Accounts Receivable - Purchases and Sales of Accounts Receivable (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	$ 1,044	$ 1,023
Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	248	266
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	292	290
Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	222	199
Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	282	268
Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	174	166
Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	57	56
Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	51	46
Exelon Generation Co LLC Affiliate [Member] | Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	$ 4	$ 12