Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	$ 4		$ (1)
Mark-to-market derivative assets (noncurrent assets)	30		38
Total mark-to-market derivative assets	34		37
Mark-to-market derivative liabilities (current liabilities)	(6)		(1)
Mark-to-market derivative liabilities (noncurrent liabilities)	(26)		(15)
Total mark-to-market derivative liabilities	(32)		(16)
Total mark-to-market derivative net assets (liabilities)	2		21
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	4		(1)
Mark-to-market derivative assets (noncurrent assets)	13		31
Total mark-to-market derivative assets	17		30
Mark-to-market derivative liabilities (current liabilities)	(6)		(1)
Mark-to-market derivative liabilities (noncurrent liabilities)	(3)		(11)
Total mark-to-market derivative liabilities	(9)		(12)
Total mark-to-market derivative net assets (liabilities)	8		18
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0		0
Mark-to-market derivative assets (noncurrent assets)	13		26
Total mark-to-market derivative assets	13		26
Mark-to-market derivative liabilities (current liabilities)	(1)		(1)
Mark-to-market derivative liabilities (noncurrent liabilities)	(1)		(10)
Total mark-to-market derivative liabilities	(2)		(11)
Total mark-to-market derivative net assets (liabilities)	11		15
Exelon Generation Co L L C [Member] | Derivative [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	4		3
Mark-to-market derivative assets (noncurrent assets)	3		3
Total mark-to-market derivative assets	7		6
Mark-to-market derivative liabilities (current liabilities)	(7)		(1)
Mark-to-market derivative liabilities (noncurrent liabilities)	(2)		(1)
Total mark-to-market derivative liabilities	(9)		(2)
Total mark-to-market derivative net assets (liabilities)	(2)		4
Exelon Generation Co L L C [Member] | Proprietary Trading [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	14		15
Mark-to-market derivative assets (noncurrent assets)	7		15
Total mark-to-market derivative assets	21	[1]	30	[1]
Mark-to-market derivative liabilities (current liabilities)	(11)		(18)
Mark-to-market derivative liabilities (noncurrent liabilities)	(9)		(13)
Total mark-to-market derivative liabilities	(20)	[1]	(31)	[1]
Total mark-to-market derivative net assets (liabilities)	1		(1)	[1]
Exelon Generation Co L L C [Member] | Collateral And Netting [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	(14)		(19)
Mark-to-market derivative assets (noncurrent assets)	(10)		(13)
Total mark-to-market derivative assets	(24)	[2]	(32)	[2]
Mark-to-market derivative liabilities (current liabilities)	13		19
Mark-to-market derivative liabilities (noncurrent liabilities)	9		13
Total mark-to-market derivative liabilities	22	[2]	32	[2]
Total mark-to-market derivative net assets (liabilities)	(2)	[2]	0
Corporate, Non-Segment [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0		0
Mark-to-market derivative assets (noncurrent assets)	12		7
Total mark-to-market derivative assets	12		7
Mark-to-market derivative liabilities (current liabilities)	0		0
Mark-to-market derivative liabilities (noncurrent liabilities)	(10)		(4)
Total mark-to-market derivative liabilities	(10)		(4)
Total mark-to-market derivative net assets (liabilities)	2		3
Corporate, Non-Segment [Member] | Derivative [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0
Mark-to-market derivative assets (noncurrent assets)	5
Total mark-to-market derivative assets	5
Mark-to-market derivative liabilities (current liabilities)	0
Mark-to-market derivative liabilities (noncurrent liabilities)	(13)
Total mark-to-market derivative liabilities	(13)
Total mark-to-market derivative net assets (liabilities)	$ (8)

[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.