Other Assets and Other Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Components of Other Assets reported on the consolidated balance sheets
Inventory	$ 52.0us-gaap_OtherInventory	$ 45.8us-gaap_OtherInventory
Office furniture, fixtures and other equipment, net of accumulated depreciation	34.1	34.9
Derivatives	11.5us-gaap_DerivativeAssets	6.0us-gaap_DerivativeAssets
Deferred financing costs	21.6us-gaap_DeferredFinanceCostsNet	18.6us-gaap_DeferredFinanceCostsNet
Assets held for sale	6.0	6.9
Assets held for sale	12.4	12.4
Prepaid pension	0	32.9
Prepaid items	7.0	10.3
Other	84.4gmt_OtherAssetsCurrentAndNonCurrent	57.7gmt_OtherAssetsCurrentAndNonCurrent
Total	$ 229.0us-gaap_OtherAssets	$ 225.5us-gaap_OtherAssets

Office furniture, fixtures and other equipment, net.

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Other assets current and non current.

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For an unclassified balance sheet, the carrying amount (net of accumulated amortization) as of the balance sheet date of capitalized costs associated with the issuance of debt instruments (for example, legal, accounting, underwriting, printing, and registration costs) that will be charged against earnings over the life of the debt instruments to which such costs pertain.

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The amount for overfunded plans recognized in the balance sheet as a noncurrent asset associated with a defined benefit pension plan or other postretirement defined benefit plan.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Amount classified as other assets attributable to disposal group held for sale or disposed of, expected to be disposed of after one year or the normal operating cycle, if longer.

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Aggregate carrying amount, as of the balance sheet date, of investments and other noncurrent assets not separately disclosed in the balance sheet due to materiality considerations. Noncurrent assets are expected to be realized or consumed after one year (or the normal operating cycle, if longer).

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The aggregate carrying amounts, as of the balance sheet date, of assets not separately disclosed in the balance sheet.

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Amount before valuation and LIFO reserves of other inventory expected to be sold, or consumed within one year or operating cycle, if longer.

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Carrying amount as of the balance sheet date of expenditures made in advance of when the economic benefit of the cost will be realized, and which will be expensed in future periods with the passage of time or when a triggering event occurs.

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