Corporate Investments and Funds Held For Clients (Available-For-Sale Securities That Have Been In An Unrealized Loss Position) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jun. 30, 2018
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	$ (68.7)	$ (283.4)
Fair market value of securities in unrealized loss position less than 12 months	7,095.6	16,606.5
Unrealized losses greater than 12 months	(214.9)	(109.0)
Fair market value of securities in unrealized loss positions greater than 12 months	11,480.1	3,256.8
Total gross unrealized losses	(283.6)	(392.4)
Total fair market value	18,575.7	19,863.3
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(42.0)	(118.2)
Fair market value of securities in unrealized loss position less than 12 months	4,142.5	7,132.9
Unrealized losses greater than 12 months	(82.6)	(42.7)
Fair market value of securities in unrealized loss positions greater than 12 months	3,700.2	994.2
Total gross unrealized losses	(124.6)	(160.9)
Total fair market value	7,842.7	8,127.1
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(6.6)	(47.4)
Fair market value of securities in unrealized loss position less than 12 months	1,081.7	3,515.9
Unrealized losses greater than 12 months	(37.6)	(16.7)
Fair market value of securities in unrealized loss positions greater than 12 months	2,888.3	867.7
Total gross unrealized losses	(44.2)	(64.1)
Total fair market value	3,970.0	4,383.6
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(2.2)	(31.2)
Fair market value of securities in unrealized loss position less than 12 months	383.4	2,013.8
Unrealized losses greater than 12 months	(32.6)	(16.5)
Fair market value of securities in unrealized loss positions greater than 12 months	1,936.5	431.1
Total gross unrealized losses	(34.8)	(47.7)
Total fair market value	2,319.9	2,444.9
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(0.5)	(46.9)
Fair market value of securities in unrealized loss position less than 12 months	94.9	1,676.8
Unrealized losses greater than 12 months	(52.0)	(30.0)
Fair market value of securities in unrealized loss positions greater than 12 months	2,321.2	864.0
Total gross unrealized losses	(52.5)	(76.9)
Total fair market value	2,416.1	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	(13.5)	(20.6)
Fair market value of securities in unrealized loss position less than 12 months	821.2	1,020.3
Unrealized losses greater than 12 months	(0.3)	0.0
Fair market value of securities in unrealized loss positions greater than 12 months	50.7	0.0
Total gross unrealized losses	(13.8)	(20.6)
Total fair market value	871.9	1,020.3
Canadian provincial bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(1.7)	(6.3)
Fair market value of securities in unrealized loss position less than 12 months	192.0	387.7
Unrealized losses greater than 12 months	(2.7)	(1.1)
Fair market value of securities in unrealized loss positions greater than 12 months	203.8	50.4
Total gross unrealized losses	(4.4)	(7.4)
Total fair market value	395.8	438.1
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(0.7)	(3.6)
Fair market value of securities in unrealized loss position less than 12 months	118.1	285.8
Unrealized losses greater than 12 months	(1.6)	(0.7)
Fair market value of securities in unrealized loss positions greater than 12 months	93.7	16.0
Total gross unrealized losses	(2.3)	(4.3)
Total fair market value	211.8	301.8
Other securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(1.5)	(9.2)
Fair market value of securities in unrealized loss position less than 12 months	261.8	573.3
Unrealized losses greater than 12 months	(5.5)	(1.3)
Fair market value of securities in unrealized loss positions greater than 12 months	285.7	33.4
Total gross unrealized losses	(7.0)	(10.5)
Total fair market value	$ 547.5	$ 606.7