Asset Retirement Obligations - Unrealized Gains on NDT Funds (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments		$ 9	$ 4	$ 7	$ 5
Collateral Pledged [Member] | Regulated Operation [Member]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments	[1]	(66)	44	(335)	253
Collateral Pledged [Member] | Unregulated Operation [Member]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments	[2],[3]	$ 72	$ 111	$ (143)	$ 347

[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 $9 million and $4 million of net unrealized losses related to the Zion Station pledged assets for the three months ended September 30, 2018 and 2017, respectively. Excludes $7 million and $5 million of net unrealized losses related to the Zion Station pledged assets for the nine months ended September 30, 2018 and 2017, respectively. Net unrealized losses related to Zion Station pledged assets are included in Other current liabilities 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 in Other, net on Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.