Investment Securities (Cost or Amortized Cost, Gross Unrealized Investment Gains and Losses) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investment securities
Sales and maturities of investment securities	$ 4,924.8	$ 6,997.5	$ 5,034.0
Fixed maturity investments, at fair value	5,030.5	5,196.2
Common Stock
Investment securities
Trading Securities, Cost	890.2	895.2
Net foreign currency losses	(0.8)	(0.1)
Fixed maturity investments, at fair value	1,156.8	1,029.7
Trading Securities, Unrealized Holding Gain	271.0	143.4
Trading Securities, Unrealized Holding Loss	(3.6)	(8.8)
Convertible fixed maturity investments
Investment securities
Trading Securities, Cost	71.7	121.7
Net foreign currency losses	(0.2)	0
Fixed maturity investments, at fair value	80.5	127.4
Trading Securities, Unrealized Holding Gain	9.9	6.1
Trading Securities, Unrealized Holding Loss	(0.9)	(0.4)
Other long-term investments
Investment securities
Trading Securities, Cost	238.3	257.2
Net foreign currency losses	(2.4)	(6.1)
Fixed maturity investments, at fair value	288.9	294.2
Trading Securities, Unrealized Holding Gain	79.6	65.9
Trading Securities, Unrealized Holding Loss	$ (26.6)	$ (22.8)