Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017	May 31, 2017
Discontinued Operations
Liabilities of discontinued operations	$ 26.5		$ 26.5		$ 33.4
Interest expense	2.2	$ 1.4	5.8	$ 3.8
Operating results for discontinued operations
Sales	8.8	39.5	79.2	135.1
Cost of sales	(15.8)	(37.3)	(81.6)	(125.1)
Asset impairments	(11.0)		(65.2)
Selling, general and administrative expenses	(2.6)	(4.3)	(9.6)	(11.7)
Loss from discontinued operations before provision for income tax benefit	(20.6)	(2.1)	(77.2)	(1.7)
Provision for income tax benefit	(4.8)	(1.4)	(25.2)	(1.3)
Loss from discontinued operations	(15.8)	(0.7)	(52.0)	(0.4)
Carrying amounts of the major classes of assets and liabilities for our discontinued operations
Inventory, rotable assets, and equipment	110.4		110.4		183.7
Goodwill					9.8
Other assets	12.3		12.3		25.9
Assets of discontinued operations	122.7		122.7		219.4
Liabilities - current	26.5		26.5		30.8
Liabilities - non-current					2.6
Liabilities of discontinued operations	26.5		26.5		$ 33.4
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	0.0	0.0
Interest expense	$ 0.0	$ 0.0	$ 0.0	$ 0.0