Interim Financial Data by Segment (Financial Data By Strategic Business Unit Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Revenues	$ 4,513.0	$ 4,102.0	$ 12,370.6	$ 11,268.4
Earnings before Income Taxes	1,189.9	1,066.2	3,000.7	2,664.1
Employer Services
Segment Reporting Information [Line Items]
Revenues	3,002.0	2,780.0	8,244.8	7,667.4
Earnings before Income Taxes	1,095.7	980.0	2,697.0	2,427.8
PEO Services
Segment Reporting Information [Line Items]
Revenues	1,513.8	1,324.1	4,136.7	3,606.1
Earnings before Income Taxes	227.2	198.7	632.9	545.5
Other
Segment Reporting Information [Line Items]
Revenues	(2.8)	(2.1)	(10.9)	(5.1)
Earnings before Income Taxes	$ (133.0)	$ (112.5)	$ (329.2)	$ (309.2)