Nuclear Decommissioning (Tables)

9 Months Ended

Sep. 30, 2012

Schedule Of Nuclear Decommissioning [Line Items]

Nuclear decommissioning asset retirement obligation rollforward

Nuclear decommissioning ARO at December 31, 2011 (a)	$	3,680
Accretion expense		169
Net increase due to changes in estimated cash flows		749
Costs incurred to decommission retired plants		(2)
Nuclear decommissioning ARO at September 30, 2012 (a)	$	4,596

(a)Includes $6 million and$5millionas 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.

Unrealized Gains (Losses) on nuclear decommissioning trust funds

		Exelon and Generation
			Three Months Ended				Nine Months Ended
			September 30,				September 30,
			2012		2011		2012		2011
Net unrealized gains (losses) on decommissioning trust funds —
	Regulatory Agreement Units (a)	$	202	$	(363)	$	352	$	(223)
Net unrealized gains (losses) on decommissioning trust funds —
	Non-Regulatory Agreement Units (b)(c)		71		(141)		101		(88)

(a)       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.

(b)       Excludes$22million 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 gainsrelated to the Zion Station pledged assetsfor the nine months ended September 30, 2012 and 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 (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.

Exelon Generation Co L L C [Member]

Schedule Of Nuclear Decommissioning [Line Items]

Nuclear decommissioning asset retirement obligation rollforward

Nuclear decommissioning ARO at December 31, 2011 (a)	$	3,680
Accretion expense		169
Net increase due to changes in estimated cash flows		749
Costs incurred to decommission retired plants		(2)
Nuclear decommissioning ARO at September 30, 2012 (a)	$	4,596

(a)Includes $6 million and$5millionas 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.

Unrealized Gains (Losses) on nuclear decommissioning trust funds

		Exelon and Generation
			Three Months Ended				Nine Months Ended
			September 30,				September 30,
			2012		2011		2012		2011
Net unrealized gains (losses) on decommissioning trust funds —
	Regulatory Agreement Units (a)	$	202	$	(363)	$	352	$	(223)
Net unrealized gains (losses) on decommissioning trust funds —
	Non-Regulatory Agreement Units (b)(c)		71		(141)		101		(88)

(a)       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.

(b)       Excludes$22million 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 gainsrelated to the Zion Station pledged assetsfor the nine months ended September 30, 2012 and 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 (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.