Income Tax Expense - Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Unrecognized Tax Benefits
Unrecognized tax benefit, if recognized, would have an impact on effective tax rate	$ 13.9
Payment of interest and penalties accrued	1.0	0.4
Activity for unrecognized tax benefits [Roll Forward]
Balance at beginning of period	8.1us-gaap_UnrecognizedTaxBenefits	1.8us-gaap_UnrecognizedTaxBenefits	1.9us-gaap_UnrecognizedTaxBenefits
Tax positions related to current year additions	0.5	0	0
Additions for tax positions of prior years	0	7.2	0.1
Tax positions related to prior years reductions	(3.5)	(0.8)	0
Reductions due to lapse of statute of limitations on tax positions	0	(0.1)	0
Current year acquisitions	9.8	0	0
Settlements	(1.0)	0	(0.2)
Balance at end of period	$ 13.9us-gaap_UnrecognizedTaxBenefits	$ 8.1us-gaap_UnrecognizedTaxBenefits	$ 1.8us-gaap_UnrecognizedTaxBenefits

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

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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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 accrued for interest on an underpayment of income taxes and 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 acquisitions.

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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 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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