| Document and Entity Information | Jun. 22, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | JONES LANG LASALLE INC |
| Amendment Flag | false |
| Entity Central Index Key | 0001037976 |
| Document Type | 8-K |
| Document Period End Date | Jun. 22, 2020 |
| Entity Incorporation State Country Code | MD |
| Entity File Number | 001-13145 |
| Entity Tax Identification Number | 36-4150422 |
| Entity Address, Address Line One | 200 East Randolph Drive |
| Entity Address, City or Town | Chicago |
| Entity Address, State or Province | IL |
| Entity Address, Postal Zip Code | 60601 |
| City Area Code | 312 |
| Local Phone Number | 782-5800 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.01 |
| Trading Symbol | JLL |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
