Retirement Plans - Fair Value of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
United States
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 48.8	$ 49.8	$ 59.1
International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.5	15.2	$ 18.6
Fair Value, Measurements, Recurring | United States
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	48.8	49.8
Fair Value, Measurements, Recurring | United States | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.1	4.8
Fair Value, Measurements, Recurring | United States | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fair Value, Measurements, Recurring | United States | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fair Value, Measurements, Recurring | United States | Short-term investments | Money market securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	0.5
Fair Value, Measurements, Recurring | United States | Short-term investments | Money market securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	0.5
Fair Value, Measurements, Recurring | United States | Short-term investments | Money market securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fair Value, Measurements, Recurring | United States | Short-term investments | Money market securities | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fair Value, Measurements, Recurring | United States | Equity securities | Large-cap growth funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at net asset value	19.0	11.5
Fair Value, Measurements, Recurring | United States | Equity securities | International growth fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets at net asset value	15.7	3.4
Fair Value, Measurements, Recurring | United States | Equity securities | Common stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.6	4.3
Fair Value, Measurements, Recurring | United States | Equity securities | Common stocks | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.6	4.3
Fair Value, Measurements, Recurring | United States | Equity securities | Common stocks | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fair Value, Measurements, Recurring | United States | Equity securities | Common stocks | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fair Value, Measurements, Recurring | United States | Equity securities | Commingled trust funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets at net asset value	13.0	30.1
Fair Value, Measurements, Recurring | International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.5	15.2
Fair Value, Measurements, Recurring | International | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fair Value, Measurements, Recurring | International | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.5	15.2
Fair Value, Measurements, Recurring | International | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fair Value, Measurements, Recurring | International | Other investments | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.5	15.2
Fair Value, Measurements, Recurring | International | Other investments | Insurance contracts | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fair Value, Measurements, Recurring | International | Other investments | Insurance contracts | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.5	15.2
Fair Value, Measurements, Recurring | International | Other investments | Insurance contracts | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0.0	$ 0.0