Investments (Gross Unrealized Holding Gains And Losses Recognized In Other Accumulated Comprehensive Income From Available-For-Sale Investments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 247.5	$ 225.8
Gross Unrealized Holding Gains	12.8	19.2
Gross Unrealized Holding Losses	(4.4)	(0.9)
Available for sale investments	255.9	244.1
Seed Money [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	237.7	215.7
Gross Unrealized Holding Gains	12.8	19.0
Gross Unrealized Holding Losses	(4.3)	(0.9)
Available for sale investments	246.2	233.8
CLO [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	3.5	3.8
Gross Unrealized Holding Gains	0	0.2
Gross Unrealized Holding Losses	(0.1)	0
Available for sale investments	3.4	4.0
Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	6.3	6.3
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Available for sale investments	$ 6.3	$ 6.3