Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Interest Rate Fair Value Hedge Asset at Fair Value		$ 9
Derivative Asset, Current		847	$ 917
Derivative Asset, Noncurrent		539	492
Derivative Liability, Current		(228)	(282)
Derivative Liability, Noncurrent		(420)	(392)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Interest Rate Fair Value Hedge Asset at Fair Value		3
Derivative Asset, Current		847	917
Derivative Asset, Noncurrent		527	476
Derivative Liability, Current		(209)	(263)
Derivative Liability, Noncurrent		(157)	(153)
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current		5	8
Derivative Asset, Noncurrent		3	4
Derivative Asset		8	12
Derivative Liability, Current		(7)	8
Derivative Liability, Noncurrent		(4)	(4)
Derivative Liability		(11)	12
Derivative, Fair Value, Net		(3)	0
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member] | Economic Hedges [Member]
Derivative [Line Items]
Derivative Asset, Current		15	17
Derivative Asset, Noncurrent		7	11
Derivative Asset		22	28
Derivative Liability, Current		(17)	13
Derivative Liability, Noncurrent		(8)	(8)
Derivative Liability		(25)	21
Derivative, Fair Value, Net		(3)	(7)
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member] | Collateral And Netting [Member]
Derivative [Line Items]
Derivative Asset, Current		(13)	(13)
Derivative Asset, Noncurrent		(5)	(8)
Derivative Asset		(18)	(21)
Derivative Liability, Current		13	(14)
Derivative Liability, Noncurrent		5	(9)
Derivative Liability		18	(23)
Derivative, Fair Value, Net		0	(2)
Derivative [Member]
Derivative [Line Items]
Derivative Asset, Current		842	909
Derivative Asset, Noncurrent		524	472
Derivative Asset		1,366	1,381
Derivative Liability, Current		(221)	(274)
Derivative Liability, Noncurrent		(416)	(388)
Derivative Liability		(637)	(662)
Derivative, Fair Value, Net		(729)	(719)
Derivative [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current	[1]	842	909
Derivative Asset, Noncurrent	[1]	524	472
Derivative Asset	[1]	1,366	1,381
Derivative Liability, Current	[1]	(202)	(255)
Derivative Liability, Noncurrent	[1]	(153)	(149)
Derivative Liability	[1]	(355)	(404)
Derivative, Fair Value, Net	[1]	(1,011)	(977)
Not Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Asset, Current		3	4
Derivative Asset, Noncurrent		1	1
Derivative Asset		4	5
Derivative Liability, Current		(2)	2
Derivative Liability, Noncurrent		(1)	(2)
Derivative Liability		(3)	4
Derivative, Fair Value, Net		1	(1)
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative Asset, Current		5	8
Derivative Asset, Noncurrent		15	20
Derivative Asset		20	28
Derivative Liability, Current		(7)	8
Derivative Liability, Noncurrent		(4)	(4)
Derivative Liability		(11)	12
Derivative, Fair Value, Net			(16)
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		(1)	7
Derivative Liability, Noncurrent		0	(3)
Derivative Liability		(1)	10
Derivative, Fair Value, Net		(1)	10
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Derivative Asset, Current		0	0
Derivative Asset, Noncurrent		12	16
Derivative Asset		12	16
Derivative Liability, Current		0	0
Derivative Liability, Noncurrent		0	0
Derivative Liability		0	0
Derivative, Fair Value, Net		$ 12	$ (16)

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