Interim Financial Data by Segment - Financial Data By Strategic Business Unit Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Revenues	$ 5,253.8	$ 4,927.8	$ 14,434.1	$ 13,534.4
Earnings before Income Taxes	1,546.3	1,364.0	3,783.0	3,432.0
Employer Services
Segment Reporting Information [Line Items]
Revenues	3,590.7	3,339.1	9,762.3	9,021.3
Earnings before Income Taxes	1,421.7	1,244.5	3,492.1	3,042.6
PEO Services
Segment Reporting Information [Line Items]
Revenues	1,665.6	1,592.0	4,681.2	4,524.7
Earnings before Income Taxes	235.9	261.0	713.8	747.0
Other
Segment Reporting Information [Line Items]
Revenues	(2.5)	(3.3)	(9.4)	(11.6)
Earnings before Income Taxes	$ (111.3)	$ (141.5)	$ (422.9)	$ (357.6)