Accounts Receivable - Purchases and Sales of Accounts Receivable (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Jun. 24, 2021	Feb. 17, 2021	Apr. 08, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loss on Sale of Receivables	$ 36	$ 30
Proceeds from New Transfers	6,095	2,816
Cash Collections received on Deferred Purchase Price	3,502	3,771
Cash Collections Reinvested in the Facility	9,597	6,587
Accounts Receivable, Purchase	3,817	3,529
Accounts Receivable, Sale	124	572
Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	1,031	1,094
Accounts Receivable, Sale	0	0
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	1,041	1,020
Accounts Receivable, Sale	0	0
Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	687	652
Accounts Receivable, Sale	0	0
Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	1,081	1,015
Accounts Receivable, Sale	0	0
Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	660	622
Accounts Receivable, Sale	0	0
Delmarva Power & Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	217	207
Accounts Receivable, Sale	0	0
Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	204	186
Accounts Receivable, Sale	0	0
Exelon Generation Co LLC Affiliate [Member] | Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	1	34
Exelon Generation Co LLC Affiliate [Member] | PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	1	67
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	21	79
Exelon Generation Co LLC Affiliate [Member] | Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	0	72
Exelon Generation Co LLC Affiliate [Member] | Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	0	51
Exelon Generation Co LLC Affiliate [Member] | Delmarva Power & Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	0	13
Exelon Generation Co LLC Affiliate [Member] | Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase	0	8
Sale of Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Derecognized receivables transferred at fair value	1,265	1,139			$ 1,200
Cash proceeds received	900	500	$ 50	$ 250	500
Deferred purchase price	365	639			$ 650
Transfer of Financial Assets Accounted for as Sale, Additional Transfers	9,747	$ 6,608
Sale of Accounts Receivable_Three Months Ended Q1 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds received	$ 400