Nuclear Decommissioning (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			12 Months Ended
	Mar. 31, 2014		Mar. 31, 2013	Dec. 31, 2013
Nuclear Decommissioning Trust Fund Investments [Abstract]
NDT fund investments	$ 8,215			$ 8,071
Current annual recovery of decommissioning costs	24
Shortfall of decommissioning funds with recourse	50
Decommissioning Shortfall Percentage	5.00%
Decommissioning [Abstract]
Pledged assets for Zion Station decommissioning	429			458
Total payable to ZionSolutions	385	[1]		414	[1]
Current payable to ZionSolutions	103	[2]		109	[2]
Zion Station decommissioning costs withdrawn	537	[3]		498	[3]
NRC Minimum Funding Requirements [Abstract]
Additional NRC funding assurance parent guarantees				115
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - Regulatory Agreement Units	61	[4]		195	[4]
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units	13	[5],[6]		64	[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	66
Costs incurred to decommission retired plants	(1)
ARO ending balance	4,920	[7]
Footnotes To Asset Retirement Obligation [Abstract]
Current Portion of ARO	9			9
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Trust Fund Investments [Abstract]
NDT fund investments	8,215			8,071
Shortfall of decommissioning funds with recourse	50
Decommissioning Shortfall Percentage	5.00%
Decommissioning [Abstract]
Pledged assets for Zion Station decommissioning	429			458
Total payable to ZionSolutions	385	[1]		414	[1]
Current payable to ZionSolutions	103	[2]		109	[2]
Zion Station decommissioning costs withdrawn	537	[3]		498	[3]
NRC Minimum Funding Requirements [Abstract]
Additional NRC funding assurance parent guarantees				115
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - Regulatory Agreement Units	61	[4]		195	[4]
Net unrealized gains (losses) on decommissioning trust funds - Non-Regulatory Agreement Units	13	[5],[6]		64	[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	66
Costs incurred to decommission retired plants	(1)
ARO ending balance	4,920	[7]
Footnotes To Asset Retirement Obligation [Abstract]
Current Portion of ARO	9			9
PECO Energy Co [Member]
Nuclear Decommissioning Trust Fund Investments [Abstract]
Current annual recovery of decommissioning costs	$ 24

[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 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 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 March 31, 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 March 31, 2014 and December 31, 2013 which is included in Other current liabilities on Exelon's and Generation's Consolidated Balance Sheets.