| Document and Entity Information Document | Feb. 09, 2021 | Feb. 08, 2021 |
| Entity Information [Line Items] | ||
| Document Type | 8-K | |
| Document Period End Date | Feb. 9, 2021 | |
| Entity Registrant Name | Jones Lang LaSalle Incorporated | |
| Entity Central Index Key | 0001037976 | |
| Amendment Flag | false | |
| Entity Incorporation, State or Country Code | MD | 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 |
