Revenue Recognition - Contract Assets and Liabilities and Remaining Performance Obligations (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Feb. 29, 2024	Nov. 30, 2023	Feb. 28, 2023	Feb. 29, 2024	Feb. 28, 2023	May 31, 2023
Contract assets and liabilities
Contract assets - current	$ 86.5			$ 86.5		$ 86.9
Contract assets - non-current	33.5			33.5		27.5
Contract liabilities:
Deferred revenue - current	(16.2)			(16.2)		(19.7)
Deferred revenue on long-term contracts	(6.1)			(6.1)		(12.7)
Net contract assets	97.7			97.7		$ 82.0
Change in contract assets - current				(0.4)
Change in contract assets - non-current				6.0
Change in deferred revenue - current				3.5
Change in deferred revenue on long-term contracts				6.6
Change in net contract assets				15.7
Change in contract assets and revenue				(0.5)	$ 18.5
Changes in deferred revenue
Deferred revenue at beginning of period	(26.4)		$ (28.8)	(32.4)	(30.6)
Revenue deferred	(86.4)		(81.0)	(222.6)	(208.1)
Revenue recognized	85.6		73.9	228.0	194.0
Other	4.9		1.7	4.7	10.5
Deferred revenue at end of period	(22.3)	$ (26.4)	$ (34.2)	(22.3)	$ (34.2)
Remaining Performance Obligations
Remaining performance obligation	$ 825.0			$ 825.0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-03-01
Remaining Performance Obligations
Remaining performance obligation (as a percent)	45.00%			45.00%
Expected timing of satisfaction of remaining performance obligation	12 months			12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-03-01
Remaining Performance Obligations
Remaining performance obligation (as a percent)	55.00%			55.00%
Expected timing of satisfaction of remaining performance obligation	3 years			3 years
PBH contracts
Contract liabilities:
Commercial power by hour, contract, amount derecognized from remaining loss reserves		$ 2.0