Interim Financial Data by Segment (Financial Data By Strategic Business Unit Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 3,470.7	$ 3,495.7
Earnings before Income Taxes	765.2	739.1
Employer Services
Segment Reporting Information [Line Items]
Revenues	2,376.8	2,441.4
Earnings before Income Taxes	689.3	679.4
PEO Services
Segment Reporting Information [Line Items]
Revenues	1,095.9	1,056.9
Earnings before Income Taxes	159.4	149.3
Other
Segment Reporting Information [Line Items]
Revenues	(2.0)	(2.6)
Earnings before Income Taxes	$ (83.5)	$ (89.6)