Corporate Investments and Funds Held For Clients (Available-For-Sale Securities That Have Been In An Unrealized Loss Position) (Details) - USD ($) $ in Millions	Mar. 31, 2023	Jun. 30, 2022
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	$ (169.6)	$ (1,305.8)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	8,440.4	20,798.8
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(1,773.6)	(425.3)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	19,076.9	4,005.8
Total, Gross Unrealized Losses	(1,943.2)	(1,731.1)
Total, Fair Market Value	27,517.3	24,804.6
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(91.0)	(824.0)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	3,301.0	11,525.4
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(1,094.1)	(259.0)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	10,800.6	2,356.7
Total, Gross Unrealized Losses	(1,185.1)	(1,083.0)
Total, Fair Market Value	14,101.6	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	(47.1)	(126.4)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	3,676.4	2,919.6
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(182.9)	(44.7)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	2,761.7	464.6
Total, Gross Unrealized Losses	(230.0)	(171.1)
Total, Fair Market Value	6,438.1	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	(4.8)	(52.6)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	375.4	1,444.9
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(59.1)	(6.2)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	848.1	59.9
Total, Gross Unrealized Losses	(63.9)	(58.8)
Total, Fair Market Value	1,223.5	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	(5.1)	(110.0)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	272.9	1,782.6
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(114.9)	(13.5)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	1,475.5	113.3
Total, Gross Unrealized Losses	(120.0)	(123.5)
Total, Fair Market Value	1,748.4	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	(1.4)	(75.3)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	56.1	859.3
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(163.1)	(62.9)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	1,420.9	695.6
Total, Gross Unrealized Losses	(164.5)	(138.2)
Total, Fair Market Value	1,477.0	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	(2.9)	(45.4)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	145.5	726.9
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(60.2)	(17.3)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	703.3	133.2
Total, Gross Unrealized Losses	(63.1)	(62.7)
Total, Fair Market Value	848.8	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	(8.2)	(29.5)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	214.3	802.8
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(33.9)	(0.4)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	458.7	4.3
Total, Gross Unrealized Losses	(42.1)	(29.9)
Total, Fair Market Value	673.0	807.1
Other securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(9.1)	(42.6)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	398.8	737.3
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(65.4)	(21.3)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	608.1	178.2
Total, Gross Unrealized Losses	(74.5)	(63.9)
Total, Fair Market Value	$ 1,006.9	$ 915.5