| Document and Entity Information | Feb. 13, 2020 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Feb. 13, 2020 |
| Entity Registrant Name | KELLY SERVICES, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 0-1088 |
| Entity Tax Identification Number | 38-1510762 |
| Entity Address, Address Line One | 999 West Big Beaver Road |
| Entity Address, City or Town | Troy |
| Entity Address, State or Province | MI |
| Entity Address, Postal Zip Code | 48084 |
| City Area Code | 248 |
| Local Phone Number | 362-4444 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Entity Emerging Growth Company | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Central Index Key | 0000055135 |
| Amendment Flag | false |
| NASDAQ Global Market | Class A Common | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Class A Common |
| Trading Symbol | KELYA |
| Security Exchange Name | NASDAQ |
| NASDAQ Global Market | Class B Common | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Class B Common |
| Trading Symbol | KELYB |
| Security Exchange Name | NASDAQ |
