Corporate Investments and Funds Held For Clients (Available-For-Sale Securities That Have Been In An Unrealized Loss Position) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jun. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	$ (240.2)	$ (73.5)
Fair market value of securities in unrealized loss position less than 12 months	16,183.3	8,915.3
Unrealized losses greater than 12 months	(99.2)	(0.3)
Fair market value of securities in unrealized loss positions greater than 12 months	3,215.3	29.8
Total gross unrealized losses	(339.4)	(73.8)
Total fair market value	19,398.6	8,945.1
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(96.7)	(22.0)
Fair market value of securities in unrealized loss position less than 12 months	6,932.3	2,619.9
Unrealized losses greater than 12 months	(37.8)	0.0
Fair market value of securities in unrealized loss positions greater than 12 months	987.4	7.4
Total gross unrealized losses	(134.5)	(22.0)
Total fair market value	7,919.7	2,627.3
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(40.1)	(8.5)
Fair market value of securities in unrealized loss position less than 12 months	3,327.7	1,916.1
Unrealized losses greater than 12 months	(16.5)	(0.1)
Fair market value of securities in unrealized loss positions greater than 12 months	837.0	11.3
Total gross unrealized losses	(56.6)	(8.6)
Total fair market value	4,164.7	1,927.4
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(25.8)	(13.4)
Fair market value of securities in unrealized loss position less than 12 months	2,160.9	1,935.3
Unrealized losses greater than 12 months	(14.7)	0.0
Fair market value of securities in unrealized loss positions greater than 12 months	433.1	0.0
Total gross unrealized losses	(40.5)	(13.4)
Total fair market value	2,594.0	1,935.3
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(38.9)	(14.3)
Fair market value of securities in unrealized loss position less than 12 months	1,584.2	1,317.8
Unrealized losses greater than 12 months	(27.5)	0.0
Fair market value of securities in unrealized loss positions greater than 12 months	867.7	1.0
Total gross unrealized losses	(66.4)	(14.3)
Total fair market value	2,451.9	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	(20.7)	(11.4)
Fair market value of securities in unrealized loss position less than 12 months	927.4	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	(20.7)	(11.4)
Total fair market value	927.4	699.6
Canadian provincial bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(5.6)	(1.4)
Fair market value of securities in unrealized loss position less than 12 months	412.3	179.8
Unrealized losses greater than 12 months	(0.8)	0.0
Fair market value of securities in unrealized loss positions greater than 12 months	40.1	0.0
Total gross unrealized losses	(6.4)	(1.4)
Total fair market value	452.4	179.8
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(4.6)	(1.2)
Fair market value of securities in unrealized loss position less than 12 months	331.8	98.8
Unrealized losses greater than 12 months	(0.7)	(0.1)
Fair market value of securities in unrealized loss positions greater than 12 months	16.0	1.2
Total gross unrealized losses	(5.3)	(1.3)
Total fair market value	347.8	100.0
Other securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(7.8)	(1.3)
Fair market value of securities in unrealized loss position less than 12 months	506.7	148.0
Unrealized losses greater than 12 months	(1.2)	(0.1)
Fair market value of securities in unrealized loss positions greater than 12 months	34.0	8.9
Total gross unrealized losses	(9.0)	(1.4)
Total fair market value	$ 540.7	$ 156.9