Accounts Receivable - Purchases and Sales of Accounts Receivable (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Feb. 17, 2021	Dec. 31, 2020	Apr. 08, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loss on sale receivables	$ 17
Proceeds from new transfers	1,036
Cash collections received on deferred purchase price and reinvested in the Facility	1,174
Cash collections reinvested in the Facility	2,210
Accounts Receivable, Purchase	1,011	$ 781
Accounts Receivable, Sale	69	507
Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loss on sale receivables	17
Proceeds from new transfers	1,036
Cash collections received on deferred purchase price and reinvested in the Facility	1,174
Cash collections reinvested in the Facility	2,210
Accounts Receivable, Purchase	0	0
Accounts Receivable, Sale	81	749
Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	266	280
Accounts Receivable, Sale	0	0
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	290	284
Accounts Receivable, Sale	0	0
Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	199	195
Accounts Receivable, Sale	0	0
Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	268	264
Accounts Receivable, Sale	0	0
Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	166	165
Accounts Receivable, Sale	0	0
Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	56	53
Accounts Receivable, Sale	0	0
Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase	46	46
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	12	69
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	12	$ 242
Sale of accounts receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Derecognized receivables transferred at fair value	1,301			$ 1,139	$ 1,200
Cash proceeds received	900		$ 250	500	500
DPP consideration	401			639	650
Transfer of Financial Assets Accounted for as Sales, Additional Transfers	2,375
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	1,301			1,139	1,200
Cash proceeds received	900		$ 250	500	500
DPP consideration	401			$ 639	$ 650
Transfer of Financial Assets Accounted for as Sales, Additional Transfers	2,375
Sale of Accounts Receivable_Three Months Ended Q1 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds received	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