Ambac Financial (AMBC) 10-Q 9 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - $ / shares	9 Months Ended
	Sep. 30, 2020	Nov. 06, 2020	Apr. 30, 2013
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Entity Ex Transition Period	false
Entity File Number	1-10777
Entity Registrant Name	AMBAC FINANCIAL GROUP, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	13-3621676
Entity Address, Address Line One	One World Trade Center
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10007
City Area Code	(212)
Local Phone Number	658-7470
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Bankruptcy Proceedings, Reporting Current	true
Entity Common Stock, Shares Outstanding		45,809,139
Common Stock, Par or Stated Value Per Share	$ 0.01		$ 0.01
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Entity Central Index Key	0000874501
Current Fiscal Year End Date	--12-31
Common Stock [Member]
Entity Information [Line Items]
Title of 12(b) Security	Common stock par value $0.01 per share
Trading Symbol	AMBC
Security Exchange Name	NYSE
Warrants [Member]
Entity Information [Line Items]
Title of 12(b) Security	Warrants
Trading Symbol	AMBC WS
Security Exchange Name	NYSE

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Fixed income securities, at fair value	$ 3,048,000
Total investments (net of allowance for credit losses of $0 at September 30, 2020)	3,551,000	$ 3,792,000
Cash and cash equivalents	37,000	24,000
Restricted Cash	10,000	55,000
Premiums Receivable, Net	372,000	416,000
Reinsurance Recoverable, Allowance for Credit Loss	0
Reinsurance Recoverables, Including Reinsurance Premium Paid	37,000	26,000
Deferred ceded premium	73,000	82,000
Subrogation recoverable	2,194,000	2,029,000
Derivative assets	95,000	75,000
Income Taxes Receivable	2,000	11,000
Insurance intangible asset	383,000	427,000
Other assets	60,000	95,000
Total assets	12,812,000	13,320,000
Liabilities:
Unearned premiums	468,000	518,000
Loss and loss expense reserves	1,801,000	1,548,000
Ceded premiums payable	27,000	29,000
Long-term debt	2,737,000	2,822,000
Accrued interest payable	499,000	441,000
Derivative Liability	126,000	90,000
Other liabilities	91,000	93,000
Total liabilities	11,718,000	11,783,000
Stockholders’ equity:
Preferred stock, par value $0.01 per share; 20,000,000 shares authorized; issued and outstanding shares—none	0	0
Common Stock, Value, Issued	0	0
Additional paid-in capital	240,000	232,000
Accumulated other comprehensive income	22,000	42,000
Retained earnings	773,000	1,203,000
Treasury stock, shares at cost: 0 and 8,202	(1,000)	0
Total Ambac Financial Group, Inc. stockholders’ equity	1,035,000	1,477,000
Noncontrolling interest	60,000	60,000
Total stockholders’ equity	1,095,000	1,536,000
Total liabilities and stockholders’ equity	12,812,000	13,320,000
Deferred Income Tax Liabilities, Net	28,000	32,000
Available-for-sale Securities, Amortized Cost Basis	2,914,000	3,187,000
Short-term Investments [Member]
Assets:
Fixed income securities, at fair value	586,000	653,000
Stockholders’ equity:
Available-for-sale Securities, Amortized Cost Basis	586,000	653,000
Fixed Income Securities [Member]
Assets:
Fixed income securities, at fair value	2,311,000	2,577,000
Stockholders’ equity:
Available-for-sale Securities, Amortized Cost Basis	2,176,000	2,450,000
Available-for-sale Securities	2,311,000	2,577,000
Short-term Investments [Member]
Stockholders’ equity:
Available-for-sale Securities	586,000	653,000
Other Investments [Member]
Stockholders’ equity:
Available-for-sale Securities	502,000	478,000
Collateral Pledged [Member] | Short-term Investments [Member]
Assets:
Fixed income securities, at fair value		85,000
Collateral Pledged [Member] | Fixed Income Securities [Member]
Assets:
Fixed income securities, at fair value	152,000	85,000
Collateral Pledged [Member] | Fixed Income Securities [Member] | Short-term Investments [Member]
Assets:
Fixed income securities, at fair value	152,000
Stockholders’ equity:
Available-for-sale Securities, Amortized Cost Basis	152,000	85,000
Collateral Pledged [Member] | Short-term Investments
Stockholders’ equity:
Available-for-sale Securities, Amortized Cost Basis	152,000	85,000
Collateralized Securities | Short-term Investments [Member]
Stockholders’ equity:
Available-for-sale Securities	$ 152,000	$ 85,000

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Amortized Cost	$ 2,914,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Premium Receivable, Allowance for Credit Loss	$ 18,000,000
Preferred stock, par value	$ 0.01
Preferred stock, shares authorized	20,000,000
Preferred Stock, Shares Issued	0
Common stock, par value	$ 0.01
Common stock, shares authorized	130,000,000
Common stock, shares issued	45,865,081	45,571,743
Common stock, shares outstanding	45,809,139
Treasury stock, shares	55,942	16,343
Equity investments in pooled funds [Member]
Other Investment Not Readily Marketable, Fair Value	$ 453,000,000	$ 432,000,000
Variable Interest Entity, Primary Beneficiary [Member]
Long-term debt	$ 4,002,000,000	$ 4,351,000,000

Consolidated Statements of Tota

Consolidated Statements of Total Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Net premiums earned	$ 15	$ 10	$ 36	$ 46
Net investment income:
Securities available-for-sale and short-term	24	36	80	161
Net investment income	37	45	69	186
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments	2	18	20	71
Realized Investment Gains (Losses)	2	18	20	71
Change in fair value of credit derivatives:
Unrealized gains (losses)			(1)	1
Derivative, Gain (Loss) on Derivative, Net	7	(10)	(61)	(61)
Other Operating Income (Expense), Net	2	141	2	133
Income (loss) on variable interest entities	0	11	3	30
Total revenues	62	216	68	406
Expenses:
Losses and loss expenses (benefit)	83	37	216	(84)
Insurance intangible amortization	14	17	41	280
Operating expenses	23	26	67	80
Interest expense	50	67	172	202
Total expenses	170	147	495	478
Pre-tax income (loss)	(108)	69	(427)	(72)
Provision (benefit) for income taxes	0	3	(5)	33
Net income (loss)	(108)	66	(423)	(106)
Net income (loss) attributable to common stockholders	(108)	66	(423)	(106)
Other comprehensive income (loss), after tax:
Net income (loss)	(108)	66	(423)	(106)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	42	31	1	103
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	29	(24)	(20)	(28)
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax	0	0	2	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	0	0	(3)	0
Total other comprehensive income (loss), net of income tax	71	7	(20)	75
Total comprehensive income (loss)	(37)	73	(442)	(30)
Less: comprehensive (gain) loss attributable to the noncontrolling interest:
Total comprehensive income (loss) attributable to common stockholders	$ (37)	$ 73	$ (442)	$ (30)
Earnings Per Share, Basic	$ (2.33)	$ 1.44	$ (9.16)	$ (2.30)
Earnings Per Share, Diluted	$ (2.33)	$ 1.41	$ (9.16)	$ (2.30)
Weighted Average Number of Shares Outstanding, Basic	46,178,730	45,997,694	46,135,399	45,939,284
Weighted Average Number of Shares Outstanding, Diluted	46,178,730	47,020,058	46,135,399	45,939,284

Consolidated Statements of To_2

Consolidated Statements of Total Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Unrealized (loss) gain on securities, taxes	$ 0	$ 1	$ 1	$ (7)
Gain (loss) on foreign currency translation, taxes	0	0	0	0
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, Tax	0	0	0	0
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Tax Effect	$ 0	$ 0	$ 0	$ 0

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Noncontrolling Interest [Member]
Beginning balance at Dec. 31, 2018	$ 1,633	$ 1,421	$ (49)	$ 0	$ 0	$ 219	$ 0	$ 41
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	(30)	(106)	75	0	0	0	0	0
Stock-based compensation	10	0	0	0	0	10	0	0
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture	(3)	(3)	0	0	0	0	0	0
Ending balance at Sep. 30, 2019	1,629	1,313	26	0	0	229	0	60
Increase (Decrease) in Stockholders' Equity [Roll Forward]
AMPS Impact on Stockholders Equity	19	0	0	0	0	0	0	19
Beginning balance at Jun. 30, 2019	1,553	1,247	19	0	0	227	0	60
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	73	66	7	0	0	0	0	0
Stock-based compensation	2	0	0	0	0	2	0	0
Ending balance at Sep. 30, 2019	1,629	1,313	26	0	0	229	0	60
Beginning balance at Dec. 31, 2019	1,536	1,203	42	0	0	232	0	60
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	(442)	(423)	(20)	0	0	0	0	0
Stock-based compensation	8	0	0	0	0	8	0	0
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture	(3)	(2)	0	0	0	0	(1)	0
Ending balance at Sep. 30, 2020	1,095	773	22	0	0	240	(1)	60
Beginning balance at Jun. 30, 2020	1,129	881	(48)	0	0	237	(1)	60
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	(37)	(108)	71	0	0	0	0	0
Stock-based compensation	3	0	0	0	0	3	0	0
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture	0	0	0	0	0	0	0	0
Ending balance at Sep. 30, 2020	1,095	773	22	$ 0	$ 0	$ 240	$ (1)	$ 60
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-13 [Member]	$ (4)	$ (4)	$ 0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income (loss)	$ (423)	$ (106)
Adjustments to reconcile net income to net cash used in operating activities:
Amortization of bond premium and discount	(12)	(59)
Share-based compensation	8	10
Deferred income taxes	(5)	(3)
Current income taxes	9	28
Unearned premiums, net	(40)	(118)
Losses and loss expenses, net	78	(461)
Ceded premiums payable	(2)	(3)
Premium receivables	44	81
Accrued interest payable	69	65
Amortization of insurance intangible assets	41	280
Net mark-to-market (gains) losses	1	(1)
Net realized investment gains	(20)	(71)
Variable interest entity activities	(3)	(30)
Derivative assets and liabilities	15	5
Other, net	72	87
Net cash used in operating activities	(167)	(296)
Cash flows from investing activities:
Proceeds from sales of bonds	974	1,052
Proceeds from matured bonds	105	317
Purchases of bonds	(844)	(866)
Proceeds from sales of other invested assets	377	73
Purchases of other invested assets	(425)	(135)
Change in short-term investments	67	(235)
Change in cash collateral receivable	(2)	75
Proceeds from paydowns of consolidated VIE assets	142	512
Other, net	2	0
Net cash provided by (used in) investing activities	396	791
Cash flows from financing activities:
Proceeds from issuance of Ambac UK debt	0	12
Paydowns of Ambac note	(115)	(29)
Issuance of auction market preferred shares of Ambac Assurance	0	19
Tax payments related to shares withheld for share-based compensation plans	(3)	(3)
Payments of consolidated VIE liabilities	(143)	(510)
Net cash used in financing activities	(260)	(511)
Effect of foreign exchange on cash, cash equivalents and restricted cash	0	0
Net cash flow	(31)	(16)
Cash, cash equivalents, and restricted cash at beginning of period	81	83
Cash, cash equivalents, and restricted cash at end of period	$ 50	$ 68

Background and Business Descrip

Background and Business Description	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Background and Business Description	1. BACKGROUND AND BUSINESS DESCRIPTION The following description provides an update of Note 1. Background and Business Description in the Notes to Consolidated Financial Statements included Part II, Item 8 in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019, and should be read in conjunction with the complete descriptions provided in the Form 10-K. Capitalized terms used, but not defined herein, and in the other footnotes to the Consolidated Financial Statements included in this Quarterly Report on Form 10-Q shall have the meanings ascribed thereto in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. Ambac Financial Group, Inc. (“AFG”), headquartered in New York City, is a financial services holding company incorporated in the state of Delaware on April 29, 1991. References to “Ambac,” the “Company,” “we,” “our,” and “us” are to AFG and its subsidiaries, as the context requires. AFG’s insurance subsidiary, Ambac Assurance Corporation (“Ambac Assurance" or "AAC") and its subsidiary, Ambac Assurance UK Limited (“Ambac UK”), are both financial guarantee insurance companies in run-off. Ambac Assurance and Ambac UK's outstanding insurance policies generally guarantee payment when due of the principal and interest on the obligations guaranteed. During the three month period ended September 30, 2020, AFG acquired its insurance subsidiary, Everspan Insurance Company ("Everspan"), from AAC repositioning it as a subsidiary of a new intermediary holding company that is directly owned by AFG. This was done in an effort to optimize the legal organization structure to support potential new property and casualty insurance business initiatives. Management reviews financial information, allocates resources and measures financial performance on a consolidated basis. As a result, the Company has a single reportable segment. Strategies to Enhance Shareholder Value The Company's primary goal is to maximize shareholder value through executing the following key strategies: • Active runoff of Ambac Assurance and its subsidiaries through transaction terminations, policy commutations, reinsurance, settlements and restructurings, with a focus on our watch list credits and known and potential future adversely classified credits, that we believe will improve our risk profile, and maximizing the risk-adjusted return on invested assets; • Ongoing rationalization of Ambac's capital and liability structures; • Loss recovery through active litigation management and exercise of contractual and legal rights; • Ongoing review of the effectiveness and efficiency of Ambac's operating platform; and • Evaluation of opportunities in certain business sectors that meet acceptable criteria that will generate long-term stockholder value with attractive risk-adjusted returns. With respect to our new business strategy, we continue to evaluate and pursue strategic opportunities in insurance, credit, asset management and other financial services that we believe would be synergistic to Ambac and would leverage our core competencies. While we have increased our efforts in evaluating such potential opportunities, we continue to be measured and disciplined in our approach as we seek to deploy our capital on opportunities that will generate sustainable long-term shareholder value. Although we are exploring new business opportunities for AFG, no assurance can be given that we will be able to identify or execute a suitable transaction and/or obtain the financial and other resources that may be required to finance an acquisition or develop any new businesses or assets. As a consequence of the novel coronavirus disease 2019 ("COVID-19") pandemic, risks associated with our new businesses strategy have increased given uncertainties related to the resulting global recession, increase in business risk in our target sectors and disruption to the capital markets. Due to these factors, as well as uncertainties relating to the ability of Ambac Assurance to deliver value to Ambac, the value of our securities remains speculative. The execution of AFG’s strategy to extract and increase the value of its investment in Ambac Assurance is subject to the restrictions set forth in the Settlement Agreement, dated as of June 7, 2010 (the "Settlement Agreement"), by and among Ambac Assurance, Ambac Credit Products LLC ("ACP"), AFG and certain counterparties to credit default swaps with ACP that were guaranteed by Ambac Assurance, as well as the Stipulation and Order among the OCI (as defined below), AFG and Ambac Assurance that became effective on February 12, 2018, as amended (the “Stipulation and Order”), and in the indenture for the Tier 2 Notes issued by Ambac Assurance on February 12, 2018, each of which requires the Office of the Commissioner of Insurance for the State of Wisconsin (“OCI”) and, under certain circumstances, holders of the debt instruments benefiting from such restrictions, to approve certain actions taken by or in respect of Ambac Assurance. In exercising its approval rights, OCI will act for the benefit of policyholders, and will not take into account the interests of AFG. AFG's strategy to extract and increase the value of its investment in Ambac Assurance is also subject to significantly more risk and uncertainty due to the consequences of the COVID-19 pandemic on the global economy, issuers of debt insured by Ambac, and issuers of debt and other investments owned by Ambac. These consequences may include material losses in Ambac's insured and investment portfolios, higher earnings volatility, increased liquidity demands and greater counterparty risk. Opportunities for remediating losses on poorly performing insured transactions also depend on market conditions, including the perception of Ambac Assurance’s creditworthiness, the structure of the underlying risk and associated policy as well as

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies (Notes)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block]	2. BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES The Company has disclosed its significant accounting policies in Note 2. Basis of Presentation and Significant Accounting Policies in the Notes to Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. The following significant accounting policies provide an update to those included in the Company’s Annual Report on Form 10-K. Consolidation: The consolidated financial statements include the accounts of AFG and all other entities in which AFG (directly or through its subsidiaries) has a controlling financial interest, including variable interest entities (“VIEs”) for which AFG or an AFG subsidiary is deemed the primary beneficiary in accordance with the Consolidation Topic of the Accounting Standards Codification ("ASC"). All significant intercompany balances have been eliminated. The usual condition for a controlling financial interest is ownership of a majority of the voting interests of an entity. However, a controlling financial interest may also exist in entities, such as VIEs, through arrangements that do not involve controlling voting interests. A VIE is an entity: a) that lacks enough equity investment at risk to permit the entity to finance its activities without additional subordinated financial support from other parties; or b) where the group of equity holders does not have: (1) the power, through voting rights or similar rights, to direct the activities of an entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb the entity’s expected losses; or (3) the right to receive the entity’s expected residual returns. The determination of whether a variable interest holder is the primary beneficiary involves performing a qualitative analysis of the VIE that includes, among other factors, its capital structure, contractual terms including the rights of each variable interest holder, the activities of the VIE, whether the variable interest holder has the power to direct the activities of a VIE that most significantly impact the VIE’s economic performance, whether the variable interest holder has the obligation to absorb losses of the VIE that could potentially be significant to the VIE or the right to receive benefits from the VIE that could potentially be significant to the VIE, related party relationships and the design of the VIE. An entity that is deemed the primary beneficiary of a VIE is required to consolidate the VIE. See Note 3. Variable Interest Entities , for a detailed discussion of Ambac’s involvement in VIEs, Ambac’s methodology for determining whether Ambac is required to consolidate a VIE and the effects of VIEs being consolidated and deconsolidated. Basis of Presentation: The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles ("GAAP") for interim financial reporting and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and disclosures required by GAAP for annual periods. These consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Annual Report on Form 10-K for the year ended December 31, 2019. The accompanying consolidated financial statements have not been audited by an independent registered public accounting firm in accordance with the standards of the Public Company Accounting Oversight Board (U.S.), but in the opinion of management such financial statements include all adjustments necessary for the fair presentation of the Company’s consolidated financial position and results of operations. The results of operations for the three and nine months ended September 30, 2020, may not be indicative of the results that may be expected for the year ending December 31, 2020. The December 31, 2019, consolidated balance sheet was derived from audited financial statements. The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. As additional information becomes available or actual amounts become determinable, the recorded estimates are revised and reflected in operating results. Foreign Currency: Financial statement accounts expressed in foreign currencies are translated into U.S. dollars in accordance with the Foreign Currency Matters Topic of the ASC. The functional currencies of AFG's subsidiaries are the local currencies of the country where the respective subsidiaries are based, which are also the primary operating environments in which the subsidiaries operate. Foreign currency translation : Functional currency assets and liabilities of AFG’s foreign subsidiaries are translated into U.S. dollars using exchange rates in effect at the balance sheet dates and the related translation adjustments, net of deferred taxes, are included as a component of Accumulated Other Comprehensive Income in Stockholders' Equity. Functional currency operating results of foreign subsidiaries are translated using average exchange rates. Foreign currency transactions : The impact of non-functional currency transactions and the remeasurement of non-functional currency assets and liabilities into the respective subsidiaries' functional currency (collectively "foreign currency transactions gains/(losses)") are $2 and $19 for the nine months ended September 30, 2020 and 2019, respectively. Foreign currency transactions gains/(losses) are primarily the result of remeasuring Ambac UK's assets and liabilities denominated in currencies other than its functional currency, primarily the U.S. dollar and the Euro. Supplemental Disclosure of Cash Flow Information Nine Months Ended September 30, 2020 2019 Cash paid during the period for: Income taxes $ 11 $ 11 Interest on long-term debt 83 110 Non-cash financing activities: Exchange of investments in Puerto Rico COFINA bonds for new bonds issued in the Plan of Adjustment $ — $ 510 September 30, 2020 2019 Reconciliation of cash, cash equivalents, and restricted cash reported within the Consolidated Balance Sheets to the Consolidated Statements of Cash Flows: Cash and cash equivalents $ 37 $ 52 Restricted cash 10 13 Variable Interest Entity Restricted cash 2 3 Total cash, cash equivalents, and restricted cash shown on the Consolidated Statements of Cash Flows $ 50 $ 68 Reclassifications and Rounding Reclassifications may have been made to prior years' amounts to conform to the current year's presentation. Certain amounts and tables in the consolidated financial statements and associated notes may not add due to rounding. Adopted Accounting Standards: Effective January 1, 2020, the Company adopted the following accounting standards: Measurement of Credit Losses on Financial Instruments (CECL) In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326) - Measurement of Credit Losses on Financial Instruments, subsequently amended by ASU 2018-19 , Codification Improvements to Topic 326, Financial Instruments - Credit Losses; ASU 2019-04 , Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments ; ASU 2019-05, Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief ; and ASU 2019-11, Codification Improvements to Topic 326, Financial Instruments - Credit Losses (collectively the Current Expected Credit Loss standard or "CECL") The new CECL standard affects how reporting entities measure credit losses for financial assets that are not accounted for at fair value through net income. For Ambac, these financial assets include available-for-sale debt securities and amortized cost assets, specifically premium receivables, reinsurance recoverables and loans. CECL does not apply to recoveries of previously paid losses on financial guarantee insurance contracts accounted for under ASC 944 nor does it apply to equity method investments accounted for under ASC 323. For available-for-sale debt securities, the updated guidance was applied prospectively and for financial instruments measured at amortized cost, the updated guidance was applied by a cumulative effect adjustment to the opening balance of retained earnings at January 1, 2020. This adjustment was not material to retained earnings or any individual balance sheet line item. As a result of adopting CECL, management revised its policies and procedures around the credit impairment evaluation process. CECL also introduced new disclosures related to the credit impairment process, including certain accounting policy elections that Ambac made under the the new standard. Enhanced disclosures related to accounting policies for each type of asset impacted by CECL are discussed below. The disclosures below should be read in conjunction with disclosures in Note 2. Basis of Presentation and Significant Accounting Policies , Note 6. Financial Guarantee Insurance Contracts and Note 8. Investments in the Notes to Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. Available-for-Sale Debt Securities For available-for-sale debt securities, credit losses under CECL are measured similarly to other-than-temporary impairments under prior GAAP. However, under CECL, the recognition of credit losses for available-for-sale debt securities will be recorded as an allowance for credit losses with an offsetting charge to net income, rather than as a direct write-down of the security as was required under prior GAAP. As a result, improvements to estimated credit losses for available-for-sale debt securities will be recognized immediately in net income rather than as interest income over time. Furthermore, as required under CECL, Ambac no longer considers the length of time a security has continuously been in an unrealized loss in the credit impairment process. Ambac has made certain accounting policy elections related to accrued interest receivable ("AIR") for available-for-sale investments under CECL, which are consistent with past practices under prior GAAP. Elections include: i) not measuring AIR for credit impairment, instead AIR is written off when it becomes 90 days past due; ii) writing off AIR by reversing interest income; iii) presenting AIR separately in Other Assets on the balance sheet and iv) excluding AIR from amortized cost balances in required CECL disclosures found in Note 8. Investments . AIR at September 30, 2020 was $10. Refer to Note 8. Investments for further credit impairment disclosures. Amortized cost assets For financial assets measured at amortized cost, CECL replaces the "incurred loss" model used for certain types of assets which generally delayed recognition of the full amount of credit losses until the loss was probable of occurring, with an "expected loss" model, which reflects an entity's current estimate of all expected lifetime credit losses. The estimate of expected lifetime credit losses should consider historical information, current information, as well as reasonable and supportable forecasts. Expected lifetime credit losses for amortized cost assets will be recorded as an allowance for credit losses, with subsequent increases or decreases in the allowance reflected in net income each period. The CECL measurement approach for Ambac's affected asset types were not materially different than the approaches under prior GAAP. Refer to the discussion below for each asset type. Premium receivables. For financial guarantee contracts, the issuer's ability and willingness to pay its insured debt obligation impacts the payment of policy losses by Ambac as well as the receipt of premiums from the issuer. As such, management leverages its existing loss reserve estimation process to evaluate credit impairment for premium receivables. Key factors in assessing credit impairment include historical premium collection data, internal risk classifications, credit ratings and loss severities. For structured finance transactions involving special purpose entities, we further evaluate the priority of premiums paid to Ambac within the contractual waterfall, as required by bond indentures. Management utilizes either a discounted cash flow ("DCF") or probability of default/loss given default ("PD/LGD") approach to estimate credit impairment. The DCF approach utilizes expected cash flows developed by Ambac's Risk Management Group using the same (or similar) models used for estimating loss reserves where such models can identify shortfalls in premiums. Credit impairment using the DCF approach is equal to the difference between amortized cost and the present value of expected cash flows. Credit impairment under the PD/LGD approach is the product of (i) the premium receivable carrying value, (ii) internally developed default probability (considering internal ratings and average life), and (iii) internally developed loss severities. Refer to Note 6. Financial Guarantee Insurance Contracts for further credit impairment disclosures. Loans. The key factors in assessing credit impairment for loans are internal credit ratings and loss severities. Management utilizes a PD/LGD approach, similar to the one described above for premium receivables, which is applied to the loan carrying value. Reinsurance recoverables. Ambac has elected the to use the practical expedient of considering the fair value of collateral posted by reinsurers when evaluating credit impairment. To determine the total unsecured recoverable to be evaluated for impairment, Ambac nets the reinsurance recoverable amount by ceded premiums payable and the fair value of collateral posted, if any. The key factors in assessing credit impairment for reinsurance recoverables are independent rating agency credit ratings and loss severities. Management utilizes a PD/LGD approach, similar to the one described above for premium receivables, which is applied to the net unsecured reinsurance recoverable amount. Refer to Note 6. Financial Guarantee Insurance Contracts for further credit impairment disclosures. Fair Value Measurement Disclosures In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820) - Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement . The ASU modified various disclosure requirements on fair value measurements. Relevant disclosures that were removed, modified and added are as follows: • Removals : 1) Amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, 2) Policy for timing of transfers between levels, and 3) Valuation processes for Level 3 fair value measurements. • Modifications : 1) For investments in certain entities that calculate net asset value, disclosures are required for the timing of liquidation of an investee's assets and the date when restrictions from redemption might lapse, only if the investee has communicated the timing to the reporting entity or publicly announced it and 2) Clarification that the measurement uncertainty disclosure is to communicate information about the uncertainty in measurement as of the reporting date and not possible future changes. • Additions : 1) Changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and 2) Range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. Alternatively, an entity may disclose other quantitative information (such as the median or arithmetic average) if it determines that it is a more reasonable and rational method to reflect the distribution of unobservable inputs used. Disclosure amendments related to changes in unrealized gains and losses included in other comprehensive income (loss) for Level 3 instruments, the range and weighted average of significant unobservable inputs, and the narrative description of measurement uncertainty were applied prospectively only for the most recent interim or annual period presented. All other disclosure amendments were applied retrospectively to all periods presented. Refer to Note 7. Fair Value Measurements for further disclosures. VIE Related Party Guidance In October 2018, the FASB issued ASU 2018-17, Consolidation (Topic 810) - Targeted Improvements to Related Party Guidance for Variable Interest Entities. To determine whether a decision- making fee is a variable interest, under the new guidance a reporting entity must consider indirect interests held through related parties under common control on a proportional basis rather than as a direct interest in its entirety (as was previously required under prior GAAP). These amendments create alignment between determining whether a decision making fee is a variable interest and determining whether a reporting entity within a related party group is the primary beneficiary of a VIE. Adoption of this ASU did not impact Ambac's financial statements. Cloud Computing Arrangement Service Contracts In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other— Internal-Use Software (Subtopic 350-40) - Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The new guidance requires a customer in a cloud computing arrangement that is a service contract to capitalize certain implementation costs as if the arrangement was an internal-use software project. The internal-use software guidance requires the capitalization of certain costs incurred only during the application development stage. That guidance also requires entities to expense costs during the preliminary project and post-implementation stages as they are incurred. Adoption of this ASU did not impact Ambac's financial statements. Future Application of Accounting Standards: Reference Rate Reform In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848) - Facilitation of the Effects of Reference Rate Reform on Financial Reporting . The ASU provides companies with optional guidance to ease the potential accounting burden related to transitioning away from reference rates, such as LIBOR, that are expected to be discontinued as a result of initiatives undertaken by various jurisdictions around the world. For example, under current GAAP, contract modifications which change a reference rate are required to be evaluated in determining whether the modifications result in the establishment of new contracts or the continuation of existing contracts. The amendments in this ASU provide optional expedients and exceptions for applying GAAP to contracts, hedging relationships, and other transactions affected by reference rate reform if certain criteria are met. The ASU can be applied prospectively as of the beginning of the interim period that includes March 12, 2020, (January 1, 2020 for calendar year companies) or any date thereafter, but does not apply to contract modifications and other transactions entered into or evaluated after December 31, 2022. Management has not determined if and when it will adopt this ASU, and the impact on Ambac's financial statements is being evaluated.

Comprehensive Income

Comprehensive Income	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Comprehensive Income	4. COMPREHENSIVE INCOME The following tables detail the changes in the balances of each component of accumulated other comprehensive income for the affected periods: Unrealized Gains (1) Amortization of (1) Gain (Loss) on (1) Credit Risk Changes of Fair Value Option Liabilities (1) (2) Total Three Months Ended September 30, 2020: Beginning Balance $ 109 $ 6 $ (164) $ — $ (48) Other comprehensive income (loss) before reclassifications 45 — 29 — 74 Amounts reclassified from accumulated other comprehensive income (loss) (2) — — — (3) Net current period other comprehensive income (loss) 42 — 29 — 71 Balance at September 30, 2020 $ 152 $ 6 $ (135) $ — $ 22 Three Months Ended September 30, 2019: Beginning Balance $ 157 $ 9 $ (145) $ (2) $ 19 Other comprehensive income (loss) before reclassifications 50 — (24) — 26 Amounts reclassified from accumulated other comprehensive income (loss) (18) — — — (19) Net current period other comprehensive income (loss) 31 — (24) — 7 Balance at September 30, 2019 $ 189 $ 9 $ (169) $ (2) $ 26 Unrealized Gains (1) Amortization of (1) Gain (Loss) on (1) Credit Risk Changes of Fair Value Option Liabilities (1) (2) Total Nine Months Ended September 30, 2020: Beginning Balance $ 151 $ 8 $ (116) $ (2) $ 42 Other comprehensive income (loss) before reclassifications 20 (2) (20) — (2) Amounts reclassified from accumulated other comprehensive income (loss) (19) (1) — 2 (18) Net current period other comprehensive income (loss) 1 (3) (20) 2 (20) Balance at September 30, 2020 $ 152 $ 6 $ (135) $ — $ 22 Nine Months Ended September 30, 2019: Beginning Balance $ 86 $ 9 $ (142) $ (2) $ (49) Other comprehensive income before reclassifications 174 1 (28) — 147 Amounts reclassified from accumulated other comprehensive income (71) (1) — — (72) Net current period other comprehensive income $ 103 $ — $ (28) $ — $ 75 Balance at September 30, 2019 $ 189 $ 9 $ (169) $ (2) $ 26 (1) All amounts are net of tax and noncontrolling interest. Amounts in parentheses indicate reductions to Accumulated Other Comprehensive Income. (2) Represents the changes in fair value attributable to instrument-specific credit risk of liabilities for which the fair value option is elected. The following table details the significant amounts reclassified from each component of accumulated other comprehensive income, shown in the above rollforward tables, for the affected periods: Details about Accumulated Amount Reclassified from Accumulated Other Comprehensive Income Affected Line Item in the Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Unrealized Gains (Losses) on Available-for-Sale Securities $ (2) $ (20) $ (20) $ (77) Net realized investment gains (losses) and other-than-temporary impairment losses — 1 1 6 Provision for income taxes $ (2) $ (18) $ (19) $ (71) Net of tax and noncontrolling interest Amortization of Postretirement Benefit Prior service cost $ — $ — $ (1) $ (1) Other income Actuarial (losses) — — — — Other income — — (1) (1) Total before tax — — — — Provision for income taxes $ — $ — $ (1) $ (1) Net of tax and noncontrolling interest Credit risk changes of fair value option liabilities $ — $ — $ 2 $ — Credit Risk Changes of Fair Value Option Liabilities — — — — Provision for income taxes $ — $ — $ 2 $ — Net of tax and noncontrolling interest Total reclassifications for the period $ (3) $ (19) $ (18) $ (72) Net of tax and noncontrolling interest

Net Income Per Share

Net Income Per Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Income Per Share	5. NET INCOME PER SHARE As of September 30, 2020, 45,809,139 shares of Ambac's common stock (par value $0.01) and warrants entitling holders to acquire up to 4,877,749 shares of new common stock at an exercise price of $16.67 per share were issued and outstanding. Common shares outstanding increased by 253,739 during the nine months ended September 30, 2020, primarily due to settlements of employee restricted and performance stock units. Basic net income per share is computed by dividing net income attributable to common stockholders by the weighted-average number of common shares outstanding and vested restricted stock units (together, "Basic Weighted Average Shares Outstanding"). Diluted net income per share is computed by dividing net income attributable to common stockholders by the Basic Weighted Average Shares Outstanding plus all potential dilutive common shares outstanding during the period. All potential dilutive common shares outstanding consider common stock deliverable pursuant to warrants, vested and unvested options, unvested restricted stock units and performance stock units granted under existing compensation plans. The following table provides a reconciliation of the common shares used for basic net income per share to the diluted shares used for diluted net income per share: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Basic weighted average shares outstanding 46,178,730 45,997,694 46,135,399 45,939,284 Effect of potential dilutive shares (1) : Stock options — — — — Warrants — 450,384 — — Restricted stock units — 78,751 — — Performance stock units (2) — 493,229 — — Diluted weighted average shares outstanding 46,178,730 47,020,058 46,135,399 45,939,284 Anti-dilutive shares excluded from the above reconciliation: Stock options 16,667 16,667 16,667 16,667 Warrants 4,877,749 — 4,877,754 4,877,783 Restricted stock units 333,526 — 286,279 249,025 Performance stock units (2) 972,138 — 932,777 748,700 (1) For the three and nine months ended September 30, 2020, and the nine months ended September 30, 2019, Ambac had a net loss and accordingly excluded all potentially dilutive securities from the determination of diluted loss per share as their impact was anti-dilutive. (2) Performance stock units are reflected based on the performance metrics through the balance sheet date. Vesting of these units is contingent upon meeting certain performance metrics. Although a portion of these performance metrics have been achieved as of the respective period end, it is possible that awards may no longer meet the metric at the end of the performance period.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	7. FAIR VALUE MEASUREMENTS The Fair Value Measurement Topic of the ASC establishes a framework for measuring fair value and disclosures about fair value measurements. Fair Value Hierarchy: The Fair Value Measurement Topic of the ASC specifies a fair value hierarchy based on whether the inputs to valuation techniques used to measure fair value are observable or unobservable. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect Company-based assumptions. The fair value hierarchy prioritizes model inputs into three broad levels as follows: l Level 1 Quoted prices for identical instruments in active markets. Assets and liabilities classified as Level 1 include US Treasury and other foreign government obligations traded in highly liquid and transparent markets, certain highly liquid pooled fund investments, exchange traded futures contracts, variable rate demand obligations and money market funds. l Level 2 Quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations in which all significant inputs and significant value drivers are observable in active markets. Assets and liabilities classified as Level 2 generally include investments in fixed income securities representing municipal, asset-backed and corporate obligations, certain interest rate swap contracts and most long-term debt of variable interest entities consolidated under the Consolidation Topic of the ASC. l Level 3 Model derived valuations in which one or more significant inputs or significant value drivers are unobservable. This hierarchy requires the use of observable market data when available. Assets and liabilities classified as Level 3 include credit derivative contracts, certain uncollateralized interest rate swap contracts, equity interests in Ambac sponsored special purpose entities and certain investments in fixed income securities. Additionally, Level 3 assets and liabilities generally include loan receivables, and certain long-term debt of variable interest entities consolidated under the Consolidation Topic of the ASC. The Fair Value Measurement Topic of the ASC permits, as a practical expedient, the estimation of fair value of certain investments in funds using the net asset value per share of the investment or its equivalent (“NAV”). Investments in funds valued using NAV are not categorized as Level 1, 2 or 3 under the fair value hierarchy. The following table sets forth the carrying amount and fair value of Ambac’s financial assets and liabilities as of September 30, 2020 and December 31, 2019, including the level within the fair value hierarchy at which fair value measurements are categorized. As required by the Fair Value Measurement Topic of the ASC, financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Carrying Total Fair Fair Value Measurements Categorized as: September 30, 2020: Level 1 Level 2 Level 3 Financial assets: Fixed income securities: Municipal obligations $ 351 $ 351 $ — $ 351 $ — Corporate obligations 1,091 1,091 2 1,089 — Foreign obligations 77 77 77 — — U.S. government obligations 122 122 122 — — Residential mortgage-backed securities 296 296 — 296 — Collateralized debt obligations 73 73 — 73 — Other asset-backed securities 300 300 — 225 75 Fixed income securities, pledged as collateral: Short-term 152 152 152 — — Short term investments 586 586 509 77 — Other investments (1) 502 488 62 — 35 Cash, cash equivalents and restricted cash 48 48 39 9 — Derivative assets: Interest rate swaps—asset position 95 95 — 9 86 Other assets - equity in sponsored VIE 2 2 — — 2 Other assets-Loans 3 3 — — 3 Variable interest entity assets: Fixed income securities: Corporate obligations 3,029 3,029 — — 3,029 Fixed income securities: Municipal obligations 131 131 — 131 — Restricted cash 2 2 2 — — Loans 2,783 2,783 — — 2,783 Derivative assets: Currency swaps-asset position 53 53 — 53 — Total financial assets $ 9,696 $ 9,682 $ 965 $ 2,312 $ 6,013 Financial liabilities: Long term debt, including accrued interest $ 3,236 $ 3,056 $ — $ 2,679 $ 377 Derivative liabilities: Credit derivatives 1 1 — — 1 Interest rate swaps—liability position 125 125 — 125 — Liabilities for net financial guarantees written (2) (744) 436 — — 436 Variable interest entity liabilities: Long-term debt (includes $4,002 at fair value) 4,169 4,179 — 4,026 153 Derivative liabilities: Interest rate swaps—liability position 1,771 1,771 — 1,771 — Total financial liabilities $ 8,558 $ 9,569 $ — $ 8,601 $ 968 Carrying Total Fair Fair Value Measurements Categorized as: December 31, 2019: Level 1 Level 2 Level 3 Financial assets: Fixed income securities: Municipal obligations $ 215 $ 215 $ — $ 215 $ — Corporate obligations 1,430 1,430 — 1,430 — Foreign obligations 44 44 44 — — U.S. government obligations 156 156 156 — — Residential mortgage-backed securities 248 248 — 248 — Commercial mortgage-backed securities 50 50 — 50 — Collateralized debt obligations 146 146 — 146 — Other asset-backed securities 287 287 — 215 72 Fixed income securities, pledged as collateral: Short-term 85 85 85 — — Short term investments 653 653 598 55 — Other investments (1) 478 493 136 — 61 Cash and cash equivalents and restricted cash 79 79 70 9 — Derivative assets: Interest rate swaps—asset position 75 75 — 8 67 Other assets - equity in sponsored VIE 3 3 — — 3 Other assets-loans 10 13 — — 13 Variable interest entity assets: Fixed income securities: Corporate obligations 2,957 2,957 — — 2,957 Fixed income securities: Municipal obligations 164 164 — 164 — Restricted cash 2 2 2 — — Loans 3,108 3,108 — — 3,108 Derivative assets: Currency swaps—asset position 52 52 — 52 — Total financial assets $ 10,242 $ 10,260 $ 1,091 $ 2,593 $ 6,281 Financial liabilities: Long term debt, including accrued interest $ 3,262 $ 3,274 $ — $ 2,829 $ 445 Derivative liabilities: Interest rate swaps—liability position 89 89 — 89 — Liabilities for net financial guarantees written (2) (863) 284 — — 284 Variable interest entity liabilities: Long-term debt (includes $4,351 at fair value) 4,554 4,567 — 4,408 159 Derivative liabilities: Interest rate swaps—liability position 1,657 1,657 — 1,657 — Total financial liabilities $ 8,699 $ 9,872 $ — $ 8,983 $ 889 (1) Excluded from the fair value measurement categories in the table above are investment funds of $391 and $296 as of September 30, 2020 and December 31, 2019, respectively, which are measured using NAV as a practical expedient. (2) The carrying value of net financial guarantees written includes the following balance sheet items: Premium receivables; Reinsurance recoverable on paid and unpaid losses; Deferred ceded premium; Subrogation recoverable; Insurance intangible asset; Unearned premiums; Loss and loss expense reserves; Ceded premiums payable, premiums taxes payable and other deferred fees recorded in Other liabilities. Determination of Fair Value: When available, Ambac uses quoted active market prices specific to the financial instrument to determine fair value, and classifies such items within Level 1. The determination of fair value for financial instruments categorized in Level 2 or 3 involves judgment due to the complexity of factors contributing to the valuation. Third-party sources from which we obtain independent market quotes also use assumptions, judgments and estimates in determining financial instrument values and different third parties may use different methodologies or provide different values for financial instruments. In addition, the use of internal valuation models may require assumptions about hypothetical or inactive markets. As a result of these factors, the actual trade value of a financial instrument in the market, or exit value of a financial instrument position by Ambac, may be significantly different from its recorded fair value. Ambac’s financial instruments carried at fair value are mainly comprised of investments in fixed income securities, equity interests in pooled investment funds, derivative instruments, certain variable interest entity assets and liabilities and interests in Ambac sponsored special purpose entities. Valuation of financial instruments is performed by Ambac’s finance group using methods approved by senior financial management with consultation from risk management and portfolio managers as appropriate. Preliminary valuation results are discussed with portfolio managers quarterly to assess consistency with market transactions and trends as applicable. Market transactions such as trades or negotiated settlements of similar positions, if any, are reviewed to validate fair value model results. However, many of the financial instruments valued using significant unobservable inputs have very little or no observable market activity. Methods and significant inputs and assumptions used to determine fair values across portfolios are reviewed quarterly by senior financial management. Other valuation control procedures specific to particular portfolios are described further below. Fixed Income Securities: The fair values of fixed income investment securities are based primarily on market prices received from broker quotes or alternative pricing sources. Because many fixed income securities do not trade on a daily basis, pricing sources apply available market information through processes such as matrix pricing to calculate fair value. Such prices generally consider a variety of factors, including recent trades of the same and similar securities. In those cases, the items are classified within Level 2. For those fixed income investments where quotes were not available or cannot be reasonably corroborated, fair values are based on internal valuation models. Key inputs to the internal valuation models generally include maturity date, coupon and yield curves for asset-type and credit rating characteristics that closely match those characteristics of the specific investment securities being valued. Items valued using valuation models are classified according to the lowest level input or value driver that is significant to the valuation. Thus, an item may be classified in Level 3 even though there may be significant inputs that are readily observable. Longer (shorter) expected maturities or higher (lower) yields used in the valuation model will, in isolation, result in decreases (increases) in fair value. Generally, lower credit ratings or longer expected maturities will be accompanied by higher yields used to value a security. At September 30, 2020, approximately 4%, 94% and 2% of the fixed income investment portfolio (excluding variable interest entity investments) was valued using broker quotes, alternative pricing sources and internal valuation models, respectively. At December 31, 2019, approximately 4%, 94% and 2% of the fixed income investment portfolio (excluding variable interest entity investments) was valued using broker quotes, alternative pricing sources and internal valuation models, respectively. Ambac performs various review and validation procedures to quoted and modeled prices for fixed income securities, including price variance analyses, missing and static price reviews, overall valuation analysis by portfolio managers and finance managers and reviews associated with our ongoing impairment analysis. Unusual prices identified through these procedures will be evaluated further against alternative third party quotes (if available), internally modeled prices and/or other relevant data, and the pricing source values will be challenged as necessary. Price challenges generally result in the use of the pricing source’s quote as originally provided or as revised by the source following their internal diligence process. A price challenge may result in a determination by either the pricing source or Ambac management that the pricing source cannot provide a reasonable value for a security or cannot adequately support a quote, in which case Ambac would resort to using either other quotes or internal models. Results of price challenges are reviewed by portfolio managers and finance managers. Information about the valuation inputs for fixed income securities classified as Level 3 is included below: Other asset-backed securities: This security is a subordinated tranche of a re-securitization collateralized by Ambac-insured military housing bonds. The fair value classified as Level 3 was $75 and $72 at September 30, 2020 and December 31, 2019, respectively. Fair value was calculated using a discounted cash flow approach with expected future cash flows discounted using a yield consistent with the security type and rating. Significant inputs for the valuation at September 30, 2020 and December 31, 2019 include the following: September 30, 2020: a. Coupon rate: 5.98% b. Average Life: 15.01 years c. Yield: 11.00% December 31, 2019: a. Coupon rate: 5.97% b. Average Life: 15.58 years c. Yield: 11.75% Other Investments: Other investments primarily relate to investments in pooled investment funds. The fair value of pooled investment funds is determined using dealer quotes or alternative pricing sources when such investments have readily determinable fair values. When fair value is not readily determinable, pooled investment funds are valued using NAV as a practical expedient as permitted under the Fair Value Measurement Topic of the ASC. Refer to Note 8. Investments for additional information about such investments in pooled funds that are reported at fair value using NAV as a practical expedient. Other investments also includes Ambac's equity interest in a non-consolidated VIE created in connection with Ambac's monetization of Ambac Assurance junior surplus notes. This equity interest is carried under the equity method. Fair value for the non-consolidated VIE equity interest is internally calculated using a market approach and is classified as Level 3. Derivative Instruments: Ambac’s derivative instruments primarily comprise interest rate swaps, credit default swaps and exchange traded futures contracts. Fair value is determined based upon market quotes from independent sources, when available. When independent quotes are not available, fair value is determined using valuation models. These valuation models require market-driven inputs, including contractual terms, credit spreads and ratings on underlying referenced obligations, yield curves and tax-exempt interest ratios. The valuation of certain derivative contracts also require the use of data inputs and assumptions that are determined by management and are not readily observable in the market. Under the Fair Value Measurement Topic of the ASC, Ambac is required to consider its own credit risk when measuring the fair value of derivatives and other liabilities. Factors considered in estimating the amount of any Ambac credit valuation adjustment ("CVA") on such contracts include collateral posting provisions, right of set-off with the counterparty, the period of time remaining on the derivative and the pricing of recent terminations. The fair value of credit derivative liabilities was reduced by less than a million dollars at September 30, 2020 and December 31, 2019, respectively, as a result of incorporating an Ambac CVA into the valuation model for these contracts. Interest rate swap liabilities are collateralized and are not adjusted with an Ambac CVA at September 30, 2020 and December 31, 2019. Interest rate swaps that are not centrally cleared are valued using vendor-developed models that incorporate interest rates and yield curves that are observable and regularly quoted. These models provide the net present value of the derivatives based on contractual terms and observable market data. Generally, the need for counterparty (or Ambac) CVAs on interest rate derivatives is mitigated by the existence of collateral posting agreements under which adequate collateral has been posted. Certain of these derivative contracts entered into with financial guarantee customers are not subject to collateral posting agreements. Counterparty credit risk related to such customer derivative assets is included in our determination of their fair value. Ambac's credit derivatives ("CDS") are valued using an internal model that uses traditional financial guarantee CDS pricing to calculate the fair value of the derivative contract based on the reference obligation's current pricing, remaining life and credit rating and Ambac's own credit risk. The model calculates the difference between the present value of the projected fees receivable under the CDS and our estimate of the fees a financial guarantor of comparable credit quality would charge to provide the same protection at the balance sheet date. Unobservable inputs used include Ambac's internal reference obligation credit ratings and expected life, estimates of fees that would be charged to assume the credit derivative obligation and Ambac's CVA. Ambac is party to only one remaining credit derivative with internal credit rating of AA at September 30, 2020. Ambac has not made any significant changes to its modeling techniques or related model inputs for the periods presented. Financial Guarantees: Fair value of net financial guarantees written represents our estimate of the cost to Ambac to completely transfer its insurance obligation to another market participant of comparable credit worthiness. In theory, this amount should be the same amount that another market participant of comparable credit worthiness would hypothetically charge in the market place, on a present value basis, to provide the same protection as of the balance sheet date. This fair value estimate of financial guarantees is presented on a net basis and includes direct and assumed contracts written, net of ceded reinsurance contracts. Long-term Debt: Long-term debt includes Ambac Assurance surplus notes and junior surplus notes, the Ambac Note and Tier 2 Notes issued in connection with the Rehabilitation Exit Transactions and the Ambac UK debt issued in connection with the Ballantyne commutation. The fair values of surplus notes, the Ambac Note and Tier 2 Notes are classified as Level 2. The fair value of junior surplus notes and Ambac UK debt are classified as Level 3. Other Financial Assets and Liabilities: Included in Other assets are Loans and Ambac’s equity interest in an Ambac sponsored VIE established to provide certain financial guarantee clients with funding for their debt obligations. The fair values of these financial assets are estimated based upon internal valuation models and are classified as Level 3. Variable Interest Entity Assets and Liabilities: The financial assets and liabilities of FG VIEs consolidated under the Consolidation Topic of the ASC consist primarily of fixed income securities and loans held by the VIEs, derivative instruments and notes issued by the VIEs which are reported as long-term debt. As described in Note 3. Variable Interest Entities , these FG VIEs are securitization entities which have liabilities and/or assets guaranteed by Ambac Assurance or Ambac UK. The fair values of FG VIE long-term debt are based on price quotes received from independent market sources when available. Such quotes are considered Level 2 and generally consider a variety of factors, including recent trades of the same and similar securities. For those instruments where quotes were not available or cannot be reasonably corroborated, fair values are based on internal valuation models. Comparable to the sensitivities of investments in fixed income securities described above, longer (shorter) expected maturities or higher (lower) yields used in the valuation model will, in isolation, result in decreases (increases) in fair value liability measurement for FG VIE long-term debt. FG VIE derivative asset and liability fair values are determined using vendor-developed valuation models, which incorporate observable market data related to specific derivative contractual terms including interest rates, foreign exchange rates and yield curves. The fair value of FG VIE fixed income securities and loan assets are based on Level 2 market price quotes received from independent market sources when available. Typically, FG VIE asset fair values are not readily available from market quotes and are estimated internally. Internal valuation of each FG VIE’s fixed income securities or loan assets are derived from the fair values of the notes issued by the respective VIE and the VIE’s derivatives, determined as described above, adjusted for the fair values of Ambac’s financial guarantees associated with the VIE. The fair value of financial guarantees consist of: (i) estimated future premium cash flows discounted at a rate consistent with that implicit in the fair value of the VIE’s liabilities and (ii) estimates of future claim payments discounted at a rate that includes Ambac’s own credit risk. Estimated future premium payments to be paid by the VIEs were discounted at a par-weighted average rate of 3.3% and 2.7% at September 30, 2020 and December 31, 2019, respectively. At September 30, 2020, the range of these discount rates was between 2.1% and 5.5%. Additional Fair Value Information for Financial Assets and Liabilities Accounted for at Fair Value: The following tables present the changes in the Level 3 fair value category for the periods presented in 2020 and 2019. Ambac classifies financial instruments in Level 3 of the fair value hierarchy when there is reliance on at least one significant unobservable input to the valuation model. In addition to these unobservable inputs, the valuation models for Level 3 financial instruments typically also rely on a number of inputs that are readily observable either directly or indirectly. Thus, the gains and losses presented below include changes in the fair value related to both observable and unobservable inputs. Level 3 - Financial Assets and Liabilities Accounted for at Fair Value VIE Assets and Liabilities Investments Other (1) Derivatives Investments Loans Long-term Total Three Months Ended September 30, 2020: Balance, beginning of period $ 66 $ 2 $ 86 $ 2,907 $ 2,787 $ — $ 5,848 Total gains/(losses) realized and unrealized: Included in earnings — — 1 1 (43) — (40) Included in other comprehensive income 9 — — 121 116 — 246 Purchases — — — — — — — Issuances — — — — — — — Sales — — — — — — — Settlements — — (2) — (78) — (80) Balance, end of period $ 75 $ 2 $ 85 $ 3,029 $ 2,783 $ — $ 5,974 The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ — $ — $ 1 $ 1 $ (43) $ — $ (41) The amount of total gains/(losses) included in other comprehensive income attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ 9 $ — $ — $ 121 $ 116 $ — $ 246 Three Months Ended September 30, 2019: Balance, beginning of period $ 74 $ 4 $ 62 $ 2,882 $ 4,289 $ (231) $ 7,080 Total gains/(losses) realized and unrealized: Included in earnings 1 — 12 206 127 — 345 Included in other comprehensive income 5 — — (92) (133) 7 (213) Purchases — — — — — — — Issuances — — — — — — — Sales — — — — — — — Settlements — — (1) — (466) — (467) Deconsolidation of VIEs — — — — (851) 223 (627) Balance, end of period $ 79 $ 3 $ 73 $ 2,996 $ 2,966 $ — $ 6,117 The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ — $ — $ 12 $ 206 $ 115 $ — $ 332 (1) Other assets carried at fair value and classified as Level 3 relate to an equity interest in an Ambac sponsored VIE. Level 3 - Financial Assets and Liabilities Accounted for at Fair Value VIE Assets and Liabilities Investments Other Derivatives Investments Loans Long-term Total Nine Months Ended September 30, 2020: Balance, beginning of period $ 72 $ 3 $ 66 $ 2,957 $ 3,108 $ — $ 6,207 Total gains/(losses) realized and unrealized: Included in earnings 1 (1) 24 160 (22) — 161 Included in other comprehensive income 3 — — (71) (85) — (152) Purchases — — — — — — — Issuances — — — — — — — Sales — — — — — — — Settlements (1) — (5) (17) (219) — (242) Balance, end of period $ 75 $ 2 $ 85 $ 3,029 $ 2,783 $ — $ 5,974 The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ — $ (1) $ 23 $ 160 $ (22) $ — $ 160 The amount of total gains/(losses) included in other comprehensive income attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ 3 $ — $ — $ (71) $ (85) $ — $ (152) Nine Months Ended September 30, 2019: Balance, beginning of period $ 72 $ 5 $ 46 $ 2,737 $ 4,288 $ (217) $ 6,930 Total gains/(losses) realized and unrealized: Included in earnings 1 (1) 30 382 301 (15) 698 Included in other comprehensive income 7 — — (106) (151) 8 (241) Purchases — — — — — — — Issuances — — — — — — — Sales — — — — — — — Settlements (1) — (3) (17) (621) — (643) Deconsolidation of VIEs — — — — (851) 223 (627) Balance, end of period $ 79 $ 3 $ 73 $ 2,996 $ 2,966 $ — $ 6,117 The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ — $ (1) $ 30 $ 382 $ 229 $ — $ 639 The tables below provide roll-forward information by class of derivatives measured using significant unobservable inputs. Level 3 - Derivatives by Class Three Months Ended September 30, 2020 Three Months Ended September 30, 2019 Interest Credit Total Interest Credit Total Balance, beginning of period $ 87 $ (1) $ 86 $ 63 $ (1) $ 62 Total gains/(losses) realized and unrealized: Included in earnings 1 — 1 11 1 12 Included in other comprehensive income — — — — — — Purchases — — — — — — Issuances — — — — — — Sales — — — — — — Settlements (2) — (2) (1) — (1) Balance, end of period $ 86 $ (1) $ 85 $ 73 $ — $ 73 The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ 1 $ — $ 1 $ 11 $ — $ 12 Level 3 - Derivatives by Class Nine Months Ended September 30, 2020 Nine Months Ended September 30, 2019 Interest Credit Total Interest Credit Total Balance, beginning of period $ 67 $ — $ 66 $ 47 $ (1) $ 46 Total gains/(losses) realized and unrealized: Included in earnings 24 (1) 24 29 1 30 Included in other comprehensive income — — — — — — Purchases — — — — — — Issuances — — — — — — Sales — — — — — — Settlements (5) — (5) (3) — (3) Balance, end of period $ 86 $ (1) $ 85 $ 73 $ — $ 73 The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ 24 $ (1) $ 23 $ 29 $ 1 $ 30 Invested assets and VIE long-term debt are transferred into Level 3 when internal valuation models that include significant unobservable inputs are used to estimate fair value. All such securities that have internally modeled fair values have been classified as Level 3. Derivative instruments are transferred into Level 3 when the use of unobservable inputs becomes significant to the overall valuation. There were no transfers of financial instruments into or out of Level 3 in the periods disclosed. Gains and losses (realized and unrealized) relating to Level 3 assets and liabilities included in earnings for the affected periods are reported as follows: Net Net Gains Income Other Three Months Ended September 30, 2020: Total gains or losses included in earnings for the period $ — $ 1 $ (41) $ — Changes in unrealized gains or losses included in earnings relating to the assets and liabilities still held at the reporting date — 1 (41) — Three Months Ended September 30, 2019: Total gains or losses included in earnings for the period $ 1 $ 12 $ 333 $ — Changes in unrealized gains or losses included in earnings relating to the assets and liabilities still held at the reporting date — 12 321 — Nine Months Ended September 30, 2020: Total gains or losses included in earnings for the period $ 1 $ 24 $ 137 $ (1) Changes in unrealized gains or losses included in earnings relating to the assets and liabilities still held at the reporting date — 23 137 (1) Nine Months Ended September 30, 2019: Total gains or losses included in earnings for the period 1 30 668 (1) Changes in unrealized gains or losses included in earnings relating to the assets and liabilities still held at the reporting date — 30 611 (1)

Investments

Investments	9 Months Ended
	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Investments	8. INVESTMENTS Ambac’s non-VIE invested assets are primarily comprised of fixed income securities classified as available-for-sale and interests in pooled investment funds, which are reported within Other investments on the Consolidated Balance Sheets. Interests in pooled investment funds in the form of common stock or in-substance common stock are classified as trading securities, while limited partner interests in such funds are reported using the equity method. Other investments also include equity interests held by AFG, including in an unconsolidated trust created in connection with its sale of Segregated Account junior surplus notes on August 28, 2014. Disclosures in this Note for the period ended September 30, 2020, are in accordance with the new CECL standard adopted January 1, 2020, which is more fully described in Note 2, Basis of Presentation and Significant Accounting Policies . To the extent disclosures for periods prior to January 1, 2020, made in accordance with prior GAAP rules differ from disclosures under the new CECL standard, such differences are explained below. Fixed Income Securities: The amortized cost and estimated fair value of available-for-sale investments, excluding VIE investments, at September 30, 2020 and December 31, 2019, were as follows: Amortized Allowance for Credit Losses Gross Gross Estimated September 30, 2020: Fixed income securities: Municipal obligations $ 322 $ — $ 29 $ 1 $ 351 Corporate obligations (1) 1,066 — 28 3 1,091 Foreign obligations 76 — 1 — 77 U.S. government obligations 118 — 4 1 122 Residential mortgage-backed securities 251 — 45 — 296 Collateralized debt obligations 74 — — 1 73 Other asset-backed securities 268 — 33 1 300 2,176 — 140 6 2,311 Short-term 586 — — — 586 2,761 — 141 6 2,896 Fixed income securities pledged as collateral: Short-term 152 — — — 152 Total collateralized investments 152 — — — 152 Total available-for-sale investments $ 2,914 $ — $ 141 $ 6 $ 3,048 Amortized Gross Gross Estimated Non-credit (2) December 31, 2019: Fixed income securities: Municipal obligations $ 194 $ 22 $ — $ 215 $ — Corporate obligations (1) 1,396 36 2 1,430 — Foreign obligations 44 1 — 44 — U.S. government obligations 157 2 2 156 — Residential mortgage-backed securities 200 47 — 248 — Commercial mortgage-backed securities 49 1 — 50 — Collateralized debt obligations 147 — 1 146 — Other asset-backed securities 263 24 — 287 — 2,450 132 5 2,577 — Short-term 653 — — 653 — 3,103 132 5 3,230 — Fixed income securities pledged as collateral: Short-term 85 — — 85 — Total collateralized investments 85 — — 85 — Total available-for-sale investments $ 3,187 $ 132 $ 5 $ 3,314 $ — (1) Includes Ambac's holdings of the secured notes issued by Ambac LSNI in connection with the Rehabilitation Exit Transactions. (2) At December 31, 2019, represents the amount of non-credit other-than-temporary impairment losses remaining in accumulated other comprehensive income on securities that also had a credit impairment. These losses are included in gross unrealized losses at December 31, 2019. The amortized cost and estimated fair value of available-for-sale investments, excluding VIE investments, at September 30, 2020, by contractual maturity, were as follows: Amortized Estimated Due in one year or less $ 830 $ 832 Due after one year through five years 876 888 Due after five years through ten years 432 453 Due after ten years 182 206 2,320 2,379 Residential mortgage-backed securities 251 296 Collateralized debt obligations 74 73 Other asset-backed securities 268 300 Total $ 2,914 $ 3,048 Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay certain obligations with or without call or prepayment penalties. Unrealized Losses on Fixed Income Securities: The following table shows gross unrealized losses and fair values of Ambac’s available-for-sale investments, excluding VIE investments, which at September 30, 2020, did not have an allowance for credit losses under the new CECL standard and, at December 31, 2019, did not have other-than-temporary impairments recorded in earnings under prior GAAP. This information is aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position, at September 30, 2020 and December 31, 2019: Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross September 30, 2020: Fixed income securities: Municipal obligations $ 64 $ 1 $ 6 $ — $ 70 $ 1 Corporate obligations 179 3 — — 179 3 Foreign obligations 12 — — — 12 — U.S. government obligations 11 1 — — 11 1 Residential mortgage-backed securities 19 — — — 19 — Collateralized debt obligations 53 1 15 — 67 1 Other asset-backed securities 1 — 4 1 5 1 338 5 25 1 363 6 Short-term 152 — — — 152 — Total securities $ 490 $ 5 $ 25 $ 1 $ 515 $ 6 Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross December 31, 2019: Fixed income securities: Municipal obligations $ 13 $ — $ 10 $ — $ 23 $ — Corporate obligations 63 2 5 — 68 2 Foreign obligations 20 — — — 20 — U.S. government obligations 36 2 2 — 38 2 Residential mortgage-backed securities 5 — — — 5 — Commercial mortgage-backed securities 7 — — — 7 — Collateralized debt obligations 53 — 63 1 116 1 Other asset-backed securities 2 — 7 — 10 — 200 4 88 1 288 5 Short-term 201 — — — 201 — Total securities $ 401 $ 4 $ 88 $ 1 $ 489 $ 5 Management has determined that the securities in the above table do not have credit impairment as of September 30, 2020 and December 31, 2019, based upon various factors, including (i) no actual or expected principal and interest payment defaults on these securities; (ii) analysis of the creditworthiness of the issuer and financial guarantor, as applicable, and (iii) for debt securities that are non-highly rated beneficial interests in securitized financial assets, analysis of whether there was an adverse change in projected cash flows. Management's evaluation as of September 30, 2020, includes the expectation that all principal and interest payments on securities guaranteed by Ambac Assurance or Ambac UK will be made timely and in full. Ambac’s assessment about whether a decline in value is other-than-temporary reflects management’s current judgment regarding facts and circumstances specific to a security and other factors. If that judgment changes, Ambac may record a charge for credit impairment in future periods. Realized Gains and Losses including Impairments: The following table details amounts included in net realized gains (losses) and impairments included in earnings for the affected periods: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Gross realized gains on securities $ 5 $ 12 $ 32 $ 46 Gross realized losses on securities (1) — (12) (5) Net foreign exchange (losses) gains (2) 7 — 30 Credit impairments (1) — — — — Intent / requirement to sell impairments (2) — — — — Net realized gains (losses) $ 2 $ 18 $ 20 $ 71 (1) Includes securities which management does not intend to sell and it is not more likely than not that the Company will be required to sell before recovery of the amortized cost basis. (2) Includes securities which management either intends sell or it is more likely than not that the Company will be required to sell before recovery of the amortized cost basis. The following table presents a roll-forward of Ambac’s cumulative credit losses on debt securities for which a portion of an other-than-temporary impairment was recognized in other comprehensive income under prior GAAP for the nine months ended September 30, 2019: Balance, beginning of period $ 12 Reductions for credit impairments previously recognized on: Securities that matured or were sold during the period (1) Balance, end of period $ 12 Ambac had zero allowance for credit losses at September 30, 2020. Ambac did not purchase any financial assets with credit deterioration for the nine months ended September 30, 2020. Counterparty Collateral, Deposits with Regulators and Other Restrictions: Ambac routinely pledges and receives collateral related to certain transactions. Securities held directly in Ambac’s investment portfolio with a fair value of $152 and $85 at September 30, 2020 and December 31, 2019, respectively, were pledged to derivative counterparties. Ambac’s derivative counterparties have the right to re-pledge the investment securities and as such, these pledged securities are separately classified on the Consolidated Balance Sheets as “Fixed income securities pledged as collateral, at fair value”. Refer to Note 9. Derivative Instruments for further information on cash collateral. There were no securities received from other counterparties that were re-pledged by Ambac. Securities carried at $7 and $6 at September 30, 2020 and December 31, 2019, respectively, were deposited by Ambac Assurance and Everspan with governmental authorities or designated custodian banks as required by laws affecting insurance companies. Invested assets carried at $1 at September 30, 2020 and December 31, 2019, were deposited as security in connection with a letter of credit issued for an office lease. Securities with a fair value of $181 and $197 at September 30, 2020 and December 31, 2019, respectively, were pledged as collateral and as sources of funding to repay the Secured Notes issued by Ambac LSNI. The securities may not be transferred or repledged by Ambac LSNI. Collateral may be sold to fund redemptions of the Secured Notes. Ambac Assurance also pledged for the benefit of the holders of Secured Notes (other than Ambac Assurance) the proceeds of interest payments and partial redemptions of the Secured Notes held by Ambac Assurance. The amount of such proceeds held by Ambac Assurance was $10 and $55 at September 30, 2020 and December 31, 2019, respectively, and is included in Restricted cash on the Consolidated Balance Sheet. Ambac Assurance may, from time to time, sell all or a portion of the Secured Notes it owns. In the event that Ambac Assurance sells any of the Secured Notes it owns, the proceeds must be used to redeem a like amount of the Ambac Note at par. The price at which Ambac Assurance sells the Secured Notes may differ from the price at which it redeems the Secured Notes. Guaranteed Securities: Ambac’s fixed income portfolio includes securities covered by guarantees issued by Ambac Assurance and other financial guarantors (“insured securities”). The published rating agency ratings on these securities reflect the higher of the financial strength rating of the financial guarantor or the rating of the underlying issuer. Rating agencies do not always publish separate underlying ratings (those ratings excluding the insurance by the financial guarantor). In the event these underlying ratings are not available from the rating agencies, Ambac will assign an internal rating. The following table represents the fair value and weighted-average underlying rating of insured securities in Ambac's investment portfolio at September 30, 2020 and December 31, 2019, respectively: Municipal Corporate (2) Mortgage Total Weighted (1) September 30, 2020: Ambac Assurance Corporation $ 310 $ 470 $ 473 $ 1,253 CCC+ National Public Finance Guarantee Corporation 6 — — 6 BBB- Assured Guaranty Municipal Corporation 1 — — 1 C Total $ 318 $ 470 $ 473 $ 1,260 CCC+ December 31, 2019: Ambac Assurance Corporation $ 176 $ 535 $ 442 $ 1,153 B- National Public Finance Guarantee Corporation 11 — — 11 BBB- Total $ 186 $ 535 $ 442 $ 1,164 B- (1) Ratings are based on the lower of Standard & Poor’s or Moody’s rating. If unavailable, Ambac’s internal rating is used. (2) Represents Ambac's holdings of secured notes issued by Ambac LSNI in connection with the Rehabilitation Exit Transactions. These secured notes are insured by Ambac Assurance. Other Investments: Ambac's investment portfolio includes interests in various pooled investment funds. Fair value and additional information about investments in pooled funds, by investment type, is summarized in the table below. Except as noted in the table, fair value as reported is determined using net asset value ("NAV") as a practical expedient. In addition to these investments, Ambac has unfunded commitments of $48 to private credit and private equity funds at September 30, 2020. Fair Value Class of Funds September 30, December 31, Redemption Frequency Redemption Notice Period Real estate properties (1) $ 15 $ 16 quarterly 10 business days Hedge funds (2) 182 65 quarterly 90 days High yields and leveraged loans (3) (10) 53 176 daily 0 - 30 days Private credit (4) 57 51 quarterly 180 days if permitted Insurance-linked investments (5) 2 3 fully redeemed none Equity market investments (6) (10) 33 55 daily 0 days Investment grade floating rate income (7) 69 66 weekly 0 days Private equity (8) 16 — quarterly 90 days if permitted Emerging markets debt (9) (10) 23 — daily 0 days Total equity investments in pooled funds $ 451 $ 432 (1) Investments consist of UK property to generate income and capital growth. (2) This class seeks to generate superior risk-adjusted returns through selective asset sourcing, active trading and hedging strategies across a range of asset types. (3) This class of funds includes investments in a range of instruments including high-yield bonds, leveraged loans, CLOs, ABS and floating rate notes to generate income and capital appreciation. (4) This class aims to obtain high long-term return primarily through credit and preferred equity investments with low liquidity and defined term. (5) This class seeks to generate returns from insurance markets through investments in catastrophe bonds, life insurance and other insurance linked investments. (6) This class of funds aim to achieve long term growth through diversified exposure to global equity markets. (7) This class of funds includes investments in high quality floating rate debt securities including ABS and corporate floating rate notes as well as ultra-short term bonds and money market instruments. (8) This class seeks to generate long-term capital appreciation through investments in private equity, equity-related and other instruments. (9) This class seeks long-term income and growth through investments in the bonds of issuers in emerging markets. (10) These categories include fair value amounts totaling $60 and $136 at September 30, 2020 and December 31, 2019, respectively, that are readily determinable and are priced through pricing vendors, including for High yield and leveraged loans products: $3 and $81; for Equity market investments: $33 and $55; and for Emerging markets debt $23 and $0 Ambac also holds direct equity interests, including in an unconsolidated trust created in connection with the 2014 sale of Segregated Account junior surplus notes, which is accounted for under the equity method. Investment Income (loss): Net investment income (loss) was comprised of the following for the affected periods: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Fixed income securities $ 24 $ 33 $ 79 $ 151 Short-term investments 1 4 4 14 Loans — — — 1 Investment expense (1) (1) (4) (4) Securities available-for-sale and short-term 24 36 80 161 Other investments 14 8 (11) 25 Total net investment income (loss) $ 37 $ 45 $ 69 $ 186 Net investment income (loss) from Other investments primarily represents changes in fair value on securities classified as trading or accounted for under the fair value option, income from investment limited partnerships accounted for under the equity method and the above noted equity interest in an unconsolidated trust accounted for under the equity method. The portion of net unrealized gains (losses) related to trading securities still held at the end of each period is as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Net gains (losses) recognized during the period on trading securities $ 3 $ 6 $ (12) $ 19 Less: net gains (losses) recognized during the reporting period on trading securities sold during the period — 2 (19) 4 Unrealized gains (losses) recognized during the reporting period on trading securities still held at the reporting date $ 3 $ 4 $ 7 $ 15

Derivative Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	9. DERIVATIVE INSTRUMENTS The following tables summarize the gross fair values of individual derivative instruments and the impact of legal rights of offset as reported in the Consolidated Balance Sheets as of September 30, 2020 and December 31, 2019: Gross Gross Net Amounts Gross Amount Net September 30, 2020: Derivative Assets: Interest rate swaps $ 95 $ — $ 94 $ — $ 94 Total non-VIE derivative assets $ 95 $ — $ 95 $ — $ 95 Derivative Liabilities: Credit derivatives $ 1 $ — $ 1 $ — $ 1 Interest rate swaps 125 — 125 124 1 Total non-VIE derivative liabilities $ 126 $ — $ 126 $ 124 $ 2 Variable Interest Entities Derivative Assets: Currency swaps $ 53 $ — $ 53 $ — $ 53 Total VIE derivative assets $ 53 $ — $ 53 $ — $ 53 Variable Interest Entities Derivative Liabilities: Interest rate swaps $ 1,771 $ — $ 1,771 $ — $ 1,771 Total VIE derivative liabilities $ 1,771 $ — $ 1,771 $ — $ 1,771 December 31, 2019: Derivative Assets: Interest rate swaps $ 75 $ — $ 75 $ — $ 75 Total non-VIE derivative assets $ 75 $ — $ 75 $ — $ 75 Derivative Liabilities: Interest rate swaps 89 — 90 89 1 Total non-VIE derivative liabilities $ 90 $ — $ 90 $ 89 $ 1 Variable Interest Entities Derivative Assets: Currency swaps $ 52 $ — $ 52 $ — $ 52 Total VIE derivative assets $ 52 $ — $ 52 $ — $ 52 Variable Interest Entities Derivative Liabilities: Interest rate swaps $ 1,657 $ — $ 1,657 $ — $ 1,657 Total VIE derivative liabilities $ 1,657 $ — $ 1,657 $ — $ 1,657 Amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral are not offset against fair value amounts recognized for derivative instruments on the Unaudited Consolidated Balance Sheets. The amounts representing the right to reclaim cash collateral and posted margin, recorded in “Other assets” were $1 and $36 as of September 30, 2020 and December 31, 2019, respectively. There were no amounts held representing an obligation to return cash collateral as of September 30, 2020 and December 31, 2019. The following tables summarize the location and amount of gains and losses of derivative contracts in the Unaudited Consolidated Statements of Total Comprehensive Income (Loss) for the three and nine months ended September 30, 2020 and 2019: Location of Gain or (Loss) Amount of Gain or (Loss) Recognized in Consolidated Statement of Total Comprehensive Income (Loss) Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Non-VIE derivatives: Credit derivatives Net gains (losses) on derivative contracts $ — $ 1 $ (1) $ 1 Interest rate swaps Net gains (losses) on derivative contracts 7 (1) (20) (11) Futures contracts Net gains (losses) on derivative contracts — (10) (41) (52) Total Non-VIE derivatives $ 7 $ (10) (61) (61) Variable Interest Entities: Currency swaps Income (loss) on variable interest entities $ (10) $ 10 7 6 Interest rate swaps Income (loss) on variable interest entities (4) (166) (177) (272) Total Variable Interest Entities (14) (156) (170) (266) Total derivative contracts $ (7) $ (166) $ (231) $ (327) Credit Derivatives: Credit derivatives, which are privately negotiated contracts, provide the counterparty with credit protection against the occurrence of a specific event such as a payment default or bankruptcy relating to an underlying obligation. Credit derivatives issued are insured by Ambac Assurance. The outstanding credit derivative transaction at September 30, 2020, does not include ratings based collateral-posting triggers or otherwise require Ambac to post collateral regardless of Ambac’s ratings or the size of the mark to market exposure to Ambac. Our credit derivatives were written on a “pay-as-you-go” basis. Similar to an insurance policy, pay-as-you-go provides that Ambac pays interest shortfalls on the referenced transaction as they are incurred on each scheduled payment date, but only pays principal shortfalls upon the earlier of (i) the date on which the assets designated to fund the referenced obligation have been disposed of and (ii) the legal final maturity date of the referenced obligation. Ambac maintains internal credit ratings on its guaranteed obligations, including credit derivative contracts, solely to indicate management’s view of the underlying credit quality of the guaranteed obligations. The gross principal notional outstanding for credit derivative contracts was $293 and $280 as of September 30, 2020 and December 31, 2019, respectively, all of which had internal Ambac ratings of AA in both periods. Interest Rate Derivatives: Ambac, through its subsidiary Ambac Financial Services (“AFS”), uses interest rate swaps, US Treasury futures contracts and other derivatives, to provide a partial economic hedge against the effects of rising interest rates elsewhere in the Company, including on Ambac’s financial guarantee exposures. Additionally, AFS provided interest rate swaps to states, municipalities and their authorities, asset-backed issuers and other entities in connection with their financings. As of September 30, 2020 and December 31, 2019, the notional amounts of AFS’s derivatives were as follows: Notional Type of Derivative September 30, December 31, Interest rate swaps—receive-fixed/pay-variable $ 240 $ 332 Interest rate swaps—pay-fixed/receive-variable 726 1,261 US Treasury futures contracts—short 240 755 Derivatives of Consolidated Variable Interest Entities Certain VIEs consolidated under the Consolidation Topic of the ASC entered into derivative contracts to meet specified purposes within the securitization structure. The notional for VIE derivatives outstanding as of September 30, 2020 and December 31, 2019, were as follows: Notional Type of VIE Derivative September 30, December 31, Interest rate swaps—receive-fixed/pay-variable $ 1,164 $ 1,194 Interest rate swaps—pay-fixed/receive-variable 1,103 1,176 Currency swaps 298 329 Credit derivatives — 9 Contingent Features in Derivatives Related to Ambac Credit Risk Ambac’s over-the-counter interest rate swaps are centrally cleared when eligible. Certain interest rate swaps remain with professional swap-dealer counterparties and direct customer counterparties. These non-cleared swaps are generally executed under standardized derivative documents including collateral support and master netting agreements. Under these agreements, Ambac is required to post collateral in the event net unrealized losses exceed predetermined threshold levels. Additionally, given that Ambac Assurance is no longer rated by an independent rating agency, counterparties have the right to terminate the swap positions. As of September 30, 2020 and December 31, 2019, the net liability fair value of derivative instruments with contingent features linked to Ambac’s own credit risk was $124 and $89, respectively, related to which Ambac had posted cash and securities as collateral with a fair value of $144 and $109, respectively. All such ratings-based contingent features have been triggered requiring maximum collateral levels to be posted by Ambac while preserving counterparties’ rights to terminate the contracts. Assuming all such contracts terminated on September 30, 2020, settlement of collateral balances and net derivative liabilities would result in a net receipt of cash and/or securities by Ambac. If counterparties elect to exercise their right to terminate, the actual termination payment amounts will be determined in accordance with derivative contract terms, which may result in amounts that differ from market values as reported in Ambac’s financial statements.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	10. INCOME TAXES AFG files a consolidated Federal income tax return with its subsidiaries. AFG and its subsidiaries also file separate or combined income tax returns in various states, local and foreign jurisdictions. The following are the major jurisdictions in which Ambac and its subsidiaries operate and the earliest tax years subject to examination: Jurisdiction Tax Year United States 2010 New York State 2013 New York City 2016 United Kingdom 2016 Italy 2015 In accordance with the Income Tax Topic of the ASC, a valuation allowance is recognized if, based on the weight of available evidence, it is more-likely-than-not that some, or all, of the deferred tax asset will not be realized. As a result of the risks and uncertainties associated with future operating results, management believes it is more likely than not that the Company will not generate sufficient U.S. federal, state and/or local taxable income to recover the deferred tax operating assets and therefore maintains a full valuation allowance. Consolidated Pretax Income (Loss) U.S. and foreign components of pre-tax income (loss) were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 U.S. $ (106) $ 60 $ (412) $ (61) Foreign (2) 9 (15) (11) Total $ (108) $ 69 $ (427) $ (72) Provision (Benefit) for Income Taxes The components of the provision for income taxes were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Current taxes U. S. federal $ — $ — $ — $ — U.S. state and local — — — (3) Foreign (1) 4 — 38 Current taxes (1) 4 1 35 Deferred taxes Foreign 1 (1) (5) (2) Deferred taxes 1 (1) (5) (2) Provision for income taxes $ — $ 3 $ (5) $ 33 NOL Usage Pursuant to an intercompany tax sharing agreement, to the extent Ambac Assurance generates taxable income after September 30, 2011, which is offset with "Allocated NOLs" of $3,650, it is obligated to make payments (“Tolling Payments”), subject to certain credits, to AFG in accordance with the following NOL usage table, where the “Applicable Percentage” is applied to the aggregate amount of federal income tax liability that would have been paid if the Allocated NOLs were not available. Pursuant to the Closing Agreement between Ambac and the Internal Revenue Service ("IRS"), the IRS will receive 12.5% of Tier C and 17.5% of Tier D payments, if made. NOL Usage Table NOL Usage Tier Allocated NOLs Applicable A The first $479 15% B The next $1,057 after Tier A 40% C The next $1,057 after Tier B 10% D The next $1,057 after Tier C 15% As of December 31, 2018, Ambac Assurance generated cumulative taxable income of $1,508, leaving $2,142 of the $3,650 Allocated NOLs subject to Tolling Payments. For the year ended December 31, 2019, and nine months ended September 30, 2020, Ambac Assurance generated NOLs of approximately $143 and $197, respectively, which will need to be utilized before any new Tolling Payments will be generated. If not utilized, the NOLs will begin expiring in 2029, and will fully expire in 2040, with the exception of the tax loss generated during the nine months ended September 30, 2020, of approximately $196, which if Ambac remains in a loss position at year end 2020, will expire in 2041. As a result of positive income at Ambac Assurance in 2017, Ambac accrued $28 of tax tolling payments. In May 2018, AFG executed a waiver under the intercompany tax sharing agreement pursuant to which Ambac Assurance was relieved of the requirement to make the 2017 tax tolling payment by June 1, 2018. AFG also agreed to continue to defer receipt of the 2017 tax tolling payment from Ambac Assurance until such time as OCI consents to the payment. OCI has indicated that it will consider a number of factors, including asset quality and loss and reserve trends when considering whether or not to consent to the 2017 tax tolling payment. We can provide no assurance as to whether, or when, OCI will consent to the 2017 tax tolling payment. Ambac's tax positions are subject to review by the OCI, which may lead to the adoption of positions that reduce the amount of tolling payments otherwise available to Ambac. As of September 30, 2020, the remaining balance of the $3,650 NOL allocated to Ambac Assurance, and new NOLs accrued during 2019 and 2020, totaled approximately $2,482. As of September 30, 2020, the consolidated group's NOL was approximately $3,731, of which Ambac's NOL was approximately $1,249.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. COMMITMENTS AND CONTINGENCIES The following commitments and contingencies provide an update of those discussed in Note 17: Commitments and Contingencies in the Notes to Consolidated Financial Statements included Part II, Item 8 in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019, and should be read in conjunction with the complete descriptions provided in the aforementioned Form 10-K. Litigation Against Ambac Financial Oversight and Management Board for Puerto Rico, et al. v. Autonomy Master Fund Limited, et al. (United States District Court, District of Puerto Rico, No. 19-ap-00291, filed May 2, 2019). On May 2, 2019, the Financial Oversight and Management Board for Puerto Rico (the "Oversight Board"), together with the Official Committee of Unsecured Creditors for the Commonwealth (the "Committee") filed an adversary proceeding against certain parties that filed proofs of claim on account of general obligation bonds issued by the Commonwealth of Puerto Rico, including Ambac Assurance. The complaint seeks declarations that the general obligation bonds are unsecured obligations and, in the alternative, seeks to avoid any security interests that holders of such bonds may have. On June 12, 2019, a group of general obligation bondholders moved to dismiss the complaint. On June 13, 2019, at the request of the Plaintiffs, the District Court stayed the case until September 1, 2019 as to all defendants; on July 24, 2019, the District Court referred this matter to mediation and ordered it stayed during the pendency of such mediation. Ambac Assurance filed a statement of position and reservation of rights on February 5, 2020; certain other defendants filed motions to dismiss on this same date. On February 9, 2020, the Oversight Board announced that it intends to file, and to seek to confirm, an amended plan of adjustment (the “Amended POA”). On March 10, 2020, the District Court ordered that this case remain stayed while the Oversight Board attempts to confirm the Amended POA. Financial Oversight and Management Board for Puerto Rico v. Ambac Assurance Corp., et al. (United States District Court, District of Puerto Rico, No. 20-ap-00003, filed Jan. 16, 2020). Pursuant to an order of the District Court setting out an agreed schedule for litigation submitted by the team of mediators designated in the Commonwealth’s restructuring cases (the “Mediation Team“), on January 16, 2020, the Oversight Board filed an adversary proceeding against monoline insurers insuring bonds issued by the Puerto Rico Infrastructure Financing Authority (“PRIFA”) and the PRIFA bond trustee, all of which Defendants filed proofs of claim against the Commonwealth relating to PRIFA bonds. The complaint seeks to disallow Defendants’ proofs of claim against the Commonwealth in their entirety, including for lack of secured status. Oral argument on motions for summary judgment was held on September 23, 2020. Financial Oversight and Management Board for Puerto Rico v. Ambac Assurance Corp., et al. (United States District Court, District of Puerto Rico, No. 20-ap-00004, filed Jan. 16, 2020). Pursuant to an order of the District Court setting out an agreed schedule for litigation submitted by the Mediation Team, on January 16, 2020, the Oversight Board filed an adversary proceeding against monoline insurers insuring bonds issued by the Puerto Rico Convention Center District Authority (“PRCCDA”) and the PRCCDA bond trustee, all of which Defendants filed proofs of claim against the Commonwealth relating to PRCCDA bonds. The complaint seeks to disallow Defendants’ proofs of claim against the Commonwealth in their entirety, including for lack of secured status. Oral argument on motions for summary judgment was held on September 23, 2020. Financial Oversight and Management Board for Puerto Rico v. Ambac Assurance Corp., et al. (United States District Court, District of Puerto Rico, No. 20-ap-00005, filed Jan. 16, 2020). Pursuant to an order of the District Court setting out an agreed schedule for litigation submitted by the Mediation Team, on January 16, 2020, the Oversight Board filed an adversary proceeding against monoline insurers insuring bonds issued by the Puerto Rico Highways and Transportation Authority ("PRHTA“), certain PRHTA bondholders, and the PRHTA fiscal agent for bondholders, all of which Defendants filed proofs of claim against the Commonwealth relating to PRHTA bonds. The complaint seeks to disallow Defendants’ proofs of claim against the Commonwealth in their entirety, including for lack of secured status. Oral argument on motions for summary judgment was held on September 23, 2020. Financial Oversight and Management Board for Puerto Rico v. Ambac Assurance Corp., et al. (United States District Court, District of Puerto Rico, No. 20-ap-00007, filed Jan. 16, 2020). Pursuant to an order of the District Court setting out an agreed schedule for litigation submitted by the Mediation Team, on January 16, 2020, the Oversight Board and the Committee filed an adversary proceeding against monoline insurers insuring bonds issued by PRHTA, certain PRHTA bondholders, and the PRHTA fiscal agent for bondholders, all of which Defendants filed proofs of claim against PRHTA relating to PRHTA bonds. The complaint seeks to disallow portions of Defendants’ proofs of claim against the PRHTA, including for lack of secured status. On March 10, 2020, the District Court stayed this case. NC Residuals Owners Trust, et al. v. Wilmington Trust Co., et al. (Delaware Court of Chancery, C.A. No. 2019-0880, filed Nov. 1, 2019). On November 1, 2019, Ambac Assurance became aware of a new declaratory judgment action filed by certain residual equity interest holders (“NC Owners” or “Plaintiffs”) in fourteen National Collegiate Student Loan Trusts (the “Trusts”) against Wilmington Trust Company, the Owner Trustee for the Trusts; U.S. Bank National Association, the Indenture Trustee; GSS Data Services, Inc., the Administrator; and Ambac Assurance. Through this action, Plaintiffs seek a number of judicial determinations. On January 21, 2020, the presiding Vice Chancellor entered an order consolidating the action with previously filed litigation relating to the Trusts. On February 13, 2020, Ambac Assurance, the Owner Trustee, the Indenture Trustee, and other parties filed declaratory judgment counterclaims. Several parties, including Plaintiffs and Ambac Assurance, filed motions for judgment on the pleadings in support of their requested judicial determinations. On August 27, 2020, the Vice Chancellor issued an opinion addressing all of the pending motions for judgment on the pleadings, which granted certain of the parties’ requested judicial determinations and denied others. He deferred judgment on still other declarations pending further factual development. Ambac Assurance’s estimates of projected losses for RMBS transactions consider, among other things, the RMBS transactions’ payment waterfall structure, including the application of interest and principal payments and recoveries, and depend in part on our interpretations of contracts and other bases of our legal rights. From time to time, bond trustees and other transaction participants have employed different contractual interpretations and have commenced, or threatened to commence, litigation to resolve these differences. It is not possible to predict whether additional disputes will arise, nor the outcomes of any potential litigation. It is possible that there could be unfavorable outcomes in this or other disputes or proceedings and that our interpretations may prove to be incorrect, which could lead to changes to our estimate of loss reserves. Ambac Assurance has periodically received various regulatory inquiries and requests for information with respect to investigations and inquiries that such regulators are conducting. Ambac Assurance has complied with all such inquiries and requests for information. The Company is involved from time to time in various routine legal proceedings, including proceedings related to litigation with present or former employees. Although the Company’s litigation with present or former employees is routine and incidental to the conduct of its business, such litigation can result in large monetary awards when a civil jury is allowed to determine compensatory and/or punitive damages for, among other things, termination of employment that is wrongful or in violation of implied contracts. From time to time, Ambac is subject to allegations concerning its corporate governance that may lead to litigation, including derivative litigation, and while the monetary impacts may not be material, the matters may distract management and the Board of Directors from their principal focus on Ambac's business, strategy and objectives. It is not reasonably possible to predict whether additional suits will be filed or whether additional inquiries or requests for information will be made, and it is also not possible to predict the outcome of litigation, inquiries or requests for information. It is possible that there could be unfavorable outcomes in these or other proceedings. Legal accruals for litigation against the Company which are probable and reasonably estimable, and management's estimated range of loss for such matters, are either not applicable or are not material to the operating results or financial position of the Company. For the litigation matters the Company is defending that do not meet the “probable and reasonably estimable” accrual threshold and where no loss estimates have been provided above, management is unable to make a meaningful estimate of the amount or range of loss that could result from unfavorable outcomes. Under some circumstances, adverse results in any such proceedings could be material to our business, operations, financial position, profitability or cash flows. The Company believes that it has substantial defenses to the claims above and, to the extent that these actions proceed, the Company intends to defend itself vigorously; however, the Company is not able to predict the outcomes of these actions. Litigation Filed or Joined by Ambac In the ordinary course of their businesses, certain of Ambac’s subsidiaries assert claims in legal proceedings against third parties to recover losses already paid and/or mitigate future losses. The amounts recovered and/or losses avoided which may result from these proceedings is uncertain, although recoveries and/or losses avoided in any one or more of these proceedings during any quarter or fiscal year could be material to Ambac’s results of operations in that quarter or fiscal year. Puerto Rico Financial Oversight and Management Board for Puerto Rico v. Public Buildings Authority (United States District Court, District of Puerto Rico, No. 1:18-ap-00149, filed December 21, 2018). On December 21, 2018, the Oversight Board, together with the Committee, as Plaintiffs, filed a complaint against the Puerto Rico Public Buildings Authority (“PBA”) seeking declaratory judgment that the leases between PBA and its lessees-many of whom are agencies and instrumentalities of the Commonwealth-are “disguised financings,” not true leases, and therefore should not be afforded administrative expense priority under the Bankruptcy Code. On March 12, 2019, Ambac Assurance and other interested parties were permitted to intervene in order to argue that the PBA leases are valid leases, and are entitled to administrative expense treatment under the Bankruptcy Code. On June 16, 2019, the Oversight Board announced that it had entered into a plan support agreement ("PSA") with certain general obligation and PBA bondholders that includes a proposed resolution of claim objections to and issues surrounding both general obligation and PBA bonds, including a proposed settlement of this adversary proceeding. On July 24, 2019, the District Court referred this matter to mediation and ordered it stayed during the pendency of such mediation. On September 27, 2019, the Oversight Board filed a joint plan of adjustment and disclosure statement for the Commonwealth, PBA, and the Employees’ Retirement System for Puerto Rico. On February 9, 2020, the Oversight Board executed a new plan support agreement with additional creditors (the “New PSA”) and announced that it intends to file, and seek to confirm, the Amended POA. On March 10, 2020, the District Court ordered that this case remain stayed while the Oversight Board attempts to confirm the Amended POA. In re Financial Oversight and Management Board for Puerto Rico (United States District Court, District of Puerto Rico, No. 1:17-bk-03283), Omnibus Objection of (I) Financial Oversight and Management Board, Acting Through its Special Claims Committee, and (II) Official Committee of Unsecured Creditors, Pursuant to Bankruptcy Code Section 502 and Bankruptcy Rule 3007, to Claims Filed or Asserted by Holders of Certain Commonwealth General Obligation Bonds (Dkt. No. 4784, filed January 14, 2019) (“GO Bond Claim Objection Procedures”). On January 14, 2019, the Oversight Board and the Committee filed an omnibus claim objection in the Commonwealth’s Title III case challenging claims arising from certain general obligation bonds issued by the Commonwealth in 2012 and 2014 totaling approximately $6 billion, none of which are held or insured by Ambac Assurance. The court subsequently ordered certain consolidated procedures permitting parties in interest an opportunity to participate in litigation of the objection. On April 11, 2019, Ambac Assurance filed a notice of participation in support of the objection, advancing the argument, among other things, that the PBA leases are true leases, but the associated debt nonetheless should be included in the Commonwealth’s debt ceiling calculation such that the 2012 and 2014 general obligation bond issuances are null and void and claims arising therefrom should be disallowed. On June 16, 2019, the Oversight Board announced that it had entered into a PSA with certain general obligation and PBA bondholders that includes a proposed resolution of claim objections to and issues surrounding both general obligation and PBA bonds, including a proposed settlement of this omnibus claim objection. On June 25, 2019, the Oversight Board moved to stay proceedings related to this omnibus claim objection while it pursues confirmation of the plan contemplated in the PSA. On July 24, 2019, the District Court referred this matter to mediation and ordered it stayed during the pendency of such mediation. On February 5, 2020, certain parties filed motions to dismiss the claim objection. On February 9, 2020, the Oversight Board executed the New PSA and announced that it intends to file, and seek to confirm, the Amended POA. Additional motions to dismiss were filed on February 19, 2020. On March 10, 2020, the District Court ordered that this matter remain stayed while the Oversight Board attempts to confirm the Amended POA. On July 19, 2020, the Committee filed a motion to lift the stay on this claim objection in light of the changes to the fiscal plan and likely changes to the Commonwealth plan of adjustment in light of COVID-19. On September 1, 2020, Ambac Assurance filed a partial joinder to the Committee’s motion. On September 17, 2020, the District Court denied the Committee’s motion without prejudice, indicating that the stay likely would remain in place until at least March 2021. On October 1, 2020, the Committee moved the District Court to reconsider its denial of the Committee’s motion to lift the stay in light of materials released by the parties to the New PSA that the Committee argued demonstrate a lack of agreement between those parties. On October 5, 2020, the District Court denied the Committee’s motion for consideration. On October 16, 2020, the Committee appealed to the First Circuit the District Court’s order denying the Committee’s motion to lift the stay on its claim objection. In re Financial Oversight and Management Board for Puerto Rico (United States District Court, District of Puerto Rico, No. 1:17-bk-03283), Ambac Assurance Corporation’s Motion to Strike Certain Provisions of the Plan Support Agreement By and Among the Financial Oversight and Management Board for Puerto Rico, Certain GO Holders, and Certain PBA Holders (Dkt. No. 13573, filed July 7, 2020) (“Amended Motion to Strike PSA”). On June 16, 2019, the Oversight Board announced that it had entered into a PSA with certain general obligation and PBA bondholders that includes a proposed resolution of claim objections to and issues surrounding both general obligation and PBA bonds. On July 16, 2019, Ambac Assurance filed a motion to strike certain provisions of the PSA that it believes violate PROMESA, including the potential payment of a breakup fee to creditors who have supported the PSA (Dkt. No. 8020) (Original Motion to Strike PSA). On February 9, 2020, the Oversight Board executed the New PSA and on March 10, 2020, the District Court denied the Original Motion to Strike PSA without prejudice given the execution of the New PSA. On July 7, 2020, Ambac Assurance filed the Amended Motion to Strike PSA seeking similar relief with respect to the New PSA. Briefing on the Amended Motion to Strike PSA concluded on October 20, 2020, and the District Court has taken the matter on submission. In re Financial Oversight and Management Board for Puerto Rico (United States District Court, District of Puerto Rico, No. 1:17-bk-03283), Ambac Assurance Corporation's Motion and Memorandum of Law in Support of Its Motion Concerning Application of the Automatic Stay to the Revenues Securing PRIFA Rum Tax Bonds (Dkt. No. 7176, filed May 30, 2019) (“PRIFA Stay Motion”). On May 30, 2019, Ambac Assurance filed a motion seeking an order that the automatic stay does not apply to certain lawsuits Ambac Assurance seeks to bring or to continue relating to bonds issued by PRIFA, or, in the alternative, for relief from the automatic stay to pursue such lawsuits or for adequate protection of Ambac Assurance's collateral. On July 24, 2019, the District Court referred this matter to mediation and ordered it stayed during the pendency of such mediation. On January 31, 2020, the District Court granted a motion filed by Ambac Assurance, together with Assured Guaranty Corporation, Assured Guaranty Municipal Corporation, and Financial Guaranty Insurance Company to amend the PRIFA Stay Motion in order to allow the PRIFA bond trustee to join the amended motion and to allow movants to address recent, controlling precedent from the First Circuit, and Ambac Assurance filed the amended motion the same day. On July 2, 2020, the Court denied the motion to lift the stay on certain grounds. Briefing regarding additional grounds on which Ambac Assurance and other movants seek stay relief concluded on August 5, 2020; on September 9, 2020, the District Court denied the motion to lift the stay on the additional grounds. On September 23, 2020, Ambac Assurance and the other movants appealed this decision to the First Circuit. Briefing is expected to be completed by December 21, 2020, with argument heard in February 2021. In re Financial Oversight and Management Board for Puerto Rico (United States District Court, District of Puerto Rico, No. 1:17-bk-03283), Motion of Assured Guaranty Corp., Assured Municipal Corp., Ambac Assurance Corporation, National Public Finance Guarantee Corporation, and Financial Guaranty Insurance Company for Relief from the Automatic Stay, or, in the Alternative, Adequate Protection (Dkt. No. 10102, filed January 16, 2020) (“PRHTA Stay Motion”). Pursuant to an order of the District Court setting out an agreed schedule for litigation submitted by the Mediation Team, on January 16, 2020, Ambac Assurance, together with Assured Guaranty Corp., Assured Municipal Corp., National Public Finance Guarantee Corporation, and Financial Guaranty Insurance Company filed a motion seeking an order that the automatic stay does not apply to movants’ enforcement of the application of pledged revenues to the PRHTA bonds or the enforcement of movants’ liens on revenues pledged to such bonds, or, in the alternative, for adequate protection of movants’ interests in the revenues pledged to PRHTA bonds. On July 2, 2020, the Court denied the motion to lift the stay on certain grounds. Briefing regarding additional grounds on which Ambac Assurance and other movants seek stay relief concluded on August 5, 2020; on September 9, 2020, the District Court denied the motion to lift the stay on the additional grounds. On September 23, 2020, Ambac Assurance and the other movants appealed this decision to the First Circuit. Briefing is expected to be completed by December 21, 2020, with argument heard in February 2021. In re Financial Oversight and Management Board for Puerto Rico (United States District Court, District of Puerto Rico, No. 1:17-bk-03283), Ambac Assurance Corporation, Financial Guaranty Insurance Company, Assured Guaranty Corp., Assured Municipal Corp., and the Bank of New York Mellon’s Motion Concerning Application of the Automatic Stay to the Revenues Securing the CCDA Bonds (Dkt. No. 10104, filed January 16, 2020) (“PRCCDA Stay Motion”). Pursuant to an order of the District Court setting out an agreed schedule for litigation submitted by the Mediation Team, on January 16, 2020, Ambac Assurance, together with Financial Guaranty Insurance Company, Assured Guaranty Corp., Assured Municipal Corp., and the PRCCDA bond trustee, filed a motion seeking an order either (i) that the automatic stay does not apply to movants’ enforcement of their rights to revenues pledged to PRCCDA bonds by bringing an enforcement action against PRCCDA; or, in the alternative, (ii) lifting the automatic stay to enable movants to pursue an enforcement action against PRCCDA; or, in the further alternative, (iii) ordering adequate protection of movants’ interests in the PRCCDA pledged to PRCCDA bonds. On July 2, 2020, the Court denied the motion to lift the stay on certain grounds, but found that the movants had stated a colorable claim that a certain account was the “Transfer Account” on which movants hold a lien. Briefing regarding additional grounds on which Ambac Assurance and other movants seek stay relief concluded on August 5, 2020; on September 9, 2020, the District Court denied the motion to lift the stay on the additional grounds, and found that a final determination on issues related to the identity of the Transfer Account would be made in the decision on the motions for summary judgment issued in the CCDA-related adversary proceeding, No. 20-ap-00004. Ambac Assurance Corporation v. Merrill Lynch, Pierce, Fenner & Smith Incorporated, Goldman Sachs & Co. LLC, Citigroup Global Markets Inc., J.P. Morgan Securities LLC, Morgan Stanley & Co. LLC, Samuel A. Ramirez & Co. Inc., Raymond James & Associates, Inc., and UBS Financial Services Inc. (Commonwealth of Puerto Rico, Court of First Instance, San Juan Superior Court, Case No. CV-000248923, filed February 19, 2020). On February 19, 2020, Ambac Assurance filed a complaint in the Commonwealth of Puerto Rico, Court of First Instance, San Juan Superior Court, against certain underwriters of Ambac-insured bonds issued by PRIFA and PRCCDA, with causes of action under the Puerto Rico civil law doctrines of actos proprios and Unilateral Declaration of Will. Ambac Assurance alleges defendants engaged in inequitable conduct in underwriting Ambac-insured bonds issued by PRIFA and PRCCDA, including failing to investigate and adequately disclose material information in the official statements for the bonds that defendants provided to Ambac Assurance regarding systemic deficiencies in the Commonwealth’s financial reporting. Ambac Assurance seeks damages in compensation for claims paid by Ambac Assurance on its financial guaranty insurance policies insuring such bonds, pre-judgment and post-judgment interest, and attorneys’ fees. On March 20, 2020, Defendants removed this case to the Title III Court. On April 20, 2020, Ambac moved to remand the case back to the Court of First Instance. On July 29, 2020, the District Court granted Ambac Assurance’s motion to remand the case to the Commonwealth court. Ambac Assurance filed an amended complaint in the Commonwealth court on October 28, 2020. Ambac Assurance Corporation v. Autopistas Metropolitanas de Puerto Rico, LLC (United States District Court, District of Puerto Rico, No. 3:20-cv-01094, filed February 19, 2020). On February 19, 2020, Ambac Assurance filed a complaint in the U.S. District Court for the District of Puerto Rico, against Autopistas Metropolitanas de Puerto Rico, LLC (“Metropistas”), which holds a concession from PRHTA for two Puerto Rico highways, PR-5 and PR-22, in connection with a 10-year extension of the concession that was entered into in April 2016. The complaint includes claims for fraudulent conveyance and unjust enrichment, alleging that the consideration paid by Metropistas for the extension was less than reasonably equivalent value and most of the benefit of such payment was received by the Commonwealth instead of PRHTA. Ambac Assurance also seeks a declaratory judgment that it has a valid and continuing lien on certain toll revenues that are being collected by Metropistas. On March 31, 2020, the Oversight Board filed a motion before the Title III Court seeking an order directing Ambac to withdraw its complaint. On April 20, 2020, the District Court ordered this case stayed pending briefing before the Title III Court on the Oversight Board’s motion to withdraw. On June 16, 2020, the Title III Court ordered Ambac Assurance to withdraw its complaint. Ambac Assurance withdrew its complaint on June 23, 2020, and noticed an appeal from the Title III Court’s order to withdraw on June 30, 2020. Ambac Assurance’s opening appeal brief was filed before the First Circuit on October 19, 2020; opposition briefs are due to be filed on December 18, 2020. Ambac Assurance Corporation v. Financial Oversight and Management Board for Puerto Rico (United States District Court, District of Puerto Rico, No. 3:20-bk-00068, filed May 26, 2020). On May 26, 2020, Ambac Assurance filed an adversary complaint before the Title III Court seeking (i) a declaration that titles I, II, and III of PROMESA are unconstitutional because they violate the Bankruptcy Clause of the U.S. Constitution (which requires all bankruptcy laws to be uniform) and (ii) dismissal of the pending Title III petitions. On August 17, 2020, the Oversight Board filed a motion to dismiss the complaint; on August 18, 2020, the Official Committee of Retired Employees of the Commonwealth of Puerto Rico (the “Retiree Committee”) and the Puerto Rico Fiscal Agency and Financial Advisory Authority (“AAFAF”) filed joinders to the motion to dismiss. The United States filed a motion to dismiss on October 2, 2020. Briefing on the motions to dismiss are expected to conclude on November 23, 2020, with a hearing on January 12, 2021. In re Financial Oversight and Management Board for Puerto Rico (United States District Court, District of Puerto Rico, No. 1:17-bk-03283), Urgent Motion for Bridge Order, and Motion for Appointment as Trustees Under 11 U.S.C. § 926, of Ambac Assurance Corporation, Assured Guaranty Corp., Assured Guaranty Municipal Corp., Financial Guaranty Insurance Company, and National Public Finance Guarantee Corporation (Dkt. No. 13708, filed July 17, 2020) (“HTA Trustee Motion”). On July 17, 2020, Ambac Assurance, together with Assured Guaranty Corporation, Assured Guaranty Municipal Corporation, and Financial Guaranty Insurance Company, filed a motion seeking appointment as trustees under Section 926 of the Bankruptcy Code to pursue certain avoidance actions on behalf of HTA against the Commonwealth of Puerto Rico. The HTA Trustee Motion attached a proposed complaint detailing the avoidance claims that movants would pursue. On August 11, 2020, the District Court denied the HTA Trustee Motion; on August 24, 2020, movants noticed an appeal of the denial of the HTA Trustee Motion to the First Circuit. On September 30, 2020, movants filed a motion with the First Circuit to hold this appeal in abeyance pending the First Circuit’s resolution of the appeal from the District Court’s denial of the HTA Lift-Stay Motion. On October 13, 2020, the Oversight Board opposed the motion to hold the appeal in abeyance and cross-moved to dismiss the appeal as moot, arguing that the statute of limitations on the avoidance actions movants wish to pursue has expired. On October 20, 2020, movants filed a reply in support of their motion to hold the appeal in abeyance, and opposed the Oversight Board’s cross-motion to dismiss the appeal as moot. On October 27, 2020, the Oversight Board filed a reply in support of its cross-motion to dismiss the appeal as moot. Student Loans Exposure CFPB v. Nat’l Collegiate Master Student Loan Trust (United States District Court, District of Delaware, Case No. 1:17-cv-01323, filed September 18, 2017). The Consumer Financial Protection Bureau (“CFPB”) filed a complaint against fifteen National Collegiate Student Loan Trusts, regarding alleged improprieties and deficiencies in servicing practices. Simultaneous with the filing of its complaint, CFPB also filed a motion to approve a proposed consent judgment that would have granted monetary damages and injunctive relief against the Trusts. Ambac Assurance guaranteed certain securities issued by three of the Trusts and indirectly insures six other Trusts. On September 20, 2017, Ambac Assurance filed a motion to intervene in the action, which motion was granted on October 19, 2018. Following discovery and briefing, on May 31, 2020, the District Court denied the CFPB’s motion to approve the proposed consent judgment. On March 19, 2020, Intervenor Transworld Systems Inc. filed a motion to dismiss the action for lack of subject matter jurisdiction. On July 10, 2020, Ambac Assurance and several other intervenors filed a motion to dismiss the action for lack of subject matter jurisdiction and for failure to state a claim. Briefing on both motions to dismiss is complete. Additionally, on July 2, 2020, the CFPB submitted an application for entry of default against the Trusts. Ambac Assurance and the Owner Trustee opposed the CFPB’s application, which remains pending. RMBS Litigation In connection with Ambac Assurance’s efforts to seek redress for breaches of representations and warranties and fraud related to the information provided by both the underwriters and the sponsors of various transactions and for failure to comply with the obligation by the sponsors to repurchase ineligible loans, Ambac Assurance has filed various lawsuits: • Ambac Assurance Corporation and The Segregated Account of Ambac Assurance Corporation v. Countrywide Securities Corp., Countrywide Financial Corp. (a.k.a. Bank of America Home Loans) and Bank of America Corp. (Supreme Court of the State of New York, County of New York, Case No. 651612/2010, filed on September 28, 2010). Ambac Assurance’s Second Amended Complaint, filed on May 28, 2013, asserted claims against Countrywide and Bank of America (as successor to Countrywide’s liabilities) for, among other things, breach of contract and fraudulent inducement. In August and October 2018, Defendants filed various pre-trial motions. On December 30, 2018, the court denied all of these pre-trial motions in their entirety and Defendants appealed. On September 17, 2019, the First Department affirmed in part and reversed in part the trial court’s rulings. On October 17, 2019, Countrywide filed a motion for leave to appeal certain issues to the New York Court of Appeals and for reargument or leave to appeal certain other issues. On January 16, 2020, the First Department recalled and vacated its September 17, 2019 decision and order and substituted a new decision and order. On the same date, the First Department denied Countrywide’s motion seeking leave to appeal, without prejudice to seeking such leave from the reissued decision and order. On January 30, 2020, Countrywide filed a new motion for leave to appeal the First Department’s denial of its motions, which Ambac Assurance opposed. On June 11, 2020, the First Department denied Countrywide’s motion for leave to appeal. On January 14, 2020, the trial court granted Ambac Assurance’s motion to supplement and amend certain of its expert reports, and expert discovery is ongoing. On June 25, 2020, the trial court scheduled trial to commence on February 22, 2021 (which could be rescheduled if the COVID-19 pandemic prevents the court system from ho

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Organization, Consolidation and Presentation of Financial Statements Disclosure	Consolidation: The consolidated financial statements include the accounts of AFG and all other entities in which AFG (directly or through its subsidiaries) has a controlling financial interest, including variable interest entities (“VIEs”) for which AFG or an AFG subsidiary is deemed the primary beneficiary in accordance with the Consolidation Topic of the Accounting Standards Codification ("ASC"). All significant intercompany balances have been eliminated. The usual condition for a controlling financial interest is ownership of a majority of the voting interests of an entity. However, a controlling financial interest may also exist in entities, such as VIEs, through arrangements that do not involve controlling voting interests. A VIE is an entity: a) that lacks enough equity investment at risk to permit the entity to finance its activities without additional subordinated financial support from other parties; or b) where the group of equity holders does not have: (1) the power, through voting rights or similar rights, to direct the activities of an entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb the entity’s expected losses; or (3) the right to receive the entity’s expected residual returns. The determination of whether a variable interest holder is the primary beneficiary involves performing a qualitative analysis of the VIE that includes, among other factors, its capital structure, contractual terms including the rights of each variable interest holder, the activities of the VIE, whether the variable interest holder has the power to direct the activities of a VIE that most significantly impact the VIE’s economic performance, whether the variable interest holder has the obligation to absorb losses of the VIE that could potentially be significant to the VIE or the right to receive benefits from the VIE that could potentially be significant to the VIE, related party relationships and the design of the VIE. An entity that is deemed the primary beneficiary of a VIE is required to consolidate the VIE. See Note 3. Variable Interest Entities
Basis of Presentation and Significant Accounting Policies [Text Block]	Basis of Presentation: The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles ("GAAP") for interim financial reporting and with the instructions to Form 10-Q and Article 10 of
Foreign Currency Transactions and Translations Policy [Policy Text Block]	Foreign Currency: Financial statement accounts expressed in foreign currencies are translated into U.S. dollars in accordance with the Foreign Currency Matters Topic of the ASC. The functional currencies of AFG's subsidiaries are the local currencies of the country where the respective subsidiaries are based, which are also the primary operating environments in which the subsidiaries operate. Foreign currency translation : Functional currency assets and liabilities of AFG’s foreign subsidiaries are translated into U.S. dollars using exchange rates in effect at the balance sheet dates and the related translation adjustments, net of deferred taxes, are included as a component of Accumulated Other Comprehensive Income in Stockholders' Equity. Functional currency operating results of foreign subsidiaries are translated using average exchange rates.
Reclassifications	Reclassifications and Rounding Reclassifications may have been made to prior years' amounts to conform to the current year's presentation. Certain amounts and tables in the consolidated financial statements and associated notes may not add due to rounding.
New Accounting Pronouncements and Changes in Accounting Principles	Adopted Accounting Standards: Effective January 1, 2020, the Company adopted the following accounting standards: Measurement of Credit Losses on Financial Instruments (CECL) In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326) - Measurement of Credit Losses on Financial Instruments, subsequently amended by ASU 2018-19 , Codification Improvements to Topic 326, Financial Instruments - Credit Losses; ASU 2019-04 , Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments ; ASU 2019-05, Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief ; and ASU 2019-11, Codification Improvements to Topic 326, Financial Instruments - Credit Losses (collectively the Current Expected Credit Loss standard or "CECL") The new CECL standard affects how reporting entities measure credit losses for financial assets that are not accounted for at fair value through net income. For Ambac, these financial assets include available-for-sale debt securities and amortized cost assets, specifically premium receivables, reinsurance recoverables and loans. CECL does not apply to recoveries of previously paid losses on financial guarantee insurance contracts accounted for under ASC 944 nor does it apply to equity method investments accounted for under ASC 323. For available-for-sale debt securities, the updated guidance was applied prospectively and for financial instruments measured at amortized cost, the updated guidance was applied by a cumulative effect adjustment to the opening balance of retained earnings at January 1, 2020. This adjustment was not material to retained earnings or any individual balance sheet line item. As a result of adopting CECL, management revised its policies and procedures around the credit impairment evaluation process. CECL also introduced new disclosures related to the credit impairment process, including certain accounting policy elections that Ambac made under the the new standard. Enhanced disclosures related to accounting policies for each type of asset impacted by CECL are discussed below. The disclosures below should be read in conjunction with disclosures in Note 2. Basis of Presentation and Significant Accounting Policies , Note 6. Financial Guarantee Insurance Contracts and Note 8. Investments in the Notes to Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. Available-for-Sale Debt Securities For available-for-sale debt securities, credit losses under CECL are measured similarly to other-than-temporary impairments under prior GAAP. However, under CECL, the recognition of credit losses for available-for-sale debt securities will be recorded as an allowance for credit losses with an offsetting charge to net income, rather than as a direct write-down of the security as was required under prior GAAP. As a result, improvements to estimated credit losses for available-for-sale debt securities will be recognized immediately in net income rather than as interest income over time. Furthermore, as required under CECL, Ambac no longer considers the length of time a security has continuously been in an unrealized loss in the credit impairment process. Ambac has made certain accounting policy elections related to accrued interest receivable ("AIR") for available-for-sale investments under CECL, which are consistent with past practices under prior GAAP. Elections include: i) not measuring AIR for credit impairment, instead AIR is written off when it becomes 90 days past due; ii) writing off AIR by reversing interest income; iii) presenting AIR separately in Other Assets on the balance sheet and iv) excluding AIR from amortized cost balances in required CECL disclosures found in Note 8. Investments . AIR at September 30, 2020 was $10. Refer to Note 8. Investments for further credit impairment disclosures. Amortized cost assets For financial assets measured at amortized cost, CECL replaces the "incurred loss" model used for certain types of assets which generally delayed recognition of the full amount of credit losses until the loss was probable of occurring, with an "expected loss" model, which reflects an entity's current estimate of all expected lifetime credit losses. The estimate of expected lifetime credit losses should consider historical information, current information, as well as reasonable and supportable forecasts. Expected lifetime credit losses for amortized cost assets will be recorded as an allowance for credit losses, with subsequent increases or decreases in the allowance reflected in net income each period. The CECL measurement approach for Ambac's affected asset types were not materially different than the approaches under prior GAAP. Refer to the discussion below for each asset type. Premium receivables. For financial guarantee contracts, the issuer's ability and willingness to pay its insured debt obligation impacts the payment of policy losses by Ambac as well as the receipt of premiums from the issuer. As such, management leverages its existing loss reserve estimation process to evaluate credit impairment for premium receivables. Key factors in assessing credit impairment include historical premium collection data, internal risk classifications, credit ratings and loss severities. For structured finance transactions involving special purpose entities, we further evaluate the priority of premiums paid to Ambac within the contractual waterfall, as required by bond indentures. Management utilizes either a discounted cash flow ("DCF") or probability of default/loss given default ("PD/LGD") approach to estimate credit impairment. The DCF approach utilizes expected cash flows developed by Ambac's Risk Management Group using the same (or similar) models used for estimating loss reserves where such models can identify shortfalls in premiums. Credit impairment using the DCF approach is equal to the difference between amortized cost and the present value of expected cash flows. Credit impairment under the PD/LGD approach is the product of (i) the premium receivable carrying value, (ii) internally developed default probability (considering internal ratings and average life), and (iii) internally developed loss severities. Refer to Note 6. Financial Guarantee Insurance Contracts for further credit impairment disclosures. Loans. The key factors in assessing credit impairment for loans are internal credit ratings and loss severities. Management utilizes a PD/LGD approach, similar to the one described above for premium receivables, which is applied to the loan carrying value. Reinsurance recoverables. Ambac has elected the to use the practical expedient of considering the fair value of collateral posted by reinsurers when evaluating credit impairment. To determine the total unsecured recoverable to be evaluated for impairment, Ambac nets the reinsurance recoverable amount by ceded premiums payable and the fair value of collateral posted, if any. The key factors in assessing credit impairment for reinsurance recoverables are independent rating agency credit ratings and loss severities. Management utilizes a PD/LGD approach, similar to the one described above for premium receivables, which is applied to the net unsecured reinsurance recoverable amount. Refer to Note 6. Financial Guarantee Insurance Contracts for further credit impairment disclosures. Fair Value Measurement Disclosures In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820) - Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement . The ASU modified various disclosure requirements on fair value measurements. Relevant disclosures that were removed, modified and added are as follows: • Removals : 1) Amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, 2) Policy for timing of transfers between levels, and 3) Valuation processes for Level 3 fair value measurements. • Modifications : 1) For investments in certain entities that calculate net asset value, disclosures are required for the timing of liquidation of an investee's assets and the date when restrictions from redemption might lapse, only if the investee has communicated the timing to the reporting entity or publicly announced it and 2) Clarification that the measurement uncertainty disclosure is to communicate information about the uncertainty in measurement as of the reporting date and not possible future changes. • Additions : 1) Changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and 2) Range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. Alternatively, an entity may disclose other quantitative information (such as the median or arithmetic average) if it determines that it is a more reasonable and rational method to reflect the distribution of unobservable inputs used. Disclosure amendments related to changes in unrealized gains and losses included in other comprehensive income (loss) for Level 3 instruments, the range and weighted average of significant unobservable inputs, and the narrative description of measurement uncertainty were applied prospectively only for the most recent interim or annual period presented. All other disclosure amendments were applied retrospectively to all periods presented. Refer to Note 7. Fair Value Measurements for further disclosures. VIE Related Party Guidance In October 2018, the FASB issued ASU 2018-17, Consolidation (Topic 810) - Targeted Improvements to Related Party Guidance for Variable Interest Entities. To determine whether a decision- making fee is a variable interest, under the new guidance a reporting entity must consider indirect interests held through related parties under common control on a proportional basis rather than as a direct interest in its entirety (as was previously required under prior GAAP). These amendments create alignment between determining whether a decision making fee is a variable interest and determining whether a reporting entity within a related party group is the primary beneficiary of a VIE. Adoption of this ASU did not impact Ambac's financial statements. Cloud Computing Arrangement Service Contracts In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other— Internal-Use Software (Subtopic 350-40) - Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The new guidance requires a customer in a cloud computing arrangement that is a service contract to capitalize certain implementation costs as if the arrangement was an internal-use software project. The internal-use software guidance requires the capitalization of certain costs incurred only during the application development stage. That guidance also requires entities to expense costs during the preliminary project and post-implementation stages as they are incurred. Adoption of this ASU did not impact Ambac's financial statements.
Description of New Accounting Pronouncements Not yet Adopted [Text Block]	Future Application of Accounting Standards: Reference Rate Reform In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848) - Facilitation of the Effects of Reference Rate Reform on Financial Reporting . The ASU provides companies with optional guidance to ease the potential accounting burden related to transitioning away from reference rates, such as LIBOR, that are expected to be discontinued as a result of initiatives undertaken by various jurisdictions around the world. For example, under current GAAP, contract modifications which change a reference rate are required to be evaluated in determining whether the modifications result in the establishment of new contracts or the continuation of existing contracts. The amendments in this ASU provide optional expedients and exceptions for applying GAAP to contracts, hedging relationships, and other transactions affected by reference rate reform if certain criteria are met. The ASU can be applied prospectively as of the beginning of the interim period that includes March 12, 2020, (January 1, 2020 for calendar year companies) or any date thereafter, but does not apply to contract modifications and other transactions entered into or evaluated after December 31, 2022. Management has not determined if and when it will adopt this ASU, and the impact on Ambac's financial statements is being evaluated.

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2020
Supplemental Cash Flow Elements [Abstract]
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	Supplemental Disclosure of Cash Flow Information Nine Months Ended September 30, 2020 2019 Cash paid during the period for: Income taxes $ 11 $ 11 Interest on long-term debt 83 110 Non-cash financing activities: Exchange of investments in Puerto Rico COFINA bonds for new bonds issued in the Plan of Adjustment $ — $ 510 September 30, 2020 2019 Reconciliation of cash, cash equivalents, and restricted cash reported within the Consolidated Balance Sheets to the Consolidated Statements of Cash Flows: Cash and cash equivalents $ 37 $ 52 Restricted cash 10 13 Variable Interest Entity Restricted cash 2 3 Total cash, cash equivalents, and restricted cash shown on the Consolidated Statements of Cash Flows $ 50 $ 68

Special Purpose Entities, Inclu

Special Purpose Entities, Including Variable Interest Entities (Tables)	9 Months Ended
	Sep. 30, 2020
Variable Interest Entity [Line Items]
Components of VIE Gain (Loss) [Table Text Block]	The following schedule details the components of Income (loss) on variable interest entities for the affected periods: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Net change in fair value of VIE assets and liabilities reported under the fair value option $ (1) $ 2 $ (3) $ 7 Less: Credit risk changes of fair value option long-term debt reported through other comprehensive income (loss) — — (2) — Net change in fair value of VIE assets and liabilities reported in earnings — 2 (5) 6 Investment income on available-for-sale securities 2 3 5 8 Net realized investment gains (losses) on available-for-sale securities — 12 8 13 Interest expense on long-term debt carried at par less unamortized cost (1) (3) (5) (9) Other expenses — — — (1) Gain (loss) from consolidating FG VIEs — — — 15 Gain (loss) from de-consolidating FG VIEs — (2) — (2) Income (loss) on variable interest entities $ — $ 11 $ 3 $ 30
Summary of Carrying Amount of Assets, Liabilities and Maximum Exposure to Loss of Ambac's Variable Interests in Non-Consolidated Variable Interest Entities	The following table displays the carrying amount of the assets, liabilities and maximum exposure to loss of Ambac’s variable interests in non-consolidated VIEs resulting from financial guarantee and derivative contracts by major underlying asset classes, as of September 30, 2020 and December 31, 2019: Carrying Value of Assets and Liabilities Maximum (1) Insurance (2) Insurance (3) Net Derivative (4) September 30, 2020: Global structured finance: Mortgage-backed—residential $ 4,535 $ 2,063 $ 604 $ — Other consumer asset-backed 1,120 26 240 — Other commercial asset-backed 52 3 1 — Other 991 — 15 8 Total global structured finance 6,698 2,093 860 8 Global public finance 22,183 268 316 (1) Total $ 28,881 $ 2,361 $ 1,177 $ 7 December 31, 2019: Global structured finance: Mortgage-backed—residential $ 5,373 $ 1,913 $ 523 $ — Other consumer asset-backed 1,373 31 216 — Other commercial asset-backed 314 9 6 — Other 1,107 7 18 8 Total global structured finance 8,165 1,961 762 8 Global public finance 23,341 287 321 — Total $ 31,506 $ 2,247 $ 1,083 $ 7 (1) Maximum exposure to loss represents the maximum future payments of principal and interest on insured obligations and derivative contracts. Ambac’s maximum exposure to loss does not include the benefit of any financial instruments (such as reinsurance or hedge contracts) that Ambac may utilize to mitigate the risks associated with these variable interests. (2) Insurance assets represent the amount included in “Premium receivables” and “Subrogation recoverable” for financial guarantee insurance contracts on Ambac’s Consolidated Balance Sheets. (3) Insurance liabilities represent the amount included in “Loss and loss expense reserves” and “Unearned premiums” for financial guarantee insurance contracts on Ambac’s Consolidated Balance Sheets. (4) Net derivative assets (liabilities) represent the fair value recognized on credit derivative contracts and interest rate swaps on Ambac’s Consolidated Balance Sheets.
Schedule of Variable Interest Entities Assets and Liabilities [Table Text Block]	The following table summarizes the carrying values of assets and liabilities, along with other supplemental information related to VIEs that are consolidated as a result of financial guarantees of Ambac UK and Ambac Assurance: September 30, 2020 December 31, 2019 Ambac UK Ambac Assurance Total VIEs Ambac UK Ambac Assurance Total VIEs Fixed income securities, at fair value: Corporate obligations, fair value option $ 3,029 $ — $ 3,029 $ 2,957 $ — $ 2,957 Municipal obligations, available-for-sale (1) — 131 131 — 164 164 Total FG VIE fixed income securities, at fair value 3,029 131 3,160 2,957 164 3,121 Restricted cash 1 1 2 1 1 2 Loans, at fair value (2) 2,783 — 2,783 3,108 — 3,108 Derivative assets 53 — 53 52 — 52 Other assets — 1 1 1 2 3 Total FG VIE assets $ 5,865 $ 133 $ 5,998 $ 6,119 $ 167 $ 6,286 Accrued interest payable $ — $ — $ — $ 1 $ — $ 1 Long-term debt: Long-term debt, at fair value (3) 4,002 — 4,002 4,351 — 4,351 Long-term debt, at par less unamortized discount — 167 167 — 203 203 Total long-term debt 4,002 167 4,169 4,351 203 4,554 Derivative liabilities 1,771 — 1,771 1,657 — 1,657 Total FG VIE liabilities $ 5,773 $ 167 $ 5,940 $ 6,009 $ 203 $ 6,212 Number of FG VIEs consolidated 5 1 6 6 1 7 (1) Available-for-sale FG VIE fixed income securities consist of municipal obligations with an amortized cost basis of $112 and $139, and aggregate gross unrealized gains of $19 and $25 at September 30, 2020 and December 31, 2019, respectively. All such securities had contractual maturities due after ten years as of September 30, 2020. (2) The unpaid principal balances of loan assets carried at fair value were $2,450 as of September 30, 2020 and $2,618 as of December 31, 2019. (3) The unpaid principal balances of long-term debt carried at fair value were $3,604 as of September 30, 2020 and $3,800 as of December 31, 2019.

Comprehensive Income (Tables)

Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income	The following tables detail the changes in the balances of each component of accumulated other comprehensive income for the affected periods: Unrealized Gains (1) Amortization of (1) Gain (Loss) on (1) Credit Risk Changes of Fair Value Option Liabilities (1) (2) Total Three Months Ended September 30, 2020: Beginning Balance $ 109 $ 6 $ (164) $ — $ (48) Other comprehensive income (loss) before reclassifications 45 — 29 — 74 Amounts reclassified from accumulated other comprehensive income (loss) (2) — — — (3) Net current period other comprehensive income (loss) 42 — 29 — 71 Balance at September 30, 2020 $ 152 $ 6 $ (135) $ — $ 22 Three Months Ended September 30, 2019: Beginning Balance $ 157 $ 9 $ (145) $ (2) $ 19 Other comprehensive income (loss) before reclassifications 50 — (24) — 26 Amounts reclassified from accumulated other comprehensive income (loss) (18) — — — (19) Net current period other comprehensive income (loss) 31 — (24) — 7 Balance at September 30, 2019 $ 189 $ 9 $ (169) $ (2) $ 26 Unrealized Gains (1) Amortization of (1) Gain (Loss) on (1) Credit Risk Changes of Fair Value Option Liabilities (1) (2) Total Nine Months Ended September 30, 2020: Beginning Balance $ 151 $ 8 $ (116) $ (2) $ 42 Other comprehensive income (loss) before reclassifications 20 (2) (20) — (2) Amounts reclassified from accumulated other comprehensive income (loss) (19) (1) — 2 (18) Net current period other comprehensive income (loss) 1 (3) (20) 2 (20) Balance at September 30, 2020 $ 152 $ 6 $ (135) $ — $ 22 Nine Months Ended September 30, 2019: Beginning Balance $ 86 $ 9 $ (142) $ (2) $ (49) Other comprehensive income before reclassifications 174 1 (28) — 147 Amounts reclassified from accumulated other comprehensive income (71) (1) — — (72) Net current period other comprehensive income $ 103 $ — $ (28) $ — $ 75 Balance at September 30, 2019 $ 189 $ 9 $ (169) $ (2) $ 26 (1) All amounts are net of tax and noncontrolling interest. Amounts in parentheses indicate reductions to Accumulated Other Comprehensive Income. (2) Represents the changes in fair value attributable to instrument-specific credit risk of liabilities for which the fair value option is elected.
Schedule of Amounts Reclassed Out of Each Component of Accumulated Other Comprehensive Income	The following table details the significant amounts reclassified from each component of accumulated other comprehensive income, shown in the above rollforward tables, for the affected periods: Details about Accumulated Amount Reclassified from Accumulated Other Comprehensive Income Affected Line Item in the Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Unrealized Gains (Losses) on Available-for-Sale Securities $ (2) $ (20) $ (20) $ (77) Net realized investment gains (losses) and other-than-temporary impairment losses — 1 1 6 Provision for income taxes $ (2) $ (18) $ (19) $ (71) Net of tax and noncontrolling interest Amortization of Postretirement Benefit Prior service cost $ — $ — $ (1) $ (1) Other income Actuarial (losses) — — — — Other income — — (1) (1) Total before tax — — — — Provision for income taxes $ — $ — $ (1) $ (1) Net of tax and noncontrolling interest Credit risk changes of fair value option liabilities $ — $ — $ 2 $ — Credit Risk Changes of Fair Value Option Liabilities — — — — Provision for income taxes $ — $ — $ 2 $ — Net of tax and noncontrolling interest Total reclassifications for the period $ (3) $ (19) $ (18) $ (72) Net of tax and noncontrolling interest

Net Income Per Share (Tables)

Net Income Per Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Reconciliation of Common Shares Used for Basic and Diluted Earnings Per Share	The following table provides a reconciliation of the common shares used for basic net income per share to the diluted shares used for diluted net income per share: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Basic weighted average shares outstanding 46,178,730 45,997,694 46,135,399 45,939,284 Effect of potential dilutive shares (1) : Stock options — — — — Warrants — 450,384 — — Restricted stock units — 78,751 — — Performance stock units (2) — 493,229 — — Diluted weighted average shares outstanding 46,178,730 47,020,058 46,135,399 45,939,284 Anti-dilutive shares excluded from the above reconciliation: Stock options 16,667 16,667 16,667 16,667 Warrants 4,877,749 — 4,877,754 4,877,783 Restricted stock units 333,526 — 286,279 249,025 Performance stock units (2) 972,138 — 932,777 748,700 (1) For the three and nine months ended September 30, 2020, and the nine months ended September 30, 2019, Ambac had a net loss and accordingly excluded all potentially dilutive securities from the determination of diluted loss per share as their impact was anti-dilutive. (2) Performance stock units are reflected based on the performance metrics through the balance sheet date. Vesting of these units is contingent upon meeting certain performance metrics. Although a portion of these performance metrics have been achieved as of the respective period end, it is possible that awards may no longer meet the metric at the end of the performance period.

Financial Guarantee Insurance C

Financial Guarantee Insurance Contracts (Tables)	9 Months Ended
	Sep. 30, 2020
Insurance [Line Items]
Schedule of Loss And Loss Expense Reserves And Subrogation Recoverable Table [Table Text Block]	Below are the components of the loss reserves liability and the Subrogation recoverable asset at September 30, 2020 and December 31, 2019: September 30, 2020: December 31, 2019: Present Value of Expected Unearned Gross Loss and Present Value of Expected Unearned Gross Loss and Balance Sheet Line Item Claims and Recoveries Claims and Recoveries Loss and loss expense reserves $ 2,116 $ (235) $ (80) $ 1,801 $ 1,835 $ (233) $ (54) $ 1,548 Subrogation recoverable 109 (2,303) — (2,194) 131 (2,160) — (2,029) Totals $ 2,225 $ (2,538) $ (80) $ (393) $ 1,966 $ (2,394) $ (54) $ (482)
Summary of Gross Premium Receivable Roll-Forward (Direct and Assumed Contracts)	Below is the gross premium receivable roll-forward for the respective periods, net of allowance for credit losses: Nine Months Ended September 30, 2020 2019 Beginning premium receivable $ 416 $ 495 Adjustment to initially apply ASU 2016-13 (3) — Premium receipts (36) (37) Adjustments for changes in expected and contractual cash flows (1) (4) (33) Accretion of premium receivable discount 7 9 Deconsolidation of certain VIEs — 3 Changes to allowance for credit losses (5) (7) Other adjustments (including foreign exchange) (2) (16) Ending premium receivable (2) $ 372 $ 415 (1) Adjustments for changes in expected and contractual cash flows primarily due to reductions in insured exposure as a result of early policy terminations and unscheduled principal paydowns. (2) Premium receivable includes premiums to be received in foreign denominated currencies most notably in British Pounds and Euros.
Effect of Reinsurance on Premiums Written and Earned	The effect of reinsurance on premiums written and earned for the respective periods was as follows: Three Months Ended September 30, 2020 2019 Written Earned Written Earned Direct $ (13) $ 18 $ (13) $ 13 Assumed — — — — Ceded — 3 23 3 Net premiums $ (13) $ 15 $ (36) $ 10 Nine Months Ended September 30, 2020 2019 Written Earned Written Earned Direct $ (2) $ 45 $ (31) $ 53 Assumed — 1 — — Ceded (1) 9 22 7 Net premiums $ (2) $ 36 $ (53) $ 46
Schedule of Revenue from External Customers Attributed to Foreign Countries by Geographic Area [Table Text Block]	The following table summarizes net premiums earned by location of risk for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 United States $ 9 $ 11 $ 24 $ 44 United Kingdom 7 4 15 13 Other international (1) (4) (2) (11) Total $ 15 $ 10 $ 36 $ 46
Summarized Future Gross Undiscounted Premiums Expected to be Collected and Future Expected Premiums Earned, Net of Reinsurance	The table below summarizes the future gross undiscounted premiums to be collected and future premiums earned, net of reinsurance at September 30, 2020: Future Premiums Collected (1) Future (2) Three months ended: December 31, 2020 $ 11 $ 10 Twelve months ended: December 31, 2021 36 35 December 31, 2022 34 33 December 31, 2023 33 30 December 31, 2024 31 29 Five years ended: December 31, 2029 138 120 December 31, 2034 101 81 December 31, 2039 50 37 December 31, 2044 22 14 December 31, 2049 9 5 December 31, 2054 1 1 Total $ 467 $ 395 (1) Future premiums to be collected are undiscounted, gross of allowance for credit losses, and are used to derive the discounted premium receivable asset recorded on Ambac's balance sheet. (2) Future premiums to be earned, net of reinsurance relate to the unearned premiums liability and deferred ceded premium asset recorded on Ambac’s balance sheet. The use of contractual lives for many bond types which do not have homogeneous pools of underlying collateral is required in the calculation of the premium receivable, as further described in Note 2. Basis of Presentation and Significant Accounting Policies
Premiums Receivable by Risk Classification Code [Table Text Block]	Below is the amortized cost basis of premium receivables by risk classification code and asset class as of September 30, 2020: Surveillance Categories as of September 30, 2020 Type of Guaranteed Bond I IA II III IV Total Public Finance: Housing revenue $ 158 $ 13 $ — $ — $ — $ 171 Other 2 13 — — — 16 Total Public Finance 160 26 — — — 186 Structured Finance: Mortgage-backed and home equity 3 1 3 16 23 Structured insurance 16 — — — — 16 Student loan 3 — 2 12 — 17 Other 7 — — — — 7 Total Structured Finance 29 — 3 15 16 63 International: Sovereign/sub-sovereign 78 13 — 15 — 105 Investor-owned and public utilities 29 — — — — 29 Other 6 — — — — 6 Total International 113 13 — 15 — 141 Total (1) $ 302 $ 39 $ 3 $ 29 $ 16 $ 390 (1) The underwriting origination dates for all policies included are greater than five years prior to the current reporting date.
Premium Receivable, Allowance for Credit Loss [Table Text Block]	Below is a rollforward of the premium receivable allowance for credit losses as of September 30, 2020: Three Months Ended September 30, 2020 Nine Months Ended September 30, 2020 Beginning balance (1) $ 16 $ 9 Current period provision (2) 2 9 Write-offs of the allowance — — Recoveries of previously written-off amounts — — Ending balance $ 18 $ 18 (1) At December 31, 2019, $9 of premiums receivable were deemed uncollectible as determined under prior GAAP rules. (2) The nine months ended September 30, 2020, includes $3 from the adoption of CECL.
Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance	Below is the loss reserves roll-forward, net of subrogation recoverable and reinsurance, for the affected periods: Nine Months Ended September 30, 2020 2019 Beginning gross loss and loss expense reserves $ (482) $ (107) Reinsurance recoverable 26 23 Beginning balance of net loss and loss expense reserves (508) (130) Losses and loss expenses (benefit): Current year 18 1 Prior years 198 (85) Total (1) (2) 216 (84) Loss and loss expenses paid (recovered): Current year 1 — Prior years 137 299 Total 138 299 Foreign exchange effect 1 (1) Ending net loss and loss expense reserves (429) (514) Impact of VIE consolidation — (72) Reinsurance recoverable (3) 36 26 Ending gross loss and loss expense reserves $ (393) $ (560) (1) Total losses and loss expenses (benefit) includes $(14) and $(6) for the nine months ended September 30, 2020 and 2019, respectively, related to ceded reinsurance. (2) Ambac records the impact of estimated recoveries related to securitized loans in RMBS transactions that breached certain representations and warranties ("R&W's) by transaction sponsors within losses and loss expenses (benefit). The losses and loss expense (benefit) incurred associated with changes in estimated R&W's for the nine months ended September 30, 2020 and 2019, was $(29) and $15, respectively. (3) Represents reinsurance recoverable on future loss and loss expenses. Additionally, the Balance Sheet line "Reinsurance recoverable on paid and unpaid losses" includes reinsurance recoverables (payables) of $1 and $0 as of September 30, 2020 and 2019, respectively, related to previously presented loss and loss expenses and subrogation.
Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable	The tables below summarize information related to policies currently included in Ambac’s loss reserves or subrogation recoverable at September 30, 2020 and December 31, 2019. Gross par exposures include capital appreciation bonds which are reported at the par amount at the time of issuance of the insurance policy as opposed to the current accreted value of the bond. The weighted average risk-free rate used to discount loss reserves at September 30, 2020 and December 31, 2019,was 0.9% and 2.1%, respectively. Surveillance Categories as of September 30, 2020 I IA II III IV V Total Number of policies 46 26 16 16 135 3 242 Remaining weighted-average contract period (in years) (1) 10 19 8 16 14 2 15 Gross insured contractual payments outstanding: Principal $ 1,064 $ 1,146 $ 614 $ 1,511 $ 3,386 $ 32 $ 7,752 Interest 329 1,083 492 260 1,465 10 3,639 Total $ 1,393 $ 2,229 $ 1,106 $ 1,771 $ 4,851 $ 41 $ 11,391 Gross undiscounted claim liability $ 4 $ 56 $ 41 $ 536 $ 1,726 $ 41 $ 2,404 Discount, gross claim liability — (2) (1) (71) (185) — (259) Gross claim liability before all subrogation and before reinsurance 4 54 41 465 1,541 41 2,145 Less: Gross RMBS subrogation (2) — — — — (1,760) — (1,760) Discount, RMBS subrogation — — — — 2 — 2 Discounted RMBS subrogation, before reinsurance — — — — (1,757) — (1,757) Less: Gross other subrogation (3) — — — (37) (749) (13) (799) Discount, other subrogation — — — 1 16 1 18 Discounted other subrogation, before reinsurance — — — (36) (734) (11) (781) Gross claim liability, net of all subrogation and discounts, before reinsurance 4 54 40 429 (950) 30 (393) Less: Unearned premium revenue (3) (22) (5) (18) (32) — (80) Plus: Loss expense reserves 2 2 1 7 68 — 80 Gross loss and loss expense reserves $ 2 $ 34 $ 37 $ 418 $ (913) $ 30 $ (393) Reinsurance recoverable reported on Balance Sheet (4) $ — $ 6 $ 10 $ 27 $ (6) $ — $ 37 (1) Remaining weighted-average contract period is weighted based on projected gross claims over the lives of the respective policies. (2) RMBS subrogation represents Ambac’s estimate of subrogation recoveries from RMBS transaction sponsors for R&W breaches. (3) Other subrogation represents subrogation related to excess spread and other contractual cash flows on public finance and structured finance transactions, including RMBS. (4) Reinsurance recoverable reported on the Balance Sheet includes reinsurance recoverables of $36 related to future loss and loss expenses and $1 related to presented loss and loss expenses and subrogation. Surveillance Categories as of December 31, 2019 I IA II III IV V Total Number of policies 34 18 11 16 139 3 221 Remaining weighted-average contract period (in years) (1) 8 21 9 17 14 3 15 Gross insured contractual payments outstanding: Principal $ 668 $ 510 $ 277 $ 857 $ 3,819 $ 37 $ 6,168 Interest 340 507 128 366 1,678 11 3,029 Total $ 1,007 $ 1,016 $ 404 $ 1,223 $ 5,498 $ 48 $ 9,197 Gross undiscounted claim liability $ 2 $ 44 $ 21 $ 541 $ 1,778 $ 48 $ 2,434 Discount, gross claim liability — (5) (1) (152) (381) (2) (541) Gross claim liability before all subrogation and before reinsurance 2 39 20 389 1,397 46 1,893 Less: Gross RMBS subrogation (2) — — — — (1,777) — (1,777) Discount, RMBS subrogation — — — — 49 — 49 Discounted RMBS subrogation, before reinsurance — — — — (1,727) — (1,727) Less: Gross other subrogation (3) — — — (41) (666) (13) (720) Discount, other subrogation — — — 4 47 3 53 Discounted other subrogation, before reinsurance — — — (37) (620) (10) (666) Gross claim liability, net of all subrogation and discounts, before reinsurance 2 39 20 353 (950) 36 (501) Less: Unearned premium revenue (1) (9) (1) (7) (35) — (54) Plus: Loss expense reserves 1 1 1 4 67 — 73 Gross loss and loss expense reserves $ 1 $ 30 $ 20 $ 349 $ (918) $ 36 $ (482) Reinsurance recoverable reported on Balance Sheet (4) $ — $ 6 $ 7 $ 24 $ (10) $ — $ 26 (1) Remaining weighted-average contract period is weighted based on projected gross claims over the lives of the respective policies. (2) RMBS subrogation represents Ambac’s estimate of subrogation recoveries from RMBS transaction sponsors for R&W breaches. (3) Other subrogation represents subrogation related to excess spread and other contractual cash flows on public finance and structured finance transactions, including RMBS. (4) Reinsurance recoverable reported on Balance Sheet includes reinsurance recoverables of $26 related to future loss and loss expenses and $0 related to presented loss and loss expenses and subrogation.
Summary of Rollforward of RMBS Subrogation, by Estimation Approach	Below is the rollforward of R&W subrogation for the affected periods: Nine Months Ended September 30, 2020 2019 Discounted R&W subrogation (gross of reinsurance) at beginning of period $ 1,727 $ 1,771 All other changes (1) 30 (16) Discounted R&W subrogation (gross of reinsurance) at end of period $ 1,757 $ 1,755
Intangible Assets Disclosure [Text Block]	The insurance intangible amortization expense is included in the Consolidated Statements of Total Comprehensive Income (Loss), as shown below. Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Insurance amortization expense $ 14 $ 17 $ 41 $ 280 The insurance intangible asset and accumulated amortization are included in the Consolidated Balance Sheets, as shown below. September 30, December 31, Gross carrying value of insurance intangible asset $ 1,268 $ 1,273 Accumulated amortization of insurance intangible asset 885 847 Net insurance intangible asset $ 383 $ 427
Insurance Intangible Asset [Member]
Insurance [Line Items]
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	The estimated future amortization expense for the net insurance intangible asset is as follows: Amortization expense (1) (2) 2020 (three months) $ 11 2021 39 2022 35 2023 32 2024 29 Thereafter 239 (1) The insurance intangible asset will be amortized using a level-yield method based on par exposure of the related financial guarantee insurance or reinsurance contracts. Future amortization considers the use of contractual lives for many bond types which do not have homogeneous pools of underlying collateral. Actual maturities will differ from contractual maturities because borrowers may have the right to call or prepay certain obligations. If those bonds types are retired early, amortization expense may differ in the period of call or refinancing. (2) The weighted-average amortizations period is 7.6 years.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities	The following table sets forth the carrying amount and fair value of Ambac’s financial assets and liabilities as of September 30, 2020 and December 31, 2019, including the level within the fair value hierarchy at which fair value measurements are categorized. As required by the Fair Value Measurement Topic of the ASC, financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Carrying Total Fair Fair Value Measurements Categorized as: September 30, 2020: Level 1 Level 2 Level 3 Financial assets: Fixed income securities: Municipal obligations $ 351 $ 351 $ — $ 351 $ — Corporate obligations 1,091 1,091 2 1,089 — Foreign obligations 77 77 77 — — U.S. government obligations 122 122 122 — — Residential mortgage-backed securities 296 296 — 296 — Collateralized debt obligations 73 73 — 73 — Other asset-backed securities 300 300 — 225 75 Fixed income securities, pledged as collateral: Short-term 152 152 152 — — Short term investments 586 586 509 77 — Other investments (1) 502 488 62 — 35 Cash, cash equivalents and restricted cash 48 48 39 9 — Derivative assets: Interest rate swaps—asset position 95 95 — 9 86 Other assets - equity in sponsored VIE 2 2 — — 2 Other assets-Loans 3 3 — — 3 Variable interest entity assets: Fixed income securities: Corporate obligations 3,029 3,029 — — 3,029 Fixed income securities: Municipal obligations 131 131 — 131 — Restricted cash 2 2 2 — — Loans 2,783 2,783 — — 2,783 Derivative assets: Currency swaps-asset position 53 53 — 53 — Total financial assets $ 9,696 $ 9,682 $ 965 $ 2,312 $ 6,013 Financial liabilities: Long term debt, including accrued interest $ 3,236 $ 3,056 $ — $ 2,679 $ 377 Derivative liabilities: Credit derivatives 1 1 — — 1 Interest rate swaps—liability position 125 125 — 125 — Liabilities for net financial guarantees written (2) (744) 436 — — 436 Variable interest entity liabilities: Long-term debt (includes $4,002 at fair value) 4,169 4,179 — 4,026 153 Derivative liabilities: Interest rate swaps—liability position 1,771 1,771 — 1,771 — Total financial liabilities $ 8,558 $ 9,569 $ — $ 8,601 $ 968 Carrying Total Fair Fair Value Measurements Categorized as: December 31, 2019: Level 1 Level 2 Level 3 Financial assets: Fixed income securities: Municipal obligations $ 215 $ 215 $ — $ 215 $ — Corporate obligations 1,430 1,430 — 1,430 — Foreign obligations 44 44 44 — — U.S. government obligations 156 156 156 — — Residential mortgage-backed securities 248 248 — 248 — Commercial mortgage-backed securities 50 50 — 50 — Collateralized debt obligations 146 146 — 146 — Other asset-backed securities 287 287 — 215 72 Fixed income securities, pledged as collateral: Short-term 85 85 85 — — Short term investments 653 653 598 55 — Other investments (1) 478 493 136 — 61 Cash and cash equivalents and restricted cash 79 79 70 9 — Derivative assets: Interest rate swaps—asset position 75 75 — 8 67 Other assets - equity in sponsored VIE 3 3 — — 3 Other assets-loans 10 13 — — 13 Variable interest entity assets: Fixed income securities: Corporate obligations 2,957 2,957 — — 2,957 Fixed income securities: Municipal obligations 164 164 — 164 — Restricted cash 2 2 2 — — Loans 3,108 3,108 — — 3,108 Derivative assets: Currency swaps—asset position 52 52 — 52 — Total financial assets $ 10,242 $ 10,260 $ 1,091 $ 2,593 $ 6,281 Financial liabilities: Long term debt, including accrued interest $ 3,262 $ 3,274 $ — $ 2,829 $ 445 Derivative liabilities: Interest rate swaps—liability position 89 89 — 89 — Liabilities for net financial guarantees written (2) (863) 284 — — 284 Variable interest entity liabilities: Long-term debt (includes $4,351 at fair value) 4,554 4,567 — 4,408 159 Derivative liabilities: Interest rate swaps—liability position 1,657 1,657 — 1,657 — Total financial liabilities $ 8,699 $ 9,872 $ — $ 8,983 $ 889 (1) Excluded from the fair value measurement categories in the table above are investment funds of $391 and $296 as of September 30, 2020 and December 31, 2019, respectively, which are measured using NAV as a practical expedient. (2) The carrying value of net financial guarantees written includes the following balance sheet items: Premium receivables; Reinsurance recoverable on paid and unpaid losses; Deferred ceded premium; Subrogation recoverable; Insurance intangible asset; Unearned premiums; Loss and loss expense reserves; Ceded premiums payable, premiums taxes payable and other deferred fees recorded in Other liabilities.
Summary of Changes in Level 3 Fair Value Category	The following tables present the changes in the Level 3 fair value category for the periods presented in 2020 and 2019. Ambac classifies financial instruments in Level 3 of the fair value hierarchy when there is reliance on at least one significant unobservable input to the valuation model. In addition to these unobservable inputs, the valuation models for Level 3 financial instruments typically also rely on a number of inputs that are readily observable either directly or indirectly. Thus, the gains and losses presented below include changes in the fair value related to both observable and unobservable inputs. Level 3 - Financial Assets and Liabilities Accounted for at Fair Value VIE Assets and Liabilities Investments Other (1) Derivatives Investments Loans Long-term Total Three Months Ended September 30, 2020: Balance, beginning of period $ 66 $ 2 $ 86 $ 2,907 $ 2,787 $ — $ 5,848 Total gains/(losses) realized and unrealized: Included in earnings — — 1 1 (43) — (40) Included in other comprehensive income 9 — — 121 116 — 246 Purchases — — — — — — — Issuances — — — — — — — Sales — — — — — — — Settlements — — (2) — (78) — (80) Balance, end of period $ 75 $ 2 $ 85 $ 3,029 $ 2,783 $ — $ 5,974 The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ — $ — $ 1 $ 1 $ (43) $ — $ (41) The amount of total gains/(losses) included in other comprehensive income attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ 9 $ — $ — $ 121 $ 116 $ — $ 246 Three Months Ended September 30, 2019: Balance, beginning of period $ 74 $ 4 $ 62 $ 2,882 $ 4,289 $ (231) $ 7,080 Total gains/(losses) realized and unrealized: Included in earnings 1 — 12 206 127 — 345 Included in other comprehensive income 5 — — (92) (133) 7 (213) Purchases — — — — — — — Issuances — — — — — — — Sales — — — — — — — Settlements — — (1) — (466) — (467) Deconsolidation of VIEs — — — — (851) 223 (627) Balance, end of period $ 79 $ 3 $ 73 $ 2,996 $ 2,966 $ — $ 6,117 The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ — $ — $ 12 $ 206 $ 115 $ — $ 332 (1) Other assets carried at fair value and classified as Level 3 relate to an equity interest in an Ambac sponsored VIE. Level 3 - Financial Assets and Liabilities Accounted for at Fair Value VIE Assets and Liabilities Investments Other Derivatives Investments Loans Long-term Total Nine Months Ended September 30, 2020: Balance, beginning of period $ 72 $ 3 $ 66 $ 2,957 $ 3,108 $ — $ 6,207 Total gains/(losses) realized and unrealized: Included in earnings 1 (1) 24 160 (22) — 161 Included in other comprehensive income 3 — — (71) (85) — (152) Purchases — — — — — — — Issuances — — — — — — — Sales — — — — — — — Settlements (1) — (5) (17) (219) — (242) Balance, end of period $ 75 $ 2 $ 85 $ 3,029 $ 2,783 $ — $ 5,974 The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ — $ (1) $ 23 $ 160 $ (22) $ — $ 160 The amount of total gains/(losses) included in other comprehensive income attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ 3 $ — $ — $ (71) $ (85) $ — $ (152) Nine Months Ended September 30, 2019: Balance, beginning of period $ 72 $ 5 $ 46 $ 2,737 $ 4,288 $ (217) $ 6,930 Total gains/(losses) realized and unrealized: Included in earnings 1 (1) 30 382 301 (15) 698 Included in other comprehensive income 7 — — (106) (151) 8 (241) Purchases — — — — — — — Issuances — — — — — — — Sales — — — — — — — Settlements (1) — (3) (17) (621) — (643) Deconsolidation of VIEs — — — — (851) 223 (627) Balance, end of period $ 79 $ 3 $ 73 $ 2,996 $ 2,966 $ — $ 6,117 The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ — $ (1) $ 30 $ 382 $ 229 $ — $ 639 The tables below provide roll-forward information by class of derivatives measured using significant unobservable inputs. Level 3 - Derivatives by Class Three Months Ended September 30, 2020 Three Months Ended September 30, 2019 Interest Credit Total Interest Credit Total Balance, beginning of period $ 87 $ (1) $ 86 $ 63 $ (1) $ 62 Total gains/(losses) realized and unrealized: Included in earnings 1 — 1 11 1 12 Included in other comprehensive income — — — — — — Purchases — — — — — — Issuances — — — — — — Sales — — — — — — Settlements (2) — (2) (1) — (1) Balance, end of period $ 86 $ (1) $ 85 $ 73 $ — $ 73 The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ 1 $ — $ 1 $ 11 $ — $ 12 Level 3 - Derivatives by Class Nine Months Ended September 30, 2020 Nine Months Ended September 30, 2019 Interest Credit Total Interest Credit Total Balance, beginning of period $ 67 $ — $ 66 $ 47 $ (1) $ 46 Total gains/(losses) realized and unrealized: Included in earnings 24 (1) 24 29 1 30 Included in other comprehensive income — — — — — — Purchases — — — — — — Issuances — — — — — — Sales — — — — — — Settlements (5) — (5) (3) — (3) Balance, end of period $ 86 $ (1) $ 85 $ 73 $ — $ 73 The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date $ 24 $ (1) $ 23 $ 29 $ 1 $ 30
Summary of Gains and Losses (Realized and Unrealized) Relating to Level 3 Assets and Liabilities Included in Earnings	Gains and losses (realized and unrealized) relating to Level 3 assets and liabilities included in earnings for the affected periods are reported as follows: Net Net Gains Income Other Three Months Ended September 30, 2020: Total gains or losses included in earnings for the period $ — $ 1 $ (41) $ — Changes in unrealized gains or losses included in earnings relating to the assets and liabilities still held at the reporting date — 1 (41) — Three Months Ended September 30, 2019: Total gains or losses included in earnings for the period $ 1 $ 12 $ 333 $ — Changes in unrealized gains or losses included in earnings relating to the assets and liabilities still held at the reporting date — 12 321 — Nine Months Ended September 30, 2020: Total gains or losses included in earnings for the period $ 1 $ 24 $ 137 $ (1) Changes in unrealized gains or losses included in earnings relating to the assets and liabilities still held at the reporting date — 23 137 (1) Nine Months Ended September 30, 2019: Total gains or losses included in earnings for the period 1 30 668 (1) Changes in unrealized gains or losses included in earnings relating to the assets and liabilities still held at the reporting date — 30 611 (1)

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments	The amortized cost and estimated fair value of available-for-sale investments, excluding VIE investments, at September 30, 2020 and December 31, 2019, were as follows: Amortized Allowance for Credit Losses Gross Gross Estimated September 30, 2020: Fixed income securities: Municipal obligations $ 322 $ — $ 29 $ 1 $ 351 Corporate obligations (1) 1,066 — 28 3 1,091 Foreign obligations 76 — 1 — 77 U.S. government obligations 118 — 4 1 122 Residential mortgage-backed securities 251 — 45 — 296 Collateralized debt obligations 74 — — 1 73 Other asset-backed securities 268 — 33 1 300 2,176 — 140 6 2,311 Short-term 586 — — — 586 2,761 — 141 6 2,896 Fixed income securities pledged as collateral: Short-term 152 — — — 152 Total collateralized investments 152 — — — 152 Total available-for-sale investments $ 2,914 $ — $ 141 $ 6 $ 3,048 Amortized Gross Gross Estimated Non-credit (2) December 31, 2019: Fixed income securities: Municipal obligations $ 194 $ 22 $ — $ 215 $ — Corporate obligations (1) 1,396 36 2 1,430 — Foreign obligations 44 1 — 44 — U.S. government obligations 157 2 2 156 — Residential mortgage-backed securities 200 47 — 248 — Commercial mortgage-backed securities 49 1 — 50 — Collateralized debt obligations 147 — 1 146 — Other asset-backed securities 263 24 — 287 — 2,450 132 5 2,577 — Short-term 653 — — 653 — 3,103 132 5 3,230 — Fixed income securities pledged as collateral: Short-term 85 — — 85 — Total collateralized investments 85 — — 85 — Total available-for-sale investments $ 3,187 $ 132 $ 5 $ 3,314 $ — (1) Includes Ambac's holdings of the secured notes issued by Ambac LSNI in connection with the Rehabilitation Exit Transactions. (2) At December 31, 2019, represents the amount of non-credit other-than-temporary impairment losses remaining in accumulated other comprehensive income on securities that also had a credit impairment. These losses are included in gross unrealized losses at December 31, 2019.
Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments Held by Successor Ambac, by Contractual Maturity	The amortized cost and estimated fair value of available-for-sale investments, excluding VIE investments, at September 30, 2020, by contractual maturity, were as follows: Amortized Estimated Due in one year or less $ 830 $ 832 Due after one year through five years 876 888 Due after five years through ten years 432 453 Due after ten years 182 206 2,320 2,379 Residential mortgage-backed securities 251 296 Collateralized debt obligations 74 73 Other asset-backed securities 268 300 Total $ 2,914 $ 3,048
Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments	The following table shows gross unrealized losses and fair values of Ambac’s available-for-sale investments, excluding VIE investments, which at September 30, 2020, did not have an allowance for credit losses under the new CECL standard and, at December 31, 2019, did not have other-than-temporary impairments recorded in earnings under prior GAAP. This information is aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position, at September 30, 2020 and December 31, 2019: Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross September 30, 2020: Fixed income securities: Municipal obligations $ 64 $ 1 $ 6 $ — $ 70 $ 1 Corporate obligations 179 3 — — 179 3 Foreign obligations 12 — — — 12 — U.S. government obligations 11 1 — — 11 1 Residential mortgage-backed securities 19 — — — 19 — Collateralized debt obligations 53 1 15 — 67 1 Other asset-backed securities 1 — 4 1 5 1 338 5 25 1 363 6 Short-term 152 — — — 152 — Total securities $ 490 $ 5 $ 25 $ 1 $ 515 $ 6 Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross December 31, 2019: Fixed income securities: Municipal obligations $ 13 $ — $ 10 $ — $ 23 $ — Corporate obligations 63 2 5 — 68 2 Foreign obligations 20 — — — 20 — U.S. government obligations 36 2 2 — 38 2 Residential mortgage-backed securities 5 — — — 5 — Commercial mortgage-backed securities 7 — — — 7 — Collateralized debt obligations 53 — 63 1 116 1 Other asset-backed securities 2 — 7 — 10 — 200 4 88 1 288 5 Short-term 201 — — — 201 — Total securities $ 401 $ 4 $ 88 $ 1 $ 489 $ 5
Summary of Amounts Included in Net Realized (Losses) Gains and Other-Than-Temporary Impairments	The following table details amounts included in net realized gains (losses) and impairments included in earnings for the affected periods: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Gross realized gains on securities $ 5 $ 12 $ 32 $ 46 Gross realized losses on securities (1) — (12) (5) Net foreign exchange (losses) gains (2) 7 — 30 Credit impairments (1) — — — — Intent / requirement to sell impairments (2) — — — — Net realized gains (losses) $ 2 $ 18 $ 20 $ 71 (1) Includes securities which management does not intend to sell and it is not more likely than not that the Company will be required to sell before recovery of the amortized cost basis. (2) Includes securities which management either intends sell or it is more likely than not that the Company will be required to sell before recovery of the amortized cost basis.
Summary of Roll-Forward of Ambac's Cumulative Credit Losses on Debt Securities for Which Portion of Other-than-Temporary Impairment was Recognized in Other Comprehensive Income	The following table presents a roll-forward of Ambac’s cumulative credit losses on debt securities for which a portion of an other-than-temporary impairment was recognized in other comprehensive income under prior GAAP for the nine months ended September 30, 2019: Balance, beginning of period $ 12 Reductions for credit impairments previously recognized on: Securities that matured or were sold during the period (1) Balance, end of period $ 12
Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities	The following table represents the fair value and weighted-average underlying rating of insured securities in Ambac's investment portfolio at September 30, 2020 and December 31, 2019, respectively: Municipal Corporate (2) Mortgage Total Weighted (1) September 30, 2020: Ambac Assurance Corporation $ 310 $ 470 $ 473 $ 1,253 CCC+ National Public Finance Guarantee Corporation 6 — — 6 BBB- Assured Guaranty Municipal Corporation 1 — — 1 C Total $ 318 $ 470 $ 473 $ 1,260 CCC+ December 31, 2019: Ambac Assurance Corporation $ 176 $ 535 $ 442 $ 1,153 B- National Public Finance Guarantee Corporation 11 — — 11 BBB- Total $ 186 $ 535 $ 442 $ 1,164 B- (1) Ratings are based on the lower of Standard & Poor’s or Moody’s rating. If unavailable, Ambac’s internal rating is used. (2) Represents Ambac's holdings of secured notes issued by Ambac LSNI in connection with the Rehabilitation Exit Transactions. These secured notes are insured by Ambac Assurance.
Equity Method Investments [Table Text Block]	Ambac has unfunded commitments of $48 to private credit and private equity funds at September 30, 2020. Fair Value Class of Funds September 30, December 31, Redemption Frequency Redemption Notice Period Real estate properties (1) $ 15 $ 16 quarterly 10 business days Hedge funds (2) 182 65 quarterly 90 days High yields and leveraged loans (3) (10) 53 176 daily 0 - 30 days Private credit (4) 57 51 quarterly 180 days if permitted Insurance-linked investments (5) 2 3 fully redeemed none Equity market investments (6) (10) 33 55 daily 0 days Investment grade floating rate income (7) 69 66 weekly 0 days Private equity (8) 16 — quarterly 90 days if permitted Emerging markets debt (9) (10) 23 — daily 0 days Total equity investments in pooled funds $ 451 $ 432 (1) Investments consist of UK property to generate income and capital growth. (2) This class seeks to generate superior risk-adjusted returns through selective asset sourcing, active trading and hedging strategies across a range of asset types. (3) This class of funds includes investments in a range of instruments including high-yield bonds, leveraged loans, CLOs, ABS and floating rate notes to generate income and capital appreciation. (4) This class aims to obtain high long-term return primarily through credit and preferred equity investments with low liquidity and defined term. (5) This class seeks to generate returns from insurance markets through investments in catastrophe bonds, life insurance and other insurance linked investments. (6) This class of funds aim to achieve long term growth through diversified exposure to global equity markets. (7) This class of funds includes investments in high quality floating rate debt securities including ABS and corporate floating rate notes as well as ultra-short term bonds and money market instruments. (8) This class seeks to generate long-term capital appreciation through investments in private equity, equity-related and other instruments. (9) This class seeks long-term income and growth through investments in the bonds of issuers in emerging markets.
Summary of Net Investment Income	Net investment income (loss) was comprised of the following for the affected periods: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Fixed income securities $ 24 $ 33 $ 79 $ 151 Short-term investments 1 4 4 14 Loans — — — 1 Investment expense (1) (1) (4) (4) Securities available-for-sale and short-term 24 36 80 161 Other investments 14 8 (11) 25 Total net investment income (loss) $ 37 $ 45 $ 69 $ 186 Net investment income (loss) from Other investments primarily represents changes in fair value on securities classified as trading or accounted for under the fair value option, income from investment limited partnerships accounted for under the equity method and the above noted equity interest in an unconsolidated trust accounted for under the equity method. The portion of net unrealized gains (losses) related to trading securities still held at the end of each period is as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Net gains (losses) recognized during the period on trading securities $ 3 $ 6 $ (12) $ 19 Less: net gains (losses) recognized during the reporting period on trading securities sold during the period — 2 (19) 4 Unrealized gains (losses) recognized during the reporting period on trading securities still held at the reporting date $ 3 $ 4 $ 7 $ 15

Derivative Instruments (Tables)

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2020
Summary of Gross Fair Values of Individual Derivative Instruments	The following tables summarize the gross fair values of individual derivative instruments and the impact of legal rights of offset as reported in the Consolidated Balance Sheets as of September 30, 2020 and December 31, 2019: Gross Gross Net Amounts Gross Amount Net September 30, 2020: Derivative Assets: Interest rate swaps $ 95 $ — $ 94 $ — $ 94 Total non-VIE derivative assets $ 95 $ — $ 95 $ — $ 95 Derivative Liabilities: Credit derivatives $ 1 $ — $ 1 $ — $ 1 Interest rate swaps 125 — 125 124 1 Total non-VIE derivative liabilities $ 126 $ — $ 126 $ 124 $ 2 Variable Interest Entities Derivative Assets: Currency swaps $ 53 $ — $ 53 $ — $ 53 Total VIE derivative assets $ 53 $ — $ 53 $ — $ 53 Variable Interest Entities Derivative Liabilities: Interest rate swaps $ 1,771 $ — $ 1,771 $ — $ 1,771 Total VIE derivative liabilities $ 1,771 $ — $ 1,771 $ — $ 1,771 December 31, 2019: Derivative Assets: Interest rate swaps $ 75 $ — $ 75 $ — $ 75 Total non-VIE derivative assets $ 75 $ — $ 75 $ — $ 75 Derivative Liabilities: Interest rate swaps 89 — 90 89 1 Total non-VIE derivative liabilities $ 90 $ — $ 90 $ 89 $ 1 Variable Interest Entities Derivative Assets: Currency swaps $ 52 $ — $ 52 $ — $ 52 Total VIE derivative assets $ 52 $ — $ 52 $ — $ 52 Variable Interest Entities Derivative Liabilities: Interest rate swaps $ 1,657 $ — $ 1,657 $ — $ 1,657 Total VIE derivative liabilities $ 1,657 $ — $ 1,657 $ — $ 1,657
Summary of Location and Amount of Gains and Losses of Derivative Contracts	The following tables summarize the location and amount of gains and losses of derivative contracts in the Unaudited Consolidated Statements of Total Comprehensive Income (Loss) for the three and nine months ended September 30, 2020 and 2019: Location of Gain or (Loss) Amount of Gain or (Loss) Recognized in Consolidated Statement of Total Comprehensive Income (Loss) Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Non-VIE derivatives: Credit derivatives Net gains (losses) on derivative contracts $ — $ 1 $ (1) $ 1 Interest rate swaps Net gains (losses) on derivative contracts 7 (1) (20) (11) Futures contracts Net gains (losses) on derivative contracts — (10) (41) (52) Total Non-VIE derivatives $ 7 $ (10) (61) (61) Variable Interest Entities: Currency swaps Income (loss) on variable interest entities $ (10) $ 10 7 6 Interest rate swaps Income (loss) on variable interest entities (4) (166) (177) (272) Total Variable Interest Entities (14) (156) (170) (266) Total derivative contracts $ (7) $ (166) $ (231) $ (327)
Summary of Notional Amounts of AFS's Trading Derivative Products	As of September 30, 2020 and December 31, 2019, the notional amounts of AFS’s derivatives were as follows: Notional Type of Derivative September 30, December 31, Interest rate swaps—receive-fixed/pay-variable $ 240 $ 332 Interest rate swaps—pay-fixed/receive-variable 726 1,261 US Treasury futures contracts—short 240 755
Variable Interest Entity, Primary Beneficiary [Member]
Summary of Notional Amounts of AFS's Trading Derivative Products	The notional for VIE derivatives outstanding as of September 30, 2020 and December 31, 2019, were as follows: Notional Type of VIE Derivative September 30, December 31, Interest rate swaps—receive-fixed/pay-variable $ 1,164 $ 1,194 Interest rate swaps—pay-fixed/receive-variable 1,103 1,176 Currency swaps 298 329 Credit derivatives — 9

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Major Jurisdictions	The following are the major jurisdictions in which Ambac and its subsidiaries operate and the earliest tax years subject to examination: Jurisdiction Tax Year United States 2010 New York State 2013 New York City 2016 United Kingdom 2016 Italy 2015
Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]	U.S. and foreign components of pre-tax income (loss) were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 U.S. $ (106) $ 60 $ (412) $ (61) Foreign (2) 9 (15) (11) Total $ (108) $ 69 $ (427) $ (72)
Schedule of Components of Income Tax Expense (Benefit)	The components of the provision for income taxes were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Current taxes U. S. federal $ — $ — $ — $ — U.S. state and local — — — (3) Foreign (1) 4 — 38 Current taxes (1) 4 1 35 Deferred taxes Foreign 1 (1) (5) (2) Deferred taxes 1 (1) (5) (2) Provision for income taxes $ — $ 3 $ (5) $ 33
Schedule of Net Operating Loss And Tax Credit Carryovers	Pursuant to an intercompany tax sharing agreement, to the extent Ambac Assurance generates taxable income after September 30, 2011, which is offset with "Allocated NOLs" of $3,650, it is obligated to make payments (“Tolling Payments”), subject to certain credits, to AFG in accordance with the following NOL usage table, where the “Applicable Percentage” is applied to the aggregate amount of federal income tax liability that would have been paid if the Allocated NOLs were not available. Pursuant to the Closing Agreement between Ambac and the Internal Revenue Service ("IRS"), the IRS will receive 12.5% of Tier C and 17.5% of Tier D payments, if made. NOL Usage Table NOL Usage Tier Allocated NOLs Applicable A The first $479 15% B The next $1,057 after Tier A 40% C The next $1,057 after Tier B 10% D The next $1,057 after Tier C 15% As of December 31, 2018, Ambac Assurance generated cumulative taxable income of $1,508, leaving $2,142 of the $3,650 Allocated NOLs subject to Tolling Payments. For the year ended December 31, 2019, and nine months ended September 30, 2020, Ambac Assurance generated NOLs of approximately $143 and $197, respectively, which will need to be utilized before any new Tolling Payments will be generated.

Background and Business Descr_2

Background and Business Description - Additional Information (Details)	9 Months Ended
	Sep. 30, 2020
Background And Basis Of Presentation [Line Items]
Entity Incorporation, Date of Incorporation	Apr. 29, 1991

Basis of Presentation and Sig_4

Basis of Presentation and Significant Accounting Policies FX gain (loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Foreign Currency Transaction Gain (Loss), before Tax			$ 2	$ 19
Gain (Loss) on Investments [Member]
Foreign Currency Transaction Gain (Loss), before Tax	$ (2)	$ 7	$ 0	$ 30

Basis of Presentation and Sig_5

Basis of Presentation and Significant Accounting Policies Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Stockholders' Equity Attributable to Noncontrolling Interest	$ 60	$ 60
Preferred Stock, Shares Issued	0
Fixed Income Securities [Member]
Derivative [Line Items]
Accrued Investment Income Receivable	$ 10

Basis of Presentation and Sig_6

Basis of Presentation and Significant Accounting Policies Supplemental Cash Flow information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Non Cash Exchange of Puerto Rico Bonds		$ 510
Income Taxes Paid	$ 11	11
Cash and cash equivalents	37	52	$ 24
Restricted Cash	10	13	55
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	50	68	81	$ 83
Long-term Debt [Member]
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	83	110
Variable Interest Entity, Primary Beneficiary [Member]
Restricted Cash	$ 2	$ 3	$ 2

Available-for-sale Debt Securit

Available-for-sale Debt Securities (Details) $ in Millions	Sep. 30, 2020USD ($)
Fixed Income Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Accrued Investment Income Receivable	$ 10

Special Purpose Entities, Inc_2

Special Purpose Entities, Including Variable Interest Entities - Additional Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020USD ($)Entity	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)Entity	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)Entity
Variable Interest Entities [Line Items]
Variable Interest Entity Change in Fair Value of Assets and Liabilities	$ (1)	$ 2	$ (3)	$ 7
Realized Investment Gains (Losses)	2	18	20	71
Other Operating Income (Expense), Net	2	141	2	133
Fair value of special purpose entities	2		2		$ 3
Gain (loss) from consolidating FG VIEs	0	0	0	15
Variable Interest Entity Deconsolidation Gain Loss	0	(2)	0	(2)
Variable Interest Entity, Measure of Activity, Income or Loss before Tax	0	11	3	30
Long-term debt	2,737		2,737		2,822
Equity Method Investments	49		$ 49		46
Asset-Backed Securities and Utility Obligations [Member]
Variable Interest Entities [Line Items]
Weighted average life			4 months 24 days
Average rating of assets held by sponsored special purpose entities			BBB+
Sponsored Variable Interest Entities [Member]
Variable Interest Entities [Line Items]
Total principal amount of debt outstanding	$ 392		$ 392		$ 403
Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number Of Consolidated Variable Interest Entities | Entity	6		6		7
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, before Tax	$ 0	0	$ (2)	0
VIE Change in FV of Assets Liabilities, Net of Credit Risk Change	0	2	(5)	6
Interest Expense, Long-term Debt	(1)	(3)	(5)	(9)
Other Operating Income (Expense), Net	0	$ 0	0	(1)
Long-term debt	$ 4,169		$ 4,169		$ 4,554
Consolidated Variable Interest Entities [Member]
Variable Interest Entities [Line Items]
Number of DeConsolidated Variable Interest Entities	0	1	1
Ambac UK [Member] | Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number Of Consolidated Variable Interest Entities | Entity	5		5		6
Ambac UK [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Long-term debt	$ 4,002		$ 4,002		$ 4,351
Ambac Assurance [Member]
Variable Interest Entities [Line Items]
Carry Value Secured Notes from LSNI	470		470		535
Fixed Income Investments [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Gross Investment Income, Operating	2	$ 3	5	8
Realized Investment Gains (Losses)	0	$ 12	8	$ 13
Ambac Note Post Exit From Rehabilitation [Member] | Ambac Assurance Corporation [Member]
Variable Interest Entities [Line Items]
Long-term debt	$ 1,648		$ 1,648		$ 1,763

Special Purpose Entities, Inc_3

Special Purpose Entities, Including Variable Interest Entities - Summary of Fair Value of Fixed Income Securities, by Asset-Type, Held by Consolidated Variable Interest Entities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 2,914
Investments:
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	141	$ 132
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 6	$ 5

Special Purpose Entities, Inc_4

Special Purpose Entities, Including Variable Interest Entities - Supplemental Information about Loans Held as Assets and Long-Term Debt Associated with Consolidated Variable Interest Entities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entities [Line Items]
Long-term debt	$ 2,737	$ 2,822
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Long-term debt	4,169	4,554
Long-term debt, Estimated fair value	4,002	4,351
Loans Unpaid Principal Balance	2,450	2,618
Long Term Debt Unpaid Principal Balance	$ 3,604	$ 3,800

Special Purpose Entities, Inc_5

Special Purpose Entities, Including Variable Interest Entities - Summary of Carrying Amount of Assets, Liabilities and Maximum Exposure to Loss of Ambac's Variable Interests in Non-Consolidated Variable Interest Entities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	$ 28,881	$ 31,506
Insurance Assets	2,361	2,247
Insurance Liabilities	1,177	1,083
Derivative Liabilities	7
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Derivative Liabilities		7
Global Public Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	22,183	23,341
Insurance Assets	268	287
Insurance Liabilities	316	321
Derivative Liabilities	(1)	0
Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	6,698	8,165
Insurance Assets	2,093	1,961
Insurance Liabilities	860	762
Derivative Liabilities	8	8
Global Structured Finance [Member] | Residential Mortgage-Backed Securities [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	4,535	5,373
Insurance Assets	2,063	1,913
Insurance Liabilities	604	523
Derivative Liabilities	0	0
Global Structured Finance [Member] | Other Consumer Asset-Backed [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	1,120	1,373
Insurance Assets	26	31
Insurance Liabilities	240	216
Derivative Liabilities	0	0
Global Structured Finance [Member] | Other Commercial Asset-Backed [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	52	314
Insurance Assets	3	9
Insurance Liabilities	1	6
Derivative Liabilities	0	0
Global Structured Finance [Member] | Other [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	991	1,107
Insurance Assets	0	7
Insurance Liabilities	15	18
Derivative Liabilities	$ 8	$ 8

Variable Interest Entities Spec

Variable Interest Entities Special Purpose Entities, including Variable Interest Entities - Summary of Assets and Liabilities (Details) $ in Millions	Sep. 30, 2020USD ($)Entity	Dec. 31, 2019USD ($)Entity	Sep. 30, 2019USD ($)
Debt Securities, Available-for-sale, Amortized Cost	$ 2,914
Fixed income securities, at fair value	3,048
Restricted Cash	10	$ 55	$ 13
Derivative assets	95	75
Other assets	60	95
Total assets	12,812	13,320
Interest Payable	499	441
Long-term debt	2,737	2,822
Derivative Liability	126	90
Other Liabilities	91	93
Liabilities	11,718	11,783
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	141	132
Variable Interest Entity, Primary Beneficiary [Member]
Fixed income securities, at fair value	3,160	3,121
Restricted Cash	2	2	$ 3
Financing Receivable, after Allowance for Credit Loss	2,783	3,108
Derivative assets	53	52
Other assets	1	3
Total assets	5,998	6,286
Interest Payable	0	1
Long-term debt	4,002	4,351
Long-term Debt, at par less amortized discount	167	203
Long-term debt	4,169	4,554
Derivative Liability	1,771	1,657
Liabilities	5,940	6,212
Variable Interest Entity, Primary Beneficiary [Member] | Corporate Debt Securities [Member]
Fixed income securities, at fair value	3,029	2,957
Variable Interest Entity, Primary Beneficiary [Member] | Municipal Bonds [Member]
Debt Securities, Available-for-sale, Amortized Cost	112	139
Fixed income securities, at fair value	131	164
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	19	25
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member]
Fixed income securities, at fair value	3,029	2,957
Restricted Cash	1	1
Financing Receivable, after Allowance for Credit Loss	2,783	3,108
Derivative assets	53	52
Other assets	0	1
Total assets	5,865	6,119
Interest Payable	0	1
Long-term debt	4,002	4,351
Long-term Debt, at par less amortized discount	0	0
Long-term debt	4,002	4,351
Derivative Liability	1,771	1,657
Liabilities	5,773	6,009
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member] | Corporate Debt Securities [Member]
Fixed income securities, at fair value	3,029	2,957
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member] | Municipal Bonds [Member]
Fixed income securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Ambac Assurance [Member]
Fixed income securities, at fair value	131	164
Restricted Cash	1	1
Financing Receivable, after Allowance for Credit Loss	0	0
Derivative assets	0	0
Other assets	1	2
Total assets	133	167
Interest Payable	0	0
Long-term debt	0	0
Long-term Debt, at par less amortized discount	167	203
Long-term debt	167	203
Derivative Liability	0	0
Liabilities	167	203
Variable Interest Entity, Primary Beneficiary [Member] | Ambac Assurance [Member] | Corporate Debt Securities [Member]
Fixed income securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Ambac Assurance [Member] | Municipal Bonds [Member]
Fixed income securities, at fair value	$ 131	$ 164
Consolidated Entities [Member]
Number Of Consolidated Variable Interest Entities | Entity	6	7
Consolidated Entities [Member] | Ambac UK [Member]
Number Of Consolidated Variable Interest Entities | Entity	5	6
Consolidated Entities [Member] | Ambac Assurance [Member]
Number Of Consolidated Variable Interest Entities | Entity	1	1

Comprehensive Income - Schedule

Comprehensive Income - Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ (48)	$ 19	$ 42	$ (49)
Other comprehensive income before reclassifications	(74)	(26)	2	(147)
Amounts reclassified from accumulated other comprehensive income	(3)	(19)	(18)	(72)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	71	7	(20)	75
Ending Balance	22	26	22	26
Income Tax Expense (Benefit)	0	3	(5)	33
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	109	157	151	86
Other comprehensive income before reclassifications	(45)	(50)	(20)	(174)
Amounts reclassified from accumulated other comprehensive income	(2)	(18)	(19)	(71)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	42	31	1	103
Ending Balance	152	189	152	189
Accumulated Translation Adjustment [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(164)	(145)	(116)	(142)
Other comprehensive income before reclassifications	(29)	24	20	28
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	29	(24)	(20)	(28)
Ending Balance	(135)	(169)	(135)	(169)
Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	0	(2)	(2)	(2)
Other comprehensive income before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income	0	0	2	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0	0	2	0
Ending Balance	0	(2)	0	(2)
Other Postretirement Benefits Plan [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	6	9	8	9
Other comprehensive income before reclassifications	0	0	2	(1)
Amounts reclassified from accumulated other comprehensive income	0	0	(1)	(1)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0	0	(3)	0
Ending Balance	6	9	6	9
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Income Tax Expense (Benefit)	0	1	1	6
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Income Tax Expense (Benefit)			0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Other Postretirement Benefits Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	0	0	(1)	(1)
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income	0	0	(1)	(1)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	0	0	0	0
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	0	0	(1)	(1)
Income Tax Expense (Benefit)	$ 0	$ 0	$ 0	$ 0

Comprehensive Income - Schedu_2

Comprehensive Income - Schedule of Amounts Reclassed Out of Each Component of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	$ 0	$ (3)	$ 5	$ (33)
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax	0	0	2	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(3)	(19)	(18)	(72)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized investment gains	(2)	(20)	(20)	(77)
Net of tax and noncontrolling interest	(2)	(18)	(19)	(71)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(2)	(18)	(19)	(71)
Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax	0	0	2	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0	2	0
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, before Tax, after Reclassification Adjustment	0	0	2	0
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax and noncontrolling interest	(3)	(19)	(18)	(72)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	0	(1)	(1)	(6)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)			0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Gain (Loss), Financial Liability, Fair Value Option, Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	0	0		0
Other Postretirement Benefits Plan [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0	(1)	(1)
Other Postretirement Benefits Plan [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	0	0	0	0
Prior service cost	0	0	(1)	(1)
Actuarial gains (losses)	0	0	0	0
Total before tax	0	0	(1)	(1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 0	$ 0	$ (1)	$ (1)

Net Income Per Share - Addition

Net Income Per Share - Additional Information (Details) - $ / shares	9 Months Ended
	Sep. 30, 2020	May 01, 2013	Apr. 30, 2013
Schedule Of Earnings Per Share [Line Items]
Common stock, shares outstanding	45,809,139
Par value of common stock issued	$ 0.01		$ 0.01
Exercise price of common stock		$ 16.67
Warrants outstanding	4,877,749
Common Stock [Member]
Schedule Of Earnings Per Share [Line Items]
Number of new common stock issued	253,739

Net Income Per Share - Reconcil

Net Income Per Share - Reconciliation of Common Shares Used for Basic and Diluted Earnings Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of common shares used for basic earnings per share	46,178,730	45,997,694	46,135,399	45,939,284
Effect of potential dilutive shares:
Weighted average number of common shares and potential dilutive shares used for diluted earnings per share	46,178,730	47,020,058	46,135,399	45,939,284
Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	4,877,749	0	4,877,754	4,877,783
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	16,667	16,667	16,667	16,667
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	333,526	0	286,279	249,025
Performance Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	972,138	0	932,777	748,700
Warrants [Member]
Effect of potential dilutive shares:
Effect of potential dilutive shares	0	450,384	0	0
Share-based Payment Arrangement, Option [Member]
Effect of potential dilutive shares:
Effect of potential dilutive shares	0	0	0	0
Restricted Stock Units (RSUs) [Member]
Effect of potential dilutive shares:
Effect of potential dilutive shares	0	78,751	0	0
Performance Shares [Member]
Effect of potential dilutive shares:
Effect of potential dilutive shares	0	493,229	0	0

Net Income Per Share Schedule o

Net Income Per Share Schedule of Basic and Dilutive Securities for EPS (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Weighted Average Number of Shares Outstanding, Basic	46,178,730	45,997,694	46,135,399	45,939,284
Weighted Average Number of Shares Outstanding, Diluted	46,178,730	47,020,058	46,135,399	45,939,284
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	333,526	0	286,279	249,025
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	16,667	16,667	16,667	16,667
Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	4,877,749	0	4,877,754	4,877,783
Performance Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	972,138	0	932,777	748,700
Performance Shares [Member]
Weighted Average Number Diluted Shares Outstanding Adjustment	0	493,229	0	0
Restricted Stock Units (RSUs) [Member]
Weighted Average Number Diluted Shares Outstanding Adjustment	0	78,751	0	0

Financial Guarantee Insurance_2

Financial Guarantee Insurance Contracts - Additional Information (Details) $ in Thousands, € in Millions, £ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2020USD ($)	Mar. 31, 2020	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2020GBP (£)	Sep. 30, 2020EUR (€)	Jun. 30, 2020USD ($)	Sep. 30, 2019GBP (£)	Sep. 30, 2019EUR (€)	Jun. 30, 2019USD ($)	Dec. 31, 2018USD ($)
Insurance [Line Items]
Reinsurance Recoverable Credit Exposure	$ 1,000			$ 1,000
Reinsurance Recoverable, Allowance for Credit Loss	0			0
Public Finance Puerto Rico Net Par Outstanding	1,070,000			1,070,000
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	1,757,000			1,757,000		$ 1,727,000
Financial Guarantee Insurance Contracts, Premium Receivable	$ 372,000		$ 415,000	$ 372,000	$ 415,000	$ 416,000							$ 495,000
Estimated Future Premium Payments Weighted Average Discounted Rate	2.20%			2.20%		2.40%	2.20%	2.20%
Reinsurance Payable	$ 27,000			$ 27,000		$ 29,000
Weighted average period of future premiums				8 years 6 months		8 years 6 months
Uncollectable premium receivables	18,000			$ 18,000
Accelerated premium revenue for retired obligations	5,000		2,000	6,000	8,000
Reinsurance recoveries of losses included in losses and loss expenses				(14,000)	(6,000)
Losses and loss expense reserves ceded to reinsurers	36,000		26,000	36,000	26,000	$ 26,000							23,000
Subrogation recoveries, net of reinsurance	(1,731,000)			(1,731,000)		(1,702,000)
Amortization of insurance intangible assets	14,000		17,000	41,000	280,000
Intangible Assets, Gross (Excluding Goodwill)	1,268,000			1,268,000		1,273,000
Finite-Lived Intangible Assets, Accumulated Amortization	885,000			885,000		847,000
Insurance intangible asset	383,000			383,000		427,000
Possible Increase in Loss Reserves Related to Puerto Rico	1,200,000			1,200,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,095,000		1,629,000	1,095,000	1,629,000	$ 1,536,000			$ 1,129,000			$ 1,553,000	$ 1,633,000
Stockholders Equity After Possible Increase in Domestic Public Finance Loss Reserves	(105,000)			(105,000)
Stockholders Equity After Possible Inability to Realize R&W Subrogation Recoveries	(636,000)			$ (636,000)
Loss Reserves [Member]
Insurance [Line Items]
Weighted average risk-free rate used to discount loss reserves		2.10%		0.90%
United Kingdom, Pounds
Insurance [Line Items]
Financial Guarantee Insurance Contracts, Premium Receivable	112,000		124,000	$ 112,000	124,000		£ 87			£ 101
Euro Member Countries, Euro
Insurance [Line Items]
Financial Guarantee Insurance Contracts, Premium Receivable	21,000		$ 22,000	21,000	$ 22,000			€ 18			€ 20
Commonwealth of Puerto Rico [Member]
Insurance [Line Items]
Domestic Public Finance Losses	43,000			263,000
Long-term Debt [Member]
Insurance [Line Items]
Gain Contingency, Unrecorded Amount	1,600,000			1,600,000
Long-term Debt [Member]
Insurance [Line Items]
Gain Contingency, Unrecorded Amount	$ 1,400,000			$ 1,400,000

Financial Guarantee Insurance_3

Financial Guarantee Insurance Contracts - Summary of Gross Premium Receivable Roll-Forward (Direct and Assumed Contracts) (Details) $ in Thousands, € in Millions, £ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2020GBP (£)	Sep. 30, 2020EUR (€)	Sep. 30, 2019USD ($)	Sep. 30, 2019GBP (£)	Sep. 30, 2019EUR (€)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2020USD ($)	Jan. 01, 2020USD ($)	Dec. 31, 2019USD ($)
Insurance [Line Items]
Allowance for Doubtful Accounts, Premiums and Other Receivables	$ 18,000						$ 18,000		$ 16,000		$ 9,000
Premiums Receivable, Gross	390,000						390,000
Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount	5,000			$ 2,000			6,000	$ 8,000
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Beginning premium receivable							416,000	495,000
Premium receipts							36,000	37,000
Adjustments for changes in expected and contractual cash flows							(4,000)	(33,000)
Accretion of premium receivable discount							7,000	9,000
financial guarantee insurance contracts premium receivable deconsolidation of VIE								3,000
Uncollectable premiums							(5,000)	(7,000)
Other adjustments (including foreign exchange)							(2,000)	(16,000)
Ending premium receivable	372,000			415,000			372,000	415,000
Premium Receivable, Allowance for Credit Loss	18,000						18,000
Premium Receivable, Credit Loss Expense (Reversal)	2,000						9,000
Premium Receivable, Allowance for Credit Loss, Writeoff	0						0
Premium Receivable, Allowance for Credit Loss, Recovery	0						0
Financing Receivable, Past Due	2,000						2,000
Financing Receivable, 90 Days or More Past Due, Still Accruing	2,000						2,000
Reinsurance Recoverable, Allowance for Credit Loss	0						0
United Kingdom, Pounds
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Ending premium receivable	112,000	£ 87		124,000	£ 101		112,000	124,000
Euro Member Countries, Euro
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Ending premium receivable	21,000		€ 18	$ 22,000		€ 20	21,000	$ 22,000
Accounting Standards Update 2016-13 [Member]
Insurance [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	(4,000)						(4,000)
Premiums Receivable [Member] | Accounting Standards Update 2016-13 [Member]
Insurance [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption										$ (3,000)
Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross	39,000						39,000
Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	3,000						3,000
Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	29,000						29,000
Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	16,000						16,000
Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	302,000						302,000
Structured Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	63,000						63,000
Structured Finance [Member] | Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Structured Finance [Member] | Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	3,000						3,000
Structured Finance [Member] | Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	15,000						15,000
Structured Finance [Member] | Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	16,000						16,000
Structured Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	29,000						29,000
International Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	141,000						141,000
International Finance [Member] | Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross	13,000						13,000
International Finance [Member] | Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
International Finance [Member] | Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	15,000						15,000
International Finance [Member] | Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
International Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	113,000						113,000
Public Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	186,000						186,000
Public Finance [Member] | Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross	26,000						26,000
Public Finance [Member] | Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Public Finance [Member] | Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Public Finance [Member] | Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Public Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	160,000						160,000
Other Public Finance Sectors [Member] | Public Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	16,000						16,000
Other Public Finance Sectors [Member] | Public Finance [Member] | Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross	13,000						13,000
Other Public Finance Sectors [Member] | Public Finance [Member] | Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Other Public Finance Sectors [Member] | Public Finance [Member] | Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Other Public Finance Sectors [Member] | Public Finance [Member] | Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Other Public Finance Sectors [Member] | Public Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	2,000						2,000
Other International [Member] | International Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	6,000						6,000
Other International [Member] | International Finance [Member] | Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Other International [Member] | International Finance [Member] | Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Other International [Member] | International Finance [Member] | Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Other International [Member] | International Finance [Member] | Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Other International [Member] | International Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	6,000						6,000
Mortgage Backed And Home Equity [Member] | Structured Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	23,000						23,000
Mortgage Backed And Home Equity [Member] | Structured Finance [Member] | Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross
Mortgage Backed And Home Equity [Member] | Structured Finance [Member] | Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	1,000						1,000
Mortgage Backed And Home Equity [Member] | Structured Finance [Member] | Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	3,000						3,000
Mortgage Backed And Home Equity [Member] | Structured Finance [Member] | Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	16,000						16,000
Mortgage Backed And Home Equity [Member] | Structured Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	3,000						3,000
Structured Insurance [Domain] | Structured Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	16,000						16,000
Structured Insurance [Domain] | Structured Finance [Member] | Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Structured Insurance [Domain] | Structured Finance [Member] | Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Structured Insurance [Domain] | Structured Finance [Member] | Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Structured Insurance [Domain] | Structured Finance [Member] | Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Structured Insurance [Domain] | Structured Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	16,000						16,000
Student Loans [Member] | Structured Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	17,000						17,000
Student Loans [Member] | Structured Finance [Member] | Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Student Loans [Member] | Structured Finance [Member] | Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	2,000						2,000
Student Loans [Member] | Structured Finance [Member] | Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	12,000						12,000
Student Loans [Member] | Structured Finance [Member] | Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Student Loans [Member] | Structured Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	3,000						3,000
Other Structured Finance [Member] | Structured Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	7,000						7,000
Other Structured Finance [Member] | Structured Finance [Member] | Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Other Structured Finance [Member] | Structured Finance [Member] | Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Other Structured Finance [Member] | Structured Finance [Member] | Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Other Structured Finance [Member] | Structured Finance [Member] | Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Other Structured Finance [Member] | Structured Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	7,000						7,000
Sovereign And Sub Sovereign [Member] | International Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	105,000						105,000
Sovereign And Sub Sovereign [Member] | International Finance [Member] | Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross	13,000						13,000
Sovereign And Sub Sovereign [Member] | International Finance [Member] | Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Sovereign And Sub Sovereign [Member] | International Finance [Member] | Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	15,000						15,000
Sovereign And Sub Sovereign [Member] | International Finance [Member] | Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Sovereign And Sub Sovereign [Member] | International Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	78,000						78,000
Investor Owned And Public Utilities [Member] | International Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	29,000						29,000
Investor Owned And Public Utilities [Member] | International Finance [Member] | Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Investor Owned And Public Utilities [Member] | International Finance [Member] | Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Investor Owned And Public Utilities [Member] | International Finance [Member] | Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Investor Owned And Public Utilities [Member] | International Finance [Member] | Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Investor Owned And Public Utilities [Member] | International Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	29,000						29,000
Housing Revenue [Member] | Public Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	171,000						171,000
Housing Revenue [Member] | Public Finance [Member] | Surveillance Category Onea [Member]
Insurance [Line Items]
Premiums Receivable, Gross	13,000						13,000
Housing Revenue [Member] | Public Finance [Member] | Surveillance Category Two [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Housing Revenue [Member] | Public Finance [Member] | Surveillance Category Three [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Housing Revenue [Member] | Public Finance [Member] | Surveillance Category Four [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0						0
Housing Revenue [Member] | Public Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	$ 158,000						$ 158,000

Financial Guarantee Insurance_4

Financial Guarantee Insurance Contracts - Effect of Reinsurance on Premiums Written and Earned (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Written	$ (13)	$ (13)	$ (2)	$ (31)
Assumed Reinsurance Premiums Written	0	0	0	0
Ceded Reinsurance Premiums Written	0	23	(1)	22
Premiums written, net of reinsurance	13	36	2	53
Direct Premiums Earned	18	13	45	53
Assumed Reinsurance Premiums Earned	0	0	1	0
Ceded Reinsurance Premiums Earned	3	3	9	7
Reinsurance on premiums earned, Net	$ 15	$ 10	$ 36	$ 46

Financial Guarantee Insurance_5

Financial Guarantee Insurance Contracts - Summarized Future Gross Undiscounted Premiums Expected to be Collected, and Future Expected Premiums Earned, Net of Reinsurance (Details) $ in Millions	Sep. 30, 2020USD ($)
Future premiums expected to be collected, December 31, 2020	$ 11
Future premiums expected to be collected, December 31, 2021	36
Future premiums expected to be collected, December 31, 2022	34
Future premiums expected to be collected, December 31, 2023	33
Future premiums expected to be collected, December 31, 2024	31
Future premiums expected to be collected, December 31, 2029	138
Future premiums expected to be collected, December 31, 2034	101
Future premiums expected to be collected, December 31, 2039	50
Future premiums expected to be collected, December 31, 2044	22
Future premiums expected to be collected, December 31, 2049	9
Future premiums expected to be collected, December 31, 2054	1
Future premiums expected to be collected, Total	467
Future expected premiums to be earned, net of reinsurance, December 31, 2020	10
Future expected premiums to be earned, net of reinsurance, December 31, 2021	35
Future expected premiums to be earned, net of reinsurance, December 31, 2022	33
Future expected premiums to be earned, net of reinsurance, December 31, 2023	30
Future expected premiums to be earned, net of reinsurance, December 31, 2024	29
Future expected premiums to be earned, net of reinsurance, December 31, 2029	120
Future expected premiums to be earned, net of reinsurance, December 31, 2034	81
Future expected premiums to be earned, net of reinsurance, December 31, 2039	37
Future expected premiums to be earned, net of reinsurance, December 31, 2044	14
Future expected premiums to be earned, net of reinsurance, December 31, 2049	5
Future expected premiums to be earned, net of reinsurance, December 31, 2054	1
Future expected premiums to be earned, net of reinsurance, Total	$ 395

Financial Guarantee Insurance_6

Financial Guarantee Insurance Contracts Financial Guarantee Insurance Contracts - Components of Loss and Loss Expense Reserves and Subrogation Recoverable (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$ 1	$ 0	$ 0
Loss Reserves Ceded To Reinsurers	36	26	26	$ 23
Policyholder Benefits and Claims Incurred, Ceded	14	6
Liability for Unpaid Claims and Claims Adjustment Expense, Net	(429)	$ (514)	(508)	$ (130)
Loss and loss expense reserves	1,801		1,548
Subrogation recoverable	(2,194)		(2,029)
Claim liability reported on Balance Sheet, before reinsurance	(393)		(482)
Present Value of Expected Net Cash Flows- Claims and Loss Expenses [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	2,116		1,835
Subrogation recoverable	109		131
Claim liability reported on Balance Sheet, before reinsurance	2,225		1,966
Present Value of Expected Net Cash Flows-Recoveries [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	(235)		(233)
Subrogation recoverable	(2,303)		(2,160)
Claim liability reported on Balance Sheet, before reinsurance	(2,538)		(2,394)
Unearned Premium Reserve [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	(80)		(54)
Subrogation recoverable	0		0
Claim liability reported on Balance Sheet, before reinsurance	$ (80)		$ (54)

Financial Guarantee Insurance_7

Financial Guarantee Insurance Contracts - Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Loss And Loss Adjustment Expense Reserves [Line Items]
Impact of VIE Consolidation on Gross Loss and Loss Reserves			$ 0		$ (72)
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross loss and loss expense reserves	$ (482)	$ (107)
Less reinsurance on loss and loss expense reserves	26	23
Beginning balance of net loss and loss expense reserves	(508)	(130)
Current Year Claims and Claims Adjustment Expense	18	1
Prior Year Claims and Claims Adjustment Expense	198	(85)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	216	(84)
Claim and loss expense payments, net of subrogation and reinsurance	(1)	0
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance	(137)	(299)
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	138	299
Liability for Unpaid Claims and Claims Adjustment Expense, Foreign Currency Translation Gain (Loss)	1	(1)
Liability for Unpaid Claims and Claims Adjustment Expense, Net	(508)	(130)	(429)	$ (508)	(514)
Add reinsurance on loss and loss expense reserves	36	26
Ending gross loss and loss expense reserves	(393)	(560)
Policyholder Benefits and Claims Incurred, Ceded	14	6
Net Incurred RMBS Subrogation Recoveries	$ 29	$ (15)
Ceded Loss And Loss Expenses Paid Not Yet Recovered			$ 1	$ 0	$ 0

Financial Guarantee Insurance_8

Financial Guarantee Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020USD ($)Policies	Dec. 31, 2019USD ($)Policies	Sep. 30, 2019USD ($)	Dec. 31, 2018USD ($)
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	$ 36	$ 26	$ 26	$ 23
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$ 1	$ 0	$ 0
Number of policies | Policies	242	221
Remaining weighted-average contract period (in years)	15 years	15 years
Gross insured contractual payments outstanding:
Principal	$ 7,752	$ 6,168
Interest	3,639	3,029
Total	11,391	9,197
Gross undiscounted claim liability	2,404	2,434
Discount, gross claim liability	259	541
Gross claim liability before all subrogation and before reinsurance	2,145	1,893
Less:
Gross RMBS subrogation	(1,760)	(1,777)
Discount, RMBS subrogation	2	49
Discounted RMBS subrogation, before reinsurance	(1,757)	(1,727)
Less:
Gross other subrogation	(799)	(720)
Discount, other subrogation	18	53
Discounted other subrogation, before reinsurance	(781)	(666)
Gross claim liability, net of all subrogation and discounts, before reinsurance	(393)	(501)
Less: Unearned premium reserves	(80)	(54)
Plus: Loss adjustment expenses reserves	80	73
Claim liability reported on Balance Sheet, before reinsurance	(393)	(482)
Reinsurance recoverable reported on Balance Sheet	$ 37	$ 26
I/SL [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	46	34
Remaining weighted-average contract period (in years)	10 years	8 years
Gross insured contractual payments outstanding:
Principal	$ 1,064	$ 668
Interest	329	340
Total	1,393	1,007
Gross undiscounted claim liability	4	2
Discount, gross claim liability	0	0
Gross claim liability before all subrogation and before reinsurance	4	2
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	0	0
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	4	2
Less: Unearned premium reserves	(3)	(1)
Plus: Loss adjustment expenses reserves	2	1
Claim liability reported on Balance Sheet, before reinsurance	2	1
Reinsurance recoverable reported on Balance Sheet	$ 0	$ 0
IA [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	26	18
Remaining weighted-average contract period (in years)	19 years	21 years
Gross insured contractual payments outstanding:
Principal	$ 1,146	$ 510
Interest	1,083	507
Total	2,229	1,016
Gross undiscounted claim liability	56	44
Discount, gross claim liability	2	5
Gross claim liability before all subrogation and before reinsurance	54	39
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	0	0
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	54	39
Less: Unearned premium reserves	(22)	(9)
Plus: Loss adjustment expenses reserves	2	1
Claim liability reported on Balance Sheet, before reinsurance	34	30
Reinsurance recoverable reported on Balance Sheet	$ 6	$ 6
II [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	16	11
Remaining weighted-average contract period (in years)	8 years	9 years
Gross insured contractual payments outstanding:
Principal	$ 614	$ 277
Interest	492	128
Total	1,106	404
Gross undiscounted claim liability	41	21
Discount, gross claim liability	1	1
Gross claim liability before all subrogation and before reinsurance	41	20
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	0	0
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	40	20
Less: Unearned premium reserves	(5)	(1)
Plus: Loss adjustment expenses reserves	1	1
Claim liability reported on Balance Sheet, before reinsurance	37	20
Reinsurance recoverable reported on Balance Sheet	$ 10	$ 7
III [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	16	16
Remaining weighted-average contract period (in years)	16 years	17 years
Gross insured contractual payments outstanding:
Principal	$ 1,511	$ 857
Interest	260	366
Total	1,771	1,223
Gross undiscounted claim liability	536	541
Discount, gross claim liability	71	152
Gross claim liability before all subrogation and before reinsurance	465	389
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(37)	(41)
Discount, other subrogation	1	4
Discounted other subrogation, before reinsurance	(36)	(37)
Gross claim liability, net of all subrogation and discounts, before reinsurance	429	353
Less: Unearned premium reserves	(18)	(7)
Plus: Loss adjustment expenses reserves	7	4
Claim liability reported on Balance Sheet, before reinsurance	418	349
Reinsurance recoverable reported on Balance Sheet	$ 27	$ 24
IV [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	135	139
Remaining weighted-average contract period (in years)	14 years	14 years
Gross insured contractual payments outstanding:
Principal	$ 3,386	$ 3,819
Interest	1,465	1,678
Total	4,851	5,498
Gross undiscounted claim liability	1,726	1,778
Discount, gross claim liability	185	381
Gross claim liability before all subrogation and before reinsurance	1,541	1,397
Less:
Gross RMBS subrogation	(1,760)	(1,777)
Discount, RMBS subrogation	2	49
Discounted RMBS subrogation, before reinsurance	(1,757)	(1,727)
Less:
Gross other subrogation	(749)	(666)
Discount, other subrogation	16	47
Discounted other subrogation, before reinsurance	(734)	(620)
Gross claim liability, net of all subrogation and discounts, before reinsurance	(950)	(950)
Less: Unearned premium reserves	(32)	(35)
Plus: Loss adjustment expenses reserves	68	67
Claim liability reported on Balance Sheet, before reinsurance	(913)	(918)
Reinsurance recoverable reported on Balance Sheet	$ (6)	$ (10)
V [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	3	3
Remaining weighted-average contract period (in years)	2 years	3 years
Gross insured contractual payments outstanding:
Principal	$ 32	$ 37
Interest	10	11
Total	41	48
Gross undiscounted claim liability	41	48
Discount, gross claim liability	0	2
Gross claim liability before all subrogation and before reinsurance	41	46
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(13)	(13)
Discount, other subrogation	1	3
Discounted other subrogation, before reinsurance	(11)	(10)
Gross claim liability, net of all subrogation and discounts, before reinsurance	30	36
Less: Unearned premium reserves	0	0
Plus: Loss adjustment expenses reserves	0	0
Claim liability reported on Balance Sheet, before reinsurance	30	36
Reinsurance recoverable reported on Balance Sheet	$ 0	$ 0

Financial Guarantee Insurance_9

Financial Guarantee Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Phantom) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	$ 36	$ 26	$ 26	$ 23
Loss and loss expense reserves	1,801	1,548
Subrogation recoverable	(2,194)	(2,029)
Liability for Claims	(393)	(482)	(560)	$ (107)
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$ 1	$ 0	$ 0

Financial Guarantee Insuranc_10

Financial Guarantee Insurance Contracts - Summary of Balance of RMBS Subrogation Recoveries and Related Claim Liabilities, by Estimation Approach (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Balance Of Rmbs Subrogation Recoveries Net Of Reinsurance	$ (1,731)		$ (1,702)
Subrogation recoveries	1,757		1,727
Random Samples [Member]
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Subrogation recoveries	1,757	$ 1,755	$ 1,727	$ 1,771
Other Changes Rmbs Subrogation	$ 30	$ (16)

Financial Guarantee Insuranc_11

Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	$ 1,727
Changes recognized
Discounted RMBS subrogation (gross of reinsurance), ending balance	1,757
Random Samples [Member]
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	1,727	$ 1,771
Changes recognized
Other Changes Rmbs Subrogation	30	(16)
Discounted RMBS subrogation (gross of reinsurance), ending balance	$ 1,757	$ 1,755

Financial Guarantee Insuranc_12

Financial Guarantee Insurance Contracts Financial Guarantee Insurance Contracts - Summary of Percentage Ceded to Reinsurers and Reinsurance Recoverable and Rating Levels (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Insurance [Abstract]
Loss Reserves Ceded To Reinsurers	$ 36	$ 26	$ 26	$ 23
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$ 1	$ 0	$ 0

Financial Guarantee Insuranc_13

Financial Guarantee Insurance Contracts - Estimated Future Amortization Expense for Insurance Intangible Asset (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Amortization Of Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			7 years 7 months 6 days
Amortization of insurance intangible assets	$ 14	$ 17	$ 41	$ 280
Intangible Assets, Gross (Excluding Goodwill)	1,268		1,268		$ 1,273
Finite-Lived Intangible Assets, Accumulated Amortization	885		885		847
2019	11		11
2020	39		39
2021	35		35
2022	32		32
2023	29		29
Thereafter	239		239
Insurance intangible asset	$ 383		$ 383		$ 427

Financial Guarantee Insuranc_14

Financial Guarantee Insurance Contracts Earned Premiums by Geographic Location (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Premiums Earned, Net, Financial Guarantee Insurance Contracts	$ 15	$ 10	$ 36	$ 46
United States [Member] | Reportable Geographical Components [Member]
Premiums Earned, Net, Financial Guarantee Insurance Contracts	9	11	24	44
United Kingdom [Member] | Reportable Geographical Components [Member]
Premiums Earned, Net, Financial Guarantee Insurance Contracts	7	4	15	13
Other International [Member] | Reportable Geographical Components [Member]
Premiums Earned, Net, Financial Guarantee Insurance Contracts	$ (1)	$ (4)	$ (2)	$ (11)

Financial Guarantee Insuranc_15

Financial Guarantee Insurance Contracts Financial Guarantee Insurance Contracts - Insurance Intangible Asset Details (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Intangible Assets, Gross (Excluding Goodwill)	$ 1,268		$ 1,268		$ 1,273
Finite-Lived Intangible Assets, Accumulated Amortization	885		885		847
Insurance intangible asset	383		383		$ 427
Amortization of insurance intangible assets	$ 14	$ 17	$ 41	$ 280

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	$ 3,048
Financial assets:
Derivative assets	95	$ 75
Other assets	2	3
Long-term Debt	2,737	2,822
Financial liabilities:
Derivative liabilities	126	90
Short-term Investments [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	586	653
Total Fair Value [Member]
Financial assets:
Cash	48	79
Reported Value Measurement [Member]
Financial assets:
Other investments	60	136
Cash	48	79
Loans	3	10
Other assets	2	3
Total financial assets	9,696	10,242
Financial liabilities:
Liabilities for net financial guarantees written	(744)	(863)
Long-term debt	3,236	3,262
Total financial liabilities	8,558	8,699
Reported Value Measurement [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	586	653
Reported Value Measurement [Member] | Other Debt Obligations [Member]
Financial assets:
Other investments	502	478
Reported Value Measurement [Member] | Interest Rate Swap [Member]
Financial liabilities:
Derivative liabilities	125	89
Reported Value Measurement [Member] | Other Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities	1
Other Assets [Member] | Reported Value Measurement [Member] | Interest Rate Swap [Member]
Financial assets:
Derivative assets	95	75
Level 1 [Member]
Financial assets:
Cash	39	70
Total financial assets	965	1,091
Financial liabilities:
Liabilities for net financial guarantees written	0	0
Long-term debt	0	0
Total financial liabilities	0	0
Level 1 [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	509	598
Level 1 [Member] | Equity Method Investments [Member]
Financial assets:
Other assets	0	0
Level 1 [Member] | Loans Receivable [Member]
Financial assets:
Loans	0	0
Level 1 [Member] | Other Debt Obligations [Member]
Financial assets:
Other investments	62	136
Level 1 [Member] | Interest Rate Swap [Member]
Financial liabilities:
Derivative liabilities	0	0
Level 1 [Member] | Other Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities	0
Level 1 [Member] | Other Assets [Member] | Interest Rate Swap [Member]
Financial assets:
Derivative assets	0	0
Level 2 [Member]
Financial assets:
Cash	9	9
Total financial assets	2,312	2,593
Financial liabilities:
Liabilities for net financial guarantees written	0	0
Long-term debt	2,679	2,829
Total financial liabilities	8,601	8,983
Level 2 [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	77	55
Level 2 [Member] | Equity Method Investments [Member]
Financial assets:
Other assets	0	0
Level 2 [Member] | Loans Receivable [Member]
Financial assets:
Loans	0	0
Level 2 [Member] | Other Debt Obligations [Member]
Financial assets:
Other investments	0	0
Level 2 [Member] | Interest Rate Swap [Member]
Financial liabilities:
Derivative liabilities	125	89
Level 2 [Member] | Other Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities	0
Level 2 [Member] | Other Assets [Member] | Interest Rate Swap [Member]
Financial assets:
Derivative assets	9	8
Level 3 [Member]
Financial assets:
Cash	0	0
Total financial assets	6,013	6,281
Financial liabilities:
Liabilities for net financial guarantees written	436	284
Long-term debt	377	445
Total financial liabilities	968	889
Level 3 [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	0	0
Level 3 [Member] | Equity Method Investments [Member]
Financial assets:
Other assets	2	3
Level 3 [Member] | Loans Receivable [Member]
Financial assets:
Loans	3	13
Level 3 [Member] | Other Debt Obligations [Member]
Financial assets:
Other investments	35	61
Level 3 [Member] | Interest Rate Swap [Member]
Financial liabilities:
Derivative liabilities	0	0
Level 3 [Member] | Other Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities	1
Level 3 [Member] | Other Assets [Member] | Interest Rate Swap [Member]
Financial assets:
Derivative assets	86	67
Commercial Mortgage Backed Securities [Member] | Reported Value Measurement [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value		50
Municipal Bonds [Member] | Reported Value Measurement [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	351	215
Corporate Debt Securities [Member] | Reported Value Measurement [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	1,091	1,430
Debt Security, Government, Non-US [Member] | Reported Value Measurement [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	77	44
US Government Debt Securities [Member] | Reported Value Measurement [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	122	156
Residential Mortgage-Backed Securities [Member] | Reported Value Measurement [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	296	248
Collateralized Debt Obligations [Member] | Reported Value Measurement [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	73	146
Asset-backed Securities [Member] | Reported Value Measurement [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	300	287
Fair Value, Recurring [Member]
Financial assets:
Total financial assets	9,682	10,260
Financial liabilities:
Liabilities for net financial guarantees written	436	284
Long-term debt	3,056	3,274
Total financial liabilities	9,569	9,872
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value		50
Fair Value, Recurring [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	586	653
Fair Value, Recurring [Member] | Equity Method Investments [Member]
Financial assets:
Other assets	2	3
Fair Value, Recurring [Member] | Loans Receivable [Member]
Financial assets:
Loans	3	13
Fair Value, Recurring [Member] | Other Debt Obligations [Member]
Financial assets:
Other investments	488	493
Fair Value, Recurring [Member] | Asset-backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	300	287
Fair Value, Recurring [Member] | Collateralized Debt Obligations [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	73	146
Fair Value, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	296	248
Fair Value, Recurring [Member] | US Government Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	122	156
Fair Value, Recurring [Member] | Debt Security, Government, Non-US [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	77	44
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	1,091	1,430
Fair Value, Recurring [Member] | Municipal Bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	351	215
Fair Value, Recurring [Member] | Interest Rate Swap [Member]
Financial liabilities:
Derivative liabilities	125	89
Fair Value, Recurring [Member] | Other Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities	1
Fair Value, Recurring [Member] | Other Assets [Member] | Interest Rate Swap [Member]
Financial assets:
Derivative assets	95	75
Fair Value, Recurring [Member] | Level 1 [Member] | Commercial Mortgage Backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value		0
Fair Value, Recurring [Member] | Level 1 [Member] | Asset-backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Collateralized Debt Obligations [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | US Government Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	122	156
Fair Value, Recurring [Member] | Level 1 [Member] | Debt Security, Government, Non-US [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	77	44
Fair Value, Recurring [Member] | Level 1 [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	2	0
Fair Value, Recurring [Member] | Level 1 [Member] | Municipal Bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Fair Value, Recurring [Member] | Level 2 [Member] | Commercial Mortgage Backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value		50
Fair Value, Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	225	215
Fair Value, Recurring [Member] | Level 2 [Member] | Collateralized Debt Obligations [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	73	146
Fair Value, Recurring [Member] | Level 2 [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	296	248
Fair Value, Recurring [Member] | Level 2 [Member] | US Government Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Fair Value, Recurring [Member] | Level 2 [Member] | Debt Security, Government, Non-US [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Fair Value, Recurring [Member] | Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	1,089	1,430
Fair Value, Recurring [Member] | Level 2 [Member] | Municipal Bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	351	215
Fair Value, Recurring [Member] | Level 3 [Member] | Commercial Mortgage Backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value		0
Fair Value, Recurring [Member] | Level 3 [Member] | Asset-backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	75	72
Fair Value, Recurring [Member] | Level 3 [Member] | Collateralized Debt Obligations [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | US Government Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Debt Security, Government, Non-US [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Municipal Bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Collateral Pledged [Member] | Short-term Investments [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value		85
Collateral Pledged [Member] | Short-term Investments [Member] | Reported Value Measurement [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	152	85
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Short-term Investments [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	152	85
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 1 [Member] | Short-term Investments [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	152	85
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 2 [Member] | Short-term Investments [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 3 [Member] | Short-term Investments [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	3,160	3,121
Financial assets:
Loans	2,783	3,108
Derivative assets	53	52
Long-term Debt	4,169	4,554
Financial liabilities:
Derivative liabilities	1,771	1,657
Long-term debt	4,002	4,351
Variable Interest Entity, Primary Beneficiary [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	3,029	2,957
Variable Interest Entity, Primary Beneficiary [Member] | Municipal Bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	131	164
Variable Interest Entity, Primary Beneficiary [Member] | Reported Value Measurement [Member]
Financial assets:
Restricted Cash and Cash Equivalents, Current	2	2
Loans	2,783	3,108
Financial liabilities:
Long-term debt	4,169	4,554
Variable Interest Entity, Primary Beneficiary [Member] | Reported Value Measurement [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	3,029	2,957
Variable Interest Entity, Primary Beneficiary [Member] | Reported Value Measurement [Member] | Municipal Bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	131	164
Variable Interest Entity, Primary Beneficiary [Member] | Reported Value Measurement [Member] | Interest Rate Swap [Member]
Financial liabilities:
Derivative liabilities	1,771	1,657
Variable Interest Entity, Primary Beneficiary [Member] | Reported Value Measurement [Member] | Currency Swaps [Member]
Financial assets:
Derivative assets	53	52
Variable Interest Entity, Primary Beneficiary [Member] | Level 1 [Member]
Financial assets:
Restricted Cash and Cash Equivalents, Current	2	2
Loans	0	0
Financial liabilities:
Long-term debt	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Level 1 [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Level 1 [Member] | Municipal Bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Level 1 [Member] | Interest Rate Swap [Member]
Financial liabilities:
Derivative liabilities	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Level 1 [Member] | Currency Swaps [Member]
Financial assets:
Derivative assets	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Level 2 [Member]
Financial assets:
Restricted Cash and Cash Equivalents, Current	0	0
Loans	0	0
Financial liabilities:
Long-term debt	4,026	4,408
Variable Interest Entity, Primary Beneficiary [Member] | Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Level 2 [Member] | Municipal Bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	131	164
Variable Interest Entity, Primary Beneficiary [Member] | Level 2 [Member] | Interest Rate Swap [Member]
Financial liabilities:
Derivative liabilities	1,771	1,657
Variable Interest Entity, Primary Beneficiary [Member] | Level 2 [Member] | Currency Swaps [Member]
Financial assets:
Derivative assets	53	52
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member]
Financial assets:
Restricted Cash and Cash Equivalents, Current	0	0
Loans	2,783	3,108
Financial liabilities:
Long-term debt	153	159
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	3,029	2,957
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Municipal Bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Interest Rate Swap [Member]
Financial liabilities:
Derivative liabilities	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Currency Swaps [Member]
Financial assets:
Derivative assets	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Fair Value, Recurring [Member]
Financial assets:
Restricted Cash and Cash Equivalents, Current	2	2
Loans	2,783	3,108
Financial liabilities:
Long-term debt	4,179	4,567
Variable Interest Entity, Primary Beneficiary [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	3,029	2,957
Variable Interest Entity, Primary Beneficiary [Member] | Fair Value, Recurring [Member] | Municipal Bonds [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fixed income securities, at fair value	131	164
Variable Interest Entity, Primary Beneficiary [Member] | Fair Value, Recurring [Member] | Interest Rate Swap [Member]
Financial liabilities:
Derivative liabilities	1,771	1,657
Variable Interest Entity, Primary Beneficiary [Member] | Fair Value, Recurring [Member] | Currency Swaps [Member]
Financial assets:
Derivative assets	$ 53	$ 52

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	$ 283	$ 19
Derivative liabilities	$ 126,000	$ 90,000
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs	2.20%	2.40%
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Derivative liabilities	$ 1,771,000	$ 1,657,000
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs	3.30%	2.70%
Fair Value Measured at Net Asset Value Per Share [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other investments	$ 391,000	$ 296,000
Fixed Income Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage of investment portfolio valued using dealer quotes	4.00%	4.00%
Minimum [Member] | Fixed Income Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage of investment portfolio valued using internal valuation models	2.00%	2.00%
Maximum [Member] | Fixed Income Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage of investment portfolio valued using external pricing services	94.00%	94.00%

Fair Value Measurements - Infor

Fair Value Measurements - Information about Valuation Inputs for Fixed Income Securities Classified as Level 3 (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		$ 0
Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	$ 5,974,000	6,117,000	$ 5,974,000	$ 6,117,000	$ 5,848,000	$ 6,207,000	$ 7,080,000	$ 6,930,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(40,000)	345,000	161,000	698,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	246,000	(213,000)	(152,000)	(241,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(80,000)	(467,000)	(242,000)	(643,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			160,000	639,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		(627,000)		(627,000)
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	(41,000)	332,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	246,000		(152,000)
Fair Value, Inputs, Level 3 [Member] | Investments [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	75,000	79,000	75,000	79,000	66,000	72,000	74,000	72,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	1,000	1,000	1,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	9,000	5,000	3,000	7,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0	(1,000)	(1,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		0		0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	9,000		3,000
Fair Value, Inputs, Level 3 [Member] | Other Assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	2,000	3,000	2,000	3,000	2,000	3,000	4,000	5,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	0	(1,000)	(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			0	0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			(1,000)	(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		0		0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	0	0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	0		0
Fair Value, Inputs, Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	85,000	73,000	85,000	73,000		66,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			24,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			(5,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			23,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies				0
Derivative [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	85,000	73,000	85,000	73,000	86,000	66,000	62,000	46,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,000	12,000	24,000	30,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2,000)	(1,000)	(5,000)	3,000
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			23,000	30,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	1,000	12,000
Interest Rate Swap [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	86,000		86,000			67,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			24,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			(5,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			24,000
Credit Derivative [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	(1,000)		(1,000)			$ 0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			(1,000)
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability								46,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				30,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				(3,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held				30,000
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	85,000	73,000	85,000	73,000	86,000		62,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,000	12,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2,000)	(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	1,000	12,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	0		0
Credit Derivative [Member] | Derivative [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability		0		0				(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				1,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held				1,000
Credit Derivative [Member] | Credit Derivative [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	(1,000)	0	(1,000)	0	(1,000)		(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	1,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	0	0
Interest Rate Swap [Member] | Derivative [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability		73,000		73,000				$ 47,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				29,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				(3,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held				29,000
Interest Rate Swap [Member] | Interest Rate Swap [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	86,000	73,000	$ 86,000	$ 73,000	$ 87,000		$ 63,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,000	11,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2,000)	(1,000)
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	$ 1,000	$ 11,000

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Information about Described Model Inputs Used to Determine Fair Value of Each Class of Credit Derivatives (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair value of derivative liabilities		$ 124
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair value of derivative liabilities		0
Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other investments		15	$ 16
Interest Rate Contract [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other investments		53	176
Illiquid Investments [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other investments		$ 57	$ 51
Asset-backed Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Inputs Coupon Rate		5.98%	5.97%
Fair Value Inputs Maturity	15 years 6 months 29 days	15 years 3 days
Fair Value Inputs Yield		11.00%	11.75%

Fair Value Measurements - Inf_2

Fair Value Measurements - Information about Valuation Inputs for Variable Interest Entity Assets and Liabilities Classified as Level 3 (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Estimated Future Premium Payments Minimum Discounted Rate	2.10%		2.10%
Estimated Future Premium Payments Maximum Discounted Rate	5.50%		5.50%
Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	$ 5,974,000	$ 6,117,000	$ 5,974,000	$ 6,117,000	$ 5,848,000	$ 6,207,000	$ 7,080,000	$ 6,930,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(40,000)	345,000	161,000	698,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	246,000	(213,000)	(152,000)	(241,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(80,000)	(467,000)	(242,000)	(643,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			160,000	639,000
Fair Value, Inputs, Level 3 [Member] | Investments [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	75,000	79,000	75,000	79,000	66,000	72,000	74,000	72,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	1,000	1,000	1,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	9,000	5,000	3,000	7,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0	(1,000)	(1,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			0	0
Fair Value, Inputs, Level 3 [Member] | Other Assets [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	2,000	3,000	2,000	3,000	2,000	3,000	4,000	5,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	0	(1,000)	(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			0	0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			(1,000)	(1,000)
Fair Value, Inputs, Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	85,000	73,000	85,000	73,000		66,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			24,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			(5,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			23,000
Fair Value, Inputs, Level 3 [Member] | Loans Receivable [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability								4,288,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				301,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				(151,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				(621,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held				229,000
Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability								2,737,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				382,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				(106,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				(17,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held				382,000
Loan Origination Commitments [Member] | Fair Value, Inputs, Level 3 [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	2,783,000	2,966,000	2,783,000	2,966,000		3,108,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			(22,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			(85,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			(219,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			(22,000)
Loan Origination Commitments [Member] | Fair Value, Inputs, Level 3 [Member] | Loans Receivable [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	2,783,000	2,966,000	2,783,000	2,966,000	2,787,000		4,289,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(43,000)	127,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	116,000	(133,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(78,000)	(466,000)
Long-term Debt [Member] | Fair Value, Inputs, Level 3 [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	0	0	0	0	0	0	(231,000)	(217,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	0	0	(15,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	7,000	0	8,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0	0	0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			0	0
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability								$ 46,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				30,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				(3,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held				30,000
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	85,000	73,000	85,000	73,000	86,000		62,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,000	12,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2,000)	(1,000)
Investment Contracts [Member] | Fair Value, Inputs, Level 3 [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	3,029,000	2,996,000	3,029,000	2,996,000		$ 2,957,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			160,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			(71,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			(17,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			160,000
Investment Contracts [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	3,029,000	2,996,000	$ 3,029,000	$ 2,996,000	$ 2,907,000		$ 2,882,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,000	206,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	$ 121,000	$ (92,000)

Fair Value Measurements - Sum_3

Fair Value Measurements - Summary of Changes in Level 3 Fair Value Category (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)level3FinancialInstruments	Sep. 30, 2019USD ($)level3FinancialInstruments	Jun. 30, 2020USD ($)	Dec. 31, 2019USD ($)	Jun. 30, 2019USD ($)	Dec. 31, 2018USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis Asset or Liability, Transfers into or out of Level 3 | level3FinancialInstruments			0	0
Interest Rate Swap [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	$ 86,000		$ 86,000			$ 67,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			24,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			(5,000)
Interest Rate Swap [Member] | Interest Rate Swap [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	86,000	73,000	86,000	$ 73,000	$ 87,000		$ 63,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	1,000	11,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,000	11,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2,000)	(1,000)
Credit Derivative [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	(1,000)		(1,000)			0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			0
Credit Derivative [Member] | Credit Derivative [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	(1,000)	0	(1,000)	0	(1,000)		(1,000)
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	1,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0
Derivative [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	85,000	73,000	85,000	73,000	86,000	66,000	62,000	$ 46,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	1,000	12,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,000	12,000	24,000	30,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2,000)	(1,000)	(5,000)	3,000
Derivative [Member] | Credit Derivative [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability		0		0				(1,000)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				1,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				0
Derivative [Member] | Interest Rate Swap [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability		73,000		73,000				47,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				29,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				(3,000)
Level 3 [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	5,974,000	6,117,000	5,974,000	6,117,000	5,848,000	6,207,000	7,080,000	6,930,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	(41,000)	332,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	246,000		(152,000)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(40,000)	345,000	161,000	698,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	246,000	(213,000)	(152,000)	(241,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(80,000)	(467,000)	(242,000)	(643,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		(627,000)		(627,000)
Level 3 [Member] | Investment Contracts [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	3,029,000	2,996,000	3,029,000	2,996,000		2,957,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			160,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			(71,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			(17,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies				0
Level 3 [Member] | Loans [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	2,783,000	2,966,000	2,783,000	2,966,000		3,108,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			(22,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			(85,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			(219,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies				(851,000)
Level 3 [Member] | Long-term Debt [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	0	0	0	0	0	0	(231,000)	(217,000)
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	0	0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	0		0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	0	0	(15,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	7,000	0	8,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		223,000		223,000
Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability								46,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				30,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				(3,000)
Level 3 [Member] | Loans Receivable [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability								4,288,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				301,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				(151,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				(621,000)
Level 3 [Member] | Loans Receivable [Member] | Loans [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	2,783,000	2,966,000	2,783,000	2,966,000	2,787,000		4,289,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	(43,000)	115,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	116,000		(85,000)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(43,000)	127,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	116,000	(133,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(78,000)	(466,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		(851,000)
Level 3 [Member] | Investments [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	75,000	79,000	75,000	79,000	66,000	72,000	74,000	72,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	9,000		3,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	1,000	1,000	1,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	9,000	5,000	3,000	7,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0	(1,000)	(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		0		0
Level 3 [Member] | Other Assets [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	2,000	3,000	2,000	3,000	2,000	3,000	4,000	5,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	0	0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	0		0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	0	(1,000)	(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		0		0
Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	85,000	73,000	85,000	73,000		$ 66,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			24,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			(5,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies				0
Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	85,000	73,000	85,000	73,000	86,000		62,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	1,000	12,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	0		0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,000	12,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2,000)	(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		0
Level 3 [Member] | Corporate Debt Securities [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability								$ 2,737,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				382,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				(106,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				(17,000)
Level 3 [Member] | Corporate Debt Securities [Member] | Investment Contracts [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	3,029,000	2,996,000	3,029,000	$ 2,996,000	$ 2,907,000		$ 2,882,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	1,000	206,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	121,000		$ (71,000)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,000	206,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	$ 121,000	$ (92,000)

Fair Value Measurements - Sum_4

Fair Value Measurements - Summary of Gains and Losses (Realized and Unrealized) Relating to Level 3 Assets and Liabilities Included in Earnings (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Net Investment Income [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings for the period	$ 0	$ 1		$ 1	$ 1
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	0	0	$ 0	0
Interest Rate Swap [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			30	23
Gain (Loss) on Derivative Instruments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings for the period	1	12		24	$ 30
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	1	12
Income Loss On Variable Interest Entities [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings for the period	(41)	333	668	137
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	(41)	321	611	137
Other Income or (Loss) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings for the period	0	0	(1)	(1)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	$ 0	$ 0	$ (1)	$ (1)

Investments - Summary of Amorti

Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 515,000,000	$ 489,000,000
Debt Securities, Available-for-sale, Amortized Cost	2,914,000,000	3,187,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	141,000,000	132,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	490,000,000	401,000,000
Non - credit other - than - temporary Impairments		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5,000,000	4,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	25,000,000	88,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,000,000	1,000,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	6,000,000	5,000,000
Available-for-sale Securities, Current	3,048,000,000	3,314,000,000
Fixed income securities, at fair value	3,048,000,000
Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	152,000,000	201,000,000
Debt Securities, Available-for-sale, Amortized Cost	586,000,000	653,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	152,000,000	201,000,000
Non - credit other - than - temporary Impairments		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed income securities, at fair value	586,000,000	653,000,000
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	363,000,000	288,000,000
Debt Securities, Available-for-sale, Amortized Cost	2,176,000,000	2,450,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	140,000,000	132,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	338,000,000	200,000,000
Non - credit other - than - temporary Impairments		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5,000,000	4,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	25,000,000	88,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,000,000	1,000,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	6,000,000	5,000,000
Fixed income securities, at fair value	2,311,000,000	2,577,000,000
Fixed Income Securities [Member] | Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	70,000,000	23,000,000
Debt Securities, Available-for-sale, Amortized Cost	322,000,000	194,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	29,000,000	22,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	64,000,000	13,000,000
Non - credit other - than - temporary Impairments		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,000,000	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	6,000,000	10,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,000,000	0
Fixed income securities, at fair value	351,000,000	215,000,000
Fixed Income Securities [Member] | Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	179,000,000	68,000,000
Debt Securities, Available-for-sale, Amortized Cost	1,066,000,000	1,396,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	28,000,000	36,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	179,000,000	63,000,000
Non - credit other - than - temporary Impairments		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,000,000	2,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	5,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	3,000,000	2,000,000
Fixed income securities, at fair value	1,091,000,000	1,430,000,000
Fixed Income Securities [Member] | Foreign Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	12,000,000	20,000,000
Debt Securities, Available-for-sale, Amortized Cost	76,000,000	44,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1,000,000	1,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	12,000,000	20,000,000
Non - credit other - than - temporary Impairments		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed income securities, at fair value	77,000,000	44,000,000
Fixed Income Securities [Member] | US Government Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	11,000,000	38,000,000
Debt Securities, Available-for-sale, Amortized Cost	118,000,000	157,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	4,000,000	2,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	11,000,000	36,000,000
Non - credit other - than - temporary Impairments		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,000,000	2,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	2,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,000,000	2,000,000
Fixed income securities, at fair value	122,000,000	156,000,000
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	19,000,000	5,000,000
Debt Securities, Available-for-sale, Amortized Cost	251,000,000	200,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	45,000,000	47,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	19,000,000	5,000,000
Non - credit other - than - temporary Impairments		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed income securities, at fair value	296,000,000	248,000,000
Fixed Income Securities [Member] | Collateralized Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		49,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss		1,000,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax		0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax		50,000,000
Fixed income securities, at fair value		0
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	67,000,000	116,000,000
Debt Securities, Available-for-sale, Amortized Cost	74,000,000	147,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	53,000,000	53,000,000
Non - credit other - than - temporary Impairments		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,000,000	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	15,000,000	63,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	1,000,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,000,000	1,000,000
Fixed income securities, at fair value	73,000,000	146,000,000
Fixed Income Securities [Member] | Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	5,000,000	10,000,000
Debt Securities, Available-for-sale, Amortized Cost	268,000,000	263,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	33,000,000	24,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,000,000	2,000,000
Non - credit other - than - temporary Impairments		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	4,000,000	7,000,000
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,000,000	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,000,000	0
Fixed income securities, at fair value	300,000,000	287,000,000
Fixed Income Investments And Other Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	2,761,000,000	3,103,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	132,000,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	141,000,000	5,000,000
Non - credit other - than - temporary Impairments		0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	6,000,000
Fixed income securities, at fair value	2,896,000,000	3,230,000,000
Collateral Pledged [Member] | Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax		0
Non - credit other - than - temporary Impairments		0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax		0
Fixed income securities, at fair value		85,000,000
Collateral Pledged [Member] | Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed income securities, at fair value	152,000,000	85,000,000
Collateral Pledged [Member] | Fixed Income Securities [Member] | Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	152,000,000	85,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0
Fixed income securities, at fair value	152,000,000
Asset Pledged as Collateral [Member] | Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	152,000,000	$ 85,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 0

Investments - Summary of Amor_2

Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments Held by Successor Ambac, by Contractual Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 2,914
Fixed income securities, at fair value	3,048
Amortized Cost, Due in one year or less	830
Amortized Cost, Due after one year through five years	876
Amortized Cost, Due after five years through ten years	432
Amortized Cost, Due after ten years	182
Amortized Cost, Total	2,320
Estimated Fair Value, Due in one year or less	832
Estimated Fair Value, Due after one year through five years	888
Estimated Fair Value, Due after five years through ten years	453
Estimated Fair Value, Due after ten years	206
Estimated Fair Value due, Total	2,379
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, at fair value	2,311	$ 2,577
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	251
Fixed income securities, at fair value	296	248
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	74
Fixed income securities, at fair value	73	146
Fixed Income Securities [Member] | Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	268
Fixed income securities, at fair value	$ 300	$ 287

Investments - Summary of Gross

Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 490	$ 401
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	25	88
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	1
Debt Securities, Available-for-sale, Unrealized Loss Position	515	489
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	6	5
Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	152	201
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	152	201
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed Income Investments And Other Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	6
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	338	200
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	25	88
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	1
Debt Securities, Available-for-sale, Unrealized Loss Position	363	288
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	6	5
Fixed Income Securities [Member] | Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	64	13
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	6	10
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	70	23
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1	0
Fixed Income Securities [Member] | Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	179	63
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	179	68
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	3	2
Fixed Income Securities [Member] | Debt Security, Government, Non-US [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	12	20
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	12	20
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed Income Securities [Member] | US Government Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	11	36
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	11	38
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1	2
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	19	5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	19	5
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months		7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Debt Securities, Available-for-sale, Unrealized Loss Position		7
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax		0
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	53	53
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	15	63
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	1
Debt Securities, Available-for-sale, Unrealized Loss Position	67	116
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1	1
Fixed Income Securities [Member] | Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	4	7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	0
Debt Securities, Available-for-sale, Unrealized Loss Position	5	10
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1	0
Collateral Pledged [Member] | Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax		0
Collateral Pledged [Member] | Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	$ 0
Collateral Pledged [Member] | Fixed Income Securities [Member] | Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 0

Investments - Additional Inform

Investments - Additional Information (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 0
Securities fair value	7,000,000	$ 6,000,000
Ambac Assurance [Member]
Schedule of Investments [Line Items]
Unsettled Amounts Secured Notes from LSNI	10,000,000	55,000,000
Interest Rate Contract [Member]
Schedule of Investments [Line Items]
Other investments	53,000,000	176,000,000
Reported Value Measurement [Member]
Schedule of Investments [Line Items]
Other investments	60,000,000	136,000,000
Reported Value Measurement [Member] | Interest Rate Contract [Member]
Schedule of Investments [Line Items]
Other investments	3,000,000	$ 81,000,000
Commitments [Member] | Partnership Interest [Member]
Schedule of Investments [Line Items]
Other investments	$ 48,000,000

Investments - Summary of Amount

Investments - Summary of Amounts Included in Net Realized (Losses) Gains and Other-Than-Temporary Impairments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held		$ 12		$ 12	$ 12
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold				(1)
Gross realized gains on securities	$ 5	12	$ 32	46
Gross realized losses on securities	(1)	0	(12)	(5)
Foreign exchange (losses) gains			2	19
Debt Securities, Available-for-sale, Allowance for Credit Loss, Not to Sell before Recovery, Credit Loss, Previously Recorded, Expense (Reversal)	0	0	0	0
Debt Securities, Available-for-sale, Allowance for Credit Loss, Sell before Recovery	0	0	0	0
Net realized (losses) gains	2	18	20	71
Gain (Loss) on Investments [Member]
Investment [Line Items]
Foreign exchange (losses) gains	$ (2)	$ 7	$ 0	$ 30

Investments - Summary of Roll-F

Investments - Summary of Roll-Forward of Ambac's Cumulative Credit Losses on Debt Securities for Which Portion of Other-than-Temporary Impairment was Recognized in Other Comprehensive Income (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance at beginning	$ 12
Reductions for credit impairments previously recognized on:
Securities that matured or were sold during the period	1
Balance at end	$ 12

Investments - Summary of Source

Investments - Summary of Sources of Collateral Received and Various Investment Agreement in which Collateral Pledged (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Investment [Line Items]
Fair Value Of Securities Deposited With Governmental Authorities	$ 7	$ 6
Fair Value of Securities Deposited in Connection wtih Letter of Credit	1
Market Value of Secured Note Collateral	181	197
Investment Portfolio [Member]
Investment [Line Items]
Fair Value of Cash and Securities Pledged to Derivative Counterparties	152	85
Ambac Assurance [Member]
Investment [Line Items]
Unsettled Amounts Secured Notes from LSNI	10	55
Standard & Poor's, B- Rating [Member]
Investment [Line Items]
Investment Owned, at Fair Value	1,260	1,164
Standard & Poor's, B- Rating [Member] | Municipal Bonds [Member]
Investment [Line Items]
Investment Owned, at Fair Value	318	186
Standard & Poor's, B- Rating [Member] | Corporate Debt Securities [Member]
Investment [Line Items]
Investment Owned, at Fair Value	470	535
Standard & Poor's, B- Rating [Member] | Mortgage And Other Asset Backed Securities [Member]
Investment [Line Items]
Investment Owned, at Fair Value	473	442
Ambac Assurance Corporation [Member] | Standard & Poor's, B Rating [Member]
Investment [Line Items]
Investment Owned, at Fair Value	1,253
Ambac Assurance Corporation [Member] | Standard & Poor's, B Rating [Member] | Municipal Bonds [Member]
Investment [Line Items]
Investment Owned, at Fair Value	310
Ambac Assurance Corporation [Member] | Standard & Poor's, B Rating [Member] | Corporate Debt Securities [Member]
Investment [Line Items]
Investment Owned, at Fair Value	470
Ambac Assurance Corporation [Member] | Standard & Poor's, B Rating [Member] | Mortgage And Other Asset Backed Securities [Member]
Investment [Line Items]
Investment Owned, at Fair Value	473
Ambac Assurance Corporation [Member] | Standard & Poor's, B- Rating [Member]
Investment [Line Items]
Investment Owned, at Fair Value		1,153
Ambac Assurance Corporation [Member] | Standard & Poor's, B- Rating [Member] | Municipal Bonds [Member]
Investment [Line Items]
Investment Owned, at Fair Value		176
Ambac Assurance Corporation [Member] | Standard & Poor's, B- Rating [Member] | Corporate Debt Securities [Member]
Investment [Line Items]
Investment Owned, at Fair Value		535
Ambac Assurance Corporation [Member] | Standard & Poor's, B- Rating [Member] | Mortgage And Other Asset Backed Securities [Member]
Investment [Line Items]
Investment Owned, at Fair Value		442
National Public Finance Guarantee Corporation [Member] | Standard & Poor's, BBB- Rating [Member]
Investment [Line Items]
Investment Owned, at Fair Value	6	11
National Public Finance Guarantee Corporation [Member] | Standard & Poor's, BBB- Rating [Member] | Municipal Bonds [Member]
Investment [Line Items]
Investment Owned, at Fair Value	6	11
National Public Finance Guarantee Corporation [Member] | Standard & Poor's, BBB- Rating [Member] | Corporate Debt Securities [Member]
Investment [Line Items]
Investment Owned, at Fair Value	$ 0	$ 0

Investments - Summary of Fair V

Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Standard & Poor's, B Rating [Member] | Ambac Assurance Corporation [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	$ 1,253
Standard & Poor's, B- Rating [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	1,260	$ 1,164
Standard & Poor's, B- Rating [Member] | Ambac Assurance Corporation [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		1,153
Standard & Poor's, BBB- Rating [Member] | National Public Finance Guarantee Corporation [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	6	11
Standard & Poor's, C Rating | Assured Guaranty Municipal Corporation
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	1
Municipal Bonds [Member] | Standard & Poor's, B Rating [Member] | Ambac Assurance Corporation [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	310
Municipal Bonds [Member] | Standard & Poor's, B- Rating [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	318	186
Municipal Bonds [Member] | Standard & Poor's, B- Rating [Member] | Ambac Assurance Corporation [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		176
Municipal Bonds [Member] | Standard & Poor's, BBB- Rating [Member] | National Public Finance Guarantee Corporation [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	6	11
Municipal Bonds [Member] | Standard & Poor's, C Rating | Assured Guaranty Municipal Corporation
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	1
Corporate Debt Securities [Member] | Standard & Poor's, B Rating [Member] | Ambac Assurance Corporation [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	470
Corporate Debt Securities [Member] | Standard & Poor's, B- Rating [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	470	535
Corporate Debt Securities [Member] | Standard & Poor's, B- Rating [Member] | Ambac Assurance Corporation [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		535
Corporate Debt Securities [Member] | Standard & Poor's, BBB- Rating [Member] | National Public Finance Guarantee Corporation [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0	0
Corporate Debt Securities [Member] | Standard & Poor's, C Rating | Assured Guaranty Municipal Corporation
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0
Mortgage And Other Asset Backed Securities [Member] | Standard & Poor's, B Rating [Member] | Ambac Assurance Corporation [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	473
Mortgage And Other Asset Backed Securities [Member] | Standard & Poor's, B- Rating [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	$ 473	442
Mortgage And Other Asset Backed Securities [Member] | Standard & Poor's, B- Rating [Member] | Ambac Assurance Corporation [Member]
Schedule of Investments [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		$ 442

Investments - Summary of Fair_2

Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Phantom) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ 3	$ 6
Trading Securities, Realized Gain (Loss)	0	2
Investment expense	(1)	(1)	$ (4)	$ (4)
Securities available-for-sale and short-term	24	36	80	161
Net investment income	37	45	69	186
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities			(12)	19
Trading Securities, Realized Gain (Loss)			(19)	4
Other Investments Income	3	4	7	15
Fixed Income Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	24	33	79	151
Short-Term [Member]
Investment [Line Items]
Gross Investment Income, Operating	1	4	4	14
Other Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	$ 14	$ 8	$ (11)	$ 25

Investments - Summary of Net In

Investments - Summary of Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Short-term Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	$ 1	$ 4	$ 4	$ 14
Principal Amount Outstanding of Loans Held-in-portfolio
Investment [Line Items]
Gross Investment Income, Operating	$ 0	$ 0	$ 0	$ 1

Investments Investments - Equit

Investments Investments - Equity Investments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Real Estate [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	$ 15	$ 16
Hedge Funds, Multi-strategy [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	182	65
Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	53	176
Illiquid Investments [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	57	51
Insurance Linked [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	2	3
Equity [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	33	55
Credit Index Product [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	69	66
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	16	0
Emerging Market Debt [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	23	0
Equity investments in pooled funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	451	432
Priced Through Pricing Vendors [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	60	136
Priced Through Pricing Vendors [Member] | Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	3	81
Priced Through Pricing Vendors [Member] | Equity [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	33	55
Priced Through Pricing Vendors [Member] | Emerging Market Debt [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	23	$ 0
Commitments [Member] | Partnership Interest [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	$ 48

Derivative Instruments - Summar

Derivative Instruments - Summary of Gross Fair Values of Individual Derivative Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Derivative, Collateral, Right to Reclaim Cash	$ 1	$ 36
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	95	75
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	126	90
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	124
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities		89
Net Amount, Derivative Assets	95	75
Derivative Asset, Fair Value, Gross Asset	95	75
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative liabilities	126	90
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liabilities Net Amount	2	1
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	94	75
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	125	90
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	124	89
Net Amount, Derivative Assets	94	75
Derivative Asset, Fair Value, Gross Asset	95	75
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative liabilities	125	89
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liabilities Net Amount	1	1
Other Credit Derivatives [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	1
Derivative liabilities	1
Derivative Liability, Fair Value, Amount Offset Against Collateral	0
Derivative Liabilities Net Amount	1
Variable Interest Entity, Primary Beneficiary [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	53	52
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	1,771	1,657
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities		0
Net Amount, Derivative Assets	53	52
Derivative Asset, Fair Value, Gross Asset	53	52
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative liabilities	1,771	1,657
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liabilities Net Amount	1,771	1,657
Variable Interest Entity, Primary Beneficiary [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	1,771	1,657
Derivative liabilities	1,771	1,657
Derivative Liabilities Net Amount	1,771	1,657
Variable Interest Entity, Primary Beneficiary [Member] | Currency Swaps [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	53	52
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		0
Net Amount, Derivative Assets	53	52
Derivative Asset, Fair Value, Gross Asset	53	$ 52
Derivative Asset, Fair Value, Amount Offset Against Collateral	$ 0

Derivative Instruments - Additi

Derivative Instruments - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Value of right to reclaim cash collateral and posted margin, recorded in Other assets	$ 1,000,000		$ 1,000,000		$ 36,000,000
Value of obligation to return cash collateral, recorded in "Other liabilities"	0		0
Gains in change in fair value of the call options	7,000,000	$ (10,000,000)	(61,000,000)	$ (61,000,000)
Net liability fair value of all derivative instruments linked to Ambac's own credit risk	124,000,000		124,000,000		89,000,000
Fair value of posted assets as collateral	$ 144,000,000		$ 144,000,000		$ 109,000,000

Derivative Instruments - Summ_2

Derivative Instruments - Summary of Location and Amount of Gains and Losses of Derivative Contracts (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Debt and Equity Securities, FV-NI [Line Items]
Unrealized gains (losses)			$ (1)	$ 1
Derivative, Gain (Loss) on Derivative, Net	$ 7	$ (10)	(61)	(61)
Derivative, Gain (Loss) on Derivatives, Total Net	(7)	(166)	(231)	(327)
Net gains (losses) on derivative contracts [Domain] | Credit Derivatives [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	1
Net gains (losses) on derivative contracts [Domain] | Interest Rate Swap [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net	7	(1)
Net gains (losses) on derivative contracts [Domain] | Futures Contracts [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	(10)
Derivative Products [Member] | Interest Rate Swap [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net			(20)	(11)
Derivative Products [Member] | Other Contracts [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net			(41)	(52)
Net Change In Fair Value Of Credit Derivatives [Member] | Credit Derivatives [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net			(1)	1
Income Loss On Variable Interest Entities [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(14)	(156)	(170)	(266)
Income Loss On Variable Interest Entities [Member] | Interest Rate Swap [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(4)	(166)	(177)	(272)
Income Loss On Variable Interest Entities [Member] | Currency Swaps [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ (10)	$ 10	$ 7	$ 6

Derivative Instruments - Summ_3

Derivative Instruments - Summary of Notional Amounts of AFS's Trading Derivative Products (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
AFS [Member] | Interest Rate Swap [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	$ 240	$ 332
AFS [Member] | Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	726	1,261
AFS [Member] | Futures Contracts [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	240	755
Other Credit Derivatives [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	$ 293	$ 280

Derivative Instruments - Summ_4

Derivative Instruments - Summary of Notional for VIE Derivatives Outstanding (Details) - Variable Interest Entity, Primary Beneficiary [Member] - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Interest Rate Swap [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	$ 1,164	$ 1,194
Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	1,103	1,176
Currency Swaps [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	298	329
Other Credit Derivatives [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	$ 0	$ 9

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2011
Tax Credit Carryforward [Line Items]
NOL allocated amount		$ 3,650
Afg [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	$ 1,249
Minimum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2029
Maximum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2040

Income Taxes Income Taxes - Pro

Income Taxes Income Taxes - Provision for Income Taxes Charged To Income From Continuing Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Provision for Income Taxes [Line Items]
Current Federal Tax Expense (Benefit)	$ 0	$ 0	$ 0	$ 0
Income (Loss) from Continuing Operations before Income Taxes, Domestic	(106)	60	(412)	(61)
Current Income Tax Expense (Benefit)	(1)	4	1	35
Deferred Foreign Income Tax Expense (Benefit)	1	(1)	(5)	(2)
Deferred Income Tax Expense (Benefit)	1	(1)	(5)	(2)
Income Tax Expense (Benefit)	0	3	(5)	33
Income (Loss) from Continuing Operations before Income Taxes, Foreign	(2)	9	(15)	(11)
Pre-tax income (loss)	(108)	69	(427)	(72)
Current State and Local Tax Expense (Benefit)	0	0	0	(3)
Current Foreign Tax Expense (Benefit)	$ (1)	$ 4	$ 0	$ 38

Income Taxes Income Taxes - NOL

Income Taxes Income Taxes - NOL Usage Table (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	87 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2018	Dec. 31, 2011
Net Income Loss Reconciliation [Line Items]
AACNetTaxableIncome			$ 1,508
Remaining Net Operating Loss Carryforward, Amount			$ 2,142
Tolling Payment Payable to AFG, Gross		$ 28
NOL allocated amount				$ 3,650
Tier C Tolling Payments Payable to IRS		12.50%
Tier D Tolling Payments Payable to IRS		17.50%
Ambac Assurance [Member]
Net Income Loss Reconciliation [Line Items]
AACNetTaxableIncome		$ 197
NOL allocated amount		2,482
Operating Loss Generated in Current Year	$ 143
Afg [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		1,249
Operating Loss Generated in Current Year		196
Tier A [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		$ 479
NOL applicable percentage		15.00%
Tier B [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		$ 1,057
NOL applicable percentage		40.00%
Tier C [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		$ 1,057
NOL applicable percentage		10.00%
Tier D [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		$ 1,057
NOL applicable percentage		15.00%
Domestic Tax Authority [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		$ 3,731
Minimum [Member]
Net Income Loss Reconciliation [Line Items]
Operating Loss Carryforwards, Expiration Date		Dec. 31, 2029
Maximum [Member]
Net Income Loss Reconciliation [Line Items]
Operating Loss Carryforwards, Expiration Date		Dec. 31, 2040

Income Taxes Schedule of Income

Income Taxes Schedule of Income Before Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of Income Before Income Tax, Domestic and Foreign [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Domestic	$ (106)	$ 60	$ (412)	$ (61)
Income (Loss) from Continuing Operations before Income Taxes, Foreign	(2)	9	(15)	(11)
Pre-tax income (loss)	$ (108)	$ 69	$ (427)	$ (72)