Corporate Investments and Funds Held For Clients (Available-For-Sale Securities That Have Been In An Unrealized Loss Position) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Jun. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	$ (72.4)	$ (73.5)
Fair market value of securities in unrealized loss position less than 12 months	8,678.6	8,915.3
Unrealized losses greater than 12 months	(7.6)	(0.3)
Fair market value of securities in unrealized loss positions greater than 12 months	438.4	29.8
Total gross unrealized losses	(80.0)	(73.8)
Total fair market value	9,117.0	8,945.1
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(14.0)	(22.0)
Fair market value of securities in unrealized loss position less than 12 months	2,142.2	2,619.9
Unrealized losses greater than 12 months	(4.3)	0.0
Fair market value of securities in unrealized loss positions greater than 12 months	238.7	7.4
Total gross unrealized losses	(18.3)	(22.0)
Total fair market value	2,380.9	2,627.3
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(6.6)	(8.5)
Fair market value of securities in unrealized loss position less than 12 months	1,802.6	1,916.1
Unrealized losses greater than 12 months	(2.1)	(0.1)
Fair market value of securities in unrealized loss positions greater than 12 months	162.4	11.3
Total gross unrealized losses	(8.7)	(8.6)
Total fair market value	1,965.0	1,927.4
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(10.5)	(13.4)
Fair market value of securities in unrealized loss position less than 12 months	1,638.4	1,935.3
Unrealized losses greater than 12 months	(0.4)	0.0
Fair market value of securities in unrealized loss positions greater than 12 months	9.6	0.0
Total gross unrealized losses	(10.9)	(13.4)
Total fair market value	1,648.0	1,935.3
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(17.6)	(14.3)
Fair market value of securities in unrealized loss position less than 12 months	1,861.2	1,317.8
Unrealized losses greater than 12 months	(0.1)	0.0
Fair market value of securities in unrealized loss positions greater than 12 months	2.0	1.0
Total gross unrealized losses	(17.7)	(14.3)
Total fair market value	1,863.2	1,318.8
Canadian government obligations and Canadian government agency obligations
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(19.1)	(11.4)
Fair market value of securities in unrealized loss position less than 12 months	783.8	699.6
Unrealized losses greater than 12 months	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	(19.1)	(11.4)
Total fair market value	783.8	699.6
Canadian provincial bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(2.6)	(1.4)
Fair market value of securities in unrealized loss position less than 12 months	212.9	179.8
Unrealized losses greater than 12 months	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	(2.6)	(1.4)
Total fair market value	212.9	179.8
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(0.7)	(1.2)
Fair market value of securities in unrealized loss position less than 12 months	73.9	98.8
Unrealized losses greater than 12 months	(0.5)	(0.1)
Fair market value of securities in unrealized loss positions greater than 12 months	15.9	1.2
Total gross unrealized losses	(1.2)	(1.3)
Total fair market value	89.8	100.0
Other securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(1.3)	(1.3)
Fair market value of securities in unrealized loss position less than 12 months	163.6	148.0
Unrealized losses greater than 12 months	(0.2)	(0.1)
Fair market value of securities in unrealized loss positions greater than 12 months	9.8	8.9
Total gross unrealized losses	(1.5)	(1.4)
Total fair market value	$ 173.4	$ 156.9