Nuclear Decommissioning (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Nuclear Decommissioning Asset Retirement Obligations [Abstract]
Net adjustment to nuclear ARO	$ 16,000,000
Net increase (decrease) due to changes in estimated future cash flows	198,000,000		624,000,000
Zion Station Decommissioning [Abstract]
Pledged assets for Zion Station decommissioning	734,000,000		824,000,000
ZionSolutions rent payable	1
EnergySolutions letter of credit	200,000,000
Securities Lending Program [Abstract]
Percentage of collateral for borrowed securities in domestic currency	102.00%
Percentage of collateral for borrowed securities in foreign currency	105.00%
Percentage of collateral for borrowed securities required levels	100.00%
Fair value of securities on loan	17,000,000		46,000,000
Fair value of cash and non-cash collateral received for loan securities	17,000,000		47,000,000
NRC Minimum Funding Requirements [Abstract]
Assumed annual after-tax return on NDT funds	2.00%
Assumed annual after-tax return on NDT funds for former PECO units	3.00%
Historical five-year annual average after-tax return on NDT funds	3.60%
Nuclear Decommissioning Trust Fund Investments [Abstract]
NDT fund investments	6,507,000,000		6,408,000,000
Nuclear Decommissioning Asset Retirement Obligation [Abstract]
Nuclear decommissioning ARO beginning balance	3,276,000,000	[1]	3,260,000,000
Accretion expense	(209,000,000)		(191,000,000)
Net increase (decrease) due to changes in estimated future cash flows	198,000,000		624,000,000
Extinguishment of Zion Station ARO			(768,000,000)
Costs incurred to decommission retired plants	(3,000,000)		(31,000,000)
Nuclear decommissioning ARO ending balance	3,680,000,000	[1]	3,276,000,000	[1]	3,260,000,000
Footnotes To Nuclear Decommissioning Asset Retirement Obligation [Abstract]
Current Portion of ARO	5,000,000
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - Regulatory Agreement Units	(74,000,000)	[2],[3]	294,000,000	[2],[3]	799,000,000	[2],[3]
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units	(4,000,000)	[4]	104,000,000	[4]	227,000,000	[4]
Footnotes To Unrealized Gains Losses On NDT Funds [Abstract]
Gains on Zion Station Pledged Assets	20,000,000
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Asset Retirement Obligations [Abstract]
Net adjustment to nuclear ARO	16,000,000
Net increase (decrease) due to changes in estimated future cash flows	198,000,000		624,000,000
Resulting pre-tax income (loss) from nuclear ARO adjustment	(28,000,000)
Zion Station Decommissioning [Abstract]
Zion Station spent nuclear fuel obligation	65,000,000		34,000,000
Pledged assets for Zion Station decommissioning	734,000,000		824,000,000
Total payable to ZionSolutions	691,000,000		786,000,000
ZionSolutions rent payable	1
EnergySolutions letter of credit	200,000,000
Securities Lending Program [Abstract]
Percentage of collateral for borrowed securities in domestic currency	102.00%
Percentage of collateral for borrowed securities in foreign currency	105.00%
Percentage of collateral for borrowed securities required levels	100.00%
Fair value of securities on loan			51,000,000
Fair value of cash and non-cash collateral received for loan securities			51,000,000
NRC Minimum Funding Requirements [Abstract]
Assumed annual after-tax return on NDT funds	2.00%
Assumed annual after-tax return on NDT funds for former PECO units	3.00%
Annual average accretion of the ARO	6.10%
Estimated annual after-tax return on NDT funds lower bound	5.60%
Estimated annual after-tax return on NDT funds upper bound	6.70%
Historical five-year annual average after-tax return on NDT funds	3.60%
Nuclear Decommissioning Trust Fund Investments [Abstract]
NDT fund investments	6,507,000,000		6,408,000,000
Nuclear Decommissioning Asset Retirement Obligation [Abstract]
Nuclear decommissioning ARO beginning balance	3,276,000,000	[1]	3,260,000,000
Accretion expense	(209,000,000)		(191,000,000)
Net increase (decrease) due to changes in estimated future cash flows	198,000,000		624,000,000
Extinguishment of Zion Station ARO			(768,000,000)
Costs incurred to decommission retired plants	(3,000,000)		(31,000,000)
Nuclear decommissioning ARO ending balance	3,680,000,000	[1]	3,276,000,000	[1]	3,260,000,000
Footnotes To Nuclear Decommissioning Asset Retirement Obligation [Abstract]
Current Portion of ARO	5,000,000
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - Regulatory Agreement Units	(74,000,000)	[2],[3]	294,000,000	[2],[3]	799,000,000	[2],[3]
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units	(4,000,000)	[4]	104,000,000	[4]	227,000,000	[4]
Footnotes To Unrealized Gains Losses On NDT Funds [Abstract]
Gains on Zion Station Pledged Assets	$ 48,014,336.42		$ 20,000,000

[1] (a) Includes $ 5 million as the current portion of the ARO at December 31, 2011 and 2010, which is included in other current liabilities on Exelon's and Generation's Consolidated Balance Sheets.

[2] 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 $48 million and $20 million of gains related to the Zion Station pledged assets in 2011 and 2010. 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] 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.