Nuclear Decommissioning - Assets, Payables and Withdrawals by ZionSolutions (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
Nuclear Decommissioning Additional Narrative Information [Line Items]
Pledged assets for Zion Station decommissioning	$ 365				$ 458
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Pledged assets for Zion Station decommissioning	365				458
Payable to Zion Solutions	334	[1]			414	[1]
Current portion of payable to Zion Solutions	74	[2]			109	[2]
Withdrawals by Zion Solutions to pay decommissioning costs	$ 618	[3]	$ 498	[3]

[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.