Accounts Receivable - Purchases and Sales of Accounts Receivable (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 24, 2021	Feb. 17, 2021	Dec. 31, 2020	Apr. 08, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loss on sale receivables	$ 1	$ 8	$ 26	$ 23
Proceeds from new transfers			4,440	1,889
Cash collections received on deferred purchase price and reinvested in the Facility			2,652	2,518
Cash collections reinvested in the Facility			7,092	4,407
Accounts Receivable, Purchase			2,945	2,698
Accounts Receivable, Sale			100	542
Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loss on sale receivables	1	$ 8	26	23
Proceeds from new transfers			4,440	1,889
Cash collections received on deferred purchase price and reinvested in the Facility			2,652	2,518
Cash collections reinvested in the Facility			7,092	4,407
Accounts Receivable, Purchase			0	0
Accounts Receivable, Sale			117	790
Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			810	865
Accounts Receivable, Sale			0	0
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			795	786
Accounts Receivable, Sale			0	0
Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			531	508
Accounts Receivable, Sale			0	0
Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			826	787
Accounts Receivable, Sale			0	0
Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			504	484
Accounts Receivable, Sale			0	0
Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			166	160
Accounts Receivable, Sale			0	0
Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			156	143
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			0	34
Exelon Generation Co LLC Affiliate [Member] | PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase			0	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			17	75
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 and 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
Exelon Utility Registrants Affiliates [Member] | Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Related Parties, Sale			17	248
Sale of accounts receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Derecognized receivables transferred at fair value	1,401		1,401				$ 1,139	$ 1,200
Cash proceeds received	900		900		$ 50	$ 250	500	500
DPP consideration	501		501				639	650
Transfer of Financial Assets Accounted for as Sales, Additional Transfers			7,373	4,515
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	1,401		1,401				1,139	1,200
Cash proceeds received	900		900		$ 50	$ 250	500	500
DPP consideration	501		501				$ 639	$ 650
Transfer of Financial Assets Accounted for as Sales, Additional Transfers			7,373	$ 4,515
Sale of Accounts Receivable_Three Months Ended Q1 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds received	400		400
Sale of Accounts Receivable_Three Months Ended Q1 2021 | Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds received	$ 400		$ 400