Regulatory Matters Regulatory Matters - Purchase of Receivables Programs (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2017	Dec. 31, 2016
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		$ 312	$ 313
Allowance for Doubtful Accounts Receivable		(33)	(37)
Payments to Acquire Other Receivables, Net		279	276
Commonwealth Edison Co [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		89	87
Allowance for Doubtful Accounts Receivable	[1]	(13)	(14)
Payments to Acquire Other Receivables, Net		76	73
PECO Energy Co [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		68	72
Allowance for Doubtful Accounts Receivable		(5)	(6)
Payments to Acquire Other Receivables, Net		63	66
Baltimore Gas and Electric Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		55	59
Allowance for Doubtful Accounts Receivable	[1]	(4)	(4)
Payments to Acquire Other Receivables, Net		51	55
Pepco Holdings LLC [Member] | Successor [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		100	95
Allowance for Doubtful Accounts Receivable		(11)	(13)
Payments to Acquire Other Receivables, Net		89	82
Potomac Electric Power Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables	[2]	66	63
Allowance for Doubtful Accounts Receivable	[1]	(6)	(7)
Payments to Acquire Other Receivables, Net		60	56
Delmarva Power and Light Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables	[2]	10	10
Allowance for Doubtful Accounts Receivable	[1]	(1)	(2)
Payments to Acquire Other Receivables, Net		9	8
Atlantic City Electric Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		24	22
Allowance for Doubtful Accounts Receivable		(4)	(4)
Payments to Acquire Other Receivables, Net		$ 20	$ 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

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