Summary of Significant Accounting Policies - Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2019	May 31, 2018	May 31, 2017
Allowance for Doubtful Accounts
Other liabilities	$ 28.3	$ 26.4
Balance, beginning of year	7.5	4.9	$ 3.3
Provision charged to operations	15.8	0.5	2.1
Recoveries, deductions for accounts written off and other reclassifications	(7.3)	2.1	(0.5)
Balance, end of year	16.0	$ 7.5	$ 4.9
European airline customer
Allowance for Doubtful Accounts
Impairment of non-current contract assets	7.6
Other liabilities	1.5
Provision charged to operations	12.4
Balance, end of year	$ 3.3