New Accounting Pronouncements (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2018		Dec. 31, 2017	Jun. 30, 2018
Income Statement [Abstract]
Revenues, other than interest on funds held for clients and PEO revenues		$ 2,319.8		$ 2,190.3	$ 4,537.8		$ 4,269.2
Interest on funds held for clients		129.1		106.7	247.6		206.1
PEO revenues (A)	[1]	1,057.0		941.3	2,043.7		1,840.2
TOTAL REVENUES		3,505.9		3,238.3	6,829.1		6,315.5
Operating expenses		1,785.9		1,709.2	3,495.9		3,339.9
Systems development and programming costs		156.1		159.4	314.1		317.6
Depreciation and amortization		71.7		69.3	144.3		131.9
Selling, general, and administrative expenses		745.2		723.6	1,459.0		1,399.0
Interest expense		38.6		27.5	74.5		55.5
TOTAL EXPENSES		2,797.5		2,689.0	5,487.8		5,243.9
Other income, net		(32.6)		(38.2)	(46.5)		(80.8)
EARNINGS BEFORE INCOME TAXES		741.0		587.5	1,387.8		1,152.4
Provision for income taxes		182.8		(82.9)	324.2		69.4
NET EARNINGS		558.2		670.4	1,063.6		1,083.0
Other current assets		653.0			653.0			$ 531.3
Statement of Financial Position [Abstract]
Assets, Current		31,682.6			31,682.6			31,823.3
Deferred contract costs		2,338.0	[2]		2,338.0	[2]		2,377.4
Other assets		739.7			739.7			699.3
Assets		38,806.3			38,806.3			38,849.1
Short-term deferred revenues		224.0			224.0			225.7
Liabilities, Current		30,296.9			30,296.9			30,412.7
Other liabilities		752.5			752.5			728.0
Deferred income taxes		580.5			580.5			522.0
Long-term deferred revenues		410.2			410.2			448.1
Liabilities		34,042.4			34,042.4			34,113.2
Retained earnings		16,959.1			16,959.1			16,546.6
Stockholders' Equity Attributable to Parent		4,763.9			4,763.9			4,735.9
Liabilities and Equity		38,806.3			38,806.3			38,849.1
Statement of Cash Flows [Abstract]
Amortization of deferred contract costs		$ 217.7		207.6	434.6		412.3
Deferred income taxes					33.0		(162.8)
Increase (Decrease) in Other Operating Assets					(594.4)		(667.6)
Increase in accrued expenses and other liabilities					287.2		32.1
Net cash flows provided by operating activities					$ 931.5		675.1
Scenario, Previously Reported
Income Statement [Abstract]
Revenues, other than interest on funds held for clients and PEO revenues				2,188.8			4,269.8
Interest on funds held for clients				106.7			206.1
PEO revenues (A)				939.9			1,838.3
TOTAL REVENUES				3,235.4			6,314.2
Operating expenses				1,719.3			3,366.0
Systems development and programming costs				158.1			315.1
Depreciation and amortization				69.3			131.9
Selling, general, and administrative expenses				717.2			1,379.6
Interest expense				27.5			55.5
TOTAL EXPENSES				2,691.4			5,248.1
Other income, net				(21.7)			(47.8)
EARNINGS BEFORE INCOME TAXES				565.7			1,113.9
Provision for income taxes				98.2			244.9
NET EARNINGS				467.5			869.0
Other current assets								758.0
Statement of Financial Position [Abstract]
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
Statement of Cash Flows [Abstract]
Amortization of deferred contract costs							0.0
Deferred income taxes							7.3
Increase (Decrease) in Other Operating Assets							(244.7)
Increase in accrued expenses and other liabilities							65.4
Net cash flows provided by operating activities							675.1
ASU 2017-07 | Restatement Adjustment
Income Statement [Abstract]
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			18.6
Systems development and programming costs				1.3			2.5
Depreciation and amortization				0.0			0.0
Selling, general, and administrative expenses				5.9			11.9
Interest expense				0.0			0.0
TOTAL EXPENSES				16.5			33.0
Other income, net				(16.5)			(33.0)
EARNINGS BEFORE INCOME TAXES				0.0			0.0
Provision for income taxes				0.0			0.0
NET EARNINGS				0.0			0.0
ASC 606 Adjustments | Restatement Adjustment
Income Statement [Abstract]
Revenues, other than interest on funds held for clients and PEO revenues				1.5			(0.6)
Interest on funds held for clients				0.0			0.0
PEO revenues (A)				1.4			1.9
TOTAL REVENUES				2.9			1.3
Operating expenses				(19.4)			(44.7)
Systems development and programming costs				0.0			0.0
Depreciation and amortization				0.0			0.0
Selling, general, and administrative expenses				0.5			7.5
Interest expense				0.0			0.0
TOTAL EXPENSES				(18.9)			(37.2)
Other income, net				0.0			0.0
EARNINGS BEFORE INCOME TAXES				21.8			38.5
Provision for income taxes				(181.1)			(175.5)
NET EARNINGS				$ 202.9			214.0
Other current assets								(226.7)
Statement of Financial Position [Abstract]
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
Statement of Cash Flows [Abstract]
Amortization of deferred contract costs							412.3
Deferred income taxes							(170.1)
Increase (Decrease) in Other Operating Assets							(422.9)
Increase in accrued expenses and other liabilities							(33.3)
Net cash flows provided by operating activities							$ 0.0

[1] Professional Employer Organization (“PEO”) revenues are net of direct pass-through costs, primarily consisting of payroll wages and payroll taxes of $11,751.1 million and $10,632.3 million for the three months ended December 31, 2018 and 2017, respectively, and $21,380.5 million and $19,370.8 million for the six months ended December 31, 2018 and 2017, respectively.

[2] (1) The amount of total deferred costs amortized during the three and six months ended December 31, 2018 and December 31, 2017, were $217.7 million and $207.6 million, and $434.6 million and $412.3 million, respectively.