Corporate Investments and Funds Held For Clients (Available-For-Sale Securities That Have Been In An Unrealized Loss Position) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Jun. 30, 2020
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	$ (77.6)	$ (0.7)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	6,331.3	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	1.9	1.5
Total, Gross Unrealized Losses	(77.7)	(0.7)
Total, Fair Market Value	6,333.2	64.5
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(38.5)	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	3,539.6	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	(38.5)	0.0
Total, Fair Market Value	3,539.6	0.0
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(9.3)	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	580.9	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	(9.3)	0.0
Total, Fair Market Value	580.9	2.0
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(0.9)	(0.5)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	160.9	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	(0.9)	(0.5)
Total, Fair Market Value	160.9	43.9
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	(9.0)	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	721.3	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	(9.0)	0.0
Total, Fair Market Value	721.3	0.0
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(9.4)	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	749.7	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	(9.4)	0.0
Total, Fair Market Value	749.7	0.0
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(5.3)	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	253.7	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	(5.3)	0.0
Total, Fair Market Value	253.7	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	0.0	0.0
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	16.7	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	1.5
Total, Gross Unrealized Losses	0.0	0.0
Total, Fair Market Value	16.7	1.5
Other securities
Debt Securities, Available-for-sale [Line Items]
Securities in Unrealized Loss Position Less Than 12 Months, Gross Unrealized Losses	(5.2)	(0.2)
Securities in Unrealized Loss Position Less Than 12 Months, Fair Market Value	308.5	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	(5.3)	(0.2)
Total, Fair Market Value	$ 310.4	$ 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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