Accounts Receivable - Purchases and Sales of Accounts Receivable (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Apr. 08, 2020
Purchases of Accounts Receivable [Line Items]
Loss on sale receivables	$ 8	$ 23
Proceeds from new transfers		1,889
Cash collections received on deferred purchase price		2,518
Cash collections reinvested in the Facility		4,407
Accounts Receivable, Purchase		2,698
Accounts Receivable, Sale		542
Exelon Generation Co L L C [Member]
Purchases of Accounts Receivable [Line Items]
Loss on sale receivables	8	23
Proceeds from new transfers		1,889
Cash collections received on deferred purchase price		2,518
Cash collections reinvested in the Facility		4,407
Accounts Receivable, Purchase		0
Accounts Receivable, Sale		790
Commonwealth Edison Co [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		865
Accounts Receivable, Sale		0
PECO Energy Co [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		786
Accounts Receivable, Sale		0
Baltimore Gas and Electric Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		508
Accounts Receivable, Sale		0
Pepco Holdings LLC [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		787
Accounts Receivable, Sale		0
Potomac Electric Power Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		484
Accounts Receivable, Sale		0
Delmarva Power and Light Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		160
Accounts Receivable, Sale		0
Atlantic City Electric Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		143
Accounts Receivable, Sale		0
Exelon Generation Co LLC Affiliate [Member] | Commonwealth Edison Co [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase		34
Exelon Generation Co LLC Affiliate [Member] | PECO Energy Co [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase		67
Exelon Generation Co LLC Affiliate [Member] | Baltimore Gas and Electric Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase		75
Exelon Generation Co LLC Affiliate [Member] | Pepco Holdings LLC [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase		72
Exelon Generation Co LLC Affiliate [Member] | Potomac Electric Power Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase		51
Exelon Generation Co LLC Affiliate [Member] | Delmarva Power and Light Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase		13
Exelon Generation Co LLC Affiliate [Member] | Atlantic City Electric Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Related Parties, Purchase		8
Exelon Utility Registrants Affiliates [Member] | Exelon Generation Co L L C [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Related Parties, Sale		248
Sale of accounts receivable [Member]
Purchases of Accounts Receivable [Line Items]
Derecognized receivables transferred at fair value	1,232	1,232	$ 1,200
Cash proceeds received	500	500	500
Deferred purchase price	732	732	650
Transfer of Financial Assets Accounted for as Sales [Line Items]		4,515
Sale of accounts receivable [Member] | Exelon Generation Co L L C [Member]
Purchases of Accounts Receivable [Line Items]
Derecognized receivables transferred at fair value	1,232	1,232	1,200
Cash proceeds received	500	500	500
Deferred purchase price	$ 732	732	$ 650
Transfer of Financial Assets Accounted for as Sales [Line Items]		$ 4,515