Accounts Receivable - Unbilled Customer Revenue (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenue	$ 1,178	$ 998
Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenue	671	258
Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenue	161	218
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenue	102	147
Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenue	126	197
Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenue	118	178
Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenue	58	87
Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenue	38	62
Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenue	$ 22	$ 29