Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Disaggregation of Revenue [Line Items]
Revenues	$ 5,939.2	$ 5,553.0	$ 16,473.6	$ 15,434.1
Employer Services \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	4,036.1	3,767.9	11,134.6	10,417.4
PEO \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,906.0	1,788.5	5,348.7	5,026.3
Other \| Other
Disaggregation of Revenue [Line Items]
Revenues	(2.9)	(3.4)	(9.7)	(9.6)
HCM
Disaggregation of Revenue [Line Items]
Revenues	2,492.6	2,392.3	6,884.1	6,549.6
HCM \| Employer Services \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	2,495.2	2,395.1	6,891.8	6,557.1
HCM \| PEO \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
HCM \| Other \| Other
Disaggregation of Revenue [Line Items]
Revenues	(2.6)	(2.8)	(7.7)	(7.5)
HRO, excluding PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	1,120.8	1,063.6	3,011.5	2,872.1
HRO, excluding PEO zero-margin benefits pass-throughs \| Employer Services \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	388.8	369.0	1,101.2	1,050.4
HRO, excluding PEO zero-margin benefits pass-throughs \| PEO \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	732.3	695.2	1,912.3	1,823.8
HRO, excluding PEO zero-margin benefits pass-throughs \| Other \| Other
Disaggregation of Revenue [Line Items]
Revenues	(0.3)	(0.6)	(2.0)	(2.1)
PEO zero-margin benefits pass-throughs
Disaggregation of Revenue [Line Items]
Revenues	1,170.0	1,090.0	3,427.2	3,194.4
PEO zero-margin benefits pass-throughs \| Employer Services \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
PEO zero-margin benefits pass-throughs \| PEO \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,170.0	1,090.0	3,427.2	3,194.4
PEO zero-margin benefits pass-throughs \| Other \| Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
Global
Disaggregation of Revenue [Line Items]
Revenues	751.9	651.9	2,151.4	1,936.7
Global \| Employer Services \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	751.9	651.9	2,151.4	1,936.7
Global \| PEO \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
Global \| Other \| Other
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
Interest on funds held for clients
Disaggregation of Revenue [Line Items]
Revenues	403.9	355.2	999.4	881.3
Interest on funds held for clients \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	403.9	355.2	999.4	881.3
Interest on funds held for clients \| Employer Services \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	400.2	351.9	990.2	873.2
Interest on funds held for clients \| PEO \| Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	3.7	3.3	9.2	8.1
Interest on funds held for clients \| Other \| Other
Disaggregation of Revenue [Line Items]
Revenues	$ 0.0	$ 0.0	$ 0.0	$ 0.0