Pension and Post-retirement and Other Benefit Plans - Actual Pension Plans' Asset Allocations by Level Within the Fair Value Hierarchy (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	$ 261.5	$ 233.0
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	2.7	3.4
Equity securities, Large cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	53.5	44.0
Equity securities, Small cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	48.8	71.1
Government securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	9.0	8.8
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	61.5	57.4
Real estate and other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	46.1	48.3
Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	159.4	140.0
Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	2.7	3.4
Level 1 | Equity securities, Large cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0.0	0.0
Level 1 | Equity securities, Small cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	48.8	71.1
Level 1 | Government securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0.0	0.0
Level 1 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	49.0	46.2
Level 1 | Real estate and other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	19.0	19.3
Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	102.1	93.0
Level 2 | Equity securities, Large cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	53.5	44.0
Level 2 | Equity securities, Small cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0.0	0.0
Level 2 | Government securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	9.0	8.8
Level 2 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	12.5	11.2
Level 2 | Real estate and other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	27.1	29.0
Level 3 | Equity securities, Large cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0.0	0.0
Level 3 | Equity securities, Small cap
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0.0	0.0
Level 3 | Government securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0.0	0.0
Level 3 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	0.0	0.0
Level 3 | Real estate and other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, fair value of plan assets	$ 0.0	$ 0.0