Goodwill and Intangible Assets, Net - Changes in Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2026	Jun. 30, 2025
Goodwill [Roll Forward]
Beginning balance	$ 3,273.5	$ 2,353.6
Additions and other adjustments	21.3	887.0
Currency translation adjustments	(10.4)	32.9
Ending balance	3,284.4	3,273.5
Employer Services
Goodwill [Roll Forward]
Beginning balance	3,268.7	2,348.8
Additions and other adjustments	21.3	887.0
Currency translation adjustments	(10.4)	32.9
Ending balance	3,279.6	3,268.7
PEO Services
Goodwill [Roll Forward]
Beginning balance	4.8	4.8
Additions and other adjustments	0.0	0.0
Currency translation adjustments	0.0	0.0
Ending balance	$ 4.8	$ 4.8