Employees - Fair Value of Pension Assets by Category (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 115.7	$ 108.8	$ 96.1
Quoted Prices in Active Markets For Identical Assets or Liabilities (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	99.3
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	115.7	9.5
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	62.8	67.1
U.S. companies | Quoted Prices in Active Markets For Identical Assets or Liabilities (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	67.1
U.S. companies | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	62.8	0.0
U.S. companies | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
International companies
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	14.0	18.3
International companies | Quoted Prices in Active Markets For Identical Assets or Liabilities (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	18.3
International companies | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	14.0	0.0
International companies | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Preferred securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	4.4	4.6
Preferred securities | Quoted Prices in Active Markets For Identical Assets or Liabilities (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	4.6
Preferred securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	4.4	0.0
Preferred securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Bond securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	26.6	9.5
Bond securities | Quoted Prices in Active Markets For Identical Assets or Liabilities (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Bond securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	26.6	9.5
Bond securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Real estate securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	7.9	9.3
Real estate securities | Quoted Prices in Active Markets For Identical Assets or Liabilities (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	9.3
Real estate securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	7.9	0.0
Real estate securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 0.0	$ 0.0