Interim Financial Data by Segment (Financial Data By Strategic Business Unit Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 3,832.3	$ 3,470.7
Earnings before Income Taxes	900.8	765.2
Employer Services
Segment Reporting Information [Line Items]
Revenues	2,571.5	2,376.8
Earnings before Income Taxes	784.0	689.3
PEO Services
Segment Reporting Information [Line Items]
Revenues	1,264.1	1,095.9
Earnings before Income Taxes	193.0	159.4
Other
Segment Reporting Information [Line Items]
Revenues	(3.3)	(2.0)
Earnings before Income Taxes	$ (76.2)	$ (83.5)