Benefit Plans - Allocation of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	100.00%	100.00%
Fair value of plan assets	$ 258.1	$ 244.1
Pension plan assets in the fair value hierarchy
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	43.7	39.4
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.5	7.3
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	42.2	32.1
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0
Pension plan assets measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	214.4	204.7
Cash | Pension plan assets in the fair value hierarchy
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.5	2.2
Cash | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.5	2.2
Cash | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Cash | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0.0	$ 0.0
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	34.00%	33.00%
Equity securities | United States
Defined Benefit Plan Disclosure [Line Items]
Target allocation	30.00%
Equity securities | Pension plan assets in the fair value hierarchy
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 20.6	$ 15.5
Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	1.3
Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20.6	14.2
Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0.0	$ 0.0
Debt securities
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	64.00%	65.00%
Debt securities | United States
Defined Benefit Plan Disclosure [Line Items]
Target allocation	70.00%
Other
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	2.00%	2.00%
Other | United States
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Mutual funds | Pension plan assets in the fair value hierarchy
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 18.7	$ 21.7
Mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	3.8
Mutual funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18.7	17.9
Mutual funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	$ 0.0
Other mutual funds | Pension plan assets in the fair value hierarchy
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.9
Other mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0
Other mutual funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.9
Other mutual funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0.0
Minimum | Equity securities | United States
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	27.00%
Minimum | Debt securities | United States
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	67.00%
Minimum | Other | United States
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	0.00%
Maximum | Equity securities | United States
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	33.00%
Maximum | Debt securities | United States
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	73.00%
Maximum | Other | United States
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	3.00%