Derivative Financial Instruments (Collateral and Contingent-Related Features) (Details) (USD $)	Sep. 30, 2012		Dec. 31, 2011
Collateral And Contingent Related Features [Abstract]
Aggregate fair value of derivatives with credit-risk-related contingent features	$ (2,720,000,000)	[1]	$ (1,014,000,000)	[1]
Contractual right of offset related to derivative assets	2,156,000,000	[2]	928,000,000	[2]
Net liability position after contractual right of offset	(564,000,000)	[3]	(86,000,000)	[3]
Exelon Generation Co L L C [Member]
Collateral And Contingent Related Features [Abstract]
Incremental collateral for loss of investment grade credit rating	2,004,000,000		1,612,000,000
Cash collateral held	607,000,000		542,000,000
Cash collateral posted	415,000,000
Letters of credit held	109,000,000		89,000,000
Letters of credit posted	973,000,000
Swap Contract Collateral Posting Limit [Abstract]
Fair value of interest-rate swap in asset position	0
Master Netting Arrangements [Abstract]
Cash collateral received not offset against net derivative positions	1,000,000		2,000,000
PECO Energy Co [Member]
Collateral And Contingent Related Features [Abstract]
Incremental collateral for loss of investment grade credit rating	30,000,000
Baltimore Gas and Electric Company [Member]
Collateral And Contingent Related Features [Abstract]
Incremental collateral for loss of investment grade credit rating	$ 51,000,000

[1] Amount represents the gross fair value of out-of-the-money derivative contracts containing credit-risk-related contingent features that are not fully collateralized by posted cash collateral on an individual, contract-by-contract basis 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.