Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	$ 4,927.8	$ 4,513.0	$ 13,534.4	$ 12,370.6
Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	3,339.1	3,002.0	9,021.3	8,244.8
PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	1,592.0	1,513.8	4,524.7	4,136.7
Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	(3.3)	(2.8)	(11.6)	(10.9)
HCM
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	2,163.8	2,014.0	5,836.6	5,424.6
HCM | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	2,165.8	2,015.2	5,843.2	5,430.2
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)	(1.2)	(6.6)	(5.6)
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	955.1	906.4	2,586.3	2,344.4
HRO, excluding PEO zero-margin benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	323.0	292.5	918.2	816.6
HRO, excluding PEO zero-margin benefits pass-throughs | PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	633.4	615.5	1,673.1	1,533.1
HRO, excluding PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	(1.3)	(1.6)	(5.0)	(5.3)
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	956.3	897.2	2,846.3	2,600.6
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	956.3	897.2	2,846.3	2,600.6
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	603.2	577.4	1,687.5	1,676.0
Global | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	603.2	577.4	1,687.5	1,676.0
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	249.4	118.0	577.7	325.0
Interest on funds held for clients | Employer Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	247.1	116.9	572.4	322.0
Interest on funds held for clients | PEO Services
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	2.3	1.1	5.3	3.0
Interest on funds held for clients | Other
Disaggregation of Revenue [Line Items]
TOTAL REVENUES	$ 0.0	$ 0.0	$ 0.0	$ 0.0