Corporate Investments and Funds Held for Clients - Schedule of Corporate Investments and Funds Held for Clients (Details) - USD ($) $ in Millions	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2024
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents - amortized cost	$ 4,230.1	$ 3,347.8	$ 2,913.4
Amortized Cost	38,160.5	34,203.4
Gross Unrealized  Gains	115.2	256.6
Gross Unrealized Losses	(574.4)	(682.3)
Fair Value	37,701.3	33,777.7
Total corporate investments and funds held for clients - amortized cost	48,785.7	39,258.0
Total corporate investments and funds held for clients - gross unrealized gains	115.2	256.6
Total corporate investments and funds held for clients - gross unrealized losses	(574.4)	(682.3)
Total corporate investments and funds held for clients - fair value	48,326.5	38,832.3
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	18,643.3	17,515.2
Gross Unrealized  Gains	48.1	108.7
Gross Unrealized Losses	(342.0)	(420.2)
Fair Value	18,349.4	17,203.7
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,873.1	8,416.8
Gross Unrealized  Gains	17.8	85.6
Gross Unrealized Losses	(57.4)	(43.7)
Fair Value	10,833.5	8,458.7
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,437.3	1,837.8
Gross Unrealized  Gains	10.4	22.6
Gross Unrealized Losses	(15.0)	(15.5)
Fair Value	2,432.7	1,844.9
Canadian government obligations and Canadian government agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,055.0	1,972.0
Gross Unrealized  Gains	13.9	16.4
Gross Unrealized Losses	(22.0)	(32.4)
Fair Value	2,046.9	1,956.0
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,186.2	1,155.8
Gross Unrealized  Gains	15.3	13.8
Gross Unrealized Losses	(19.6)	(27.7)
Fair Value	1,181.9	1,141.9
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	930.3	1,328.5
Gross Unrealized  Gains	1.9	2.3
Gross Unrealized Losses	(70.5)	(80.0)
Fair Value	861.7	1,250.8
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,035.3	1,977.3
Gross Unrealized  Gains	7.8	7.2
Gross Unrealized Losses	(47.9)	(62.8)
Fair Value	1,995.2	1,921.7
Corporate Investments
Debt Securities, Available-for-sale [Line Items]
Fair Value	138.6	4,498.8
Funds Held for Clients
Debt Securities, Available-for-sale [Line Items]
Fair Value	37,562.7	29,278.9
Money market securities, cash and other cash equivalents
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents - amortized cost	10,625.2	5,054.6
Money market securities and other cash equivalents - fair value	$ 10,625.2	$ 5,054.6