Net Periodic Benefit Cost (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Operating and maintenance expenses		$ 271	$ 275	$ 285
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		11	10	9
Interest cost		15	18	20
Defined Benefit Plan, Expected Return (Loss) on Plan Assets		(30)	(29)	(28)
Amortization of prior service cost		0	0	0
Defined Benefit Plan, Amortization of Gain (Loss)		14	12	11
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[1]	0	0	2
Net periodic pension cost		10	11	14
Defined Benefit Plan, Costs Not Recognized Due To Regulation		0	2	1
Net benefit cost recognized for financial reporting		$ 10	$ 13	$ 15
Discount rate (as a percent)		2.71%	3.49%	4.31%
Expected average long-term increase in compensation level (as a percent)		3.75%	3.75%	3.75%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets		6.39%	6.78%	6.78%
Defined Benefit Plan, Plan Assets, Payment for Settlement			$ 2
Operating and maintenance expenses			1	$ 1
Net loss		$ 143	186
Prior service credit		(1)	(1)
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Total		142	185
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets		11	11
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Assets		131	174
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Liabilities		0	0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Liabilities		0	0
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		1	1	1
Interest cost		1	1	2
Defined Benefit Plan, Expected Return (Loss) on Plan Assets		(2)	(2)	(2)
Amortization of prior service cost		0	0	(1)
Defined Benefit Plan, Amortization of Gain (Loss)		(1)	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[1]	0	0	0
Net periodic pension cost		(1)	0	0
Defined Benefit Plan, Costs Not Recognized Due To Regulation		0	0	0
Net benefit cost recognized for financial reporting		$ (1)	$ 0	$ 0
Discount rate (as a percent)		2.65%	3.47%	4.32%
Expected average long-term increase in compensation level (as a percent)		0.00%	0.00%	0.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets		4.10%	4.50%	5.30%
Net loss		$ (19)	$ (18)
Prior service credit		(1)	(1)
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Total		(20)	(19)
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets		0	0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Assets		0	0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Liabilities		(1)	(1)
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Liabilities		$ (19)	$ (18)

[1] A settlement charge is required when the amount of all lump-sum distributions during the year is greater than the sum of the service and interest cost components of the annual net periodic pension cost. In 2019, as a result of lump-sum distributions during each plan year, SPS recorded a total pension settlement charge of $2 million. A total of $1 million of that amount was recorded in the income statement in 2019. There were no settlement charges recorded to the qualified pension plans in 2021 or 2020.