Derivative Financial Instruments (Derivatives Not Designated as Hedging Instruments) (Detail) - Not Designated as Hedging Instruments [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]
Amount of Gain (Loss) Recognized in Income on Derivatives	[1]	$ 2	$ (1)	$ 4	$ (4)
Commodity Contract [Member] | Purchased Power [Member]
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	[1]	2	(1)	5	(3)
Interest Rate Contract [Member]
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	[1]	$ 0	$ 0	$ (1)	$ (1)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Interest Expense, Operating and Nonoperating	Interest Expense, Operating and Nonoperating	Interest Expense, Operating and Nonoperating	Interest Expense, Operating and Nonoperating

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