Borrowings and Other Financing Instruments, Short-Term Borrowings (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]
Short-term debt	$ 147	$ 147	$ 136
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	147	147	136	0
Average amount outstanding	$ 6	$ 26	$ 30	$ 154
Weighted average interest rate at period end (percentage)	0.22%	0.22%		0.20%
Line of Credit Facility, Interest Rate During Period	0.21%	0.19%	1.59%	2.67%
Maximum amount outstanding	$ 150	$ 322	$ 230	$ 432
Money Pool
Short-term Debt [Line Items]
Borrowing limit	250	250	250	250
Short-term debt	0	0	57	39
Average amount outstanding	$ 14	$ 12	$ 59	$ 7
Weighted average interest rate at period end (percentage)			0.70%	1.63%
Line of Credit Facility, Interest Rate During Period	0.05%	0.07%	0.60%	2.29%
Maximum amount outstanding	$ 74	$ 243	$ 250	$ 50