Financial Derivatives (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Derivative [Line Items]
Low range of spread on written credit derivatives	0.09%	3.50%
High range of spread on written credit derivatives	4.58%	4.42%
Credit Default Swap, Selling Protection [Member]
Derivative [Line Items]
Total net up-front payments received	$ 17.8	$ 9.6