Asset Retirement Obligations - Pledged Assets and Payables to ZionSolutions (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2016
Asset Retirement Obligations [Line Items]
Line of credit facility, maximum borrowing capacity				$ 98
Carrying value of Zion Station pledged assets		$ 0	$ 113,000,000
Decommissioning Liability, Noncurrent		0	14,000,000
Asset Retirement Obligations, Noncurrent		10,029,000,000	9,111,000,000
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Line of credit facility, maximum borrowing capacity		200,000,000
Held-to-maturity Securities Pledged as Collateral		39,000,000	113,000,000
Accounts Payable, Interest-bearing, Noncurrent	[1]	37,000,000	104,000,000
Asset Retirement Obligation, Cash Paid to Settle	[2]	942,000,000	878,000,000
Carrying value of Zion Station pledged assets		0	113,000,000
Decommissioning Liability, Noncurrent		0	14,000,000
Asset Retirement Obligations, Noncurrent		9,844,000,000	8,922,000,000
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligations [Line Items]
Accounts Payable, Interest-bearing, Current	[3]	$ 37,000,000	$ 90,000,000

[1] Included in Other current assets within Exelon’s and Generation’s Consolidated Balance Sheets in 2017

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

[3] 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.