Summary of Significant Accounting Policies Revenue Recognition Restatement (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Revenue Recognition Restatement
Revenues, other than interest on funds held for clients and PEO revenues										$ 8,985.2	$ 8,518.1	$ 8,234.0
Interest on funds held for clients										466.5	397.4	377.3
PEO revenues	[1]									3,874.1	3,464.3	3,056.5
TOTAL REVENUES		$ 3,318.6	$ 3,693.0	$ 3,235.4	$ 3,078.8	$ 3,064.8	$ 3,410.8	$ 2,987.3	$ 2,916.9	13,325.8	12,379.8	11,667.8
Operating expenses										6,937.9	6,416.1	6,025.0
Systems development and programming costs										630.2	627.5	603.7
Selling, general, and administrative expenses										2,971.5	2,783.2	2,637.0
Total Expenses										10,916.8	10,133.0	9,533.5
Other expense/(income), net										237.9	(284.3)	(100.4)
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES		$ 204.5	$ 852.6	$ 565.7	$ 548.2	$ 388.4	$ 827.9	$ 786.2	$ 528.7	2,171.1	2,531.1	2,234.7
Provision for income taxes										550.3	797.7	741.3
NET EARNINGS FROM CONTINUING OPERATIONS										1,620.8	1,733.4	$ 1,493.4
Restatement Adjustment [Member]
Revenue Recognition Restatement
Revenues, other than interest on funds held for clients and PEO revenues										8,983.4	8,510.1
Interest on funds held for clients										466.5	397.4
PEO revenues										3,877.6	3,464.6
TOTAL REVENUES										13,327.5	12,372.1
Operating expenses										6,901.1	6,386.4
Systems development and programming costs										637.8	634.1
Selling, general, and administrative expenses										2,956.9	2,771.9
Total Expenses										10,873.0	10,098.6
Other expense/(income), net										171.9	(343.4)
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES										2,282.6	2,616.9
Provision for income taxes										384.7	829.1
NET EARNINGS FROM CONTINUING OPERATIONS										1,897.9	1,787.8
ASU 2017-07 [Member]
Revenue Recognition Restatement
Revenues, other than interest on funds held for clients and PEO revenues										0.0	0.0
PEO revenues										0.0	0.0
TOTAL REVENUES										0.0	0.0
Operating expenses										37.2	33.8
Systems development and programming costs										7.6	6.6
Selling, general, and administrative expenses										21.2	18.7
Total Expenses										66.0	59.1
Other expense/(income), net										(66.0)	(59.1)
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES										0.0	0.0
Provision for income taxes										0.0	0.0
NET EARNINGS FROM CONTINUING OPERATIONS										0.0	0.0
ASC 606 Adjustments [Member]
Revenue Recognition Restatement
Revenues, other than interest on funds held for clients and PEO revenues										(1.8)	(8.0)
PEO revenues										3.5	0.3
TOTAL REVENUES										1.7	(7.7)
Operating expenses										(74.0)	(63.5)
Systems development and programming costs										0.0	0.0
Selling, general, and administrative expenses										(35.8)	(30.0)
Total Expenses										(109.8)	(93.5)
Other expense/(income), net											0.0
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES										111.5	85.8
Provision for income taxes										(165.6)	31.4
NET EARNINGS FROM CONTINUING OPERATIONS										$ 277.1	$ 54.4

[1] For the years ended June 30, 2018 ("fiscal 2018"), June 30, 2017 ("fiscal 2017"), and June 30, 2016 ("fiscal 2016"), Professional Employer Organization ("PEO") revenues are net of direct pass-through costs, primarily consisting of payroll wages and payroll taxes, of $39,140.9 million, $34,567.4 million, and $30,928.6 million, respectively.