Accounts Receivable - Allowance for Credit Losses Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	$ (150)	$ (120)	$ (159)
Exelon Generation Co L L C [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(17)	(31)	(48)
Commonwealth Edison Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(32)	(33)	(40)
PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(42)	(31)	(33)
Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(15)	(8)	(10)
Pepco Holdings LLC [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(43)	(17)	(28)
Potomac Electric Power Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(24)	(7)	(11)
Delmarva Power & Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(16)	(4)	(6)
Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(2)	(5)	$ (11)
Customer accounts receivable
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	243
Current Period Provision for Expected Credit Losses	248
Writeoffs, net of recoveries	69
Allowance change due to sale of customer accounts	56
Ending balance	366	243
Customer accounts receivable | Exelon Generation Co L L C [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	80
Current Period Provision for Expected Credit Losses	13
Writeoffs, net of recoveries	5
Allowance change due to sale of customer accounts	56
Ending balance	32	80
Customer accounts receivable | Commonwealth Edison Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	59
Current Period Provision for Expected Credit Losses	62
Writeoffs, net of recoveries	24
Allowance change due to sale of customer accounts	0
Ending balance	97	59
Customer accounts receivable | PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	55
Current Period Provision for Expected Credit Losses	79
Writeoffs, net of recoveries	18
Allowance change due to sale of customer accounts	0
Ending balance	116	55
Customer accounts receivable | Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	12
Current Period Provision for Expected Credit Losses	30
Writeoffs, net of recoveries	7
Allowance change due to sale of customer accounts	0
Ending balance	35	12
Customer accounts receivable | Pepco Holdings LLC [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	37
Current Period Provision for Expected Credit Losses	64
Writeoffs, net of recoveries	15
Allowance change due to sale of customer accounts	0
Ending balance	86	37
Customer accounts receivable | Potomac Electric Power Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	13
Current Period Provision for Expected Credit Losses	24
Writeoffs, net of recoveries	5
Allowance change due to sale of customer accounts	0
Ending balance	32	13
Customer accounts receivable | Delmarva Power & Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	11
Current Period Provision for Expected Credit Losses	15
Writeoffs, net of recoveries	4
Allowance change due to sale of customer accounts	0
Ending balance	22	11
Customer accounts receivable | Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	13
Current Period Provision for Expected Credit Losses	25
Writeoffs, net of recoveries	6
Allowance change due to sale of customer accounts	0
Ending balance	32	13
Other Receivables
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	48
Current Period Provision for Expected Credit Losses	33
Writeoffs, net of recoveries	10
Ending balance	71	48
Other Receivables | Exelon Generation Co L L C [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	0
Current Period Provision for Expected Credit Losses	0
Writeoffs, net of recoveries	0
Ending balance	0	0
Other Receivables | Commonwealth Edison Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	20
Current Period Provision for Expected Credit Losses	5
Writeoffs, net of recoveries	4
Ending balance	21	20
Other Receivables | PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	7
Current Period Provision for Expected Credit Losses	3
Writeoffs, net of recoveries	2
Ending balance	8	7
Other Receivables | Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	5
Current Period Provision for Expected Credit Losses	7
Writeoffs, net of recoveries	3
Ending balance	9	5
Other Receivables | Pepco Holdings LLC [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	16
Current Period Provision for Expected Credit Losses	18
Writeoffs, net of recoveries	1
Ending balance	33	16
Other Receivables | Potomac Electric Power Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	7
Current Period Provision for Expected Credit Losses	6
Writeoffs, net of recoveries	0
Ending balance	13	7
Other Receivables | Delmarva Power & Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	4
Current Period Provision for Expected Credit Losses	5
Writeoffs, net of recoveries	0
Ending balance	9	4
Other Receivables | Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	5
Current Period Provision for Expected Credit Losses	7
Writeoffs, net of recoveries	1
Ending balance	$ 11	$ 5