Interim Financial Data by Segment - Financial Data By Strategic Business Unit Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information [Line Items]
Revenues	$ 5,553.0	$ 5,253.8	$ 15,434.1	$ 14,434.1
Earnings before Income Taxes	1,621.9	1,546.3	4,119.4	3,783.0
Other
Segment Reporting Information [Line Items]
Revenues	(3.4)	(2.5)	(9.6)	(9.4)
Earnings before Income Taxes	(131.5)	(111.3)	(458.5)	(422.9)
Employer Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	3,767.9	3,590.7	10,417.4	9,762.3
Earnings before Income Taxes	1,500.1	1,421.7	3,847.3	3,492.1
PEO Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	1,788.5	1,665.6	5,026.3	4,681.2
Earnings before Income Taxes	$ 253.3	$ 235.9	$ 730.6	$ 713.8