Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 Years		Dec. 31, 2010		Dec. 31, 2009
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	$ 783,000,000	[1]	$ 861,000,000	[1]	$ 786,000,000	[1]
Capitalized interest	49,000,000		38,000,000		50,000,000
Credits to AFUDC debt and equity	25,000,000		16,000,000		14,000,000
Capitalized Software [Line Items]
Net unamortized software costs	280,000,000		312,000,000
Amortization of capitalized software costs	122,000,000		104,000,000		105,000,000
Consolidation Percentages Detail Tagging [Abstract]
Percentage ownership of consolidated subsidiaries	100.00%
Exelon Percentage ownership of Exelon SHC, LLC	1.00%
Generation, ComEd, PECO Percentage ownership in transmission company	12.50%
Percentage ownership of ComEd's common stock	99.00%
Percentage ownership of PECO's common stock	100.00%
Third-party monetary interest in subsidiaries	1,000,000
Third-party percentage interest in subsidiaries	12.50%
Minimum voting interest needed for a controlling financial interest	50.00%
Variable Interest Entities Detail Tagging [Abstract]
Tax benefit recognition threshold	50.00%
New Site Development Costs [Abstract]
Capitalized development costs	376,000,000		20,000,000
Development costs expensed	2,000,000		6,000,000		23,000,000
Asset Retirement Obligations Policies [Abstract]
Number of years between decommissioning cost studies	5
Exelon Generation Co L L C [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	219,000,000	[1]	191,000,000	[1]	162,000,000	[1]
Capitalized interest	49,000,000		38,000,000		49,000,000
Credits to AFUDC debt and equity	0		0		0
Capitalized Software [Line Items]
Net unamortized software costs	82,000,000		92,000,000
Amortization of capitalized software costs	41,000,000		33,000,000		24,000,000
Consolidation Percentages Detail Tagging [Abstract]
Percentage ownership of consolidated subsidiaries	100.00%
Generation, ComEd, PECO Percentage ownership in transmission company	99.00%
Ownership Interest Upper Bound	99.00%
Ownership Interest Lower Bound	94.00%
Variable Interest Entities Detail Tagging [Abstract]
Percentage ownership of JDR Projects	100.00%
Number of Exelon Wind projects with noncontrolling interest	12
Projects with significant economic power	9
Minimum minority interest percentage held by noncontrolling shareholders	1.00%
Maximum minority interest percentage held by noncontrolling shareholders	6.00%
Nuclear Fuel [Abstract]
Cost of spent nuclear fuel disposal per kWh of net nuclear generation	0.001
Commonwealth Edison Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	349,000,000	[1]	388,000,000	[1]	322,000,000	[1]
Capitalized interest	0		0		0
Credits to AFUDC debt and equity	12,000,000		5,000,000		8,000,000
Capitalized Software [Line Items]
Net unamortized software costs	120,000,000		143,000,000
Amortization of capitalized software costs	50,000,000		41,000,000		29,000,000
Consolidation Percentages Detail Tagging [Abstract]
Percentage ownership of consolidated subsidiaries	100.00%
Generation, ComEd, PECO Percentage ownership in transmission company	75.00%
Third-party monetary interest in subsidiaries	1,000,000
Third-party percentage interest in subsidiaries	25.00%
PECO Energy Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	138,000,000	[1]	197,000,000	[1]	189,000,000	[1]
Capitalized interest	0		0		0
Credits to AFUDC debt and equity	13,000,000		11,000,000		6,000,000
Capitalized Software [Line Items]
Net unamortized software costs	67,000,000		64,000,000
Amortization of capitalized software costs	25,000,000		19,000,000		15,000,000
Variable Interest Entities Detail Tagging [Abstract]
Amount of PECO's stranded costs authorized to be recovered by the PAPUC	5,000,000,000
Initial capital contribution in PETT	$ 25,000,000

[1] Includes interest expense to affiliates.