Corporate Investments and Funds Held For Clients - Corporate Investments and Funds Held for Clients (Details) - USD ($) $ in Millions	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2022
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents - amortized cost	$ 2,913.4	$ 2,083.5	$ 1,436.3
Amortized Cost	32,723.3	31,971.8
Gross Unrealized  Gains	30.9	7.5
Gross Unrealized Losses	(1,546.7)	(2,214.4)
Fair market value	31,207.5	29,764.9
Total corporate investments and funds held for clients - amortized cost	42,809.3	40,743.3
Total corporate investments and funds held for clients - gross unrealized gains	30.9	7.5
Total corporate investments and funds held for clients - gross unrealized losses	(1,546.7)	(2,214.4)
Total corporate investments and funds held for clients - fair market value	41,293.5	38,536.4
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	16,833.3	15,870.7
Gross Unrealized  Gains	11.5	4.7
Gross Unrealized Losses	(944.8)	(1,308.3)
Fair market value	15,900.0	14,567.1
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,701.2	8,054.7
Gross Unrealized  Gains	9.0	0.7
Gross Unrealized Losses	(164.5)	(290.4)
Fair market value	7,545.7	7,765.0
Canadian government obligations and Canadian government agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,130.7	2,070.4
Gross Unrealized  Gains	1.7	0.0
Gross Unrealized Losses	(86.6)	(145.0)
Fair market value	2,045.8	1,925.4
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,645.0	1,670.0
Gross Unrealized  Gains	0.5	0.2
Gross Unrealized Losses	(140.6)	(179.8)
Fair market value	1,504.9	1,490.4
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,394.9	1,234.7
Gross Unrealized  Gains	3.9	0.0
Gross Unrealized Losses	(43.0)	(69.7)
Fair market value	1,355.8	1,165.0
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,116.3	1,000.5
Gross Unrealized  Gains	2.3	0.2
Gross Unrealized Losses	(56.2)	(78.1)
Fair market value	1,062.4	922.6
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	535.9	679.2
Gross Unrealized  Gains	0.0	0.0
Gross Unrealized Losses	(35.1)	(46.7)
Fair market value	500.8	632.5
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,366.0	1,391.6
Gross Unrealized  Gains	2.0	1.7
Gross Unrealized Losses	(75.9)	(96.4)
Fair market value	1,292.1	1,296.9
Corporate Investments
Debt Securities, Available-for-sale [Line Items]
Fair market value	384.0	119.3
Funds Held For Clients
Debt Securities, Available-for-sale [Line Items]
Fair market value	30,823.5	29,645.6
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	10,086.0	8,771.5
Money market securities and other cash equivalents - fair market value	$ 10,086.0	$ 8,771.5