Income Taxes - Components of Income Tax Expense (Benefit) from Continuing Operations (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Income taxes		$ 370	$ 373	$ 774
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Income taxes		172	177	163
PECO Energy Co [Member]
Income Taxes [Line Items]
Income taxes		12	(30)	65
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Income taxes		(35)	41	79
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Income taxes		42	(77)	38
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Income taxes		15	(7)	16
Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Income taxes		42	(25)	22
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Income taxes		(13)	(41)	0
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Current		322	26	85
Deferred		(66)	156	489
Investment Tax Credit		(18)	(28)	(72)
Income taxes	$ (67)
Internal Revenue Service (IRS) [Member] \| Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current		(30)	(24)	59
Deferred		113	112	15
Investment Tax Credit		(1)	(2)	(2)
Internal Revenue Service (IRS) [Member] \| PECO Energy Co [Member]
Income Taxes [Line Items]
Current		1	(7)	45
Deferred		20	1	20
Investment Tax Credit		0	0	0
Internal Revenue Service (IRS) [Member] \| Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current		(18)	4	(51)
Deferred		34	10	95
Investment Tax Credit		0	0	0
Internal Revenue Service (IRS) [Member] \| Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Current		18	25	43
Deferred		(52)	(129)	(34)
Investment Tax Credit		(1)	(1)	(1)
Internal Revenue Service (IRS) [Member] \| Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Current		22	40	16
Deferred		(17)	(62)	(6)
Investment Tax Credit		0	0	0
Internal Revenue Service (IRS) [Member] \| Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Current		2	(13)	29
Deferred		(14)	(20)	(21)
Investment Tax Credit		0	0	0
Internal Revenue Service (IRS) [Member] \| Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Current		1	(4)	(3)
Deferred		(26)	(43)	(6)
Investment Tax Credit		0	0	0
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Current		32	42	5
Deferred		100	177	267
State and Local Jurisdiction [Member] \| Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current		(41)	(27)	(5)
Deferred		131	118	96
State and Local Jurisdiction [Member] \| PECO Energy Co [Member]
Income Taxes [Line Items]
Current		0	0	0
Deferred		(9)	(24)	0
State and Local Jurisdiction [Member] \| Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current		0	0	0
Deferred		(51)	27	35
State and Local Jurisdiction [Member] \| Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Current		0	(5)	3
Deferred		77	33	27
State and Local Jurisdiction [Member] \| Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Current		1	0	0
Deferred		9	15	6
State and Local Jurisdiction [Member] \| Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Current		1	0	0
Deferred		53	8	14
State and Local Jurisdiction [Member] \| Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Current		0	0	0
Deferred		$ 12	$ 6	$ 9

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Amount of current income tax expense (benefit) pertaining to taxable income (loss) from continuing operations.

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Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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The amount deducted from an entities' taxes, reflecting a percentage of an amount invested in certain assets spread over the useful life of those assets; includes deferred investment tax credits.

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