Investment Securities (Investment gains (losses) for Level 3) (Details) (Level 3 Inputs, USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Investment securities
Unrealized gains (losses) on investments	$ 1.8	$ 2.2	$ 8.3	$ 17.7
Fixed maturity investments.
Investment securities
Unrealized gains (losses) on investments	(0.4)	0.5	(0.2)	8.3
Common equity securities
Investment securities
Unrealized gains (losses) on investments	0.8	0.5	0.7	1.0
Other long-term investments
Investment securities
Unrealized gains (losses) on investments	$ 1.4	$ 1.2	$ 7.8	$ 8.4