Related Party Transactions - Noncurrent Receivables from/Payables to affiliates (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Noncurrent	$ 2,865	$ 3,017
Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Noncurrent	2,375	2,541
PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Noncurrent	$ 490	$ 475