Accounts Receivable - Purchases and Sales of Accounts Receivable (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase	$ 781
Accounts Receivable, Sale	507
Exelon Generation Co L L C [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase	0
Accounts Receivable, Sale	749
Commonwealth Edison Co [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase	280
Accounts Receivable, Sale	0
PECO Energy Co [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase	284
Accounts Receivable, Sale	0
Baltimore Gas and Electric Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase	195
Accounts Receivable, Sale	0
Pepco Holdings LLC [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase	264
Accounts Receivable, Sale	0
Potomac Electric Power Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase	165
Accounts Receivable, Sale	0
Delmarva Power and Light Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase	53
Accounts Receivable, Sale	0
Atlantic City Electric Company [Member]
Purchases of Accounts Receivable [Line Items]
Accounts Receivable, Purchase	46
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	69
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	$ 242