Investment Securities Investment Securities (Net Realized Investment Gain (losses) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investment securities
Trading Securities, Realized Gain (Loss)	$ 121.8	$ 76.7	$ 117.0
Foreign Currency Transaction Gain (Loss), Realized	(17.3)	(8.6)	(48.7)
Net realized investment gains, pre-tax	104.5	68.1	68.3
Trading securities, Tax on Realized Holding Gain (Loss) on Investments	(30.0)	(23.8)	(37.0)
Trading Securities, Tax on Realized Foreign Currency Transaction Gain (Loss) Tax	5.5	2.2	12.8
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(24.5)	(21.6)	(24.2)
Trading Securities Realized Holding Gain (Loss) on Investments after Tax	91.8	52.9	80.0
Trading Securities, Realized Foreign Currency Gain (Loss) Net of Tax	(11.8)	(6.4)	(35.9)
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	80.0	46.5	44.1
Fixed maturity investments
Investment securities
Trading Securities, Realized Gain (Loss)	8.6	82.5	49.4
Foreign Currency Transaction Gain (Loss), Realized	(15.0)	(2.5)	(38.3)
Net realized investment gains, pre-tax	(6.4)	80.0	11.1
Short-term investments
Investment securities
Trading Securities, Realized Gain (Loss)	0.1	0	0
Foreign Currency Transaction Gain (Loss), Realized	0	(4.3)	(9.9)
Net realized investment gains, pre-tax	0.1	(4.3)	(9.9)
Common equity securities
Investment securities
Trading Securities, Realized Gain (Loss)	104.5	1.3	34.6
Foreign Currency Transaction Gain (Loss), Realized	(3.7)	0	0
Net realized investment gains, pre-tax	100.8	1.3	34.6
Convertible fixed maturity investments
Investment securities
Trading Securities, Realized Gain (Loss)	1.0	(8.2)	(2.2)
Foreign Currency Transaction Gain (Loss), Realized	0	(1.8)	0
Net realized investment gains, pre-tax	1.0	(10.0)	(2.2)
Other long-term investments
Investment securities
Trading Securities, Realized Gain (Loss)	7.5	1.4	35.2
Foreign Currency Transaction Gain (Loss), Realized	1.4	0	(0.5)
Net realized investment gains, pre-tax	8.9	1.4	34.7
Forward contracts
Investment securities
Trading Securities, Realized Gain (Loss)	0.1	(0.3)
Foreign Currency Transaction Gain (Loss), Realized	0	0
Net realized investment gains, pre-tax	$ 0.1	$ (0.3)