Investment Securities (Investment gains (losses) for Level 3) (Details) (Level 3 Inputs, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Investment securities
Unrealized gains (losses) on investments	$ 7.1	$ 6.5
Fixed maturity investments.
Investment securities
Unrealized gains (losses) on investments	0.2	0.2
Common equity securities
Investment securities
Unrealized gains (losses) on investments	0.8	(0.1)
Other long-term investments
Investment securities
Unrealized gains (losses) on investments	$ 6.1	$ 6.4