Borrowings and Other Financing Instruments - Commercial Paper (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
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%