Basis of Presentation (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Error Corrections and Prior Period Adjustments Restatement [Line Items]
PEO revenues	[1]	$ 1,236.8	$ 1,113.9	$ 3,425.9	$ 3,131.2
TOTAL REVENUES		4,047.8	3,828.2	11,213.0	10,630.9
Operating expenses		1,974.1	1,855.3	5,597.8	5,324.8
Total Expenses		3,015.7	2,864.7	8,706.9	8,326.1
EARNINGS BEFORE INCOME TAXES		1,076.7	984.5	2,651.3	2,372.3
Provision for income taxes		255.8	230.8	596.4	554.9
NET EARNINGS		$ 820.9	753.7	$ 2,054.9	1,817.4
Revision
Error Corrections and Prior Period Adjustments Restatement [Line Items]
PEO revenues	[1]		(19.2)		(45.6)
TOTAL REVENUES			(19.2)		(45.6)
Operating expenses			(19.2)		(45.6)
Total Expenses			(19.2)		(45.6)
EARNINGS BEFORE INCOME TAXES			0.0		0.0
Provision for income taxes			0.0		0.0
NET EARNINGS			0.0		0.0
As reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
PEO revenues	[1]		1,133.1		3,176.8
TOTAL REVENUES			3,847.4		10,676.5
Operating expenses			1,874.5		5,370.4
Total Expenses			2,883.9		8,371.7
EARNINGS BEFORE INCOME TAXES			984.5		2,372.3
Provision for income taxes			230.8		554.9
NET EARNINGS			$ 753.7		$ 1,817.4

[1] Professional Employer Organization (“PEO”) revenues are net of direct pass-through costs, primarily consisting of payroll wages and payroll taxes of $12,643.6 million and $10,798.3 million for the three months ended March 31, 2020 and 2019, respectively, and $35,525.8 million and $32,178.8 million for the nine months ended March 31, 2020 and 2019, respectively.