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, 2019		Jun. 30, 2019
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	$ 24,646.0	[1]	$ 24,859.1	[2]
Unrealized losses less than 12 months	(8.4)		(7.2)
Fair market value of securities in unrealized loss position less than 12 months	1,838.5		1,107.7
Unrealized losses greater than 12 months	(11.3)		(25.9)
Fair market value of securities in unrealized loss positions greater than 12 months	3,787.1		7,192.5
Total gross unrealized losses	(19.7)		(33.1)
Total fair market value	5,625.6		8,300.2
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	10,947.3		10,867.9
Unrealized losses less than 12 months	(1.0)		(0.6)
Fair market value of securities in unrealized loss position less than 12 months	438.5		151.9
Unrealized losses greater than 12 months	(1.2)		(6.1)
Fair market value of securities in unrealized loss positions greater than 12 months	615.8		2,055.6
Total gross unrealized losses	(2.2)		(6.7)
Total fair market value	1,054.3		2,207.5
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	4,368.1		4,690.7
Unrealized losses less than 12 months	(0.9)		(0.2)
Fair market value of securities in unrealized loss position less than 12 months	327.2		171.9
Unrealized losses greater than 12 months	(1.9)		(5.2)
Fair market value of securities in unrealized loss positions greater than 12 months	1,142.8		2,083.5
Total gross unrealized losses	(2.8)		(5.4)
Total fair market value	1,470.0		2,255.4
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	2,129.6		2,623.9
Unrealized losses less than 12 months	(0.1)		0.0
Fair market value of securities in unrealized loss position less than 12 months	61.3		0.0
Unrealized losses greater than 12 months	(2.1)		(5.8)
Fair market value of securities in unrealized loss positions greater than 12 months	945.3		1,671.4
Total gross unrealized losses	(2.2)		(5.8)
Total fair market value	1,006.6		1,671.4
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	3,499.5		2,948.8
Unrealized losses less than 12 months	(0.2)		0.0
Fair market value of securities in unrealized loss position less than 12 months	90.8		1.8
Unrealized losses greater than 12 months	(5.7)		(8.0)
Fair market value of securities in unrealized loss positions greater than 12 months	979.7		1,159.4
Total gross unrealized losses	(5.9)		(8.0)
Total fair market value	1,070.5		1,161.2
Canadian government obligations and Canadian government agency obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	1,155.8		1,165.1
Unrealized losses less than 12 months	(5.7)		(6.0)
Fair market value of securities in unrealized loss position less than 12 months	794.4		662.7
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		1.1
Total gross unrealized losses	(5.7)		(6.0)
Total fair market value	795.5		663.8
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	809.4		814.2
Unrealized losses less than 12 months	(0.2)		(0.3)
Fair market value of securities in unrealized loss position less than 12 months	83.9		81.5
Unrealized losses greater than 12 months	(0.1)		(0.2)
Fair market value of securities in unrealized loss positions greater than 12 months	29.8		50.1
Total gross unrealized losses	(0.3)		(0.5)
Total fair market value	113.7		131.6
Municipal bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	578.7		612.4
Unrealized losses less than 12 months	(0.1)		0.0
Fair market value of securities in unrealized loss position less than 12 months	20.0		1.5
Unrealized losses greater than 12 months	0.0		(0.1)
Fair market value of securities in unrealized loss positions greater than 12 months	5.0		23.3
Total gross unrealized losses	(0.1)		(0.1)
Total fair market value	25.0		24.8
Other securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	1,157.6		1,136.1
Unrealized losses less than 12 months	(0.2)		(0.1)
Fair market value of securities in unrealized loss position less than 12 months	22.4		36.4
Unrealized losses greater than 12 months	(0.3)		(0.5)
Fair market value of securities in unrealized loss positions greater than 12 months	67.6		148.1
Total gross unrealized losses	(0.5)		(0.6)
Total fair market value	90.0		184.5
Fair Value, Inputs, Level 1 [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0.0		0.0
Fair Value, Inputs, Level 3 [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	$ 0.0		$ 0.0

[1] Included within available-for-sale securities are corporate investments with fair values of $4,121.1 million and funds held for clients with fair values of $20,524.9 million. All available-for-sale securities were included in Level 2 of the fair value hierarchy.

[2] Included within available-for-sale securities are corporate investments with fair values of $271.9 million and funds held for clients with fair values of $24,587.2 million. All available-for-sale securities were included in Level 2 of the fair value hierarchy.