Asset Retirement Obligations (Tables)

9 Months Ended

Sep. 30, 2011

Asset Retirement Obligations Tables [Abstract]

Nuclear decommissioning asset retirement obligation rollforward

		Exelon and Generation
Nuclear decommissioning ARO at December 31, 2010 (a)	$	3,276
Accretion expense		155
Net increase due to changes in estimated cash flows		176
Costs incurred to decommission retired plants		(3)
Nuclear decommissioning ARO at September 30, 2011 (a)	$	3,604

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(a) Includes $5 millionas the current portion of the ARO at September 30, 2011 and December 31, 2010, which is included in other current liabilities on Exelon's and Generation's Consolidated Balance Sheets.

Unrealized Gains (Losses) on nuclear decommissioning trust funds

		Exelon and Generation
			Three Months Ended				Nine Months Ended
			September 30,				September 30,
			2011		2010		2011		2010
Net unrealized gains (losses) on decommissioning trust funds
	Regulatory Agreement Units (a)	$	(363)	$	324	$	(223)	$	117
	Non-Regulatory Agreement Units (b)(c)		(141)		107		(88)		48

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(a)       Net unrealized gains and (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.

(b)       Excludes $4 million of net unrealized losses and $41 million of net unrealized gains related to the Zion Station pledged assets for the three and ninemonths ended September 30, 2011, respectively. Unrealized gains and lossesrelated to Zion Station pledged assets are included in the payable for Zion Station decommissioning on Exelon and Generation's Consolidated Balance Sheets.

(c)       Gains and (losses) related to Generation's NDT funds associated with Non-Regulatory Agreement Units are included within Other, net in Exelon and Generation's Consolidated Statements of Operations and Comprehensive Income.