Summary of Significant Accounting Policies - Goodwill (Details) $ in Millions	12 Months Ended
	May 31, 2016 USD ($) item	May 31, 2015 USD ($)
Goodwill by reportable segment
Total number of reporting units | item	5
Number of reporting units assigned for goodwill | item	4
Goodwill, Beginning Balance	$ 123.5	$ 261.7
Businesses sold or assets held for sale		(136.3)
Acquisition	1.3
Deferred tax adjustments	(6.5)
Foreign currency translation adjustments	(1.0)	(1.9)
Goodwill, Ending Balance	$ 117.3	123.5
Discontinued operations
Goodwill by reportable segment
Goodwill, Beginning Balance		141.0
Reallocation of goodwill		(4.7)
Businesses sold or assets held for sale		(136.3)
Aviation Services
Goodwill by reportable segment
Number of reporting units assigned for goodwill | item	2
Goodwill, Beginning Balance	$ 73.8	75.7
Deferred tax adjustments	(6.5)
Foreign currency translation adjustments	(1.0)	(1.9)
Goodwill, Ending Balance	$ 66.3	73.8
Expeditionary Services
Goodwill by reportable segment
Number of reporting units assigned for goodwill | item	2
Goodwill, Beginning Balance	$ 49.7	45.0
Reallocation of goodwill		4.7
Acquisition	1.3
Goodwill, Ending Balance	$ 51.0	$ 49.7