Debt - Long-term (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total long-term debt	$ 3,093.9	$ 3,094.2
Debt issuance cost	(12.3)	(13.2)
Less: debt maturing within one year	100.7	101.2
Total long-term debt, less current portion	2,993.2	2,993.0
Pollution control and industrial revenue bonds (less unamortized discounts of $0.2 and $0.2, respectively)
Debt Instrument [Line Items]
Long-term debt, gross	$ 51.6	51.6
Maturity date, minimum	2021
Maturity date, maximum	2032
Unamortized discounts	$ 0.2	0.2
Pollution control and industrial revenue bonds (less unamortized discounts of $0.2 and $0.2, respectively) \| Minimum
Debt Instrument [Line Items]
Interest Rate Percentage	1.90%
Pollution control and industrial revenue bonds (less unamortized discounts of $0.2 and $0.2, respectively) \| Maximum
Debt Instrument [Line Items]
Interest Rate Percentage	6.50%
Senior notes (less unamortized discount of $1.0 and $1.1, respectively)
Debt Instrument [Line Items]
Long-term debt, gross	$ 999.0	998.9
Maturity date, minimum	2019
Maturity date, maximum	2024
Unamortized discounts	$ 1.0	1.1
Senior notes (less unamortized discount of $1.0 and $1.1, respectively) \| Minimum
Debt Instrument [Line Items]
Interest Rate Percentage	3.95%
Senior notes (less unamortized discount of $1.0 and $1.1, respectively) \| Maximum
Debt Instrument [Line Items]
Interest Rate Percentage	5.20%
2014 Term Loan Facility
Debt Instrument [Line Items]
Interest Rate Percentage	3.10%
Maturity Date	2020
Long-term debt, gross	$ 450.0	450.0
2017 Term Loan Facility
Debt Instrument [Line Items]
Interest Rate Percentage	3.10%
Maturity Date	2022
Long-term debt, gross	$ 1,500.0	1,500.0
Credit Facility
Debt Instrument [Line Items]
Interest Rate Percentage	4.40%
Maturity Date	2022
Long-term debt, gross	$ 0.0	0.0
Letters of credit outstanding amount	157.5
Credit Agreement, available funds	1,158.0
Foreign debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 105.6	$ 106.9
Maturity date, minimum	2020
Maturity date, maximum	2024
Foreign debt \| Minimum
Debt Instrument [Line Items]
Interest Rate Percentage	0.00%
Foreign debt \| Maximum
Debt Instrument [Line Items]
Interest Rate Percentage	10.80%

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Debt Instrument, Maturity Year Range, End

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Debt Instrument, Maturity Year Range, Start

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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-Subparagraph (SX 210.5-02(22))
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Contractual interest rate for funds borrowed, under the debt agreement.

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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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Amount, after accumulated amortization, of debt discount.

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-Publisher FASB
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-SubTopic 30
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Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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