Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 3,470.7	$ 3,495.7
Employer Services
Disaggregation of Revenue [Line Items]
Revenues	2,376.8	2,441.4
Other
Disaggregation of Revenue [Line Items]
Revenues	(2.0)	(2.6)
PEO Services
Disaggregation of Revenue [Line Items]
Revenues	1,095.9	1,056.9
HCM
Disaggregation of Revenue [Line Items]
Revenues	1,530.6	1,568.5
HCM | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	1,532.3	1,570.0
HCM | Other
Disaggregation of Revenue [Line Items]
Revenues	(1.7)	(1.5)
HCM | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	582.4	591.1
HRO, excluding PEO zero-margin benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	229.1	235.7
HRO, excluding PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	(0.3)	(1.1)
HRO, excluding PEO zero-margin benefits pass-throughs | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	353.6	356.5
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	741.0	699.1
PEO zero-margin benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
PEO zero-margin benefits pass-throughs | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	741.0	699.1
Global
Disaggregation of Revenue [Line Items]
Revenues	510.2	503.1
Global | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	510.2	503.1
Global | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Global | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Interest on funds held for clients
Disaggregation of Revenue [Line Items]
Revenues	106.5	133.9
Interest on funds held for clients | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	105.2	132.6
Interest on funds held for clients | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Interest on funds held for clients | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	$ 1.3	$ 1.3