Aircraft Portfolio - Joint Venture (Details) $ in Millions	12 Months Ended
	May 31, 2016 USD ($)	May 31, 2015 USD ($) item	May 31, 2014 USD ($)
Aircraft portfolio
Sales from services	$ 761.2	$ 702.9	$ 807.8
Owned Through Joint Ventures
Aircraft portfolio
Equity investments	15.0	20.5
Investment in joint ventures, receivable from sale of aircraft	$ 2.6	5.7
Membership interest in joint ventures (as a percent)	50.00%
Sales from services	$ 0.9	0.1	0.1
Summarized income statement information
Sales	3.6	14.7	10.4
Income (Loss) before provision for income taxes	(0.3)	0.9	$ 6.7
Balance sheet information:
Assets	32.6	48.2
Debt		4.6
Members' capital	$ 27.3	$ 41.0
Number of aircraft sold by joint venture partners | item		1
Revenue from sale of aircraft by joint venture partners		$ 5.1