Pension and Other Benefits Financial Assets Recorded at Fair Value by Hierarchy (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	$ 40.9	$ 35.4
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	46.2	40.5
Pension Plan | Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	0.9	1.9
Pension Plan | Defined Benefit Plan, Equity Securities, Large Cap
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	2.0	1.4
Pension Plan | Defined Benefit Plan, Equity Securities, Small Cap
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	0.5	0.3
Pension Plan | Defined Benefit Plan, Equity Securities, Non-US
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	1.2	0.9
Pension Plan | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	36.3	30.9
Pension Plan | Defined Benefit Plan, Real Estate
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	5.3	5.1
Pension Plan | Level 2 | Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	0.9	1.9
Pension Plan | Level 2 | Defined Benefit Plan, Equity Securities, Large Cap
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	2.0	1.4
Pension Plan | Level 2 | Defined Benefit Plan, Equity Securities, Small Cap
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	0.5	0.3
Pension Plan | Level 2 | Defined Benefit Plan, Equity Securities, Non-US
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	1.2	0.9
Pension Plan | Level 2 | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	36.3	30.9
Pension Plan | Level 2 | Defined Benefit Plan, Real Estate
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	0.0	0.0
Pension Plan | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	5.3	5.1
Pension Plan | Level 3 | Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	0.0	0.0
Pension Plan | Level 3 | Defined Benefit Plan, Equity Securities, Large Cap
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	0.0	0.0
Pension Plan | Level 3 | Defined Benefit Plan, Equity Securities, Small Cap
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	0.0	0.0
Pension Plan | Level 3 | Defined Benefit Plan, Equity Securities, Non-US
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	0.0	0.0
Pension Plan | Level 3 | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	0.0	0.0
Pension Plan | Level 3 | Defined Benefit Plan, Real Estate
Defined Benefit Plan Disclosure [Line Items]
Assets, fair value disclosure	$ 5.3	$ 5.1