Corporate Investments and Funds Held For Clients - Corporate Investments And Funds Held For Clients (Details) - USD ($) $ in Millions	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2021
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents - amortized cost	$ 2,083.5	$ 1,436.3	$ 2,575.2
Amortized Cost	31,971.8	30,113.0
Gross Unrealized  Gains	7.5	9.7
Gross Unrealized Losses	(2,214.4)	(1,731.1)
Fair market value	29,764.9	28,391.6
Total corporate investments and funds held for clients - amortized cost	40,743.3	52,896.0
Total corporate investments and funds held for clients - gross unrealized gains	7.5	9.7
Total corporate investments and funds held for clients - gross unrealized losses	(2,214.4)	(1,731.1)
Total corporate investments and funds held for clients - fair market value	38,536.4	51,174.6
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	15,870.7	16,183.1
Gross Unrealized  Gains	4.7	3.9
Gross Unrealized Losses	(1,308.3)	(1,083.0)
Fair market value	14,567.1	15,104.0
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,054.7	5,003.6
Gross Unrealized  Gains	0.7	2.2
Gross Unrealized Losses	(290.4)	(171.1)
Fair market value	7,765.0	4,834.7
Canadian government obligations and Canadian government agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,070.4	2,022.9
Gross Unrealized  Gains	0.0	0.1
Gross Unrealized Losses	(145.0)	(123.5)
Fair market value	1,925.4	1,899.5
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,670.0	1,728.2
Gross Unrealized  Gains	0.2	0.1
Gross Unrealized Losses	(179.8)	(138.2)
Fair market value	1,490.4	1,590.1
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,234.7	1,995.7
Gross Unrealized  Gains	0.0	0.5
Gross Unrealized Losses	(69.7)	(58.8)
Fair market value	1,165.0	1,937.4
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,000.5	994.3
Gross Unrealized  Gains	0.2	0.4
Gross Unrealized Losses	(78.1)	(62.7)
Fair market value	922.6	932.0
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	679.2	858.7
Gross Unrealized  Gains	0.0	0.3
Gross Unrealized Losses	(46.7)	(29.9)
Fair market value	632.5	829.1
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,391.6	1,326.5
Gross Unrealized  Gains	1.7	2.2
Gross Unrealized Losses	(96.4)	(63.9)
Fair market value	1,296.9	1,264.8
Corporate Investments
Debt Securities, Available-for-sale [Line Items]
Fair market value	119.3	169.1
Funds Held For Clients
Debt Securities, Available-for-sale [Line Items]
Fair market value	29,645.6	28,222.5
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	8,771.5	22,783.0
Money market securities and other cash equivalents - fair market value	$ 8,771.5	$ 22,783.0