Employee Benefit Plans - Schedule of change in benefit obligations (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2022	May 31, 2021	May 31, 2020
Pension Plans
Change in benefit obligation:
Plan amendments	$ 0.0	$ 0.0
U.K. | Pension Plans
Change in benefit obligation:
Benefit obligation at beginning of year	47.0	41.7
Interest cost	0.8	0.7	$ 0.9
Plan participants’ contributions	0.0	0.0
Actuarial losses (gains)	(9.6)	(0.3)
Foreign currency translation	(5.3)	6.4
Benefits paid, including expenses	(1.0)	(1.5)
Benefit obligation at end of year	31.9	47.0	41.7
U.S. | Other Postretirement Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	12.1	20.8
Interest cost	0.2	0.3	0.6
Plan participants’ contributions	0.1	0.1
Actuarial losses (gains)	(1.9)	0.3
Foreign currency translation	0.0	0.0
Plan amendments	0.0	(7.6)
Benefits paid, including expenses	(1.1)	(1.8)
Benefit obligation at end of year	$ 9.4	$ 12.1	$ 20.8