Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Interest Rate Swap [Member] | Derivative [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	$ 15		$ (1)
Mark-to-market derivative assets (noncurrent assets)	8		38
Total mark-to-market derivative assets	23		37
Mark-to-market derivative liabilities (current liabilities)	1		(1)
Mark-to-market derivative liabilities (noncurrent liabilities)	(114)		(15)
Total mark-to-market derivative liabilities	(113)		(16)
Interest Rate Derivative Fair Value Of Derivative Net	(90)		21
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	12		(1)
Mark-to-market derivative assets (noncurrent assets)	6		31
Total mark-to-market derivative assets	18		30
Mark-to-market derivative liabilities (current liabilities)	1		(1)
Mark-to-market derivative liabilities (noncurrent liabilities)	(3)		(11)
Total mark-to-market derivative liabilities	(2)		(12)
Interest Rate Derivative Fair Value Of Derivative Net	16		18
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member] | Derivative [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	7		3
Mark-to-market derivative assets (noncurrent assets)	5		3
Total mark-to-market derivative assets	12		6
Mark-to-market derivative liabilities (current liabilities)	(2)		(1)
Mark-to-market derivative liabilities (noncurrent liabilities)	0		(1)
Total mark-to-market derivative liabilities	(2)		(2)
Interest Rate Derivative Fair Value Of Derivative Net	10		4
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member] | Proprietary Trading [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	20	[1]	15	[1]
Mark-to-market derivative assets (noncurrent assets)	7	[1]	15	[1]
Total mark-to-market derivative assets	27	[1]	30	[1]
Mark-to-market derivative liabilities (current liabilities)	(14)	[1]	(18)	[1]
Mark-to-market derivative liabilities (noncurrent liabilities)	(9)	[1]	(13)	[1]
Total mark-to-market derivative liabilities	(23)	[1]	(31)	[1]
Interest Rate Derivative Fair Value Of Derivative Net	4	[1]	(1)	[1]
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member] | Collateral And Netting [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	(22)	[2]	(19)	[2]
Mark-to-market derivative assets (noncurrent assets)	(7)	[2]	(13)	[2]
Total mark-to-market derivative assets	(29)	[2]	(32)	[2]
Mark-to-market derivative liabilities (current liabilities)	25	[2]	19	[2]
Mark-to-market derivative liabilities (noncurrent liabilities)	10	[2]	13	[2]
Total mark-to-market derivative liabilities	35	[2]	32	[2]
Interest Rate Derivative Fair Value Of Derivative Net	6	[2]	0	[2]
Other Segments [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	3
Mark-to-market derivative assets (noncurrent assets)	2
Total mark-to-market derivative assets	5
Mark-to-market derivative liabilities (current liabilities)	0
Mark-to-market derivative liabilities (noncurrent liabilities)	(111)
Total mark-to-market derivative liabilities	(111)
Interest Rate Derivative Fair Value Of Derivative Net	(106)
Other Segments [Member] | Interest Rate Swap [Member] | Derivative [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0
Mark-to-market derivative assets (noncurrent assets)	1
Total mark-to-market derivative assets	1
Mark-to-market derivative liabilities (current liabilities)	0
Mark-to-market derivative liabilities (noncurrent liabilities)	(101)
Total mark-to-market derivative liabilities	(101)
Interest Rate Derivative Fair Value Of Derivative Net	(100)
Other Segments [Member] | Interest Rate Swap [Member] | Collateral And Netting [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0	[2]
Mark-to-market derivative assets (noncurrent assets)	(19)	[2]
Total mark-to-market derivative assets	(19)	[2]
Mark-to-market derivative liabilities (current liabilities)	0	[2]
Mark-to-market derivative liabilities (noncurrent liabilities)	19	[2]
Total mark-to-market derivative liabilities	19	[2]
Interest Rate Derivative Fair Value Of Derivative Net	0	[2]
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	7		0
Mark-to-market derivative assets (noncurrent assets)	1		26
Total mark-to-market derivative assets	8		26
Mark-to-market derivative liabilities (current liabilities)	(8)		(1)
Mark-to-market derivative liabilities (noncurrent liabilities)	(4)		(10)
Total mark-to-market derivative liabilities	(12)		(11)
Interest Rate Derivative Fair Value Of Derivative Net	(4)		15
Designated as Hedging Instrument [Member] | Other Segments [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (current liabilities)	0
Designated as Hedging Instrument [Member] | Other Segments [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	3		0
Mark-to-market derivative assets (noncurrent assets)	20		7
Total mark-to-market derivative assets	23		7
Mark-to-market derivative liabilities (current liabilities)			0
Mark-to-market derivative liabilities (noncurrent liabilities)	(29)		(4)
Total mark-to-market derivative liabilities	(29)		(4)
Interest Rate Derivative Fair Value Of Derivative Net	$ (6)		$ 3

[1] 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 between 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.

[2] Represents the netting of fair value balances with the same counterparty and any associated cash collateral.