| Document and Entity Information Document | Nov. 02, 2020 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Nov. 2, 2020 |
| Entity Registrant Name | Jones Lang LaSalle Incorporated |
| Entity Central Index Key | 0001037976 |
| Amendment Flag | false |
| Entity Incorporation, State or 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 |
| Title of 12(b) Security | Common Stock, par value $0.01 |
| Trading Symbol | JLL |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
