Asset Retirement Obligation (Details) (USD $)	3 Months Ended			12 Months Ended
	Mar. 31, 2012		Mar. 31, 2011	Dec. 31, 2011		Feb. 29, 2012
Nuclear Decommissioning Asset Retirement Obligations [Abstract]
Net adjustment to nuclear ARO	$ 134,000,000
Net increase (decrease) due to changes in estimated future cash flows	80,000,000
Zion Station Decommissioning [Abstract]
Zion Station spent nuclear fuel obligation	66,000,000
Pledged assets for Zion Station decommissioning	708,000,000			734,000,000
Total payable to ZionSolutions	660,000,000
Current payable to ZionSolutions	86,000,000			128,000,000
Nuclear Decommissioning Trust Fund Investments [Abstract]
NDT fund investments	6,927,000,000			6,507,000,000
NRC Minimum Funding Requirements [Abstract]
NRC funding assurance parent guarantees						115,000,000
Nuclear Decommissioning Asset Retirement Obligation Rollforward [Abstract]
Nuclear decommissioning ARO beginning balance	3,680,000,000	[1]
Accretion expense	55,000,000
Net increase (decrease) due to changes in estimated future cash flows	80,000,000
Costs incurred to decommission retired plants	(1,000,000)
Nuclear decommissioning ARO ending balance	3,814,000,000	[1]		3,680,000,000	[1]
Footnotes To Nuclear Decommissioning Asset Retirement Obligation [Abstract]
Current Portion of ARO	5,000,000			5,000,000
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - Regulatory Agreement Units	246,647,882	[2]		111,000,000	[2]
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units	65,374,958	[3],[4]		43,000,000	[3],[4]
Footnotes To Unrealized Gains Losses On NDT Funds [Abstract]
Gains on Zion Station Pledged Assets	35,000,000		23,000,000
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Asset Retirement Obligations [Abstract]
Net adjustment to nuclear ARO	134,000,000
Net increase (decrease) due to changes in estimated future cash flows	80,000,000
Zion Station Decommissioning [Abstract]
Zion Station spent nuclear fuel obligation	66,000,000
Pledged assets for Zion Station decommissioning	708,000,000			734,000,000
Total payable to ZionSolutions	660,000,000
Current payable to ZionSolutions	86,000,000			128,000,000
Nuclear Decommissioning Trust Fund Investments [Abstract]
NDT fund investments	6,927,000,000			6,507,000,000
NRC Minimum Funding Requirements [Abstract]
NRC funding assurance parent guarantees						115,000,000
Nuclear Decommissioning Asset Retirement Obligation Rollforward [Abstract]
Nuclear decommissioning ARO beginning balance	3,680,000,000	[1]
Accretion expense	55,000,000
Net increase (decrease) due to changes in estimated future cash flows	80,000,000
Costs incurred to decommission retired plants	(1,000,000)
Nuclear decommissioning ARO ending balance	3,814,000,000	[1]		3,680,000,000	[1]
Footnotes To Nuclear Decommissioning Asset Retirement Obligation [Abstract]
Current Portion of ARO	5,000,000			5,000,000
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - Regulatory Agreement Units	246,647,882	[2]		111,000,000	[2]
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units	65,374,958	[3],[4]		43,000,000	[3],[4]
Footnotes To Unrealized Gains Losses On NDT Funds [Abstract]
Gains on Zion Station Pledged Assets	$ 35,000,000		$ 23,000,000

[1] Includes $5 million as the current portion of the ARO at March 31, 2012 and December 31, 2011, which is included in other current liabilities on Exelon's and Generation's Consolidated Balance Sheets.

[2] Net unrealized gains related to Generation's NDT funds associated with Regulatory Agreement Units are included in regulatory liabilities on Exelon's Consolidated Balance Sheets and noncurrent payables to affiliates on Generation's Consolidated Balance Sheets.

[3] Excludes $35 million and $23 million of net unrealized gains related to the Zion Station pledged assets for the three months ended March 31, 2012 and March 31, 2011, respectively. Net unrealized gains related to Zion Station pledged assets are included in the payable for Zion Station decommissioning on Exelon's and Generation's Consolidated Balance Sheets.

[4] Net unrealized gains related to Generation's NDT funds associated with Non-Regulatory Agreement Units are included within Other, net in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income.