Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Revenues	$ 5,175.2	$ 4,832.7
Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	3,491.2	3,261.0
PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,687.5	1,574.5
Other | Other
Disaggregation of Revenue [Line Items]
Revenues	(3.5)	(2.8)
HCM
Disaggregation of Revenue [Line Items]
Revenues	2,155.7	2,025.4
HCM | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2,158.3	2,027.6
HCM | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
HCM | Other | Other
Disaggregation of Revenue [Line Items]
Revenues	(2.6)	(2.2)
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	911.4	865.2
HRO, excluding PEO zero-margin benefits pass-throughs | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	358.4	342.8
HRO, excluding PEO zero-margin benefits pass-throughs | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	553.9	523.0
HRO, excluding PEO zero-margin benefits pass-throughs | Other | Other
Disaggregation of Revenue [Line Items]
Revenues	(0.9)	(0.6)
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	1,131.0	1,049.2
PEO zero-margin benefits pass-throughs | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
PEO zero-margin benefits pass-throughs | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,131.0	1,049.2
PEO zero-margin benefits pass-throughs | Other | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Global
Disaggregation of Revenue [Line Items]
Revenues	690.3	639.6
Global | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	690.3	639.6
Global | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Global | Other | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Interest on funds held for clients
Disaggregation of Revenue [Line Items]
Revenues	286.8	253.3
Interest on funds held for clients | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	286.8	253.3
Interest on funds held for clients | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	284.2	251.0
Interest on funds held for clients | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2.6	2.3
Interest on funds held for clients | Other | Other
Disaggregation of Revenue [Line Items]
Revenues	$ 0.0	$ 0.0