Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Change in Unrealized Holding Gain (Loss)	$ 52.2	$ (102.0)	$ 81.2	$ (68.2)
Trading Securities, Tax on Unrealized Holding Gain (Loss) on Investments	(9.8)	25.8	(18.9)	21.7
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax	42.4	(76.2)	62.3	(46.5)
Foreign Currency Transaction Gain (Loss), Unrealized	31.2	41.9	44.3	46.7
Trading Securities, Unrealized Foreign Currency Transaction Gain (Loss) Tax	(6.9)	(9.2)	(9.8)	(10.3)
Trading Securities, Unrealized Foreign Currency Gain (Loss) Net of Tax	24.3	32.7	34.5	36.4
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	83.4	(60.1)	125.5	(21.5)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Tax	(16.7)	16.6	(28.7)	11.4
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	66.7	(43.5)	96.8	(10.1)
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Change in Unrealized Holding Gain (Loss)	24.9	(80.8)	44.3	(111.4)
Foreign Currency Transaction Gain (Loss), Unrealized	28.2	36.5	40.4	41.1
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	53.1	(44.3)	84.7	(70.3)
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Change in Unrealized Holding Gain (Loss)	21.0	(20.4)	25.0	41.6
Foreign Currency Transaction Gain (Loss), Unrealized	1.4	1.0	1.9	0.9
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	22.4	(19.4)	26.9	42.5
Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Change in Unrealized Holding Gain (Loss)	(2.4)	(1.7)	(1.7)	(2.9)
Foreign Currency Transaction Gain (Loss), Unrealized	0.3	0.3	0.3	0.1
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(2.1)	(1.4)	(1.4)	(2.8)
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Change in Unrealized Holding Gain (Loss)	8.7	0.9	13.6	4.5
Foreign Currency Transaction Gain (Loss), Unrealized	1.3	4.1	1.7	4.6
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	$ 10.0	$ 5.0	$ 15.3	$ 9.1