Financial Data By Segment (Financial Data By Strategic Business Unit Segment) (Details) $ in Millions	3 Months Ended								12 Months Ended
	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)		Jun. 30, 2016 USD ($)
Segment Reporting Information [Line Items]
TOTAL REVENUES	$ 3,318.6	$ 3,693.0	$ 3,235.4	$ 3,078.8	$ 3,064.8	$ 3,410.8	$ 2,987.3	$ 2,916.9	$ 13,325.8	$ 12,379.8		$ 11,667.8
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	204.5	$ 852.6	$ 565.7	$ 548.2	388.4	$ 827.9	$ 786.2	$ 528.7	2,171.1	2,531.1		2,234.7
Assets from Continuing Operations	37,088.7				37,180.0				37,088.7	37,180.0		43,670.0
Capital Expenditures from continuing operations									191.9	249.0		165.7
Depreciation, Depletion and Amortization									$ 377.6	316.1	[1]	288.6	[1]
Number of Reportable Segments | segment									2
Standard Reconciling Rate Between Actual Interest Income Earned And Interest Credited									4.50%
Employer Services [Member]
Segment Reporting Information [Line Items]
TOTAL REVENUES									$ 10,057.8	9,535.2		9,211.9
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES									3,087.4	2,918.5		2,798.4
Assets from Continuing Operations	30,250.8				30,107.7				30,250.8	30,107.7		36,637.5
Capital Expenditures from continuing operations									113.9	83.0		71.1
Depreciation, Depletion and Amortization									291.9	247.3		230.7
PEO Services [Member]
Segment Reporting Information [Line Items]
TOTAL REVENUES									3,896.6	3,483.6		3,073.1
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES									504.2	448.6		371.2
Assets from Continuing Operations	760.1				586.8				760.1	586.8		534.6
Capital Expenditures from continuing operations									0.0	0.2		1.0
Depreciation, Depletion and Amortization									3.0	1.3		1.5
Other [Member]
Segment Reporting Information [Line Items]
TOTAL REVENUES									(9.4)	(10.6)		1.9
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES									(801.3)	(207.6)		(315.8)
Assets from Continuing Operations	6,077.8				6,485.5				6,077.8	6,485.5		6,497.9
Capital Expenditures from continuing operations									78.0	165.8		93.6
Depreciation, Depletion and Amortization									82.7	67.5		56.4
Client Fund Interest [Member]
Segment Reporting Information [Line Items]
TOTAL REVENUES									(619.2)	(628.4)		(619.1)
EARNINGS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES									(619.2)	(628.4)		(619.1)
Assets from Continuing Operations	$ 0.0				$ 0.0				0.0	0.0		0.0
Capital Expenditures from continuing operations									0.0	0.0		0.0
Depreciation, Depletion and Amortization									$ 0.0	$ 0.0		$ 0.0

[1] See Note 1 for a summary of adjustments.