Investment in Constellation Energy Nuclear Group LLC - Narrative (Details) (USD $)	3 Months Ended				9 Months Ended										3 Months Ended					9 Months Ended								3 Months Ended			9 Months Ended				3 Months Ended	9 Months Ended		3 Months Ended	9 Months Ended	0 Months Ended					0 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Aug. 18, 2014	Dec. 31, 2013		Dec. 31, 2012		Sep. 30, 2014 Constellation Energy Nuclear Group [Member]	Sep. 30, 2014 Exelon Generation Co L L C [Member]		Mar. 31, 2014 Exelon Generation Co L L C [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member]		Sep. 30, 2014 Exelon Generation Co L L C [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member]		Dec. 31, 2013 Exelon Generation Co L L C [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member]		Sep. 30, 2014 Exelon Generation Co L L C [Member] Constellation Energy Nuclear Group [Member]	Mar. 31, 2014 Exelon Generation Co L L C [Member] Constellation Energy Nuclear Group [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Constellation Energy Nuclear Group [Member]	Sep. 30, 2014 Exelon Generation Co L L C [Member] Constellation Energy Nuclear Group [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Constellation Energy Nuclear Group [Member]	Sep. 30, 2014 Electricite De France LLC [Member]	Apr. 01, 2014 Constellation Energy Group LLC [Member]	Sep. 30, 2014 Constellation Energy Nuclear Group [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 Constellation Energy Nuclear Group [Member] Exelon Generation Co L L C [Member]	Apr. 01, 2014 Constellation Energy Nuclear Group [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 EDFI [Member] Exelon Generation Co L L C [Member] Constellation Energy Nuclear Group [Member]	Sep. 30, 2014 EDFI [Member] Exelon Generation Co L L C [Member] Constellation Energy Nuclear Group [Member]	Apr. 01, 2014 EDFI [Member] Constellation Energy Group LLC [Member]	Apr. 01, 2014 Payment Guarantee [Member] Constellation Energy Nuclear Group [Member]	Apr. 01, 2014 Payment Guarantee [Member] Constellation Energy Nuclear Group [Member] Exelon Generation Co L L C [Member]	Apr. 01, 2014 Financial Guarantee [Member] Constellation Energy Nuclear Group [Member]	Apr. 01, 2014 Financial Guarantee [Member] Constellation Energy Nuclear Group [Member] Electricite De France LLC [Member]	Apr. 01, 2014 Variable Interest Entity, Primary Beneficiary [Member] Exelon Generation Co L L C [Member]	Apr. 01, 2014 Variable Interest Entity, Primary Beneficiary [Member] Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage									67.00%								50.01%
Due from Affiliates																																					$ 400,000,000
Interest rate on loan to CENG																																					5.25%
Payments of Distributions to Affiliates																				440,000,000		550,000,000																		400,000,000
Reduction To Net Income Attributable To Noncontrolling Interest																																			4,000,000	8,000,000
Interest Rate On Distribution																																		8.50%
Related Party Purchase Of Nuclear Output By Third Party Percentage																				49.99%
Payables to affiliates															124,000,000					124,000,000				181,000,000																	245,000,000	205,000,000
Guarantor Obligations, Maximum Exposure, Undiscounted	9,542,000,000				9,542,000,000										6,136,000,000					6,136,000,000																							165,000,000	145,000,000
Total equity investment earnings (losses) - CENG																	(19,000,000)	37,000,000				5,000,000
Revenues	6,912,000,000	[1]	6,502,000,000	[1]	20,173,000,000	[2]	18,725,000,000	[2]							4,412,000,000			4,255,000,000		12,591,000,000		11,858,000,000						58,000,000	17,000,000	12,000,000	155,000,000	45,000,000
Investment in CENG	0				0					1,925,000,000					0					0				1,925,000,000					1,900,000,000
Accumulated other comprehensive loss, net	(1,917,000,000)	[3]	(2,661,000,000)	[3]	(1,917,000,000)	[3]	(2,661,000,000)	[3]		(2,040,000,000)	[3]	(2,767,000,000)	[3]	1,500,000,000	11,000,000	[3]		243,000,000	[3]	11,000,000	[3]	243,000,000	[3]	214,000,000	[3]	513,000,000	[3]		116,000,000
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement																																			152,000,000	152,000,000
Other Comprehensive Income (Loss), Tax	8,000,000		1,000,000		(77,000,000)		70,000,000								17,000,000			(27,000,000)		129,000,000		(177,000,000)							77,000,000
Related Party Transaction Required Purchase Of Power Percentage																				85.00%													15.00%
Revenue from Related Parties	0	[4]	2,000,000	[4]	0	[5]	2,000,000	[5]							112,000,000			384,000,000		647,000,000		1,129,000,000																52,000,000	90,000,000
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain																																													261,000,000
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value																																													136,000,000
Business Acquisition, Preexisting Relationship, Gain (Loss) Recognized																																														132,000,000
Guarantor Obligations, Current Carrying Value	75,000,000				75,000,000										4,000,000					4,000,000																										7,000,000
Net Income (Loss) Attributable to Parent																																			171,000,000	248,000,000
Business Combination, Integration Related Costs																																			$ 4,000,000	$ 22,000,000

[1] For the three months ended September 30, 2014 and 2013, utility taxes of $22 million and $21 million, respectively, are included in revenues and expenses for Generation. For the three months ended September 30, 2014 and 2013, utility taxes of $61 million and $65 million, respectively, are included in revenues and expenses for ComEd. For the three months ended September 30, 2014 and 2013, utility taxes of $34 million and $33 million, respectively, are included in revenues and expenses for PECO. For the three months ended September 30, 2014 and 2013, utility taxes of $21 million and $20 million, respectively, are included in revenues and expenses for BGE.

[2] For the nine months ended September 30, 2014 and 2013, utility taxes of $67 million and $60 million, respectively, are included in revenues and expenses for Generation. For the nine months ended September 30, 2014 and 2013, utility taxes of $180 million and $182 million, respectively, are included in revenues and expenses for ComEd. For the nine months ended September 30, 2014 and 2013, utility taxes of $99 million and $97 million, respectively, are included in revenues and expenses for PECO. For the nine months ended September 30, 2014 and 2013, utility taxes of $64 million and $62 million, respectively, are included in revenues and expenses for BGE.

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

[4] 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.

[5] Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with the 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.