Accounts Receivable - Allowance for Credit Losses Rollforward (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		$ (130)	$ (89)
Exelon Generation Co L L C [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(16)	(20)
Commonwealth Edison Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(23)	(26)
PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(38)	(22)
Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(12)	(5)
Pepco Holdings LLC [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(41)	(16)
Potomac Electric Power Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(24)	(7)
Delmarva Power and Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(15)	(2)
Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(2)	$ (6)
Customer accounts receivable
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	$ 261	243
Current Period Provision for Expected Credit Losses	114	222
Writeoffs, net of recoveries	17	51
Allowance change due to sale of customer accounts		56
Ending balance	358	358
Customer accounts receivable | Exelon Generation Co L L C [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	33	80
Current Period Provision for Expected Credit Losses	1	13
Writeoffs, net of recoveries	1	4
Allowance change due to sale of customer accounts		56
Ending balance	33	33
Customer accounts receivable | Commonwealth Edison Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	72	59
Current Period Provision for Expected Credit Losses	37	62
Writeoffs, net of recoveries	4	16
Ending balance	105	105
Customer accounts receivable | PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	71	55
Current Period Provision for Expected Credit Losses	27	56
Writeoffs, net of recoveries	2	15
Ending balance	96	96
Customer accounts receivable | Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	23	12
Current Period Provision for Expected Credit Losses	14	28
Writeoffs, net of recoveries	2	5
Ending balance	35	35
Customer accounts receivable | Pepco Holdings LLC [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	62	37
Current Period Provision for Expected Credit Losses	35	63
Writeoffs, net of recoveries	8	11
Ending balance	89	89
Customer accounts receivable | Potomac Electric Power Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	24	13
Current Period Provision for Expected Credit Losses	11	24
Writeoffs, net of recoveries	0	2
Ending balance	35	35
Customer accounts receivable | Delmarva Power and Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	18	11
Current Period Provision for Expected Credit Losses	7	14
Writeoffs, net of recoveries	3	3
Ending balance	22	22
Customer accounts receivable | Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	20	13
Current Period Provision for Expected Credit Losses	17	25
Writeoffs, net of recoveries	5	6
Ending balance	32	32
Other receivables
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	61	48
Current Period Provision for Expected Credit Losses	15	36
Writeoffs, net of recoveries	1	9
Ending balance	75	75
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	22	20
Current Period Provision for Expected Credit Losses	5	9
Writeoffs, net of recoveries	0	2
Ending balance	27	27
Other receivables | PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	7	7
Current Period Provision for Expected Credit Losses	1	3
Writeoffs, net of recoveries	1	3
Ending balance	7	7
Other receivables | Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	6	5
Current Period Provision for Expected Credit Losses	3	7
Writeoffs, net of recoveries	0	3
Ending balance	9	9
Other receivables | Pepco Holdings LLC [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	26	16
Current Period Provision for Expected Credit Losses	6	17
Writeoffs, net of recoveries	0	1
Ending balance	32	32
Other receivables | Potomac Electric Power Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	11	7
Current Period Provision for Expected Credit Losses	2	6
Writeoffs, net of recoveries	0	0
Ending balance	13	13
Other receivables | Delmarva Power and Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	7	4
Current Period Provision for Expected Credit Losses	1	4
Writeoffs, net of recoveries	0	0
Ending balance	8	8
Other receivables | Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	8	5
Current Period Provision for Expected Credit Losses	3	7
Writeoffs, net of recoveries	0	1
Ending balance	$ 11	$ 11