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, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Derivative [Line Items]
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[1],[2]	$ 1	$ 1	$ 1	$ 1
Interest Rate Contract [Member]
Derivative [Line Items]
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[1],[2]	$ 1	$ 1	$ 1	$ 1

[1] All derivatives in cash flow hedging relationships have settled and are being amortized over the life of the debt.

[2] 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.