Financial Derivatives (Narrative) (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Credit Default Swap, Selling Protection [Member]	Mar. 31, 2012 Credit Default Swap, Selling Protection [Member]
Derivative [Line Items]
Low range of spread on written credit derivatives	1.47%	0.35%
High range of spread on written credit derivatives	4.58%	4.58%
Total net up-front payments received			$ 14.3	$ 12.6