Investment in Constellation Energy Nuclear Group LLC - Narrative (Details) - USD ($)		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Apr. 01, 2014
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 53,000,000
Revenues		7,573,000,000	$ 8,830,000,000
Accumulated other comprehensive loss, net	[1]	(2,596,000,000)	(2,673,000,000)	$ (2,624,000,000)	$ (2,684,000,000)
Other Comprehensive Income (Loss), Tax		(17,000,000)	(12,000,000)
Guarantor Obligations, Current Carrying Value		75,000,000
Business Combination, Integration Related Costs		$ 102,000,000	108,000,000
Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		50.01%
Payments of Distributions to Affiliates		$ 55,000,000	1,356,000,000
Related Party Purchase Of Nuclear Output By Third Party Percentage		49.99%
Total equity investment earnings (losses) - CENG			(19,000,000)
Revenues		$ 4,739,000,000	5,840,000,000
Accumulated other comprehensive loss, net	[1]	(64,000,000)	(53,000,000)	$ (63,000,000)	$ (36,000,000)
Other Comprehensive Income (Loss), Tax		$ 4,000,000	5,000,000
Related Party Transaction Required Purchase Of Power Percentage		85.00%
Revenue from Related Parties		$ 268,000,000	211,000,000
Business Combination, Integration Related Costs		16,000,000	7,000,000
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Revenues		$ 306,000,000	17,000,000
Investment in CENG			1,900,000,000
Other Comprehensive Income (Loss), Tax			$ 77,000,000
Electricite De France LLC [Member]
Schedule of Equity Method Investments [Line Items]
Related Party Transaction Required Purchase Of Power Percentage		15.00%
Constellation Energy Nuclear Group [Member] | Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Due from Affiliates		$ 304,000,000				$ 400,000,000
Net Income (Loss) Attributable to Parent		93,000,000
Payment Guarantee [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Payables to affiliates						245,000,000
Financial Guarantee [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted						$ 165,000,000
Variable Interest Entity, Primary Beneficiary [Member]
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Current Carrying Value		275,000,000
Variable Interest Entity, Primary Beneficiary [Member] | Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Current Carrying Value		$ 7,000,000

[1] All amounts are net of tax. Amounts in parenthesis represent a decrease in AOCI.