| Cover | Apr. 14, 2021 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Apr. 14, 2021 |
| Entity File Number | 1-6263 |
| Entity Registrant Name | AAR CORP. |
| Entity Central Index Key | 0000001750 |
| Entity Tax Identification Number | 36-2334820 |
| Entity Incorporation, State or Country Code | DE |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | CHICAGO STOCK EXCHANGE, INC [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock, $1.00 par value |
| Trading Symbol | AIR |
| Security Exchange Name | CHX |
| Common Stock [Member] | NEW YORK STOCK EXCHANGE, INC. [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock, $1.00 par value |
| Trading Symbol | AIR |
| Security Exchange Name | NYSE |
