Derivative Financial Instruments - Summary of Credit Risk Related Contingent Features (Details) - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Derivative, Collateral, Obligation to Return Cash		$ 13
Derivative, Collateral, Obligation to Return Securities		25
ReNewAble Energy Contract [Member]
Derivative [Line Items]
Derivative Asset, Fair Value of Collateral		19
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Aggregate fair value of derivatives with credit-risk-related contingent features		(1,533)	$ (1,433)
Contractual right of offset related to derivative assets		1,302	1,140
Net liability position after contractual right of offset	[1]	(231)	(293)
Derivative, Collateral, Right to Reclaim Cash		1,065	1,497
Derivative, Collateral, Right to Reclaim Securities		474	672
Derivative, Collateral, Obligation to Return Cash		21	77
Derivative, Collateral, Obligation to Return Securities		$ 40	$ 24

[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.