Investment in Constellation Energy Nuclear Group, LLC - Narrative (Details) - USD ($) $ in Millions		2 Months Ended		3 Months Ended									12 Months Ended					20 Months Ended
	Apr. 01, 2014	Dec. 31, 2014		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2015	Jun. 09, 2015
Schedule of Equity Method Investments [Line Items]
Purchase of nuclear output by EDF													49.99%
Guarantee obligations maximum exposure				$ 9,206									$ 9,206					$ 9,206
Revenues				6,702	$ 7,401	$ 6,514	$ 8,830	$ 7,255		$ 6,912	$ 6,024	$ 7,237	29,447	$ 27,429		$ 24,888
Accumulated other comprehensive loss, net		$ (2,684)	[1]	(2,624)				(2,684)	[1]				$ (2,624)	(2,684)	[1]	(2,040)	[1]	(2,624)
Required purchases of power from CENG's nuclear plants not sold to third parties													85.00%
Operating revenues from affiliates													$ 9	23		70
Parental guarantee provided				$ 75									75					75
Business Combination, Integration Related Costs													$ 80	179				$ 121
Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Accumulated other comprehensive loss, net	$ 1,500
Constellation Energy Nuclear Group [Member] | Payment Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Due to affiliate	245
Constellation Energy Nuclear Group [Member] | Financial Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Guarantee obligations maximum exposure	$ 165
Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest				50.01%									50.01%					50.01%
Cash distribution paid to member													$ 2,474	645		625
Purchase of nuclear output by EDF	49.99%
Guarantee obligations maximum exposure				$ 6,832									6,832					$ 6,832
Total equity investment earnings (losses) - CENG												19				9
Revenues		386		4,294	$ 4,768	$ 4,232	$ 5,840	4,802		$ 4,412	$ 3,789	4,390	19,135	17,393		15,630
Accumulated other comprehensive loss, net		(36)	[1]	(63)				(36)	[1]				$ (63)	(36)	[1]	214	[1]	(63)
Allocation of federal tax benefit under tax sharing agreement		$ 55						$ 55				77		55
Required purchases of power from CENG's nuclear plants not sold to third parties	85.00%
Subsequent purchases of power from CENG's nuclear plants not sold to third parties													50.01%
Operating revenues from affiliates													$ 749	779		1,423
Parental guarantee provided				12									12					12
Business Combination, Integration Related Costs													25	11
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Schedule of Equity Method Investments [Line Items]
Remeasurement gain from derecognition of equity method investment	$ 261
Business combination, step acquisition, equity interest in acquiree, fair value	136
Business acquisition, preexisting relationship, gain (loss) recognized	132
Parental guarantee provided	7			7									7					7	$ 275
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Revenues												17	509	218		$ 56
Investment in CENG												1,900
Accumulated other comprehensive loss, net												$ 116
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Due from affiliates	$ 400			$ 300									300					$ 300
Interest rate on loan to CENG	5.25%
Allocation of federal tax benefit under tax sharing agreement	$ 152
Reduction to net income attributable to noncontrolling interest													18	13
Net Income (Loss) Attributable to Parent													(11)	407
Business Combination, Integration Related Costs													2	26
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member] | Payment Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Due to affiliate	$ 205
Exelon Generation Co L L C [Member] | EDFI [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Operating revenues from affiliates													$ 488	$ 137
Electricite De France LLC [Member]
Schedule of Equity Method Investments [Line Items]
Required purchases of power from CENG's nuclear plants not sold to third parties	15.00%
Subsequent purchases of power from CENG's nuclear plants not sold to third parties													49.99%
Electricite De France LLC [Member] | Constellation Energy Nuclear Group [Member] | Financial Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Guarantee obligations maximum exposure	$ 145
Constellation Energy Group LLC [Member]
Schedule of Equity Method Investments [Line Items]
Interest rate on distribution	8.50%
Constellation Energy Group LLC [Member] | EDFI [Member]
Schedule of Equity Method Investments [Line Items]
Cash distribution paid to member	$ 400

[1] All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.