Asset Retirement Obligations - Pledged Assets and Payables to ZionSolutions (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Asset Retirement Obligations [Line Items]
Carrying value of Zion Station pledged assets	$ 319		$ 458
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Carrying value of Zion Station pledged assets	319		458
Payable to Zion Solutions	292	[1]	414	[1]
Current portion of payable to Zion Solutions	137	[2]	109	[2]
Withdrawals by Zion Solutions to pay decommissioning costs	$ 666		$ 498

[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.