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, 2016	Jun. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	$ (122.4)	$ (0.8)
Fair market value of securities in unrealized loss position less than 12 months	10,215.3	295.9
Unrealized losses greater than 12 months	(0.6)	(0.7)
Fair market value of securities in unrealized loss positions greater than 12 months	123.4	217.9
Total gross unrealized losses	(123.0)	(1.5)
Total fair market value	10,338.7	513.8
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(49.2)	(0.5)
Fair market value of securities in unrealized loss position less than 12 months	3,958.2	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	22.5	35.1
Total gross unrealized losses	(49.2)	(0.6)
Total fair market value	3,980.7	173.1
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(20.5)	0.0
Fair market value of securities in unrealized loss position less than 12 months	1,765.9	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	(20.5)	0.0
Total fair market value	1,765.9	0.0
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(17.2)	(0.1)
Fair market value of securities in unrealized loss position less than 12 months	2,264.8	58.8
Unrealized losses greater than 12 months	(0.1)	(0.2)
Fair market value of securities in unrealized loss positions greater than 12 months	77.8	154.8
Total gross unrealized losses	(17.3)	(0.3)
Total fair market value	2,342.6	213.6
Canadian government obligations and Canadian government agency obligations
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(5.8)	0.0
Fair market value of securities in unrealized loss position less than 12 months	501.5	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	(5.8)	0.0
Total fair market value	501.5	53.2
Canadian provincial bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(1.2)	(0.1)
Fair market value of securities in unrealized loss position less than 12 months	180.4	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	7.6	7.8
Total gross unrealized losses	(1.2)	(0.1)
Total fair market value	188.0	26.9
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(21.6)	0.0
Fair market value of securities in unrealized loss position less than 12 months	1,186.7	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	(21.6)	0.0
Total fair market value	1,186.7	5.0
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(5.4)	0.0
Fair market value of securities in unrealized loss position less than 12 months	275.7	12.9
Unrealized losses greater than 12 months	(0.3)	(0.3)
Fair market value of securities in unrealized loss positions greater than 12 months	6.6	10.6
Total gross unrealized losses	(5.7)	(0.3)
Total fair market value	282.3	23.5
Other securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses less than 12 months	(1.5)	(0.1)
Fair market value of securities in unrealized loss position less than 12 months	82.1	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	(1.7)	(0.2)
Total fair market value	$ 91.0	$ 18.5