XML 216 R95.htm IDEA: XBRL DOCUMENT v2.4.1.9
Pension and Other Post-Retirement Benefits (Details 8) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Fair value of pension plan assets    
Assets $ 457.0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets  
Fair Value, Inputs, Level 1 [Member]    
Fair value of pension plan assets    
Assets 15.8us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member		 447.8us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Fair Value, Inputs, Level 2 [Member]    
Fair value of pension plan assets    
Assets 441.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member		 25.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Fair Value, Inputs, Level 3 [Member]    
Fair value of pension plan assets    
Assets   422.7us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Short-term investment funds [Member]    
Fair value of pension plan assets    
Assets 0.9us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_ShortTermInvestmentFundsMember		  
Short-term investment funds [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair value of pension plan assets    
Assets 0.9us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_ShortTermInvestmentFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member		 1.3us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_ShortTermInvestmentFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Short-term investment funds [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair value of pension plan assets    
Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_ShortTermInvestmentFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member		 1.3us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_ShortTermInvestmentFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Short-term investment funds [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair value of pension plan assets    
Assets   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_ShortTermInvestmentFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Common stock [Member]    
Fair value of pension plan assets    
Assets     
Common stock [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair value of pension plan assets    
Assets      
Common stock [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair value of pension plan assets    
Assets      
Common stock [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair value of pension plan assets    
Assets     
Common stock collective funds [Member]    
Fair value of pension plan assets    
Assets 215.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_StockCollectiveFundsMember		  
Common stock collective funds [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair value of pension plan assets    
Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_StockCollectiveFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member		 263.0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_StockCollectiveFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Common stock collective funds [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair value of pension plan assets    
Assets 215.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_StockCollectiveFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member		 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_StockCollectiveFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Common stock collective funds [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair value of pension plan assets    
Assets   263.0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_StockCollectiveFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Fixed income collective trust funds [Member]    
Fair value of pension plan assets    
Assets 208.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_FixedIncomeCollectiveTrustFundsMember		  
Fixed income collective trust funds [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair value of pension plan assets    
Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_FixedIncomeCollectiveTrustFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member		 138.0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_FixedIncomeCollectiveTrustFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Fixed income collective trust funds [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair value of pension plan assets    
Assets 208.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_FixedIncomeCollectiveTrustFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member		 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_FixedIncomeCollectiveTrustFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Fixed income collective trust funds [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair value of pension plan assets    
Assets   138.0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gmt_FixedIncomeCollectiveTrustFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Real estate investment funds [Member]    
Fair value of pension plan assets    
Assets 17.9us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_RealEstateInvestmentMember		  
Real estate investment funds [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair value of pension plan assets    
Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_RealEstateInvestmentMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member		 21.7us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_RealEstateInvestmentMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Real estate investment funds [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair value of pension plan assets    
Assets 17.9us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_RealEstateInvestmentMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member		 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_RealEstateInvestmentMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Real estate investment funds [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair value of pension plan assets    
Assets   21.7us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_RealEstateInvestmentMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
UNITED STATES | Common stock [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair value of pension plan assets    
Assets 13.3us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_CommonStockMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_StatementGeographicalAxis
= country_US		 21.4us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_CommonStockMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_StatementGeographicalAxis
= country_US
International [Member] | Common stock [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair value of pension plan assets    
Assets $ 1.6us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_CommonStockMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_StatementGeographicalAxis
= gmt_InternationalMember		 $ 2.4us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_CommonStockMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_StatementGeographicalAxis
= gmt_InternationalMember