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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. 29, 2024 | Dec. 31, 2023 | Jan. 01, 2023 | 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 | $ 0.0 | $ 196.9 |
Loss on investment in Persol Holdings |  |  |  |  | 0.0 | 0.0 | (67.2) |
Equity securities gain (loss) |  |  | $ (52.4) |  | 3.8 |  |  |
Loss on currency translation from liquidation of subsidiary |  |  |  |  | 0.0 | 0.0 | (20.4) |
Gain on foreign currency remeasurement |  |  |  |  | $ 0.0 | $ 0.0 | 5.5 |
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 |  |  |  |  |  |  |
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 |

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