Investment Securities (Investment Gains (Losses) For Level 3) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investment securities
Realized gains	$ 221.4	$ 162.2	$ 191.6
Realized losses	116.9	94.1	123.3
Accounts payable on unsettled investment purchases	20.5	11.4
Accounts receivable on unsettled investment sales	12.1	3.9
Level 3 Inputs
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	9.8	17.7	(45.6)
Fixed maturity investments | Level 3 Inputs
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	(2.3)	7.7	(12.2)
Common equity securities | Level 3 Inputs
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	0.9	3.0	(16.6)
Convertible fixed maturity investments | Level 3 Inputs
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	0	0	0
Other long-term investments | Level 3 Inputs
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	$ 11.2	$ 7.0	$ (16.8)