Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 4,391.0	$ 4,025.4	$ 8,606.6	$ 7,857.7
Employer Services
Disaggregation of Revenue [Line Items]
Revenues	2,891.9	2,671.3	5,682.2	5,242.8
PEO Services
Disaggregation of Revenue [Line Items]
Revenues	1,503.3	1,358.8	2,932.7	2,622.9
Other
Disaggregation of Revenue [Line Items]
Revenues	(4.2)	(4.7)	(8.3)	(8.0)
HCM
Disaggregation of Revenue [Line Items]
Revenues	1,861.8	1,743.8	3,672.8	3,410.4
HCM | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	1,864.1	1,745.7	3,677.4	3,414.7
HCM | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
HCM | Other
Disaggregation of Revenue [Line Items]
Revenues	(2.3)	(1.9)	(4.6)	(4.3)
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	853.9	758.7	1,631.2	1,438.0
HRO, excluding PEO zero-margin benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	298.4	267.8	595.2	524.1
HRO, excluding PEO zero-margin benefits pass-throughs | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	557.4	493.7	1,039.7	917.6
HRO, excluding PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	(1.9)	(2.8)	(3.7)	(3.7)
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	944.2	863.9	1,890.0	1,703.4
PEO zero-margin benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
PEO zero-margin benefits pass-throughs | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	944.2	863.9	1,890.0	1,703.4
PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
Global
Disaggregation of Revenue [Line Items]
Revenues	543.9	553.0	1,084.3	1,098.8
Global | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	543.9	553.0	1,084.3	1,098.8
Global | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
Global | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
Interest on funds held for clients
Disaggregation of Revenue [Line Items]
Revenues	187.2	106.0	328.3	207.1
Interest on funds held for clients | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	185.5	104.8	325.3	205.2
Interest on funds held for clients | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	1.7	1.2	3.0	1.9
Interest on funds held for clients | Other
Disaggregation of Revenue [Line Items]
Revenues	$ 0.0	$ 0.0	$ 0.0	$ 0.0