Goodwill and Intangible Assets, net - Changes in Goodwill (Details) $ in Millions	3 Months Ended
	Sep. 30, 2024 USD ($)
Goodwill [Roll Forward]
Balance at June 30, 2024	$ 2,353.6
Currency translation adjustments	15.4
Balance at September 30, 2024	2,369.0
Employer Services
Goodwill [Roll Forward]
Balance at June 30, 2024	2,348.8
Currency translation adjustments	15.4
Balance at September 30, 2024	2,364.2
PEO Services
Goodwill [Roll Forward]
Balance at June 30, 2024	4.8
Currency translation adjustments	0.0
Balance at September 30, 2024	$ 4.8