Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 29, 2018
Document Information [Line Items]
Entity Registrant Name	KELLY SERVICES INC
Document Type	10-Q
Current Fiscal Year End Date	--12-30
Amendment Flag	false
Entity Central Index Key	0000055135
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Entity Emerging Growth Company	false
Entity Small Business	false
Class A Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		35,434,862
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,432,072