Investment in PersolKelly Pte Ltd. (Details)		3 Months Ended
	Apr. 01, 2020 USD ($)	Mar. 29, 2020 USD ($) country	Mar. 31, 2019 USD ($)	Dec. 29, 2019 USD ($)	Sep. 29, 2019 USD ($)	Dec. 30, 2018 USD ($)
Schedule of Equity Method Investments [Line Items]
Equity in net earnings (loss) of affiliate		$ (1,500,000)	$ (400,000)
Investment in equity affiliate		116,300,000		$ 117,200,000
Accounts payable and accrued liabilities		$ 475,500,000		503,600,000
PersolKelly Pte. Ltd.
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		49.00%
Number of countries in which entity operates (country) (more than) | country		10
Due from PersolKelly Pte. Ltd.		$ 10,000,000.0		10,900,000
Advances to PersolKelly Pte. Ltd.					$ 4,400,000	$ 7,000,000.0
Accrued interest receivable		100,000		200,000
Accounts payable and accrued liabilities		$ 100,000		$ 200,000
Subsequent Event | 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 | Subsequent Event | 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