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General Devaluation of Venezuelan Bolivar (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Devaluation of Venezuelan Bolivar $ 26wft_ForeignCurrencyDevaluationLossbeforeTax $ 0wft_ForeignCurrencyDevaluationLossbeforeTax
VENEZUELA    
Net Monetary Asset Position $ 11wft_NetMonetaryAssetPosition
/ invest_InvestmentGeographicRegionAxis
= country_VE