Summary of Significant Accounting Policies (Schedule of Weighted Average Depreciation Rates) (Parenthetical) (Detail) $ in Millions	12 Months Ended
Dec. 31, 2021 USD ($)
Accounting Policies [Abstract]
Public utilities, decrease in depreciation expense	$ 6
Public utilities, annual decrease in depreciation expense	$ 12

Amount of increase or decrease in depreciation expense on property, plant and equipment (PPE) for utilities.

No definition available.

Name:	ck91882_PublicUtilitiesPropertyPlantAndEquipmentIncreaseDecreaseInDepreciationExpense
Namespace Prefix:	ck91882_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration