Borrowings and Other Financing Instruments - Money Pool (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Short-term Debt [Line Items]
Short-term debt	$ 0	$ 34
Money Pool
Short-term Debt [Line Items]
Borrowing limit	100	100
Short-term debt	0	0
Average amount outstanding	73	35
Maximum amount outstanding	$ 100	$ 100
Weighted average interest rate, computed on a daily basis	5.19%	0.44%
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	$ 500	$ 500
Short-term debt	0	34
Average amount outstanding	47	100
Maximum amount outstanding	$ 119	$ 324
Weighted average interest rate, computed on a daily basis	5.35%	0.79%
Weighted average interest rate at period end		4.55%