Earnings per Share (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2012	Nov. 30, 2011	Nov. 30, 2012	Nov. 30, 2011
Basic EPS:
Net income attributable to AAR and noncontrolling interest	$ 17.9	$ 17.6	$ 36.2	$ 34.2
Less income attributable to participating shares	(0.7)	(0.7)	(1.3)	(1.3)
Less income attributable to noncontrolling interest	(0.1)		(0.2)
Net income attributable to AAR available to common shareholders	17.1	16.9	34.7	32.9
Basic shares:
Weighted average common shares outstanding	38,200,000	38,700,000	38,400,000	38,800,000
Earnings per share - basic:
Earnings per share - basic (in dollars per share)	$ 0.45	$ 0.44	$ 0.90	$ 0.85
Diluted EPS:
Net income attributable to AAR and noncontrolling interest	17.9	17.6	36.2	34.2
Less income attributable to participating shares	(0.7)	(0.6)	(1.3)	(1.2)
Less income attributable to noncontrolling interest	(0.1)		(0.2)
Add after-tax interest on convertible debt	1.2	1.5	2.4	2.9
Net income attributable to AAR available to common shareholders - Diluted	$ 18.3	$ 18.5	$ 37.1	$ 35.9
Diluted shares:
Weighted average common shares outstanding	38,200,000	38,700,000	38,400,000	38,800,000
Additional shares from the assumed exercise of stock options	100,000	200,000		300,000
Additional shares from the assumed conversion of convertible debt	3,200,000	4,100,000	3,200,000	4,100,000
Weighted average common shares outstanding - diluted	41,500,000	43,000,000	41,600,000	43,200,000
Earnings per share - diluted:
Earnings per share - diluted (in dollars per share)	$ 0.44	$ 0.43	$ 0.89	$ 0.83
Antidilutive stock options excluded from the computation of diluted earnings per share (in shares)	1,434,020	267,000