Summary of Significant Accounting Policies - Inventory (Details) $ in Millions	3 Months Ended	12 Months Ended
	May 31, 2015 USD ($) aircraft	May 31, 2015 USD ($) aircraft	May 31, 2017 USD ($)	May 31, 2016 USD ($)
Inventories
Raw materials and parts			$ 45.0	$ 46.3
Work-in-process			25.8	23.4
Aircraft and engine parts, components and finished goods			393.1	366.6
Aircraft held for sale and related support parts			19.2	15.7
Total inventories			$ 483.1	$ 452.0
Inventory impairment charge		$ 8.9
Sales Proceeds from sale-leaseback advance		$ 40.3
Rotary-wing aircraft
Inventories
Number of aircrafts under sale leaseback transaction | aircraft	2	2
Sale leaseback transaction loss	$ 1.1