Financial Data By Segment And Geographic Area - Financial Data by Strategic Business Unit Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Revenues	$ 19,202.6	$ 18,012.2	$ 16,498.3
Earnings before income taxes	4,872.3	4,437.6	3,804.1
Capital expenditures	211.7	206.0	177.1
Depreciation and amortization	561.9	549.3	515.1
Other
Segment Reporting Information [Line Items]
Revenues	(11.8)	(14.6)	(15.1)
Earnings before income taxes	(604.7)	(513.9)	(473.4)
Capital expenditures	54.4	44.6	51.7
Depreciation and amortization	68.5	74.2	78.3
Employer Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	12,980.8	12,042.6	10,967.7
Earnings before income taxes	4,555.5	3,974.2	3,406.3
Capital expenditures	157.3	161.4	125.4
Depreciation and amortization	486.6	467.6	428.5
PEO Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	6,233.6	5,984.2	5,545.7
Earnings before income taxes	921.5	977.3	871.2
Capital expenditures	0.0	0.0	0.0
Depreciation and amortization	$ 6.8	$ 7.5	$ 8.3