Interim Financial Data by Segment (Financial Data By Strategic Business Unit Segment) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues	$ (3,669.5)	$ (3,492.4)	$ (7,165.2)	$ (6,802.7)
Earnings before Income Taxes	835.5	741.0	1,574.6	1,387.8
Employer Services
Segment Reporting Information [Line Items]
Revenues	(2,537.5)	(2,450.4)	(4,978.9)	(4,788.6)
Earnings before Income Taxes	767.4	733.0	1,448.4	1,372.9
PEO Services
Segment Reporting Information [Line Items]
Revenues	(1,134.7)	(1,044.7)	(2,191.5)	(2,019.6)
Earnings before Income Taxes	167.1	157.3	315.5	301.1
Other
Segment Reporting Information [Line Items]
Revenues	(2.7)	(2.7)	(5.2)	(5.5)
Earnings before Income Taxes	$ (99.0)	$ (149.3)	$ (189.3)	$ (286.2)