Accounts Receivable - Purchases and Sales of Accounts Receivable (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 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	$ 8	$ 15	$ 25	$ 15
Proceeds from new transfers			2,689	927
Cash collections received on deferred purchase price and reinvested in the Facility			1,809	1,102
Cash collections reinvested in the Facility			4,498	2,029
Accounts Receivable, Purchase			1,823	1,584
Accounts Receivable, Sale			92	533
Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loss on sale receivables	8	$ 15	25	15
Proceeds from new transfers			2,689	927
Cash collections received on deferred purchase price and reinvested in the Facility			1,809	1,102
Cash collections reinvested in the Facility			4,498	2,029
Accounts Receivable, Purchase			0	0
Accounts Receivable, Sale			107	779
Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			485	518
Accounts Receivable, Sale			0	0
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			507	494
Accounts Receivable, Sale			0	0
Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			343	333
Accounts Receivable, Sale			0	0
Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			503	485
Accounts Receivable, Sale			0	0
Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			310	303
Accounts Receivable, Sale			0	0
Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			103	98
Accounts Receivable, Sale			0	0
Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Purchase			90	84
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			15	73
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			15	246
Sale of accounts receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Derecognized receivables transferred at fair value	1,274		1,274				$ 1,139	$ 1,200
Cash proceeds received	900		900		$ 50	$ 250	500	500
DPP consideration	374		374				639	650
Transfer of Financial Assets Accounted for as Sales, Additional Transfers			4,647	2,032
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	1,274		1,274				1,139	1,200
Cash proceeds received	900		900		$ 50	$ 250	500	500
DPP consideration	374		374				$ 639	$ 650
Transfer of Financial Assets Accounted for as Sales, Additional Transfers			4,647	$ 2,032
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