Accounts Receivable - Allowance for Credit Losses Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			$ (155)	$ (130)
Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(59)	(16)
Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(34)	(23)
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(36)	(38)
Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(7)	(12)
Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(18)	(41)
Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(9)	(24)
Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(3)	(15)
Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current period provision for expected credit losses			(6)	(2)
Customer accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 395	$ 261	366	243
Current period provision for expected credit losses	47	114	122	222
Writeoffs, net of recoveries	33	17	79	51
Allowance change due to sale of customer accounts				56
Ending balance	409	358	409	358
Customer accounts receivable | Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	75	33	32	80
Current period provision for expected credit losses	10	1	57	13
Writeoffs, net of recoveries	1	1	5	4
Allowance change due to sale of customer accounts				56
Ending balance	84	33	84	33
Customer accounts receivable | Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	89	72	97	59
Current period provision for expected credit losses	11	37	23	62
Writeoffs, net of recoveries	12	4	32	16
Ending balance	88	105	88	105
Customer accounts receivable | PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	111	71	116	55
Current period provision for expected credit losses	1	27	7	56
Writeoffs, net of recoveries	11	2	22	15
Ending balance	101	96	101	96
Customer accounts receivable | Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	27	23	35	12
Current period provision for expected credit losses	7	14	2	28
Writeoffs, net of recoveries	3	2	6	5
Ending balance	31	35	31	35
Customer accounts receivable | Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	93	62	86	37
Current period provision for expected credit losses	18	35	33	63
Writeoffs, net of recoveries	6	8	14	11
Ending balance	105	89	105	89
Customer accounts receivable | Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	38	24	32	13
Current period provision for expected credit losses	5	11	15	24
Writeoffs, net of recoveries	2	0	6	2
Ending balance	41	35	41	35
Customer accounts receivable | Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	19	18	22	11
Current period provision for expected credit losses	3	7	4	14
Writeoffs, net of recoveries	4	3	8	3
Ending balance	18	22	18	22
Customer accounts receivable | Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	36	20	32	13
Current period provision for expected credit losses	10	17	14	25
Writeoffs, net of recoveries	0	5	0	6
Ending balance	46	32	46	32
Other receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	72	61	71	48
Current period provision for expected credit losses	9	15	15	36
Writeoffs, net of recoveries	4	1	9	9
Ending balance	77	75	77	75
Other receivables | Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	1	0	0	0
Current period provision for expected credit losses	3	0	4	0
Writeoffs, net of recoveries	0	0	0	0
Ending balance	4	0	4	0
Other receivables | Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	18	22	21	20
Current period provision for expected credit losses	2	5	0	9
Writeoffs, net of recoveries	1	0	2	2
Ending balance	19	27	19	27
Other receivables | PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	7	7	8	7
Current period provision for expected credit losses	1	1	2	3
Writeoffs, net of recoveries	1	1	3	3
Ending balance	7	7	7	7
Other receivables | Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	8	6	9	5
Current period provision for expected credit losses	1	3	2	7
Writeoffs, net of recoveries	1	0	3	3
Ending balance	8	9	8	9
Other receivables | Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	38	26	33	16
Current period provision for expected credit losses	2	6	7	17
Writeoffs, net of recoveries	0	0	0	1
Ending balance	40	32	40	32
Other receivables | Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	16	11	13	7
Current period provision for expected credit losses	1	2	4	6
Writeoffs, net of recoveries	0	0	0	0
Ending balance	17	13	17	13
Other receivables | Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	9	7	9	4
Current period provision for expected credit losses	(1)	1	(1)	4
Writeoffs, net of recoveries	0	0	0	0
Ending balance	8	8	8	8
Other receivables | Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	13	8	11	5
Current period provision for expected credit losses	2	3	4	7
Writeoffs, net of recoveries	0	0	0	1
Ending balance	$ 15	$ 11	$ 15	$ 11