Corporate Investments and Funds Held For Clients (Corporate Investments And Funds Held For Clients) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents - amortized cost	$ 1,891.5	$ 1,908.5	$ 1,705.0
Amortized Cost	22,823.2	20,699.8
Gross Unrealized  Gains	591.1	877.5
Gross Unrealized Losses	(143.1)	(0.7)
Fair market value	23,271.2	21,576.6
Total corporate investments and funds held for clients - amortized cost	42,945.0	27,753.4
Total corporate investments and funds held for clients - gross unrealized gains	591.1	877.5
Total corporate investments and funds held for clients - gross unrealized losses	(143.1)	(0.7)
Total corporate investments and funds held for clients - fair market value	43,393.0	28,630.2
Corporate Investments
Debt Securities, Available-for-sale [Line Items]
Fair market value	10.5	13.6
Funds Held For Clients
Debt Securities, Available-for-sale [Line Items]
Fair market value	23,260.7	21,563.0
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	11,122.8	9,188.7
Gross Unrealized  Gains	314.7	473.4
Gross Unrealized Losses	(83.8)	0.0
Fair market value	11,353.7	9,662.1
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,538.5	3,274.6
Gross Unrealized  Gains	68.6	96.0
Gross Unrealized Losses	(1.9)	(0.5)
Fair market value	2,605.2	3,370.1
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,595.5	3,580.6
Gross Unrealized  Gains	76.6	120.8
Gross Unrealized Losses	(13.3)	0.0
Fair market value	3,658.8	3,701.4
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,428.2	1,128.2
Gross Unrealized  Gains	20.1	35.6
Gross Unrealized Losses	(15.2)	0.0
Fair market value	1,433.1	1,163.8
Canadian government obligations and Canadian government agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,406.0	1,018.7
Gross Unrealized  Gains	15.8	23.1
Gross Unrealized Losses	(10.8)	0.0
Fair market value	1,411.0	1,041.8
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	795.3	814.3
Gross Unrealized  Gains	39.8	53.9
Gross Unrealized Losses	(0.3)	0.0
Fair market value	834.8	868.2
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	887.2	676.6
Gross Unrealized  Gains	22.9	33.6
Gross Unrealized Losses	(8.2)	0.0
Fair market value	901.9	710.2
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,049.7	1,018.1
Gross Unrealized  Gains	32.6	41.1
Gross Unrealized Losses	(9.6)	(0.2)
Fair market value	1,072.7	1,059.0
Money Market Funds
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents - amortized cost	20,121.8	7,053.6
Money market securities and other cash equivalents - fair market value	$ 20,121.8	$ 7,053.6