Investment in Constellation Energy Nuclear Group, LLC - Narrative (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended									12 Months Ended
	Apr. 01, 2014	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Purchase of nuclear output by EDF											49.99%
Guarantee obligations maximum exposure		$ 9,402									$ 9,402
Revenues		7,255	6,912	6,024	7,237	6,163		6,502	6,141	6,082	27,429	[1]	24,888	[1]	23,489	[1]
Investment in CENG		0				1,925					0		1,925
Accumulated other comprehensive loss, net		(2,684)				(2,040)	[2]				(2,684)		(2,040)	[2]	(2,767)	[2]
Required purchases of power from CENG's nuclear plants not sold to third parties											85.00%
Operating revenues from affiliates											23		70		48
Parental guarantee provided		75									75
Business Combination, Integration Related Costs											19		28
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%
Cash distribution paid to member											645		625		1,626
Purchase of nuclear output by EDF	49.99%
Guarantee obligations maximum exposure		6,384									6,384
Total equity investment earnings (losses) - CENG					19								9
Revenues		4,802	4,412	3,789	4,390	3,772		4,255	4,070	3,533	17,393		15,630		14,437
Investment in CENG		0				1,925					0		1,925
Accumulated other comprehensive loss, net		(36)				214	[2]				(36)		214	[2]	513	[2]
Allocation of federal tax benefit under tax sharing agreement					77	26							26
Required purchases of power from CENG's nuclear plants not sold to third parties	85.00%										85.00%
Subsequent purchases of power from CENG's nuclear plants not sold to third parties	50.01%
Operating revenues from affiliates											779		1,423		1,702
Parental guarantee provided		5									5
Business Combination, Integration Related Costs		19
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
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Revenues					17						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	400									400
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											13
Net Income (Loss) Attributable to Parent											407
Business Combination, Integration Related Costs											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											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] For the years ended December 31, 2014, 2013 and 2012, utility taxes of $89 million, $79 million and $82 million, respectively, are included in revenues and expenses for Generation. For the years ended December 31, 2014, 2013 and 2012, utility taxes of $238 million, $241 million and $239 million, respectively, are included in revenues and expenses for ComEd. For the years ended December 31, 2014, 2013 and 2012, utility taxes of $128 million, $129 million and $141 million, respectively, are included in revenues and expenses for PECO. For the years ended December 31, 2014, December 31, 2013 and for the period of March 12, 2012 through December 31, 2012, utility taxes of $86 million, $82 million and $59 million are included in revenues and expenses for BGE, respectively.

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