Regulatory Matters - Purchase of Receivables Programs (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Purchase Of Receivables [Line Items]
Purchased receivables	$ 290	[1]	$ 263	[1]
Allowance for uncollectible accounts	(42)	[2]	(30)	[2]
Purchased receivables, net	248		233
Commonwealth Edison Co [Member]
Purchase Of Receivables [Line Items]
Purchased receivables	139	[1]	105	[1]
Allowance for uncollectible accounts	(21)	[2]	(16)	[2]
Purchased receivables, net	118		89
PECO Energy Co [Member]
Purchase Of Receivables [Line Items]
Purchased receivables	76	[1]	72	[1]
Allowance for uncollectible accounts	(8)	[2]	(7)	[2]
Purchased receivables, net	68		65
Baltimore Gas and Electric Company [Member]
Purchase Of Receivables [Line Items]
Purchased receivables	75	[1]	86	[1]
Allowance for uncollectible accounts	(13)	[2]	(7)	[2]
Purchased receivables, net	$ 62		$ 79

[1] 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. If the costs are not fully recovered when PECO files its next gas distribution rate case, PECO will propose a mechanism to recover the remaining implementation costs as a distribution charge to low volume transportation customers or apply future discounts on purchased receivables from natural gas suppliers serving those customers.

[2] 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.