Employee Benefits - Schedule of Pension Assets at Fair Value Hierarchy Level (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	$ 900.0	$ 874.9	$ 998.3
Fair Value, Measurements, Recurring
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	900.0	874.9
Fair Value, Measurements, Recurring | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	137.1	129.9
Fair Value, Measurements, Recurring | Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	181.9	163.9
Fair Value, Measurements, Recurring | Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	44.8	44.3	$ 52.6
Fair Value, Measurements, Recurring | Equities
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	67.0	67.7
Fair Value, Measurements, Recurring | Equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	66.6	65.5
Fair Value, Measurements, Recurring | Equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	0.4	2.2
Fair Value, Measurements, Recurring | Private Equities
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	36.4	43.4
Fair Value, Measurements, Recurring | Private Equities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	36.4	43.4
Fair Value, Measurements, Recurring | Corporate and Other
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	29.0	24.8
Fair Value, Measurements, Recurring | Corporate and Other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	2.2	7.7
Fair Value, Measurements, Recurring | Corporate and Other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	18.4	16.2
Fair Value, Measurements, Recurring | Corporate and Other | Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	8.4	0.9
Fair Value, Measurements, Recurring | Government
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	204.2	177.1
Fair Value, Measurements, Recurring | Government | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	53.3	67.2
Fair Value, Measurements, Recurring | Government | Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	150.9	109.9
Fair Value, Measurements, Recurring | Interest Bearing
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	27.2	25.1
Fair Value, Measurements, Recurring | Interest Bearing | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	15.0	(10.5)
Fair Value, Measurements, Recurring | Interest Bearing | Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	12.2	35.6
Fair Value, Measurements, Recurring | Investments Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Pension assets at fair value	$ 536.2	$ 536.8