Pension Plans - Fair Value of Plans Assets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 423.4	$ 403.9	$ 371.1
Equities and growth funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	149.9	179.2
Government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64.6	63.1
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	194.1	159.7
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.8	1.9
U.K.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	376.6	358.9	328.7
U.K. | Equities and growth funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	149.9	152.3
U.K. | Government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64.6	63.1
U.K. | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	147.5	141.6
U.K. | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.6	1.9
U.S. / other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	46.8	45.0	$ 42.4
U.S. / other | Equities and growth funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	26.9
U.S. / other | Government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. / other | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	46.6	18.1
U.S. / other | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0.2	$ 0.0