v3.8.0.1
Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2017
Feb. 06, 2018
Jul. 02, 2017
Document Information [Line Items]      
Entity Registrant Name Kelly Services Inc    
Document Type 10-K    
Current Fiscal Year End Date --12-31    
Entity Public Float     $ 699,819,783
Amendment Flag false    
Entity Central Index Key 0000055135    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Filer Category Accelerated Filer    
Entity Well-known Seasoned Issuer No    
Document Period End Date Dec. 31, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
Class A common stock      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   34,997,715  
Class B common stock      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   3,431,862