New Accounting Pronouncements (Details) - USD ($) $ in Millions		3 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other current assets		$ 846.5		$ 531.3
TOTAL EXPENSES		2,690.3	$ 2,554.9
Nonoperating Income (Expense)		(13.9)	(42.6)
Revenues, other than interest on funds held for clients and PEO revenues		2,218.6	2,078.9
Amortization of deferred contract costs		216.9	204.7
Deferred income taxes		26.4	55.4
Increase (Decrease) in Other Operating Assets		(471.2)	(460.7)
Decrease in accrued expenses and other liabilities		(77.8)	(19.0)
Net cash flows provided by operating activities		149.2	244.7
Interest on funds held for clients		118.5	99.4
PEO revenues (A)	[1]	986.1	898.9
TOTAL REVENUES		3,323.2	3,077.2
Operating expenses		1,709.9	1,630.7
Systems development and programming costs		158.0	158.2
Depreciation and amortization		72.6	62.6
Selling, general, and administrative expenses		713.9	675.4
Interest expense		35.9	28.0
EARNINGS BEFORE INCOME TAXES		646.8	564.9
Provision for income taxes		141.4	152.3
NET EARNINGS		505.4	412.6
Assets, Current		29,955.9		31,823.3
Deferred contract costs		2,352.3		2,377.4
Other assets		1,053.4		699.3
Assets		37,416.7		38,849.1
Short-term deferred revenues		229.0		225.7
Liabilities, Current		29,037.3		30,412.7
Other liabilities		736.4		728.0
Deferred income taxes		533.2		522.0
Long-term deferred revenues		428.6		448.1
Liabilities		32,737.9		34,113.2
Retained earnings		16,741.1		16,546.6
Stockholders' Equity Attributable to Parent		4,678.8		4,735.9
Liabilities and Equity		$ 37,416.7		38,849.1
Scenario, Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other current assets				758.0
TOTAL EXPENSES			2,556.8
Nonoperating Income (Expense)			(26.2)
Revenues, other than interest on funds held for clients and PEO revenues			2,080.9
Amortization of deferred contract costs			0.0
Deferred income taxes			46.4
Increase (Decrease) in Other Operating Assets			(259.5)
Decrease in accrued expenses and other liabilities			4.6
Net cash flows provided by operating activities			244.7
Interest on funds held for clients			99.4
PEO revenues (A)			898.5
TOTAL REVENUES			3,078.8
Operating expenses			1,646.9
Systems development and programming costs			156.9
Depreciation and amortization			62.6
Selling, general, and administrative expenses			662.4
Interest expense			28.0
EARNINGS BEFORE INCOME TAXES			548.2
Provision for income taxes			146.7
NET EARNINGS			401.5
Assets, Current				32,050.0
Deferred contract costs				0.0
Other assets				1,089.6
Assets				37,088.7
Short-term deferred revenues				226.5
Liabilities, Current				30,413.6
Deferred income taxes				107.3
Long-term deferred revenues				377.8
Liabilities				33,629.1
Retained earnings				15,271.3
Stockholders' Equity Attributable to Parent				3,459.6
Liabilities and Equity				37,088.7
ASU 2017-07 | Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
TOTAL EXPENSES			16.5
Nonoperating Income (Expense)			(16.5)
Revenues, other than interest on funds held for clients and PEO revenues			0.0
Interest on funds held for clients			0.0
PEO revenues (A)			0.0
TOTAL REVENUES			0.0
Operating expenses			9.3
Systems development and programming costs			1.3
Depreciation and amortization			0.0
Selling, general, and administrative expenses			5.9
Interest expense			0.0
EARNINGS BEFORE INCOME TAXES			0.0
Provision for income taxes			0.0
NET EARNINGS			0.0
ASC 606 Adjustments | Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other current assets				(226.7)
TOTAL EXPENSES			(18.3)
Nonoperating Income (Expense)			0.0
Revenues, other than interest on funds held for clients and PEO revenues			(2.0)
Amortization of deferred contract costs			204.7
Deferred income taxes			9.0
Increase (Decrease) in Other Operating Assets			(201.2)
Decrease in accrued expenses and other liabilities			(23.6)
Net cash flows provided by operating activities			0.0
Interest on funds held for clients			0.0
PEO revenues (A)			0.4
TOTAL REVENUES			(1.6)
Operating expenses			(25.3)
Systems development and programming costs			0.0
Depreciation and amortization			0.0
Selling, general, and administrative expenses			7.0
Interest expense			0.0
EARNINGS BEFORE INCOME TAXES			16.7
Provision for income taxes			5.6
NET EARNINGS			$ 11.1
Assets, Current				(226.7)
Deferred contract costs				2,377.4
Other assets				(390.3)
Assets				1,760.4
Short-term deferred revenues				(0.8)
Liabilities, Current				(0.8)
Deferred income taxes				414.7
Long-term deferred revenues				70.2
Liabilities				484.1
Retained earnings				1,275.3
Stockholders' Equity Attributable to Parent				1,276.3
Liabilities and Equity				$ 1,760.4

[1] Professional Employer Organization (“PEO”) revenues are net of direct pass-through costs, primarily consisting of payroll wages and payroll taxes of $9,629.4 million and $8,738.5 million for the three months ended September 30, 2018 and 2017, respectively.