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, 2020	Jun. 30, 2019
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (0.7)	$ (7.2)
Fair market value of securities in unrealized loss position less than 12 months	63.0	1,107.7
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	(25.9)
Fair market value of securities in unrealized loss positions greater than 12 months	1.5	7,192.5
Total Gross Unrealized Losses	(0.7)	(33.1)
Total fair market value of securities in unrealized loss position	64.5	8,300.2
Corporate Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.0	(0.6)
Fair market value of securities in unrealized loss position less than 12 months	0.0	151.9
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	(6.1)
Fair market value of securities in unrealized loss positions greater than 12 months	0.0	2,055.6
Total Gross Unrealized Losses	0.0	(6.7)
Total fair market value of securities in unrealized loss position	0.0	2,207.5
Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(0.5)	(0.2)
Fair market value of securities in unrealized loss position less than 12 months	43.9	171.9
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	(5.2)
Fair market value of securities in unrealized loss positions greater than 12 months	0.0	2,083.5
Total Gross Unrealized Losses	(0.5)	(5.4)
Total fair market value of securities in unrealized loss position	43.9	2,255.4
U.S. Treasury And Direct Obligations Of U.S. Government Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.0	0.0
Fair market value of securities in unrealized loss position less than 12 months	0.0	0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	(5.8)
Fair market value of securities in unrealized loss positions greater than 12 months	0.0	1,671.4
Total Gross Unrealized Losses	0.0	(5.8)
Total fair market value of securities in unrealized loss position	0.0	1,671.4
US Treasury and Government [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.0	0.0
Fair market value of securities in unrealized loss position less than 12 months	2.0	1.8
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	(8.0)
Fair market value of securities in unrealized loss positions greater than 12 months	0.0	1,159.4
Total Gross Unrealized Losses	0.0	(8.0)
Total fair market value of securities in unrealized loss position	2.0	1,161.2
Canadian Government Obligations And Canadian Government Agency Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.0	(6.0)
Fair market value of securities in unrealized loss position less than 12 months	0.0	662.7
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	0.0
Fair market value of securities in unrealized loss positions greater than 12 months	0.0	1.1
Total Gross Unrealized Losses	0.0	(6.0)
Total fair market value of securities in unrealized loss position	0.0	663.8
Canadian Provincial Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.0	(0.3)
Fair market value of securities in unrealized loss position less than 12 months	0.0	81.5
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	(0.2)
Fair market value of securities in unrealized loss positions greater than 12 months	0.0	50.1
Total Gross Unrealized Losses	0.0	(0.5)
Total fair market value of securities in unrealized loss position	0.0	131.6
Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0.0
Fair market value of securities in unrealized loss position less than 12 months		1.5
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(0.1)
Fair market value of securities in unrealized loss positions greater than 12 months		23.3
Total Gross Unrealized Losses		(0.1)
Total fair market value of securities in unrealized loss position		24.8
Other Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(0.2)	(0.1)
Fair market value of securities in unrealized loss position less than 12 months	17.1	36.4
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	(0.5)
Fair market value of securities in unrealized loss positions greater than 12 months	0.0	148.1
Total Gross Unrealized Losses	(0.2)	(0.6)
Total fair market value of securities in unrealized loss position	17.1	$ 184.5
Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.0
Fair market value of securities in unrealized loss position less than 12 months	0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0
Fair market value of securities in unrealized loss positions greater than 12 months	1.5
Total Gross Unrealized Losses	0.0
Total fair market value of securities in unrealized loss position	$ 1.5