Commitments and Contingencies	9 Months Ended
Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Proceedings Lawsuits arise in the ordinary course of the Company’s business. It is the opinion of the Company’s management, based upon the information available, that the expected outcome of litigation against the Company, individually or in the aggregate, will not have a material adverse effect on the Company’s financial position or liquidity, although an adverse resolution of litigation against the Company in a fiscal quarter or year could have a material adverse effect on the Company’s results of operations in a particular quarter or year. In addition, in the ordinary course of their respective businesses, certain of the Company's subsidiaries assert claims in legal proceedings against third parties to recover losses paid in prior periods or prevent losses in the future. For example, the Company has commenced a number of legal actions in the U.S. District Court for the District of Puerto Rico to enforce its rights with respect to the obligations it insures of Puerto Rico and various of its related authorities and public corporations. See the "Exposure to Puerto Rico" section of Note 4, Outstanding Exposure, for a description of such actions. See also the "Recovery Litigation" section of Note 5, Expected Loss to be Paid, for a description of recovery litigation unrelated to Puerto Rico. The amounts, if any, the Company will recover in these and other proceedings to recover losses are uncertain, and recoveries, or failure to obtain recoveries, in any one or more of these proceedings during any quarter or year could be material to the Company's results of operations in that particular quarter or year. The Company also receives subpoenas duces tecum and interrogatories from regulators from time to time. The Company establishes accruals for litigation and regulatory matters to the extent it is probable that a loss has been incurred and the amount of that loss can be reasonably estimated. For litigation and regulatory matters where a loss may be reasonably possible, but not probable, or is probable but not reasonably estimable, no accrual is established, but if the matter is material, it is disclosed, including matters discussed below. The Company reviews relevant information with respect to its litigation and regulatory matters on a quarterly basis and updates its accruals, disclosures and estimates of reasonably possible loss based on such reviews. Litigation On November 28, 2011, Lehman Brothers International (Europe) (in administration) (LBIE) sued AG Financial Products Inc. (AGFP), an affiliate of AGC which in the past had provided credit protection to counterparties under CDS. AGC acts as the credit support provider of AGFP under these CDS. LBIE’s complaint, which was filed in the Supreme Court of the State of New York, alleged that AGFP improperly terminated nine credit derivative transactions between LBIE and AGFP and improperly calculated the termination payment in connection with the termination of 28 other credit derivative transactions between LBIE and AGFP. Following defaults by LBIE, AGFP properly terminated the transactions in question in compliance with the agreement between AGFP and LBIE, and calculated the termination payment properly. AGFP calculated that LBIE owes AGFP approximately $29 million in connection with the termination of the credit derivative transactions, whereas LBIE asserted in the complaint that AGFP owes LBIE a termination payment of approximately $1.4 billion. On February 3, 2012, AGFP filed a motion to dismiss certain of the counts in the complaint, and on March 15, 2013, the court granted AGFP's motion to dismiss the count relating to improper termination of the nine credit derivative transactions and denied AGFP's motion to dismiss the counts relating to the remaining transactions. On February 22, 2016, AGFP filed a motion for summary judgment on the remaining causes of action asserted by LBIE and on AGFP's counterclaims. Oral argument on AGFP's motion took place on July 21, 2016. LBIE's administrators disclosed in an April 10, 2015 report to LBIE’s unsecured creditors that LBIE's valuation expert has calculated LBIE's claim for damages in aggregate for the 28 transactions to range between a minimum of approximately $200 million and a maximum of approximately $500 million, depending on what adjustment, if any, is made for AGFP's credit risk and excluding any applicable interest. Proceedings Resolved Since December 31, 2016 On December 22, 2014, Deutsche Bank National Trust Company, as indenture trustee for the AAA Trust 2007-2 Re-REMIC (the Trustee), filed a “trust instructional proceeding” petition in the State of California Superior Court (Probate Division, Orange County), seeking the court’s instruction as to how it should allocate the losses resulting from its December 2014 sale of four RMBS owned by the AAA Trust 2007-2 Re-REMIC. This sale of approximately $70 million principal balance of RMBS was made pursuant to AGC’s liquidation direction in November 2014, and resulted in approximately $27 million of gross proceeds to the Re-REMIC. On December 22, 2014, AGC directed the indenture trustee to allocate to the uninsured Class A-3 Notes the losses realized from the sale. On May 4, 2015, the Superior Court rejected AGC’s allocation direction, and ordered the Trustee to allocate to the Class A-3 noteholders a pro rata share of the $27 million of gross proceeds. On May 17, 2017, the California Court of Appeal upheld the Superior Court’s rejection of AGC’s allocation direction. On June 15, 2017, the California Court of Appeal denied AGC’s petition for a rehearing, pursuant to an order that modified its initial opinion and affirmed the Superior Court’s May 4, 2015 order. On September 25, 2013, Wells Fargo Bank, N.A., as trust administrator of the MASTR Adjustable Rate Mortgages Trust 2007-3 (Wells Fargo), filed an interpleader complaint in the U.S. District Court for the Southern District of New York seeking adjudication of a dispute between Wales LLC (Wales) and AGM as to whether AGM is entitled to reimbursement from certain cashflows for principal claims paid in respect of insured certificates. After the court issued an opinion on September 30, 2016, denying a motion for judgment on the pleadings filed by Wales, Wales sold its interests in the MASTR Adjustable Rate Mortgage Trust 2007-3 certificates, and on March 20, 2017, the court dismissed the case.

Commitments and Contingencies

Legal Proceedings

Lawsuits arise in the ordinary course of the Company’s business. It is the opinion of the Company’s management, based upon the information available, that the expected outcome of litigation against the Company, individually or in the aggregate, will not have a material adverse effect on the Company’s financial position or liquidity, although an adverse resolution of litigation against the Company in a fiscal quarter or year could have a material adverse effect on the Company’s results of operations in a particular quarter or year.

In addition, in the ordinary course of their respective businesses, certain of the Company's subsidiaries assert claims in legal proceedings against third parties to recover losses paid in prior periods or prevent losses in the future. For example, the Company has commenced a number of legal actions in the U.S. District Court for the District of Puerto Rico to enforce its rights with respect to the obligations it insures of Puerto Rico and various of its related authorities and public corporations. See the "Exposure to Puerto Rico" section of Note 4, Outstanding Exposure, for a description of such actions. See also the "Recovery Litigation" section of Note 5, Expected Loss to be Paid, for a description of recovery litigation unrelated to Puerto Rico. The amounts, if any, the Company will recover in these and other proceedings to recover losses are uncertain, and recoveries, or failure to obtain recoveries, in any one or more of these proceedings during any quarter or year could be material to the Company's results of operations in that particular quarter or year.

The Company also receives subpoenas duces tecum and interrogatories from regulators from time to time.

The Company establishes accruals for litigation and regulatory matters to the extent it is probable that a loss has been incurred and the amount of that loss can be reasonably estimated. For litigation and regulatory matters where a loss may be reasonably possible, but not probable, or is probable but not reasonably estimable, no accrual is established, but if the matter is material, it is disclosed, including matters discussed below. The Company reviews relevant information with respect to its litigation and regulatory matters on a quarterly basis and updates its accruals, disclosures and estimates of reasonably possible loss based on such reviews.

Litigation

On November 28, 2011, Lehman Brothers International (Europe) (in administration) (LBIE) sued AG Financial Products Inc. (AGFP), an affiliate of AGC which in the past had provided credit protection to counterparties under CDS. AGC acts as the credit support provider of AGFP under these CDS. LBIE’s complaint, which was filed in the Supreme Court of the State of New York, alleged that AGFP improperly terminated nine credit derivative transactions between LBIE and AGFP and improperly calculated the termination payment in connection with the termination of 28 other credit derivative transactions between LBIE and AGFP. Following defaults by LBIE, AGFP properly terminated the transactions in question in compliance with the agreement between AGFP and LBIE, and calculated the termination payment properly. AGFP calculated that LBIE owes AGFP approximately $29 million in connection with the termination of the credit derivative transactions, whereas LBIE asserted in the complaint that AGFP owes LBIE a termination payment of approximately $1.4 billion. On February 3, 2012, AGFP filed a motion to dismiss certain of the counts in the complaint, and on March 15, 2013, the court granted AGFP's motion to dismiss the count relating to improper termination of the nine credit derivative transactions and denied AGFP's motion to dismiss the counts relating to the remaining transactions. On February 22, 2016, AGFP filed a motion for summary judgment on the remaining causes of action asserted by LBIE and on AGFP's counterclaims. Oral argument on AGFP's motion took place on July 21, 2016. LBIE's administrators disclosed in an April 10, 2015 report to LBIE’s unsecured creditors that LBIE's valuation expert has calculated LBIE's claim for damages in aggregate for the 28 transactions to range between a minimum of approximately $200 million and a maximum of approximately $500 million, depending on what adjustment, if any, is made for AGFP's credit risk and excluding any applicable interest.

Proceedings Resolved Since December 31, 2016

On December 22, 2014, Deutsche Bank National Trust Company, as indenture trustee for the AAA Trust 2007-2 Re-REMIC (the Trustee), filed a “trust instructional proceeding” petition in the State of California Superior Court (Probate Division, Orange County), seeking the court’s instruction as to how it should allocate the losses resulting from its December 2014 sale of four RMBS owned by the AAA Trust 2007-2 Re-REMIC. This sale of approximately $70 million principal balance of RMBS was made pursuant to AGC’s liquidation direction in November 2014, and resulted in approximately $27 million of gross proceeds to the Re-REMIC. On December 22, 2014, AGC directed the indenture trustee to allocate to the uninsured Class A-3 Notes the losses realized from the sale. On May 4, 2015, the Superior Court rejected AGC’s allocation direction, and ordered the Trustee to allocate to the Class A-3 noteholders a pro rata share of the $27 million of gross proceeds. On May 17, 2017, the California Court of Appeal upheld the Superior Court’s rejection of AGC’s allocation direction. On June 15, 2017, the California Court of Appeal denied AGC’s petition for a rehearing, pursuant to an order that modified its initial opinion and affirmed the Superior Court’s May 4, 2015 order.

On September 25, 2013, Wells Fargo Bank, N.A., as trust administrator of the MASTR Adjustable Rate Mortgages Trust 2007-3 (Wells Fargo), filed an interpleader complaint in the U.S. District Court for the Southern District of New York seeking adjudication of a dispute between Wales LLC (Wales) and AGM as to whether AGM is entitled to reimbursement from certain cashflows for principal claims paid in respect of insured certificates. After the court issued an opinion on September 30, 2016, denying a motion for judgment on the pleadings filed by Wales, Wales sold its interests in the MASTR Adjustable Rate Mortgage Trust 2007-3 certificates, and on March 20, 2017, the court dismissed the case.