Revenue (Details) - USD ($) $ in Millions		12 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Capitalized Contract Cost, Amortization		$ 915.0	$ 874.0	$ 837.4
Deferred contract costs	[1]	2,401.6	2,428.5
Contract with Customer, Liability		522.7	563.4
Revenue from Contract with Customer, Excluding Assessed Tax		14,589.8	14,110.2	13,274.2
Contract with Customer, Liability, Revenue Recognized		168.5
Contract With Customer, Liability, Deferral Net Of Revenue Recognized And Foreign Currency Translation		134.2
Contract With Customer, Liability, Increase (Decrease) From Foreign Currency Translation		(6.4)
Capitalized Contract Cost [Line Items]
Deferred contract costs	[1]	2,401.6	2,428.5
HCM [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		6,540.9	6,441.8	6,204.9
HRO [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,543.2	2,444.4	2,261.9
PEO [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,907.7	2,647.5	2,409.6
Global [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,052.8	2,014.6	1,931.3
client fund interest [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		545.2	561.9	466.5
Employer Services Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		10,086.6	9,942.8	9,454.8
Employer Services Segment [Member] | HCM [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		6,546.4	6,447.5	6,210.2
Employer Services Segment [Member] | HRO [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		947.2	924.0	851.3
Employer Services Segment [Member] | PEO [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		0.0	0.0	0.0
Employer Services Segment [Member] | Global [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,052.8	2,014.6	1,931.3
Employer Services Segment [Member] | client fund interest [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		540.2	556.7	462.0
Professional Employee Organization Services Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		4,511.5	4,177.7	3,828.8
Professional Employee Organization Services Segment [Member] | HCM [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		0.0	0.0	0.0
Professional Employee Organization Services Segment [Member] | HRO [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1,598.8	1,525.0	1,414.7
Professional Employee Organization Services Segment [Member] | PEO [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,907.7	2,647.5	2,409.6
Professional Employee Organization Services Segment [Member] | Global [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		0.0	0.0	0.0
Professional Employee Organization Services Segment [Member] | client fund interest [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		5.0	5.2	4.5
Other Segments [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		(8.3)	(10.3)	(9.4)
Other Segments [Member] | HCM [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		(5.5)	(5.7)	(5.3)
Other Segments [Member] | HRO [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		(2.8)	(4.6)	(4.1)
Other Segments [Member] | PEO [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		0.0	0.0	0.0
Other Segments [Member] | Global [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		0.0	0.0	0.0
Other Segments [Member] | client fund interest [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		0.0	0.0	$ 0.0
Deferred costs to obtain a contract [Member]
Disaggregation of Revenue [Line Items]
Deferred contract costs		977.8	992.3
Capitalized Contract Cost [Line Items]
Deferred contract costs		977.8	992.3
Deferred costs to fulfill a contract [Member]
Disaggregation of Revenue [Line Items]
Deferred contract costs		1,423.8	1,436.2
Capitalized Contract Cost [Line Items]
Deferred contract costs		$ 1,423.8	$ 1,436.2

[1] (1) The amount of total deferred costs amortized during the twelve months ended June 30, 2020, June 30, 2019, and June 30, 2018 were $915.0 million, $874.0 million, and $837.4 million, respectively.