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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES STOCK-BASED COMPENSATION (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Stock Options  
Information related to share based awards  
Maximum term of awards 10 years
Percentage of retirees' options that becomes exercisable each year 25.00%wps_Percentagethatbecomesexercisable
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Period of historical volatility used to estimate expected volatility 10 years
Performance Stock Rights  
Information related to share based awards  
Vesting period 3 years
Percentage value of award that can be deferred into deferred compensation plan 80.00%wps_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageValueOfAwardThatCanBeDeferredIntoDeferredCompensationPlan
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Period prior to the end of the performance period during which employees cannot change their election to defer the value of awards into the deferred compensation plan 6 months
Remaining performance period for which fair value on the modification date is used to measure the awards 6 months
Incremental compensation expense due to an award modification 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Performance Stock Rights | Minimum  
Information related to share based awards  
Amount of performance payout (as a percent) 0.00%wps_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutRatio
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Period of historical volatility used to estimate expected volatility 1 year
Performance Stock Rights | Maximum  
Information related to share based awards  
Amount of performance payout (as a percent) 200.00%wps_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutRatio
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Period of historical volatility used to estimate expected volatility 3 years
Restricted Share Units  
Information related to share based awards  
Vesting period 4 years
Vesting rights percentage 25.00%wps_VestingRightsPercentage
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
Percentage value of award that can be deferred into deferred compensation plan 80.00%wps_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageValueOfAwardThatCanBeDeferredIntoDeferredCompensationPlan
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember