Asset Retirement Obligation (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended				12 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013
Nuclear Decommissioning Trust Fund Investments [Abstract]
Shortfall of decommissioning funds with recourse	$ 50				$ 50
Percent of additional decommissioning shortfall with recourse	5.00%				5.00%
NDT fund investments	10,437				10,437				8,071
NRC Minimum Funding Requirements [Abstract]
Additional NRC funding assurance parent guarantees									115
Nuclear Decommissioning Obligation [Line Items]
Pledged assets for Zion Station decommissioning	402		458		402		458		458
Total payable to ZionSolutions	357	[1]			357	[1]			414	[1]
Current payable to ZionSolutions	93	[2]			93	[2]			109	[2]
Zion Station decommissioning costs withdrawn					575	[3]			498	[3]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - Regulatory Agreement Units	172	[4]	(102)	[4]	234	[4]	92	[4]
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units	128	[5],[6]	(40)	[5],[6]	141	[5],[6]	24	[5],[6]
Footnotes To Unrealized Gains Losses On NDT Funds [Abstract]
Gains on Zion Station Pledged Assets					10		2
Nuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation Roll Forward Analysis [Roll Forward]
ARO beginning balance					4,855	[7]
Accretion expense					154
Costs incurred to decommission retired plants					(3)
ARO ending balance	6,707	[7]			6,707	[7]
Footnotes To Asset Retirement Obligation [Abstract]
Current Portion of ARO	9				9				9
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Trust Fund Investments [Abstract]
Shortfall of decommissioning funds with recourse	50				50
Percent of additional decommissioning shortfall with recourse	5.00%				5.00%
NDT fund investments	10,437				10,437				8,071
NRC Minimum Funding Requirements [Abstract]
Additional NRC funding assurance parent guarantees									115
Nuclear Decommissioning Obligation [Line Items]
Pledged assets for Zion Station decommissioning	402		458		402		458		458
Total payable to ZionSolutions	357	[1]			357	[1]			414	[1]
Current payable to ZionSolutions	93	[2]			93	[2]			109	[2]
Zion Station decommissioning costs withdrawn					575	[3]			498	[3]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - Regulatory Agreement Units	172	[4]	(102)	[4]	234	[4]	92	[4]
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units	128	[5],[6]	(40)	[5],[6]	141	[5],[6]	24	[5],[6]
Footnotes To Unrealized Gains Losses On NDT Funds [Abstract]
Gains on Zion Station Pledged Assets					10		2
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation Roll Forward Analysis [Roll Forward]
ARO beginning balance					4,855	[7]
Accretion expense					154
Costs incurred to decommission retired plants					(3)
ARO ending balance	6,707	[7]			6,707	[7]
Footnotes To Asset Retirement Obligation [Abstract]
Current Portion of ARO	$ 9				$ 9				$ 9

[1] Excludes a liability recorded within Exelon’s and 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.

[2] Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets.

[3] Cumulative withdrawals since September 1, 2010.

[4] 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.

[5] Net unrealized gains (losses) related to Generation's NDT funds with Non-Regulatory Agreement Units are included within Other, net in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income.

[6] Excludes $ 10 million and $2 million of net unrealized gains related to the Zion Station pledged assets for the three months ended June 30, 2014 and 2013, respectively, and $20 million and $3 million of net unrealized gains related to the Zion Station pledged assets for the six months ended June 30, 2014 and 2013, respectively. Net unrealized gains (losses) related to Zion Station pledged assets are included in the Payable for Zion Station decommissioning on Exelon's and Generation's Consolidated Balance Sheets.

[7] Includes $9 million as the current portion of the ARO at June 30, 2014 and December 31, 2013 which is included in Other current liabilities on Exelon's and Generation's Consolidated Balance Sheets.