Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Revenues	$ 19,202.6	$ 18,012.2	$ 16,498.3
HCM
Disaggregation of Revenue [Line Items]
Revenues	8,155.7	7,716.1	7,174.9
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	3,544.2	3,386.0	3,116.3
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	3,975.9	3,800.9	3,514.4
Global
Disaggregation of Revenue [Line Items]
Revenues	2,502.1	2,295.8	2,240.9
Interest on funds held for clients
Disaggregation of Revenue [Line Items]
Revenues	1,024.7	813.4	451.8
Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	12,980.8	12,042.6	10,967.7
Employer Services | HCM | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	8,164.2	7,724.7	7,183.1
Employer Services | HRO, excluding PEO zero-margin benefits pass-throughs | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,299.1	1,216.1	1,096.1
Employer Services | PEO zero-margin benefits pass-throughs | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
Employer Services | Global | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2,502.1	2,295.8	2,240.9
Employer Services | Interest on funds held for clients | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,015.4	806.0	447.6
PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	6,233.6	5,984.2	5,545.7
PEO | HCM | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
PEO | HRO, excluding PEO zero-margin benefits pass-throughs | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2,248.4	2,175.9	2,027.1
PEO | PEO zero-margin benefits pass-throughs | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	3,975.9	3,800.9	3,514.4
PEO | Global | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
PEO | Interest on funds held for clients | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	9.3	7.4	4.2
Other | Other
Disaggregation of Revenue [Line Items]
Revenues	(11.8)	(14.6)	(15.1)
Other | HCM | Other
Disaggregation of Revenue [Line Items]
Revenues	(8.5)	(8.6)	(8.2)
Other | HRO, excluding PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	(3.3)	(6.0)	(6.9)
Other | PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
Other | Global | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
Other | Interest on funds held for clients | Other
Disaggregation of Revenue [Line Items]
Revenues	$ 0.0	$ 0.0	$ 0.0