Asset Retirement Obligations - Pledged Assets and Payables to ZionSolutions (Details) - USD ($)		Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Asset Retirement Obligations [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	$ 9,704,000,000
Asset retirement obligations, noncurrent		9,679,000,000		$ 10,029,000,000
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Line of credit facility, maximum borrowing capacity		200,000,000	$ 45,000,000
Asset retirement obligations, noncurrent		9,450,000,000		9,844,000,000
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligations [Line Items]
Held-to-maturity Securities Pledged as Collateral	[2]	9,000,000		39,000,000
Accounts Payable, Interest-bearing, Noncurrent		9,000,000		37,000,000
Accounts Payable, Interest-bearing, Current		$ 965		$ 942,000,000

[1] Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.

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