Borrowings and Other Financing Instruments, Commercial Paper (Details) - USD ($)		3 Months Ended	12 Months Ended
		Jun. 30, 2024	Dec. 31, 2023
Short-term Debt [Line Items]
Amount outstanding at period end		$ 0	$ 60,000,000
Credit Facility
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1]	150,000,000
Long-term Line of Credit		0	0
Commercial Paper
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		150,000,000	150,000,000
Amount outstanding at period end		0	60,000,000
Average amount outstanding		0	15,000,000
Maximum amount outstanding			$ 93,000,000
Weighted average interest rate, computed on a daily basis			4.85%
Weighted average interest rate at period end			5.50%
Money Pool
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		150,000,000	$ 150,000,000
Amount outstanding at period end		0	0
Average amount outstanding		5,000,000	6,000,000
Maximum amount outstanding		$ 38,000,000	$ 43,000,000
Weighted average interest rate, computed on a daily basis		5.33%	4.98%
Series Due June 15, 2054 | Bonds [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 400,000,000
Debt Instrument, Interest Rate, Stated Percentage		5.65%

[1] Expires in September 2027.