Derivative Financial Instruments - Summary of Proprietary Trading Activities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (24,000,000)	$ 367,000,000	$ (716,000,000)
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(41,000,000)	357,000,000	(693,000,000)
Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	1,000,000	(8,000,000)	(26,000,000)
Interest Expense [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts		100,000,000	(100,000,000)
Commodity Contract [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	213,000,000	404,000,000	(607,000,000)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(244,000,000)	(154,000,000)	8,000,000
Unrealized Gain (Loss) on Commodity Contracts	(31,000,000)	250,000,000	(599,000,000)
Commodity Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	23,000,000	8,000,000	(1,000,000)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(21,000,000)	(14,000,000)	(29,000,000)
Unrealized Gain (Loss) on Commodity Contracts	2,000,000	(6,000,000)	(30,000,000)
Commodity Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge		0	0
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		0	0
Unrealized Gain (Loss) on Commodity Contracts		0	0
Foreign Exchange Contract [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	(2,000,000)	49,000,000	(92,000,000)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(8,000,000)	58,000,000	(2,000,000)
Unrealized Gain (Loss) on Derivatives	(10,000,000)	107,000,000	(94,000,000)
Foreign Exchange Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	(1,000,000)	8,000,000	1,000,000
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	(10,000,000)	3,000,000
Unrealized Gain (Loss) on Derivatives	(1,000,000)	(2,000,000)	4,000,000
Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge		36,000,000	(100,000,000)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		64,000,000	0
Unrealized Gain (Loss) on Derivatives		100,000,000	(100,000,000)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(40,000,000)	249,000,000	(635,000,000)
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(41,000,000)	257,000,000	(593,000,000)
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(500,000,000)	203,000,000	(174,000,000)
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	459,000,000	54,000,000	(417,000,000)
Exelon Generation Co L L C [Member] | Interest Expense [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts			(2,000,000)
Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	213,000,000	404,000,000	(607,000,000)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(244,000,000)	(154,000,000)	8,000,000
Unrealized Gain (Loss) on Commodity Contracts	(31,000,000)	250,000,000	(599,000,000)
Exelon Generation Co L L C [Member] | Commodity Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	5,000,000	759,000,000	(413,000,000)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(495,000,000)	(563,000,000)	231,000,000
Unrealized Gain (Loss) on Commodity Contracts	(490,000,000)	196,000,000	(182,000,000)
Exelon Generation Co L L C [Member] | Commodity Contract [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	208,000,000	(355,000,000)	(194,000,000)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	251,000,000	409,000,000	(223,000,000)
Unrealized Gain (Loss) on Commodity Contracts	459,000,000	54,000,000	(417,000,000)
Exelon Generation Co L L C [Member] | Commodity Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge			0
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net			0
Unrealized Gain (Loss) on Commodity Contracts			0
Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	(2,000,000)	13,000,000	8,000,000
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(8,000,000)	(6,000,000)	(2,000,000)
Unrealized Gain (Loss) on Derivatives	(10,000,000)	7,000,000	6,000,000
Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	(2,000,000)	13,000,000	10,000,000
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(8,000,000)	(6,000,000)	(2,000,000)
Unrealized Gain (Loss) on Derivatives	(10,000,000)	7,000,000	8,000,000
Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge	0	0	0
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	0	0
Unrealized Gain (Loss) on Derivatives	$ 0	$ 0	0
Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Foreign Currency Fair Value Hedge			(2,000,000)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net			0
Unrealized Gain (Loss) on Derivatives			$ (2,000,000)