Investment in Constellation Energy Nuclear Group LLC - Narrative (Details) - USD ($)		3 Months Ended				6 Months Ended
		Jun. 30, 2015		Jun. 30, 2014		Jun. 30, 2015		Jun. 30, 2014		Jun. 09, 2015	Dec. 31, 2014	Apr. 01, 2014	Mar. 31, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 10,509,000,000				$ 10,509,000,000
Revenues		6,514,000,000	[1]	$ 6,024,000,000	[1]	15,345,000,000	[2]	$ 13,261,000,000	[2]
Accumulated other comprehensive loss, net	[3]	(2,626,000,000)		(1,906,000,000)		(2,626,000,000)		(1,906,000,000)			$ (2,684,000,000)			$ (2,040,000,000)
Other Comprehensive Income (Loss), Tax		(28,000,000)		(79,000,000)		(42,000,000)		(82,000,000)
Revenue from Related Parties		1,000,000	[4]	0	[4]	3,000,000		0
Guarantor Obligations, Current Carrying Value		75,000,000				75,000,000
Business Combination, Integration Related Costs						89,000,000
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						$ 2,262,000,000		235,000,000
Related Party Purchase Of Nuclear Output By Third Party Percentage						49.99%
Payables to affiliates		98,000,000				$ 98,000,000					107,000,000
Guarantor Obligations, Maximum Exposure, Undiscounted		7,674,000,000				7,674,000,000
Total equity investment earnings (losses) - CENG								19,000,000
Revenues		4,232,000,000		3,789,000,000		10,074,000,000		8,179,000,000
Accumulated other comprehensive loss, net	[3]	(47,000,000)		37,000,000		(47,000,000)		37,000,000			$ (36,000,000)			$ 214,000,000
Other Comprehensive Income (Loss), Tax		(1,000,000)		102,000,000		$ 2,000,000		112,000,000
Related Party Transaction Required Purchase Of Power Percentage						85.00%
Revenue from Related Parties		153,000,000		$ 201,000,000		$ 365,000,000		535,000,000
Guarantor Obligations, Current Carrying Value		8,000,000				8,000,000
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Revenues		109,000,000				$ 306,000,000		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				$ 288,000,000						$ 400,000,000
Reduction To Net Income Attributable To Noncontrolling Interest		4,000,000				9,000,000
Net Income (Loss) Attributable to Parent		(4,000,000)				93,000,000
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		$ 106,000,000				$ 288,000,000
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										$ 275,000,000		$ 7,000,000

[1] (c)For the three months ended June 30, 2015 and 2014, utility taxes of $24 million and $21 million, respectively, are included in revenues and expenses for Generation. For the three months ended June 30, 2015 and 2014, utility taxes of $55 million and $56 million, respectively, are included in revenues and expenses for ComEd. For the three months ended June 30, 2015 and 2014, utility taxes of $32 million and $30 million, respectively, are included in revenues and expenses for PECO. For the three months ended June 30, 2015 and 2014, utility taxes of $21 million and $19 million, respectively, are included in revenues and expenses for BGE.

[2] (d)Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.

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

[4] (d)Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.