Asset Retirement Obligation (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011		Feb. 29, 2012	Dec. 31, 2011
Nuclear Decommissioning Asset Retirement Obligations [Abstract]
Net adjustment to nuclear ARO	$ 80,000,000				$ 80,000,000
Net increase (decrease) due to changes in estimated future cash flows					80,000,000
Zion Station Decommissioning [Abstract]
Zion Station spent nuclear fuel obligation	67,000,000				67,000,000
Pledged assets for Zion Station decommissioning	650,000,000				650,000,000					734,000,000
Total payable to ZionSolutions	604,000,000				604,000,000
Nuclear Decommissioning Trust Fund Investments [Abstract]
NDT fund investments	6,841,000,000				6,841,000,000					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					111,000,000
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	3,870,000,000	[1]			3,870,000,000	[1]
Footnotes To Nuclear Decommissioning Asset Retirement Obligation [Abstract]
Current Portion of ARO	6,000,000				6,000,000					5,000,000
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - Regulatory Agreement Units	(96,000,000)	[2]	28,000,000	[2]	150,000,000	[2]	140,000,000	[2]
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units	(35,000,000)	[3],[4]	11,000,000	[3],[4]	30,000,000	[3],[4]	54,000,000	[3],[4]
Footnotes To Unrealized Gains Losses On NDT Funds [Abstract]
Gains on Zion Station Pledged Assets	4,000,000		22,000,000		38,000,000		45,000,000
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Asset Retirement Obligations [Abstract]
Net adjustment to nuclear ARO	80,000,000				80,000,000
Net increase (decrease) due to changes in estimated future cash flows					80,000,000
Zion Station Decommissioning [Abstract]
Zion Station spent nuclear fuel obligation	67,000,000				67,000,000
Pledged assets for Zion Station decommissioning	650,000,000				650,000,000					734,000,000
Total payable to ZionSolutions	604,000,000				604,000,000
Current payable to ZionSolutions	141,000,000				141,000,000					128,000,000
Nuclear Decommissioning Trust Fund Investments [Abstract]
NDT fund investments	6,841,000,000				6,841,000,000					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					111,000,000
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	3,870,000,000	[1]			3,870,000,000	[1]
Footnotes To Nuclear Decommissioning Asset Retirement Obligation [Abstract]
Current Portion of ARO	6,000,000				6,000,000					5,000,000
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - Regulatory Agreement Units	(96,000,000)	[2]	28,000,000	[2]	150,000,000	[2]	140,000,000	[2]
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units	(35,000,000)	[3],[4]	11,000,000	[3],[4]	30,000,000	[3],[4]	54,000,000	[3],[4]
Footnotes To Unrealized Gains Losses On NDT Funds [Abstract]
Gains on Zion Station Pledged Assets	$ 4,000,000		$ 22,000,000		$ 38,000,000		$ 45,000,000

[1] Includes $6 million and $5 million as the current portion of the ARO at June 30, 2012 and December 31, 2011, respectively, which is included in other current liabilities on Exelon's and Generation's Consolidated Balance Sheets.

[2] Net unrealized gains (losses) 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] Net unrealized gains (losses) 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.

[4] Excludes $4 million and $22 million of net unrealized gains related to the Zion Station pledged assets for the three months ended June 30, 2012 and 2011, respectively, and $38 million and $45 million of net unrealized gains related to the Zion Station pledged assets for the six months ended June 30, 2012 and 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.