Nuclear Decommissioning - Assets, Payables and Withdrawals by ZionSolutions (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2017	Dec. 31, 2016
Nuclear Decommissioning Additional Narrative Information [Line Items]
Pledged assets for Zion Station decommissioning		$ 57	$ 113
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Held-to-maturity Securities Pledged as Collateral		57	113
Accounts Payable, Interest-bearing, Noncurrent	[1]	53	104
Accounts Payable, Interest-bearing, Current	[2]	53	90
Asset Retirement Obligation, Cash Paid to Settle	[3]	928	878
Pledged assets for Zion Station decommissioning		$ 57	$ 113

[1] 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.

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

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