Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Line Items]
Revenues	$ 20,560.9	$ 19,202.6	$ 18,012.2
Other
Disaggregation of Revenue [Line Items]
Revenues	(12.6)	(11.8)	(14.6)
Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	13,883.1	12,980.8	12,042.6
PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	6,690.4	6,233.6	5,984.2
HCM
Disaggregation of Revenue [Line Items]
Revenues	8,674.5	8,155.7	7,716.1
HCM | Other
Disaggregation of Revenue [Line Items]
Revenues	(10.0)	(8.5)	(8.6)
HCM | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	8,684.5	8,164.2	7,724.7
HCM | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	3,782.3	3,544.2	3,386.0
HRO, excluding PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	(2.6)	(3.3)	(6.0)
HRO, excluding PEO zero-margin benefits pass-throughs | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,394.3	1,299.1	1,216.1
HRO, excluding PEO zero-margin benefits pass-throughs | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2,390.6	2,248.4	2,175.9
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	4,289.0	3,975.9	3,800.9
PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
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		3,975.9	3,800.9
Global
Disaggregation of Revenue [Line Items]
Revenues	2,626.0	2,502.1	2,295.8
Global | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
Global | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2,626.0	2,502.1	2,295.8
Global | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
Interest on funds held for clients
Disaggregation of Revenue [Line Items]
Revenues	1,189.1	1,024.7	813.4
Interest on funds held for clients | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,189.1	1,024.7	813.4
Interest on funds held for clients | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
Interest on funds held for clients | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,178.3	1,015.4	806.0
Interest on funds held for clients | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	$ 10.8	$ 9.3	$ 7.4