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v2.4.1.9

Pension and Other Post-Retirement Benefits (Details 4) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Medical Claims [Member] |  |
Review of historical returns |  |
Health care cost trend assumed for next year | 7.50%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = gmt_MedicalClaimsMember | 8.00%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = gmt_MedicalClaimsMember
Rate to which the cost trend is expected to decline (the ultimate trend rate) | 5.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = gmt_MedicalClaimsMember | 5.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = gmt_MedicalClaimsMember
Year that rate reaches the ultimate trend rate | 2023 | 2020
Prescription Drugs Claims [Member] |  |
Review of historical returns |  |
Health care cost trend assumed for next year | 7.00%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = gmt_PrescriptionDrugsClaimsMember | 7.00%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = gmt_PrescriptionDrugsClaimsMember
Rate to which the cost trend is expected to decline (the ultimate trend rate) | 5.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = gmt_PrescriptionDrugsClaimsMember | 5.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = gmt_PrescriptionDrugsClaimsMember
Year that rate reaches the ultimate trend rate | 2023 | 2020

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- Definition The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Health Care Cost Trend Rate -URI http://asc.fasb.org/extlink&oid=6514820 + Details
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- Definition The ultimate trend rate for health care costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Year the ultimate health care cost trend rate is expected to be reached, in CCYY format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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