Segment information - Revenue, Properties and Outsourcing Assets by Geographic Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 1,979.9	$ 2,054.4	$ 2,026.3
Properties, net	75.9	86.5	110.5
Outsourcing assets, net	66.4	124.6	173.9
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	854.9	856.2	781.5
Properties, net	52.5	62.5	82.0
Outsourcing assets, net	36.0	66.2	93.1
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	228.0	284.9	228.0
Outsourcing assets, net	17.9	36.3	55.3
Australia
Revenues from External Customers and Long-Lived Assets [Line Items]
Outsourcing assets, net	9.5	16.7	19.3
Other foreign
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	897.0	913.3	1,016.8
Properties, net	23.4	24.0	28.5
Outsourcing assets, net	$ 3.0	$ 5.4	$ 6.2