Affiliated and Related Party Transactions (Schedule of Affiliated Transactions - Income Statement) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Purchases of fuel used in electric generation from affiliate			$ 0	$ 43
Operating Revenues – Electric from sales to affiliate		$ 4	4	4
Operating Revenues – Gas from sales to affiliate		1	1	1
Operating Expenses – Other taxes from affiliate		7	9	6
D E S And D E S S
Related Party Transaction [Line Items]
Direct and allocated costs	[1]	226	294	297
Canadys Refined Coal [Member]
Related Party Transaction [Line Items]
Purchases from affiliate			0	121
Sales of coal to affiliate			0	120
Solar Affiliates [Member]
Related Party Transaction [Line Items]
Purchases from affiliate		$ 14	12	8
DECG [Member]
Related Party Transaction [Line Items]
Purchases of fuel used in electric generation from affiliate			16	19
Gas purchased for resale			$ 36	$ 44

[1] Includes capitalized expenditures of $37 million, $81 million and $53 million for the years ended December 31, 2021, 2020 and 2019, respectively.