Derivative Financial Instruments (Collateral and Contingent-Related Features) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Exelon Generation Co L L C [Member]
Collateral And Contingent Related Features [Abstract]
Aggregate fair value of derivatives with credit-risk-related contingent features	$ (1,178)	[1]	$ (1,056)	[1]
Contractual right of offset related to derivative assets	902	[2]	846	[2]
Net liability position after contractual right of offset	(276)	[3]	(210)	[3]
Incremental collateral for loss of investment grade credit rating	2,100		2,000
Cash collateral held	148		206
Cash collateral posted	713		72
Letters of credit held	14		34
Letters of credit posted	555		364
Master Netting Arrangements [Abstract]
Cash collateral received not offset against net derivative positions	8		10
Commonwealth Edison Co [Member]
Collateral And Contingent Related Features [Abstract]
Cash collateral held	19
PECO Energy Co [Member]
Collateral And Contingent Related Features [Abstract]
Incremental collateral for loss of investment grade credit rating	43
Baltimore Gas and Electric Company [Member]
Collateral And Contingent Related Features [Abstract]
Incremental collateral for loss of investment grade credit rating	$ 153

[1] Amount represents the gross fair value of out-of-the-money derivative contracts containing credit-risk related contingent features ignoring the effects of master netting agreements.

[2] Amount represents the offsetting fair value of in-the-money derivative contracts under legally enforceable master netting agreements with the same counterparty, which reduces the amount of any liability for which a Registrant could potentially be required to post collateral.

[3] Amount represents the net fair value of out-of-the-money derivative contracts containing credit-risk related contingent features after considering the mitigating effects of offsetting positions under master netting arrangements and reflects the actual net liability upon which any potential contingent collateral obligations would be based.