New Accounting Pronouncements Not Yet Adopted (Policies)	3 Months Ended
Mar. 31, 2017
Accounting Policies [Abstract]
Description of New Accounting Pronouncements Not yet Adopted [Text Block]	Future Application of Accounting Standards: Premium Amortization on Callable Debt Securities In March 2017, the FASB issued ASU 2017-08, Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20) - Premium Amortization on Purchased Callable Debt Securities. The ASU shortens the amortization period for the premium on callable debt securities to the earliest call date. Under current GAAP, a reporting entity generally amortizes the premium as yield adjustment over the contractual life (i.e. maturity) of the debt security and if that debt security is called, the entity would record a loss equal to the unamortized premium. The ASU does not change the accounting for callable debt securities held at a discount, which will continue to be amortized to maturity. ASU 2017-08 is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, with early adoption permitted. The ASU must be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings as of the beginning of the period of adoption. We have not determined whether Ambac will early adopt this ASU and are evaluating the impact on Ambac's financial statements. Net Periodic Pension and Postretirement Costs In March 2017, the FASB issued ASU 2017-07, Compensation-Retirement Benefits (Topic 715) - Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. The objective of the ASU is to increase transparency in the reporting of net pension cost and net postretirement cost (collectively "net benefit cost"). The ASU requires that the service cost component of net benefit cost be reported on the same line item as other compensation costs arising from services rendered by employees. It further requires that the other components of net benefit costs (i.e. interest costs, amortization of prior service cost, etc.) be presented separately from the service cost component and outside the subtotal of income from operations, if one is presented. ASU 2017-09 is effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, with early adoption permitted. Ambac will adopt this ASU on January 1, 2018. The adoption of this ASU is not expected to have a consequential impact on Ambac's financial statements.

Future Application of Accounting Standards:

Premium Amortization on Callable Debt Securities

In March 2017, the FASB issued ASU 2017-08, Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20) - Premium Amortization on Purchased Callable Debt Securities. The ASU shortens the amortization period for the premium on callable debt securities to the earliest call date. Under current GAAP, a reporting entity generally amortizes the premium as yield adjustment over the contractual life (i.e. maturity) of the debt security and if that debt security is called, the entity would record a loss equal to the unamortized premium. The ASU does not change the accounting for callable debt securities held at a discount, which will continue to be amortized to maturity. ASU 2017-08 is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, with early adoption permitted. The ASU must be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings as of the beginning of the period of adoption. We have not determined whether Ambac will early adopt this ASU and are evaluating the impact on Ambac's financial statements.

Net Periodic Pension and Postretirement Costs

In March 2017, the FASB issued ASU 2017-07, Compensation-Retirement Benefits (Topic 715) - Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. The objective of the ASU is to increase transparency in the reporting of net pension cost and net postretirement cost (collectively "net benefit cost"). The ASU requires that the service cost component of net benefit cost be reported on the same line item as other compensation costs arising from services rendered by employees. It further requires that the other components of net benefit costs (i.e. interest costs, amortization of prior service cost, etc.) be presented separately from the service cost component and outside the subtotal of income from operations, if one is presented. ASU 2017-09 is effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, with early adoption permitted. Ambac will adopt this ASU on January 1, 2018. The adoption of this ASU is not expected to have a consequential impact on Ambac's financial statements.