Interim Financial Data by Segment (Financial Data By Strategic Business Unit Segment) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 3,235.4	$ 2,987.3	$ 6,314.2	$ 5,904.2
Earnings before Income Taxes	565.7	786.2	1,113.9	1,314.8
Employer Services
Segment Reporting Information [Line Items]
Revenues	2,437.6	2,309.3	4,754.0	4,570.6
Earnings before Income Taxes	706.4	681.1	1,353.0	1,337.1
PEO Services
Segment Reporting Information [Line Items]
Revenues	945.3	822.9	1,848.8	1,617.6
Earnings before Income Taxes	128.2	114.5	245.0	221.6
Other
Segment Reporting Information [Line Items]
Revenues	(1.9)	(2.3)	(3.9)	(6.0)
Earnings before Income Taxes	(123.3)	133.2	(199.4)	34.1
Client Fund Interest Reconciling Item [Member]
Segment Reporting Information [Line Items]
Revenues	(145.6)	(142.6)	(284.7)	(278.0)
Earnings before Income Taxes	$ (145.6)	$ (142.6)	$ (284.7)	$ (278.0)

Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h)(1)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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