Derivative Financial Instruments (Derivatives in Cash Flow Hedging Relationships) (Detail) - Cash Flow Hedging [Member] - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative [Line Items]
Gain (loss) Reclassified from Deferred Accounts into Income		$ 0	$ (1)	$ 0	$ (1)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[1]	0	0	(2)	2
Interest Rate Contract [Member]
Derivative [Line Items]
Gain (loss) Reclassified from Deferred Accounts into Income	[2]	0	(1)	0	(1)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[1],[2]	$ 0	$ 0	$ (2)	$ 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 Income (Loss).

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