Interim Financial Data by Segment - Financial Data By Strategic Business Unit Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Revenues	$ 4,832.7	$ 4,512.4
Earnings before Income Taxes	1,236.2	1,092.8
Other
Segment Reporting Information [Line Items]
Revenues	(2.8)	(3.6)
Earnings before Income Taxes	(153.7)	(138.6)
Employer Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	3,261.0	3,046.4
Earnings before Income Taxes	1,164.3	1,008.5
PEO Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	1,574.5	1,469.6
Earnings before Income Taxes	$ 225.6	$ 222.9