Benefit Plans and Other Postretirement Benefits, Pension Plan Benefit Obligations, Cash Flows and Benefit Costs (Details)		12 Months Ended
		Dec. 31, 2021 USD ($) Plan		Dec. 31, 2020 USD ($)		Dec. 31, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Operating and maintenance expenses		$ 271,000,000		$ 275,000,000		$ 285,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Liability, Defined Benefit Plan, Noncurrent		(8,000,000)		(42,000,000)
Significant Assumptions Used to Measure Costs [Abstract]
annual interest crediting rates		2.35		2.37		3.12
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Payment for Settlement				2,000,000
Accumulated Benefit Obligation at Dec. 31		506,000,000		519,000,000
Operating and maintenance expenses				1,000,000		1,000,000
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 amendments		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
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)
Liability, Defined Benefit Plan, Noncurrent		0		(35,000,000)
Assets for Plan Benefits, Defined Benefit Plan		12,000,000		0
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 Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Current regulatory assets		11,000,000		11,000,000
Noncurrent regulatory assets		131,000,000		174,000,000
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
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%
Expected average long-term increase in compensation level (as a percent)		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
Net periodic pension cost		10,000,000		11,000,000		14,000,000
Net benefit cost recognized for financial reporting		$ 10,000,000		$ 13,000,000		$ 15,000,000
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%
Plan participant's contributions		$ 0		$ 0
Plan participant's contributions		0		0
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position		12,000,000		(35,000,000)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[2]	0		0		$ 2,000,000
Defined Benefit Plan, Costs Not Recognized Due To Regulation		0		2,000,000		1,000,000
Pension Plan [Member] | SPS [Member]
Cash Flows [Abstract]
Payment for Pension Benefits		15,000,000		14,000,000		18,000,000
Other Postretirement Benefits Plan [Member]
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 amendments		0		0
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
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
Liability, Defined Benefit Plan, Noncurrent		0		0
Assets for Plan Benefits, Defined Benefit Plan		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 Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Current regulatory assets		0		0
Noncurrent regulatory assets		0		0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Liabilities		(1,000,000)		(1,000,000)
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As 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%
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
Net periodic pension cost		(1,000,000)		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%
Plan participant's contributions		$ 0		$ 1,000,000
Plan participant's contributions		1,000,000		1,000,000
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position		$ 9,000,000		$ 6,000,000
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
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[2]	0		0		$ 0
Defined Benefit Plan, Costs Not Recognized Due To Regulation		$ 0		$ 0		$ 0
Parent Company [Member] | Pension Plan [Member]
Cash Flows [Abstract]
Number of pension plans to which contributions were made | Plan		4

[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.