Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Nov. 30, 2018	Feb. 28, 2018	Nov. 30, 2017	Nov. 30, 2018	Nov. 30, 2017	May 31, 2018
Discontinued Operations
Interest expense	$ 2.5		$ 1.9	$ 4.6	$ 3.6
Operating results for discontinued operations
Sales	22.2		29.1	42.2	70.4
Cost of sales	(25.4)		(27.4)	(47.7)	(65.8)
Asset impairments			(54.2)		(54.2)
Selling, general and administrative expenses	(2.3)		(3.4)	(4.8)	(7.0)
Loss from discontinued operations before provision for income tax benefit	(5.5)		(55.9)	(10.3)	(56.6)
Provision for income tax benefit	(1.3)		(20.1)	(2.3)	(20.4)
Loss from discontinued operations	(4.2)		(35.8)	(8.0)	$ (36.2)
Carrying amounts of the major classes of assets and liabilities for our discontinued operations
Inventory, rotable assets, and equipment	93.5			93.5		$ 106.1
Accounts receivable, net	13.1			13.1		14.7
Other assets	3.3			3.3		4.2
Assets of discontinued operations	109.9			109.9		125.0
Liabilities of discontinued operations	24.6			24.6		$ 25.0
Contractor-Owned, Contractor-Operated | Discontinued Operations, Held-for-sale or Disposed of by Sale
Discontinued Operations
Goodwill impairment charge		$ 9.8
Impairment and other charges			$ 54.2
General corporate overhead	0.0			0.0
Interest expense	$ 0.0			$ 0.0