Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	May 31, 2020	Jun. 30, 2020	Nov. 29, 2019
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	May 31, 2020
Entity File Number	1-6263
Entity Registrant Name	AAR CORP
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	36-2334820
Entity Address, Address Line One	One AAR Place
Entity Address, Address Line Two	1100 N. Wood Dale Road
Entity Address, City or Town	Wood Dale
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60191
City Area Code	630
Local Phone Number	227-2000
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 1,474
Entity Common Stock, Shares Outstanding		35,155,371
Entity Central Index Key	0000001750
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--05-31
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2020
Amendment Flag	false
Common Stock | NEW YORK STOCK EXCHANGE, INC.
Title of 12(b) Security	Common Stock, $1.00 par value
Trading Symbol	AIR
Security Exchange Name	NYSE
Common Stock | CHICAGO STOCK EXCHANGE, INC
Title of 12(b) Security	Common Stock, $1.00 par value
Trading Symbol	AIR
Security Exchange Name	CHX
Preferred Stock Purchase Rights | NEW YORK STOCK EXCHANGE, INC.
Title of 12(b) Security	Preferred Stock Purchase Rights
Trading Symbol	AIR
Security Exchange Name	NYSE
Preferred Stock Purchase Rights | CHICAGO STOCK EXCHANGE, INC
Title of 12(b) Security	Preferred Stock Purchase Rights
Trading Symbol	AIR
Security Exchange Name	CHX