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, 2019	Jun. 30, 2018
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (7.2)	$ (283.4)
Fair market value of securities in unrealized loss position less than 12 months	1,107.7	16,606.5
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(25.9)	(109.0)
Fair market value of securities in unrealized loss positions greater than 12 months	7,192.5	3,256.8
Total Gross Unrealized Losses	(33.1)	(392.4)
Total fair market value of securities in unrealized loss position	8,300.2	19,863.3
Corporate Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(0.6)	(118.2)
Fair market value of securities in unrealized loss position less than 12 months	151.9	7,132.9
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(6.1)	(42.7)
Fair market value of securities in unrealized loss positions greater than 12 months	2,055.6	994.2
Total Gross Unrealized Losses	(6.7)	(160.9)
Total fair market value of securities in unrealized loss position	2,207.5	8,127.1
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	(0.2)	(47.4)
Fair market value of securities in unrealized loss position less than 12 months	171.9	3,515.9
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(5.2)	(16.7)
Fair market value of securities in unrealized loss positions greater than 12 months	2,083.5	867.7
Total Gross Unrealized Losses	(5.4)	(64.1)
Total fair market value of securities in unrealized loss position	2,255.4	4,383.6
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	(31.2)
Fair market value of securities in unrealized loss position less than 12 months	0.0	2,013.8
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(5.8)	(16.5)
Fair market value of securities in unrealized loss positions greater than 12 months	1,671.4	431.1
Total Gross Unrealized Losses	(5.8)	(47.7)
Total fair market value of securities in unrealized loss position	1,671.4	2,444.9
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	(46.9)
Fair market value of securities in unrealized loss position less than 12 months	1.8	1,676.8
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(8.0)	(30.0)
Fair market value of securities in unrealized loss positions greater than 12 months	1,159.4	864.0
Total Gross Unrealized Losses	(8.0)	(76.9)
Total fair market value of securities in unrealized loss position	1,161.2	2,540.8
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	(6.0)	(20.6)
Fair market value of securities in unrealized loss position less than 12 months	662.7	1,020.3
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	1.1	0.0
Total Gross Unrealized Losses	(6.0)	(20.6)
Total fair market value of securities in unrealized loss position	663.8	1,020.3
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	(0.3)	(6.3)
Fair market value of securities in unrealized loss position less than 12 months	81.5	387.7
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(0.2)	(1.1)
Fair market value of securities in unrealized loss positions greater than 12 months	50.1	50.4
Total Gross Unrealized Losses	(0.5)	(7.4)
Total fair market value of securities in unrealized loss position	131.6	438.1
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	(3.6)
Fair market value of securities in unrealized loss position less than 12 months	1.5	285.8
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(0.1)	(0.7)
Fair market value of securities in unrealized loss positions greater than 12 months	23.3	16.0
Total Gross Unrealized Losses	(0.1)	(4.3)
Total fair market value of securities in unrealized loss position	24.8	301.8
Other Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(0.1)	(9.2)
Fair market value of securities in unrealized loss position less than 12 months	36.4	573.3
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(0.5)	(1.3)
Fair market value of securities in unrealized loss positions greater than 12 months	148.1	33.4
Total Gross Unrealized Losses	(0.6)	(10.5)
Total fair market value of securities in unrealized loss position	$ 184.5	$ 606.7