Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	$ 5,253.8	$ 4,927.8	$ 14,434.1	$ 13,534.4
Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	3,590.7	3,339.1	9,762.3	9,021.3
PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	1,665.6	1,592.0	4,681.2	4,524.7
Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	(2.5)	(3.3)	(9.4)	(11.6)
HCM
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	2,278.8	2,163.8	6,168.3	5,836.6
HCM | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	2,280.8	2,165.8	6,174.8	5,843.2
HCM | PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	0.0	0.0	0.0	0.0
HCM | Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	(2.0)	(2.0)	(6.5)	(6.6)
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	988.1	955.1	2,688.5	2,586.3
HRO, excluding PEO zero-margin benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	342.2	323.0	980.7	918.2
HRO, excluding PEO zero-margin benefits pass-throughs | PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	646.4	633.4	1,710.7	1,673.1
HRO, excluding PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	(0.5)	(1.3)	(2.9)	(5.0)
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	1,016.3	956.3	2,963.7	2,846.3
PEO zero-margin benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	0.0	0.0	0.0	0.0
PEO zero-margin benefits pass-throughs | PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	1,016.3	956.3	2,963.7	2,846.3
PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	0.0	0.0	0.0	0.0
Global
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	649.8	603.2	1,865.7	1,687.5
Global | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	649.8	603.2	1,865.7	1,687.5
Global | PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	0.0	0.0	0.0	0.0
Global | Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	0.0	0.0	0.0	0.0
Interest on funds held for clients
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	320.8	249.4	747.9	577.7
Interest on funds held for clients | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	317.9	247.1	741.1	572.4
Interest on funds held for clients | PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	2.9	2.3	6.8	5.3
Interest on funds held for clients | Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	$ 0.0	$ 0.0	$ 0.0	$ 0.0