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, 2022	Jun. 30, 2021
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	$ (803.1)	$ (77.6)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	16,558.1	6,331.3
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(330.1)	(0.1)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	4,031.8	1.9
Total, Gross Unrealized Losses	(1,133.2)	(77.7)
Total, Fair Market Value	20,589.9	6,333.2
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(489.9)	(38.5)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	9,213.9	3,539.6
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(195.6)	0.0
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	2,351.9	0.0
Total, Gross Unrealized Losses	(685.5)	(38.5)
Total, Fair Market Value	11,565.8	3,539.6
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(96.3)	(9.3)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	2,432.3	580.9
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(38.6)	0.0
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	471.1	0.0
Total, Gross Unrealized Losses	(134.9)	(9.3)
Total, Fair Market Value	2,903.4	580.9
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(31.7)	(0.9)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	881.3	160.9
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(4.5)	0.0
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	54.6	0.0
Total, Gross Unrealized Losses	(36.2)	(0.9)
Total, Fair Market Value	935.9	160.9
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	(74.3)	(9.0)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	1,485.3	721.3
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(10.3)	0.0
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	116.7	0.0
Total, Gross Unrealized Losses	(84.6)	(9.0)
Total, Fair Market Value	1,602.0	721.3
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(39.4)	(9.4)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	806.9	749.7
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(52.4)	0.0
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	706.3	0.0
Total, Gross Unrealized Losses	(91.8)	(9.4)
Total, Fair Market Value	1,513.2	749.7
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(27.3)	(5.3)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	636.7	253.7
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(12.8)	0.0
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	139.5	0.0
Total, Gross Unrealized Losses	(40.1)	(5.3)
Total, Fair Market Value	776.2	253.7
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(16.1)	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	540.9	16.7
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	0.0	0.0
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	0.0	0.0
Total, Gross Unrealized Losses	(16.1)	0.0
Total, Fair Market Value	540.9	16.7
Other securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(28.1)	(5.2)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	560.8	308.5
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(15.9)	(0.1)
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	191.7	1.9
Total, Gross Unrealized Losses	(44.0)	(5.3)
Total, Fair Market Value	$ 752.5	$ 310.4