Asset Retirement Obligations - Assets, Payables and Withdrawals by ZionSolutions (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Nuclear Decommissioning Additional Narrative Information [Line Items]
Held-to-maturity Securities Pledged as Collateral	[1]	$ 9	$ 39
Accounts Payable, Interest-bearing, Noncurrent	[2],[3]	9	37
Accounts Payable, Interest-bearing, Current	[4]	$ 965	$ 942

[1] Included in Other current assets within Exelon's and Generation's Consolidated Balance sheets.

[2] Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT funds. The NDT funds will be utilized to satisfy the tax obligations as gains and losses are realized.

[3] Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets.

[4] Includes project expenses to decommission Zion Station and estimated tax payments on Zion Station NDT fund earnings.