Accounts Receivable - Allowance for Credit Losses Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			$ (100)	$ (92)
Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(46)	(13)
Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(24)	(17)
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(17)	(29)
Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(4)	(10)
Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(9)	(22)
Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(5)	(12)
Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(2)	(8)
Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(2)	(2)
Customer accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 442	$ 278	366	243
Current period provision for expected credit losses	(29)	51	75	106
Writeoffs, net of recoveries	18	12	46	32
Allowance change due to sale of customer accounts		56		56
Ending balance	395	261	395	261
Customer accounts receivable | Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	65	81	32	80
Current period provision for expected credit losses	13	9	47	13
Writeoffs, net of recoveries	3	1	4	4
Allowance change due to sale of customer accounts		56		56
Ending balance	75	33	75	33
Customer accounts receivable | Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	103	71	97	59
Current period provision for expected credit losses	(9)	7	12	25
Writeoffs, net of recoveries	5	6	20	12
Ending balance	89	72	89	72
Customer accounts receivable | PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	130	66	116	55
Current period provision for expected credit losses	(14)	10	6	28
Writeoffs, net of recoveries	5	5	11	12
Ending balance	111	71	111	71
Customer accounts receivable | Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	43	18	35	12
Current period provision for expected credit losses	(14)	6	(5)	14
Writeoffs, net of recoveries	2	1	3	3
Ending balance	27	23	27	23
Customer accounts receivable | Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	101	42	86	37
Current period provision for expected credit losses	(5)	19	15	26
Writeoffs, net of recoveries	3	(1)	8	1
Ending balance	93	62	93	62
Customer accounts receivable | Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	41	15	32	13
Current period provision for expected credit losses	(1)	8	10	11
Writeoffs, net of recoveries	2	(1)	4	0
Ending balance	38	24	38	24
Customer accounts receivable | Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	25	13	22	11
Current period provision for expected credit losses	(5)	5	1	7
Writeoffs, net of recoveries	1	0	4	0
Ending balance	19	18	19	18
Customer accounts receivable | Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	35	14	32	13
Current period provision for expected credit losses	1	6	4	8
Writeoffs, net of recoveries	0	0	0	1
Ending balance	36	20	36	20
Other receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	79	52	71	48
Current period provision for expected credit losses	(4)	12	6	20
Writeoffs, net of recoveries	3	3	5	7
Ending balance	72	61	72	61
Other receivables | Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	0	0	0	0
Current period provision for expected credit losses	1	0	1	0
Writeoffs, net of recoveries	0	0	0	0
Ending balance	1	0	1	0
Other receivables | Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	22	22	21	20
Current period provision for expected credit losses	(3)	1	(2)	4
Writeoffs, net of recoveries	1	1	1	2
Ending balance	18	22	18	22
Other receivables | PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	11	7	8	7
Current period provision for expected credit losses	(3)	1	1	2
Writeoffs, net of recoveries	1	1	2	2
Ending balance	7	7	7	7
Other receivables | Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	9	5	9	5
Current period provision for expected credit losses	0	2	1	4
Writeoffs, net of recoveries	1	1	2	3
Ending balance	8	6	8	6
Other receivables | Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	37	18	33	16
Current period provision for expected credit losses	1	8	5	10
Writeoffs, net of recoveries	0	0	0	0
Ending balance	38	26	38	26
Other receivables | Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	15	8	13	7
Current period provision for expected credit losses	1	3	3	4
Writeoffs, net of recoveries	0	0	0	0
Ending balance	16	11	16	11
Other receivables | Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	10	4	9	4
Current period provision for expected credit losses	(1)	3	0	3
Writeoffs, net of recoveries	0	0	0	0
Ending balance	9	7	9	7
Other receivables | Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	12	6	11	5
Current period provision for expected credit losses	1	2	2	3
Writeoffs, net of recoveries	0	0	0	0
Ending balance	$ 13	$ 8	$ 13	$ 8