Accounts Receivable - Purchases and Sales of Accounts Receivable (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 17, 2021	Apr. 08, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loss on Sale of Receivables	$ 30
Proceeds from New Transfers	2,816
Cash Collections received on Deferred Purchase Price	3,771
Cash Collections Reinvested in the Facility	6,587
Accounts Receivable, Purchase	3,529
Accounts Receivable, Sale	572
Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loss on Sale of Receivables	30
Proceeds from New Transfers	2,816
Cash Collections received on Deferred Purchase Price	3,771
Cash Collections Reinvested in the Facility	6,587
Accounts Receivable, Purchase	0
Accounts Receivable, Sale	824
Exelon Generation Co L L C [Member] | Exelon Utility Registrants Affiliates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Sale	252
Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	1,094
Accounts Receivable, Sale	0
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	34
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	1,020
Accounts Receivable, Sale	0
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	67
Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	652
Accounts Receivable, Sale	0
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	79
Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	1,015
Accounts Receivable, Sale	0
Pepco Holdings LLC [Member] | Exelon Generation Co LLC Affiliate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	72
Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	622
Accounts Receivable, Sale	0
Potomac Electric Power Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	51
Delmarva Power & Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	207
Accounts Receivable, Sale	0
Delmarva Power & Light Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	13
Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	186
Accounts Receivable, Sale	0
Atlantic City Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	8
Sale of Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Derecognized receivables transferred at fair value	1,139		$ 1,200
Cash proceeds received	500		500
Deferred purchase price	639		650
Transfer of Financial Assets Accounted for as Sale, Additional Transfers	6,608
Sale of Accounts Receivable [Member] | Subsequent Event [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds received		$ 250
Sale of Accounts Receivable [Member] | Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Derecognized receivables transferred at fair value	1,139		1,200
Cash proceeds received	500		500
Deferred purchase price	639		$ 650
Transfer of Financial Assets Accounted for as Sale, Additional Transfers	$ 6,608