Regulatory Matters - Purchase of Receivables Programs (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Purchase Of Receivables [Line Items]
Purchased receivables	[1]	$ 229	$ 290
Allowance for uncollectible accounts	[2]	(31)	(42)
Purchased receivables, net		198	248
Commonwealth Edison Co [Member]
Purchase Of Receivables [Line Items]
Purchased receivables	[1]	103	139
Allowance for uncollectible accounts	[2]	(16)	(21)
Purchased receivables, net		$ 87	118
PECO Energy Co [Member]
Purchase Of Receivables [Line Items]
Purchase of Receivables, Discount Rate related to Implementation Costs		1.00%
Purchased receivables	[1]	$ 67	76
Allowance for uncollectible accounts	[2]	(7)	(8)
Purchased receivables, net		60	68
Baltimore Gas and Electric Company [Member]
Purchase Of Receivables [Line Items]
Purchased receivables	[1]	59	75
Allowance for uncollectible accounts	[2]	(8)	(13)
Purchased receivables, net		$ 51	$ 62

[1] (a) PECO’s gas POR program became effective on January 1, 2012 and includes 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.

[2] (b) For ComEd and BGE, 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 (PORCB) tariff.