Benefit Plans and Other Postretirement Benefits, Postretirement Benefit Plan Benefit Obligations, Cash Flows and Benefit Costs (Details) - USD ($)		12 Months Ended
		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Operating and maintenance expenses		$ 271,000,000		$ 275,000,000		$ 285,000,000
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan amendments		0		0
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		38,000,000		44,000,000
Service cost		1,000,000		1,000,000		1,000,000
Interest cost		1,000,000		1,000,000		2,000,000
Plan participant's contributions		0		1,000,000
Actuarial loss		(3,000,000)		(5,000,000)
Benefit payments		(3,000,000)		(4,000,000)
Obligation at Dec. 31		34,000,000		38,000,000		44,000,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		44,000,000	[1]	44,000,000
Actual return on plan assets		1,000,000		3,000,000
Plan participant's contributions		1,000,000		1,000,000
Employer contributions		0		0
Benefit payments		(3,000,000)		(4,000,000)
Fair value of plan assets at Dec. 31		43,000,000	[1]	44,000,000	[1]	44,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Funded status		9,000,000		6,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery Rates [Abstract]
Net loss		(19,000,000)		(18,000,000)
Prior service credit		(1,000,000)		(1,000,000)
Total		(20,000,000)		(19,000,000)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost (Credit) Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
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
Current regulatory liabilities		(1,000,000)		(1,000,000)
Noncurrent regulatory liabilities		(19,000,000)		(18,000,000)
Total		$ (20,000,000)		$ (19,000,000)
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)		3.09%		2.65%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Pre-65		5.30%		5.50%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Post-65		4.90%		5.00%
Ultimate health care trend assumption rate (as a percent)		4.50%		4.50%
Period until ultimate trend rate is reached (in years)		$ 4		$ 5
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		1,000,000		1,000,000		1,000,000
Interest cost		1,000,000		1,000,000		2,000,000
Expected return on plan assets		(2,000,000)		(2,000,000)		(2,000,000)
Amortization of prior service cost		0		0		(1,000,000)
Amortization of net loss		(1,000,000)		0		0
Settlement charge (a)	[2]	0		0		0
Net periodic pension cost		(1,000,000)		0		0
Defined Benefit Plan, Costs Not Recognized Due To Regulation		0		0		0
Net benefit cost recognized for financial reporting		$ (1,000,000)		$ 0		$ 0
Significant Assumptions Used to Measure Costs [Abstract]
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%
Expected average long-term rate of return on assets (as a percent)		4.10%		4.50%		5.30%
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Payment for Settlement				$ 2,000,000
Plan amendments		$ 0		0
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		562,000,000		519,000,000
Service cost		11,000,000		10,000,000		$ 9,000,000
Interest cost		15,000,000		18,000,000		20,000,000
Plan participant's contributions		0		0
Actuarial loss		(13,000,000)		45,000,000
Benefit payments		(30,000,000)		(30,000,000)
Obligation at Dec. 31		545,000,000		562,000,000		519,000,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		527,000,000	[1]	458,000,000
Actual return on plan assets		46,000,000		84,000,000
Plan participant's contributions		0		0
Employer contributions		14,000,000		15,000,000
Benefit payments		(30,000,000)		(30,000,000)
Fair value of plan assets at Dec. 31		557,000,000	[1]	527,000,000	[1]	458,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Funded status		12,000,000		(35,000,000)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery Rates [Abstract]
Net loss		143,000,000		186,000,000
Prior service credit		(1,000,000)		(1,000,000)
Total		142,000,000		185,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost (Credit) Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets		11,000,000		11,000,000
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Assets		131,000,000		174,000,000
Current regulatory liabilities		0		0
Noncurrent regulatory liabilities		0		0
Total		$ 142,000,000		$ 185,000,000
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)		3.08%		2.71%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase		3.75%		3.75%
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 11,000,000		$ 10,000,000		9,000,000
Interest cost		15,000,000		18,000,000		20,000,000
Expected return on plan assets		(30,000,000)		(29,000,000)		(28,000,000)
Amortization of prior service cost		0		0		0
Amortization of net loss		14,000,000		12,000,000		11,000,000
Settlement charge (a)	[2]	0		0		(2,000,000)
Net periodic pension cost		10,000,000		11,000,000		14,000,000
Defined Benefit Plan, Costs Not Recognized Due To Regulation		0		(2,000,000)		(1,000,000)
Net benefit cost recognized for financial reporting		$ 10,000,000		13,000,000		15,000,000
Operating and maintenance expenses				$ 1,000,000		$ 1,000,000
Significant Assumptions Used to Measure Costs [Abstract]
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%
Expected average long-term rate of return on assets (as a percent)		6.39%		6.78%		6.78%

[1] See Note 8 for further information on fair value measurement inputs and methods.

[2] 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.