Commitments, Guarantees and Contingent Liabilities (Details 2) (USD $)	12 Months Ended			12 Months Ended					1 Months Ended		12 Months Ended		1 Months Ended
	Dec. 31, 2012 FL Citizens	Jun. 30, 2012 FL Citizens	Dec. 31, 2012 LA Citizens	Dec. 31, 2012 Florida Hurricane Catastrophe Fund	Dec. 31, 2010 Florida Hurricane Catastrophe Fund	Dec. 31, 2008 Florida Hurricane Catastrophe Fund	Dec. 31, 2012 California Earthquake Authority	Apr. 02, 2012 California Earthquake Authority	Sep. 30, 2008 Texas Windstorm Insurance Association	Dec. 31, 2012 Texas Windstorm Insurance Association	Dec. 31, 2012 Guaranty Funds	Dec. 31, 2011 Guaranty Funds	Oct. 31, 2011 PMI runoff support agreement
Loss Contingencies
Assessment rate, percent of deficit or prior year premiums	2.00%	6.00%	10.00%
Surcharge on policies, deadline for filing prior to imposing	15 days
Deficit assessment recouped to date										$ 28,000,000
Deficit assessment expected to be recouped										7,000,000
Maximum emergency assessment as percent of premiums, first year				6.00%
Maximum emergency assessment as percent of premiums, second and subsequent years				10.00%
Catastrophe fund, bonds issued					676,000,000	625,000,000
Emergency assessment ordered as percent of premiums from January 1, 2007 through December 31, 2010				1.00%
Emergency assessment ordered as percent of premiums after January 1, 2011				1.30%
CEA capital balance							4,200,000,000
CEA existing reinsurance layer							3,560,000,000
Current estimated maximum CEA assessment							1,560,000,000
CEA capital balance threshold							350,000,000
Estimated maximum second CEA assessment							500,000,000
CEA threshold earthquake losses							10,140,000,000
CEA capital balance to be restored							350,000,000
Projected aggregate claim paying capacity							10,140,000,000
Share of the CEA (as a percent)								15.80%
Maximum possible CEA assessment							325,000,000
Liability for insurance assessments									66,000,000		49,000,000	53,000,000
Insurance assessments, premium tax offsets									35,000,000		32,000,000	35,000,000
Period for realization of premium tax offsets									five years
Remaining assessment eligible for cession										$ 31,000,000
Percentage of claim payments to be made													50.00%