Investment in Persol Holdings - Narrative (Details) - USD ($) $ in Millions			2 Months Ended	3 Months Ended	12 Months Ended
	Feb. 15, 2022	Feb. 14, 2022	Feb. 15, 2022	Apr. 03, 2022	Dec. 31, 2023	Jan. 01, 2023	Jan. 02, 2022	Jan. 31, 2022
Schedule of Investments [Line Items]
Stock repurchased during period, amount in excess of par value		$ 25.6
Proceeds from sale of Persol Holdings investment					$ 0.0	$ 196.9	$ 0.0
Gain (loss) on investment in Persol Holdings					0.0	(67.2)	121.8
Equity securities gain (loss)			$ (52.4)			121.8
Loss on currency translation from liquidation of subsidiary					0.0	(20.4)	0.0
Gain on foreign currency remeasurement					$ 0.0	5.5	$ 0.0
Persol Holdings | Persol Asia Pacific Pte.
Schedule of Investments [Line Items]
Subsidiary, ownership percentage, parent								100.00%
Persol Holdings Investment
Schedule of Investments [Line Items]
Stock Repurchased and Retired During Period, Value		$ 27.2
Proceeds from sale of Persol Holdings investment	$ 196.9
Gain (loss) on investment in Persol Holdings				$ (67.2)
Equity securities gain (loss)	$ (14.8)
Persol Holdings Investment | Class A common stock
Schedule of Investments [Line Items]
Stock repurchased during period, shares		1,576,169
Persol Holdings Investment | Class B common stock
Schedule of Investments [Line Items]
Stock repurchased during period, shares		1,475
Kelly Services Japan, Inc.
Schedule of Investments [Line Items]
Loss on currency translation from liquidation of subsidiary				(20.4)
Gain on foreign currency remeasurement				$ 5.5		$ 5.5