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]
Amount outstanding at period end	$ 0	$ 207
Series Due May 15, 2053 | Bonds [Member]
Short-term Debt [Line Items]
Debt Instrument, Face Amount	$ 800
Series Due May 15, 2023 | Bonds [Member]
Short-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.10%
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	$ 700	700
Amount outstanding at period end	0	207
Average amount outstanding	0	21
Maximum amount outstanding	$ 0	$ 290
Weighted average interest rate, computed on a daily basis		4.14%
Weighted average interest rate at period end		4.64%