Asset Retirement Obligations (Tables)

3 Months Ended

Mar. 31, 2012

Asset Retirement Obligations Tables [Abstract]

Nuclear decommissioning asset retirement obligation rollforward

Nuclear decommissioning ARO at December 31, 2011 (a)	$	3,680
Accretion expense		55
Net increase due to changes in estimated cash flows		80
Costs incurred to decommission retired plants		(1)
Nuclear decommissioning ARO at March 31, 2012 (a)	$	3,814

(a)Includes $5 millionas 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.

Unrealized Gains (Losses) on nuclear decommissioning trust funds

		Three Months Ended
		March 31,
			2012		2011
Net unrealized gains on decommissioning trust funds —
	Regulatory Agreement Units (a)	$	247	$	111
Net unrealized gains on decommissioning trust funds —
	Non-Regulatory Agreement Units (b)(c)		65		43

(a)       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.

(b)       Excludes $35million and $23 millionof net unrealized gains related to the Zion Station pledged assets for the threemonths ended March 31, 2012 and March 31, 2011, respectively.Net unrealized gainsrelated to Zion Station pledged assets are included in the payable for Zion Station decommissioning on Exelon's and Generation's Consolidated Balance Sheets.

(c)       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.