New Accounting Pronouncements (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Mar. 31, 2019		Mar. 31, 2018	Mar. 31, 2019		Mar. 31, 2018	Jul. 01, 2019	Jun. 30, 2018
Statements of Consolidated Earnings
Revenues, other than interest on funds held for clients and PEO revenues		$ 2,546.9		$ 2,495.2	$ 7,084.7		$ 6,764.5
Interest on funds held for clients		167.4		134.8	415.0		340.9
PEO revenues (A)	[1]	1,133.1		1,066.0	3,176.8		2,906.1
TOTAL REVENUES		3,847.4		3,696.0	10,676.5		10,011.5
Operating expenses		1,874.5		1,845.2	5,370.4		5,185.0
Systems development and programming costs		160.1		163.9	474.2		481.5
Depreciation and amortization		77.2		70.2	221.5		202.1
Selling, general, and administrative expenses		750.4		750.1	2,209.4		2,149.0
Interest expense		21.7		18.6	96.2		74.1
TOTAL EXPENSES		2,883.9		2,848.0	8,371.7		8,091.7
Other income, net		(21.0)		(27.2)	(67.5)		(107.9)
EARNINGS BEFORE INCOME TAXES		984.5		875.2	2,372.3		2,027.7
Provision for income taxes		230.8		214.2	554.9		283.7
NET EARNINGS		753.7		661.0	1,817.4		1,744.0
Consolidated Balance Sheets
Other current assets		534.4			534.4				$ 531.3
Total current assets		40,924.0			40,924.0				31,823.3
Deferred contract costs		2,361.6	[2]		2,361.6	[2]			2,377.4
Other assets		740.3			740.3				699.3
Total assets		48,196.3			48,196.3				38,849.1
Short-term deferred revenues		228.3			228.3				225.7
Total current liabilities		39,166.0			39,166.0				30,412.7
Deferred income taxes		615.8			615.8				522.0
Long-term deferred revenues		406.2			406.2				448.1
Total liabilities		42,950.1			42,950.1				34,113.2
Retained earnings		17,368.6			17,368.6				16,546.6
Total stockholders’ equity		5,246.2			5,246.2				4,735.9
Total liabilities and stockholders’ equity		48,196.3			48,196.3				38,849.1
Statements of Consolidated Cash Flows
Net earnings		753.7		661.0	1,817.4		1,744.0
Amortization of deferred contract costs		220.6		211.2	655.2		623.5
Deferred income taxes					4.1		(145.5)
Increase in other assets					(748.9)		(696.1)
Increase in accrued expenses and other liabilities					194.5		71.0
Net cash flows provided by operating activities					1,956.0		1,810.0
Reclassification of Stranded Tax Effect
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings				0.0			0.0
As Previously Reported
Statements of Consolidated Earnings
Revenues, other than interest on funds held for clients and PEO revenues				2,492.9			6,762.7
Interest on funds held for clients				134.8			340.9
PEO revenues (A)				1,065.3			2,903.6
TOTAL REVENUES				3,693.0			10,007.2
Operating expenses				1,844.7			5,210.6
Systems development and programming costs				162.5			477.6
Depreciation and amortization				70.2			202.1
Selling, general, and administrative expenses				755.1			2,134.8
Interest expense				18.6			74.1
TOTAL EXPENSES				2,851.1			8,099.2
Other income, net				(10.7)			(58.5)
EARNINGS BEFORE INCOME TAXES				852.6			1,966.5
Provision for income taxes				209.5			454.4
NET EARNINGS				643.1			1,512.1
Consolidated Balance Sheets
Other current assets									758.0
Total current assets									32,050.0
Deferred contract costs									0.0
Other assets									1,089.6
Total assets									37,088.7
Short-term deferred revenues									226.5
Total current liabilities									30,413.6
Deferred income taxes									107.3
Long-term deferred revenues									377.8
Total liabilities									33,629.1
Retained earnings									15,271.3
Total stockholders’ equity									3,459.6
Total liabilities and stockholders’ equity									37,088.7
Statements of Consolidated Cash Flows
Net earnings				643.1			1,512.1
Amortization of deferred contract costs							0.0
Deferred income taxes							18.0
Increase in other assets							(38.6)
Increase in accrued expenses and other liabilities							105.4
Net cash flows provided by operating activities							1,810.0
ASC 606 | Adjustments
Statements of Consolidated Earnings
Revenues, other than interest on funds held for clients and PEO revenues				2.3			1.8
Interest on funds held for clients				0.0			0.0
PEO revenues (A)				0.7			2.5
TOTAL REVENUES				3.0			4.3
Operating expenses				(8.8)			(53.6)
Systems development and programming costs				0.0			0.0
Depreciation and amortization				0.0			0.0
Selling, general, and administrative expenses				(10.8)			(3.3)
Interest expense				0.0			0.0
TOTAL EXPENSES				(19.6)			(56.9)
Other income, net				0.0			0.0
EARNINGS BEFORE INCOME TAXES				22.6			61.2
Provision for income taxes				4.7			(170.7)
NET EARNINGS				17.9			231.9
Consolidated Balance Sheets
Other current assets									(226.7)
Total current assets									(226.7)
Deferred contract costs									2,377.4
Other assets									(390.3)
Total assets									1,760.4
Short-term deferred revenues									(0.8)
Total current liabilities									(0.8)
Deferred income taxes									414.7
Long-term deferred revenues									70.2
Total liabilities									484.1
Retained earnings									1,275.3
Total stockholders’ equity									1,276.3
Total liabilities and stockholders’ equity									$ 1,760.4
Statements of Consolidated Cash Flows
Net earnings				17.9			231.9
Amortization of deferred contract costs							623.5
Deferred income taxes							(163.5)
Increase in other assets							(657.5)
Increase in accrued expenses and other liabilities							(34.4)
Net cash flows provided by operating activities							0.0
ASU 2017-07 | Adjustments
Statements of Consolidated Earnings
Revenues, other than interest on funds held for clients and PEO revenues				0.0			0.0
Interest on funds held for clients				0.0			0.0
PEO revenues (A)				0.0			0.0
TOTAL REVENUES				0.0			0.0
Operating expenses				9.3			28.0
Systems development and programming costs				1.4			3.9
Depreciation and amortization				0.0			0.0
Selling, general, and administrative expenses				5.8			17.5
Interest expense				0.0			0.0
TOTAL EXPENSES				16.5			49.4
Other income, net				(16.5)			(49.4)
EARNINGS BEFORE INCOME TAXES				0.0			0.0
Provision for income taxes				0.0			0.0
NET EARNINGS				0.0			0.0
Statements of Consolidated Cash Flows
Net earnings				0.0			0.0
ASU 2016-02 | Forecast | Minimum
Adoption of Lease Standard
Right-of-use assets								$ 600.0
Operating lease liabilities								500.0
ASU 2016-02 | Forecast | Maximum
Adoption of Lease Standard
Right-of-use assets								700.0
Operating lease liabilities								$ 600.0
Retained Earnings
Statements of Consolidated Earnings
NET EARNINGS		753.7		661.0	1,817.4		1,744.0
Statements of Consolidated Cash Flows
Net earnings		$ 753.7		661.0	$ 1,817.4		1,744.0
Reclassification of Stranded Tax Effect
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings				$ 42.3			$ 42.3

[1] Professional Employer Organization (“PEO”) revenues are net of direct pass-through costs, primarily consisting of payroll wages and payroll taxes of $10,798.3 million and $10,176.2 million for the three months ended March 31, 2019 and 2018, respectively, and $32,178.8 million and $29,547.0 million for the nine months ended March 31, 2019 and 2018, respectively.

[2] (1) The amount of total deferred costs amortized during the three and nine months ended March 31, 2019 and March 31, 2018, were $220.6 million and $655.2 million, and $211.2 million and $623.5 million, respectively.