Interim Financial Data by Segment (Financial Data By Strategic Business Unit Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 4,102.0	$ 4,047.8	$ 11,268.4	$ 11,213.0
Earnings before Income Taxes	1,066.2	1,076.7	2,664.1	2,651.3
Employer Services
Segment Reporting Information [Line Items]
Revenues	2,780.0	2,811.7	7,667.4	7,790.6
Earnings before Income Taxes	980.0	1,023.7	2,427.8	2,469.4
PEO Services
Segment Reporting Information [Line Items]
Revenues	1,324.1	1,238.3	3,606.1	3,429.8
Earnings before Income Taxes	198.7	173.6	545.5	490.9
Other
Segment Reporting Information [Line Items]
Revenues	(2.1)	(2.2)	(5.1)	(7.4)
Earnings before Income Taxes	$ (112.5)	$ (120.6)	$ (309.2)	$ (309.0)