Derivative Financial Instruments - Summary of Gains and Losses on Hedges (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016
Derivative [Line Items]
Income taxes		$ 215		$ 184
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net	[1]	4		2
Derivative, Loss on Derivative			$ 3
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value		1			$ 2
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes		127		151
Interest Expense [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Increase (Decrease) in Fair Value of Hedged Item in Price Risk Fair Value Hedge		8		(15)
Interest Rate Swap [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings		$ (4)		$ 17

[1] Three Months Ended March 31, Income StatementLocation 2017 2016 2017 2016 Gain (loss) on Swaps Gain (loss) on BorrowingsExelonInterest expense $(4) $17 $8 $(15)