Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 3,832.3	$ 3,470.7
Employer Services
Disaggregation of Revenue [Line Items]
Revenues	2,571.5	2,376.8
PEO Services
Disaggregation of Revenue [Line Items]
Revenues	1,264.1	1,095.9
Other
Disaggregation of Revenue [Line Items]
Revenues	(3.3)	(2.0)
HCM
Disaggregation of Revenue [Line Items]
Revenues	1,666.7	1,536.9
HCM | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	1,669.1	1,538.6
HCM | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
HCM | Other
Disaggregation of Revenue [Line Items]
Revenues	(2.4)	(1.7)
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	679.3	581.4
HRO, excluding PEO zero-margin benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	256.2	228.1
HRO, excluding PEO zero-margin benefits pass-throughs | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	424.0	353.6
HRO, excluding PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	(0.9)	(0.3)
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	839.5	741.0
PEO zero-margin benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
PEO zero-margin benefits pass-throughs | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	839.5	741.0
PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Global
Disaggregation of Revenue [Line Items]
Revenues	545.7	504.9
Global | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	545.7	504.9
Global | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Global | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Interest on funds held for clients
Disaggregation of Revenue [Line Items]
Revenues	101.1	106.5
Interest on funds held for clients | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	100.5	105.2
Interest on funds held for clients | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	0.6	1.3
Interest on funds held for clients | Other
Disaggregation of Revenue [Line Items]
Revenues	$ 0.0	$ 0.0