed Energy Company [Member]
Investments [Abstract]
Equity Method Investments		0
Baltimore Gas and Electric Company [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments	0	0
Baltimore Gas and Electric Company [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	7	5
Baltimore Gas and Electric Company [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments	0	0
Pepco Holdings LLC [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	131	124	30	170
Restricted cash	36	43	42	43
Restricted cash included in other long-term assets	14	19	23	23
Total cash, cash equivalents and restricted cash	181	186	95	236
Contracts Receivable [Abstract]
Unbilled customer revenues	194	186
Investments [Abstract]
Total equity method investments		0
Equity investments without readily determinable fair values	0	0
Total Investments	135	130
Accrued Expenses [Abstract]
Compensation-related accruals	101	99
Taxes accrued	117	74
Interest accrued	49	50
Pepco Holdings LLC [Member] | Distributed Energy Company [Member]
Investments [Abstract]
Equity Method Investments		0
Pepco Holdings LLC [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments	0	0
Pepco Holdings LLC [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	135	130
Pepco Holdings LLC [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments	0	0
Potomac Electric Power Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	30	16	5	9
Restricted cash	33	37	35	33
Restricted cash included in other long-term assets	0	0	0	0
Total cash, cash equivalents and restricted cash	63	53	40	42
Contracts Receivable [Abstract]
Unbilled customer revenues	100	97
Investments [Abstract]
Total equity method investments		0
Equity investments without readily determinable fair values	0	0
Total Investments	110	105
Accrued Expenses [Abstract]
Compensation-related accruals	28	29
Taxes accrued	90	58
Interest accrued	23	25
Potomac Electric Power Company [Member] | Distributed Energy Company [Member]
Investments [Abstract]
Equity Method Investments		0
Potomac Electric Power Company [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments	0	0
Potomac Electric Power Company [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	110	105
Potomac Electric Power Company [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments	0	0
Delmarva Power & Light Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	13	23	2	46
Restricted cash	0	1	0	0
Restricted cash included in other long-term assets	0	0	0	0
Total cash, cash equivalents and restricted cash	13	24	2	46
Contracts Receivable [Abstract]
Unbilled customer revenues	61	59
Investments [Abstract]
Total equity method investments		0
Equity investments without readily determinable fair values	0	0
Total Investments	0	0
Accrued Expenses [Abstract]
Compensation-related accruals	19	19
Taxes accrued	14	4
Interest accrued	8	8
Delmarva Power & Light Company [Member] | Distributed Energy Company [Member]
Investments [Abstract]
Equity Method Investments		0
Delmarva Power & Light Company [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments	0	0
Delmarva Power & Light Company [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	0	0
Delmarva Power & Light Company [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments	0	0
Atlantic City Electric Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	12	7	2	101
Restricted cash	2	4	6	9
Restricted cash included in other long-term assets	14	19	23	23
Total cash, cash equivalents and restricted cash	28	30	$ 31	$ 133
Contracts Receivable [Abstract]
Unbilled customer revenues	33	30
Investments [Abstract]
Total equity method investments		0
Equity investments without readily determinable fair values	0	0
Total Investments	0	0
Accrued Expenses [Abstract]
Compensation-related accruals	15	12
Taxes accrued	8	5
Interest accrued	12	12
Atlantic City Electric Company [Member] | Distributed Energy Company [Member]
Investments [Abstract]
Equity Method Investments		0
Atlantic City Electric Company [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments	0	0
Atlantic City Electric Company [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	0	0
Atlantic City Electric Company [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments	$ 0	$ 0

Related Party Transactions - Op

Related Party Transactions - Operating Revenues and Purchased Power and Fuel From Affiliates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	$ 1,172	$ 1,268	$ 1,115
Related Party Transaction, Purchases from Related Party	7	14	19
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	369	523	121
Related Party Transaction, Purchases from Related Party	(7)	6
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	158	128	138
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	289	260	388
Exelon Generation Co L L C [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	353	355	463
Exelon Generation Co L L C [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	264	206	255
Exelon Generation Co L L C [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	70	120	179
Exelon Generation Co L L C [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	19	29	29
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	3	2	5
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	30	27	15
Related Party Transaction, Purchases from Related Party	376	529	$ 108
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	$ 376	$ 529

Related Party Transactions - BS

Related Party Transactions - BSC and PHISCO Service Companies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	$ 516	$ 448	$ 330
PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	72	79	0
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	587	661	697
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	570	652	689
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	66	67	98
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	264	267	270
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	263	265	270
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	148	135	118
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	154	156	149
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	149	146	146
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	88	64	59
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	160	162	153
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	157	157	152
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	126	79	54
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	143	152	150
Pepco Holdings LLC [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	139	147	145
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	88	102	0
Pepco Holdings LLC [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	0	0	0
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	72	79	0
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	209	226	58
Potomac Electric Power Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	85	89	53
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	38	40	0
Potomac Electric Power Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	124	137	5
Other Cost and Expense, Operating			219
Related Party Transaction Capitalized Costs Support Services	33	32	0
Potomac Electric Power Company [Member] | Pepco Energy Services Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	0	0	0
Other Cost and Expense, Operating			29
Related Party Transaction Capitalized Costs Support Services	0	0	0
Delmarva Power & Light Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	152	162	32
Delmarva Power & Light Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	52	51	31
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	25	28	0
Delmarva Power & Light Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	100	111	0
Other Cost and Expense, Operating			165
Related Party Transaction Capitalized Costs Support Services	20	25	0
Delmarva Power & Light Company [Member] | Pepco Energy Services Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	0	0	0
Other Cost and Expense, Operating			9
Related Party Transaction Capitalized Costs Support Services	0	0	0
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	133	142	28
Atlantic City Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	42	42	25
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	19	20	0
Atlantic City Electric Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	90	98	0
Other Cost and Expense, Operating			135
Related Party Transaction Capitalized Costs Support Services	$ 19	$ 21	$ 0

Related Party Transactions - Cu

Related Party Transactions - Current Receivables From/Payables To Affiliates (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	$ 5	$ 5
Related Party Transaction, Due from (to) Related Party, Current	528	543
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	190	173
Accounts Payable, Related Parties, Current	117	139
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	78	69
Due to Related Parties, Current	37	14
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	27	30
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	28	24
Exelon Generation Co L L C [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Exelon Generation Co L L C [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	34	28
Exelon Generation Co L L C [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	7	7
Exelon Generation Co L L C [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	7	5
Exelon Generation Co L L C [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	9	10
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	28	20
Accounts Payable, Related Parties, Current	103	119
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	41	55
Related Party Transaction, Due from (to) Related Party, Current	27	19
Commonwealth Edison Co [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Commonwealth Edison Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Commonwealth Edison Co [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Commonwealth Edison Co [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Commonwealth Edison Co [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Commonwealth Edison Co [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Commonwealth Edison Co [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	1	1
Commonwealth Edison Co [Member] | Affiliated Entities [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	140	133
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	1	0
Accounts Payable, Related Parties, Current	55	59
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
PECO Energy Co [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
PECO Energy Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
PECO Energy Co [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
PECO Energy Co [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
PECO Energy Co [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
PECO Energy Co [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
PECO Energy Co [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	1
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	1	1
Accounts Payable, Related Parties, Current	66	65
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	1	1
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	1	0
Accounts Payable, Related Parties, Current	98	94
Pepco Holdings LLC [Member] | Affiliated Entities [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	14	12
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	0	1
Accounts Payable, Related Parties, Current	66	62
Potomac Electric Power Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current		0
Potomac Electric Power Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current		0
Potomac Electric Power Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current		0
Potomac Electric Power Company [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current		0
Potomac Electric Power Company [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current		0
Potomac Electric Power Company [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current		1
Potomac Electric Power Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current		0
Potomac Electric Power Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current		0
Delmarva Power & Light Company [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	32	33
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	4	1
Accounts Payable, Related Parties, Current	25	28
Atlantic City Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	3	1
Atlantic City Electric Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current
Atlantic City Electric Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	1	0
Business Services Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	217	256
Business Services Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	67	95
Business Services Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	54	56
Business Services Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	25	26
Business Services Company [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	34	38
Business Services Company [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	4	3
Business Services Company [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	16	19
Business Services Company [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	10	11
Business Services Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	7	8
Business Services Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PHI Service Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	36	39
PHI Service Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PHI Service Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PHI Service Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PHI Service Company [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PHI Service Company [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PHI Service Company [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	15	14
PHI Service Company [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	11	12
PHI Service Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	10	13
PHI Service Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Other Legal Entities [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	51	52
Accounts Payable, Related Parties, Current	13	12
Other Legal Entities [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	23	25
Other Legal Entities [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	8	8
Other Legal Entities [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	3	3
Other Legal Entities [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	4	3
Other Legal Entities [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	10	9
Other Legal Entities [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	1	1
Other Legal Entities [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	1	1
Other Legal Entities [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 1	$ 2

Related Party Transactions - No

Related Party Transactions - Noncurrent Receivables from/Payables to affiliates (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Noncurrent	$ 3,103	$ 2,606
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Noncurrent	2,622	2,217
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Noncurrent	480	389
Other Legal Entities [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Noncurrent	$ 1	$ 0

Related Party Transactions - Lo

Related Party Transactions - Long Term Debt to Financing Trusts (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	$ 390	$ 390
ComEd Financing III Affiliate [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	206	206
PECO Trust III Affiliate [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	81	81
PECO Trust IV Affiliate [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	103	103
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	205	205
Commonwealth Edison Co [Member] | ComEd Financing III Affiliate [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	205	205
Commonwealth Edison Co [Member] | PECO Trust III Affiliate [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	0	0
Commonwealth Edison Co [Member] | PECO Trust IV Affiliate [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	0	0
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	184	184
PECO Energy Co [Member] | ComEd Financing III Affiliate [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	0	0
PECO Energy Co [Member] | PECO Trust III Affiliate [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	81	81
PECO Energy Co [Member] | PECO Trust IV Affiliate [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	$ 103	$ 103

Quarterly Data (Unaudited) - Qu

Quarterly Data (Unaudited) - Quarterly Operating Results (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected Quarterly Financial Information [Line Items]
Revenues	$ 8,343	$ 8,929	$ 7,689	$ 9,477	$ 8,812	$ 9,401	$ 8,074	$ 9,691	$ 34,438	$ 35,978	$ 33,558
Operating income (loss)	962	1,353	841	1,218	706	1,144	940	1,099	4,374	3,891	4,388
Net income attributable to common shareholders	773	772	484	907	152	731	537	583	2,936	2,005	3,779
Net income (loss)									3,028	2,079	3,869
Quarterly Financial Information, Quarterly Charges and Credits, Amount Reconciling to Previously Reported Results	6
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	4,644	4,774	4,210	5,296	5,069	5,278	4,579	5,512	18,924	20,437	18,500
Operating income (loss)	362	482	147	333	35	311	282	347	1,323	975	947
Net Income (Loss) Attributable to Parent	397	257	108	363	(178)	234	178	136	1,125	370	2,710
Net income (loss)									1,217	443	2,798
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	1,405	1,583	1,351	1,408	1,373	1,598	1,398	1,512	5,747	5,882	5,536
Operating income (loss)	255	328	311	276	242	323	288	292	1,171	1,146	1,323
Net income (loss)	144	200	186	157	141	193	164	165	688	664	567
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	766	778	655	900	765	757	653	866	3,100	3,038	2,870
Operating income (loss)	162	183	145	222	165	154	127	142	713	587	655
Net income (loss)	118	140	102	168	124	126	96	113	528	460	434
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	779	703	649	976	799	731	662	977	3,106	3,169	3,176
Operating income (loss)	142	91	80	220	109	103	85	177	532	474	614
Net income (loss)	99	55	45	160	71	63	51	128	360	313	307
Pepco Holdings LLC [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	1,107	1,380	1,091	1,228	1,115	1,359	1,074	1,249	4,806	4,798	4,672
Operating income (loss)	128	256	165	175	124	243	151	124	722	643	762
Net income (loss)	65	189	106	117	62	185	82	63	477	393	355
Quarterly Financial Information, Quarterly Charges and Credits, Amount Reconciling to Previously Reported Results	6
Potomac Electric Power Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	513	642	531	575	529	626	521	555	2,260	2,232	2,151
Operating income (loss)	57	127	93	84	63	110	83	54	361	313	392
Net income (loss)	26	98	64	55	36	87	52	29	243	205	198
Quarterly Financial Information, Quarterly Charges and Credits, Amount Reconciling to Previously Reported Results	6
Delmarva Power & Light Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	319	319	287	380	331	328	289	384	1,306	1,332	1,300
Operating income (loss)	50	51	44	72	48	51	42	49	217	190	229
Net income (loss)	31	33	30	53	30	33	26	31	147	120	121
Atlantic City Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	274	419	274	273	254	406	265	310	1,240	1,236	1,186
Operating income (loss)	23	79	28	21	14	84	25	23	151	149	157
Net income (loss)	$ 12	$ 63	$ 14	$ 10	$ (1)	$ 61	$ 8	$ 7	$ 99	$ 75	$ 77

Quarterly Data (Unaudited) - _2

Quarterly Data (Unaudited) - Quarterly Per Share Information (Details) - $ / shares	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Net Income per Basic Share	$ 0.79	$ 0.79	$ 0.50	$ 0.93	$ 0.16	$ 0.76	$ 0.56	$ 0.60	$ 3.02	$ 2.07	$ 3.99
Net Income per Diluted Share	$ 0.79	$ 0.79	$ 0.50	$ 0.93	$ 0.16	$ 0.75	$ 0.55	$ 0.60	$ 3.01	$ 2.07	$ 3.98

Schedule I - Condensed Financia

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Statements of Operations and Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Expenses [Abstract]
Total operating expenses									$ 30,096	$ 32,143	$ 29,619
Operating income (loss)	$ 962	$ 1,353	$ 841	$ 1,218	$ 706	$ 1,144	$ 940	$ 1,099	4,374	3,891	4,388
Other income and (deductions)
Interest expense, net									(1,591)	(1,529)	(1,524)
Other, net									1,227	(112)	947
Total other income and (deductions)									(389)	(1,666)	(613)
Income taxes									774	118	(126)
Net income (loss)									3,028	2,079	3,869
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost									(65)	(66)	(56)
Actuarial loss reclassified to periodic cost, net of tax									149	247	197
Unrealized gain on cash flow hedges									0	12	3
Unrealized gain on marketable securities									0	0	6
Unrealized (loss) gain on foreign currency translation									6	(10)	7
Other comprehensive income (loss)									(198)	42	171
Comprehensive Income									2,737	2,046	3,952
Exelon Corporate [Member]
Operating Expenses [Abstract]
Operating and maintenance									33	(5)	10
Operating and maintenance from affiliates									9	9	25
Other									1	4	4
Total operating expenses									43	8	39
Operating income (loss)									(43)	(8)	(39)
Other income and (deductions)
Interest expense, net									(321)	(312)	(315)
Equity in earnings (losses) of unconsolidated affiliates									3,254	2,183	4,407
Interest income from affiliates, net									39	42	40
Other, net									14	3	1
Total other income and (deductions)									2,986	1,916	4,133
Income before income taxes									2,943	1,908	4,094
Income taxes									7	(97)	315
Net income (loss)									2,936	2,005	3,779
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost									(64)	(66)	(56)
Actuarial loss reclassified to periodic cost, net of tax									148	247	197
Pension and non-pension postretirement benefit plan valuation adjustment									(289)	(143)	10
Unrealized gain on cash flow hedges									1	12	3
Unrealized gain on marketable securities									0	0	6
Unrealized gain (loss) on equity investments									0	1	6
Unrealized (loss) gain on foreign currency translation									0	(10)	7
Other comprehensive income (loss)									(204)	41	173
Comprehensive Income									$ 2,732	$ 2,046	$ 3,952

Schedule I - Condensed Financ_2

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net cash flows provided by operating activities	$ 6,659	$ 8,644	$ 7,480
Cash flows from investing activities
Other investing activities	12	58	(43)
Net cash flows used in investing activities	(7,260)	(7,834)	(7,971)
Cash flows from financing activities
Changes in short-term borrowings	781	(338)	(261)
Proceeds from short-term borrowings with maturities greater than 90 days	0	126	621
Issuance of long-term debt	1,951	3,115	3,470
Retirement of long-term debt	(1,287)	(1,786)	(2,490)
Common stock issued from treasury stock	0	0	1,150
Dividends paid on common stock	(1,408)	(1,332)	(1,236)
Proceeds from employee stock plans	112	105	150
Other financing activities	(82)	(108)	(83)
Net cash flows provided by (used in) financing activities	(58)	(219)	767
(Decrease) Increase in cash, cash equivalents and restricted cash	(659)	591	276
Cash, cash equivalents and restricted cash at beginning of period	1,349	898	635
Cash, cash equivalents and restricted cash at end of period	587	1,349	898
Exelon Corporate [Member]
Net cash flows provided by operating activities	1,948	2,576	1,914
Cash flows from investing activities
Changes in Exelon intercompany money pool	95	1	(129)
Investment in affiliates	(1,071)	(1,231)	(1,710)
Other investing activities	0	0	(5)
Net cash flows used in investing activities	(976)	(1,230)	(1,844)
Cash flows from financing activities
Changes in short-term borrowings	136	0	0
Proceeds from short-term borrowings with maturities greater than 90 days	0	0	500
Retirement of long-term debt	0	0	(569)
Common stock issued from treasury stock	0	0	1,150
Dividends paid on common stock	(1,408)	(1,332)	(1,236)
Proceeds from employee stock plans	112	105	150
Other financing activities	0	(4)	(9)
Net cash flows provided by (used in) financing activities	(1,160)	(1,231)	(14)
(Decrease) Increase in cash, cash equivalents and restricted cash	(188)	115	56
Cash, cash equivalents and restricted cash at beginning of period	189	74	18
Cash, cash equivalents and restricted cash at end of period	$ 1	$ 189	$ 74

Schedule I - Condensed Financ_3

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Balance Sheet (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents		$ 587	$ 1,349		$ 898	$ 635
Accounts receivable, net
Other accounts receivable		1,583	1,256
Mark-to-market derivative assets, current		679	804
Regulatory assets, current		1,170	1,190
Other		1,253	1,238
Total current assets		12,037	13,328
Property, plant and equipment, net		80,233	76,707
Deferred debits and other assets
Regulatory assets, noncurrent		8,335	8,237
Other		3,197	1,575
Total assets	[1]	124,977	119,634
Current liabilities
Short-term borrowings		1,370	714
Long-term debt due within one year		4,710	1,349
Accounts payable		3,560	3,800
Accrued expenses		1,981	2,112
Payables to affiliates, current		5	5
Regulatory Liability, Current		406	644
Other		1,331	1,035
Total current liabilities		14,185	11,404
Long-term debt		31,329	34,075
Deferred credits and other liabilities
Regulatory liabilities, noncurrent		9,986	9,559
Pension obligations		4,247	3,988
Non-pension postretirement benefit obligations		2,076	1,928
Other		3,064	2,130
Total deferred credits and other liabilities		44,500	40,718
Total liabilities		90,404	86,587	[1]
Commitments and Contingencies
Shareholders’ equity
Common stock		19,274	19,116
Treasury stock, at cost		(123)	(123)
Retained earnings		16,267	14,743
Accumulated other comprehensive income (loss), net		(3,194)	(2,995)
Total shareholders’ equity		32,224	30,741
Total liabilities and equity		124,977	119,634
Exelon Corporate [Member]
Current assets
Cash and cash equivalents		1	189		$ 74	$ 18
Accounts receivable, net
Other accounts receivable		168	48
Accounts receivable from affiliates, current		41	44
Mark-to-market derivative assets, current		3	0
Note receivable from affiliates, current		679	216
Regulatory assets, current		253	182
Other		4	4
Total current assets		1,149	683
Property, plant and equipment, net		47	48
Deferred debits and other assets
Regulatory assets, noncurrent		3,772	3,742
Investments in affiliates		42,245	40,425
Deferred income taxes		1,524	1,455
Notes receivable from affiliates, noncurrent		329	898
Other		308	235
Total deferred debits and other assets		48,178	46,755
Total assets		49,374	47,486
Current liabilities
Short-term borrowings		636	500
Long-term debt due within one year		1,458	0
Accounts payable		1	1
Accrued expenses		131	184
Payables to affiliates, current		363	360
Regulatory Liability, Current		13	15
Pension obligations		77	63
Other		10	14
Total current liabilities		2,689	1,137
Long-term debt		5,717	7,147
Deferred credits and other liabilities
Regulatory liabilities, noncurrent		31	32
Pension obligations		7,960	7,795
Non-pension postretirement benefit obligations		403	199
Deferred income taxes		263	233
Other		87	202
Total deferred credits and other liabilities		8,744	8,461
Total liabilities		17,150	16,745
Commitments and Contingencies
Shareholders’ equity
Common stock		19,274	19,116
Treasury stock, at cost		(123)	(123)
Retained earnings		16,267	14,743
Accumulated other comprehensive income (loss), net		(3,194)	(2,995)
Total shareholders’ equity		32,224	30,741
Total liabilities and equity		$ 49,374	$ 47,486
[1]	Exelon’s consolidated assets include $9,532 million and $9,667 million at December 31, 2019 and 2018 , respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,473 million and $3,548 million at December 31, 2019 and 2018 , respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 22 – Variable Interest Entities for additional information.

Schedule I - Condensed Financ_4

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Balance Sheet - Parenthetical (Details) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Common stock, par value	$ 0	$ 0
Common Stock, Shares Authorized	2,000,000,000	2,000,000,000
Common Stock, Shares, Outstanding	973,000,000	968,000,000
Treasury stock, shares held	2,000,000	2,000,000
Exelon Corporate [Member]
Common stock, par value	$ 0	$ 0
Common Stock, Shares Authorized	2,000,000,000	2,000,000,000
Treasury stock, shares held	2,000,000	2,000,000

Schedule I - Condensed Financ_5

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Basis of Presentation - Narrative (Details) - Exelon Corporate [Member]	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Ownership interest	100.00%
Commonwealth Edison Co [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	99.00%
Baltimore Gas and Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	100.00%
Preferred Stock [Member] | Baltimore Gas and Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	0.00%

Schedule I - Condensed Financ_6

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Debt and Credit Agreements - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 25
Commercial Paper [Member]
Line of Credit Facility [Line Items]
Commercial Paper	870	$ 89
Line of credit facility, maximum borrowing capacity	9,000	$ 9,000
Commercial Paper [Member] | Exelon Corporate [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	600
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	10,559
Line of Credit Facility, Capacity Available for Trade Purchases	7,353
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	600
Line of Credit Facility, Capacity Available for Trade Purchases	458
Corporate, Non-Segment [Member] | Exelon Corporate [Member]
Line of Credit Facility [Line Items]
Short-term Bank Loans and Notes Payable	$ 500
London Interbank Offered Rate (LIBOR) [Member] | Corporate, Non-Segment [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Interest Rate Terms	0.95%
Exelon Corporate [Member] | Commercial Paper [Member]
Line of Credit Facility [Line Items]
Commercial Paper	$ 136

Schedule I - Condensed Financ_7

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Debt and Credit Agreements - Schedule of Outstanding Long-term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Schedule I - Condensed Financial Information of Parent (Exelon Corporate)	Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Statements of Operations and Other Comprehensive Income For the Years Ended December 31, (In millions) 2019 2018 2017 Operating expenses Operating and maintenance $ 33 $ (5 ) $ 10 Operating and maintenance from affiliates 9 9 25 Other 1 4 4 Total operating expenses 43 8 39 Operating loss (43 ) (8 ) (39 ) Other income and (deductions) Interest expense, net (321 ) (312 ) (315 ) Equity in earnings of investments 3,254 2,183 4,407 Interest income from affiliates, net 39 42 40 Other, net 14 3 1 Total other income 2,986 1,916 4,133 Income before income taxes 2,943 1,908 4,094 Income taxes 7 (97 ) 315 Net income $ 2,936 $ 2,005 $ 3,779 Other comprehensive income (loss) Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic costs $ (64 ) $ (66 ) $ (56 ) Actuarial loss reclassified to periodic cost 148 247 197 Pension and non-pension postretirement benefit plan valuation adjustment (289 ) (143 ) 10 Unrealized gain on cash flow hedges 1 12 3 Unrealized gain on marketable securities — — 6 Unrealized gain on equity investments — 1 6 Unrealized (loss) gain on foreign currency translation — (10 ) 7 Other comprehensive income (loss) (204 ) 41 173 Comprehensive income $ 2,732 $ 2,046 $ 3,952 Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Statements of Cash Flows For the Years Ended December 31, (In millions) 2019 2018 2017 Net cash flows provided by operating activities $ 1,948 $ 2,576 $ 1,914 Cash flows from investing activities Changes in Exelon intercompany money pool 95 1 (129 ) Investment in affiliates (1,071 ) (1,231 ) (1,710 ) Other investing activities — — (5 ) Net cash flows used in investing activities (976 ) (1,230 ) (1,844 ) Cash flows from financing activities Changes in short-term borrowings 136 — — Proceeds from short-term borrowings with maturities greater than 90 days — — 500 Retirement of long-term debt — — (569 ) Common stock issued from treasury stock — — 1,150 Dividends paid on common stock (1,408 ) (1,332 ) (1,236 ) Proceeds from employee stock plans 112 105 150 Other financing activities — (4 ) (9 ) Net cash flows used in financing activities (1,160 ) (1,231 ) (14 ) (Decrease) Increase in cash, cash equivalents and restricted cash (188 ) 115 56 Cash, cash equivalents and restricted cash at beginning of period 189 74 18 Cash, cash equivalents and restricted cash at end of period $ 1 $ 189 $ 74 Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Balance Sheets December 31, (In millions) 2019 2018 ASSETS Current assets Cash and cash equivalents $ 1 $ 189 Accounts receivable, net Other accounts receivable 168 48 Accounts receivable from affiliates 41 44 Mark-to-market derivative assets 3 — Notes receivable from affiliates 679 216 Regulatory assets 253 182 Other 4 4 Total current assets 1,149 683 Property, plant and equipment, net 47 48 Deferred debits and other assets Regulatory assets 3,772 3,742 Investments in affiliates 42,245 40,425 Deferred income taxes 1,524 1,455 Notes receivable from affiliates 329 898 Other 308 235 Total deferred debits and other assets 48,178 46,755 Total assets $ 49,374 $ 47,486 Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Balance Sheets December 31, (In millions) 2019 2018 LIABILITIES AND SHAREHOLDERS’ EQUITY Current liabilities Short-term borrowings $ 636 $ 500 Long-term debt due within one year 1,458 — Accounts payable 1 1 Accrued expenses 131 184 Payables to affiliates 363 360 Regulatory liabilities 13 15 Pension obligations 77 63 Other 10 14 Total current liabilities 2,689 1,137 Long-term debt 5,717 7,147 Deferred credits and other liabilities Regulatory liabilities 31 32 Pension obligations 7,960 7,795 Non-pension postretirement benefit obligations 403 199 Deferred income taxes 263 233 Other 87 202 Total deferred credits and other liabilities 8,744 8,461 Total liabilities 17,150 16,745 Commitments and contingencies Shareholders’ equity Common stock (No par value, 2,000 shares authorized, 973 shares and 968 shares outstanding at December 31, 2019 and 2018, respectively) 19,274 19,116 Treasury stock, at cost (2 shares at December 31, 2019 and 2018) (123 ) (123 ) Retained earnings 16,267 14,743 Accumulated other comprehensive loss, net (3,194 ) (2,995 ) Total shareholders’ equity 32,224 30,741 Total liabilities and shareholders’ equity $ 49,374 $ 47,486 Exelon Corporate is a holding company that conducts substantially all of its business operations through its subsidiaries. These condensed financial statements and related footnotes have been prepared in accordance with Rule 12-04, Schedule I of Regulation S-X. These statements should be read in conjunction with the consolidated financial statements and notes thereto of Exelon Corporation. Exelon Corporate owns 100% of all of its significant subsidiaries, either directly or indirectly, except for Commonwealth Edison Company (ComEd), of which Exelon Corporate owns more than 99% , and Baltimore Gas and Electric Company (BGE), of which Exelon owns 100% Short-Term Borrowings Exelon Corporate meets its short-term liquidity requirements primarily through the issuance of commercial paper. Exelon Corporate had $136 million of outstanding commercial paper borrowings at December 31, 2019 and no outstanding commercial paper borrowings at December 31, 2018 . Short-Term Loan Agreements On March 23, 2017, Exelon Corporate entered into a $500 million term loan agreement, 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. Revolving Credit Agreements On May 26, 2016, Exelon Corporate amended its syndicated revolving credit facility with aggregate bank commitments of $600 million through May 26, 2021. On May 26, 2018, Exelon Corporate had its maturity date extended to May 26, 2023. As of December 31, 2019 , Exelon Corporation had available capacity under those commitments of $458 million . See Note 16 — Debt and Credit Agreements of the Combined Notes to Consolidated Financial Statements for additional information regarding Exelon Corporation’s credit agreement. Long-Term Debt The following tables present the outstanding long-term debt for Exelon Corporate as of December 31, 2019 and December 31, 2018 : Maturity Date December 31, Rates 2019 2018 Long-term debt Junior subordinated notes 3.50 % 2022 $ 1,150 $ 1,150 Senior unsecured notes (a) 2.45 % - 7.60 % 2020 - 2046 5,889 5,889 Total long-term debt 7,039 7,039 Unamortized debt discount and premium, net (7 ) (7 ) Unamortized debt issuance costs (39 ) (47 ) Fair value adjustment 182 162 Long-term debt due within one year (1,458 ) — Long-term debt $ 5,717 $ 7,147 __________ (a) Senior unsecured notes include mirror debt that is held on both Generation and Exelon Corporation's balance sheets. The debt maturities for Exelon Corporate for the periods 2020 , 2021 , 2022 , 2023 , 2024 and thereafter are as follows: 2020 $ 1,458 2021 300 2022 1,150 2023 — 2024 — Remaining years 4,131 Total long-term debt $ 7,039 See Note 18 — Commitments and Contingencies of the Combined Notes to Consolidated Financial Statements for Exelon Corporate’s commitments and contingencies related to environmental matters and fund transfer restrictions. The financial statements of Exelon Corporate include related party transactions as presented in the tables below: For the Years Ended December 31, (In millions) 2019 2018 2017 Operating and maintenance from affiliates: BSC (a) $ 9 $ 11 $ 23 Other — (2 ) 2 Total operating and maintenance from affiliates: $ 9 $ 9 $ 25 Interest income from affiliates, net: Generation $ 36 $ 36 $ 37 BSC 3 4 3 Exelon Energy Delivery Company, LLC (b) — 2 — Total interest income from affiliates, net: $ 39 $ 42 $ 40 Equity in earnings (losses) of investments: Exelon Energy Delivery Company, LLC (b) $ 2,054 $ 1,830 $ 1,663 Generation 1,125 369 2,710 UII, LLC 97 — 41 PCI 1 (17 ) 1 BSC — — 1 Exelon Enterprises (16 ) — 1 Exelon INQB8R (8 ) — — Exelon Transmission Company, LLC (2 ) 1 (10 ) Other 3 — — Total equity in earnings of investments: $ 3,254 $ 2,183 $ 4,407 Cash contributions received from affiliates $ 2,514 $ 2,302 $ 1,879 December 31, (in millions) 2019 2018 Accounts receivable from affiliates (current): BSC (a) $ 11 $ 13 Generation 13 17 ComEd 2 4 PECO 2 2 BGE 1 2 PHISCO 7 6 Exelon VTI, LLC 5 — Total accounts receivable from affiliates (current): $ 41 $ 44 Notes receivable from affiliates (current): BSC (a) $ 109 $ 116 Generation (c) 558 100 PHI 12 — Total notes receivable from affiliates (current): $ 679 $ 216 Investments in affiliates: BSC (a) $ 197 $ 197 Exelon Energy Delivery Company, LLC (b) 28,147 26,679 Generation 13,484 13,204 PCI 62 61 UII, LLC 365 268 Exelon Transmission Company, LLC — 1 Voluntary Employee Beneficiary Association trust (4 ) (1 ) Exelon Enterprises 6 22 Exelon INQB8R, LLC (8 ) — Other (4 ) (6 ) Total investments in affiliates: $ 42,245 $ 40,425 Notes receivable from affiliates (non-current): Generation (c) $ 329 $ 898 Accounts payable to affiliates (current): UII, LLC $ 360 $ 360 Exelon Enterprises 3 — Total accounts payable to affiliates (current): $ 363 $ 360 __________ (a) Exelon Corporate receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. (b) Exelon Energy Delivery Company, LLC consists of ComEd, PECO, BGE, PHI, Pepco, DPL and ACE. (c) In connection with the debt obligations assumed by Exelon as part of the Constellation merger, Exelon and subsidiaries of Generation (former Constellation subsidiaries) assumed intercompany loan agreements that mirror the terms and amounts of the third-party debt obligations of Exelon, resulting in intercompany notes payable included in Long-Term Debt to affiliates in Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation in Exelon’s Consolidated Balance Sheets.
Long-term Debt, Gross	$ 35,560	$ 34,911
Unamortized debt discount and premium, net	(72)	(66)
Unamortized debt issuance costs	214	216
Long-term debt	31,329	34,075
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	1,150	1,150
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 10,685	11,285
Maximum [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.50%
Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.60%
Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.45%
Exelon Corporate [Member]
Debt Instrument [Line Items]
Fair value adjustment	$ 182	162
Long-term Debt, Gross	7,039	7,039
Unamortized debt discount and premium, net	(7)	(7)
Unamortized debt issuance costs	(39)	(47)
Long-term debt due within one year	(1,458)	0
Long-term debt	5,717	7,147
Exelon Corporate [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	1,150	1,150
Exelon Corporate [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 5,889	$ 5,889
Exelon Corporate [Member] | Maximum [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.50%
Exelon Corporate [Member] | Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.60%
Exelon Corporate [Member] | Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.45%

Schedule I - Condensed Financ_8

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Debt and Credit Agreements - Schedule of Debt Maturities (Details) $ in Millions	Dec. 31, 2019USD ($)
Debt Instrument [Line Items]
2020	$ 4,710
2021	1,517
2022	3,088
2023	855
2024	1,596
Thereafter	24,184
Total	35,950
Exelon Corporate [Member]
Debt Instrument [Line Items]
2020	1,458
2021	300
2022	1,150
2023	0
2024	0
Thereafter	4,131
Total	$ 7,039

Schedule I - Condensed Financ_9

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Related Party Transactions - Summary of Related Party Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Payables to affiliates, current	$ 5	$ 5
Exelon Corporate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	9	9	$ 25
Interest income from affiliates, net	39	42	40
Equity in earnings (losses) of unconsolidated affiliates	3,254	2,183	4,407
Cash contributions received from affiliates	2,514	2,302	1,879
Accounts receivable from affiliates, current	41	44
Note receivable from affiliates, current	679	216
Investments in affiliates	42,245	40,425
Notes receivable from affiliates, noncurrent	329	898
Payables to affiliates, current	363	360
Exelon Corporate [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	9	11	23
Interest income from affiliates, net	3	4	3
Equity in earnings (losses) of unconsolidated affiliates	0	0	1
Accounts receivable from affiliates, current	11	13
Note receivable from affiliates, current	109	116
Investments in affiliates	197	197
Exelon Corporate [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	0	(2)	2
Equity in earnings (losses) of unconsolidated affiliates	3	0	0
Investments in affiliates	(4)	(6)
Exelon Corporate [Member] | Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Interest income from affiliates, net	36	36	37
Equity in earnings (losses) of unconsolidated affiliates	1,125	369	2,710
Accounts receivable from affiliates, current	13	17
Note receivable from affiliates, current	558	100
Investments in affiliates	13,484	13,204
Notes receivable from affiliates, noncurrent	329	898
Exelon Corporate [Member] | Exelon Energy Delivery Company LLC [Member]
Related Party Transaction [Line Items]
Interest income from affiliates, net	0	2	0
Equity in earnings (losses) of unconsolidated affiliates	2,054	1,830	1,663
Investments in affiliates	28,147	26,679
Exelon Corporate [Member] | UII LLC [Member]
Related Party Transaction [Line Items]
Equity in earnings (losses) of unconsolidated affiliates	97	0	41
Investments in affiliates	365	268
Payables to affiliates, current	360	360
Exelon Corporate [Member] | Potomac Capital Investment Affiliate [Member]
Related Party Transaction [Line Items]
Equity in earnings (losses) of unconsolidated affiliates	1	(17)	1
Investments in affiliates	62	61
Exelon Corporate [Member] | Exelon Enterprise [Member]
Related Party Transaction [Line Items]
Equity in earnings (losses) of unconsolidated affiliates	(16)	0	1
Investments in affiliates	6	22
Payables to affiliates, current	3	0
Exelon Corporate [Member] | Exelon INQB8R, LLC [Member] [Member]
Related Party Transaction [Line Items]
Equity in earnings (losses) of unconsolidated affiliates	(8)	0	0
Investments in affiliates	(8)	0
Exelon Corporate [Member] | Exelon Transmission Company LLC [Member]
Related Party Transaction [Line Items]
Equity in earnings (losses) of unconsolidated affiliates	(2)	1	$ (10)
Investments in affiliates	0	1
Exelon Corporate [Member] | Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates, current	2	4
Exelon Corporate [Member] | PECO Energy Co [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates, current	2	2
Exelon Corporate [Member] | Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates, current	1	2
Exelon Corporate [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates, current	7	6
Exelon Corporate [Member] | Exelon VTI, LLC [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates, current	5	0
Exelon Corporate [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Note receivable from affiliates, current	12	0
Exelon Corporate [Member] | VEBA [Member]
Related Party Transaction [Line Items]
Investments in affiliates	$ (4)	$ (1)

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 319	$ 322	$ 334
Charged to Costs and Expenses	119	159	126
Charged to Other Accounts	26	35	27
Deductions	170	197	165
Balance at End of Period	294	319	322
Deferred Tax Valuation Allowance [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	35	37	20
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	(9)	5	17
Deductions	0	7	0
Balance at End of Period	26	35	37
Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	156	174	113
Charged to Costs and Expenses	6	25	56
Charged to Other Accounts	0	(31)	10
Deductions	7	12	5
Balance at End of Period	155	156	174
Exelon Generation Co L L C [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	104	114	91
Charged to Costs and Expenses	27	44	34
Charged to Other Accounts	(11)	4	0
Deductions	39	58	11
Balance at End of Period	81	104	114
Exelon Generation Co L L C [Member] | Deferred Tax Valuation Allowance [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	26	23	9
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	(2)	3	14
Deductions	0	0	0
Balance at End of Period	24	26	23
Exelon Generation Co L L C [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	145	166	106
Charged to Costs and Expenses	0	20	51
Charged to Other Accounts	0	(32)	9
Deductions	2	9	0
Balance at End of Period	143	145	166
Commonwealth Edison Co [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	81	73	70
Charged to Costs and Expenses	35	44	39
Charged to Other Accounts	20	23	20
Deductions	57	59	56
Balance at End of Period	79	81	73
Commonwealth Edison Co [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	6	5	4
Charged to Costs and Expenses	6	3	3
Charged to Other Accounts	0	1	1
Deductions	5	3	3
Balance at End of Period	7	6	5
PECO Energy Co [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	61	56	61
Charged to Costs and Expenses	31	33	26
Charged to Other Accounts	3	3	4
Deductions	33	31	35
Balance at End of Period	62	61	56
PECO Energy Co [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	2	2	2
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Period	2	2	2
PECO Energy Co [Member] | SEC Schedule, 12-09, Allowance, Notes Receivable [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	13	15
Balance at End of Period	9	13	15
Baltimore Gas and Electric Company [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	20	24	32
Charged to Costs and Expenses	8	10	8
Charged to Other Accounts	7	(2)	(3)
Deductions	18	12	13
Balance at End of Period	17	20	24
Baltimore Gas and Electric Company [Member] | Deferred Tax Valuation Allowance [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	1	1	1
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Period	1	1	1
Baltimore Gas and Electric Company [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	1	0	0
Charged to Costs and Expenses	0	1	0
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Period	1	1	0
Pepco Holdings LLC [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	53	55	80
Charged to Costs and Expenses	17	28	19
Charged to Other Accounts	7	7	6
Deductions	24	37	50
Balance at End of Period	53	53	55
Pepco Holdings LLC [Member] | Deferred Tax Valuation Allowance [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	8	13	10
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	(8)	2	3
Deductions	0	7	0
Balance at End of Period	0	8	13
Pepco Holdings LLC [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	2	2	2
Charged to Costs and Expenses	1	0	2
Charged to Other Accounts	0	0	0
Deductions	0	0	2
Balance at End of Period	3	2	2
Potomac Electric Power Company [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	21	21	29
Charged to Costs and Expenses	7	11	8
Charged to Other Accounts	2	3	2
Deductions	10	14	18
Balance at End of Period	20	21	21
Potomac Electric Power Company [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	1	1	1
Charged to Costs and Expenses	0	0	1
Charged to Other Accounts	0	0	0
Deductions	0	0	1
Balance at End of Period	1	1	1
Delmarva Power & Light Company [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	13	16	24
Charged to Costs and Expenses	4	6	3
Charged to Other Accounts	3	2	2
Deductions	5	11	13
Balance at End of Period	15	13	16
Delmarva Power & Light Company [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	0	0	0
Charged to Costs and Expenses	0	0	1
Charged to Other Accounts	0	0	0
Deductions	0	0	1
Balance at End of Period	0	0	0
Atlantic City Electric Company [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	19	18	27
Charged to Costs and Expenses	5	11	8
Charged to Other Accounts	2	2	2
Deductions	8	12	19
Balance at End of Period	18	19	18
Atlantic City Electric Company [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	1	1	1
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Period	$ 1	$ 1	$ 1