Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	$ 4,512.4	$ 4,215.6
Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	3,046.4	2,790.2
PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	1,469.6	1,429.4
Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	(3.6)	(4.0)
HCM
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	1,914.4	1,811.0
HCM | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	1,916.7	1,813.2
HCM | PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	0.0	0.0
HCM | Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	(2.3)	(2.2)
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	811.7	777.3
HRO, excluding PEO zero-margin benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	322.0	296.8
HRO, excluding PEO zero-margin benefits pass-throughs | PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	491.0	482.3
HRO, excluding PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	(1.3)	(1.8)
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	976.7	945.8
PEO zero-margin benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	0.0	0.0
PEO zero-margin benefits pass-throughs | PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	976.7	945.8
PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	0.0	0.0
Global
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	607.9	540.5
Global | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	607.9	540.5
Global | PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	0.0	0.0
Global | Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	0.0	0.0
Interest on funds held for clients
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	201.7	141.0
Interest on funds held for clients | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	199.8	139.7
Interest on funds held for clients | PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	1.9	1.3
Interest on funds held for clients | Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	$ 0.0	$ 0.0