Borrowings and Other Financing Instruments - Short-Term Borrowings (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2022	Dec. 31, 2021
Short-term Debt [Line Items]
Short-term debt	$ 0	$ 147,000,000
Money Pool
Short-term Debt [Line Items]
Borrowing limit	250,000,000	250,000,000
Short-term debt	165,000,000	0
Average amount outstanding	49,000,000	12,000,000
Maximum amount outstanding	$ 197,000,000	$ 243,000,000
Weighted average interest rate, computed on a daily basis (percentage)	2.06%	0.07%
Short-term Debt, Weighted Average Interest Rate, at Point in Time	2.33%
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	$ 700,000,000	$ 700,000,000
Short-term debt	0	147,000,000
Average amount outstanding	14,000,000	26,000,000
Maximum amount outstanding	$ 170,000,000	$ 322,000,000
Weighted average interest rate, computed on a daily basis (percentage)	2.07%	0.19%
Short-term Debt, Weighted Average Interest Rate, at Point in Time		0.22%