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, 2017	Jun. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (73.5)	$ (0.8)
Fair market value of securities in unrealized loss position less than 12 months	8,915.3	295.9
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.3	0.7
Fair market value of securities in unrealized loss positions greater than 12 months	29.8	217.9
Total Gross Unrealized Losses	(73.8)	(1.5)
Total fair market value of securities in unrealized loss position	8,945.1	513.8
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(22.0)	(0.5)
Fair market value of securities in unrealized loss position less than 12 months	2,619.9	138.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	0.1
Fair market value of securities in unrealized loss positions greater than 12 months	7.4	35.1
Total Gross Unrealized Losses	(22.0)	(0.6)
Total fair market value of securities in unrealized loss position	2,627.3	173.1
U.S. Treasury And Direct Obligations Of U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(13.4)	0.0
Fair market value of securities in unrealized loss position less than 12 months	1,935.3	0.0
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	0.0
Total Gross Unrealized Losses	(13.4)	0.0
Total fair market value of securities in unrealized loss position	1,935.3	0.0
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(14.3)	0.0
Fair market value of securities in unrealized loss position less than 12 months	1,317.8	3.4
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	1.0	1.6
Total Gross Unrealized Losses	(14.3)	0.0
Total fair market value of securities in unrealized loss position	1,318.8	5.0
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(8.5)	(0.1)
Fair market value of securities in unrealized loss position less than 12 months	1,916.1	58.8
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.1	0.2
Fair market value of securities in unrealized loss positions greater than 12 months	11.3	154.8
Total Gross Unrealized Losses	(8.6)	(0.3)
Total fair market value of securities in unrealized loss position	1,927.4	213.6
Canadian Government Obligations And Canadian Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(11.4)	0.0
Fair market value of securities in unrealized loss position less than 12 months	699.6	53.2
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	0.0
Total Gross Unrealized Losses	(11.4)	0.0
Total fair market value of securities in unrealized loss position	699.6	53.2
Canadian Provincial Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1.4)	(0.1)
Fair market value of securities in unrealized loss position less than 12 months	179.8	19.1
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	7.8
Total Gross Unrealized Losses	(1.4)	(0.1)
Total fair market value of securities in unrealized loss position	179.8	26.9
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1.2)	0.0
Fair market value of securities in unrealized loss position less than 12 months	98.8	12.9
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.1	0.3
Fair market value of securities in unrealized loss positions greater than 12 months	1.2	10.6
Total Gross Unrealized Losses	(1.3)	(0.3)
Total fair market value of securities in unrealized loss position	100.0	23.5
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1.3)	(0.1)
Fair market value of securities in unrealized loss position less than 12 months	148.0	10.5
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.1	0.1
Fair market value of securities in unrealized loss positions greater than 12 months	8.9	8.0
Total Gross Unrealized Losses	(1.4)	(0.2)
Total fair market value of securities in unrealized loss position	$ 156.9	$ 18.5