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Derivative Financial Instruments - Summary of Proprietary Trading Activities (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Derivative [Line Items]    
Unrealized Gain (Loss) on Derivatives $ (47) $ 107
Unrealized Gain (Loss) on Derivatives and Commodity Contracts (49) 103
Operating Revenue [Member]    
Derivative [Line Items]    
Unrealized Gain (Loss) on Derivatives and Commodity Contracts (2) 3
Exelon Generation Co L L C [Member]    
Derivative [Line Items]    
Unrealized Gain (Loss) on Derivatives (51) 106
Unrealized Gain (Loss) on Derivatives and Commodity Contracts (49) 103
Commodity Contract [Member] | Operating Revenue [Member]    
Derivative [Line Items]    
Unrealized Gain (Loss) on Commodity Contracts 0 7
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net (1) (3)
Unrealized Gain (Loss) on Derivatives (1) 4
Foreign Exchange Contract [Member] | Operating Revenue [Member]    
Derivative [Line Items]    
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net (1) 1
Unrealized Gain (Loss) on Derivatives (1) (1)
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge $ 0 $ (2)