Investment Securities (Net Realized 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, Realized Gain (Loss)	$ 27.2	$ 29.1	$ 52.5	$ 80.3
Trading securities, tax on realized holding gain (loss) on investments	(5.3)	(5.5)	(9.9)	(17.3)
Trading securities realized holding gain (loss) on investments after tax	21.9	23.6	42.6	63.0
Foreign Currency Transaction Gain (Loss), Realized	3.3	(6.3)	(0.3)	(20.9)
Trading securities, realized foreign currency transaction gain (loss) t	(1.0)	1.4	(0.1)	4.7
Trading securities, realized foreign currency gain (loss) net of tax	2.3	(4.9)	(0.4)	(16.2)
Trading Securities, Realized Gain (Loss), Total	30.5	22.8	52.2	59.4
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(6.3)	(4.1)	(10.0)	(12.6)
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	24.2	18.7	42.2	46.8
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	5.7	6.8	10.1	29.4
Foreign Currency Transaction Gain (Loss), Realized	3.0	(4.0)	(0.5)	(18.6)
Trading Securities, Realized Gain (Loss), Total	8.7	2.8	9.6	10.8
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	0	0.2	0	0.1
Foreign Currency Transaction Gain (Loss), Realized	0	0.5	0	0.7
Trading Securities, Realized Gain (Loss), Total	0	0.7	0	0.8
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	19.4	22.7	38.3	45.3
Foreign Currency Transaction Gain (Loss), Realized	0	0.2	(0.1)	0
Trading Securities, Realized Gain (Loss), Total	19.4	22.9	38.2	45.3
Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	1.5	(3.4)	3.9	(0.6)
Foreign Currency Transaction Gain (Loss), Realized	0	0	0	0
Trading Securities, Realized Gain (Loss), Total	1.5	(3.4)	3.9	(0.6)
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	0.6	3.0	0.3	5.9
Foreign Currency Transaction Gain (Loss), Realized	0.3	(3.0)	0.3	(3.0)
Trading Securities, Realized Gain (Loss), Total	0.9	0	0.6	2.9
Forward Contracts
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	0	(0.2)	(0.1)	0.2
Foreign Currency Transaction Gain (Loss), Realized	0	0	0	0
Trading Securities, Realized Gain (Loss), Total	$ 0	$ (0.2)	$ (0.1)	$ 0.2