Accounts Receivable - Allowance for Credit Losses Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current period provision for expected credit losses	$ (85)	$ (45)
Exelon Generation Co L L C [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current period provision for expected credit losses	(34)	(4)
Commonwealth Edison Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current period provision for expected credit losses	(13)	(7)
PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current period provision for expected credit losses	(24)	(17)
Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current period provision for expected credit losses	(4)	(7)
Pepco Holdings LLC [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current period provision for expected credit losses	(10)	(10)
Potomac Electric Power Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current period provision for expected credit losses	(5)	(4)
Delmarva Power and Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current period provision for expected credit losses	(4)	(3)
Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current period provision for expected credit losses	(1)	(3)
Customer accounts receivable
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	366	243
Current period provision for expected credit losses	104	55
Writeoffs, net of recoveries	28	20
Ending balance	442	278
Customer accounts receivable | Exelon Generation Co L L C [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	32	80
Current period provision for expected credit losses	34	4
Writeoffs, net of recoveries	1	3
Ending balance	65	81
Customer accounts receivable | Commonwealth Edison Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	97	59
Current period provision for expected credit losses	21	18
Writeoffs, net of recoveries	15	6
Ending balance	103	71
Customer accounts receivable | PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	116	55
Current period provision for expected credit losses	20	18
Writeoffs, net of recoveries	6	7
Ending balance	130	66
Customer accounts receivable | Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	35	12
Current period provision for expected credit losses	9	8
Writeoffs, net of recoveries	1	2
Ending balance	43	18
Customer accounts receivable | Pepco Holdings LLC [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	86	37
Current period provision for expected credit losses	20	7
Writeoffs, net of recoveries	5	2
Ending balance	101	42
Customer accounts receivable | Potomac Electric Power Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	32	13
Current period provision for expected credit losses	11	3
Writeoffs, net of recoveries	2	1
Ending balance	41	15
Customer accounts receivable | Delmarva Power and Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	22	11
Current period provision for expected credit losses	6	2
Writeoffs, net of recoveries	3	0
Ending balance	25	13
Customer accounts receivable | Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	32	13
Current period provision for expected credit losses	3	2
Writeoffs, net of recoveries	0	1
Ending balance	35	14
Other receivables
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	71	48
Current period provision for expected credit losses	10	8
Writeoffs, net of recoveries	2	4
Ending balance	79	52
Other receivables | Exelon Generation Co L L C [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	0	0
Current period provision for expected credit losses	0	0
Writeoffs, net of recoveries	0	0
Ending balance	0	0
Other receivables | Commonwealth Edison Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	21	20
Current period provision for expected credit losses	1	3
Writeoffs, net of recoveries	0	1
Ending balance	22	22
Other receivables | PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	8	7
Current period provision for expected credit losses	4	1
Writeoffs, net of recoveries	1	1
Ending balance	11	7
Other receivables | Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	9	5
Current period provision for expected credit losses	1	2
Writeoffs, net of recoveries	1	2
Ending balance	9	5
Other receivables | Pepco Holdings LLC [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	33	16
Current period provision for expected credit losses	4	2
Writeoffs, net of recoveries	0	0
Ending balance	37	18
Other receivables | Potomac Electric Power Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	13	7
Current period provision for expected credit losses	2	1
Writeoffs, net of recoveries	0	0
Ending balance	15	8
Other receivables | Delmarva Power and Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	9	4
Current period provision for expected credit losses	1	0
Writeoffs, net of recoveries	0	0
Ending balance	10	4
Other receivables | Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	11	5
Current period provision for expected credit losses	1	1
Writeoffs, net of recoveries	0	0
Ending balance	$ 12	$ 6