XML 53 R100.htm IDEA: XBRL DOCUMENT v2.4.1.9
FAIR VALUE - ASSETS AND LIABILITIES MEASURED ON A RECURRING BASIS (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2014
Fair Value    
Risk Management Asset $ 2.4us-gaap_DerivativeAssetFairValueGrossAssetIncludingNotSubjectToMasterNettingArrangement $ 2.3us-gaap_DerivativeAssetFairValueGrossAssetIncludingNotSubjectToMasterNettingArrangement
Liabilities    
Risk Management Liability 3.1us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement 7.0us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement
Transfers Between the Levels of the Fair Value Hierarchy    
Fair Value Transfers, Amount 0wps_FairValueTransfersAmount  
Coal contract    
Transfers Between the Levels of the Fair Value Hierarchy    
Fair Value, Level 3 to Level 2 Transfers, Amount   1.2wps_FairValueLevel3ToLevel2TransfersAmount
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Fair value measurements on a recurring basis | Level 1    
Fair Value    
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Liabilities    
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Fair value measurements on a recurring basis | Level 2    
Fair Value    
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Liabilities    
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Fair value measurements on a recurring basis | Level 3    
Fair Value    
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Liabilities    
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Fair value measurements on a recurring basis | Total    
Fair Value    
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Liabilities    
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Fair value measurements on a recurring basis | Natural gas contracts | Level 1    
Fair Value    
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Fair value measurements on a recurring basis | Natural gas contracts | Level 2    
Fair Value    
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Fair value measurements on a recurring basis | Natural gas contracts | Level 3    
Fair Value    
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Fair value measurements on a recurring basis | Natural gas contracts | Total    
Fair Value    
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Fair value measurements on a recurring basis | FTRs | Level 1    
Fair Value    
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Fair value measurements on a recurring basis | FTRs | Level 3    
Fair Value    
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Liabilities    
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Fair value measurements on a recurring basis | FTRs | Total    
Fair Value    
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Fair Value    
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Fair value measurements on a recurring basis | Petroleum product contracts | Total    
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Fair Value    
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Fair value measurements on a recurring basis | Coal contract | Level 2    
Fair Value    
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Liabilities    
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/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Fair value measurements on a recurring basis | Coal contract | Level 3    
Fair Value    
Risk Management Asset 0.2us-gaap_DerivativeAssetFairValueGrossAssetIncludingNotSubjectToMasterNettingArrangement
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CoalContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0us-gaap_DerivativeAssetFairValueGrossAssetIncludingNotSubjectToMasterNettingArrangement
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CoalContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Liabilities    
Risk Management Liability 2.7us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CoalContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
2.2us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CoalContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Fair value measurements on a recurring basis | Coal contract | Total    
Fair Value    
Risk Management Asset 0.2us-gaap_DerivativeAssetFairValueGrossAssetIncludingNotSubjectToMasterNettingArrangement
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CoalContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
 
Liabilities    
Risk Management Liability $ 2.7us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CoalContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
$ 3.4us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CoalContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember