Interim Financial Data by Segment (Financial Data By Strategic Business Unit Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
Revenues	$ 4,512.4	$ 4,215.6
Earnings before Income Taxes	1,092.8	1,010.0
Employer Services
Segment Reporting Information [Line Items]
Revenues	3,046.4	2,790.2
Earnings before Income Taxes	1,008.5	863.5
PEO Services
Segment Reporting Information [Line Items]
Revenues	1,469.6	1,429.4
Earnings before Income Taxes	222.9	230.3
Other
Segment Reporting Information [Line Items]
Revenues	(3.6)	(4.0)
Earnings before Income Taxes	$ (138.6)	$ (83.8)