Employee benefit plans - changes in benefit obligations and plan assets and funded status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
United States | Pension plans
Benefit obligation:
Beginning balance	$ 230.1	$ 246.0
Service cost	3.4	3.6
Interest cost	5.3	4.4
Employee contributions	0.0	0.0
Actuarial gain	(54.4)	(7.6)
Benefits paid	(15.7)	(16.3)
Settlements and curtailments	0.0	0.0
Currency translation	0.0	0.0
Other	0.0	0.0
Ending balance	168.7	230.1
Fair value of plan assets:
Beginning balance	268.9	286.6
(Loss) return on plan assets	(42.5)	(2.1)
Employer contributions	0.7	0.7
Employee contributions	0.0	0.0
Benefits paid	(15.7)	(16.3)
Settlements and curtailments	0.0	0.0
Currency translation	0.0	0.0
Other	0.0	0.0
Ending balance	211.4	268.9
Defined benefit plan, funded status of plan
Funded status at end of year	42.7	38.8
United States | Medical plans
Benefit obligation:
Beginning balance	14.9	15.3
Service cost	0.1	0.2
Interest cost	0.3	0.3
Employee contributions	0.0	0.0
Actuarial gain	(4.7)	(0.5)
Benefits paid	(0.4)	(0.4)
Settlements and curtailments	0.0	0.0
Currency translation	0.0	0.0
Other	0.0	0.0
Ending balance	10.2	14.9
Fair value of plan assets:
Beginning balance	0.0	0.0
(Loss) return on plan assets	0.0	0.0
Employer contributions	0.4	0.4
Employee contributions	0.0	0.0
Benefits paid	(0.4)	(0.4)
Settlements and curtailments	0.0	0.0
Currency translation	0.0	0.0
Other	0.0	0.0
Ending balance	0.0	0.0
Defined benefit plan, funded status of plan
Funded status at end of year	(10.2)	(14.9)
Non-U.S. | Pension plans
Benefit obligation:
Beginning balance	291.6	301.4
Service cost	4.1	5.5
Interest cost	3.3	2.6
Employee contributions	1.2	1.2
Actuarial gain	(92.6)	(1.7)
Benefits paid	(5.6)	(3.3)
Settlements and curtailments	(1.5)	(1.7)
Currency translation	(21.1)	(11.1)
Other	(0.1)	(1.3)
Ending balance	179.3	291.6
Fair value of plan assets:
Beginning balance	182.8	167.5
(Loss) return on plan assets	(49.4)	16.9
Employer contributions	5.6	5.2
Employee contributions	1.2	1.2
Benefits paid	(5.6)	(3.3)
Settlements and curtailments	(1.5)	(1.7)
Currency translation	(14.7)	(3.0)
Other	0.2	0.0
Ending balance	118.6	182.8
Defined benefit plan, funded status of plan
Funded status at end of year	$ (60.7)	$ (108.8)