Revenue (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 3,495.7	$ 3,310.3
Employer Services
Disaggregation of Revenue [Line Items]
Revenues	2,441.4	2,338.2
PEO
Disaggregation of Revenue [Line Items]
Revenues	1,056.9	974.9
Other
Disaggregation of Revenue [Line Items]
Revenues	(2.6)	(2.8)
HCM
Disaggregation of Revenue [Line Items]
Revenues	1,568.5	1,520.3
HCM | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	1,570.0	1,521.8
HCM | PEO
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
HCM | Other
Disaggregation of Revenue [Line Items]
Revenues	(1.5)	(1.5)
HRO [Member]
Disaggregation of Revenue [Line Items]
Revenues	591.1	557.5
HRO [Member] | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	235.7	226.1
HRO [Member] | PEO
Disaggregation of Revenue [Line Items]
Revenues	356.5	332.7
HRO [Member] | Other
Disaggregation of Revenue [Line Items]
Revenues	(1.1)	(1.3)
PEO Benefits Pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	699.1	640.5
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	699.1	640.5
PEO Benefits Pass-throughs | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0
Global
Disaggregation of Revenue [Line Items]
Revenues	503.1	473.5
Global | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	503.1	473.5
Global | PEO
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0
Global | Other
Disaggregation of Revenue [Line Items]
Revenues	0.0
Client Fund Interest
Disaggregation of Revenue [Line Items]
Revenues	133.9	118.5
Client Fund Interest | Employer Services
Disaggregation of Revenue [Line Items]
Revenues	132.6	116.8
Client Fund Interest | PEO
Disaggregation of Revenue [Line Items]
Revenues	1.3	1.7
Client Fund Interest | Other
Disaggregation of Revenue [Line Items]
Revenues	$ 0.0