Income Tax Expense - Gross Unrecognized Income Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of Gross Unrecognized Income Tax Benefits [Roll Forward]
Balance at January 1	$ 1.2us-gaap_UnrecognizedTaxBenefits	$ 2.7us-gaap_UnrecognizedTaxBenefits	$ 11.4us-gaap_UnrecognizedTaxBenefits
Additions for Tax Positions Related to the Current Year	0	0.1	0
Additions for Tax Positions Related to Prior Years	1.0	1.3	0
Reduction for Tax Positions Related to Prior Years	0	0	(8.7)
Reductions for Settlements	0	(2.9)	0
Lapse of Statute	(0.2)	0	0
Balance as of December 31	2.0us-gaap_UnrecognizedTaxBenefits	1.2us-gaap_UnrecognizedTaxBenefits	2.7us-gaap_UnrecognizedTaxBenefits
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0.4
Unrecognized Tax Benefits, Accrued Interest	0	0.5	0.5
Unrecognized Tax Benefits, Interest Expense (Reduction)	0.5	0	0.6
Unrecognized Tax Benefits, Penalties	0	0	0
Reasonably Possible Change in Unrecognized Tax Benefits in Next 12 Months	$ 0.1

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The amount of the unrecognized tax benefit of a position taken for which it is reasonably possible that the total amount thereof will significantly increase or decrease within twelve months of the balance sheet date.

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Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of expense for penalties related to a tax position claimed or expected to be claimed in the tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of interest expense accrued for an underpayment of income taxes.

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Amount of interest expense for an underpayment of income taxes.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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