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, 2019	Jun. 30, 2018
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	$ (9.1)	$ (283.4)
Fair market value of securities in unrealized loss position less than 12 months	906.6	16,606.5
Unrealized losses greater than 12 months	(117.8)	(109.0)
Fair market value of securities in unrealized loss positions greater than 12 months	13,645.6	3,256.8
Total gross unrealized losses	(126.9)	(392.4)
Total fair market value	14,552.2	19,863.3
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(0.7)	(118.2)
Fair market value of securities in unrealized loss position less than 12 months	117.3	7,132.9
Unrealized losses greater than 12 months	(39.1)	(42.7)
Fair market value of securities in unrealized loss positions greater than 12 months	5,048.6	994.2
Total gross unrealized losses	(39.8)	(160.9)
Total fair market value	5,165.9	8,127.1
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(0.1)	(47.4)
Fair market value of securities in unrealized loss position less than 12 months	25.0	3,515.9
Unrealized losses greater than 12 months	(22.6)	(16.7)
Fair market value of securities in unrealized loss positions greater than 12 months	3,430.9	867.7
Total gross unrealized losses	(22.7)	(64.1)
Total fair market value	3,455.9	4,383.6
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	0.0	(31.2)
Fair market value of securities in unrealized loss position less than 12 months	0.0	2,013.8
Unrealized losses greater than 12 months	(18.4)	(16.5)
Fair market value of securities in unrealized loss positions greater than 12 months	2,153.4	431.1
Total gross unrealized losses	(18.4)	(47.7)
Total fair market value	2,153.4	2,444.9
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	0.0	(46.9)
Fair market value of securities in unrealized loss position less than 12 months	0.0	1,676.8
Unrealized losses greater than 12 months	(33.4)	(30.0)
Fair market value of securities in unrealized loss positions greater than 12 months	2,340.9	864.0
Total gross unrealized losses	(33.4)	(76.9)
Total fair market value	2,340.9	2,540.8
Canadian government obligations and Canadian government agency obligations
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(7.9)	(20.6)
Fair market value of securities in unrealized loss position less than 12 months	667.1	1,020.3
Unrealized losses greater than 12 months	(0.1)	0.0
Fair market value of securities in unrealized loss positions greater than 12 months	51.0	0.0
Total gross unrealized losses	(8.0)	(20.6)
Total fair market value	718.1	1,020.3
Canadian provincial bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(0.4)	(6.3)
Fair market value of securities in unrealized loss position less than 12 months	80.4	387.7
Unrealized losses greater than 12 months	(1.1)	(1.1)
Fair market value of securities in unrealized loss positions greater than 12 months	220.2	50.4
Total gross unrealized losses	(1.5)	(7.4)
Total fair market value	300.6	438.1
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	0.0	(3.6)
Fair market value of securities in unrealized loss position less than 12 months	4.7	285.8
Unrealized losses greater than 12 months	(0.3)	(0.7)
Fair market value of securities in unrealized loss positions greater than 12 months	46.1	16.0
Total gross unrealized losses	(0.3)	(4.3)
Total fair market value	50.8	301.8
Other securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	0.0	(9.2)
Fair market value of securities in unrealized loss position less than 12 months	12.1	573.3
Unrealized losses greater than 12 months	(2.8)	(1.3)
Fair market value of securities in unrealized loss positions greater than 12 months	354.5	33.4
Total gross unrealized losses	(2.8)	(10.5)
Total fair market value	$ 366.6	$ 606.7