Summary of Significant Accounting Policies Revenue Recognition Restatement (Details) - USD ($) $ in Millions		3 Months Ended												12 Months Ended
		Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Revenue Recognition Restatement
Other Assets, Current		$ 506.2				$ 509.1								$ 506.2	$ 509.1
Interest on funds held for clients														545.2	561.9	$ 466.5
PEO revenues	[1]													4,506.5	4,172.5	3,824.3
TOTAL REVENUES		3,376.8	$ 4,047.8	$ 3,669.5	$ 3,495.7	3,479.3	[2]	$ 3,828.2	[2]	$ 3,492.4	[2]	$ 3,310.3	[2]	14,589.8	14,110.2	13,274.2
Revenues, Net														9,538.1	9,375.8	8,983.4
Operating expenses														7,404.1	7,080.9	6,847.5
Systems development and programming costs														674.1	636.3	635.4
Cost, Depreciation and Amortization														366.9	304.4	274.5
Selling, general, and administrative expenses														3,003.0	3,064.2	2,959.4
Interest Expense														107.1	129.9	102.7
Total Expenses														11,555.2	11,215.7	10,819.5
Other expense/(income), net														(148.0)	(111.1)	172.1
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES		531.3	1,076.7	835.5	739.1	633.3		984.5		741.0		646.8		3,182.6	3,005.6	2,282.6
Provision for income taxes														716.1	712.8	397.7
NET EARNINGS		411.5	$ 820.9	$ 651.6	$ 582.4	475.5		$ 753.7		$ 558.2		$ 505.4		2,466.5	2,292.8	1,884.9
Assets, Current		31,564.1				34,342.3								31,564.1	34,342.3
Deferred contract costs	[3]	2,401.6				2,428.5								2,401.6	2,428.5
Other Assets, Noncurrent		458.4				934.4								458.4	934.4
Total assets		39,165.5				41,887.7								39,165.5	41,887.7	38,849.1
Liabilities, Current		30,126.6				32,627.7								30,126.6	32,627.7
Deferred Revenue, Noncurrent		370.6				399.3								370.6	399.3
Liabilities		33,413.3				36,487.8								33,413.3	36,487.8
Retained Earnings (Accumulated Deficit)		18,436.3				17,500.6								18,436.3	17,500.6
Stockholders' Equity Attributable to Parent		5,752.2				5,399.9								5,752.2	5,399.9
Liabilities and Equity		$ 39,165.5				$ 41,887.7								39,165.5	41,887.7
Capitalized Contract Cost, Amortization														915.0	874.0	837.4
Deferred Income Tax Expense (Benefit), Net of Disposals														26.0	9.3	(152.0)
Increase (Decrease) in Other Operating Assets														910.4	987.2	858.3
Increase (Decrease) in Accrued Liabilities														(77.5)	266.0	110.5
Net Cash Provided by (Used in) Operating Activities														$ 3,026.2	2,688.3	2,515.2
Previously Reported [Member]
Revenue Recognition Restatement
PEO revenues															4,237.5	3,877.8
TOTAL REVENUES															14,175.2	13,327.7
Operating expenses															7,145.9	6,901.0
Total Expenses															11,280.7	10,873.0
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES															3,005.6	2,282.6
Provision for income taxes															712.8	397.7
NET EARNINGS															2,292.8	1,884.9
Restatement Adjustment [Member]
Revenue Recognition Restatement
PEO revenues															(65.0)	(53.5)
TOTAL REVENUES															(65.0)	(53.5)
Operating expenses															(65.0)	(53.5)
Total Expenses															(65.0)	(53.5)
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES															0.0	0.0
Provision for income taxes															0.0	0.0
NET EARNINGS															$ 0.0	$ 0.0
Minimum [Member]
Revenue Recognition Restatement
Revenue, Service Agreements, Term														30 days

[1] For the years ended June 30, 2020 (“fiscal 2020”), June 30, 2019 (“fiscal 2019”), and June 30, 2018 (“fiscal 2018”), Professional Employer Organization (“PEO”) revenues are net of direct pass-through costs, primarily consisting of payroll wages and payroll taxes, of $45,826.1 million, $42,688.8 million, and $39,140.9 million, respectively.

[2] (A) The prior period amounts presented have been revised to correct the amounts previously reported on a gross basis to a net basis by reducing PEO revenues and operating expenses for associated costs of an equal amount of $12.9 million, $13.5 million, $19.2 million and $19.4 million for the first quarter, second quarter, third quarter and fourth quarter, respectively. Refer to Note 1 to our consolidated financial statements for more information on this revision.

[3] (1) The amount of total deferred costs amortized during the twelve months ended June 30, 2020, June 30, 2019, and June 30, 2018 were $915.0 million, $874.0 million, and $837.4 million, respectively.