Commitments and Contingencies, Capital Commitments (Details)	12 Months Ended
Dec. 31, 2013 Project
Capital Commitments [Abstract]
Number of major projects with capital commitments	1
Minimum annual tolerance band percentage for future rate recovery or refund of fuel costs	2.00%
Capital Commitments [Member] \| CapX2020 [Member]
Capital Commitments [Abstract]
Number of transmission lines in Group 1 project	4

The minimum annual tolerance band percentage for future rate recovery or refund related to the deferral of the under-collection or over-collection of fuel costs.

No definition available.

Name:	nspw_MinimumAnnualToleranceBandPercentageForFutureRateRecoveryOrRefundOfFuelCosts
Namespace Prefix:	nspw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration