Accounts Receivable - Allowance for Credit Losses Rollforward (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		$ (92)	$ (45)
Exelon Generation Co L L C [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(13)	(12)
Commonwealth Edison Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(17)	(16)
PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(29)	(10)
Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(10)	(4)
Pepco Holdings LLC [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(22)	(3)
Potomac Electric Power Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(12)	(2)
Delmarva Power and Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(8)	(1)
Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses		(2)	$ 0
Customer accounts receivable
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	$ 278	243
Current Period Provision for Expected Credit Losses	51	106
Writeoffs, net of recoveries	12	32
Allowance change due to sale of customer accounts	56	56
Ending balance	261	261
Customer accounts receivable | Exelon Generation Co L L C [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	81	80
Current Period Provision for Expected Credit Losses	9	13
Writeoffs, net of recoveries	1	4
Allowance change due to sale of customer accounts	56	56
Ending balance	33	33
Customer accounts receivable | Commonwealth Edison Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	71	59
Current Period Provision for Expected Credit Losses	7	25
Writeoffs, net of recoveries	6	12
Ending balance	72	72
Customer accounts receivable | PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	66	55
Current Period Provision for Expected Credit Losses	10	28
Writeoffs, net of recoveries	5	12
Ending balance	71	71
Customer accounts receivable | Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	18	12
Current Period Provision for Expected Credit Losses	6	14
Writeoffs, net of recoveries	1	3
Ending balance	23	23
Customer accounts receivable | Pepco Holdings LLC [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	42	37
Current Period Provision for Expected Credit Losses	19	26
Writeoffs, net of recoveries	(1)	1
Ending balance	62	62
Customer accounts receivable | Potomac Electric Power Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	15	13
Current Period Provision for Expected Credit Losses	8	11
Writeoffs, net of recoveries	(1)	0
Ending balance	24	24
Customer accounts receivable | Delmarva Power and Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	13	11
Current Period Provision for Expected Credit Losses	5	7
Writeoffs, net of recoveries	0	0
Ending balance	18	18
Customer accounts receivable | Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	14	13
Current Period Provision for Expected Credit Losses	6	8
Writeoffs, net of recoveries	0	1
Ending balance	20	20
Other receivables
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	52	48
Current Period Provision for Expected Credit Losses	12	20
Writeoffs, net of recoveries	3	7
Ending balance	61	61
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	1	4
Writeoffs, net of recoveries	1	2
Ending balance	22	22
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	2
Writeoffs, net of recoveries	1	2
Ending balance	7	7
Other receivables | Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	5	5
Current Period Provision for Expected Credit Losses	2	4
Writeoffs, net of recoveries	1	3
Ending balance	6	6
Other receivables | Pepco Holdings LLC [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	18	16
Current Period Provision for Expected Credit Losses	8	10
Writeoffs, net of recoveries	0	0
Ending balance	26	26
Other receivables | Potomac Electric Power Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	8	7
Current Period Provision for Expected Credit Losses	3	4
Writeoffs, net of recoveries	0	0
Ending balance	11	11
Other receivables | Delmarva Power and Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	4	4
Current Period Provision for Expected Credit Losses	3	3
Writeoffs, net of recoveries	0	0
Ending balance	7	7
Other receivables | Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	6	5
Current Period Provision for Expected Credit Losses	2	3
Writeoffs, net of recoveries	0	0
Ending balance	$ 8	$ 8