Derivative Financial Instruments - Summary of Economic Hedges (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 84		$ (731)
Gain (Loss) on Sale of Derivatives	(23)	[1]
Unrealized Gain (Loss) on Derivatives	91		(730)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	162		(731)
Gain (Loss) on Sale of Derivatives	3	[1]
Unrealized Gain (Loss) on Derivatives	165		(737)
Unrealized Gain (Loss) on Commodity Contracts	154		(760)
Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	8		30
Interest Expense [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(78)		0
Interest Expense [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0		(1)
Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	154		(760)
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(67)		(2)
Not Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	11		(2)
Not Designated as Hedging Instrument [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0		0
Not Designated as Hedging Instrument [Member] | Interest Expense [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(78)		0
Not Designated as Hedging Instrument [Member] | Interest Expense [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0		(1)
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	151		(729)
Gain (Loss) on Sale of Derivatives	66		(48)
Unrealized Gain (Loss) on Commodity Contracts	85		(681)
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	151		(729)
Gain (Loss) on Sale of Derivatives	66		(48)
Unrealized Gain (Loss) on Commodity Contracts	85		(681)
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	8		30
Gain (Loss) on Sale of Derivatives	87		(141)
Unrealized Gain (Loss) on Commodity Contracts	(79)		171
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0		0
Gain (Loss) on Sale of Derivatives	0		0
Unrealized Gain (Loss) on Commodity Contracts	0		0
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Interest Expense [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0		0
Gain (Loss) on Sale of Derivatives	0		0
Unrealized Gain (Loss) on Commodity Contracts	0		0
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	143		(759)
Gain (Loss) on Sale of Derivatives	(21)		93
Unrealized Gain (Loss) on Commodity Contracts	164		(852)
Not Designated as Hedging Instrument [Member] | InterestRateandForeignExchange [Member]
Derivative [Line Items]
Gain (Loss) on Sale of Derivatives	(2)		0
Unrealized Gain (Loss) on Derivatives	(65)		(2)
Not Designated as Hedging Instrument [Member] | InterestRateandForeignExchange [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Gain (Loss) on Sale of Derivatives	(2)		0
Unrealized Gain (Loss) on Derivatives	13		(2)
Not Designated as Hedging Instrument [Member] | InterestRateandForeignExchange [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Gain (Loss) on Sale of Derivatives	0		0
Unrealized Gain (Loss) on Derivatives	0		0
Not Designated as Hedging Instrument [Member] | InterestRateandForeignExchange [Member] | Interest Expense [Member]
Derivative [Line Items]
Gain (Loss) on Sale of Derivatives	0		0
Unrealized Gain (Loss) on Derivatives	0		(1)
Not Designated as Hedging Instrument [Member] | InterestRateandForeignExchange [Member] | Interest Expense [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Gain (Loss) on Sale of Derivatives	0		0
Unrealized Gain (Loss) on Derivatives	(78)		0
Not Designated as Hedging Instrument [Member] | InterestRateandForeignExchange [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	11		(1)
Gain (Loss) on Sale of Derivatives	(2)		0
Unrealized Gain (Loss) on Derivatives	$ 13		$ (1)

[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.