Financial Data By Segment And Geographic Area - Revenues, Significant Segment Expenses and Earnings before Income Taxes by Reportable Segments (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Revenues	$ 20,560.9	$ 19,202.6	$ 18,012.2
Less segment expenses:
Total consolidated earnings before income taxes	5,310.1	4,872.3	4,437.6
Operating Segments
Less segment expenses:
Total consolidated earnings before income taxes	5,959.0	5,477.0	4,951.5
Intercompany eliminations
Segment Reporting Information [Line Items]
Revenues	(12.6)	(11.8)	(14.6)
Operating Segments, Excluding Intersegment Elimination
Segment Reporting Information [Line Items]
Revenues	20,573.5	19,214.4	18,026.8
Other
Less segment expenses:
Total consolidated earnings before income taxes	(648.9)	(604.7)	(513.9)
Employer Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	13,883.1	12,980.8	12,042.6
Less segment expenses:
Selling and marketing	2,177.1	2,025.0	1,885.3
Zero-margin benefits pass-through costs	0.0	0.0	0.0
Worker's compensation coverage and state unemployment taxes	0.0	0.0	0.0
Other segment expenses	6,697.5	6,400.3	6,183.1
Total consolidated earnings before income taxes	5,008.5	4,555.5	3,974.2
Employer Services | Intercompany eliminations
Segment Reporting Information [Line Items]
Revenues	(12.6)	(11.8)	(14.6)
Employer Services | Operating Segments, Excluding Intersegment Elimination
Segment Reporting Information [Line Items]
Revenues	13,883.1	12,980.8	12,042.6
PEO Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	6,690.4	6,233.6	5,984.2
Less segment expenses:
Selling and marketing	362.8	330.5	307.4
Zero-margin benefits pass-through costs	4,289.0	3,975.9	3,800.9
Worker's compensation coverage and state unemployment taxes	681.3	613.4	606.3
Other segment expenses	406.8	392.3	292.3
Total consolidated earnings before income taxes	950.5	921.5	977.3
PEO Services | Intercompany eliminations
Segment Reporting Information [Line Items]
Revenues	0.0	0.0	0.0
PEO Services | Operating Segments, Excluding Intersegment Elimination
Segment Reporting Information [Line Items]
Revenues	6,690.4	6,233.6	5,984.2
Revenues from external customers | Operating Segments
Segment Reporting Information [Line Items]
Revenues	19,371.8	18,177.9	17,198.8
Revenues from external customers | Employer Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	12,692.2	11,953.6	11,222.0
Revenues from external customers | PEO Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	6,679.6	6,224.3	5,976.8
Interest on funds held for clients
Segment Reporting Information [Line Items]
Revenues	1,189.1	1,024.7	813.4
Interest on funds held for clients | Operating Segments
Segment Reporting Information [Line Items]
Revenues	1,189.1	1,024.7	813.4
Interest on funds held for clients | Employer Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	1,178.3	1,015.4	806.0
Interest on funds held for clients | PEO Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	$ 10.8	$ 9.3	$ 7.4