Employee Benefit Plans - Schedule of Plan Assets Using the Fair Value Hierarchy (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 161.3	$ 150.4
Net Asset Value ("NAV")
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	142.2	135.0
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.7	0.9
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.4	14.5
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.7	0.9
Cash | Net Asset Value ("NAV")
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Cash | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.7	0.9
Cash | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Cash | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Insurance Group Annuity Contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.4	14.5
Insurance Group Annuity Contracts | Net Asset Value ("NAV")
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Insurance Group Annuity 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
Insurance Group Annuity Contracts | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Insurance Group Annuity Contracts | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.4	14.5	$ 106.5
Common/Collective Trust Funds — Government, Corporate and Other Non-government Debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	70.4	0.0
Common/Collective Trust Funds — Government, Corporate and Other Non-government Debt | Net Asset Value ("NAV")
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	70.4	93.7
Common/Collective Trust Funds — Government, Corporate and Other Non-government Debt | 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
Common/Collective Trust Funds — Government, Corporate and Other Non-government Debt | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Common/Collective Trust Funds — Government, Corporate and Other Non-government Debt | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Common/Collective Trust Funds — Corporate Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	71.8	0.0
Common/Collective Trust Funds — Corporate Equity | Net Asset Value ("NAV")
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	71.8	41.3
Common/Collective Trust Funds — Corporate Equity | 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
Common/Collective Trust Funds — Corporate Equity | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Common/Collective Trust Funds — Corporate Equity | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0.0	$ 0.0