Employee Benefit Plans - Schedule of net periodic costs (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2024	May 31, 2023	May 31, 2022
Components of net periodic (benefit) cost:
Amortization of net actuarial (gain) loss	$ 0.4	$ (0.4)	$ (0.0)
U.K. | Pension Plans
Components of net periodic (benefit) cost:
Interest cost	1.3	1.0	0.8
Expected return on assets	(1.1)	(1.3)	(1.2)
Prior service credit (cost)	0.0	0.0	0.0
Amortization of net actuarial (gain) loss	1.3	0.5	0.9
Net periodic (benefit) cost	1.5	0.2	0.5
U.S. | Other Postretirement Benefits
Components of net periodic (benefit) cost:
Interest cost	0.3	0.3	0.2
Expected return on assets	0.0	0.0	0.0
Prior service credit (cost)	(0.8)	(0.8)	(0.8)
Amortization of net actuarial (gain) loss	(0.0)	0.0	0.0
Net periodic (benefit) cost	$ (0.5)	$ (0.5)	$ (0.6)