Accounts Receivable - Purchases and Sales of Accounts Receivable (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Apr. 08, 2020
Purchases of Accounts Receivable [Line Items]
Loss on sale receivables	$ 15	$ 15
Proceeds from new transfers		927
Cash collections received on deferred purchase price		1,102
Cash collections reinvested in the Facility		2,029
Accounts Receivable, Purchase		1,584
Accounts Receivable, Sale		533
Exelon Generation Co L L C [Member]
Purchases of Accounts Receivable [Line Items]
Loss on sale receivables	15	15
Proceeds from new transfers		927
Cash collections received on deferred purchase price		1,102
Cash collections reinvested in the Facility		2,029
Accounts Receivable, Purchase		0
Accounts Receivable, Sale		779
Commonwealth Edison Co [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		518
Accounts Receivable, Sale		0
PECO Energy Co [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		494
Accounts Receivable, Sale		0
Baltimore Gas and Electric Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		333
Accounts Receivable, Sale		0
Pepco Holdings LLC [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		485
Accounts Receivable, Sale		0
Potomac Electric Power Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		303
Accounts Receivable, Sale		0
Delmarva Power and Light Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		98
Accounts Receivable, Sale		0
Atlantic City Electric Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase		84
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		73
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		246
Sale of accounts receivable [Member]
Purchases of Accounts Receivable [Line Items]
Transfer of Financial Assets Accounted for as Sales [Line Items]		2,032
Derecognized receivables transferred at fair value	1,135	1,135	$ 1,200
Cash proceeds received	500	500	500
Deferred purchase price	635	635	650
Sale of accounts receivable [Member] | Exelon Generation Co L L C [Member]
Purchases of Accounts Receivable [Line Items]
Transfer of Financial Assets Accounted for as Sales [Line Items]		2,032
Derecognized receivables transferred at fair value	1,135	1,135	1,200
Cash proceeds received	500	500	500
Deferred purchase price	$ 635	$ 635	$ 650