Commitments, Guarantees and Contingent Liabilities (Details 2) (USD $)	12 Months Ended				1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2010	Dec. 31, 2008	Oct. 31, 2011	Sep. 30, 2014
Loss Contingencies
Limit of partial payments increased by directors (as a percent)	67.00%
FL Citizens
Loss Contingencies
Assessment rate, percent of deficit or prior year premiums	2.00%
Surcharge on policies, deadline for filing prior to imposing	15 days
LA Citizens
Loss Contingencies
Assessment rate, percent of deficit or prior year premiums	10.00%
Florida Hurricane Catastrophe Fund
Loss Contingencies
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		$ 2,000,000,000	$ 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%
California Earthquake Authority
Loss Contingencies
CEA capital balance						4,680,000,000
CEA existing reinsurance layer						3,560,000,000
Current estimated maximum CEA assessment						1,660,000,000
CEA capital balance threshold						350,000,000
Estimated maximum second CEA assessment						312,000,000
CEA threshold earthquake losses						10,520,000,000
CEA capital balance to be restored						350,000,000
Projected aggregate claim paying capacity						10,520,000,000
Share of the CEA (as a percent)		13.90%
Maximum possible assessment		273,000,000
Guaranty Funds
Loss Contingencies
Liability for insurance assessments	16,000,000	36,000,000
Insurance assessments, premium tax offsets	15,000,000	31,000,000
PMI runoff support agreement
Loss Contingencies
Percentage of claim payments to be made					50.00%
Texas Windstorm Insurance Association
Loss Contingencies
Maximum possible assessment	800,000,000
Issuance of securities to participating insurers upon utilization of funds set aside	1,000,000,000
Percentage of securities to be repaid by participating insurers' assessments	30.00%
Percentage of securities to be repaid by surcharges on coastal property policies	70.00%
Additional securities to be issued to participating insurers	500,000,000
Participation ratio	13.00%
New Jersey Unsatisfied Claim and Judgment Fund
Loss Contingencies
Minimum medical benefits portion of personal injury protection coverage for reimbursement to insurers for policies issued or renewed prior to January 1, 1991	75,000
Minimum medical benefits portion of personal injury protection coverage for reimbursement to insurers for policies issued or renewed from January 1, 1991 to December 31, 2004	75,000
Maximum reimbursement to insurers for medical benefits paid under personal injury protection coverage.	250,000
Liability for insurance assessments	9,000,000
North Carolina Reinsurance Facility
Loss Contingencies
Fund's surplus to cover future losses						15,000,000
North Carolina Joint Underwriters Association
Loss Contingencies
Plan surplus receivable	3,000,000
North Carolina Insurance Underwriting Association
Loss Contingencies
Maximum possible assessment	1,000,000,000
Percentage of surcharge on property insurance policy statewide to be remitted to the plan	10.00%