XML 149 R56.htm IDEA: XBRL DOCUMENT v2.4.1.9
Significant Accounting Policies (Gain on Asset Dispositions) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Significant Acquisitions and Disposals [Line Items]      
Disposition gains $ 63.1us-gaap_GainsLossesOnSalesOfAssets $ 60.0us-gaap_GainsLossesOnSalesOfAssets $ 42.7us-gaap_GainsLossesOnSalesOfAssets
Residual sharing income 9.4gmt_NonoperatingIncomeResidualSharingIncome 10.8gmt_NonoperatingIncomeResidualSharingIncome 22.6gmt_NonoperatingIncomeResidualSharingIncome
Non-remarketing disposition gains 16.0gmt_NonremarketingDispositionGainLoss 20.7gmt_NonremarketingDispositionGainLoss 19.2gmt_NonremarketingDispositionGainLoss
Asset impairments (1.3)us-gaap_AssetImpairmentCharges (5.9)us-gaap_AssetImpairmentCharges (5.0)us-gaap_AssetImpairmentCharges
Net Gain on Asset Dispositions $ 87.2us-gaap_GainLossOnSalesOfAssetsAndAssetImpairmentCharges $ 85.6us-gaap_GainLossOnSalesOfAssetsAndAssetImpairmentCharges $ 79.5us-gaap_GainLossOnSalesOfAssetsAndAssetImpairmentCharges