Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivative Asset, Current	$ 1,185	$ 1,365
Derivative Asset, Noncurrent	841	758
Derivative Liability, Current	203	205
Derivative Liability, Noncurrent	408	374
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current	1,185	1,365
Derivative Asset, Noncurrent	799	733
Derivative Liability, Current	177	182
Derivative Liability, Noncurrent	166	150
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative Asset, Current	13	15
Derivative Asset, Noncurrent	53	39
Derivative Asset	66	54
Derivative Liability, Current	8	8
Derivative Liability, Noncurrent	18	8
Derivative Liability	26	16
Derivative, Fair Value, Net	40	38
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current	13	15
Derivative Asset, Noncurrent	11	14
Derivative Asset	24	29
Derivative Liability, Current	8	8
Derivative Liability, Noncurrent	15	8
Derivative Liability	23	16
Derivative, Fair Value, Net	1	13
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member] | Economic Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Current	10	10
Derivative Asset, Noncurrent	10	10
Derivative Asset	20	20
Derivative Liability, Current	3	2
Derivative Liability, Noncurrent	5	1
Derivative Liability	8	3
Derivative, Fair Value, Net	12	17
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member] | Proprietary Trading [Member]
Derivative [Line Items]
Derivative Asset, Current	8	10
Derivative Asset, Noncurrent	5	5
Derivative Asset	13	15
Derivative Liability, Current	6	9
Derivative Liability, Noncurrent	5	3
Derivative Liability	11	12
Derivative, Fair Value, Net	2	3
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member] | Collateral And Netting [Member]
Derivative [Line Items]
Derivative Asset, Current	(5)	(5)
Derivative Asset, Noncurrent	(4)	(1)
Derivative Asset	(9)	(6)
Derivative Liability, Current	(9)	(11)
Derivative Liability, Noncurrent	(7)	(4)
Derivative Liability	(16)	(15)
Derivative, Fair Value, Net	7	9
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Liability, Current	3
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative Asset, Current	0	0
Derivative Asset, Noncurrent	42	25
Derivative Asset	42	25
Derivative Liability, Current	0	0
Derivative Liability, Noncurrent	3	0
Derivative Liability	3	0
Derivative, Fair Value, Net	39	25
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	12	8
Derivative Liability	20	16
Derivative, Fair Value, Net	$ (20)	$ (16)