Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		$ (2)	$ (6)
Unrealized Gain (Loss) on Derivatives				$ 507	$ (751)
Gain (Loss) on Sale of Derivatives	[1]			(26)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives				396	(760)
Gain (Loss) on Sale of Derivatives	[1]			0
Unrealized Gain (Loss) on Commodity Contracts		25	(83)	179	(843)
Operating Revenue [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net				1	(7)
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		413	(15)	497	(745)
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		235	(15)	397	(745)
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		210	69	218	99
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		178	0	100	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)	0	(1)
Not Designated as Hedging Instrument [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		25	(83)	179	(843)
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		240	(10)	391	(739)
Gain (Loss) on Sale of Derivatives		(67)	3	(1)	(46)
Unrealized Gain (Loss) on Commodity Contracts		307	(13)	392	(693)
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		240	(10)	391	(739)
Gain (Loss) on Sale of Derivatives		(67)	3	(1)	(46)
Unrealized Gain (Loss) on Commodity Contracts		307	(13)	392	(693)
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		210	69	218	99
Gain (Loss) on Sale of Derivatives		100	(42)	203	(183)
Unrealized Gain (Loss) on Commodity Contracts		110	111	15	282
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		0
Gain (Loss) on Sale of Derivatives		0		0	0
Unrealized Gain (Loss) on Commodity Contracts		0	0		0
Not Designated as Hedging Instrument [Member] | Commodity Contract [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	0	0	0
Gain (Loss) on Sale of Derivatives		0	0	0	0
Unrealized Gain (Loss) on Commodity Contracts		0	0	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		30	(79)	173	(838)
Gain (Loss) on Sale of Derivatives		(167)	45	(204)	137
Unrealized Gain (Loss) on Commodity Contracts		197	(124)	377	(975)
Not Designated as Hedging Instrument [Member] | InterestRateandForeignExchange [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		173	(5)	106	(6)
Unrealized Gain (Loss) on Derivatives		111	(4)		(5)
Unrealized Gain (Loss) on Foreign Currency Derivatives, Net, before Tax				46
Gain (Loss) on Sale of Derivatives		62	(1)	60	(1)
Not Designated as Hedging Instrument [Member] | InterestRateandForeignExchange [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		(5)	(5)	6	(6)
Unrealized Gain (Loss) on Derivatives		(3)	(4)		(5)
Unrealized Gain (Loss) on Foreign Currency Derivatives, Net, before Tax				10
Gain (Loss) on Sale of Derivatives		(2)	(1)	(4)	(1)
Not Designated as Hedging Instrument [Member] | InterestRateandForeignExchange [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	0	0
Unrealized Gain (Loss) on Derivatives		0	0		0
Unrealized Gain (Loss) on Foreign Currency Derivatives, Net, before Tax				0
Gain (Loss) on Sale of Derivatives		0	0	0	0
Not Designated as Hedging Instrument [Member] | InterestRateandForeignExchange [Member] | Interest Expense [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		178	0	100	0
Unrealized Gain (Loss) on Derivatives		114			0
Unrealized Gain (Loss) on Foreign Currency Derivatives, Net, before Tax				36
Gain (Loss) on Sale of Derivatives		64		64	0
Not Designated as Hedging Instrument [Member] | InterestRateandForeignExchange [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)	0	(1)
Unrealized Gain (Loss) on Derivatives		0	(1)		(1)
Unrealized Gain (Loss) on Foreign Currency Derivatives, Net, before Tax				0
Gain (Loss) on Sale of Derivatives		0	0	0	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		(5)	(4)	6	(5)
Unrealized Gain (Loss) on Derivatives		(3)	(3)		(4)
Unrealized Gain (Loss) on Foreign Currency Derivatives, Net, before Tax				10
Gain (Loss) on Sale of Derivatives		$ (2)	$ (1)	$ (4)	$ (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.