Nuclear Decommissioning - Unrealized Gains on NDT Funds (Details) (Exelon Generation Co L L C [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Exelon Generation Co L L C [Member]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - regulatory agreement units	$ 48	[1]	$ 61	[1]
Net unrealized gains (losses) on decommissioning trust funds - non-regulatory agreement units	40	[2],[3]	13	[2],[3]
Unrealized Gain Loss Investment Income Pledged Assets	$ 10

[1] 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.

[2] Excludes $10 million of net unrealized gains related to the Zion Station pledged assets for the three months ended March 31, 2015 and 2014. Net unrealized gains related to Zion Station pledged assets are included in the Payable for Zion Station decommissioning on Exelon’s and Generation’s Consolidated Balance Sheets.

[3] 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.