Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	$ 1,117		$ 1,279
Mark-to-market derivative assets	913		773
Derivative Liability, Current	(117)		(234)
Derivative Liability, Noncurrent	(491)		(403)
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	15		15
Mark-to-market derivative assets	21		8
Derivative Liability, Current	(7)		1
Derivative Liability, Noncurrent	(159)		(114)
Total mark-to-market derivative net assets (liabilities)	(130)	[1]	(90)	[1]
Total mark-to-market derivative assets	36	[1]	23	[1]
Derivative Liability	(166)	[1]	(113)	[1]
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	1,116		1,276
Mark-to-market derivative assets	911		771
Derivative Liability, Current	(97)		(214)
Derivative Liability, Noncurrent	(121)		(105)
Exelon Generation Co L L C [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	14		12
Mark-to-market derivative assets	19		6
Derivative Liability, Current	(7)		1
Derivative Liability, Noncurrent	(10)		(3)
Total mark-to-market derivative net assets (liabilities)	16	[1]	16	[1]
Total mark-to-market derivative assets	33	[1]	18	[1]
Derivative Liability	(17)	[1]	(2)	[1]
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Liability, Current	(3)
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0		7
Mark-to-market derivative assets	0		1
Derivative Liability, Current	(8)		(8)
Derivative Liability, Noncurrent	(9)		(4)
Total mark-to-market derivative net assets (liabilities)	(17)		(4)
Total mark-to-market derivative assets	0		8
Derivative Liability	(17)		(12)
Exelon Generation Co L L C [Member] | Proprietary Trading [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	11		20
Mark-to-market derivative assets	8		7
Derivative Liability, Current	(8)		(14)
Derivative Liability, Noncurrent	(7)		(9)
Total mark-to-market derivative net assets (liabilities)	4		4
Total mark-to-market derivative assets	19	[2]	27	[2]
Derivative Liability	(15)	[2]	(23)	[2]
Exelon Generation Co L L C [Member] | Collateral And Netting [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	(10)		(22)
Mark-to-market derivative assets	(3)		(7)
Derivative Liability, Current	15		25
Derivative Liability, Noncurrent	6		10
Total mark-to-market derivative net assets (liabilities)	8	[1]	6	[1]
Total mark-to-market derivative assets	(13)	[1]	(29)	[1]
Derivative Liability	21	[1]	35	[1]
Exelon Generation Co L L C [Member] | Economic Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	13		7
Mark-to-market derivative assets	14		5
Derivative Liability, Current	(6)		(2)
Derivative Liability, Noncurrent	0		0
Total mark-to-market derivative net assets (liabilities)	21		10
Total mark-to-market derivative assets	27		12
Derivative Liability	(6)		(2)
Corporate, Non-Segment [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	1		3
Mark-to-market derivative assets	2		2
Derivative Liability, Current	0		0
Derivative Liability, Noncurrent	(149)		(111)
Total mark-to-market derivative net assets (liabilities)	(146)	[1]	(106)	[1]
Total mark-to-market derivative assets	3	[1]	5	[1]
Derivative Liability	(149)	[1]	(111)	[1]
Corporate, Non-Segment [Member] | Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	1		3
Mark-to-market derivative assets	31		20
Derivative Liability, Current	0		0
Derivative Liability, Noncurrent	0		(29)
Total mark-to-market derivative net assets (liabilities)	32		(6)
Total mark-to-market derivative assets	32		23
Derivative Liability	0		(29)
Corporate, Non-Segment [Member] | Collateral And Netting [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0		0
Mark-to-market derivative assets	(31)		(19)
Derivative Liability, Current	0		0
Derivative Liability, Noncurrent	31		19
Total mark-to-market derivative net assets (liabilities)	0	[1]	0	[1]
Total mark-to-market derivative assets	(31)	[1]	(19)	[1]
Derivative Liability	31	[1]	19	[1]
Corporate, Non-Segment [Member] | Economic Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0		0
Mark-to-market derivative assets	2		1
Derivative Liability, Current	0		0
Derivative Liability, Noncurrent	(180)		(101)
Total mark-to-market derivative net assets (liabilities)	(178)		(100)
Total mark-to-market derivative assets	2		1
Derivative Liability	$ (180)		$ (101)

[1] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246MzFGMzlBOEZENkM2MzU4RDBBNzEwOTNBRjYwNTQzOEQM}

[2] Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The characterization of the interest rate derivative contracts within the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure. Generation does not utilize proprietary trading interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates.