Summary of Significant Accounting Policies Revenue Recognition Restatement (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017
Revenue Recognition Restatement
Other Assets, Current		$ 519.6				$ 531.3				$ 519.6	$ 531.3
Interest on funds held for clients										561.9	466.5	$ 397.4
PEO revenues	[1]									4,237.5	3,877.8	3,464.5
TOTAL REVENUES		3,498.7	$ 3,847.4	$ 3,505.9	$ 3,323.2	3,316.2	$ 3,696.0	$ 3,238.3	$ 3,077.2	14,175.2	13,327.7	12,372.0
Revenues, Net										9,375.8	8,983.4	8,510.1
Operating expenses										7,145.9	6,901.0	6,386.2
Systems development and programming costs										636.3	635.4	632.1
Cost, Depreciation and Amortization										304.4	274.5	226.2
Selling, general, and administrative expenses										3,064.2	2,959.4	2,773.8
Interest Expense										129.9	102.7	80.0
Total Expenses										11,280.7	10,873.0	10,098.3
Other expense/(income), net										(111.1)	172.1	(343.2)
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES		633.3	984.5	741.0	646.8	254.9	875.2	587.5	564.9	3,005.6	2,282.6	2,616.9
Provision for income taxes										712.8	397.7	829.1
NET EARNINGS		475.5	$ 753.7	$ 558.2	$ 505.4	140.9	$ 661.0	$ 670.4	$ 412.6	2,292.8	1,884.9	1,787.8
Assets, Current		34,342.3				31,823.3				34,342.3	31,823.3
Capitalized Contract Cost, Net		2,428.5				2,377.4				2,428.5	2,377.4
Other Assets, Noncurrent		934.4				699.3				934.4	699.3
Total assets		41,887.7				38,849.1				41,887.7	38,849.1	38,886.9
Deferred Revenue and Credits, Current		220.7				225.7				220.7	225.7
Liabilities, Current		32,627.7				30,412.7				32,627.7	30,412.7
Deferred Tax Liabilities, Net, Noncurrent		659.9				522.0				659.9	522.0
Deferred Revenue, Noncurrent		399.3				448.1				399.3	448.1
Liabilities		36,487.8				34,113.2				36,487.8	34,113.2
Retained Earnings (Accumulated Deficit)		17,500.6				16,546.6				17,500.6	16,546.6
Stockholders' Equity Attributable to Parent		5,399.9				4,735.9				5,399.9	4,735.9
Liabilities and Equity		$ 41,887.7				38,849.1				41,887.7	38,849.1
Capitalized Contract Cost, Amortization										874.0	837.4	787.9
Deferred Income Tax Expense (Benefit), Net of Disposals										9.3	(152.0)	41.3
Increase (Decrease) in Other Operating Assets										987.2	858.3	1,139.4
Increase (Decrease) in Accrued Liabilities										266.0	110.5	155.7
Net Cash Provided by (Used in) Operating Activities										$ 2,688.3	2,515.2	2,125.9
Previously Reported [Member]
Revenue Recognition Restatement
Other Assets, Current						758.0					758.0
Interest on funds held for clients											466.5	397.4
PEO revenues											3,874.1	3,464.3
TOTAL REVENUES											13,325.8	12,379.8
Revenues, Net											8,985.2	8,518.1
Operating expenses											6,937.9	6,416.1
Systems development and programming costs											630.2	627.5
Cost, Depreciation and Amortization											274.5	226.2
Selling, general, and administrative expenses											2,971.5	2,783.2
Interest Expense											102.7	80.0
Total Expenses											10,916.8	10,133.0
Other expense/(income), net											237.9	(284.3)
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES											2,171.1	2,531.1
Provision for income taxes											550.3	797.7
NET EARNINGS											1,620.8	1,733.4
Assets, Current						32,050.0					32,050.0
Capitalized Contract Cost, Net						0.0					0.0
Other Assets, Noncurrent						1,089.6					1,089.6
Total assets						37,088.7					37,088.7
Deferred Revenue and Credits, Current						226.5					226.5
Liabilities, Current						30,413.6					30,413.6
Deferred Tax Liabilities, Net, Noncurrent						107.3					107.3
Deferred Revenue, Noncurrent						377.8					377.8
Liabilities						33,629.1					33,629.1
Retained Earnings (Accumulated Deficit)						15,271.3					15,271.3
Stockholders' Equity Attributable to Parent						3,459.6					3,459.6
Liabilities and Equity						37,088.7					37,088.7
Capitalized Contract Cost, Amortization											0.0	0.0
Deferred Income Tax Expense (Benefit), Net of Disposals											0.5	10.0
Increase (Decrease) in Other Operating Assets											(93.5)	269.1
Increase (Decrease) in Accrued Liabilities											107.7	159.0
Net Cash Provided by (Used in) Operating Activities											2,515.2	2,125.9
Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member]
Revenue Recognition Restatement
Other Assets, Current						(226.7)					(226.7)
Interest on funds held for clients											0.0	0.0
PEO revenues											3.7	0.2
TOTAL REVENUES											1.9	(7.8)
Revenues, Net											(1.8)	(8.0)
Operating expenses											(74.0)	(63.6)
Systems development and programming costs											0.0	0.0
Cost, Depreciation and Amortization											0.0	0.0
Selling, general, and administrative expenses											(35.6)	(30.0)
Interest Expense											0.0	0.0
Total Expenses											(109.6)	(93.6)
Other expense/(income), net											0.0	0.0
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES											111.5	85.8
Provision for income taxes											(152.6)	31.4
NET EARNINGS											264.1	54.4
Assets, Current						(226.7)					(226.7)
Capitalized Contract Cost, Net						2,377.4					2,377.4
Other Assets, Noncurrent						(390.3)					(390.3)
Total assets						1,760.4					1,760.4
Deferred Revenue and Credits, Current						(0.8)					(0.8)
Liabilities, Current						(0.8)					(0.8)
Deferred Tax Liabilities, Net, Noncurrent						414.7					414.7
Deferred Revenue, Noncurrent						70.2					70.2
Liabilities						484.1					484.1
Retained Earnings (Accumulated Deficit)						1,275.3					1,275.3
Stockholders' Equity Attributable to Parent						1,276.3					1,276.3
Liabilities and Equity						$ 1,760.4					1,760.4
Capitalized Contract Cost, Amortization											837.4	787.9
Deferred Income Tax Expense (Benefit), Net of Disposals											(152.5)	31.3
Increase (Decrease) in Other Operating Assets											951.8	870.3
Increase (Decrease) in Accrued Liabilities											2.8	(3.3)
Net Cash Provided by (Used in) Operating Activities											0.0	0.0
ASU 2017-07 [Member] | Restatement Adjustment [Member]
Revenue Recognition Restatement
Interest on funds held for clients											0.0	0.0
PEO revenues											0.0	0.0
TOTAL REVENUES											0.0	0.0
Revenues, Net											0.0	0.0
Operating expenses											37.1	33.7
Systems development and programming costs											5.2	4.6
Cost, Depreciation and Amortization											0.0	0.0
Selling, general, and administrative expenses											23.5	20.6
Interest Expense											0.0	0.0
Total Expenses											65.8	58.9
Other expense/(income), net											(65.8)	(58.9)
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, 2019 ("fiscal 2019"), June 30, 2018 ("fiscal 2018"), and June 30, 2017 ("fiscal 2017"), Professional Employer Organization ("PEO") revenues are net of direct pass-through costs, primarily consisting of payroll wages and payroll taxes, of $42,688.8 million, $39,140.9 million, and $34,567.4 million, respectively.