Long-Term and Short-Term Debt (Schedule of Debt) (Detail) - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Total principal		$ 3,987	$ 3,620
Securities due within one year		0	(33)
Unamortized discount, premium and debt issuance costs, net		(33)	(30)
Finance leases		14
Total long-term debt		3,964	3,572
First Mortgage Bonds
Debt Instrument [Line Items]
Total principal		$ 3,634
First Mortgage Bonds | DESC
Debt Instrument [Line Items]
Weighted-average coupon rate	[1]	5.09%
Total principal		$ 3,634	3,267
Tax Exempt Financings Variable Rate Due 2038 | DESC
Debt Instrument [Line Items]
Weighted-average coupon rate	[1]	0.14%
Total principal	[2]	$ 35	35
Tax Exempt Financings Variable Rate Due 2038 | Genco
Debt Instrument [Line Items]
Weighted-average coupon rate	[1]	0.14%
Total principal		$ 33	33
Tax Exempt Financings 3.625% and 4.00% Due 2028 and 2033 | DESC
Debt Instrument [Line Items]
Weighted-average coupon rate	[1]	3.90%
Total principal	[2]	$ 54	54
Other Debt
Debt Instrument [Line Items]
Total principal		$ 231
Other Debt | DESC
Debt Instrument [Line Items]
Weighted-average coupon rate	[1]	3.65%
Total principal		$ 1	1
3.05% Affiliated Note Due 2024 | Genco
Debt Instrument [Line Items]
Weighted-average coupon rate	[1]	3.05%
Total principal		$ 230	230
Finance Lease
Debt Instrument [Line Items]
Finance leases		$ 10	$ 15

[1] Represents weighted-average coupon rates for debt outstanding as of December 31, 2021.

[2] Industrial revenue bonds totaling $68 million are secured by letters of credit that expire, subject to renewal, in the fourth quarter of 2022.