Indeterminate AROs (Details) $ in Millions	Dec. 31, 2021 USD ($)
Asset Retirement Obligations [Line Items]
Indeterminate Costs Incurred, Asset Retirement Obligation Due to Asbestos	$ 0

Indeterminate Costs Incurred, Asset Retirement Obligation Due to Asbestos

No definition available.

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