Borrowings and Other Financing Instruments - Short-Term Borrowings (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Short-term Debt [Line Items]
Short-term debt	$ 0	$ 294,000,000
Money Pool
Short-term Debt [Line Items]
Borrowing limit	250,000,000	250,000,000
Short-term debt	188,000,000	0
Average amount outstanding	27,000,000	29,000,000
Maximum amount outstanding	$ 188,000,000	$ 250,000,000
Weighted average interest rate, computed on a daily basis (percentage)	5.26%	1.66%
Short-term Debt, Weighted Average Interest Rate, at Point in Time	5.30%
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	$ 700,000,000	$ 700,000,000
Short-term debt	0	294,000,000
Average amount outstanding	5,000,000	71,000,000
Maximum amount outstanding	$ 72,000,000	$ 328,000,000
Weighted average interest rate, computed on a daily basis (percentage)	5.45%	2.56%
Short-term Debt, Weighted Average Interest Rate, at Point in Time		4.73%