Borrowings and Other Financing Instruments Short-Term Debt (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Short-term Debt [Line Items]
Amount outstanding at period end	$ 695	$ 695	$ 785
Commercial Paper
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	3,550	3,550	3,550	$ 3,550
Amount outstanding at period end	695	695	785	813
Average amount outstanding	133	508	491	552
Maximum amount outstanding	$ 695	$ 1,314	$ 1,241	$ 1,357
Weighted average interest rate, computed on a daily basis (percentage)	4.77%	5.47%	5.12%	1.47%
Weighted average interest rate at period end (percentage)	4.64%	4.64%	5.52%	4.66%