Investment Securities (Net Realized Investment Gains (Losses)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Investment securities
Trading Securities, Realized Gain (Loss)	$ 23.7	$ 38.3	$ 40.5	$ 67.7
Trading Securities, Realized Gain (Loss) Tax	7.4	8.3	12.8	20.7
Trading Securities, Realized Gain (Loss) Net of Tax	16.3	30.0	27.7	47.0
Fixed maturity investments.
Investment securities
Trading Securities, Realized Gain (Loss)	29.0	14.1	69.5	3.3
Short-term investments
Investment securities
Trading Securities, Realized Gain (Loss)	(3.4)	0.4	(3.9)	(10.9)
Common equity securities
Investment securities
Trading Securities, Realized Gain (Loss)	3.9	23.1	(2.2)	41.0
Convertible Debt Securities [Member]
Investment securities
Trading Securities, Realized Gain (Loss)	1.1	(0.7)	3.2	6.3
Other long-term investments
Investment securities
Trading Securities, Realized Gain (Loss)	(7.2)	1.4	(26.4)	28.0
Forward Contracts [Member]
Investment securities
Trading Securities, Realized Gain (Loss)	$ 0.3	$ 0	$ 0.3	$ 0