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, 2018	Jun. 30, 2018
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	$ (230.7)	$ (283.4)
Fair market value of securities in unrealized loss position less than 12 months	14,479.7	16,606.5
Unrealized losses greater than 12 months	(199.9)	(109.0)
Fair market value of securities in unrealized loss positions greater than 12 months	6,271.5	3,256.8
Total gross unrealized losses	(430.6)	(392.4)
Total fair market value	20,751.2	19,863.3
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(105.1)	(118.2)
Fair market value of securities in unrealized loss position less than 12 months	6,919.2	7,132.9
Unrealized losses greater than 12 months	(62.1)	(42.7)
Fair market value of securities in unrealized loss positions greater than 12 months	1,598.9	994.2
Total gross unrealized losses	(167.2)	(160.9)
Total fair market value	8,518.1	8,127.1
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(39.2)	(47.4)
Fair market value of securities in unrealized loss position less than 12 months	2,907.1	3,515.9
Unrealized losses greater than 12 months	(27.0)	(16.7)
Fair market value of securities in unrealized loss positions greater than 12 months	1,544.5	867.7
Total gross unrealized losses	(66.2)	(64.1)
Total fair market value	4,451.6	4,383.6
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(18.8)	(31.2)
Fair market value of securities in unrealized loss position less than 12 months	1,312.2	2,013.8
Unrealized losses greater than 12 months	(34.4)	(16.5)
Fair market value of securities in unrealized loss positions greater than 12 months	1,148.9	431.1
Total gross unrealized losses	(53.2)	(47.7)
Total fair market value	2,461.1	2,444.9
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(20.1)	(46.9)
Fair market value of securities in unrealized loss position less than 12 months	847.6	1,676.8
Unrealized losses greater than 12 months	(70.3)	(30.0)
Fair market value of securities in unrealized loss positions greater than 12 months	1,787.6	864.0
Total gross unrealized losses	(90.4)	(76.9)
Total fair market value	2,635.2	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	(24.7)	(20.6)
Fair market value of securities in unrealized loss position less than 12 months	1,071.4	1,020.3
Unrealized losses greater than 12 months	0.0	0.0
Fair market value of securities in unrealized loss positions greater than 12 months	1.1	0.0
Total gross unrealized losses	(24.7)	(20.6)
Total fair market value	1,072.5	1,020.3
Canadian provincial bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(8.3)	(6.3)
Fair market value of securities in unrealized loss position less than 12 months	459.7	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	50.2	50.4
Total gross unrealized losses	(9.4)	(7.4)
Total fair market value	509.9	438.1
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(5.4)	(3.6)
Fair market value of securities in unrealized loss position less than 12 months	391.7	285.8
Unrealized losses greater than 12 months	(0.9)	(0.7)
Fair market value of securities in unrealized loss positions greater than 12 months	19.7	16.0
Total gross unrealized losses	(6.3)	(4.3)
Total fair market value	411.4	301.8
Other securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(9.1)	(9.2)
Fair market value of securities in unrealized loss position less than 12 months	570.8	573.3
Unrealized losses greater than 12 months	(4.1)	(1.3)
Fair market value of securities in unrealized loss positions greater than 12 months	120.6	33.4
Total gross unrealized losses	(13.2)	(10.5)
Total fair market value	$ 691.4	$ 606.7