Borrowings and Other Financing Instruments Borrowings and Other Financing Instruments, Commercial Paper (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Amount outstanding at period end	$ 83	$ 83	$ 19
money pool
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	150	150
Amount outstanding at period end	0	0
Average amount outstanding	31	16
Maximum amount outstanding	$ 78	$ 78
Line of Credit Facility, Interest Rate During Period	0.05%	0.05%
Commercial Paper [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 150	$ 150	150	$ 150
Amount outstanding at period end	83	83	19	65
Average amount outstanding	3	3	30	51
Maximum amount outstanding	$ 83	$ 83	$ 95	$ 93
Line of Credit Facility, Interest Rate During Period	0.21%	0.18%	1.59%	2.38%
Weighted average interest rate at period end (percentage)	0.21%	0.21%	0.17%	1.97%