Investment Securities Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	$ 38.9	$ 98.7	$ (63.6)
Foreign Currency Transaction Gain (Loss), Unrealized	18.3	(48.6)	69.4
Net unrealized investment gains, pre-tax	57.2	50.1	5.8
Trading Securities, Tax on Unrealized Holding Gain (Loss) on Investments	8.2	(17.9)	24.0
Trading Securities, Unrealized Foreign Currency Transaction Gain (Loss) Tax	(5.6)	12.7	(17.9)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Tax	2.6	(5.2)	6.1
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax	47.1	80.8	(39.6)
Trading Securities, Unrealized Foreign Currency Gain (Loss) Net of Tax	12.7	(35.9)	51.5
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	59.8	44.9	11.9
Fixed maturity investments
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	(93.9)	18.5	7.6
Foreign Currency Transaction Gain (Loss), Unrealized	15.3	(45.9)	68.9
Net unrealized investment gains, pre-tax	(78.6)	(27.4)	76.5
Short-term investments
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	0.1	0	0
Foreign Currency Transaction Gain (Loss), Unrealized	0	0.1	(1.1)
Net unrealized investment gains, pre-tax	0.1	0.1	(1.1)
Common equity securities
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	119.2	65.9	(40.6)
Foreign Currency Transaction Gain (Loss), Unrealized	(0.4)	(0.1)	(1.8)
Net unrealized investment gains, pre-tax	118.8	65.8	(42.4)
Convertible fixed maturity investments
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	3.2	1.1	(11.5)
Foreign Currency Transaction Gain (Loss), Unrealized	0	0	0
Net unrealized investment gains, pre-tax	3.2	1.1	(11.5)
Other long-term investments
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	10.3	13.2	(19.1)
Foreign Currency Transaction Gain (Loss), Unrealized	3.4	(2.7)	3.4
Net unrealized investment gains, pre-tax	13.7	10.5	(15.7)
Forward contracts
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	0
Foreign Currency Transaction Gain (Loss), Unrealized	0
Net unrealized investment gains, pre-tax	$ 0