Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Interest Rate Fair Value Hedge Asset at Fair Value		$ 35
Derivative Asset, Current		754	$ 1,365
Derivative Asset, Noncurrent		669	758
Derivative Liability, Current		222	205
Derivative Liability, Noncurrent		422	374
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Interest Rate Fair Value Hedge Asset at Fair Value		(4)
Derivative Asset, Current		754	1,365
Derivative Asset, Noncurrent		630	733
Derivative Liability, Current		203	182
Derivative Liability, Noncurrent		197	150
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current		9	15
Derivative Asset, Noncurrent		6	14
Derivative Asset		15	29
Derivative Liability, Current		(9)	(8)
Derivative Liability, Noncurrent		(10)	(8)
Derivative Liability		(19)	(16)
Derivative, Fair Value, Net		(4)	13
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member] | Economic Hedges [Member]
Derivative [Line Items]
Derivative Asset, Current		15	10
Derivative Asset, Noncurrent		13	10
Derivative Asset		28	20
Derivative Liability, Current		(10)	(2)
Derivative Liability, Noncurrent		(9)	(1)
Derivative Liability		(19)	(3)
Derivative, Fair Value, Net		9	17
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member] | Collateral And Netting [Member]
Derivative [Line Items]
Derivative Asset, Current		(10)	(5)
Derivative Asset, Noncurrent		(11)	(1)
Derivative Asset		(21)	(6)
Derivative Liability, Current		12	11
Derivative Liability, Noncurrent		12	4
Derivative Liability		24	15
Derivative, Fair Value, Net		3	9
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Liability, Current		3
Derivative [Member]
Derivative [Line Items]
Derivative Asset, Current		745	1,350
Derivative Asset, Noncurrent		624	719
Derivative Asset		1,369	2,069
Derivative Liability, Current		213	197
Derivative Liability, Noncurrent		412	366
Derivative Liability		625	563
Derivative, Fair Value, Net		744	1,506
Derivative [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current	[1]	745	1,350
Derivative Asset, Noncurrent	[1]	624	719
Derivative Asset	[1]	1,369	2,069
Derivative Liability, Current	[1]	194	174
Derivative Liability, Noncurrent	[1]	187	142
Derivative Liability	[1]	381	316
Derivative, Fair Value, Net	[1]	988	1,753
Not Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current		4	10
Derivative Asset, Noncurrent		4	5
Derivative Asset		8	15
Derivative Liability, Current		(3)	(9)
Derivative Liability, Noncurrent		(3)	(3)
Derivative Liability		(6)	(12)
Derivative, Fair Value, Net		2	3
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative Asset, Current		9	15
Derivative Asset, Noncurrent		45	39
Derivative Asset		54	54
Derivative Liability, Current		(9)	(8)
Derivative Liability, Noncurrent		(10)	(8)
Derivative Liability		(19)	(16)
Derivative, Fair Value, Net			38
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current		0	0
Derivative Asset, Noncurrent		0	0
Derivative Asset		0	0
Derivative Liability, Current		(8)	(8)
Derivative Liability, Noncurrent		(10)	(8)
Derivative Liability		(18)	(16)
Derivative, Fair Value, Net		(18)	(16)
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Derivative Asset, Current		0	0
Derivative Asset, Noncurrent		39	25
Derivative Asset		39	25
Derivative Liability, Current		0	0
Derivative Liability, Noncurrent		0	0
Derivative Liability		0	0
Derivative, Fair Value, Net		$ 39	$ 25

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