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, 2021	Jun. 30, 2020
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	$ (143.0)	$ (0.7)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	6,822.9	63.0
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(0.1)	0.0
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	3.2	1.5
Total, Gross Unrealized Losses	(143.1)	(0.7)
Total, Fair Market Value	6,826.1	64.5
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(83.8)	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	3,777.0	0.0
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	(83.8)	0.0
Total, Fair Market Value	3,777.0	0.0
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(1.9)	(0.5)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	191.9	43.9
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	(1.9)	(0.5)
Total, Fair Market Value	191.9	43.9
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(13.3)	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	768.8	2.0
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	(13.3)	0.0
Total, Fair Market Value	768.8	2.0
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(15.2)	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	871.0	0.0
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	(15.2)	0.0
Total, Fair Market Value	871.0	0.0
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	(10.8)	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	663.3	0.0
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	(10.8)	0.0
Total, Fair Market Value	663.3	0.0
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(0.3)	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	10.9	0.0
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	1.3	1.5
Total, Gross Unrealized Losses	(0.3)	0.0
Total, Fair Market Value	12.2	1.5
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(8.2)	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	250.8	0.0
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	(8.2)	0.0
Total, Fair Market Value	250.8	0.0
Other securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(9.5)	(0.2)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	289.2	17.1
Securities in Unrealized Loss Position Greater Than 12 Months, Gross Unrealized Losses	(0.1)	0.0
Securities in Unrealized Loss Position Greater Than 12 Months, Fair Market Value	1.9	0.0
Total, Gross Unrealized Losses	(9.6)	(0.2)
Total, Fair Market Value	$ 291.1	$ 17.1

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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