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, 2017	Jun. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	$ (92.1)	$ (0.8)
Fair market value of securities in unrealized loss position less than 12 months	9,358.4	295.9
Unrealized losses greater than 12 months	(0.3)	(0.7)
Fair market value of securities in unrealized loss positions greater than 12 months	33.0	217.9
Total gross unrealized losses	(92.4)	(1.5)
Total fair market value	9,391.4	513.8
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(35.0)	(0.5)
Fair market value of securities in unrealized loss position less than 12 months	2,986.3	138.0
Unrealized losses greater than 12 months	0.0	(0.1)
Fair market value of securities in unrealized loss positions greater than 12 months	7.4	35.1
Total gross unrealized losses	(35.0)	(0.6)
Total fair market value	2,993.7	173.1
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(16.5)	0.0
Fair market value of securities in unrealized loss position less than 12 months	2,093.3	0.0
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	(16.5)	0.0
Total fair market value	2,093.3	0.0
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(13.3)	(0.1)
Fair market value of securities in unrealized loss position less than 12 months	2,261.3	58.8
Unrealized losses greater than 12 months	0.0	(0.2)
Fair market value of securities in unrealized loss positions greater than 12 months	12.4	154.8
Total gross unrealized losses	(13.3)	(0.3)
Total fair market value	2,273.7	213.6
Canadian government obligations and Canadian government agency obligations
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(4.3)	0.0
Fair market value of securities in unrealized loss position less than 12 months	468.3	53.2
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	(4.3)	0.0
Total fair market value	468.3	53.2
Canadian provincial bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(0.8)	(0.1)
Fair market value of securities in unrealized loss position less than 12 months	121.7	19.1
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	7.8
Total gross unrealized losses	(0.8)	(0.1)
Total fair market value	121.7	26.9
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(18.0)	0.0
Fair market value of securities in unrealized loss position less than 12 months	1,167.2	3.4
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	1.6
Total gross unrealized losses	(18.0)	0.0
Total fair market value	1,167.2	5.0
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(2.8)	0.0
Fair market value of securities in unrealized loss position less than 12 months	143.1	12.9
Unrealized losses greater than 12 months	(0.1)	(0.3)
Fair market value of securities in unrealized loss positions greater than 12 months	4.3	10.6
Total gross unrealized losses	(2.9)	(0.3)
Total fair market value	147.4	23.5
Other securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(1.4)	(0.1)
Fair market value of securities in unrealized loss position less than 12 months	117.2	10.5
Unrealized losses greater than 12 months	(0.2)	(0.1)
Fair market value of securities in unrealized loss positions greater than 12 months	8.9	8.0
Total gross unrealized losses	(1.6)	(0.2)
Total fair market value	$ 126.1	$ 18.5