Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 4,513.0	$ 4,102.0	$ 12,370.6	$ 11,268.4
Employer Services
Disaggregation of Revenue [Line Items]
Revenues	3,002.0	2,780.0	8,244.8	7,667.4
PEO Services
Disaggregation of Revenue [Line Items]
Revenues	1,513.8	1,324.1	4,136.7	3,606.1
Other
Disaggregation of Revenue [Line Items]
Revenues	(2.8)	(2.1)	(10.9)	(5.1)
HCM
Disaggregation of Revenue [Line Items]
Revenues	2,014.0	1,858.1	5,424.6	5,025.8
HCM | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	2,015.2	1,859.4	5,430.2	5,030.0
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	(1.2)	(1.3)	(5.6)	(4.2)
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	906.4	790.5	2,344.4	2,039.6
HRO, excluding PEO zero-margin benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	292.5	252.6	816.6	729.1
HRO, excluding PEO zero-margin benefits pass-throughs | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	615.5	538.7	1,533.1	1,311.4
HRO, excluding PEO zero-margin benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	(1.6)	(0.8)	(5.3)	(0.9)
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	897.2	784.7	2,600.6	2,291.7
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	897.2	784.7	2,600.6	2,291.7
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	577.4	561.3	1,676.0	1,592.1
Global | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	577.4	561.3	1,676.0	1,592.1
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	118.0	107.4	325.0	319.2
Interest on funds held for clients | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	116.9	106.7	322.0	316.2
Interest on funds held for clients | PEO Services
Disaggregation of Revenue [Line Items]
Revenues	1.1	0.7	3.0	3.0
Interest on funds held for clients | Other
Disaggregation of Revenue [Line Items]
Revenues	$ 0.0	$ 0.0	$ 0.0	$ 0.0