Derivative Financial Instruments (Collateral and Contingent-Related Features) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Collateral And Contingent Related Features [Abstract]
Letters of credit posted			$ 563
Line Of Credit Facility Amount Outstanding	1,416
Exelon Generation Co L L C [Member]
Collateral And Contingent Related Features [Abstract]
Aggregate fair value of derivatives with credit-risk-related contingent features	(1,056)	[1]	(1,849)	[1]
Contractual right of offset related to derivative assets	846	[2]	1,426	[2]
Net liability position after contractual right of offset	(210)	[3]	(423)	[3]
Incremental collateral for credit rating downgrade to BBB- and Baa3	2
Cash collateral held	206		499
Cash collateral posted	72		527
Letters of credit held	34		45
Letters of credit posted	364
Line Of Credit Facility Amount Outstanding	1,413
Master Netting Arrangements [Abstract]
Cash collateral received not offset against net derivative positions	10		3
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	42
Line Of Credit Facility Amount Outstanding	1
Baltimore Gas and Electric Company [Member]
Collateral And Contingent Related Features [Abstract]
Incremental collateral for loss of investment grade credit rating	85
Other Segments [Member]
Collateral And Contingent Related Features [Abstract]
Cash collateral held	155
Letters of credit held	$ 29

[1] Amount represents the gross fair value of out-of-the-money derivative contracts containing credit-risk-related contingent 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.