Revenue Recognition - Contract Assets and Liabilities and Remaining Performance Obligations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2023	Nov. 30, 2022	Nov. 30, 2023	Nov. 30, 2022	May 31, 2023
Contract assets and liabilities
Contract assets - current	$ 99.3		$ 99.3		$ 86.9
Contract assets - non-current	33.1		33.1		27.5
Contract liabilities:
Deferred revenue - current	(16.6)		(16.6)		(19.7)
Deferred revenue on long-term contracts	(9.8)		(9.8)		(12.7)
Net contract assets	106.0		106.0		$ 82.0
Change in contract assets - current			12.4
Change in contract assets - non-current			5.6
Change in contract liabilities - current			3.1
Change in contract liabilities - non-current			2.9
Change in net contract assets			24.0
Change in contract assets and revenue			12.4	$ 9.3
Changes in deferred revenue
Deferred revenue at beginning of period	(37.1)	$ (33.5)	(32.4)	(30.6)
Revenue deferred	(69.4)	(69.6)	(136.2)	(127.1)
Revenue recognized	81.3	66.6	142.4	120.1
Other	(1.2)	7.7	(0.2)	8.8
Deferred revenue at end of period	(26.4)	$ (28.8)	(26.4)	$ (28.8)
Remaining Performance Obligations
Remaining performance obligation	$ 720.0		$ 720.0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-03-01
Remaining Performance Obligations
Remaining performance obligation (as a percent)	55.00%		55.00%
Expected timing of satisfaction of remaining performance obligation	12 months		12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-03-01
Remaining Performance Obligations
Remaining performance obligation (as a percent)	50.00%		50.00%
Expected timing of satisfaction of remaining performance obligation	3 years		3 years
PBH contracts
Contract liabilities:
Contract Charges on non-achievement of minimum volume guarantees			$ 8.1
Commercial power by hour, contract, amount derecognized from remaining loss reserves	$ 2.0
PBH contracts | Accrued liabilities
Contract liabilities:
PBH forward loss reserve	$ 3.1		$ 3.1