Derivative Financial Instruments - Summary of Proprietary Trading Activities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Derivative [Line Items]
Gain (Loss) on Sale of Derivatives	$ (23)	[1]
Unrealized Gain (Loss) on Derivatives	91		(730)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	84		(731)
Operating Revenue [Member] | Principal or Proprietary Transactions [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	3		(2)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Gain (Loss) on Sale of Derivatives	3	[1]
Unrealized Gain (Loss) on Derivatives	165		(737)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	162		(731)
Unrealized Gain (Loss) on Commodity Contracts	154		(760)
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	8		30
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	154		(760)
Exelon Generation Co L L C [Member] | Interest Expense [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0		(1)
Corporate, Non-Segment [Member] | Interest Expense [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(78)		0
Commodity Contract [Member] | Operating Revenue [Member] | Principal or Proprietary Transactions [Member]
Derivative [Line Items]
Gain (Loss) on Sale of Derivatives	2		1
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	3		(2)
Unrealized Gain (Loss) on Commodity Contracts	1		(3)
InterestRateAndForeignExchangeContract [Member] | Operating Revenue [Member] | Principal or Proprietary Transactions [Member]
Derivative [Line Items]
Gain (Loss) on Sale of Derivatives	(4)		0
Unrealized Gain (Loss) on Derivatives	4		0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 0		$ 0

[1] In January 2015, in connection with Generation's $750 million issuance of five-year Senior Unsecured Notes, Exelon terminated certain floating-to-fixed interest rate swaps. As the original forecasted transactions were a series of future interest payments over a ten year period, a portion of the anticipated interest payments are probable not to occur. As a result, $26 million of anticipated payments were reclassified from Accumulated OCI to Other, net in Exelon's Consolidated Statement of Operations and Comprehensive Income.