Supplemental Financial Information - Summary of Depreciation, Amortization, Accretion and Depletion (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment	$ 2,080		$ 1,893		$ 1,712
Regulatory assets	191		212		129
Amortization of intangible assets, net	44		48		40
Amortization of Intangible Assets	179	[1]	478	[1]	1,150	[1]
Nuclear fuel	1,073	[2]	921	[2]	848	[2]
ARO accretion	345	[3]	275	[3]	240	[3]
Total depreciation, amortization, accretion and depletion	3,868		3,779		4,079
Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment	922		813		733
Regulatory assets	0		0		0
Amortization of intangible assets, net	44		43		35
Amortization of Intangible Assets	179	[1]	550	[1]	1,145	[1]
Nuclear fuel	1,073	[2]	921	[2]	848	[2]
ARO accretion	345	[3]	275	[3]	240	[3]
Total depreciation, amortization, accretion and depletion	2,519		2,559		2,966
Commonwealth Edison Company [Member]
Supplemental Financial Information Tables [Line Items]
Energy Contract Amortization	0	[4]
Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment	588		545		525
Regulatory assets	99		119		80
Amortization of intangible assets, net	0		5		5
Amortization of Intangible Assets	7		7		7
Energy Contract Amortization			0	[4]	0	[4]
Nuclear fuel	0	[2]	0	[2]	0	[2]
ARO accretion	0	[3]	0	[3]	0	[3]
Total depreciation, amortization, accretion and depletion	687		669		610
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment	227		219		207
Regulatory assets	9		9		10
Amortization of intangible assets, net	0		0		0
Amortization of Intangible Assets	0	[4]	0	[4]	0	[4]
Nuclear fuel	0	[2]	0	[2]	0	[2]
ARO accretion	0	[3]	0	[3]	0	[3]
Total depreciation, amortization, accretion and depletion	236		228		217
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment	288		264		245
Regulatory assets	83		84		53
Amortization of intangible assets, net	0		0		0
Amortization of Intangible Assets	0	[4]	0	[4]	0	[4]
Nuclear fuel	0	[2]	0	[2]	0	[2]
ARO accretion	0	[3]	0	[3]	0	[3]
Total depreciation, amortization, accretion and depletion	371		348		298
Unamortized Energy Contracts [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	135	[5],[6]	430	[5],[6]	1,110	[5],[6]
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	$ 135	[5],[6]	$ 507	[5],[6]	$ 1,110	[4]

[1] At Exelon, amortization of unamortized energy contracts totaling $135 million, $430 million and $1,110 million for the years ended December 31, 2014, 2013 and 2012, respectively, was recorded in Purchase power and fuel expense or Operating revenues within Exelon’s Consolidated Statement of Operations and Comprehensive Income. At Generation, amortization of unamortized energy contracts totaling $135 million, $507 million and $1,110 million for the years ended December 31, 2014, 2013 and 2012, respectively, was recorded in Purchase power and fuel expense or Operating revenues within Generation’s Consolidated Statement of Operations and Comprehensive Income

[2] Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[3] Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[4] Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[5] Includes unamortized energy contract assets and liabilities on Exelon's and Generation's Consolidated Balance Sheets. Excludes $26 million of other miscellaneous unamortized energy contracts that have been acquired at various points in time. The estimated amortization for these miscellaneous unamortized energy contracts is $4 million, $3 million, $0 million, $2 million and $2 million for 2015, 2016, 2017, 2018 and 2019, respectively.

[6] In March 1999, ComEd entered into a settlement agreement with the City of Chicago associated with ComEd’s franchise agreement. Under the terms of the settlement, ComEd agreed to make payments to the City of Chicago each year from 1999 to 2002. The intangible asset recognized as a result of these payments is being amortized ratably over the remaining term of the franchise agreement, which ends in 2020.