Regulatory Matters Regulatory Matters - Purchase of Receivables Programs (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Purchase Of Receivables [Line Items]
Document Period End Date		Dec. 31, 2017
Payments to Acquire Other Receivables		$ 298	$ 313
Allowance for Doubtful Accounts Receivable	[1]	(31)	(37)
Payments to Acquire Other Receivables, Net		267	276
Commonwealth Edison Co [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		87	87
Allowance for Doubtful Accounts Receivable	[1]	(14)	(14)
Payments to Acquire Other Receivables, Net		73	73
PECO Energy Co [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		70	72
Allowance for Doubtful Accounts Receivable	[1]	(5)	(6)
Payments to Acquire Other Receivables, Net		65	66
Baltimore Gas and Electric Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		58	59
Allowance for Doubtful Accounts Receivable	[1]	(3)	(4)
Payments to Acquire Other Receivables, Net		55	55
Pepco Holdings LLC [Member] | Successor [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		83	95
Allowance for Doubtful Accounts Receivable	[1]	(9)	(13)
Payments to Acquire Other Receivables, Net		74	82
Potomac Electric Power Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		56	63
Allowance for Doubtful Accounts Receivable	[1]	(5)	(7)
Payments to Acquire Other Receivables, Net		51	56
Delmarva Power and Light Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		9	10
Allowance for Doubtful Accounts Receivable	[1]	(1)	(2)
Payments to Acquire Other Receivables, Net		8	8
Atlantic City Electric Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		18	22
Allowance for Doubtful Accounts Receivable	[1]	(3)	(4)
Payments to Acquire Other Receivables, Net		$ 15	$ 18

[1] For ComEd, BGE, Pepco and DPL, reflects the incremental allowance for uncollectible accounts recorded, which is in addition to the purchase discount. For ComEd, the incremental uncollectible accounts expense is recovered through its Purchase of Receivables with Consolidated Billing tariff.