Derivative Financial Instruments (Fair Value of Derivatives) (Detail) - USD ($) $ in Millions		Sep. 30, 2023	Dec. 31, 2022
Derivative [Line Items]
Derivative Asset, Current	[1]	$ 18	$ 41
Derivative Asset, Current, Statement of Financial Position [Extensible Enumeration]		Other Assets, Current	Other Assets, Current
Derivative Asset, Noncurrent	[2]	$ 155	$ 211
Derivative Asset, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Regulated Entity, Other Assets, Noncurrent	Regulated Entity, Other Assets, Noncurrent
Derivative Assets		$ 173	$ 252
Derivative Asset, Statement of Financial Position [Extensible Enumeration]		Assets	Assets
Derivative Liability, Noncurrent	[3]	$ 1	$ 2
Derivative Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Liabilities, Noncurrent	Liabilities, Noncurrent
Derivative Liability		$ 1	$ 2
Derivative Liability, Statement of Financial Position [Extensible Enumeration]		Liabilities and Equity	Liabilities and Equity
Commodity Contract [Member]
Derivative [Line Items]
Derivative Asset, Current		$ 18	$ 41
Derivative Asset, Current, Statement of Financial Position [Extensible Enumeration]		Other Assets, Current	Other Assets, Current
Derivative Asset, Noncurrent		$ 153	$ 210
Derivative Asset, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Regulated Entity, Other Assets, Noncurrent	Regulated Entity, Other Assets, Noncurrent
Interest Rate Contract [Member]
Derivative [Line Items]
Derivative Asset, Noncurrent		$ 2	$ 1
Derivative Asset, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Regulated Entity, Other Assets, Noncurrent
Derivative Liability, Noncurrent		$ 1	$ 2
Derivative Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Liabilities, Noncurrent	Liabilities, Noncurrent
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Current	[1]	$ 0	$ 0
Derivative Asset, Current, Statement of Financial Position [Extensible Enumeration]		Other Assets, Current	Other Assets, Current
Derivative Asset, Noncurrent	[2]	$ 0	$ 0
Derivative Asset, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Regulated Entity, Other Assets, Noncurrent	Regulated Entity, Other Assets, Noncurrent
Derivative Assets		$ 0	$ 0
Derivative Asset, Statement of Financial Position [Extensible Enumeration]		Assets	Assets
Derivative Liability, Noncurrent	[3]	$ 0	$ 2
Derivative Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Liabilities, Noncurrent	Liabilities, Noncurrent
Derivative Liability		$ 0	$ 2
Derivative Liability, Statement of Financial Position [Extensible Enumeration]		Liabilities and Equity	Liabilities and Equity
Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Derivative [Line Items]
Derivative Asset, Current		$ 0	$ 0
Derivative Asset, Current, Statement of Financial Position [Extensible Enumeration]		Other Assets, Current	Other Assets, Current
Derivative Asset, Noncurrent		$ 0	$ 0
Derivative Asset, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Regulated Entity, Other Assets, Noncurrent	Regulated Entity, Other Assets, Noncurrent
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative Asset, Noncurrent		$ 0	$ 0
Derivative Asset, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Regulated Entity, Other Assets, Noncurrent
Derivative Liability, Noncurrent		$ 0	$ 2
Derivative Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Liabilities, Noncurrent	Liabilities, Noncurrent
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Current	[1]	$ 18	$ 41
Derivative Asset, Current, Statement of Financial Position [Extensible Enumeration]		Other Assets, Current	Other Assets, Current
Derivative Asset, Noncurrent	[2]	$ 155	$ 211
Derivative Asset, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Regulated Entity, Other Assets, Noncurrent	Regulated Entity, Other Assets, Noncurrent
Derivative Assets		$ 173	$ 252
Derivative Asset, Statement of Financial Position [Extensible Enumeration]		Assets	Assets
Derivative Liability, Noncurrent	[3]	$ 1	$ 0
Derivative Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Liabilities, Noncurrent	Liabilities, Noncurrent
Derivative Liability		$ 1	$ 0
Derivative Liability, Statement of Financial Position [Extensible Enumeration]		Liabilities and Equity	Liabilities and Equity
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Derivative [Line Items]
Derivative Asset, Current		$ 18	$ 41
Derivative Asset, Current, Statement of Financial Position [Extensible Enumeration]		Other Assets, Current	Other Assets, Current
Derivative Asset, Noncurrent		$ 153	$ 210
Derivative Asset, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Regulated Entity, Other Assets, Noncurrent	Regulated Entity, Other Assets, Noncurrent
Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative Asset, Noncurrent		$ 2	$ 1
Derivative Asset, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Regulated Entity, Other Assets, Noncurrent
Derivative Liability, Noncurrent		$ 1	$ 0
Derivative Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Liabilities, Noncurrent	Liabilities, Noncurrent

[1] Current derivative assets are presented in other current assets in DESC’s Consolidated Balance Sheets.

[2] Noncurrent derivative assets are presented in other deferred debits and other assets in DESC’s Consolidated Balance Sheets.

[3] Noncurrent derivative liabilities are presented in other deferred credits and other liabilities in DESC’s Consolidated Balance Sheets.