Borrowings and Other Financing Instruments, Short-Term Borrowings (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Short-term Debt [Line Items]
Short-term debt	$ 320	$ 320	$ 294
Letter of Credit
Short-term Debt [Line Items]
Line of Credit Facility, Expiration Period		1 year
Commercial Paper [Member]
Short-term Debt [Line Items]
Borrowing limit	700	$ 700	700	$ 700
Short-term debt	320	320	294	147
Average amount outstanding	$ 189	$ 124	$ 71	$ 26
Weighted average interest rate at period end (percentage)	5.56%	5.56%	4.73%	0.22%
Line of Credit Facility, Interest Rate During Period	5.53%	5.17%	2.56%	0.19%
Maximum amount outstanding	$ 369	$ 454	$ 328	$ 322
Money Pool
Short-term Debt [Line Items]
Borrowing limit	250	250	250	250
Short-term debt	51	51	0	0
Average amount outstanding	$ 64	$ 23	$ 29	$ 12
Line of Credit Facility, Interest Rate During Period	5.33%	5.31%	1.66%	0.07%
Maximum amount outstanding	$ 250	$ 250	$ 250	$ 243
Line of Credit Facility, Interest Rate at Period End	5.34%	5.34%