Related Party Transactions - Noncurrent Receivables from/Payables to affiliates (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Noncurrent	$ 2,888	$ 3,103
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Noncurrent	2,445	2,622
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Noncurrent	443	480
Other Legal Entities [Member] | Business Services Corporation [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Noncurrent	$ 0	$ 1