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SHARE-BASED COMPENSATION - Additional Information (Detail) (USD $)
3 Months Ended
Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Shares of common stock issued as a result of restricted stock unit vesting, performance share unit vesting and stock option exercises 1,389,787us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod
Stock options  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted 2,122,608us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Weighted average exercise price of stock options granted 35.41us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Restricted stock units  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted 433,469us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Vested 339,413us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Weighted average fair value of units granted 35.41us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Performance share units  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted 238,662us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Vested 222,257us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Weighted average fair value of units granted 34.75us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Stock appreciation rights  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted 58,373us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_StockAppreciationRightsSARSMember
Minimum | Performance share units  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Final number of shares awarded of each grant's target 0.00%wy_FinalNumberOfSharesAwardedOfEachGrantsTarget
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maximum | Performance share units  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Final number of shares awarded of each grant's target 150.00%wy_FinalNumberOfSharesAwardedOfEachGrantsTarget
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember