Derivative Financial Instruments - Summary of Credit Risk Related Contingent Features (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Aggregate fair value of derivatives with credit-risk-related contingent features		$ (975)	$ (932)
Contractual right of offset related to derivative assets		664	684
Net liability position after contractual right of offset	[1]	$ (311)	$ (248)

[1] unt 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.Ge