Financial Derivatives (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Low range of spread on written credit derivatives	0.25%	0.35%
High range of spread on written credit derivatives	5.00%	4.58%
Credit Default Swap, Selling Protection [Member]
Derivative [Line Items]
Total net up-front payments received	$ 14.0	$ 12.6