Accounts Receivable - Allowance for Credit Losses Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	$ (45)	$ (43)
Exelon Generation Co L L C [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(4)	0
Commonwealth Edison Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(7)	(9)
PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(17)	(16)
Baltimore Gas and Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(7)	(8)
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	(4)	(4)
Delmarva Power and Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(3)	(4)
Atlantic City Electric Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Current Period Provision for Expected Credit Losses	(3)	$ (2)
Customer accounts receivable
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	243
Current Period Provision for Expected Credit Losses	55
Writeoffs, net of recoveries	(20)
Ending balance	278
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	4
Writeoffs, net of recoveries	(3)
Ending balance	81
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	18
Writeoffs, net of recoveries	(6)
Ending balance	71
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	18
Writeoffs, net of recoveries	(7)
Ending balance	66
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	8
Writeoffs, net of recoveries	(2)
Ending balance	18
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	7
Writeoffs, net of recoveries	(2)
Ending balance	42
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	3
Writeoffs, net of recoveries	(1)
Ending balance	15
Customer accounts receivable | Delmarva Power and Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	11
Current Period Provision for Expected Credit Losses	2
Writeoffs, net of recoveries	0
Ending balance	13
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	2
Writeoffs, net of recoveries	(1)
Ending balance	14
Other receivables
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	48
Current Period Provision for Expected Credit Losses	8
Writeoffs, net of recoveries	(4)
Ending balance	52
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
Other receivables | Commonwealth Edison Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	20
Current Period Provision for Expected Credit Losses	3
Writeoffs, net of recoveries	(1)
Ending balance	22
Other receivables | PECO Energy Co [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	7
Current Period Provision for Expected Credit Losses	1
Writeoffs, net of recoveries	(1)
Ending balance	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	2
Writeoffs, net of recoveries	(2)
Ending balance	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	2
Writeoffs, net of recoveries	0
Ending balance	18
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	1
Writeoffs, net of recoveries	0
Ending balance	8
Other receivables | Delmarva Power and Light Company [Member]
Accounts Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	4
Current Period Provision for Expected Credit Losses	0
Writeoffs, net of recoveries	0
Ending balance	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	1
Writeoffs, net of recoveries	0
Ending balance	$ 6