Fair Value of Financial Assets and Liabilities - Fair Value Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ (107)	$ (260)	$ (182)	$ (267)
Total realized / unrealized gains (losses)
Included in net income(a)	1	1	2	2
Included in regulatory assets	56	30	131	36
Purchases, sales, issuances and settlements
Settlements		(2)		(2)
Transfers out of Level 3			(1)
Ending Balance	(50)	(231)	(50)	(231)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	1	1	2	2
Commonwealth Edison Co [Member] | Derivative [Member] | Interest Rate Swap [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Realized Investment Gains (Losses)	(3)	5	3	13
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	(144)	(295)	(219)	(301)
Total realized / unrealized gains (losses)
Included in net income(a)	0	0	0	0
Included in regulatory assets	56	30	131	36
Purchases, sales, issuances and settlements
Settlements		0		0
Transfers out of Level 3			0
Ending Balance	(88)	(265)	(88)	(265)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	0	0	0	0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Period Increase (Decrease)	(59)	(25)	(128)	(23)
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	36	35	35	34
Total realized / unrealized gains (losses)
Included in net income(a)	1	1	2	2
Included in regulatory assets	0	0	0	0
Purchases, sales, issuances and settlements
Settlements		(2)		(2)
Transfers out of Level 3			0
Ending Balance	37	34	37	34
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	1	1	2	2
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 [Line Items]
Beginning Balance	36	35	35	34
Total realized / unrealized gains (losses)
Included in net income(a)	1	1	2	2
Included in regulatory assets	0	0	0	0
Purchases, sales, issuances and settlements
Settlements		(2)		(2)
Transfers out of Level 3			0
Ending Balance	37	34	37	34
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	$ 1	$ 1	$ 2	$ 2