Investment in Constellation Energy Nuclear Group LLC - Narrative (Details) (USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014		Dec. 31, 2013		Apr. 01, 2014
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 10,267,000,000
Revenues	8,830,000,000	[1]	7,237,000,000	[1]
Accumulated other comprehensive loss, net	(2,673,000,000)	[2]	(2,036,000,000)	[2]	(2,684,000,000)	[2]	(2,040,000,000)	[2]
Other Comprehensive Income (Loss), Tax	(12,000,000)		(6,000,000)
Revenue from Related Parties	1,000,000	[3]	1,000,000	[3]
Guarantor Obligations, Current Carrying Value	75,000,000
Business Combination, Integration Related Costs	69,000,000
Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage			50.01%
Interest Rate	3.71%
Payments of Distributions to Affiliates	1,356,000,000		30,000,000
Related Party Purchase Of Nuclear Output By Third Party Percentage	49.99%
Payables to affiliates	110,000,000				107,000,000
Guarantor Obligations, Maximum Exposure, Undiscounted	7,365,000,000
Total equity investment earnings (losses) - CENG			19,000,000
Revenues	5,840,000,000		4,390,000,000
Accumulated other comprehensive loss, net	(53,000,000)	[2]	193,000,000	[2]	(36,000,000)	[2]	214,000,000	[2]
Other Comprehensive Income (Loss), Tax	5,000,000		10,000,000
Related Party Transaction Required Purchase Of Power Percentage	85.00%
Revenue from Related Parties	211,000,000		334,000,000
Guarantor Obligations, Current Carrying Value	7,000,000
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Revenues	197,000,000		17,000,000
Investment in CENG			1,900,000,000
Accumulated other comprehensive loss, net			116,000,000
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	288,000,000								400,000,000
Reduction To Net Income Attributable To Noncontrolling Interest	4,000,000
Net Income (Loss) Attributable to Parent	98,000,000
EDFI [Member] | Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Revenue from Related Parties	182,000,000
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] | Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Current Carrying Value									$ 7,000,000

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

[3] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246NzEwQ0VGNzJGQTI1RkM2RDgzOUMwOTNBRjYwNUU2MTQM}