Corporate Investments and Funds Held For Clients - Corporate Investments and Funds Held for Clients (Details) - USD ($) $ in Millions	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2023
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents - amortized cost	$ 3,347.8	$ 2,913.4	$ 2,083.5
Amortized Cost	34,203.4	32,723.3
Gross Unrealized  Gains	256.6	30.9
Gross Unrealized Losses	(682.3)	(1,546.7)
Fair market value	33,777.7	31,207.5
Total corporate investments and funds held for clients - amortized cost	39,258.0	42,809.3
Total corporate investments and funds held for clients - gross unrealized gains	256.6	30.9
Total corporate investments and funds held for clients - gross unrealized losses	(682.3)	(1,546.7)
Total corporate investments and funds held for clients - fair market value	38,832.3	41,293.5
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	17,515.2	16,833.3
Gross Unrealized  Gains	108.7	11.5
Gross Unrealized Losses	(420.2)	(944.8)
Fair market value	17,203.7	15,900.0
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,416.8	7,701.2
Gross Unrealized  Gains	85.6	9.0
Gross Unrealized Losses	(43.7)	(164.5)
Fair market value	8,458.7	7,545.7
Canadian government obligations and Canadian government agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,972.0	2,130.7
Gross Unrealized  Gains	16.4	1.7
Gross Unrealized Losses	(32.4)	(86.6)
Fair market value	1,956.0	2,045.8
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,837.8	1,394.9
Gross Unrealized  Gains	22.6	3.9
Gross Unrealized Losses	(15.5)	(43.0)
Fair market value	1,844.9	1,355.8
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,328.5	1,645.0
Gross Unrealized  Gains	2.3	0.5
Gross Unrealized Losses	(80.0)	(140.6)
Fair market value	1,250.8	1,504.9
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,155.8	1,116.3
Gross Unrealized  Gains	13.8	2.3
Gross Unrealized Losses	(27.7)	(56.2)
Fair market value	1,141.9	1,062.4
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		535.9
Gross Unrealized  Gains		0.0
Gross Unrealized Losses		(35.1)
Fair market value	438.6	500.8
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,977.3	1,366.0
Gross Unrealized  Gains	7.2	2.0
Gross Unrealized Losses	(62.8)	(75.9)
Fair market value	1,921.7	1,292.1
Corporate Investments
Debt Securities, Available-for-sale [Line Items]
Fair market value	4,498.8	384.0
Funds held for clients
Debt Securities, Available-for-sale [Line Items]
Fair market value	29,278.9	30,823.5
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	5,054.6	10,086.0
Money market securities and other cash equivalents - fair market value	$ 5,054.6	$ 10,086.0