Commitments and Contingencies, Joint Operating System (Details) $ in Millions	12 Months Ended
Dec. 31, 2023 USD ($) Counterparty Reactor Plant
Joint Operating System [Abstract]
Number of companies covered by FERC approved Interchange Agreement \| Counterparty	2
NSP-Minnesota \| Nuclear Insurance
Joint Operating System [Abstract]
Nuclear insurance coverage secured for the Company's public liability exposure	$ 450.0
Nuclear insurance coverage exposure funded by the Secondary Financial Protection Program	15,800.0
Maximum assessments per reactor per accident	$ 166.0
Number of owned and licensed reactors \| Reactor	3
Maximum funding requirement per reactor for any one year	$ 24.7
Number of nuclear plant sites operated by NSP-Minnesota \| Plant	2
Maximum assessments for business interruption insurance each calendar year	$ 15.0
Maximum assessment for property damage insurance NSP-Minnesota is subject to each calendar year	32.0
NSP-Minnesota \| Maximum \| Nuclear Insurance
Joint Operating System [Abstract]
Maximum possible loss contingency	16,200.0
Insurance coverage limits for NSP-Minnesota's nuclear plant sites	2,800.0
Business Interruption Insurance Coverage Provided by NEIL	490.0
Business Interruption Insurance Coverage Provided by NEIL - Prairie Island	$ 420.0

Business Interruption Insurance Coverage Provided by NEIL - Monticello

No definition available.

Name:	nspw_BusinessInterruptionInsuranceCoverageProvidedByNEILMonticello
Namespace Prefix:	nspw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Business Interruption Insurance Coverage Provided by NEIL - Prairie Island

+ References

No definition available.

+ Details

Name:	nspw_BusinessInterruptionInsuranceCoverageProvidedByNEILPrairieIsland
Namespace Prefix:	nspw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Insurance coverage limits for property damage and site decontamination cleanup costs for each of the nuclear plant sites.

+ References

No definition available.

+ Details

Name:	nspw_InterruptionInsuranceCoverageLimitsForNuclearPlantSites
Namespace Prefix:	nspw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

-- None. No documentation exists for this element. --

+ References

No definition available.

+ Details

Name:	nspw_JointOperatingSystemAbstract
Namespace Prefix:	nspw_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The maximum assessments for business interruption insurance per calendar year if losses exceed accumulated reserve funds.

+ References

No definition available.

+ Details

Name:	nspw_MaximumAssessmentForBusinessInterruptionInsurance
Namespace Prefix:	nspw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The maximum assessment for property damage insurance per calendar year if losses exceed accumulated reserve funds.

+ References

No definition available.

+ Details

Name:	nspw_MaximumAssessmentForPropertyDamageInsurance
Namespace Prefix:	nspw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The maximum assessment the company is subject to for each reactor per accident incurred at any licensed nuclear facility within the United States, collected in annual installments.

+ References

No definition available.

+ Details

Name:	nspw_MaximumAssessmentsPerReactorPerAccident
Namespace Prefix:	nspw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The annual maximum installment payment the company is subject to until either the maximum assessment has been reached or the claim has been met.

+ References

No definition available.

+ Details

Name:	nspw_MaximumFundingRequirementPerReactorForAnyOneYear
Namespace Prefix:	nspw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of coverage secured for the public liability exposure thru the Secondary Financial Protection Program, available from assessments by the federal government in case of a nuclear accident.

+ References

No definition available.

+ Details

Name:	nspw_NuclearInsuranceCoverageExposureFundedBySecondaryFinancialProtectionProgram
Namespace Prefix:	nspw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of coverage secured for the public liability exposure thru a pool of insurance companies.

+ References

No definition available.

+ Details

Name:	nspw_NuclearInsuranceCoverageSecuredForPublicLiabilityExposure
Namespace Prefix:	nspw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The number of companies covered by a FERC approved Interchange Agreement which provides for the sharing of all costs of generation and transmission facilities of the NSP System, including capital costs.

+ References

No definition available.

+ Details

Name:	nspw_NumberOfCompaniesCoveredByFercApprovedInterchangeAgreement
Namespace Prefix:	nspw_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of nuclear plant sites operated by the entity.

+ References

No definition available.

+ Details

Name:	nspw_NumberOfNuclearPlantSites
Namespace Prefix:	nspw_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of owned and licensed reactors.

+ References

No definition available.

+ Details

Name:	nspw_NumberOfOwnedAndLicensedReactors
Namespace Prefix:	nspw_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482425/460-10-50-3

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483076/450-20-50-4

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483076/450-20-50-9

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482425/460-10-50-2

+ Details

Name:	us-gaap_LossContingencyEstimateOfPossibleLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_InsuranceRelatedAssessmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: