Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	May 31, 2017	Feb. 28, 2017	Aug. 31, 2016	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015	Aug. 31, 2015	May 31, 2015	May 31, 2017	May 31, 2016	May 31, 2015
Discontinued Operations
Impairment charges											$ 53.0
Interest expense									$ 5.5	$ 6.4	27.2
Income from discontinued operations
Provision for income taxes (benefit)	$ (6.7)				$ 2.8
Income from discontinued operations									6.3	9.4	84.3
Income from discontinued operations attributable to AAR	6.1	$ 0.6	$ (0.4)	$ 0.2	$ (5.1)	$ (1.2)	$ 15.5		6.3	9.4	84.1
Cost of Product
Discontinued Operations
Impairment charges											25.6
Telair Cargo Group and PSM | Discontinued Operations, Held-for-sale or Disposed of by Sale
Discontinued Operations
General corporate overhead									0.0	0.0	0.0
Interest expense									0.0	0.0	8.5
Assets and liabilities held for sale related to discontinued operations
Liabilities of discontinued operations	$ 6.9			$ 12.5					6.9	12.5
Income from discontinued operations
Sales									0.6	11.5	259.2
Cost of sales									1.0	15.3	219.7
Selling, general and administrative expenses									1.2	3.0	26.9
Interest expense, net											9.4
Operating income (loss) from discontinued operations									(1.6)	(6.8)	3.2
Provision for income taxes (benefit)									(7.9)	11.5	85.6
Income from discontinued operations									6.3	9.4	84.3
Income attributable to noncontrolling interest											(0.2)
Income from discontinued operations attributable to AAR									$ 6.3	9.4	84.1
Telair Cargo Group
Discontinued Operations
Gain on sale of assets							27.7
Income from discontinued operations
Gain recognized on sale of business											49.7
Telair Cargo Group | Disposed of by sale
Discontinued Operations
Cash consideration received before fees and expenses								$ 705.0
Gain on sale of assets								198.6
Telair Cargo Group | A400M | Discontinued Operations, Held-for-sale or Disposed of by Sale
Income from discontinued operations
Gain recognized on sale of business										$ 27.7	198.6
Telair Cargo Group | A400M | Disposed of by sale
Income from discontinued operations
Gain recognized on sale of business							$ 27.7
Telair Cargo Group | A400M | Maximum | Disposed of by sale
Discontinued Operations
Contingent consideration								$ 35.0
Precision Systems Manufacturing | Discontinued Operations, Held-for-sale or Disposed of by Sale
Income from discontinued operations
PSM Impairment charge											(31.9)
Precision Systems Manufacturing | Discontinued Operations, Held-for-sale
Income from discontinued operations
PSM Impairment charge											$ 57.5