Long-Term Debt (5.75% Senior Notes Due in 2022) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Book value	$ 1,085.7	$ 938.6
North America
Debt Instrument [Line Items]
Debt issuance costs	(9.1)	(10.6)
5.75% Senior Notes due 2022 \| North America
Debt Instrument [Line Items]
Face Value	600.0	600.0
Debt issuance costs	(5.8)	(7.0)
Book value	594.2	593.0
Fair Value (Level 1)	$ 619.7	$ 579.0
Stated Interest Rate	5.75%	5.75%
Interest Payment	Semi-Annual: Apr 1 & Oct 1	Semi-Annual: Apr 1 & Oct 1
Maturity Date	October 2022	October 2022
Call Option, Beginning Date, year one	Oct. 01, 2017
Call Option, Percentage, year one	102.875%
Call Option, Beginning Date, year two	Oct. 01, 2018
Call Option, Percentage, year two	101.917%
Call Option, Beginning Date, year three	Oct. 01, 2019
Call Option, Percentage, year three	100.958%
Call Option, Percentage, year four and thereafter	100.00%
Redemption price in cash equal to principal plus accrued and unpaid interest, percent	105.75%
5.75% Senior Notes due 2022 \| North America \| Maximum
Debt Instrument [Line Items]
Percent of aggregate principal amount of senior notes that can be redeemed on or prior to October 1, 2015	35.00%
5.75% Senior Notes due 2022 \| North America \| Minimum
Debt Instrument [Line Items]
Percent of aggregate principal amount of senior notes issued remains outstanding	65.00%
1.00% Senior Convertible Notes Due 2012 \| North America
Debt Instrument [Line Items]
Stated Interest Rate	1.00%

Call Option Percentage, Year Four and Thereafter

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Call Option Percentage, Year One

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Call Option Percentage, Year Three

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Call Option Percentage, Year Two

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Debt Instrument Call Date Earliest, Year One

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Debt Instrument Call Date Earliest, Year Three

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Debt instrument interest payment terms.

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Percent of Aggregate Principal Amount of Senior Notes Issued Remains Outstanding

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Percent of Aggregate Principal Amount of Senior Notes that Can be Redeemed

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Redemption Price in Cash Equal to Principal Plus Accrued and Unpaid Interest, Percent

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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.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Contractual interest rate for funds borrowed, under the debt agreement.

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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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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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