Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - Jun. 30, 2015 - USD ($) $ in Millions	Total
PECO Energy Co [Member]
Derivative [Line Items]
Total Credit Risk Exposure	$ 3
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Total Credit Risk Exposure	1
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	2,244
Credit derivative net exposure	$ 2,196
Credit Derivative, Collateral Held Directly or by Third Parties	48
Number of Credit Risk Derivatives Held	1
Derivative Credit Risk Valuation Adjustment, Derivative Assets	$ 444
Exelon Generation Co L L C [Member] | Financial institution [Member]
Derivative [Line Items]
Credit derivative net exposure	383
Exelon Generation Co L L C [Member] | Energy Cooperatives And Municipalities [Member]
Derivative [Line Items]
Credit derivative net exposure	881
Exelon Generation Co L L C [Member] | Investor Owned Utilities Marketers And Power Producers Credit Risk Exposure [Member]
Derivative [Line Items]
Credit derivative net exposure	880
Exelon Generation Co L L C [Member] | Other Credit Risk Exposure [Member]
Derivative [Line Items]
Credit derivative net exposure	52
Exelon Generation Co L L C [Member] | External Credit Rating, Investment Grade [Member]
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	1,643
Credit derivative net exposure	$ 1,619
Credit Derivative, Collateral Held Directly or by Third Parties	24
Number of Credit Risk Derivatives Held	1
Derivative Credit Risk Valuation Adjustment, Derivative Assets	$ 444
Exelon Generation Co L L C [Member] | External Credit Rating, Non Investment Grade [Member]
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	55
Credit derivative net exposure	$ 37
Credit Derivative, Collateral Held Directly or by Third Parties	18
Number of Credit Risk Derivatives Held	0
Derivative Credit Risk Valuation Adjustment, Derivative Assets	$ 0
Exelon Generation Co L L C [Member] | Risk Level, High [Member]
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	48
Credit derivative net exposure	$ 42
Credit Derivative, Collateral Held Directly or by Third Parties	6
Number of Credit Risk Derivatives Held	0
Derivative Credit Risk Valuation Adjustment, Derivative Assets	$ 0
Exelon Generation Co L L C [Member] | Risk Level, Low [Member]
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	498
Credit derivative net exposure	$ 498
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