Investment Securities (Investment gains (losses) for Level 3) (Details) (Level 3 Inputs, USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Investment securities
Unrealized gains (losses) on investments	$ (2.0)	$ 2.7	$ 6.3	$ 20.4
Fixed maturity investments.
Investment securities
Unrealized gains (losses) on investments	(2.2)	(1.0)	(2.4)	7.3
Common equity securities
Investment securities
Unrealized gains (losses) on investments	(0.7)	0.8	0	1.8
Other long-term investments
Investment securities
Unrealized gains (losses) on investments	$ 0.9	$ 2.9	$ 8.7	$ 11.3