Interim Financial Data by Segment (Financial Data By Strategic Business Unit Segment) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Revenues	$ 4,391.0	$ 4,025.4	$ 8,606.6	$ 7,857.7
Earnings before Income Taxes	1,058.1	910.1	2,068.1	1,810.9
Employer Services
Segment Reporting Information [Line Items]
Revenues	2,891.9	2,671.3	5,682.2	5,242.8
Earnings before Income Taxes	934.6	817.3	1,798.1	1,601.3
PEO Services
Segment Reporting Information [Line Items]
Revenues	1,503.3	1,358.8	2,932.7	2,622.9
Earnings before Income Taxes	255.6	212.7	485.9	405.7
Other
Segment Reporting Information [Line Items]
Revenues	(4.2)	(4.7)	(8.3)	(8.0)
Earnings before Income Taxes	$ (132.1)	$ (119.9)	$ (215.9)	$ (196.1)