Nuclear Decommissioning (Details) (USD $)	0 Months Ended	3 Months Ended				9 Months Ended
	Mar. 30, 2012	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Feb. 29, 2012	Dec. 31, 2011
Nuclear Decommissioning Asset Retirement Obligations [Abstract]
Increase (Decrease) adjustment to nuclear ARO		$ 176,000,000				$ 916,000,000
Increase in estimated cash flows associated with Zion Station decommissioning		28,000,000				10,000,000
Nuclear Decommissioning Trust Fund Investments [Abstract]
NDT fund investments		7,140,000,000				7,140,000,000					6,507,000,000
Proposed annual recovery of decommissioning costs	24,000,000
Current annual recovery of decommissioning costs	29,000,000
Zion Station Decommissioning [Abstract]
Zion Station spent nuclear fuel obligation		78,000,000				78,000,000
Pledged assets for Zion Station decommissioning		631,000,000				631,000,000					734,000,000
Total payable to ZionSolutions		582,000,000				582,000,000
Current payable to ZionSolutions		160,000,000				160,000,000					128,000,000
NRC Minimum Funding Requirements [Abstract]
NRC funding assurance parent guarantees										115,000,000
Nuclear Decommissioning Asset Retirement Obligation [Abstract]
Nuclear decommissioning ARO beginning balance						3,680,000,000	[1]
Accretion Expense						169,000,000
Net increase (decrease) due to changes in estimated future cash flows						749,000,000
Costs incurred to decommission retired plants						(2,000,000)
Nuclear decommissioning ARO ending balance		4,596,000,000	[1]			4,596,000,000	[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		202,000,000	[2]	(363,000,000)	[2]	352,000,000	[2]	(223,000,000)	[2]
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units		71,000,000	[3],[4]	(141,000,000)	[3],[4]	101,000,000	[3],[4]	(88,000,000)	[3],[4]
Footnotes To Unrealized Gains Losses On NDT Funds [Abstract]
Gains on Zion Station Pledged Assets		22,000,000		4,000,000		60,000,000		41,000,000
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Asset Retirement Obligations [Abstract]
Increase (Decrease) adjustment to nuclear ARO		176,000,000				916,000,000
Increase in estimated cash flows associated with Zion Station decommissioning		28,000,000				10,000,000
Nuclear Decommissioning Trust Fund Investments [Abstract]
NDT fund investments		7,140,000,000				7,140,000,000					6,507,000,000
Zion Station Decommissioning [Abstract]
Zion Station spent nuclear fuel obligation		78,000,000				78,000,000
Pledged assets for Zion Station decommissioning		631,000,000				631,000,000					734,000,000
Total payable to ZionSolutions		582,000,000				582,000,000
Current payable to ZionSolutions		160,000,000				160,000,000					128,000,000
NRC Minimum Funding Requirements [Abstract]
NRC funding assurance parent guarantees										115,000,000
Nuclear Decommissioning Asset Retirement Obligation [Abstract]
Nuclear decommissioning ARO beginning balance						3,680,000,000	[1]
Accretion Expense						169,000,000
Net increase (decrease) due to changes in estimated future cash flows						749,000,000
Costs incurred to decommission retired plants						(2,000,000)
Nuclear decommissioning ARO ending balance		4,596,000,000	[1]			4,596,000,000	[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		202,000,000	[2]	(363,000,000)	[2]	352,000,000	[2]	(223,000,000)	[2]
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units		71,000,000	[3],[4]	(141,000,000)	[3],[4]	101,000,000	[3],[4]	(88,000,000)	[3],[4]
Footnotes To Unrealized Gains Losses On NDT Funds [Abstract]
Gains on Zion Station Pledged Assets		22,000,000		4,000,000		60,000,000		41,000,000
PECO Energy Co [Member]
Nuclear Decommissioning Trust Fund Investments [Abstract]
Proposed annual recovery of decommissioning costs	24,000,000
Current annual recovery of decommissioning costs	$ 29,000,000

[1] Includes $6 million and $5 million as the current portion of the ARO at September 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 $22 million of net unrealized gains and $4 million of net unrealized losses related to the Zion Station pledged assets for the three months ended September 30, 2012 and 2011, respectively, and $60 million and $41 million of net unrealized gains related to the Zion Station pledged assets for the nine months ended September 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.