Borrowings and Other Financing Instruments - Money Pool (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2025	Dec. 31, 2024
Short-term Debt [Line Items]
Short-term debt	$ 0	$ 145
Money Pool
Short-term Debt [Line Items]
Borrowing limit	100	100
Short-term debt	0	7
Average amount outstanding	29	24
Maximum amount outstanding	$ 100	$ 100
Weighted average interest rate, computed on a daily basis	4.33%	5.29%
Weighted average interest rate at period end		4.58%
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	$ 600	$ 500
Short-term debt	0	145
Average amount outstanding	86	35
Maximum amount outstanding	$ 260	$ 160
Weighted average interest rate, computed on a daily basis	4.65%	5.47%
Weighted average interest rate at period end		4.66%