Investments (Breakdown Of Available-For-Sale Investments With Unrealized Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Gains and losses on trading securities	$ 3.3	$ (2.1)
Seed Money Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	23.1		$ 93.0
Less than 12 Months, Gross Unrealized Losses	(0.3)		(3.0)
12 Months or Greater, Fair Value	80.3		65.5
12 Months or Greater, Gross Unrealized Losses	(6.1)		(6.3)
Total, Fair Value	103.4		158.5
Total, Gross Unrealized Losses	$ (6.4)		$ (9.3)