FINANCIAL DATA BY SEGMENT - Schedule of Financial Data Segment Reporting Information (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Revenues	$ 6,889.1	$ 6,506.8	$ 6,060.9
Depreciation and amortization	130.7	119.8	84.4
Amortization of acquired intangibles and purchased intellectual property	196.6	200.3	214.4
Amortization of other assets	170.8	157.8	126.2
Other direct expenses	5,332.2	5,151.5	4,840.9
Other segment items	0.0	0.0	0.0
Earnings before income taxes	1,058.7	877.4	794.9
Segment Reporting, Reconciling Item, Corporate Nonsegment
Segment Reporting Information [Line Items]
Revenues	0.0	0.0	0.0
Depreciation and amortization	33.2	30.3	28.3
Amortization of acquired intangibles and purchased intellectual property	0.0	0.0	0.0
Amortization of other assets	17.5	16.7	16.9
Other direct expenses	593.4	604.3	511.9
Other segment items	(447.5)	(404.9)	(356.5)
Earnings before income taxes	(196.7)	(246.3)	(200.5)
Investor Communication Solutions
Segment Reporting Information [Line Items]
Revenues	5,113.0	4,857.9	4,535.6
Investor Communication Solutions | Operating Segments
Segment Reporting Information [Line Items]
Revenues	5,113.0	4,857.9	4,535.6
Depreciation and amortization	44.7	40.1	37.9
Amortization of acquired intangibles and purchased intellectual property	42.9	45.4	55.5
Amortization of other assets	39.4	38.5	41.1
Other direct expenses	3,633.2	3,514.5	3,356.0
Other segment items	298.8	269.0	233.7
Earnings before income taxes	1,054.0	950.4	811.4
Global Technology and Operations | Operating Segments
Segment Reporting Information [Line Items]
Revenues	1,776.1	1,648.9	1,525.2
Depreciation and amortization	52.8	49.4	18.3
Amortization of acquired intangibles and purchased intellectual property	153.7	154.9	158.9
Amortization of other assets	113.9	102.6	68.3
Other direct expenses	1,105.6	1,032.7	973.0
Other segment items	148.7	135.9	122.9
Earnings before income taxes	201.4	173.3	183.9
Total Reportable Segments | Operating Segments
Segment Reporting Information [Line Items]
Revenues	6,889.1	6,506.8	6,060.9
Depreciation and amortization	97.5	89.5	56.1
Amortization of acquired intangibles and purchased intellectual property	196.6	200.3	214.4
Amortization of other assets	153.3	141.1	109.3
Other direct expenses	4,738.8	4,547.2	4,329.0
Other segment items	447.5	404.9	356.5
Earnings before income taxes	$ 1,255.4	$ 1,123.7	$ 995.4