Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenues	$ 4,832.7	$ 4,512.4
Other
Disaggregation of Revenue [Line Items]
Revenues	(2.8)	(3.6)
Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	3,261.0	3,046.4
PEO Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,574.5	1,469.6
Other | Other
Disaggregation of Revenue [Line Items]
Revenues	(2.8)	(3.6)
HCM
Disaggregation of Revenue [Line Items]
Revenues	2,025.4	1,914.4
HCM | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2,027.6	1,916.7
HCM | PEO Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
HCM | Other | Other
Disaggregation of Revenue [Line Items]
Revenues	(2.2)	(2.3)
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	865.2	811.7
HRO, excluding PEO zero-margin benefits pass-throughs | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	342.8	322.0
HRO, excluding PEO zero-margin benefits pass-throughs | PEO Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	523.0	491.0
HRO, excluding PEO zero-margin benefits pass-throughs | Other | Other
Disaggregation of Revenue [Line Items]
Revenues	(0.6)	(1.3)
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	1,049.2	976.7
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 Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,049.2	976.7
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	639.6	607.9
Global | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	639.6	607.9
Global | PEO Services | 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	253.3	201.7
Interest on funds held for clients | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	251.0	199.8
Interest on funds held for clients | PEO Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2.3	1.9
Interest on funds held for clients | Other | Other
Disaggregation of Revenue [Line Items]
Revenues	$ 0.0	$ 0.0