Regulatory Matters - Purchase of Receivables Programs (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		$ 313	$ 229
Allowance for Doubtful Accounts Receivable		(37)	(31)	$ (37)
Payments to Acquire Other Receivables, Net		276	198	276
Commonwealth Edison Co [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		87	103
Allowance for Doubtful Accounts Receivable		(14)	(16)	(14)
Payments to Acquire Other Receivables, Net		73	87	$ 73
PECO Energy Co [Member]
Purchase Of Receivables [Line Items]
Purchase of Receivables, Discount Rate related to Implementation Costs				1.00%
Payments to Acquire Other Receivables	[1]	72	67
Allowance for Doubtful Accounts Receivable		(6)	(7)	$ (6)
Payments to Acquire Other Receivables, Net		66	60	66
Baltimore Gas and Electric Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables	[1]	59	59
Allowance for Doubtful Accounts Receivable	[2]	(4)	(8)	(4)
Payments to Acquire Other Receivables, Net		55	51	55
Pepco Holdings LLC [Member] | Successor [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		95	100
Allowance for Doubtful Accounts Receivable		(13)	(6)	(13)
Payments to Acquire Other Receivables, Net		82	94	82
Potomac Electric Power Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		63	70
Allowance for Doubtful Accounts Receivable		(7)	(4)	(7)
Payments to Acquire Other Receivables, Net		56	66	56
Delmarva Power and Light Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		10	11
Allowance for Doubtful Accounts Receivable		(2)	0	(2)
Payments to Acquire Other Receivables, Net		8	11	8
Atlantic City Electric Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		22	19
Allowance for Doubtful Accounts Receivable		(4)	(2)	(4)
Payments to Acquire Other Receivables, Net		$ 18	$ 17	$ 18

[1] (a)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.

[2] PECO’s natural gas POR program became effective on January 1, 2012 and included a 1% discount on purchased receivables in order to recover the implementation costs of the program. The implementation costs were fully recovered and the 1% discount was reset to 0%, effective July 2015.