Public Utilities, Amount of proposed changes would be recoverable

No definition available.

Name:	sps_PublicUtilitiesAmountofproposedchangeswouldberecoverable
Namespace Prefix:	sps_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Public Utilities, Amount proposed changes would increase wholesale transmission revenues

+ References

No definition available.

+ Details

Name:	sps_PublicUtilitiesAmountproposedchangeswouldincreasewholesaletransmissionrevenues
Namespace Prefix:	sps_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Public Utilities, Annual Transmission Revenue Requirement Increase

+ References

No definition available.

+ Details

Name:	sps_PublicUtilitiesAnnualTransmissionRevenueRequirementIncrease
Namespace Prefix:	sps_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Public Utilities, Annual Transmission Revenue Requirement Increase (SPS)

+ References

No definition available.

+ Details

Name:	sps_PublicUtilitiesAnnualTransmissionRevenueRequirementIncreaseSPS
Namespace Prefix:	sps_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Public Utilities, Annual Transmission Revenue Requirement (Other Utilities)

+ References

No definition available.

+ Details

Name:	sps_PublicUtilitiesAnnualTransmissionRevenueRequirementOtherUtilities
Namespace Prefix:	sps_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Public Utilities, Billed Charges For Transmission Service Upgrades

+ References

No definition available.

+ Details

Name:	sps_PublicUtilitiesBilledChargesForTransmissionServiceUpgrades
Namespace Prefix:	sps_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Total costs accrued as of the balance sheet date for environmental loss contingencies.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 25
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingencies
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_RegulatoryAgencyAxis=sps_SouthwestPowerPoolSPPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=sps_SPPOpenAccessTransmissionTariffUpgradeCostsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=sps_SpsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=sps_OtherMGPLandfillorDisposalSitesDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments and Contingencies, Rate Matters, SPS (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Aug. 31, 2018	Dec. 31, 2018	Dec. 31, 2016	Mar. 31, 2019
Public Utilities, General Disclosures [Line Items]
Public Utilities, Amount proposed changes would increase wholesale transmission revenues		$ 9.4
Public Utilities, Amount of proposed changes would be recoverable		$ 4.4
Southwest Power Pool (SPP) \| SPP Open Access Transmission Tariff Upgrade Costs
Public Utilities, General Disclosures [Line Items]
Public Utilities, Annual Transmission Revenue Requirement Increase	$ 9.5
Public Utilities, Annual Transmission Revenue Requirement Increase (SPS)	6.0
Public Utilities, Annual Transmission Revenue Requirement (Other Utilities)	$ 3.5
SPS \| Southwest Power Pool (SPP) \| SPP Open Access Transmission Tariff Upgrade Costs
Public Utilities, General Disclosures [Line Items]
Public Utilities, Billed Charges For Transmission Service Upgrades			$ 13.0
Other MGP, Landfill, or Disposal Sites [Domain]
Public Utilities, General Disclosures [Line Items]
Accrual for Environmental Loss Contingencies				$ 0.1