Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivative Asset, Current		$ 759	$ 1,365
Derivative Asset, Noncurrent		546	758
Derivative Liability, Current		152	205
Derivative Liability, Noncurrent		442	374
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current		759	1,365
Derivative Asset, Noncurrent		499	733
Derivative Liability, Current		134	182
Derivative Liability, Noncurrent		237	150
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current		9	15
Derivative Asset, Noncurrent		7	14
Derivative Asset		16	29
Derivative Liability, Current		(9)	(8)
Derivative Liability, Noncurrent		(14)	(8)
Derivative Liability		(23)	(16)
Derivative, Fair Value, Net		(7)	13
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member] | Economic Hedges [Member]
Derivative [Line Items]
Derivative Asset, Current		14	10
Derivative Asset, Noncurrent		14	10
Derivative Asset		28	20
Derivative Liability, Current		(9)	(2)
Derivative Liability, Noncurrent		(10)	(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		(11)	(5)
Derivative Asset, Noncurrent		(12)	(1)
Derivative Asset		(23)	(6)
Derivative Liability, Current		12	11
Derivative Liability, Noncurrent		14	4
Derivative Liability		26	15
Derivative, Fair Value, Net		3	9
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Liability, Current		4
Derivative [Member]
Derivative [Line Items]
Derivative Asset, Current		750	1,350
Derivative Asset, Noncurrent		492	719
Derivative Asset		1,242	2,069
Derivative Liability, Current		143	197
Derivative Liability, Noncurrent		426	366
Derivative Liability		569	563
Derivative, Fair Value, Net		673	1,506
Derivative [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current	[1]	750	1,350
Derivative Asset, Noncurrent	[1]	492	719
Derivative Asset	[1]	1,242	2,069
Derivative Liability, Current	[1]	125	174
Derivative Liability, Noncurrent	[1]	223	142
Derivative Liability	[1]	348	316
Derivative, Fair Value, Net	[1]	894	1,753
Not Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current		6	10
Derivative Asset, Noncurrent		5	5
Derivative Asset		11	15
Derivative Liability, Current		(4)	(9)
Derivative Liability, Noncurrent		(5)	(3)
Derivative Liability		(9)	(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		54	39
Derivative Asset		63	54
Derivative Liability, Current		(9)	(8)
Derivative Liability, Noncurrent		(16)	(8)
Derivative Liability		(25)	(16)
Derivative, Fair Value, Net		38	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		(13)	(8)
Derivative Liability		(21)	(16)
Derivative, Fair Value, Net		(21)	(16)
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Derivative Asset, Current		0	0
Derivative Asset, Noncurrent		47	25
Derivative Asset		47	25
Derivative Liability, Current		0	0
Derivative Liability, Noncurrent		(2)	0
Derivative Liability		(2)	0
Derivative, Fair Value, Net		$ 45	$ 25

[1] .