Borrowings and Other Financing Instruments - Money Pool (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Short-term Debt [Line Items]
Short-term Debt	$ 212	$ 137
Money Pool
Short-term Debt [Line Items]
Borrowing limit	100	100
Short-term Debt	100	91
Average amount outstanding	67	51
Maximum amount outstanding	$ 100	$ 100
Weighted average interest rate, computed on a daily basis	0.13%	0.05%
Weighted average interest rate at period end	0.19%	0.05%
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	$ 500	$ 500
Short-term Debt	212	137
Average amount outstanding	233	63
Maximum amount outstanding	$ 324	$ 342
Weighted average interest rate, computed on a daily basis	0.39%	0.21%
Weighted average interest rate at period end	0.83%	0.26%