Debt (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Debt Instrument [Line Items]
Cash payments paid for interest	$ 18.0	$ 15.8
Amortization of treasury lock settlements	1.4	1.4
Amortization of deferred financing costs	0.5	$ 0.4
Unsecured Debt \| Five-Year Term Loan, due August 2021
Debt Instrument [Line Items]
Repayment of debt	$ 29.8
Debt instrument, term	5 years
Unsecured Debt \| Seven-Year Term Loan, due October 2020
Debt Instrument [Line Items]
Repayment of debt	$ 1.6
Debt instrument, term	7 years
Senior Notes \| Fixed-Rate Senior Notes
Debt Instrument [Line Items]
Book value of fixed rate debt	$ 1,647.6
Long-term debt (fixed-rate debt), fair value	1,721.9
Term Loan \| Variable-Rate Term Loans
Debt Instrument [Line Items]
Book value of variable rate debt	$ 979.3

Amount of amortization expense attributable to debt issuance costs.

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-Name Accounting Standards Codification
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Gross amount of debt extinguished.

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The amount of cash paid for interest during the period.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

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The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

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