Earnings per Share (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	9 Months Ended
Feb. 28, 2015	Feb. 28, 2014	Feb. 28, 2015	Feb. 28, 2014
Earnings per Share
Effect to the participating securities as result of net loss			$ 0
Antidilutive stock options excluded from the computation of diluted earnings per share (in shares)			169,163	170,000
Reconciliation of the computations of basic and diluted earnings per share
Income from continuing operations	1.9	16.9	27.6	52.3
Less income attributable to participating shares	(0.1)	(0.4)	(0.6)	(1.2)
Income from continuing operations attributable to common shareholders	1.8	16.5	27.0	51.1
Income (Loss) from discontinued operations attributable to common shareholders	(36.4)	1.0	(32.5)	3.5
Net income attributable to AAR available to common shareholders	$ (34.6)	$ 17.5	$ (5.5)	$ 54.6
Weighted average common shares outstanding - basic	38,700,000	38,600,000	38,700,000	38,600,000
Additional shares from the assumed exercise of stock options	500,000	500,000	500,000	500,000
Weighted average common shares outstanding - diluted	39,200,000	39,100,000	39,200,000	39,100,000
Earnings (Loss) per share - basic:
Earnings from continuing operations (in dollors per share)	$ 0.05	$ 0.43	$ 0.70	$ 1.32
Earnings from discontinued operations (in dollors per share)	$ (0.94)	$ 0.02	$ (0.84)	$ 0.09
Earnings per share - basic (in dollars per share)	$ (0.89)us-gaap_EarningsPerShareBasic	$ 0.45us-gaap_EarningsPerShareBasic	$ (0.14)us-gaap_EarningsPerShareBasic	$ 1.41us-gaap_EarningsPerShareBasic
Earnings (Loss) per share - diluted:
Earnings from continuing operations (in dollors per share)	$ 0.05	$ 0.43	$ 0.69	$ 1.31
Earnings (loss) from discontinued operations (in dollors per share)	$ (0.94)	$ 0.02	$ (0.84)	$ 0.09
Earnings (loss) per share - diluted (in dollars per share)	$ (0.89)us-gaap_EarningsPerShareDiluted	$ 0.45us-gaap_EarningsPerShareDiluted	$ (0.15)us-gaap_EarningsPerShareDiluted	$ 1.40us-gaap_EarningsPerShareDiluted

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The value of the aggregate of earnings distributed and earnings allocated to participating securities under the two-class method for purposes of the basic earnings per share calculation to the extent that participating securities may share in earnings as if all of the earnings for the period had been distributed.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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Amount of income (loss) from continuing operations attributable to the parent. Also defined as revenue less expenses and taxes from ongoing operations before extraordinary items but after deduction of those portions of income or loss from continuing operations that are allocable to noncontrolling interests.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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