Nuclear Decommissioning (Tables)

3 Months Ended

Mar. 31, 2013

Schedule Of Nuclear Decommissioning [Line Items]

Nuclear decommissioning asset retirement obligation rollforward

Nuclear decommissioning ARO at December 31, 2012 (a)	$	4,741
Accretion expense		64
Costs incurred to decommission retired plants		(1)
Nuclear decommissioning ARO at March 31, 2013 (a)	$	4,804

(a)Includes $10 million as the current portion of the ARO at March 31, 2013 and December 31, 2012, 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,
			2013		2012
Net unrealized gains on decommissioning trust funds —
	Regulatory Agreement Units (a)	$	195	$	247
Net unrealized gains on decommissioning trust funds —
	Non-Regulatory Agreement Units (b)(c)		64		65

(a)       Net unrealized gainsrelated 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$2and $35 millionof net unrealized gains related to the Zion Station pledged assets for the three months ended March 31, 2013 and 2012, 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 gainsrelated 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.

Zion Station pledged assets

	Exelon and Generation
	March 31,		December 31,
	2013		2012
Carrying value of Zion Station pledged assets	$	580	$	614
Payable to Zion Solutions (a)		531		564
Current portion of payable to Zion Solutions (b)		159		132
Withdrawals by Zion Solutions to pay decommissioning costs (c)		371		335

(a) Excludes a liability recorded within Generation's Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT Funds. The NDT Funds will be utilized to satisfy the tax obligations as gains and losses are realized.

(b) Included in other current liabilities within Generation's Consolidated Balance Sheets.

(c) Cumulative withdrawals since September 1, 2010.

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, 2012 (a)	$	4,741
Accretion expense		64
Costs incurred to decommission retired plants		(1)
Nuclear decommissioning ARO at March 31, 2013 (a)	$	4,804

(a)Includes $10 million as the current portion of the ARO at March 31, 2013 and December 31, 2012, 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,
			2013		2012
Net unrealized gains on decommissioning trust funds —
	Regulatory Agreement Units (a)	$	195	$	247
Net unrealized gains on decommissioning trust funds —
	Non-Regulatory Agreement Units (b)(c)		64		65

(a)       Net unrealized gainsrelated 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$2and $35 millionof net unrealized gains related to the Zion Station pledged assets for the three months ended March 31, 2013 and 2012, 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 gainsrelated 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.

Zion Station pledged assets

	Exelon and Generation
	March 31,		December 31,
	2013		2012
Carrying value of Zion Station pledged assets	$	580	$	614
Payable to Zion Solutions (a)		531		564
Current portion of payable to Zion Solutions (b)		159		132
Withdrawals by Zion Solutions to pay decommissioning costs (c)		371		335

(a) Excludes a liability recorded within Generation's Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT Funds. The NDT Funds will be utilized to satisfy the tax obligations as gains and losses are realized.

(b) Included in other current liabilities within Generation's Consolidated Balance Sheets.

(c) Cumulative withdrawals since September 1, 2010.