Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended									12 Months Ended
	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	May 31, 2019	May 31, 2018	May 31, 2017
Discontinued Operations
Interest expense										$ 9.5	$ 8.0	$ 5.3
Operating results for discontinued operations
Sales										95.8	96.3	176.9
Cost of sales										(106.1)	(101.4)	(165.1)
Asset impairments										(74.1)	(65.2)
Selling, general and administrative expenses										(12.1)	(11.8)	(16.1)
Operating loss from discontinued operations										(96.5)	(82.1)	(4.3)
Provision for income taxes (benefit)									$ (6.7)	(19.9)	(24.0)	(8.8)
Income (Loss) from discontinued operations	$ (3.8)	$ (64.8)	$ (4.2)	$ (3.8)	$ (6.1)	$ (15.8)	$ (35.8)	$ (0.4)		(76.6)	(58.1)	4.5
Carrying amounts of the major classes of assets and liabilities for our discontinued operations
Accounts receivable, net	16.2				14.7					16.2	14.7
Inventory, rotable assets, and equipment	7.5				106.1					7.5	106.1
Other assets	5.5				4.2					5.5	4.2
Assets of discontinued operations	29.2				125.0					29.2	125.0
Liabilities of discontinued operations	$ 29.2				$ 25.0					29.2	25.0
Contractor-Owned, Contractor-Operated | Discontinued Operations, Held-for-sale or Disposed of by Sale
Discontinued Operations
Impairment and other charges							$ 54.2
Goodwill impairment charge		$ 74.1				$ 9.8
General corporate overhead										0.0	0.0	0.0
Interest expense										$ 0.0	$ 0.0	$ 0.0