Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2025	Dec. 31, 2024
Disaggregation of Revenue [Line Items]
Revenues	$ 5,359.3	$ 5,048.4	$ 10,534.5	$ 9,881.1
Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	3,607.4	3,388.5	7,098.6	6,649.5
PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,755.2	1,663.3	3,442.7	3,237.8
Other | Other
Disaggregation of Revenue [Line Items]
Revenues	(3.3)	(3.4)	(6.8)	(6.2)
HCM
Disaggregation of Revenue [Line Items]
Revenues	2,235.9	2,131.9	4,391.5	4,157.3
HCM | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2,238.5	2,134.4	4,396.7	4,162.0
HCM | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
HCM | Other | Other
Disaggregation of Revenue [Line Items]
Revenues	(2.6)	(2.5)	(5.2)	(4.7)
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	979.3	943.2	1,890.8	1,808.4
HRO, excluding PEO zero-margin benefits pass-throughs | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	353.8	338.5	712.3	681.3
HRO, excluding PEO zero-margin benefits pass-throughs | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	626.2	605.6	1,180.1	1,128.6
HRO, excluding PEO zero-margin benefits pass-throughs | Other | Other
Disaggregation of Revenue [Line Items]
Revenues	(0.7)	(0.9)	(1.6)	(1.5)
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	1,126.2	1,055.2	2,257.2	2,104.4
PEO zero-margin benefits pass-throughs | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
PEO zero-margin benefits pass-throughs | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,126.2	1,055.2	2,257.2	2,104.4
PEO zero-margin benefits pass-throughs | Other | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
Global
Disaggregation of Revenue [Line Items]
Revenues	709.3	645.3	1,399.5	1,284.9
Global | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	709.3	645.3	1,399.5	1,284.9
Global | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
Global | Other | 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	308.6	272.8	595.5	526.1
Interest on funds held for clients | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	308.6	272.8	595.5	526.1
Interest on funds held for clients | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	305.8	270.3	590.1	521.3
Interest on funds held for clients | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2.8	2.5	5.4	4.8
Interest on funds held for clients | Other | Other
Disaggregation of Revenue [Line Items]
Revenues	$ 0.0	$ 0.0	$ 0.0	$ 0.0