Derivative Financial Instruments (Derivatives in Cash Flow Hedging Relationships) (Detail) - Cash Flow Hedging [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Gain (loss) Reclassified from Deferred Accounts into Income		$ 0	$ (1)	$ (2)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[1]	1	1	(2)
Interest Rate Contract [Member]
Derivative [Line Items]
Gain (loss) Reclassified from Deferred Accounts into Income	[2]	0	(1)	(2)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[1],[2]	$ 1	$ 1	$ (2)

[1] Represents net derivative activity deferred into and amortized out of regulatory assets/liabilities. Amounts deferred into regulatory assets/ liabilities have no associated effect in the Consolidated Statements of Comprehensive Loss.

[2] Amounts recorded in DESC’s Consolidated Statements of Comprehensive Loss are classified in interest charges.