Derivative Financial Instruments - Summary of Credit Risk Related Contingent Features (Details) (Exelon Generation Co L L C [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Aggregate fair value of derivatives with credit-risk-related contingent features	$ (997)		$ (1,056)
Contractual right of offset related to derivative assets	694		846
Net liability position after contractual right of offset	$ (303)	[1]	$ (210)	[1]

[1] 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.