Nuclear Decommissioning - Unrealized Gains on NDT Funds (Details) (Exelon Generation Co L L C [Member], USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
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	$ (107)	[1]	$ 103	[1]	$ 126	[1]	$ 196	[1]
Net unrealized gains (losses) on decommissioning trust funds - non-regulatory agreement units	(41)	[2],[3]	46	[2],[3]	100	[2],[3]	70	[2],[3]
Unrealized Gain Loss Investment Income Pledged Assets	$ 7		$ (9)		$ 27		$ (5)

[1] 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.

[2] Excludes $7 million of net unrealized gains and $9 million of net unrealized losses related to the Zion Station pledged assets for the three months ended September 30, 2014 and 2013, respectively, and $27 million of net unrealized gains and $5 million of net unrealized losses related to the Zion Station pledged assets for the nine months ended September 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.

[3] 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.