Income Taxes - Rollforward of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning Balance	$ 507	$ 125	$ 507	$ 477
Unrecognized Tax Benefits, Period Increase (Decrease)		13	6	26
Increases based on tax positions related to current year		4	3	2
Increases based on tax positions prior to current year		4	26	34
Decreases based on tax positions prior to current year		(3)	(348)	(3)
Decrease from settlements with taxing authorities		0	(69)	(29)
Unrecognized tax benefits - Ending Balance		143	125	507
Decrease in Unrecognized Tax Benefits is Reasonably Possible	411
Tax Adjustments, Settlements, and Unusual Provisions	76
Income taxes		370	373	774
Commonwealth Edison Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Income taxes		172	177	163
PECO Energy Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Income taxes		12	(30)	65
Baltimore Gas and Electric Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Income taxes		(35)	41	79
Pepco Holdings LLC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning Balance	48	52	48	45
Unrecognized Tax Benefits, Period Increase (Decrease)		3	3	3
Increases based on tax positions related to current year		1	0	0
Increases based on tax positions prior to current year		0	1	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 - Ending Balance		56	52	48
Income taxes		42	(77)	38
Potomac Electric Power Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Income taxes		15	(7)	16
Delmarva Power & Light Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Income taxes		42	(25)	22
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	15	14	14
Unrecognized Tax Benefits, Period Increase (Decrease)		1	1	0
Increases based on tax positions related to current year		0	0	0
Increases based on tax positions prior to current year		0	0	0
Decreases based on tax positions prior to current year		0	0	0
Decrease from settlements with taxing authorities		0	0	0
Unrecognized tax benefits - Ending Balance		16	15	14
Income taxes		$ (13)	$ (41)	$ 0
Internal Revenue Service (IRS) [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Income taxes	$ (67)

Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit.

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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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Amount of increase (decrease) to previously recorded tax expense. Includes, but is not limited to, significant settlements of income tax disputes, and unusual tax positions or infrequent actions taken by the entity, including tax assessment reversal, and IRS tax settlement.

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