Corporate Investments and Funds Held For Clients (Available-For-Sale Securities That Have Been In An Unrealized Loss Position) (Details) - USD ($) $ in Millions	Sep. 30, 2022	Jun. 30, 2022
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	$ (1,380.7)	$ (1,305.8)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	20,251.1	20,798.8
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(1,174.7)	(425.3)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	8,444.9	4,005.8
Total, Gross Unrealized Losses	(2,555.4)	(1,731.1)
Total, Fair Market Value	28,696.0	24,804.6
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(876.9)	(824.0)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	9,807.2	11,525.4
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(695.9)	(259.0)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	4,775.7	2,356.7
Total, Gross Unrealized Losses	(1,572.8)	(1,083.0)
Total, Fair Market Value	14,582.9	13,882.1
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(131.7)	(126.4)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	5,103.6	2,919.6
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(172.2)	(44.7)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	1,344.7	464.6
Total, Gross Unrealized Losses	(303.9)	(171.1)
Total, Fair Market Value	6,448.3	3,384.2
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(48.2)	(52.6)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	1,363.3	1,444.9
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(33.6)	(6.2)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	248.6	59.9
Total, Gross Unrealized Losses	(81.8)	(58.8)
Total, Fair Market Value	1,611.9	1,504.8
Canadian government obligations and Canadian government agency obligations
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(67.4)	(110.0)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	982.6	1,782.6
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(82.5)	(13.5)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	806.9	113.3
Total, Gross Unrealized Losses	(149.9)	(123.5)
Total, Fair Market Value	1,789.5	1,895.9
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(104.4)	(75.3)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	795.7	859.3
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(95.3)	(62.9)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	727.8	695.6
Total, Gross Unrealized Losses	(199.7)	(138.2)
Total, Fair Market Value	1,523.5	1,554.9
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(41.0)	(45.4)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	605.9	726.9
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(40.3)	(17.3)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	232.5	133.2
Total, Gross Unrealized Losses	(81.3)	(62.7)
Total, Fair Market Value	838.4	860.1
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(44.8)	(29.5)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	681.5	802.8
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(9.2)	(0.4)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	72.3	4.3
Total, Gross Unrealized Losses	(54.0)	(29.9)
Total, Fair Market Value	753.8	807.1
Other securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(66.3)	(42.6)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	911.3	737.3
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(45.7)	(21.3)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	236.4	178.2
Total, Gross Unrealized Losses	(112.0)	(63.9)
Total, Fair Market Value	$ 1,147.7	$ 915.5