Other Gains and Losses, Net (Schedule of other gains and losses, net) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
OTHER GAINS AND LOSSES, NET
Gain on sale of investments	$ 13.0	$ 3.6	$ 5.3
Net Realized and Unrealized Gain (Loss) on Trading Securities	15.4	38.5	19.7
Gain on sale of CLO management contracts	0	0	8.3
Net foreign exchange gains	0	0	0.3
Other realized gains	0.2	3.2	4.1
Total other gains	28.6	45.3	37.7
Other-than-temporary impairment of available-for-sale investments	0	0	(0.8)
Net foreign exchange losses	(0.2)	(0.6)	0
Payment to investment trust	0	(31.9)	0
Liquidation of co-investment	0	(4.1)	0
Foreign exchange hedge loss	0	(1.8)	(2.5)
Loss on debt extinguishment	0	0	(23.5)
Other realized losses	(0.3)	(4.3)	(2.6)
Total other losses	(0.5)	(42.7)	(29.4)
Other gains and losses, net	$ 28.1	$ 2.6	$ 8.3