Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) (Exelon Generation Co L L C [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	$ 2,196
Credit derivative net exposure	2,121
Credit Derivative, Collateral Held Directly or by Third Parties	75
Number of Credit Risk Derivatives Held	1
Derivative Credit Risk Valuation Adjustment, Derivative Assets	442
Financial institution [Member]
Derivative [Line Items]
Credit derivative net exposure	324
Energy Cooperatives And Municipalities [Member]
Derivative [Line Items]
Credit derivative net exposure	869
Investor Owned Utilities Marketers And Power Producers Credit Risk Exposure [Member]
Derivative [Line Items]
Credit derivative net exposure	897
Other Credit Risk Exposure [Member]
Derivative [Line Items]
Credit derivative net exposure	31
External Credit Rating, Investment Grade [Member]
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	1,570
Credit derivative net exposure	1,514
Credit Derivative, Collateral Held Directly or by Third Parties	56
Number of Credit Risk Derivatives Held	1
Derivative Credit Risk Valuation Adjustment, Derivative Assets	442
External Credit Rating, Non Investment Grade [Member]
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	63
Credit derivative net exposure	47
Credit Derivative, Collateral Held Directly or by Third Parties	16
Number of Credit Risk Derivatives Held	0
Derivative Credit Risk Valuation Adjustment, Derivative Assets	0
Risk Level, High [Member]
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	68
Credit derivative net exposure	65
Credit Derivative, Collateral Held Directly or by Third Parties	3
Number of Credit Risk Derivatives Held	0
Derivative Credit Risk Valuation Adjustment, Derivative Assets	0
Risk Level, Low [Member]
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	495
Credit derivative net exposure	495
Credit Derivative, Collateral Held Directly or by Third Parties	0
Number of Credit Risk Derivatives Held	0
Derivative Credit Risk Valuation Adjustment, Derivative Assets	$ 0