Corporate Investments and Funds Held For Clients (Corporate Investments And Funds Held For Clients) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents - amortized cost	$ 1,602.1	$ 2,575.2	$ 1,613.1
Amortized Cost	24,920.9	23,869.5
Gross Unrealized  Gains	490.0	579.9
Gross Unrealized Losses	(118.2)	(77.7)
Fair market value	25,292.7	24,371.7
Total corporate investments and funds held for clients - amortized cost	48,113.2	37,012.7
Total corporate investments and funds held for clients - gross unrealized gains	490.0	579.9
Total corporate investments and funds held for clients - gross unrealized losses	(118.2)	(77.7)
Total corporate investments and funds held for clients - fair market value	48,485.0	37,514.9
Corporate Investments
Debt Securities, Available-for-sale [Line Items]
Fair market value	74.3	33.9
Funds Held For Clients
Debt Securities, Available-for-sale [Line Items]
Fair market value	25,218.4	24,337.8
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	12,803.0	11,732.3
Gross Unrealized  Gains	275.7	321.9
Gross Unrealized Losses	(62.5)	(38.5)
Fair market value	13,016.2	12,015.7
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,053.9	4,036.9
Gross Unrealized  Gains	52.9	64.8
Gross Unrealized Losses	(14.6)	(9.3)
Fair market value	4,092.2	4,092.4
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,259.1	2,279.8
Gross Unrealized  Gains	49.9	60.9
Gross Unrealized Losses	(2.1)	(0.9)
Fair market value	2,306.9	2,339.8
Canadian government obligations and Canadian government agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,559.7	1,542.3
Gross Unrealized  Gains	12.0	15.0
Gross Unrealized Losses	(11.8)	(9.0)
Fair market value	1,559.9	1,548.3
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,466.4	1,446.3
Gross Unrealized  Gains	17.9	22.5
Gross Unrealized Losses	(12.4)	(9.4)
Fair market value	1,471.9	1,459.4
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	871.4	956.3
Gross Unrealized  Gains	19.0	22.7
Gross Unrealized Losses	(6.5)	(5.3)
Fair market value	883.9	973.7
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	837.7	793.4
Gross Unrealized  Gains	36.0	41.2
Gross Unrealized Losses	(0.6)	0.0
Fair market value	873.1	834.6
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,069.7	1,082.2
Gross Unrealized  Gains	26.6	30.9
Gross Unrealized Losses	(7.7)	(5.3)
Fair market value	1,088.6	1,107.8
Money Market Funds
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents - amortized cost	23,192.3	13,143.2
Money market securities and other cash equivalents - fair market value	$ 23,192.3	$ 13,143.2