Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Derivative [Line Items]
Unrealized Gain (Loss) on Commodity Contracts	$ 207	$ (42)	$ 163	$ 350
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(118)	(97)	(267)	(98)
Unrealized Gain (Loss) on Derivatives			(100)	363
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	1	2	(3)	48
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Commodity Contracts	207	(42)	163	350
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(118)	(97)	(267)	(98)
Unrealized Gain (Loss) on Derivatives			(112)	252
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	1	2	(3)	12
Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Commodity Contracts	(73)	(178)	36	(163)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(26)	46	217	249
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
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net				0
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge		0		36
Interest Expense [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net
Change in fair value		0
Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Commodity Contracts	280	136	127	513
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(92)	(143)	(484)	(347)
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	1	2	(3)	12
Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(1)	(6)	1	(5)
Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(2)	(2)	(6)	58
Unrealized Gain (Loss) on Derivatives	(1)	0	(9)	106
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	88	(139)	(113)	358
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	(2)	(2)	(6)	(6)
Unrealized Gain (Loss) on Derivatives	(1)	0	(9)	6
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	88	(139)	(113)	258
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	(99)	(132)	253	86
Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		0		64
Unrealized Gain (Loss) on Derivatives		0		100
Unrealized Gain (Loss) on Derivatives and Commodity Contracts		0		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	(2)	(2)	(6)	(6)
Unrealized Gain (Loss) on Derivatives	(1)	0	(9)	6
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	187	(7)	(366)	172
Foreign Exchange Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	1	(3)	2	(9)
Unrealized Gain (Loss) on Derivatives	1	0	0	(2)
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	0	3	(2)	7
Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	89	(139)	(104)	252
Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	89	(139)	(104)	252
Commodity Contract [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(99)	(132)	253	86
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	188	(7)	(357)	166
Commodity Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Commodity Contracts	4	(4)	18	5
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(6)	(2)	(17)	(8)
Unrealized Gain (Loss) on Derivatives	$ (2)	$ (6)	$ 1	$ (3)