Interim Financial Data by Segment (Financial Data By Strategic Business Unit Segment) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 4,025.4	$ 3,695.7	$ 7,857.7	$ 7,166.5
Earnings before Income Taxes	910.1	832.6	1,810.9	1,597.8
Employer Services
Segment Reporting Information [Line Items]
Revenues	2,671.3	2,510.6	5,242.8	4,887.4
Earnings before Income Taxes	817.3	758.6	1,601.3	1,447.8
PEO Services
Segment Reporting Information [Line Items]
Revenues	1,358.8	1,186.1	2,622.9	2,282.0
Earnings before Income Taxes	212.7	187.4	405.7	346.8
Other
Segment Reporting Information [Line Items]
Revenues	(4.7)	(1.0)	(8.0)	(2.9)
Earnings before Income Taxes	$ (119.9)	$ (113.4)	$ (196.1)	$ (196.8)