Nuclear Decommissioning - Unrealized Gains on NDT Funds (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments		$ 4	$ 5	$ 5	$ 2
Collateral Pledged [Member] | Regulated Operation [Member]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments	[1]	44	155	253	286
Collateral Pledged [Member] | Unregulated Operation [Member]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments	[2],[3]	$ 111	$ 116	$ 347	$ 216

[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 $4 million and $5 million of net unrealized losses related to the Zion Station pledged assets for the three months ended September 30, 2017 and 2016 respectively. Excludes $5 million and $2 million of net unrealized losses related to the Zion Station pledged assets for the nine months ended September 30, 2017 and 2016, respectively. Net unrealized 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.

[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.