Nuclear Decommissioning - Unrealized Gains on NDT Funds (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain Loss Investment Income Pledged Assets		$ (2)	$ 1	$ (2)	$ 3
Nuclear Plant [Member] | Regulated Operation [Member]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Net unrealized gains (losses) on decommissioning trust funds - regulatory agreement units	[1],[2]	52		210	131
Net unrealized gains (losses) on decommissioning trust funds - non-regulatory agreement units	[1],[2]	48		$ 235	$ 100
Unrealized Gain (Loss) on Investments	[1],[2]	(13)
Nuclear Plant [Member] | Unregulated Operation [Member]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments	[1],[2]	$ 70

[1] Excludes $(2) million and $1 million of net unrealized gains (losses) related to the Zion Station pledged assets for the three months ended June 30, 2017 and 2016 respectively. Excludes $(2) million and $3 million of net unrealized gains (losses) related to the Zion Station pledged assets for the six months ended June 30, 2017 and 2016, respectively. Net unrealized gains (losses) related to Zion Station pledged assets are included in Other current liabilities and Payable for Zion Station decommissioning on Exelon’s and Generation’s Consolidated Balance Sheets in 2017 and 2016, respectively.

[2] 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.