Commitments, Guarantees and Contingent Liabilities (Details 2) - USD ($)		12 Months Ended
	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2010	Dec. 31, 2008	Sep. 30, 2015
Loss Contingencies
Proceeds of Revenue Bonds	$ 668,000,000
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
Emergency Assessment Maximum Percentage of Premiums Subsequent Years, FL OIR		0.00%
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%
Emergency Assessment Maximum Percentage of Premiums 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%
Emergency Assessment Maximum Percentage of Premiums Subsequent Years, FL OIR		0.00%
California Earthquake Authority
Loss Contingencies
CEA capital balance	4,880,000,000
CEA existing reinsurance layer	4,110,000,000
Current estimated maximum CEA assessment	1,660,000,000
CEA capital balance threshold	350,000,000
Estimated maximum second CEA assessment	238,000,000
CEA threshold earthquake losses	11,560,000,000
CEA capital balance to be restored	350,000,000
Projected aggregate claim paying capacity	$ 11,560,000,000
Share of the CEA (as a percent)			13.10%
Maximum possible assessment			$ 248,000,000
Guaranty Funds
Loss Contingencies
Liability for insurance assessments		$ 13,000,000	16,000,000
Insurance assessments, premium tax offsets		14,000,000	$ 15,000,000
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		8,600,000
North Carolina Reinsurance Facility
Loss Contingencies
Fund's surplus to cover future losses							$ 69,900,000
North Carolina Joint Underwriters Association
Loss Contingencies
Plan surplus receivable		1,500,000
Funds Surplus in Member's equity		11,900,000
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%