Interim Financial Data by Segment (Financial Data By Strategic Business Unit Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ (4,047.8)	$ (3,828.2)	$ (11,213.0)	$ (10,630.9)
Earnings before Income Taxes	1,076.7	984.5	2,651.3	2,372.3
Employer Services
Segment Reporting Information [Line Items]
Revenues	(2,811.7)	(2,719.1)	(7,790.6)	(7,507.7)
Earnings before Income Taxes	1,025.0	963.1	2,473.4	2,335.9
PEO Services
Segment Reporting Information [Line Items]
Revenues	(1,238.3)	(1,115.5)	(3,429.8)	(3,135.1)
Earnings before Income Taxes	172.6	154.7	488.1	455.7
Other
Segment Reporting Information [Line Items]
Revenues	(2.2)	(6.4)	(7.4)	(11.9)
Earnings before Income Taxes	$ (120.9)	$ (133.3)	$ (310.2)	$ (419.3)