The high end of the range of the amortization period for recovery of remediation costs in natural gas rates.

No definition available.

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- Definition

The low end of the range of the amortization period for recovery of remediation costs in natural gas rates.

+ References

No definition available.

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- Definition

The amortization period for recovery of remediation costs in natural gas rates, approved by the Public Service Commission of Wisconsin (PSCW).

+ References

No definition available.

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- Definition

The approved increase (decrease) in amortization expense granted by a regulatory body as part of a regulatory proceeding.

+ References

No definition available.

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- Definition

The carrying cost percentage to be applied to the unamortized regulatory asset related to costs for manufactured gas plant (MGP) remediation.

+ References

No definition available.

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- Definition

The estimated amount spent on Phase I Project Area cleanup activities.

+ References

No definition available.

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- Definition

The number of properties included in a superfund site which the entity does not own.

+ References

No definition available.

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- Definition

The number of PRPs that have reached a settlement in principle with NSP-Wisconsin in regards to the Ashland site cleanup

+ References

No definition available.

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- Definition

The potential percent of decrease to the low end of the range of the estimated loss exposure for reasonably possible environmental contingencies at an individual site.

+ References

No definition available.

+ Details

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- Definition

The potential percent of increase to the high end of the range of the estimated loss exposure for reasonably possible environmental contingencies at an individual site.

+ References

No definition available.

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- Definition

The high end of the range of the estimated loss exposure for reasonably possible environmental contingencies at an individual site.

+ References

No definition available.

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- Definition

The low end of the range of the estimated loss exposure for reasonably possible environmental contingencies at an individual site.

+ References

No definition available.

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- Definition

Undiscounted amount of the accrual for environmental loss contingencies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 5.Y.Q1)

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- Definition

Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable in twelve months or in the next operating cycle if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

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-Number 210

-Section 02

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-Article 5

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- Definition

Amount of the estimated recovery from third parties recorded in the period for an individual site that reduces environmental remediation expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 30

-Section 50

-Paragraph 12

-Subparagraph (b)

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Commitments and Contingencies, Environmental Contingencies - Site Contingencies (Details) (USD $)	3 Months Ended	1 Months Ended
	Mar. 31, 2015 Site	Apr. 30, 2015	Dec. 31, 2014
Ashland Manufactured Gas Plant (MGP) Site [Abstract]
Liability for estimated cost of remediating sites, current	$ 26,125,000		$ 29,116,000
Ashland MGP Site
Ashland Manufactured Gas Plant (MGP) Site [Abstract]
Number of properties included in superfund site which NSP-Wisconsin does not own	2
Liability for estimated cost of remediating sites	112,400,000		107,600,000
Liability for estimated cost of remediating sites, current	26,000,000		28,900,000
Amortization period for recovery of remediation costs in natural gas rates, low end of range (in years)	4 years
Amortization period for recovery of remediation costs in natural gas rates, high end of range (in years)	6 years
Ashland MGP Site - Phase I Project Area
Ashland Manufactured Gas Plant (MGP) Site [Abstract]
Liability for estimated cost of remediating sites	57,000,000
Estimated amount spent on Phase I Project Area cleanup	33,000,000
Approved amortization period for recovery of remediation costs in natural gas rates (in years)	10 years
Carrying cost percentage to be applied to the unamortized regulatory asset for MGP remediation (in hundredths)	3.00%
Approved increase (decrease) in amortization expense granted by a regulatory body	1,100,000
Ashland MGP Site - Sediments
Ashland Manufactured Gas Plant (MGP) Site [Abstract]
Estimated cost of remediating site, low end of range	63,000,000
Estimated cost of remediating site, high end of range	77,000,000
Potential percent of increase to the high end of the range of estimated site remediation costs (in hundredths)	50.00%
Potential percent of decrease to the low end of the range of estimated site remediation costs (in hundredths)	30.00%
NSP-Wisconsin \| Ashland MGP Site
Ashland Manufactured Gas Plant (MGP) Site [Abstract]
Number of PRPs that have reached a settlement in principle	2
Site Contingency, Recovery from Third Party of Environmental Remediation Cost	10,500,000
Subsequent Event [Member] \| NSP-Wisconsin \| Ashland MGP Site
Ashland Manufactured Gas Plant (MGP) Site [Abstract]
Site Contingency, Recovery from Third Party of Environmental Remediation Cost		$ 5,400,000