Revenue (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 3,323.2	$ 3,077.2
Employer Services
Disaggregation of Revenue [Line Items]
Revenues	2,338.2	2,179.4
PEO
Disaggregation of Revenue [Line Items]
Revenues	987.8	899.8
Other
Disaggregation of Revenue [Line Items]
Revenues	(2.8)	(2.0)
HCM
Disaggregation of Revenue [Line Items]
Revenues	1,520.3	1,424.1
HCM | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	1,521.8	1,425.0
HCM | PEO
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
HCM | Other
Disaggregation of Revenue [Line Items]
Revenues	(1.5)	(0.9)
HRO, excluding PEO benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	557.5	509.1
HRO, excluding PEO benefits pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	226.1	206.6
HRO, excluding PEO benefits pass-throughs | PEO
Disaggregation of Revenue [Line Items]
Revenues	332.7	303.6
HRO, excluding PEO benefits pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	(1.3)	(1.1)
PEO Benefits Pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	653.4	595.3
PEO Benefits Pass-throughs | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
PEO Benefits Pass-throughs | PEO
Disaggregation of Revenue [Line Items]
Revenues	653.4	595.3
PEO Benefits Pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Global
Disaggregation of Revenue [Line Items]
Revenues	473.5	449.3
Global | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	473.5	449.3
Global | PEO
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Global | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Client Fund Interest
Disaggregation of Revenue [Line Items]
Revenues	118.5	99.4
Client Fund Interest | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	116.8	98.5
Client Fund Interest | PEO
Disaggregation of Revenue [Line Items]
Revenues	1.7	0.9
Client Fund Interest | Other
Disaggregation of Revenue [Line Items]
Revenues	$ 0.0	$ 0.0