Corporate Investments and Funds Held For Clients (Corporate Investments And Funds Held For Clients) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents - amortized cost	$ 1,745.0	$ 2,575.2	$ 1,602.2
Amortized Cost	26,997.1	23,869.5
Gross Unrealized  Gains	353.4	579.9
Gross Unrealized Losses	(229.6)	(77.7)
Fair market value	27,120.9	24,371.7
Total corporate investments and funds held for clients - amortized cost	47,531.3	37,012.7
Total corporate investments and funds held for clients - gross unrealized gains	353.4	579.9
Total corporate investments and funds held for clients - gross unrealized losses	(229.6)	(77.7)
Total corporate investments and funds held for clients - fair market value	47,655.1	37,514.9
Corporate Investments
Debt Securities, Available-for-sale [Line Items]
Fair market value	19.7	33.9
Funds Held For Clients
Debt Securities, Available-for-sale [Line Items]
Fair market value	27,101.2	24,337.8
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	14,339.0	11,732.3
Gross Unrealized  Gains	200.1	321.9
Gross Unrealized Losses	(129.7)	(38.5)
Fair market value	14,409.4	12,015.7
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,093.2	4,036.9
Gross Unrealized  Gains	34.8	64.8
Gross Unrealized Losses	(32.7)	(9.3)
Fair market value	4,095.3	4,092.4
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,160.4	2,279.8
Gross Unrealized  Gains	33.0	60.9
Gross Unrealized Losses	(6.8)	(0.9)
Fair market value	2,186.6	2,339.8
Canadian government obligations and Canadian government agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,822.0	1,542.3
Gross Unrealized  Gains	8.5	15.0
Gross Unrealized Losses	(19.5)	(9.0)
Fair market value	1,811.0	1,548.3
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,588.4	1,446.3
Gross Unrealized  Gains	12.6	22.5
Gross Unrealized Losses	(20.7)	(9.4)
Fair market value	1,580.3	1,459.4
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	938.0	956.3
Gross Unrealized  Gains	14.0	22.7
Gross Unrealized Losses	(9.4)	(5.3)
Fair market value	942.6	973.7
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	817.5	793.4
Gross Unrealized  Gains	26.8	41.2
Gross Unrealized Losses	(1.7)	0.0
Fair market value	842.6	834.6
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,238.6	1,082.2
Gross Unrealized  Gains	23.6	30.9
Gross Unrealized Losses	(9.1)	(5.3)
Fair market value	1,253.1	1,107.8
Money Market Funds
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents - amortized cost	20,534.2	13,143.2
Money market securities and other cash equivalents - fair market value	$ 20,534.2	$ 13,143.2