Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Derivative [Line Items]
Unrealized Gain (Loss) on Commodity Contracts	$ (197)	$ 307	$ (44)	$ 392
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(105)	(67)	(149)	(1)
Unrealized Gain (Loss) on Derivatives			(194)	507
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	1	111	(4)	46
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Commodity Contracts	(197)	307	(44)	392
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(105)	(67)	(149)	(1)
Unrealized Gain (Loss) on Derivatives			(199)	396
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	1	(3)	(4)	10
Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Commodity Contracts	235	110	109	15
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	76	100	243	203
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	0	0	0	0
Interest Expense [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Commodity Contracts		0		0
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		0		0
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge		114		36
Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Commodity Contracts	(432)	197	(153)	377
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(181)	(167)	(392)	(204)
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	1	(3)	(4)	10
Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(1)	(2)	2	1
Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(3)	62	(4)	60
Unrealized Gain (Loss) on Derivatives	(2)	173	(8)	106
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(304)	413	(201)	497
Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(3)	(2)	(4)	(4)
Unrealized Gain (Loss) on Derivatives	(2)	(5)	(8)	6
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(304)	235	(201)	397
Foreign Exchange Contract [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	0	0	0
Unrealized Gain (Loss) on Derivatives	0	0	0	0
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	311	210	352	218
Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		64		64
Unrealized Gain (Loss) on Derivatives		178		100
Unrealized Gain (Loss) on Derivatives and Commodity Contracts		178		100
Foreign Exchange Contract [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(3)	(2)	(4)	(4)
Unrealized Gain (Loss) on Derivatives	(2)	(5)	(8)	6
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(615)	25	(553)	179
Foreign Exchange Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(1)	(2)	1	(6)
Unrealized Gain (Loss) on Derivatives	(1)	(2)	(1)	(2)
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	0	0	(2)	4
Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(302)	240	(193)	391
Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(302)	240	(193)	391
Commodity Contract [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	311	210	352	218
Commodity Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives		0		0
Commodity Contract [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(613)	30	(545)	173
Commodity Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Commodity Contracts	5	7	14	8
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(5)	(7)	(11)	(5)
Unrealized Gain (Loss) on Derivatives	$ 0	$ 0	$ 3	$ 3