Derivative Financial Instruments - Summary of Credit Risk Related Contingent Features (Details) (Exelon Generation Co L L C [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	$ (1,433)	[1]	$ (1,056)	[1]
Offsetting Fair Value of In-the-Money Contracts Under Master Netting Arrangements	1,140	[2]	846	[2]
Derivative liabilities, fair value	$ (293)	[3]	$ (210)	[3]

[1] (a)Amount represents the gross fair value of out-of-the-money derivative contracts containing credit-risk-related contingent features ignoring the effects of master netting agreements.

[2] (b)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] (c)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.