Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2024
Disaggregation of Revenue [Line Items]
Revenues	$ 21,947.4	$ 20,560.9	$ 19,202.6
Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	21,959.5	20,573.5	19,214.4
Intercompany eliminations
Disaggregation of Revenue [Line Items]
Revenues	(12.1)	(12.6)	(11.8)
Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	14,831.4	13,883.1	12,980.8
Employer Services | Intercompany eliminations
Disaggregation of Revenue [Line Items]
Revenues	(12.1)	(12.6)	(11.8)
PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	7,128.1	6,690.4	6,233.6
PEO | Intercompany eliminations
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
HCM
Disaggregation of Revenue [Line Items]
Revenues	9,110.6	8,674.5	8,155.7
HCM | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	9,120.4	8,684.5	8,164.2
HCM | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	9,120.4	8,684.5	8,164.2
HCM | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	3,973.5	3,782.3	3,544.2
HRO, excluding PEO zero-margin benefits pass-throughs | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	3,975.8	3,784.9	3,547.5
HRO, excluding PEO zero-margin benefits pass-throughs | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,467.4	1,394.3	1,299.1
HRO, excluding PEO zero-margin benefits pass-throughs | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2,508.4	2,390.6	2,248.4
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	4,607.3	4,289.0	3,975.9
PEO zero-margin benefits pass-throughs | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	4,607.3	4,289.0	3,975.9
PEO zero-margin benefits pass-throughs | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
PEO zero-margin benefits pass-throughs | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	4,607.3	4,289.0	3,975.9
Global
Disaggregation of Revenue [Line Items]
Revenues	2,901.2	2,626.0	2,502.1
Global | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2,901.2	2,626.0	2,502.1
Global | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2,901.2	2,626.0	2,502.1
Global | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0
Interest on funds held for clients
Disaggregation of Revenue [Line Items]
Revenues	1,354.8	1,189.1	1,024.7
Interest on funds held for clients | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,354.8	1,189.1	1,024.7
Interest on funds held for clients | Employer Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,342.4	1,178.3	1,015.4
Interest on funds held for clients | PEO | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	$ 12.4	$ 10.8	$ 9.3