Investment in PersolKelly Pte Ltd. (Details) - USD ($)		3 Months Ended		6 Months Ended
	Apr. 01, 2020	Jun. 28, 2020	Jun. 30, 2019	Jun. 28, 2020	Jun. 30, 2019	Dec. 29, 2019	Sep. 29, 2019	Dec. 30, 2018
Schedule of Equity Method Investments [Line Items]
Equity in net earnings (loss) of affiliate		$ (1,300,000)	$ 300,000	$ (2,800,000)	$ (100,000)
Investment in equity affiliate		113,600,000		113,600,000		$ 117,200,000
Accounts payable and accrued liabilities		$ 463,600,000		$ 463,600,000		503,600,000
PersolKelly Pte. Ltd.
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		49.00%		49.00%
Due from PersolKelly Pte. Ltd.		$ 10,500,000		$ 10,500,000		10,900,000
Advances to PersolKelly Pte. Ltd.							$ 4,400,000	$ 7,000,000.0
Accrued interest receivable		100,000		100,000		200,000
Accounts payable and accrued liabilities		$ 100,000		$ 100,000		$ 200,000
Kelly Services Australia Pty Ltd and Kelly Services (New Zealand) Limited
Schedule of Equity Method Investments [Line Items]
Proceeds from royalties received	$ 700,000
Joint Venture | Kelly Services Australia Pty Ltd and Kelly Services (New Zealand) Limited
Schedule of Equity Method Investments [Line Items]
Ownership percentage sold	100.00%
Proceeds from sale of equity method investments	$ 17,500,000