Ambac Financial (AMBC) 10-K 2 Mar 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 24, 2020	Dec. 31, 2018	Jun. 30, 2018	Apr. 30, 2013
Entity Information [Line Items]
Entity File Number	1-10777
Document Quarterly Report	true
Document Transition Report	false
City Area Code	(212)
Entity Incorporation, State or Country Code	DE
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Voluntary Filers	No
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Registrant Name	AMBAC FINANCIAL GROUP INC
Entity Central Index Key	0000874501
Current Fiscal Year End Date	--12-31
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		45,577,874
Entity Public Float				$ 767,503,767
Common Stock, Par or Stated Value Per Share	$ 0.01		$ 0.01		$ 0.01
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
Local Phone Number	658-7470
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
Warrant [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 Millions	Dec. 31, 2019	Dec. 31, 2018
Assets:
Estimated Fair Value	$ 3,314
Short-term investments, at fair value	653	$ 430
Other Investments	478	391
Total investments	3,792	3,937
Cash and cash equivalents	24	63
Restricted Cash	55	19
Premium receivables	416	495
Reinsurance recoverable on paid and unpaid losses	26	23
Deferred ceded premium	82	61
Subrogation recoverable	2,029	1,933
Derivative assets	75	59
Income Taxes Receivable, Current	11	47
Insurance intangible asset	427	719
Other assets	95	138
Total assets	13,320	14,589
Liabilities:
Unearned premiums	518	630
Loss and loss expense reserves	1,548	1,826
Ceded premiums payable	29	33
Deferred Income Tax Liabilities, Net	32	40
Long-term debt	2,822	2,929
Accrued interest payable	441	376
Derivative liabilities	90	77
Other liabilities	93	64
Variable interest entity liabilities:
Total liabilities	11,783	12,956
Stockholders’ equity:
Preferred stock, par value $0.01 per share; 20,000,000 shares authorized shares; issued and outstanding shares—none	0	0
Common stock, par value $0.01 per share; 130,000,000 shares authorized; issued shares: 45,571,743 and 45,365,170	0	0
Additional paid-in capital	232	219
Accumulated other comprehensive income (loss)	42	(49)
Retained earnings	1,203	1,421
Treasury stock, shares at cost: 16,343 and 28,892	0	0
Total Ambac Financial Group, Inc. stockholders’ equity	1,477	1,592
Noncontrolling interest	60	41
Total stockholders’ equity	1,536	1,633
Total liabilities and stockholders’ equity	13,320	14,589
Variable Interest Entity [Member]
Assets:
Estimated Fair Value	3,121	2,737
Restricted Cash	2	1
Loans, at fair value	3,108	4,288
Derivative assets	52	66
Other assets	3	1
Total assets	6,286	7,093
Variable interest entity assets:
Loans, at fair value	3,108	4,288
Liabilities:
Long-term debt	4,554	5,269
Accrued interest payable	1	1
Derivative liabilities	1,657	1,712
Variable interest entity liabilities:
Total liabilities	6,212	6,981
Fixed Income Securities [Member]
Assets:
Estimated Fair Value	2,577	3,116
Collateral Pledged [Member] | Fixed Income Securities [Member]
Assets:
Estimated Fair Value	$ 85	$ 0

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fixed income securities, amortized cost	$ 3,187	$ 3,451
Other Investments	$ 478	$ 391
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	130,000,000	130,000,000
Common stock, shares issued	45,571,743	45,365,170
Common Stock, Shares, Outstanding	45,555,400	45,336,278
Treasury stock, shares	16,343	28,892
Fixed Income Securities [Member]
Fixed income securities, amortized cost	$ 2,450	$ 3,021
Equity investments in pooled funds [Member]
Other Investments	432
Other Investment Not Readily Marketable, Fair Value	432	351
Collateral Pledged [Member] | Fixed Income Securities [Member]
Fixed income securities, amortized cost	85	0
Parent Company [Member]
Fixed income securities, amortized cost	71	151
Other Investments	$ 46	$ 40
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	130,000,000	130,000,000
Short-term Investments [Member]
Fixed income securities, amortized cost	$ 653	$ 430
Short-term Investments [Member] | Collateral Pledged [Member] | Fixed Income Securities [Member]
Fixed income securities, amortized cost	85
Short-term Investments [Member] | Parent Company [Member]
Fixed income securities, amortized cost	318	193
Variable Interest Entity, Primary Beneficiary [Member]
Long-term Debt	$ 4,351	$ 5,269

Consolidated Statements of Tota

Consolidated Statements of Total Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Net premiums earned	$ 66,000	$ 111,000	$ 175,000
Net investment income:
Securities available-for-sale and short-term	196,000	271,000	338,000
Other investments	32,000	2,000	23,000
Net investment income	227,000	273,000	361,000
Other-than-temporary impairment losses:
Total other-than-temporary impairment losses	0	(3,000)	(55,000)
Portion of other-than-temporary impairment recognized in other comprehensive income (loss)	0	0	34,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	(3,000)	(20,000)
Realized Investment Gains (Losses)	81,000	112,000	5,000
Derivative, Gain (Loss) on Derivative, Net	(50,000)	7,000	76,000
Net realized gains (losses) on extinguishment of debt	0	3,000	5,000
Other income	134,000	5,000	0
Income (loss) on variable interest entities	38,000	3,000	20,000
Total revenues	496,000	511,000	622,000
Expenses:
Losses and loss expenses (benefit)	13,000	(224,000)	513,000
Insurance intangible amortization	295,000	107,000	151,000
Operating expenses	103,000	112,000	122,000
Interest expense	269,000	242,000	120,000
Total expenses	680,000	238,000	906,000
Pre-tax income (loss)	(183,000)	273,000	(284,000)
Provision for income taxes	32,000	5,000	44,000
Net income (loss)	(216,000)	267,000	(329,000)
Net income (loss) attributable to common stockholders	(216,000)	186,000	(329,000)
Other comprehensive income (loss), after tax:
Net income (loss)	(216,000)	267,000	(329,000)
Unrealized gains (losses) on securities, net of income tax provision (benefit) of $(8), $2 and $0	65,000	55,000	(82,000)
Gains (losses) on foreign currency translation, net of income tax provision (benefit) of $0, $0 and $0	26,000	(48,000)	74,000
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, after Tax	0	1,000	0
Credit risk changes of fair value option liabilities, net of income tax provision (benefit) of $0, $0 and $0	(1,000)	(2,000)	1,000
Total other comprehensive income (loss), net of income tax	91,000	6,000	(7,000)
Total comprehensive income (loss)	(125,000)	274,000	(335,000)
Less: comprehensive (loss) gain attributable to the noncontrolling interest:
Total comprehensive income (loss) attributable to common stockholders	(125,000)	192,000	(335,000)
AMPS Exchange Loss Based on Carry Value	$ 0	$ 82,000	$ 0
Basic	$ (4.69)	$ 4.07	$ (7.25)
Diluted	$ (4.69)	$ 3.99	$ (7.25)
Weighted Average Number of Shares Outstanding, Basic		45,954,908	45,665,883
Weighted Average Number of Shares Outstanding, Diluted		45,954,908	46,559,835

Consolidated Statements of To_2

Consolidated Statements of Total Comprehensive Income (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Income Statement [Abstract]
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, Tax	$ 0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Proceeds From Issuance of Tier II Notes		$ 240,000
Cash flows from operating activities:
Net income (loss) attributable to common stockholders	$ (216,000)	186,000	$ (329,000)
AMPS Exchange Loss Based on Carry Value	0	82,000	0
Net income (loss)	(216,000)	267,000	(329,000)
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization	0	1,000	1,000
Amortization of bond premium and discount	(63,000)	(137,000)	(183,000)
Share-based compensation	12,000	12,000	4,000
Deferred income taxes	1,000	7,000	32,000
Current income taxes	35,000	(35,000)	(26,000)
Unearned premiums, net	(132,000)	(163,000)	(168,000)
Losses and loss expenses, net	(364,000)	(1,633,000)	400,000
Ceded premiums payable	(4,000)	(5,000)	(5,000)
Premium receivables	77,000	91,000	77,000
Accrued interest payable	87,000	9,000	50,000
Amortization of insurance intangible assets	295,000	107,000	151,000
Net mark-to-market (gains) losses	(1,000)	1,000	(15,000)
Net realized investment gains	(81,000)	(112,000)	(5,000)
Other-than-temporary impairment charges	0	3,000	20,000
Net realized gains (losses) on extinguishment of debt	0	(3,000)	(5,000)
Other, net	80,000	67,000	22,000
Net cash used in operating activities	(311,000)	(1,543,000)	(221,000)
Cash flows from investing activities:
Proceeds from sales of bonds	1,212,000	1,248,000	2,139,000
Proceeds from matured bonds	379,000	432,000	814,000
Purchases of bonds	(959,000)	(528,000)	(2,054,000)
Proceeds from sales of other invested assets	81,000	159,000	350,000
Purchases of other invested assets	(137,000)	(140,000)	(299,000)
Change in short-term investments	(218,000)	127,000	(127,000)
Change in cash collateral receivable	100,000	(58,000)	123,000
Proceeds From Financial Guaranty Variable Interest Entity Assets	543,000	349,000	235,000
Other, net	(2,000)	0	(17,000)
Net cash provided by investing activities	1,000,000	1,588,000	1,163,000
Cash flows from financing activities:
Proceeds from Sale of Senior Surplus Notes	0	24,000
Paydown of Ambac Note	(178,000)	(214,000)
Paydown Of Variable Interest Entity Secured Borrowing	0	74,000	29,000
Payments From Drawdowns Of Borrowings Under Guaranteed Investment Agreements			82,000
Payments for extinguishment of surplus notes	0	(191,000)	(69,000)
Payments of Debt Issuance Costs		(9,000)
AMPS Proceeds	19,000
AMPS Exchange Cash Paid	0	(11,000)
Payment, Tax Withholding, Share-based Payment Arrangement	(3,000)	(1,000)	(1,000)
Paydown of Financial Guaranty Variable Interest Entity Liabilities	(542,000)	(349,000)	(230,000)
Net Cash Provided by (Used in) Financing Activities	(691,000)	(585,000)	(412,000)
Effect of Exchange Rate on Cash and Cash Equivalents	0	0	(1,000)
Cash and Cash Equivalents, Period Increase (Decrease)	(2,000)	(541,000)	529,000
Cash and cash equivalents end of period	24,000	63,000	624,000
Supplemental disclosure of cash flow information
Income Taxes Paid	21,000	35,000	40,000
Cash payments related to reorganization items:
Variable interest entity activities	(38,000)	(3,000)	(20,000)
Increase (Decrease) in Derivative Assets and Liabilities	(1,000)	(17,000)	(223,000)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	81,000	83,000	625,000
Proceeds From Issuance of Ambac UK Debt	12,000
Ambac Financial Group, Inc Parent Company Only [Member]
Cash flows from operating activities:
Net income (loss) attributable to common stockholders	(216,000)	186,000	(329,000)
Net income (loss)	(216,000)	186,000	(329,000)
Adjustments to reconcile net income to net cash used in operating activities:
Amortization of bond premium and discount	(6,000)	(7,000)	(17,000)
Share-based compensation	12,000	12,000	4,000
Current income taxes	15,000	(15,000)	(1,000)
Net realized investment gains	(1,000)	1,000	7,000
Other, net	(6,000)	0	(10,000)
Net cash used in operating activities	16,000	32,000	16,000
Cash flows from investing activities:
Proceeds from matured bonds	86,000	230,000	187,000
Purchases of bonds	(2,000)	(137,000)	(196,000)
Change in short-term investments	(125,000)	(123,000)	(3,000)
Net cash provided by investing activities	(22,000)	(21,000)	(44,000)
Cash flows from financing activities:
AMPS Exchange Cash Paid	0
Cash and Cash Equivalents, Period Increase (Decrease)	(6,000)	11,000	(28,000)
Cash and cash equivalents end of period	9,000	15,000	4,000
Supplemental disclosure of cash flow information
Income Taxes Paid	$ 1,000	$ 4,000	$ 1,000

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]	Common Stock Held in Treasury, at Cost [Member]	Noncontrolling Interest [Member]	Parent Company [Member]	Parent Company [Member]Retained Earnings [Member]	Parent Company [Member]AOCI Attributable to Parent [Member]	Parent Company [Member]Additional Paid-in Capital [Member]	Parent Company [Member]Common Stock Held in Treasury, at Cost [Member]
Beginning balance at Dec. 31, 2016	$ 1,978	$ 1,558	$ (39)	$ 0	$ 0	$ 195	$ 0	$ 264
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	(335)	(329)	(7)	0	0	0	0	0	$ (335)	$ (329)	$ (7)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification | Accounting Standards Update 2018-02 [Domain]									0	7	(7)
Cost of warrants acquired	4					4			4			$ 4
Issuance of common stock	(2)	(2)					0	0	(2)	(2)			$ 0
Ending balance at Dec. 31, 2017	1,645	1,234	(52)	0	0	200	0	264
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	274	267	6	0	0	0	0	0	192	186	6
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	0			0	0	0	0	0	0
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification | Accounting Standards Update 2016-01 [Member]		3	(3)
Cost of warrants acquired	12	0	0	0	0	12	0	0	12			12	0
Issuance of common stock	(1)	(1)	0	0	0	0	0	0	(1)	(1)			0
Ending balance at Dec. 31, 2018	1,633	1,421	(49)	0	0	219	0	41
Increase (Decrease) in Stockholders' Equity [Roll Forward]
AMPS Impact on Stockholders Equity	(297)	(82)	0	0	0	8	0	(223)	8			8
Total comprehensive income (loss)	(125)	(216)	91	0	0	0	0	0	(125)	(216)	$ 91
Cost of warrants acquired	12	0	0	0	0	12	0	0	12			$ 12
Issuance of common stock	(3)	(3)	0	0	0	0	0	0	$ (3)	$ (3)			$ 0
Ending balance at Dec. 31, 2019	1,536	1,203	42	0	0	232	0	60
Increase (Decrease) in Stockholders' Equity [Roll Forward]
AMPS Impact on Stockholders Equity	$ 19	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 19

Leases Statement

Leases Statement - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Lessor, Operating Lease, Term of Contract	10 years
Operating Leases, Future Minimum Payments Receivable, Remainder of Fiscal Year	$ 1
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	4
Lessee, Operating Lease, Liability, Payments, Due Year Two	4
Lessee, Operating Lease, Liability, Payments, Due Year Three	4
Lessee, Operating Lease, Liability, Payments, Due Year Four	4
Lessee, Operating Lease, Liability, Payments, Due Year Five	4
Lessee, Operating Lease, Liability, Payments, Due after Year Five	22
Lessee, Operating Lease, Liability, Payments, Due	42
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(13)
Operating Lease, Right-of-Use Asset	25	$ 14
Operating Lease, Expense	7
Variable Lease, Cost	0
Sublease Income	(1)
Lease, Cost	7
Right of Use Assets Obtained in Exchange for Lease Obligation, Non Cash	30
Operating Lease, Liability	$ 29	$ 15
Operating Lease, Weighted Average Remaining Lease Term	9 years 10 months 24 days
Operating Lease, Weighted Average Discount Rate, Percent	7.90%
Operating Leases, Future Minimum Payments Receivable, in Two Years	$ 1
Operating Leases, Future Minimum Payments Receivable, in Three Years	1
Operating Leases, Future Minimum Payments Receivable, in Four Years	1
Operating Leases, Future Minimum Payments Receivable, in Five Years	1
Operating Leases, Future Minimum Payments, Due Thereafter	6
Lessor, Operating Lease, Payments to be Received	$ 12
Minimum [Member]
Lessee Operating Lease Remaining Lease Term	1 year
Maximum [Member]
Lessee Operating Lease Remaining Lease Term	11 years

Background and Business Descrip

Background and Business Description	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Background and Business Description	1. BACKGROUND AND BUSINESS DESCRIPTION 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 . AFG provides financial guarantee insurance policies through its principal operating subsidiary, Ambac Assurance Corporation ("Ambac Assurance" or "AAC") and its wholly owned subsidiary Ambac Assurance UK Limited (“Ambac UK”), both of which have been in runoff since 2008. References to “Ambac,” the “Company,” “we,” “our,” and “us” are to AFG and its subsidiaries, as the context requires. Insurance policies issued by Ambac Assurance and Ambac UK generally guarantee payment when due of the principal and interest on the obligations guaranteed. Ambac Assurance also has another wholly-owned subsidiary, Everspan Insurance Company (formerly known as Everspan Financial Guarantee Corp.), which has been in runoff since its acquisition in 1997. The deterioration of Ambac Assurance’s financial condition resulting from losses in its insured portfolio since 2007 has prevented Ambac Assurance and Ambac UK from being able to write new business. The inability to write new business has and will continue to negatively impact Ambac’s future operations and financial results. Ambac Assurance’s ability to pay dividends and, as a result, AFG’s liquidity, have been significantly restricted by the deterioration of Ambac Assurance’s financial condition and by the terms of the Settlement Agreement, dated as of June 7, 2010, as amended (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. Ambac Assurance is also restricted in its ability to pay dividends pursuant to regulatory restrictions; the Stipulation and Order among the Office of the Commissioner of Insurance for the State of Wisconsin (“OCI”), AFG and Ambac Assurance that became effective on February 12, 2018, as amended (the “Stipulation and Order”); the terms of the indenture for the Tier 2 Notes (as defined below), which are substantially similar to the terms of the Settlement Agreement in this regard; and the terms of its Auction Market Preferred Shares ("AMPS"). It is highly unlikely that Ambac Assurance will be able to make dividend payments to AFG for the foreseeable future. Management reviews financial information, allocates resources and measures financial performance on a consolidated basis. As a result, the Company has a single reportable segment. Limitations on Voting and Transfer of Common Stock AFG’s Amended and Restated Certificate of Incorporation limits voting and transfer rights of stockholders in significant ways. Article IV contains voting restrictions applicable to any person owning at least 10% of AFG's common stock so that such person (including any group consisting of such person and any other person with whom such person or any affiliate or associate of such person has any agreement, contract, arrangement or understanding with respect to acquiring, voting, holding or disposing of AFG’s common stock) shall not be entitled to cast votes in excess of one vote less than 10% of the votes entitled to be cast by all common stock holders, except as otherwise approved by the OCI. Article XII contains substantial restrictions on the ability to transfer AFG’s common stock. In order to preserve certain tax benefits, subject to limited exceptions, any attempted transfer of common stock shall be prohibited and void to the extent that, as a result of such transfer (or any series of transfers of which such transfer is a part), either (i) any person or group of persons shall become a holder of 5% or more of the Company’s common stock or (ii) the percentage stock ownership interest in AFG of any holder of 5% or more of the Company’s common stock shall be increased (a “Prohibited Transfer”). These restrictions shall not apply to an attempted transfer if the transferor or the transferee obtains the written approval of AFG’s Board of Directors to such transfer. A purported transferee of a Prohibited Transfer shall not be recognized as a stockholder of AFG for any purpose whatsoever in respect of the securities which are the subject of the Prohibited Transfer (the “Excess Securities”). Until the Excess Securities are acquired by another person in a transfer that is not a Prohibited Transfer, the purported transferee of a Prohibited Transfer shall not be entitled with respect to such Excess Securities to any rights of stockholders of AFG, including, without limitation, the right to vote such Excess Securities and to receive dividends or distributions, whether liquidating or otherwise, in respect thereof, if any. Once the Excess Securities have been acquired in a transfer that is not a Prohibited Transfer, the securities shall cease to be Excess Securities. If the Board determines that a transfer of securities constitutes a Prohibited Transfer then, upon written demand by AFG, the purported transferee shall transfer or cause to be transferred any certificate or other evidence of ownership of the Excess Securities within the purported transferee’s possession or control, together with any distributions paid by AFG with respect to such Excess Securities, to an agent designated by AFG. Such agent shall thereafter sell such Excess Securities and the proceeds of such sale shall be distributed as set forth in the Amended and Restated Certificate of Incorporation. If the purported transferee of a Prohibited Transfer has resold the Excess Securities before receiving such demand, such person shall be deemed to have sold the Excess Securities for AFG’s agent and shall be required to transfer to such agent the proceeds of such sale, which shall be distributed as set forth in the Amended and Restated Certificate of Incorporation. Strategies to Enhance Shareholder Value Since the exit from rehabilitation of Ambac Assurance’s Segregated Account (as defined below) in February 2018, Ambac has been focused on and continues to progress all key strategic priorities, specifically: • 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 and adjustments focused on improving 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 credit, insurance, 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 Ambac, 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 the acquisition or development of any new businesses or assets. 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 Ambac’s strategy to 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 (as defined in Note 1. Background and Business Description to the Consolidated Financial Statements included in Part II, Item 8 of this Form 10-K) and in the indenture for the Tier 2 Notes (as defined in Note 1. Background and Business Description to the Consolidated Financial Statements included in Part II, Item 8 of this Form 10-K), each of which requires OCI (as defined below) 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 Ambac. See Note 1. Background and Business Description to the Consolidated Financial Statements included in Part II, Item 8 in this Form 10-K for further information. 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 other counterparty specific factors. Ambac Assurance's ability to commute policies or purchase certain investments may also be limited by available liquidity. The Segregated Account In March 2010, Ambac Assurance established a Segregated Account pursuant to Wisc. Stat. §611.24 (2) (the “Segregated Account”) to segregate certain segments of Ambac Assurance’s liabilities, and the Wisconsin Insurance Commissioner, acting as rehabilitator (the "Rehabilitator") commenced rehabilitation proceedings in the Dane County, Wisconsin Circuit Court (the “Rehabilitation Court”) with respect to the Segregated Account (the “Segregated Account Rehabilitation Proceedings”) in order to permit OCI to facilitate an orderly run-off and/or settlement of the liabilities allocated to the Segregated Account. On October 8, 2010, OCI filed a plan of rehabilitation for the Segregated Account (the “Segregated Account Rehabilitation Plan”) in the Rehabilitation Court, which was confirmed on January 24, 2011. On June 11, 2014, the Rehabilitation Court approved amendments to the Segregated Account Rehabilitation Plan and the Segregated Account Rehabilitation Plan, as amended, became effective on June 12, 2014. Policy obligations not allocated to the Segregated Account remained in the General Account of Ambac Assurance, and such policies in the General Account were not subject to and, therefore, were not directly impacted by the Segregated Account Rehabilitation Plan. On February 12, 2018, the rehabilitation of the Segregated Account was concluded pursuant to an amendment to the Segregated Account Rehabilitation Plan (the "Second Amended Plan of Rehabilitation"). The conclusion of the rehabilitation followed the successful completion of Ambac's surplus note exchange offers and consent solicitation, which, together with the satisfaction of all conditions precedent to the effectiveness of the Second Amended Plan of Rehabilitation, including the discharge of all unpaid policy claims of the Segregated Account, including accretion amounts thereon ("Deferred Amounts"), completed the restructuring transactions (the "Rehabilitation Exit Transactions") . In exchange for an effective consideration package of 40% cash, 41% Secured Notes (as defined below) and 12.5% General Account Surplus Notes (as defined below), paid in respect of outstanding Deferred Amounts and General Account Surplus Notes. Ambac Assurance received the following benefits as a result of the completion of the Rehabilitation Exit Transactions: • Satisfaction and discharge of all outstanding Deferred Amounts (including accretion) of the Segregated Account, totaling $3,857 ; • Cancellation of $552 in principal amount outstanding, plus accrued and unpaid interest of $257 thereon, of Ambac Assurance's 5.1% surplus notes due 2020 (the "General Account Surplus Notes"); and • An effective discount of 6.5% on Deferred Amounts (applied first against accretion) and on the outstanding amount of principal and accrued and unpaid interest on tendered General Account Surplus Notes. AFG received $0.91 in principal amount of Secured Notes for each $1.00 of Deferred Amounts (including accretion) that it held, and provided a $0.09 discount in full satisfaction and discharge of its Deferred Amount claims. AFG did not participate in the voluntary surplus note exchange offers. Until the earlier of (i) June 8, 2020 and (ii) the date on which at least 25% of the principal amount of General Account Surplus Notes (other than junior surplus notes) are no longer outstanding, AFG has agreed to hold and not sell General Account Surplus Notes (other than junior surplus notes) which, as of June 30, 2017, had an aggregate of $60 of principal amount and accrued and unpaid interest outstanding. The Secured Notes A newly formed special purpose entity, Ambac LSNI, LLC ("Ambac LSNI") issued $2,154 of new secured notes (the “Secured Notes”), secured by all assets of the special purpose entity, which include a note issued by Ambac Assurance to the special purpose entity (the "Ambac Note"), which is secured by a pledge of Ambac Assurance’s right, title and interest in up to the first $1,400 of proceeds (net of reinsurance) from certain litigations in which Ambac Assurance seeks redress for breaches of representations and warranties and/or fraud related to residential mortgage-backed securitizations (the “RMBS Litigations”). In addition, the Ambac Note is secured by cash and securities having a market value of $197 as of December 31, 2019 . Ambac Assurance also pledged for the benefit of the holders of Secured Notes (other than Ambac Assurance) the proceeds of the Secured Notes held by Ambac Assurance from time to time, and issued a financial guaranty insurance policy to a trustee for the benefit of holders of Secured Notes irrevocably guarantying all principal and interest payments in respect of the Secured Notes as and when such payments become due and owing. Prior to the Rehabilitation Exit Transactions, AFG and Ambac Assurance owned securities that were insured by Ambac Assurance and allocated to the Segregated Account. As a result of the Rehabilitation Exit Transactions, AFG and Ambac Assurance received $125 and $644 , respectively, of par amount of Secured Notes issued by Ambac LSNI. The current holdings of these secured notes are reported in Investments in the Consolidated Balance Sheets at their fair value. Tier 2 Financing On the effective date of the Rehabilitation Exit Transactions, Ambac Assurance issued $240 of senior notes (the “Tier 2 Notes”) secured by Ambac Assurance’s rights, title and interest in the cash and non-cash proceeds (net of reinsurance) above $1,600 received in connection with the RMBS Litigations. The indenture for the Tier 2 Notes limits certain activities of Ambac Assurance and its subsidiaries, such as issuing certain indebtedness; engaging in mergers and similar transactions; disposing of assets; making restricted payments; and creating or permitting liens (among other restrictions and limitations). The indenture for the Tier 2 Notes includes certain allowances with respect to these activities and generally requires the approval of OCI and, in some cases, holders of the Tier 2 Notes, for consents, waivers or amendments. Bank Settlement Agreement Waiver and Amendment As part of the Rehabilitation Exit Transactions, AFG and Ambac Assurance received sufficient consents from holders of General Account Surplus Notes for a waiver and amendment (the "BSA Waiver and Amendment") of the Settlement Agreement. Among other provisions, the BSA Waiver and Amendment includes amendments to the Settlement Agreement that (i) eliminate the requirement for Ambac Assurance to have "unaffiliated qualified directors" on its Board of Directors; (ii) eliminate the prohibition on new business activities; (iii) modify the restrictions on the incurrence of indebtedness and other material obligations; (iv) modify the restrictions on liens securing permitted indebtedness; (v) modify restrictions applicable to junior surplus notes; and (vi) modify restrictions on mergers or similar transactions. After giving effect to the BSA Waiver and Amendment, the Settlement Agreement continues to limit certain activities of Ambac Assurance and its subsidiaries, such as issuing indebtedness; engaging in mergers and similar transactions; disposing of assets; making restricted payments; creating or permitting liens; engaging in transactions with affiliates; modifying or creating tax sharing agreements; and taking certain actions with respect to surplus notes (among other restrictions and limitations). The Settlement Agreement includes certain allowances with respect to these activities and generally requires the approval of OCI and, in some cases, holders of surplus notes issued pursuant to the Settlement Agreement, for consents, waivers or amendments. Stipulation and Order Upon consummation of the Rehabilitation Exit Transactions, the Stipulation and Order became effective. The Stipulation and Order includes affirmative covenants, as well as restrictions on certain business activities and transactions, of AFG and Ambac Assurance. The Stipulation and Order has no fixed term and may be terminated or modified only with the approval of OCI. OCI reserved the right to modify or terminate the Stipulation and Order in a manner consistent with the interests of policyholders, creditors and the public generally. August 2018 AMPS Exchange At June 30, 2018, Ambac Assurance had 26,411 shares of issued and outstanding AMPS with a liquidation preference of $660 (reported as noncontrolling interest of $264 on Ambac's balance sheet). On July 3, 2018, AFG and Ambac Assurance commenced an offer to exchange (the “AMPS Exchange”) all of Ambac Assurance’s outstanding AMPS for General Account Surplus Notes and, from AFG, cash and warrants to purchase AFG's common stock. The General Account Surplus Notes offered in the AMPS Exchange have the same terms as other outstanding surplus notes of Ambac Assurance (other than junior surplus notes). The offering period for the AMPS Exchange expired on August 1, 2018 and the transaction closed on August 3, 2018 (the "Settlement Date"). In exchange for each AMPS share (i.e. $25 thousand of liquidation preference), holders received General Account Surplus Notes with a total outstanding amount (including accrued and unpaid interest thereon through June 22, 2018 (the "Signing Date")) equal to $13.875 thousand (the “Repurchase”). AMPS holders who tendered on or before July 17, 2018, representing 22,096 shares of the AMPS, also received from AFG $0.500 in cash and 37.3076 warrants (rounded down to the nearest whole warrant) to purchase an equivalent number of shares of common stock of AFG at an exercise price of $16.67 per share (the “AFG Purchase” and, together with the Repurchase, the “Purchases”). As a result of the completion of the Purchases, Ambac: 1) Repurchased 84.4% or 22,296 AMPS with an aggregate liquidation preference of $557 , including $35 in aggregate liquidation preference in the AFG Purchase; 2) Captured a nominal discount of approximately $227 (a discount of approximately $253 on a fair market value basis) on $557 of the total outstanding liquidation preference of AMPS; and 3) Issued, in aggregate, $213 in current principal amount of General Account Surplus Notes with accrued interest thereon on Settlement Date of $98 , issued 824,307 warrants and paid $11 in cash. The AMPS are reported on the balance sheet within non-controlling interests and are carried at their fair value at the date AFG emerged from bankruptcy in April 2013, which is lower than the fair value of the total consideration provided to the AMPS holders in the Purchases. The difference between the fair value of consideration provided to AMPS holders and the carrying amount of the AMPS was reflected as a reduction to Net income attributable to common stockholders in 2018 for approximately $82 . At December 31, 2019, and December 31, 2018, Ambac Assurance had 5,501 and 4,115 shares of issued and outstanding AMPS with a liquidation preference of $138 and $103 (reported as noncontrolling interest of $60 and $41 on Ambac's balance sheet). The increase resulted from the re-issuance of 1,386 shares from the sale of AFG owned AMPS during 2019.

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies (Notes)	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Significant Accounting Policies	2. BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES Ambac’s consolidated financial statements have been prepared on the basis of U.S. generally accepted accounting principles (“GAAP”). The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, expenses and disclosures. Such estimates that are particularly susceptible to change are used in connection with certain fair value measurements, valuation of loss reserves for non-derivative insurance policies and the valuation allowance on the deferred tax asset, any of which individually could be material. 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. Refer to 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. AFG Unconsolidated Financial Information Financial information of AFG is presented in Schedule II to this Form 10-K as of December 31, 2019 and 2018 and for the years ended December 31, 2019, 2018 and 2017 . Investments in subsidiaries are accounted for using the equity method of accounting in Schedule II. Investments The Investments - Debt Securities Topic of the ASC requires that all debt instruments be classified in Ambac’s Consolidated Balance Sheets according to their purpose and, depending on that classification, be carried at either cost or fair market value. Ambac’s non-VIE debt investment portfolio is accounted for on a trade-date basis and consists primarily of investments in fixed income securities that are considered available-for-sale as defined by the Investments - Debt Securities Topic of the ASC. Available-for-sale debt securities are reported in the financial statements at fair value with unrealized gains and losses, net of deferred taxes, reflected in Accumulated Other Comprehensive Income (Loss) in Stockholders’ Equity and computed using amortized cost as the basis. For purposes of computing amortized cost, premiums and discounts are accounted for using the effective interest method over a future term of the security. For structured debt securities with a large underlying pool of homogenous loans, such as mortgage-backed and asset-backed securities, premiums and discounts are adjusted for the effects of actual and anticipated prepayments. For other fixed income securities, such as corporate and municipal bonds, discounts were amortized or accreted over the remaining term of the securities. Ambac adopted ASU 2017-08, Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20) - Premium Amortization on Purchased Callable Debt Securities, on January 1, 2019. ASU 2017-08 shortened the amortization period for the premium on callable debt securities to the earliest call date. Under previous GAAP, Ambac generally amortized the premium over the contractual life (i.e. maturity) of the debt security and if that debt security was called, we would record a loss equal to the unamortized premium. Ambac’s non-VIE investment portfolio also includes equity interests in pooled investment funds which are accounted for in accordance with the Investments - Equity Securities Topic of the ASC and reported as Other investments on the Consolidated Balance Sheet with income reported through Net investment income on the Statement of Total Comprehensive Income (Loss). Equity interests in the form of common stock or in-substance common stock are classified as trading securities and reported at fair value while limited partner interests in such funds are reported using the equity method. Fair value is based primarily on quotes obtained from independent market sources. When quotes are not available or cannot be reasonably corroborated, valuation models are used to estimate fair value. These models include estimates, made by management, which utilize current market information. The quotes received or modeled valuations could differ materially from amounts that would actually be realized in the market. Realized gains and losses on the sale of investments are determined on the basis of specific identification. VIE investments in fixed income securities are carried at fair value as they are either considered as available for sale securities or under the fair value option election. For additional information about VIE investments, including fair value by asset-type, see Note 3. Variable Interest Entities . Ambac has a formal impairment review process for fixed income available-for-sale securities in its investment portfolio. Ambac conducts a review each quarter to identify and evaluate investments that have indications of impairment that may be other than temporary in accordance with the Investments - Debt Securities Topic of the ASC. Factors considered to identify and assess securities for other than temporary impairment include: (i) fair values that have declined by 20% or more below amortized cost; (ii) market values that have declined by 5% or more but less than 20% below amortized cost for a continuous period of at least six months; (iii) recent downgrades by rating agencies; (iv) the financial condition of the issuer and financial guarantor, as applicable, and an analysis of projected defaults on the underlying collateral; (v) whether scheduled interest payments are past due; (vi) whether Ambac has the intent to sell the security; and (vii) whether it is more likely than not that Ambac will be required to sell a security before the anticipated recovery of its amortized cost basis. If we believe a decline in the fair value of a particular investment is temporary, we record the decline as an unrealized loss net of tax in Accumulated Other Comprehensive Income (Loss) in Stockholders’ Equity on our Consolidated Balance Sheets. If management either: (i) has the intent to sell its investment in a debt security or (ii) determines that the Company more likely than not will be required to sell the debt security before its anticipated recovery of the amortized cost basis less any current period credit impairment, then an other-than-temporary impairment charge is recognized in earnings, with the amortized cost of the security being written-down to fair value. If these conditions are not met, but it is determined that a credit loss exists, the credit impairment loss is recognized in earnings, and the other-than-temporary amount related to all other factors is recognized in other comprehensive income. For fixed income securities that have other-than-temporary impairments in a period, the previous amortized cost of the security less the amount of the other-than-temporary impairment recorded through earnings becomes the investment’s new amortized cost basis. Ambac accretes the new amortized cost basis to par or to the estimated future cash flows to be recovered over the expected remaining life of the security. The evaluation of securities for impairment is a quantitative and qualitative process, which is subject to risks and uncertainties and is intended to determine whether, and to what extent, declines in the fair value of investments should be recognized in current period earnings. The risks and uncertainties include changes in general economic conditions, the issuer’s or guarantor’s financial condition and/or future prospects, the impact of regulatory actions on the investment portfolio, the performance of the underlying collateral, the effects of changes in interest rates or credit spreads and the expected recovery period. With respect to Ambac insured securities owned, future cash flows used to measure credit impairment represents the sum of (i) the bond’s intrinsic cash flows and (ii) the estimated Ambac Assurance claim payments. Prior to the discharge and settlement of the Segregated Account's claim obligations on February 12, 2018, the estimate of Ambac's Segregated Account claim payments, including interest on Deferred Amounts, was an important consideration in the evaluation of other than temporary impairment as such payments were at the sole discretion of the Rehabilitator. Refer to Note 1. Background and Business Description for more information on the Segregated Account and the Segregated Account Rehabilitation Proceedings. 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 the factors noted above. If that judgment changes, Ambac may ultimately record a charge for other-than-temporary impairment in future periods. Net Premiums Gross premiums were received either upfront or in installments. For premiums received upfront, an unearned premium revenue (“UPR”) liability was established, which was initially recorded as the cash amount received. For installment premium transactions, a premium receivable asset and offsetting UPR liability was initially established in an amount equal to: (i) the present value of future contractual premiums due (the “contractual” method) or (ii) if the underlying insured obligation is a homogenous pool of assets which are contractually prepayable, the present value of premiums to be collected over the expected life of the transaction (the “expected” method). An appropriate risk-free rate corresponding to the weighted average life of each policy and currency is used to discount the future premiums contractually due or expected to be collected. For example, U.S. dollar exposures are discounted using U.S. Treasury rates while exposures denominated in a foreign currency are discounted using the appropriate risk-free rate for the respective currency. The weighted average risk-free rate at December 31, 2019 and 2018 , was 2.4% . and 2.7% , respectively, and the weighted average period of future premiums used to estimate the premium receivable at December 31, 2019 and 2018 , was 8.5 and 8.7 years , respectively. Insured obligations consisting of homogeneous pools for which Ambac uses expected future premiums to estimate the premium receivable include residential mortgage-backed securities ("RMBS"). As prepayment assumptions change for homogenous pool transactions, or if there is an actual prepayment for a “contractual” method installment transaction, the related premium receivable and UPR are adjusted in equal and offsetting amounts with no immediate effect on earnings using new premium cash flows and the then current risk-free rate corresponding to the initial weighted average life of the related policy. For both upfront and installment premium policies, premium revenues are earned over the life of the financial guarantee contract in proportion to the insured principal amount outstanding at each reporting date (referred to as the level-yield method). For installment paying policies, the premium receivable discount, equating to the difference between the undiscounted future installment premiums and the present value of future installment premiums, is accreted as premiums earned in proportion to the premium receivable balance at each reporting date. Additionally, the Company evaluates whether any premiums receivable are uncollectible at each balance sheet date and records an allowance for policies with a premium receivable impairment based on our expectation. Similar to gross premiums, premiums ceded to reinsurers were paid either upfront or in installments. For premiums paid upfront, a deferred ceded premium asset was established which is initially recorded as the cash amount paid. For installment premiums, a ceded premiums payable liability and offsetting deferred ceded premium asset were initially established in an amount equal to: i) the present value of future contractual premiums due or ii) if the underlying insured obligation is a homogenous pool of assets, the present value of expected premiums to be paid over the life of the transaction. An appropriate risk-free rate corresponding to the weighted average life of each policy and exposure currency is used to discount the future premiums contractually due or expected to be collected. Premiums ceded to reinsurers reduce the amount of premiums earned by Ambac from its financial guarantee insurance policies. For both upfront and installment premiums, ceded premiums written are primarily recognized in earnings in proportion to and at the same time as the related gross premium revenue is recognized. For premiums paid to reinsurers on an installment basis, Ambac records the present value of future ceding commissions as an offset to ceded premiums payable, using the same assumptions noted above for installment premiums. When a bond issue insured by Ambac has been retired early, typically due to an issuer call, any remaining UPR is recognized at that time to the extent the financial guarantee contract is legally extinguished, causing accelerated premium revenue. For installment premium paying transactions, we offset the recognition of any remaining UPR by the reduction of the related premium receivable to zero (as it will not be collected as a result of the retirement), which may cause negative accelerated premium revenue. Certain obligations insured by Ambac have been legally defeased whereby government securities are purchased by the issuer with the proceeds of a new bond issuance, or less frequently with other funds of the issuer, and held in escrow. The principal and interest received from the escrowed securities are then used to retire the Ambac-insured obligations at a future date either to their maturity date (a refunding) or a specified call date (a pre-refunding). Ambac has evaluated the provisions in policies issued on these obligations and determined those insurance policies have not been legally extinguished. For policies with refunding securities, premium revenue recognition is not impacted as the escrowed maturity date is the same as the previous legal maturity date. For policies with pre-refunding securities, the maturity date of the pre-refunded security has been shortened from its previous legal maturity. Although premium revenue recognition has not been accelerated in the period of the pre-refunding, it results in an increase in the rate at which the policy's remaining UPR is to be recognized. Loans Loans are reported at either their outstanding principal balance less unamortized discount or at fair value. • Loans not held by consolidated VIEs are reported at their outstanding principal balance less unamortized discount and are reported within Other assets on the Consolidated Balance Sheet. Interest income is earned using the effective interest method based upon interest accrued on the unpaid principal balance adjusted for accretion of discounts. A loan is considered impaired when, based on the financial condition of the borrower, it is probable that Ambac will be unable to collect all principal and interest due according to the contractual terms of the loan agreement. • Loans held by VIEs consolidated as required under the Consolidation Topic of the ASC are carried at fair value under the fair value option election with changes in fair value recorded in Income (loss) on variable interest entities on the Consolidated Statements of Total Comprehensive Income (Loss). Such loans are reported as Loans, at fair value within the Variable interest entity assets section of the Consolidated Balance Sheet. Derivative Contracts The Company has entered into derivative contracts both for trading purposes and to hedge certain economic risks inherent in its financial asset and liability portfolios. None of Ambac’s derivative contracts are designated as hedges under the Derivatives and Hedging Topic of the ASC. Ambac's derivatives consist primarily of interest rate swaps and futures contracts. • Ambac maintains a portfolio consisting primarily of interest rate swaps and futures contracts to economically hedge interest rate risk in the financial guarantee and investment portfolios. This portfolio also includes legacy interest rate swaps with asset-backed securitization issuers, states, municipalities and their authorities which were written in connection with their financings. Changes in fair value of these interest rate derivatives are recorded, along with changes in fair value of Ambac's remaining credit derivatives, within Net gains (losses) on derivative contracts on the Consolidated Statements of Total Comprehensive Income (Loss). • VIEs consolidated under the Consolidation Topic of the ASC entered into derivative contracts to meet specified purposes within their securitization structure. Changes in fair value of consolidated VIE derivatives are included within Income (loss) on variable interest entities on the Consolidated Statements of Total Comprehensive Income (Loss). All derivatives are recorded on the Consolidated Balance Sheets at fair value on a gross basis; assets and liabilities are netted by counterparty only when a legal right of offset exists. Variation payments on centrally cleared swaps and futures contracts are considered settlements of the associated derivative balances and are reflected as a reduction to derivative liabilities or assets on the Consolidated Balance Sheets. For other derivatives, Ambac has determined that the amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral may not be used to offset amounts due under the derivative instruments in the normal course of settlement. Therefore, such amounts are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement and are included in "Other assets" on the Consolidated Balance Sheets. Refer to Note 11. Derivative Instruments for further discussion of the Company’s use of derivative instruments and their impact of the consolidated financial statements. Refer to Note 9. Fair Value Measurements for further description of the methodologies used to determine the fair value of derivative contracts, including model inputs and assumptions where applicable. Insurance Intangible Asset Upon Ambac's emergence from bankruptcy in 2013, an insurance intangible asset was recorded which represented the difference between the fair value and aggregate carrying value of the financial guarantee insurance and reinsurance assets and liabilities. The carrying values of our financial guarantee insurance and reinsurance contracts continue to be reported and measured in accordance with their existing accounting policies. Pursuant to the Financial Services-Insurance Topic of the ASC, the insurance intangible is to be measured on a basis consistent with the related financial guarantee insurance and reinsurance contracts. The insurance intangible asset is amortized using a level-yield method based on par exposure of the related financial guarantee insurance or reinsurance contracts and is applied to groups of contracts with similar characteristics. Restricted Cash Cash that we do not have the right to use for general purposes is recorded as restricted cash in our consolidated balance sheets. Restricted cash includes (i) consolidated variable interest entity cash restricted to support the obligations of the consolidated VIEs and (ii) cash held by Ambac Assurance received from its investment in Secured Notes and pledged for the benefit of holders of Secured Notes (other than Ambac Assurance). Loss and Loss Expenses The loss and loss expense reserve (“loss reserve”) policy relates only to Ambac’s non-derivative insurance business for insurance policies issued to beneficiaries, including VIEs, for which we do not consolidate the VIE. Losses and loss expenses are based upon estimates of the ultimate aggregate losses inherent in the non-derivative financial guarantee portfolio as of the reporting date. The policy for derivative contracts is discussed in the “Derivative Contracts” section above. A loss reserve is recorded on the balance sheet on a policy-by-policy basis based upon the present value ("PV") of expected net claim cash outflows or expected net recovery cash inflows, discounted at risk-free rates. The estimate for future net cash flows consider the likelihood of all possible outcomes that may occur from missed principal and/or interest payments on the insured obligation. This estimate also considers future recoveries related to breaches of contractual representations and warranties by RMBS transaction sponsors, remediation strategies, excess spread and other contractual cash flows on public finance and structured finance transactions (including RMBS). Ambac’s approach to resolving disputes involving contractual breaches by transaction sponsors or other third parties has included negotiations and/or pursuing litigation. Ambac does not estimate recoveries for litigations where its sole claim is for fraudulent inducement, since any remedies under such claims would be non-contractual. • Net claim cash outflow policies represent contracts where the PV of expected cash outflows are greater than the PV of expected recovery cash inflows. For such policies, a “Loss and loss expense reserves” liability is recorded for the excess of the PV of expected net claim cash outflows over the unearned premium revenue. • Net recovery cash inflow policies represent contracts where the PV of expected recovery cash inflows are greater than the PV of expected claim cash outflows. For such policies, a “Subrogation recoverable” asset is recorded. The evaluation process for determining expected losses is subject to certain judgments based on our assumptions regarding the probability of default by the issuer of the insured security, probability of settlement outcomes (which may include commutation settlements, refinancing and/or other settlement outcomes) and expected severity of credits for each insurance contract. Ambac’s loss reserves are based on management’s ongoing review of the financial guarantee credit portfolio. Active surveillance of the insured portfolio enables Ambac’s Risk Management Group ("RMG") to track credit migration of insured obligations from period to period and update internal classifications and credit ratings for each transaction. Non-adversely classified credits are assigned a Class I rating while adversely classified credits are assigned a rating of Class IA through Class V. The criteria for an exposure to be assigned an adversely classified credit rating includes the deterioration of an issuer’s financial condition, underperformance of the underlying collateral (for collateral dependent transactions such as mortgage-backed or student loan securitizations), poor performance by the servicer of the underlying collateral and other adverse economic events or trends. The servicer of the underlying collateral of an insured securitization transaction is a consideration in assessing credit quality because the servicer’s performance can directly impact the performance of the related issue. For example, a servicer of a mortgage-backed securitization that does not remain current in its collection efforts could cause an increase in the delinquency and the potential for default of the underlying obligation. Similarly, loss severities increase when a servicer does not effectively handle loss mitigation activities such as (i) the advancing of delinquent principal and interest and of default related expenses which are deemed to be recoverable by the servicer, (ii) pursuit of loan charge-offs which maximize cash flows from the mortgage loan pool and (iii) foreclosure and real estate owned disposition strategies and timelines. All credits are assigned risk classifications by RMG using the following guidelines: CLASS I - “Fully Performing - Meets Ambac Criteria with Remote Probability of Claim” - Credits that demonstrate adequate security and structural protection with a strong capacity to pay interest, repay principal and perform as underwritten. Factors supporting debt service payment and performance are considered unlikely to change and any such change would not have a negative impact upon the fundamental credit quality. Through ongoing surveillance, Ambac may also designate Class I credits into one or more of the following categories: • Survey List - credits that may lack information or demonstrate a weakness but further deterioration is not expected. • Watch List - credits that demonstrate the potential for future material adverse development due to such factors as long-term uncertainty about a particular sector, a certain structural element or concern related to the issuer or transaction or the overall financial and economic sustainability. CLASS IA - “Potential Problem with Risks to be Dimensioned” - Credits that are fully current and monetary default or claims-payment are not anticipated. The payor’s or issuer’s financial condition may be deteriorating or the credits may lack adequate collateral. A structured financing may also evidence weakness in its fundamental credit quality as evidenced by its under-performance relative to its modeled projections at underwriting, issues related to the servicer’s ability to perform or questions about the structural integrity of the transaction. While certain of these credits may still retain an investment grade rating, they usually have experienced or are vulnerable to a ratings downgrade. Further investigation is required to dimension and correct any deficiencies. A complete legal review of documents may be required. An action plan should be developed with triggers for future classification changes upward or downward. CLASS II - “Substandard Requiring Intervention” - Credits whose fundamental credit quality has deteriorated to the point that timely payment of debt service may be jeopardized by adversely developing trends of a financial, economic, structural, managerial or political nature. No claim payment is currently foreseen but the probability of loss or claim payment over the life of the transaction is now existent (generally 10% or greater probability). Class II credits may be border-line or below investment grade (BBB- to B). Prompt and sustained action must be taken to execute a comprehensive loss mitigation plan and correct deficiencies. CLASS III - “Doubtful with Clear Potential for Loss” - Credits whose fundamental credit quality has deteriorated to the point that timely payment of debt service has been or will be jeopardized by adverse trends of a financial, economic, structural, managerial or political nature which, in the absence of positive change or corrective action, are likely to result in a loss. The probability of monetary default or claims paying over the life of the transaction is generally 50% or greater. Full exercise of all available remedial actions is required to avert or minimize losses. Class III credits will generally be rated below investment grade (B to CCC). CLASS IV - “Imminent Default or Defaulted” - Monetary default or claim payments have occurred or are expected imminently. Class IV credits are generally rated D. CLASS V - “Fully Reserved” - The credit has defaulted and payments have occurred. The claim payments are scheduled and known, reserves have been established to fully cover such claims, and no claim volatility is expected. The population of credits evaluated in Ambac’s loss reserve process are: (i) all adversely classified credits (Class IA through V) and ii) non-adversely classified credits which had an internal Ambac rating downgrade since the transaction’s inception. One of two approaches is then utilized to estimate losses to ultimately determine if a loss reserve should be established. The first approach is a statistical expected loss approach, which considers the likelihood of all possible outcomes. The “base case” statistical expected loss is the product of: (i) the par outstanding on the credit; (ii) internally developed default information (taking into consideration internal ratings and average life of an obligation); (iii) internally developed loss severities; and (iv) a discount factor. The loss severities and default information are based on rating agency information, are specific to each bond type and are established and approved by senior RMG officers. For certain credit exposures, Ambac’s additional monitoring, loss remediation efforts and probabilities of potential settlement outcomes may provide information relevant to adjust this estimate of “base case” statistical expected losses. Analysts may accept the “base case” statistical expected loss as the best estimate of expected loss or assign multiple probability weighted scenarios to determine an adjusted statistical expected loss that better reflects management’s view of a given transaction’s expected losses, as well as the potential for additional remediation activities (e.g., commutations). The second approach entails the use of cash-flow based models to estimate expected losses (future claims, net of potential recoveries, expected to be paid to the holder of the insured financial obligation). Ambac’s RMG group will consider the likelihood of all possible outcomes and develop appropriate cash flow scenarios. This approach can include the utilization of internal or third party models and tools to project future losses and resultant claim payment estimates. We utilize cash flow models for RMBS, student loan, Puerto Rico and other exposures. RMBS and student loan models use historical performance of the collateral pools in order to then derive future performance characteristics, such as default and voluntary prepayment rates, which in turn determine projected future claim payments. In other cases, such as many public finance exposures, including our Puerto Rico exposures, we do not specifically forecast resources available to pay debt service in the cash flow model itself. Rather, we consider the issuers’ overall ability and willingness to pay, including the fiscal, economic, legal and political framework. In this approach, a probability-weighted expected loss estimate is developed based on assigning probabilities to multiple claim payment scenarios and applying an appropriate discount factor. Additionally, we assign a probability to the issuer’s ability to refinance an insured issue, Ambac’s ability to execute a potential settlement (i.e., commutation) of the insurance policy, including the impact on future installment premiums, and/or other restructuring scenarios. The commutation scenarios and the related probabilities of occurrence vary by transaction, depending on our view of the likelihood of negotiating such a transaction with issuers and/or investors. The discount

Variable Interest Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Variable Interest Entities	3. VARIABLE INTEREST ENTITIES Ambac, with its subsidiaries, has engaged in transactions with variable interest entities ("VIEs") in various capacities. • Ambac provides financial guarantees, including credit derivative contracts, for various debt obligations issued by special purpose entities, including VIEs ("FG VIEs"); • Ambac sponsors special purpose entities that issued notes to investors for various purposes; and • Ambac is an investor in collateralized debt obligations, mortgage-backed and other asset-backed securities issued by VIEs and its ownership interest is generally insignificant to the VIE and/or Ambac does not have rights that direct the activities that are most significant to such VIE. FG VIEs Ambac’s subsidiaries provide financial guarantees in respect of assets held or debt obligations of VIEs. Ambac’s primary variable interest exists through this financial guarantee contract. The transaction structures provide certain financial protection to Ambac. Generally, upon deterioration in the performance of a transaction or upon an event of default as specified in the transaction legal documents, Ambac will obtain certain control rights that enable Ambac to remediate losses. These rights may enable Ambac to direct the activities of the entity that most significantly impact the entity’s economic performance. Under a 2018 Stipulation and Order, the OCI requires Ambac Assurance to obtain their approval with respect to the exercise of certain significant control rights in connection with policies that had previously been allocated to the Segregated Account. Accordingly, Ambac Assurance does not have the right to direct the most significant activities of those FG VIEs. • We determined that Ambac’s subsidiaries generally have the obligation to absorb a FG VIE's expected losses given that they have issued financial guarantees supporting certain liabilities (and in some cases certain assets). As further described below, Ambac consolidates certain FG VIEs in cases where we also have the power to direct the activities that most significantly impact the VIE’s economic performance due to one or more of the following: (i) the transaction experiencing deterioration and breaching performance triggers, giving Ambac the ability to exercise certain control rights, (ii) Ambac being involved in the design of the VIE and receiving control rights from its inception, or (iii) the transaction not experiencing deterioration, however due to the passive nature of the VIE, Ambac's contingent control rights upon a future breach of performance triggers is considered to be the power over the most significant activity. • A VIE is deconsolidated in the period that Ambac no longer has such control rights, which could occur in connection with the execution of remediation activities on the transaction or amortization of insured exposure, either of which may reduce the degree of Ambac’s control over a VIE. • Assets and liabilities of FG VIEs that are consolidated are reported within Variable interest entity assets or Variable interest entity liabilities on the Consolidated Balance Sheets. • The election to use the fair value option is made on an instrument by instrument basis. Ambac has elected the fair value option for consolidated FG VIE financial assets and financial liabilities, except in cases where Ambac was involved in the design of the VIE and was granted control rights at its inception. ◦ When the fair value option is elected, changes in the fair value of the FG VIE's financial assets and liabilities are reported within Income (loss) on variable interest entities in the Consolidated Statements of Total Comprehensive Income (Loss), except for the portion of the total change in fair value of financial liabilities caused by changes in the instrument-specific credit risk which is presented separately in Other comprehensive income (loss). ◦ In cases where the fair value option has not been elected, the FG VIE's invested assets are fixed income securities and are considered available-for-sale as defined by the Investments - Debt Securities Topic of the ASC. These assets are reported in the financial statements at fair value with unrealized gains and losses reflected in Accumulated other comprehensive income (loss) in Stockholders' equity. The financial liabilities of these FG VIEs consist of long term debt obligations and are carried at par less unamortized discount. Income from the FG VIE's available-for-sale securities (including investment income, realized gains and losses and other-than-temporary impairments as applicable) and interest expense on long term debt are reported within Income (loss) on variable interest entities in the Consolidated Statements of Total Comprehensive Income (Loss). • Upon initial consolidation of a FG VIE, Ambac recognizes a gain or loss in earnings for the difference between: (i) the fair value of the consideration paid, the fair value of any non- controlling interests and the reported amount of any previously held interests and (ii) the net amount, as measured on a fair value basis, of the assets and liabilities consolidated. Upon deconsolidation of a FG VIE, Ambac recognizes a gain or loss for the difference between: (i) the fair value of any consideration received, the fair value of any retained non-controlling investment in the VIE and the carrying amount of any non-controlling interest in the VIE and (ii) the carrying amount of the VIE’s assets and liabilities. Gains or losses from consolidation and deconsolidation that are reported in earnings are reported within Income (loss) on variable interest entities on the Consolidated Statements of Total Comprehensive Income (Loss). • The impact of consolidating such FG VIEs on Ambac’s balance sheet is the elimination of transactions between the consolidated FG VIEs and Ambac’s operating subsidiaries and the inclusion of the FG VIE’s third party assets and liabilities. For a financial guarantee insurance policy issued to a consolidated VIE, Ambac does not reflect the financial guarantee insurance policy in accordance with the related insurance accounting rules under the Financial Services – Insurance Topic of the ASC. Consequently, upon consolidation, Ambac eliminates the insurance assets and liabilities associated with the policy from the Consolidated Balance Sheets. Such insurance assets and liabilities may include premium receivables, reinsurance recoverable, deferred ceded premium, subrogation recoverable, unearned premiums, loss and loss expense reserves, ceded premiums payable and insurance intangible assets. For investment securities owned by Ambac that are debt instruments issued by the VIE, the investment securities balance is eliminated upon consolidation. FG VIEs which are consolidated may include non-recourse assets or liabilities. FG VIEs' liabilities (and in some cases assets) that are insured by the Company are with recourse, because the Company guarantees the payment of principal and interest in the event the issuer defaults. FG VIEs' assets and liabilities that are not insured by the Company are without recourse, because Ambac has not issued a financial guarantee and is under no obligation for the payment of principal and interest of these instruments. Therefore, the Company’s exposure to consolidated FG VIEs is limited to the financial guarantees issued for recourse assets and liabilities and any additional variable interests held by Ambac. Additionally, Ambac’s general creditors, other than those specific policy holders which own the VIE debt obligations, do not have rights with regard to the assets of the VIEs. Ambac evaluates the net income effects and earnings per share effects to determine attributions between Ambac and non-controlling interests as a result of consolidating a VIE. Ambac has determined that the net income and earnings per share effect of consolidated FG VIEs are attributable to Ambac’s interests through financial guarantee premium and loss payments with the VIE. 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: December 31, 2019 2018 ASSETS: Ambac UK Ambac Assurance Total VIEs Ambac UK Ambac Assurance Total VIEs Fixed income securities, at fair value: Corporate obligations, fair value option $ 2,957 $ — $ 2,957 $ 2,737 $ — $ 2,737 Municipal obligations, available-for-sale (1) — 164 164 — — — Total FG VIE fixed income securities, at fair value 2,957 164 3,121 2,737 — 2,737 Restricted cash 1 1 2 1 — 1 Loans, at fair value (2) 3,108 — 3,108 4,288 — 4,288 Derivative assets 52 — 52 66 — 66 Other assets 1 2 3 1 — 1 Total FG VIE assets $ 6,119 $ 167 $ 6,286 $ 7,093 $ — $ 7,093 LIABILITIES: Accrued interest payable $ 1 $ — $ 1 $ 1 $ — $ 1 Long-term debt: Long-term debt, at fair value (3) 4,351 — 4,351 5,269 — 5,269 Long-term debt, at par less unamortized discount — 203 203 — — — Total long-term debt 4,351 203 4,554 5,269 — 5,269 Derivative liabilities 1,657 — 1,657 1,712 — 1,712 Total FG VIE liabilities $ 6,009 $ 203 $ 6,212 $ 6,981 $ — $ 6,981 Number of FG VIEs consolidated 6 1 7 7 — 7 (1) Available-for-sale securities consist of municipal obligations with an amortized cost basis of $139 and aggregate gross unrealized gains and (losses) of $25 at December 31, 2019 . All such securities had contractual maturities due after ten years as of December 31, 2019 . (2) The unpaid principal balances of loan assets carried at fair value were $2,618 as of December 31, 2019 and $3,418 as of December 31, 2018 . (3) The unpaid principal balances of long-term debt carried at fair value were $3,800 as of December 31, 2019 and $4,553 as of December 31, 2018 . The following schedule details the components of Income (loss) on variable interest entities for the affected periods: Year ended December 31, 2019 2018 2017 Net change in fair value of VIE assets and liabilities reported under the fair value option $ 13 $ 3 $ 20 Less: Credit risk changes of fair value option long-term debt reported through other comprehensive income (loss) — (1 ) — Net change in fair value of VIE assets and liabilities reported in earnings 14 2 20 Investment income on available-for-sale securities 10 — — Net realized investment gains (losses) on available-for-sale securities 13 — — Interest expense on long-term debt carried at par less unamortized cost (11 ) — — 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 $ 38 $ 3 $ 20 As further discussed in Note 7. Financial Guarantee Insurance Contracts , on February 12, 2019, in connection with the COFINA POA, the COFINA Class 2 Trust was established. Ambac was required to consolidate the COFINA Class 2 Trust, which resulted in a gain of $15 . The 2019 balance sheet impact of this additional VIE on the date of consolidation was an increase to total consolidated assets and liabilities by $292 and $364 , respectively. Ambac deconsolidated one , four and one VIEs for the years ended December 31, 2019, 2018 and 2017 , respectively. These VIEs were deconsolidated as a result of guaranteed bond retirements or loss mitigation activities that eliminated or reduced Ambac's control rights that previously required Ambac to consolidate these entities, and resulted in the gain (loss) on deconsolidation noted in the above table. The 2019 balance sheet impact of the deconsolidation was a decline in total consolidated assets and liabilities by $1,233 and $1,230 from December 31, 2018 , to December 31, 2019 . 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 December 31, 2019 and 2018 : Carrying Value of Assets and Liabilities Maximum (1) Insurance (2) Insurance (3) Net Derivative (4) 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 December 31, 2018: Global structured finance: Collateralized debt obligations $ 10 $ — $ — $ — Mortgage-backed—residential 6,713 1,859 547 — Other consumer asset-backed 1,701 15 238 — Other commercial asset-backed 873 21 12 — Other 2,123 53 301 7 Total global structured finance 11,420 1,949 1,098 7 Global public finance 24,146 309 335 (1 ) Total $ 35,566 $ 2,258 $ 1,434 $ 6 (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. Ambac Sponsored Non-consolidated VIEs In 1994, Ambac established a VIE to provide certain financial guarantee clients with funding for their debt obligations. This VIE was established as a separate legal entity, demonstrably distinct from Ambac and that Ambac, its affiliates or its agents could not unilaterally dissolve. The permitted activities of this entity are contractually limited to purchasing assets from Ambac, issuing medium-term notes ("MTNs") to fund such purchases, executing derivative hedges and obtaining financial guarantee policies with respect to indebtedness incurred. Ambac does not consolidate this entity because the exercise of related control rights in such policies remain subject to OCI approval under the Stipulation and Order, as discussed above. Ambac elected to account for its equity interest in this entity at fair value under the fair value option in accordance with the Financial Instruments Topic of the ASC. We believe that the fair value of the investments in this entity provides for greater transparency for recording profit or loss as compared to the equity method under the Investments – Equity Method and Joint Ventures Topic of the ASC. Refer to Note 9. Fair Value Measurements for further information on the valuation technique and inputs used to measure the fair value of Ambac’s equity interest in this entity. At December 31, 2019 and 2018 the fair value of this entity was $3 and $5 , respectively, and is reported within Other assets on the Consolidated Balance Sheets. • Total principal amount of the entity's debt outstanding was $403 and $393 at December 31, 2019 and 2018 , respectively. The entity's assets are utility obligations with a weighted average rating of BBB+ at December 31, 2019 , and weighted average life of 1.1 years . Purchases by this entity of financial assets from Ambac were financed through the issuance of MTNs, which are cross-collateralized by the purchased assets. The MTNs have the same expected weighted average life as the purchased assets. Derivative contracts (interest rate swaps) are used within the entity for economic hedging purposes only. Derivative positions were established at the time MTNs were issued to purchase financial assets. As of December 31, 2019 , Ambac Assurance had financial guarantee insurance policies issued for all assets, MTNs and derivative contracts owned and outstanding by the entity. • Insurance premiums paid to Ambac Assurance by this entity are earned in a manner consistent with other insurance policies, over the risk period. Additionally, any losses incurred on such insurance policies are included in Ambac’s Consolidated Statements of Total Comprehensive Income (Loss) . Under the terms of an Administrative Agency Agreement, Ambac provides certain administrative duties, primarily collecting amounts due on the obligations and making interest payments on the MTNs. On August 28, 2014, Ambac monetized its ownership of the junior surplus note issued to it by the Segregated Account by depositing the junior surplus note into a newly formed VIE trust in exchange for cash and an owner trust certificate, which represents Ambac's right to residual cash flows from the junior surplus note. Ambac does not consolidate the VIE since it does not have a variable interest in the trust. Ambac reports its owner trust certificate as an equity investment within Other investments on the Consolidated Balance Sheets with associated results from operations included within Net investment income: Other investments on the Consolidated Statements of Total Comprehensive Income (Loss) . The equity investment had a carrying value of $46 and $40 as of December 31, 2019 and 2018 , respectively. On February 12, 2018, Ambac formed a VIE, Ambac LSNI, LLC ("Ambac LSNI"). Ambac LSNI issued Secured Notes in connection with the Rehabilitation Exit Transactions. Ambac does not consolidate the VIE since it does not have a variable interest in the trust. Ambac reports its holdings of Secured Notes within Fixed income securities in the Consolidated Balance Sheets. The carrying value of Secured Notes held by Ambac was $535 and $656 as of December 31, 2019 and 2018 , respectively. Ambac's debt obligation to the VIE (the Ambac Note) had a carrying value of $1,763 and $1,940 at December 31, 2019 and 2018

Comprehensive Income

Comprehensive Income	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Comprehensive Income	4. COMPREHENSIVE INCOME The following tables detail the changes in the balances of each component of accumulated other comprehensive income (loss) 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 Year Ended December 31, 2019: Beginning Balance $ 86 $ 9 $ (142 ) $ (2 ) $ (49 ) Other comprehensive income (loss)before reclassifications 142 1 26 — 168 Amounts reclassified from accumulated other comprehensive income (loss) (76 ) (1 ) — — (78 ) Net current period other comprehensive income (loss) 65 (1 ) 26 — 91 Balance at December 31, 2019 $ 151 $ 8 $ (116 ) $ (2 ) $ 42 Year ended December 31, 2018: Beginning Balance $ 31 $ 11 $ (94 ) $ — $ (52 ) Adjustments to opening balance, net of taxes (3) — — — (3 ) (3 ) Adjusted balance, beginning of period 31 11 (94 ) (3 ) (55 ) Other comprehensive income before reclassifications 136 (1 ) (48 ) — 87 Amounts reclassified from accumulated other comprehensive income (81 ) (1 ) — 1 (81 ) Net current period other comprehensive income (loss) 55 (2 ) (48 ) 1 6 Balance at December 31, 2018 $ 86 $ 9 $ (142 ) $ (2 ) $ (49 ) (1) All amounts are net of tax and noncontrolling interest. Amounts in parentheses indicate reductions to Accumulated Other Comprehensive Income. (2) Represents the ch anges in fair value attributable to instrument-specific credit risk of liabilities for which the fair value option is elected. (3) Beginning in 2018, credit risk changes of fair value option liabilities are reflected as a component of Accumulated Other Comprehensive Income pursuant to the adoption of ASU 2016-01. Refer to Note 2. Basis of Presentation and Significant Accounting Policies for further information regarding this change. The following table details the significant amounts reclassified from each component of accumulated other comprehensive income for the affected periods: Details about Accumulated Other Comprehensive Income Components Amount Reclassified from Accumulated Affected Line Item in the Consolidated Statement of Total Comprehensive Income Year Ended December 31, 2019 2018 Unrealized Gains (Losses) on Available-for-Sale Securities $ (81 ) $ (82 ) Net realized investment gains (loses) 4 1 Provision for income taxes $ (76 ) $ (81 ) Net of tax and noncontrolling interest Amortization of Postretirement Benefit Prior service cost $ (1 ) $ (1 ) Other income Actuarial gains (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 $ — $ 1 Credit risk changes of fair value option liabilities — — Provision for income taxes — 1 Net of tax and noncontrolling interest Total reclassifications for the period $ (78 ) $ (81 ) Net of tax and noncontrolling interest

Net Income Per Share

Net Income Per Share	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Net Income Per Share	5. NET INCOME PER SHARE As of December 31, 2019 , 45,555,400 shares of AFG's common stock (par value $0.01 ) and warrants entitling holders to acquire up to 4,877,783 shares of new common stock at an exercise price of $16.67 per share were outstanding. For the three years ended December 31, 2019, 2018 and 2017 , 0 , 194 and 0 warrants were exercised, respectively, resulting in an issuance of 0 , 194 and 0 shares of common stock, respectively. On June 30, 2015, the Board of Directors of AFG authorized the establishment of a warrant repurchase program that permits the repurchase of up to $10 of warrants. On November 3, 2016, the Board of Directors of AFG authorized a $10 increase to the warrant repurchase program. For the years ended December 31, 2019 and 2018 , AFG did not repurchase any warrants. As of December 31, 2019 , AFG had repurchased 985,331 warrants at a total cost of $8 (average cost of $8.21 per warrant). The remaining aggregate authorization at December 31, 2019 was $12 . In connection with the AMPS Exchange, AFG issued 824,307 of the repurchased warrants at a price of $9.72 per warrant on August 3, 2018. Refer to Note 1. Background and Business Description for further discussion of the AMPS Exchange. 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: Year Ended December 31, 2019 2018 2017 Basic weighted average shares outstanding 45,954,908 45,665,883 45,367,932 Effect of potential dilutive shares (1) : Warrants — 441,104 — Stock options — — — Restricted stock units — 77,572 — Performance stock units (2) — 375,276 — Diluted weighted average shares outstanding 45,954,908 46,559,835 45,367,932 Anti-dilutive shares excluded from the above reconciliation Stock options 16,667 16,667 126,667 Warrants 4,877,783 — 4,053,670 Restricted stock units 249,263 — 68,654 Performance stock units (2) 872,258 — 322,943 (1) For the years ended December 31, 2019 and 2017 , 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 Guarantees in Force (

Financial Guarantees in Force (Notes)	12 Months Ended
	Dec. 31, 2019
Guarantees [Abstract]
Financial Guarantees in Force	6. FINANCIAL GUARANTEES IN FORCE Financial guarantees outstanding includes the exposures of policies that insure variable interest entities (“VIEs”) consolidated in accordance with ASC Topic 810, Consolidation. Financial guarantees outstanding includes the exposure of policies that insure 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 bonds. Financial guarantees outstanding exclude the exposures of policies that insure bonds which have been called, pre-refunded or refunded and excludes exposure of the policy that insures the notes issued by Ambac LSNI as defined in Note 1. Background and Business Description . The gross par amount of financial guarantees outstanding was $43,908 and $52,055 at December 31, 2019 and 2018 , respectively. The par amount of financial guarantees outstanding, net of reinsurance, was $38,018 and $46,927 at December 31, 2019 and 2018 , respectively. As of December 31, 2019 and 2018 , the guarantee portfolio was diversified by type of guaranteed bond as shown in the following table: Net Par Outstanding December 31, 2019 2018 Public Finance: Housing revenue (1) $ 5,991 $ 6,159 Lease and tax-backed revenue 5,102 7,565 General obligation 3,011 4,214 Higher education 885 1,168 Transportation revenue 855 1,754 Utility revenue 768 1,178 Other 1,041 1,404 Total Public Finance 17,653 23,442 Structured Finance: Mortgage-backed and home equity 4,423 5,510 Investor-owned utilities 1,675 1,754 Student loan 769 934 Structured Insurance 395 1,365 Asset-backed and other 246 384 Total Structured Finance 7,508 9,947 International Finance: Sovereign/sub-sovereign 5,264 5,250 Investor-owned and public utilities 4,436 4,499 Asset-backed and other 1,625 2,176 Transportation 1,532 1,613 Total International Finance 12,857 13,538 Total $ 38,018 $ 46,927 (1) Includes $5,654 and $5,759 of Military Housing net par at December 31, 2019 and 2018 , respectively. As of December 31, 2019 and 2018 , the International Finance guaranteed portfolio by location of risk was as outlined in the table below: Net Par Outstanding December 31, 2019 2018 United Kingdom $ 10,593 $ 10,965 Italy 767 811 Austria 674 712 Australia 382 384 France 303 312 Other international (1) 138 354 Total International Finance $ 12,857 $ 13,538 (1) Other international may include components of U.S. exposure. Gross financial guarantees in force (principal and interest) were $69,826 and $87,543 at December 31, 2019 and 2018 , respectively. Net financial guarantees in force (after giving effect to reinsurance) were $58,245 and $77,972 as of December 31, 2019 and 2018 , respectively. In the United States, California , Colorado and New York were the states with the highest aggregate net par amounts in force, accounting for 6.7% , 6.3% and 6.1% of the total at December 31, 2019 , respectively. No other state accounted for more than 5.0% . The highest single insured risk represented 2.7% of the aggregate net par amount guaranteed.

Financial Guarantee Insurance C

Financial Guarantee Insurance Contracts	12 Months Ended
	Dec. 31, 2019
Insurance [Abstract]
Financial Guarantee Insurance Contracts	7. FINANCIAL GUARANTEE INSURANCE CONTRACTS Amounts presented in this Note relate only to Ambac’s non-derivative insurance business for insurance policies issued to beneficiaries, including VIEs, for which we do not consolidate the VIE. Net Premiums Earned Below is the gross premium receivable roll-forward (direct and assumed contracts) for the affected periods: Year Ended December 31, 2019 2018 2017 Beginning premium receivable $ 495 $ 586 $ 661 Premium receipts (48 ) (56 ) (82 ) Adjustments for changes in expected and contractual cash flows (1) (38 ) (42 ) (30 ) Accretion of premium receivable discount 11 15 16 Deconsolidation of certain VIEs 3 — — Changes to uncollectable premiums (2 ) 2 — Other adjustments (including foreign exchange) (6 ) (10 ) 21 Ending premium receivable (2) $ 416 $ 495 $ 586 (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. At December 31, 2019, 2018 and 2017 premium receivables include British Pounds of $129 ( £97 ), $131 ( £103 ) and $152 ( £112 ), respectively, and Euros of $26 ( €23 ), $31 ( €27 ) and $36 ( €30 ), respectively. In evaluating the credit quality of the premium receivables, management evaluates the obligor's ability to pay. For structured finance transactions, this evaluation will include a review of the priority for the payment of financial guarantee premiums to Ambac, as required by bond indentures, in the transaction's waterfall structure. The financial guarantee premium is generally senior in the waterfall. An allowance for uncollectable premiums are determined on a policy basis and utilize a combination of historical premium collection data in addition to cash flow analysis to determine if an impairment in the related policy's premium receivables exist. At December 31, 2019 and 2018 , $9 and $7 respectively, of premium receivables were deemed uncollectable. The effect of reinsurance on premiums written and earned was as follows: Year Ended December 31, Direct Assumed Ceded (1) Net Premiums 2019: Written $ (28 ) $ — $ 31 $ (60 ) Earned 75 — 10 66 2018: Written $ (24 ) $ — $ 17 $ (41 ) Earned 119 — 8 111 2017: Written $ (14 ) $ — $ (2 ) $ (12 ) Earned 190 — 15 175 (1) Includes ceded premium activity related to the execution of reinsurance transactions in the years ended December 31, 2019 and 2018. Ambac’s accelerated premium revenue for retired obligations for the years ended December 31, 2019, 2018 and 2017 , was $10 , $32 and $64 , respectively. The following table summarizes net premiums earned by location of risk: Year Ended December 31, 2019 2018 2017 United States $ 55 $ 88 $ 134 United Kingdom 17 19 33 Other international (6 ) 5 8 Total $ 66 $ 111 $ 175 The table below summarizes the future gross undiscounted premiums to be collected and future premiums earned, net of reinsurance at December 31, 2019 : Future Premiums Collected (1) Future to be Earned Net of (2) Three months ended: March 31, 2020 $ 14 $ 10 June 30, 2020 11 10 September 30, 2020 10 10 December 31, 2020 9 10 Twelve months ended: December 31, 2021 37 36 December 31, 2022 36 34 December 31, 2023 34 32 December 31, 2024 33 30 Five years ended: December 31, 2029 143 124 December 31, 2034 102 82 December 31, 2039 47 38 December 31, 2044 22 14 December 31, 2049 9 5 December 31, 2054 1 1 Total $ 508 $ 436 (1) Future premiums to be collected are undiscounted 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 . This results in a different premium receivable balance than if expected lives were considered. If installment paying policies are retired or prepay early, premiums reflected in the premium receivable asset and amounts reported in the above table for such policies may not be collected. Future premiums to be earned also considers the use of contractual lives for many bond types which do not have homogeneous pools of underlying collateral, which may result in different unearned premium than if expected lives were considered. If those bonds types are retired early, premium earnings may be negative in the period of call or refinancing. Loss and Loss Expense Reserves A loss reserve is recorded on the balance sheet on a policy-by-policy basis as further described in Note 2. Basis of Presentation and Significant Accounting Policies . Below are the components of the Loss and loss expense reserves liability and the Subrogation recoverable asset at December 31, 2019 and 2018 : Present Value of Expected Unearned Gross Loss and Balance Sheet Line Item Claims and Recoveries December 31, 2019: Loss and loss expense reserves $ 1,835 $ (233 ) $ (54 ) $ 1,548 Subrogation recoverable 131 (2,160 ) — (2,029 ) Totals $ 1,966 $ (2,394 ) $ (54 ) $ (482 ) December 31, 2018: Loss and loss expense reserves $ 2,246 $ (314 ) $ (107 ) $ 1,826 Subrogation recoverable 176 (2,109 ) — (1,933 ) Totals $ 2,422 $ (2,422 ) $ (107 ) $ (107 ) Below is the loss and loss expense reserve roll-forward, net of subrogation recoverable and reinsurance, for the affected periods. Year Ended December 31, 2019 2018 2017 Beginning gross loss and loss expense reserves $ (107 ) $ 4,114 $ 3,696 Reinsurance recoverable 23 41 31 Beginning balance of net loss and loss expense reserves (130 ) 4,073 3,665 Losses and loss expenses (benefit) incurred: Current year 1 5 6 Prior years (1) 12 (228 ) 507 Total (2)(3) 13 (224 ) 513 Loss and loss expenses (recovered) paid: Current year — — 1 Prior years (1) 318 3,963 133 Total 318 3,964 134 Foreign exchange effect (1 ) (15 ) 29 Ending net loss and loss expense reserves (436 ) (130 ) 4,073 Impact of VIE consolidation (72 ) — — Reinsurance recoverable (4) 26 23 41 Ending gross loss and loss expense reserves (482 ) (107 ) 4,114 (1) 2018 loss and loss expenses (recovered) paid includes the settlement of Deferred Amounts and Interest Accrued on Deferred Amounts in the amount of $3,000 and $857 , respectively in connection with the Rehabilitation Exit Transactions through a combination of cash, surplus notes and secured notes. 2018 loss and loss expenses incurred includes a $288 loss and loss expense benefit on these settled Deferred Amounts. (2) Total losses and loss expenses (benefit) includes $(7) , $(2) and $20 for the years ended December 31, 2019, 2018 and 2017 , respectively, related to ceded reinsurance. (3) Ambac records the impact of estimated recoveries related to securitized loans in RMBS transactions that breached certain representations and warranties within losses and loss expenses (benefit). The losses and loss expense (benefit) incurred associated with changes in estimated representation and warranty recoveries for the year ended December 31, 2019, 2018 and 2017 was $42 , $62 and $72 , respectively. (4) 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 $0 , $1 and $0 as of December 31, 2019, 2018 and 2017 , respectively, related to previously presented loss and loss expenses and subrogation. For 2019 , the adverse development in prior years was primarily a result of deterioration in Public Finance credits, primarily Puerto Rico, partially offset by the benefit for (i) the Ballantyne Re plc ("Ballantyne") and Puerto Rico COFINA commutations, and (ii) positive development in the RMBS and Student Loan portfolios. For 2018, the net positive development in prior years was primarily a result of the discount recorded on the Rehabilitation Exit Transactions partially offset by negative development in the Public Finance portfolio and interest accrued on Deferred Amounts prior to the Rehabilitation Exit Transactions. For 2017, the net adverse development in prior years was primarily the result of negative development in certain public finance transactions, including Puerto Rico, and interest accrued on Deferred Amounts partially offset by positive developments in certain Ambac UK transactions, including a benefit of $145 related to a confidential settlement of litigation brought by Ambac UK in the name of Ballantyne that reduced the ultimate Ballantyne claims Ambac UK was expecting to pay. The tables below summarize information related to policies currently included in Ambac’s loss and loss expense reserves or subrogation recoverable at December 31, 2019 and 2018 . 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 December 31, 2019 and 2018 was 2.1% and 2.8% , respectively. 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 representation and warranty ("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. Surveillance Categories as of December 31, 2018 I IA II III IV V Total Number of policies 21 28 18 16 145 3 231 Remaining weighted-average contract period (in years) (1) 9 19 9 22 14 3 16 Gross insured contractual payments outstanding: Principal $ 917 $ 708 $ 623 $ 1,705 $ 5,407 $ 43 $ 9,403 Interest 488 632 293 6,979 2,178 13 10,583 Total $ 1,404 $ 1,340 $ 916 $ 8,685 $ 7,585 $ 57 $ 19,986 Gross undiscounted claim liability $ 4 $ 64 $ 36 $ 992 $ 2,296 $ 57 $ 3,448 Discount, gross claim liability — (13 ) (3 ) (434 ) (638 ) (4 ) (1,092 ) Gross claim liability before all subrogation and before reinsurance $ 4 $ 51 $ 33 $ 558 $ 1,658 $ 52 $ 2,356 Less: Gross RMBS subrogation (2) $ — $ — $ — $ — $ (1,810 ) $ — $ (1,810 ) Discount, RMBS subrogation — — — — 39 — 39 Discounted RMBS subrogation, before reinsurance — — — — (1,771 ) — (1,771 ) Less: Gross other subrogation (3) — (11 ) — (137 ) (625 ) (13 ) (785 ) Discount, other subrogation — 7 — 67 55 4 133 Discounted other subrogation, before reinsurance — (3 ) — (70 ) (570 ) (9 ) (652 ) Gross claim liability, net of all subrogation and discounts, before reinsurance $ 4 $ 47 $ 33 $ 489 $ (682 ) $ 43 $ (66 ) Less: Unearned premium revenue $ (1 ) $ (10 ) $ (5 ) $ (36 ) $ (54 ) $ — $ (107 ) Plus: Loss expense reserves 1 4 3 (6 ) 63 — 66 Gross loss and loss expense reserves $ 4 $ 41 $ 30 $ 446 $ (672 ) $ 43 $ (107 ) Reinsurance recoverable reported on Balance Sheet (4) $ — $ 7 $ 4 $ 26 $ (15 ) $ — $ 23 (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 $23 related to future loss and loss expenses and $1 related to presented loss and loss expenses and subrogation. Puerto Rico Ambac has exposure to the Commonwealth of Puerto Rico (the "Commonwealth") and its instrumentalities across several different issuing entities with total net par exposure of $1,123 . Components of Puerto Rico net par outstanding include capital appreciation bonds which are reported at the par amount at the time of issuance of the related insurance policy as opposed to the current accreted value of the bonds. Each issuing entity has its own credit risk profile attributable to discrete revenue sources, direct general obligation pledges or general obligation guarantees. The Commonwealth of Puerto Rico and certain of its instrumentalities have defaulted and may continue to default on debt service payments, including payments owed on bonds insured by Ambac Assurance. Ambac Assurance may be required to make significant amounts of policy payments over the next several years, the recoverability of which is subject to great uncertainty, which may lead to a material increase in permanent losses causing a material adverse impact on our results of operations and financial condition. Our exposure to Puerto Rico is impacted by the amount of monies available for debt service, which is in turn affected by a number of factors including demographic trends, economic growth, tax policy and revenues, impact of reforms, fiscal plans, government actions, political instability, budgetary performance and flexibility, weather events, restructuring and litigation outcomes, willingness to pay, as well as federal funding of Commonwealth needs. In the near term, the financial and economic outlook for Puerto Rico is dependent upon a still fragile infrastructure, heightening its vulnerability to additional weather events. The longer term recovery of the Commonwealth economy and its essential infrastructure will likely be dependent on, among other factors, the management, usage and efficacy of federal resources. Also important to Puerto Rico's economic growth, government reform and creditor outcomes is the Commonwealth Revised Fiscal Plan, certified by the Financial Oversight and Management Board for Puerto Rico ("Oversight Board") on May 9, 2019. The Commonwealth Revised Fiscal Plan outlines a series of reforms, projects the fiscal and economic impact of those reforms, and provides forecasts of resulting budgetary surpluses over a fiscal year series. However, as was the case with prior Commonwealth fiscal plans, the Commonwealth Revised Fiscal Plan lacks a high degree of transparency regarding the underlying data, assumptions and rationales supporting those assumptions, making reconciliation and due diligence difficult. As a result, it is difficult to predict the long-term capacity and willingness of the Puerto Rico government and its instrumentalities to pay debt service on bonded debt and how their debt burden and financial flexibility might affect Ambac Assurance's claim development potential, risk profile and long-term financial strength. Substantial uncertainty exists with respect to the ultimate outcome for creditors in Puerto Rico, such as Ambac Assurance, due to, amongst other matters, the Commonwealth Plan of Adjustment or changes thereto; political uncertainty and leadership turnover; legislation enacted by the Commonwealth and the federal government, including PROMESA; and actions taken pursuant to such laws, including Title III filings. Ambac Assurance is involved in multiple litigations relating to such actions and other issues and may not be successful in pursuing claims or protecting its interests. As a result of litigation or other aspects of the restructuring processes, including the Amended POA, the differences among the credits insured by Ambac Assurance may not be respected. Ambac Assurance has participated and may continue to participate in mediation related to potential debt restructurings, which could include debt restructurings as contemplated by the Amended POA. Mediation may not be productive or may not resolve Ambac Assurance's claims in a manner that avoids significant losses. No assurances can be given that negotiations will be successfully concluded, that Commonwealth, Oversight Board and creditor parties will reach definitive agreements on additional debt restructurings, that any additional negotiated transaction debt restructuring, definitive agreement or plans of adjustment will be approved by the court and completed, or that any transaction or plans of adjustment will not have an adverse impact on Ambac's financial condition or results. It is possible that certain restructuring process solutions, together with associated legislation, budgetary, and/or public policy proposals could be adopted and could further impair our exposures, causing losses that could have a material adverse impact on our results of operations and financial condition. While our reserving scenarios account for a wide range of possible outcomes, reflecting the significant uncertainty regarding future developments and outcomes, given our exposure to Puerto Rico and the economic, fiscal, legal and political uncertainties associated therewith as well as the residual effects emanating from the damage caused by hurricanes Maria and Irma in 2017 and earthquakes that began in late December 2019, our loss reserves may ultimately prove to be insufficient to cover our losses, potentially having a material adverse effect on our results of operations and financial position, and may be subject to material volatility. Ambac has considered these developments and other factors in evaluating its Puerto Rico loss reserves. During the year ended December 31, 2019 , Ambac had incurred losses associated with its Domestic Public Finance insured portfolio of $250 , which was primarily impacted by the continued uncertainty and volatility of the situation in Puerto Rico. While management believes its reserves are adequate to cover losses in its Public Finance insured portfolio, there can be no assurance that Ambac may not incur additional losses in the future, given the circumstances described herein. Such additional losses may have a material adverse effect on Ambac’s results of operations and financial condition and may result in adverse consequences such as impairing the ability of Ambac Assurance to honor its financial obligations; the initiation of rehabilitation proceedings against Ambac Assurance; decreased likelihood of Ambac Assurance delivering value to Ambac, through dividends or otherwise; and a significant drop in the value of securities issued or insured by Ambac or Ambac Assurance. For public finance credits, including Puerto Rico, as well as other issuers, for which Ambac has an estimate of expected loss at December 31, 2019 , the possible increase in loss reserves under stress or other adverse conditions and circumstances was estimated to be approximately $1,000 . This possible increase in loss reserves under stress or other adverse conditions is very significant and if we were to experience such incremental losses, our stockholders’ equity as of December 31, 2019 would decrease from $1,536 to $536 . However, there can be no assurance that losses may not exceed such amount. COFINA Debt Restructuring On January 16-17, 2019, the hearings for the confirmation of the COFINA Plan of Adjustment ("COFINA POA") and the Commonwealth 9019 motion were held. On February 4, 2019, the COFINA POA was confirmed and the Commonwealth 9019 motion was approved by the U.S. District Court for the District of Puerto Rico. On February 12, 2019, the COFINA POA went effective. Pursuant to the POA, all existing COFINA senior and subordinate bonds were discharged and exchanged for cash and new COFINA current interest and capital appreciation bonds ("new COFINA bonds"). The cash and new COFINA bonds allocated to COFINA senior bondholders equaled approximately 93% (considering the new COFINA bonds at par) of such senior bondholders’ allowed claim, in the amount of the COFINA senior bond accreted value, as of, but not including, May 5, 2017 (the COFINA Title III Petition Date). As a result of the COFINA POA, and subsequent commutations, amendments, and redemptions of obligations of the COFINA Class 2 Trust, Ambac Assurance's net par outstanding was reduced to $101 as of December 31, 2019 . Ambac Assurance's remaining policy obligation of $101 net par is an asset of the COFINA Class 2 Trust, which holds a ratable distribution of new COFINA bonds, the interest and principal from which can be used to partially offset Ambac’s remaining insurance liability. As further discussed in Note 3. Variable Interest Entities , Ambac Assurance consolidates the COFINA Class 2 Trust. At this time, it is unclear what impact the COFINA restructuring will have on the prospective recoveries of Ambac Assurance's other insured Puerto Rico instrumentalities. Representation and Warranty Recoveries Ambac records estimated RMBS R&W subrogation recoveries for breaches of R&W by sponsors of certain RMBS transactions. For a discussion of the approach utilized to estimate RMBS R&W subrogation recoveries, see Note 2. Basis of Presentation and Significant Accounting Policies . Ambac has recorded RMBS R&W subrogation recoveries of $1,727 , ( $1,702 net of reinsurance) and $1,771 , ( $1,744 net of reinsurance) at December 31, 2019 and 2018 , respectively. Below is the rollforward of RMBS R&W subrogation for the affected periods: Year ended December 31, 2019 2018 2017 Discounted RMBS subrogation recovery (gross of reinsurance) at beginning of year $ 1,771 $ 1,834 $ 1,907 All other changes (1) (43 ) (64 ) (73 ) Discounted RMBS subrogation recovery (gross of reinsurance) at end of year $ 1,727 $ 1,771 $ 1,834 (1) All other changes which may impact RMBS R&W subrogation recoveries include changes in actual or projected collateral performance, changes in the creditworthiness of a sponsor and the projected timing of recoveries. All other changes may also include estimates of potential sponsor settlements that may not have been subject to a sampling approach or have been executed, but the settlement amounts have not yet been received. Those that have not been subject to a sampling approach are not material to Ambac’s financial results and therefore are included in this table. Assumed Reinsurance Assumed par outstanding was $219 and $219 at December 31, 2019 and 2018 , respectively. Ceded Reinsurance Ambac Assurance has reinsurance in place pursuant to surplus share treaty and facultative reinsurance agreements. The reinsurance of risk does not relieve Ambac Assurance of its original liability to its policyholders. In the event that any of Ambac Assurance’s reinsurers are unable to meet their obligations under reinsurance contracts, Ambac Assurance would, nonetheless, be liable to its policyholders for the full amount of its policy. Ambac Assurance’s reinsurance assets, including deferred ceded premiums and reinsurance recoverables on losses amounted to $109 at December 31, 2019 . Credit exposure existed at December 31, 2019 , with respect to reinsurance recoverables to the extent that any reinsurer may not be able to reimburse Ambac Assurance under the terms of these reinsurance arrangements. At December 31, 2019 , there were ceded reinsurance balances payable of $29 offsetting this credit exposure. To minimize its credit exposure to losses from reinsurer insolvencies, Ambac Assurance (i) is entitled to receive collateral from its reinsurance counterparties in certain reinsurance contracts and (ii) has certain cancellation rights that can be exercised by Ambac Assurance in the event of rating agency downgrades of a reinsurer (among other events and circumstances). Ambac Assurance held letters of credit and collateral amounting to $124 from its reinsurers at December 31, 2019 . As of December 31, 2019 , the aggregate amount of insured par ceded by Ambac Assurance to reinsurers under reinsurance agreements was $5,890 with the largest reinsurer accounting for $2,746 or 6.3% of gross par outstanding at December 31, 2019 . The following table represents the percentage ceded to reinsurers and unsecured reinsurance recoverable at December 31, 2019 . Reinsurers Percentage Ceded Par Net Unsecured Reinsurance Recoverable (1) Assured Guaranty Re Ltd 47% $ — Build America Mutual Assurance Company (2) 42 36 Assured Guaranty Corporation 8 5 Sompo Japan Nipponkoa Insurance, Inc. 3 — Total 100% $ 41 (1) Represents reinsurance recoverables on paid and unpaid losses and deferred ceded premiums, net of ceded premium payables due to reinsurers, letters of credit, and collateral posted for the benefit of Ambac Assurance. (2) Build America Mutual Assurance Company has an S&P rating of AA. Insurance Intangible Asset The insurance intangible amortization expense is included in insurance intangible amortization on the Consolidated Statements of Total Comprehensive Income (Loss) . For the years ended December 31, 2019 , 2018 and 2017 , the insurance intangible amortization expense was $295 , $107 and $151 , respectively. As of December 31, 2019 and 2018 , the gross carrying value of the insurance intangible asset was $1,273 and $1,552 , respectively. Accumulated amortization of the insurance intangible asset was $847 and $833 , as of December 31, 2019 and 2018 , respectively, resulting in a net insurance intangible asset of $427 and $719 , respectively. The estimated future amortization expense for the net insurance intangible asset is as follows: Amortization expense (1) (2) 2020 $ 45 2021 39 2022 36 2023 33 2024 30 Thereafter 244 (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 as described in Note 2. Basis of Presentation and Significant Accounting Policies . 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 from the amounts provided in the table above. (2) The weighted-average amortizations period is 7.6 years .

Insurance Regulatory Restrictio

Insurance Regulatory Restrictions (Notes)	12 Months Ended
	Dec. 31, 2019
Regulatory Assets and Liabilities Disclosure [Abstract]
Insurance Regulatory Restrictions	8. INSURANCE REGULATORY RESTRICTIONS United States Ambac Assurance and Everspan are domiciled in the State of Wisconsin and, as such, are subject to the insurance laws and regulations of the State of Wisconsin (the “Wisconsin Insurance Laws”) and are regulated by the OCI. In addition, Ambac Assurance and Everspan are subject to the insurance laws and regulations of the other jurisdictions in which they are licensed. Insurance laws and regulations applicable to financial guarantee insurers vary by jurisdiction. The laws and regulations generally require financial guarantors to maintain minimum standards of business conduct and solvency; to meet certain financial tests; and to file policy forms, premium rate schedules and certain reports with regulatory authorities, including information concerning capital structure, ownership, financial condition, corporate governance and enterprise risk. Regulated insurance companies are also required to file quarterly and annual statutory financial statements with the National Association of Insurance Commissioners (“NAIC”), and in each jurisdiction in which they are licensed. The level of supervisory authority that may be exercised by non-domiciliary insurance regulators varies by jurisdiction. Generally, however, non-domiciliary regulators are authorized to suspend or revoke the insurance license they issued and to impose restrictions on that license in the event that laws or regulations are breached by a regulated insurance company or in the event that continued or unrestricted licensing of the regulated insurance company constitutes a “hazardous condition” (or meets a similar standard) in the opinion of the regulator. As the principal, or domiciliary, regulator of Ambac Assurance and Everspan, OCI has primary regulatory authority, including with respect to the initiation and administration of rehabilitation or liquidation proceedings. Additionally, the accounts and operations of Ambac Assurance and Everspan are subject to periodic comprehensive examinations by the OCI. Wisconsin Insurance Laws require regulated insurance companies to maintain minimum standards of business conduct, maintain minimum surplus to policyholders, meet certain financial tests, and file certain reports, including information concerning their capital structure, ownership, financial condition, corporate governance and enterprise risk. Neither Ambac Assurance nor Everspan is subject to risk-based capital requirements, since its is a financial guarantee insurer. Ambac Assurance and Everspan are in compliance with minimum surplus levels. Wisconsin Insurance Laws also require prior approval by OCI of certain transactions between Ambac Assurance or Everspan and their respective affiliates. In addition, pursuant to the terms of the Settlement Agreement, the Stipulation and Order and the indenture for the Tier 2 Notes, Ambac Assurance must seek prior approval by OCI of certain corporate actions. The Settlement Agreement, Stipulation and Order and indenture for the Tier 2 Notes include covenants which restrict the operations of Ambac Assurance. The Settlement Agreement will remain in force until the surplus notes that were issued pursuant to the Settlement Agreement have been redeemed, repurchased or repaid in full. The Stipulation and Order will remain in force for so long as OCI determines it to be necessary. The indenture for the Tier 2 Notes will remain in force until the Tier 2 Notes have been redeemed, repurchased or repaid in full. Certain of the restrictions in the Settlement Agreement and the indenture for the Tier 2 Notes may be waived with the approval of the OCI and/or the requisite percentage of holders of the related debt securities. New York’s comprehensive financial guarantee insurance law defines the scope of permitted financial guarantee insurance and governs the conduct of business of all financial guarantors licensed to do business in New York, including Ambac Assurance and Everspan. The New York financial guarantee insurance law also establishes single risk and aggregate limits with respect to insured obligations insured by financial guarantee insurers. Such single risk limits are specific to the type of insured obligation (for example, municipal or asset-backed). Under the aggregate limits, policyholders’ surplus and contingency reserves must at least equal a percentage of aggregate net liability that is equal to the sum of various percentages of aggregate net liability for various categories of specified obligations. At December 31, 2019 , Ambac Assurance is in compliance with applicable aggregate risk limits but not in compliance with applicable single risk limits. Through run-off of the portfolio, Ambac Assurance will continue to seek the reduction in its exposure for compliance with applicable single and aggregate risk limits, but may not be able to do so. Everspan is in compliance with all of such limits. Ambac Assurance’s statutory financial statements are prepared on the basis of accounting practices prescribed or permitted by Wisconsin Insurance law and OCI actions thereunder. A Wisconsin insurance company uses such statutory accounting practices prescribed or permitted by the State of Wisconsin for determining and reporting its financial condition and results of operations, including for determining its solvency under Wisconsin Insurance Law. The State of Wisconsin has adopted the applicable National Association of Insurance Commissioners (“NAIC”) accounting practices and procedures manual (“NAIC SAP”) as a component of prescribed practices by the State of Wisconsin. Ambac Assurance’s statutory policyholder surplus was $1,088 at December 31, 2019 , as compared to $1,152 as of December 31, 2018 . Statutory policyholder surplus differs from stockholders’ equity determined under GAAP principally due to statutory accounting rules that treat loss reserves, investments, consolidation of subsidiaries and variable interest entities, premiums earned and surplus notes differently. The OCI has prescribed or permitted accounting practices for Ambac Assurance. As a result of the prescribed and permitted practices discussed below, Ambac Assurance’s statutory surplus at December 31, 2019 and 2018 was lower by $12 and $42 , respectively, than if Ambac Assurance had reported such amounts in accordance with NAIC SAP. Prescribed Accounting Practices OCI has prescribed the following accounting practices that differ from NAIC SAP for Ambac Assurance: • Paragraph 8 of Statement of Statutory Accounting Principles No. 60 “Financial Guaranty Insurance” allows for a deduction from loss reserves for the time value of money by application of a discount rate equal to the average rate of return on the admitted assets of the financial guaranty insurer as of the date of the computation of the reserve. The discount rate shall be adjusted at the end of each calendar year. Additionally, in accordance with paragraph 13.e of Statutory Accounting Principles No. 97 "Investments in Subsidiary, Controlled and Affiliated Entities" and paragraph 8 of Statutory Accounting Principles No. 5R “Liabilities, Contingencies and Impairments of Assets - Revised”, Ambac Assurance records probable losses on its subsidiaries for which it guarantees their obligations. Ambac Assurance also discounts probable losses on guarantees of subsidiary obligations using a discount rate equal to the average rate of return on its admitted assets. Ambac Assurance’s average rates of return on its admitted assets at December 31, 2019 and 2018 were 5.43% and 5.87% , respectively. OCI has directed Ambac Assurance to utilize a prescribed discount rate of 5.10% for the purpose of discounting both its loss reserves and its estimated impairment losses on subsidiary guarantees. • Paragraph 4 of Statement of Statutory Accounting Principles No. 41 “Surplus Notes” (“SSAP 41”) states that proceeds received by the issuer of surplus notes must be in the form of cash or other admitted assets having readily determinable values and liquidity satisfactory to the commissioner of the state of domicile. Under statutory accounting principles, surplus notes issued in conjunction with commutations or the settlement of obligations would be valued at zero upon issuance pursuant to paragraph 4, SSAP 41. OCI has directed the Company to record surplus notes issued in connection with commutations or the settlement of obligations at full par value upon issuance. The surplus notes issued have a claim against surplus senior to the preferred and common shareholders. • Paragraph 35 of Statement of Statutory Accounting Principles No. 43R ”Loan-backed and Structured Securities” states that when an other-than-temporary impairment ("OTTI") has occurred, the amount of the OTTI recognized as a realized loss shall equal the difference between the investment’s amortized cost basis and the present value of cash flows expected to be collected, discounted at the loan-backed or structured security’s effective interest rate. Beginning June 11, 2014, as a result of the amended Segregated Account Rehabilitation Plan, OCI has directed the Company to not evaluate investments in Ambac Assurance insured securities with policies that were allocated to the Segregated Account for OTTI and require all such investments be reported at amortized cost regardless of its NAIC risk designation. This accounting determination was intended to recognize that Ambac Assurance continues to maintain statutory loss reserves without adjustment for the economic effects of its ownership of the insured investment securities, improve transparency to the users of the statutory financial statements and to minimize operational risks. Effective February 12, 2018, with the Segregated Account's exit from Rehabilitation, this prescribed practice is no longer applicable for OTTI evaluations going forward. Permitted Accounting Practices OCI has allowed the following permitted practices for Ambac Assurance: • Wisconsin accounting practices for changes to contingency reserves differ from NAIC SAP. Under NAIC SAP, contributions to and releases from the contingency reserve are recorded via a direct charge or credit to surplus. Under the Wisconsin Administrative Code, contributions to and releases from the contingency reserve are to be recorded through underwriting income. Ambac Assurance received permission from OCI to record contributions to and releases from the contingency reserve, in accordance with NAIC SAP. • Ambac Assurance received permission from OCI to report investment holdings of Ambac Assurance insured securities as a separate invested asset on the balance sheet rather than combined with other bond investments. This permitted practice only impacts the balance sheet classification and has no impact on the valuation of the securities to which it applies or to statutory surplus. On April 10 2019, Ambac Assurance requested and OCI approved the termination of this permitted practice and accordingly, all such investments are being combined with other bond investments beginning on January 1, 2019. • Effective upon the exit of the Segregated Account from rehabilitation and the merger of the Segregated Account with and into Ambac Assurance, Ambac Assurance received permission from OCI to restate its unassigned funds (surplus) balance to $100 with an offsetting reduction of $3,433 to gross paid-in and contributed surplus such that total surplus remains unchanged. • In connection with the AMPS Exchange in 2018, Ambac Assurance received permission from OCI to account for the exchange of AMPS for 5.1% surplus notes in a manner that ensures compliance with certain state insurance regulations that require a minimum surplus level. Accordingly, Ambac Assurance recorded the excess of the consideration paid over the par value of the AMPS as follows: i) first as a reduction to gross paid-in and contributed surplus up to an amount that resulted in a gross paid-in and contributed surplus balance of not less than $75 and ii) for any remaining excess, as a reduction to unassigned surplus. This permitted practice only impacts the balance sheet classification and has no impact on statutory surplus. United Kingdom The Prudential Regulatory Authority (“PRA”) and Financial Conduct Authority (“FCA”) (and their predecessor regulator the Financial Services Authority (“FSA”)) are the dual statutory regulator responsible for regulating the financial services industry in the United Kingdom, with the purpose of maintaining confidence in the U.K. financial system, providing public understanding of the system, securing the proper degree of protection for consumers and helping to reduce financial crime. In addition, the regulatory regime in the United Kingdom must comply with certain EU legislation binding on all EU member states. These regulators have exercised significant oversight of Ambac UK since 2008, after Ambac, Ambac Assurance and Ambac UK began experiencing financial stress. In 2009, Ambac UK’s license to write new business was curtailed by the FSA and the insurance license was limited to undertaking only run-off related activity. As such, Ambac UK is authorized to run-off its credit, suretyship and financial guarantee insurance portfolio in the United Kingdom, and to do the same through a branch in Milan, Italy, and a number of other European Union (“EU”) countries. EU legislation has allowed Ambac UK to conduct business in EU states other than the United Kingdom through a “passporting” arrangement, which eliminates the necessity of additional licensing or authorization in those other EU jurisdictions. The PRA requires that non-life insurance companies such as Ambac UK maintain a margin of solvency at all times in respect of the liabilities of the insurance company, the calculation of which depends on the type and amount of insurance business a company writes. These solvency requirements were amended on January 1, 2016, in order to implement the European Union's "Solvency II" directive on risk-based capital. Notwithstanding the foregoing, Ambac UK is deficient in terms of compliance with currently applicable regulatory capital requirements under Solvency II directive. The PRA and FCA are aware of the same, and dialogue between Ambac UK management and its regulators remains ongoing with respect to options for addressing the shortcoming, although such options remain few. Dividend Restrictions, Including Contractual Restrictions Due to losses experienced by Ambac Assurance, it has been unable to pay common dividends to Ambac since 2008 and will be unable to pay common dividends in 2020 without the prior consent of the OCI, which is unlikely. Ambac Assurance’s ability to pay dividends is further restricted by the Settlement Agreement (as described below), by the indenture for the Tier 2 Notes (as described below), by the terms of its AMPS (as described below) and by the Stipulation and Order. See Note 1. Background and Business Description for further information. Ambac Assurance is not expected to make dividend payments to AFG for the foreseeable future. Subject to the foregoing, pursuant to the Wisconsin Insurance Laws, Ambac Assurance and Everspan may declare dividends, subject to restrictions in their respective articles of incorporation, provided that, after giving effect to the distribution, such dividends would not violate certain statutory solvency, surplus and asset tests. Board action authorizing a shareholder distribution by Ambac Assurance or Everspan (other than stock dividends) must be reported to the OCI at least 30 days prior to payment, unless the distribution is no more than 15% larger than for the corresponding period in the previous year. In addition, Wisconsin Insurance Laws restrict the payment of extraordinary dividends, which is any distribution which, together with distributions in the prior 12 months, is greater than the lesser of (a) 10% of policyholders’ surplus as of the preceding December 31, and (b) the greater of (i) statutory net income (loss) for the calendar year preceding the date of the dividend, minus realized capital gains for that calendar year or (ii) the aggregate of statutory net income (loss) for three calendar years preceding the date of the dividend, minus realized capital gains for those calendar years and minus dividends paid or credited within the first two of the three preceding calendar years. Extraordinary dividends must be reported to OCI at least 30 days prior to payment and are subject to disapproval by the OCI. UK law prohibits Ambac UK from declaring a dividend to its shareholders unless it has “profits available for distribution.” The determination of whether a company has profits available for distribution is based on its accumulated realized profits less its accumulated realized losses. While the UK insurance regulatory laws impose no statutory restrictions on a general insurer’s ability to declare a dividend, the PRA’s and FCA’s capital requirements in practice act as a restriction on the payment of dividends. Further, the FSA amended Ambac UK’s license in 2010 such that the PRA must specifically approve (“non-objection”) any transfer of value and/or assets from Ambac UK to Ambac Assurance or any other Ambac group company, other than in respect of certain disclosed contracts between the two parties (such as in respect of a management services agreement between Ambac Assurance and Ambac UK). Ambac UK is not expected to pay any dividends to Ambac Assurance for the foreseeable future. Pursuant to the Settlement Agreement, Ambac Assurance may not make any “Restricted Payment” (which includes dividends from Ambac Assurance to Ambac) in excess of $5 in the aggregate per annum, other than Restricted Payments from Ambac Assurance to Ambac in an amount up to $8 per annum solely to pay operating expenses of Ambac. Concurrent with making any such Restricted Payment, a pro rata amount of Ambac Assurance's surplus notes would also need to be redeemed at par. The indenture for the Tier 2 Notes contains a similar restrictive covenant and further requires a proportional payment of the Tier 2 Notes (or interest thereon) when payments are made on the surplus notes. Under the terms of Ambac Assurance’s AMPS, dividends may not be paid on the common stock of Ambac Assurance unless all accrued and unpaid dividends on the AMPS for the then current dividend period have been paid, provided, that dividends on the common stock may be made at all times for the purpose of, and only in such amounts as are necessary for, enabling Ambac (i) to service its indebtedness for borrowed money as such payments become due or (ii) to pay its operating expenses. If dividends are paid on the common stock as provided in the prior sentence, dividends on the AMPS become cumulative until the date that all accumulated and unpaid dividends have been paid on the AMPS. The Stipulation and Order requires OCI approval for the payment of any dividend or distribution on the common stock of Ambac Assurance.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	9. 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 certain uncollateralized derivative 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 December 31, 2019 and 2018 , 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: Level 1 Level 2 Level 3 December 31, 2019: 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, 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 Carrying Total Fair Fair Value Measurements Categorized as: Level 1 Level 2 Level 3 December 31, 2018: Financial assets: Fixed income securities: Municipal obligations $ 880 $ 880 $ — $ 880 $ — Corporate obligations 1,278 1,278 — 1,278 — Foreign obligations 31 31 30 1 — U.S. government obligations 94 94 94 — — Residential mortgage-backed securities 259 259 — 259 — Collateralized debt obligations 131 131 — 131 — Other asset-backed securities 442 442 — 370 72 Short term investments 430 430 305 125 — Other investments (1) 391 367 71 — 16 Cash and cash equivalents and restricted cash 82 82 53 30 — Derivative assets: Interest rate swaps—asset position 59 59 — 12 47 Other assets - equity in sponsored VIE 5 5 — — 5 Other assets-loans 10 12 — — 12 Variable interest entity assets: Fixed income securities: Corporate obligations 2,737 2,737 — — 2,737 Restricted cash 1 1 1 — — Loans 4,288 4,288 — — 4,288 Derivative assets; Currency swaps-asset position 66 66 — 66 — Total financial assets $ 11,186 $ 11,164 $ 554 $ 3,153 $ 7,177 Financial liabilities: Long term debt, including accrued interest $ 3,305 $ 3,260 $ — $ 2,909 $ 351 Derivative liabilities: Credit derivatives 1 1 — — 1 Interest rate swaps—liability position 72 72 — 72 — Futures contracts 3 3 3 — Liabilities for net financial guarantees written (2) (718 ) 559 — — 559 Variable interest entity liabilities: Long-term debt (includes $5,269 at fair value) 5,269 5,269 — 5,052 217 Derivative liabilities: Interest rate swaps—liability position 1,712 1,712 — 1,712 — Total financial liabilities $ 9,644 $ 10,876 3 9,745 1,128 (1) Excluded from the fair value measurement categories in the table above are investment funds of $296 and $280 as of December 31, 2019 and 2018 , respectively, which are measured using NAV per share 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 certain 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. We reflect Ambac’s own creditworthiness in the fair value of financial liabilities by including a credit valuation adjustment (“CVA”) in the determination of fair value. A decline (increase) in Ambac’s creditworthiness as perceived by market participants will generally result in a higher (lower) CVA, thereby lowering (increasing) the fair value of Ambac’s financial liabilities as reported. Fixed Income Securities The fair values of fixed income investment securities are based primarily on market prices received from 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 December 31, 2019 , approximately 4% , 94% , and 2% of the fixed income investment portfolio (excluding variable interest entity investments) was valued using dealer quotes, alternative pricing sources and internal valuation models, respectively. At December 31, 2018 , approximately 8% , 90% , and 2% of the fixed income investment portfolio (excluding variable interest entity investments) was valued using dealer 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) and/or internally modeled prices, 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: These securities are a subordinated tranche of a resecuritization collateralized by Ambac-insured military housing bonds. The fair value of such securities classified as Level 3 was $72 and $72 at December 31, 2019 and 2018 , 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 December 31, 2019 and 2018 include the following weighted averages: December 31, 2019: a. Coupon rate 5.97% b. Average Life 15.58 years c. Yield 11.75% December 31, 2018: a. Coupon rate 5.97% b. Maturity 16.29 years c. Yield 12.00% 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 10. 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 determined using a market approach at December 31, 2019 and a discounted cash flow approach at December 31, 2018. The valuation methodology was updated to incorporate more directly relevant market data from instruments issued by Ambac. Derivative Instruments Ambac’s derivative instruments comprise interest rate swaps, exchange traded futures contracts and credit default swaps. 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 counterparties or underlying referenced obligations, yield curves and tax-exempt interest ratios. The valuation of certain interest rate as well as all credit 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 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 uncollateralized derivative liabilities was reduced by $0 and $0 at December 31, 2019 and 2018 , 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 December 31, 2019 and 2018 . 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 remaining 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 December 31, 2019 . 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 VIEs consolidated under the Consolidation Topic of the ASC consist primarily of fixed income securities, loans, derivative and debt instruments and are generally carried at fair value. These consolidated VIEs are securitization entities which have liabilities and/or assets guaranteed by Ambac Assurance or Ambac UK. The fair values of VIE debt instruments are determined using the same methodologies used to value Ambac’s fixed income securities in its investment portfolio as described above. VIE debt fair value is based on market prices received from independent market sources. Such quotes are considered Level 2 and generally consider a variety of factors, including recent trades of the same and similar securities. For those VIE debt instruments where quotes were not available, the debt instrument fair values are considered Level 3 and are based on internal discounted cash flow 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 VIE debt. Information about the valuation inputs for VIE debt carried at fair value and classified as Level 3 is as follows: European ABS transactions : The fair value of such obligations classified as Level 3 was $0 and $217 at December 31, 2019 and 2018 , respectively. As a result of reductions to Ambac's control rights, this VIE was deconsolidated in 2019. Fair values were calculated by using a discounted cash flow approach. The discount rates used were based on the rates implied from the third party quoted values for comparable notes from the same securitization entity. Significant inputs for the valuation at December 31, 2018 include the following weighted averages: December 31, 2018 a. Coupon rate 2.20% b. Maturity 18.93 years c. Yield 3.18% VIE derivative asset and liability fair values are determined using valuation models. When specific derivative contractual terms are available and may be valued primarily by reference to interest rates, foreign exchange rates and yield curves that are observable and regularly quoted, the derivatives are valued using vendor-developed models. Other derivatives within the VIEs that include significant unobservable valuation inputs are valued using internally developed models. VIE derivative liability fair value balances at December 31, 2019 and 2018 were developed using vendor-developed models and do not use significant unobservable inputs. The fair value of VIE assets are obtained from market quotes when available. Typically VIE asset fair values are not readily available from market quotes and are estimated internally. The consolidated VIEs are securitization entities in which net cash flows from assets and derivatives (after adjusting for financial guarantor cash flows and other expenses) will be paid out to note holders or equity interests. Internal valuations of VIE assets (fixed income securities or loans), therefore, are generally derived from the fair value of notes and derivatives, as described above, adjusted for the fair value of cash flows from Ambac’s financial guarantee. The fair value of financial guarantee cash flows include: (i) estimated future premiums discounted at a rate consistent with that implicit in the fair value of the VIE’s liabilities and (ii) internal estimates of future loss payments by Ambac 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 weighted average rate of 2.7% and 3.1% at December 31, 2019 and 2018 , respectively. The value of future loss payments to be paid by Ambac to the VIEs was adjusted to include an Ambac CVA appropriate for the term of expected Ambac claim payments. 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 2019 , 2018 and 2017. 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 Year Ended December 31, 2019 Investments Other (1) Derivatives Investments Loans Long-term Total Balance, beginning of period $ 72 $ 5 $ 46 $ 2,737 $ 4,288 $ (217 ) $ 6,930 Total gains/(losses) realized and unrealized: Included in earnings 2 (2 ) 25 138 287 (15 ) 436 Included in other comprehensive income — — — 116 74 8 199 Purchases — — — — — — — Issuances — — — — — — — Sales — — — — — — — Settlements (2 ) — (5 ) (35 ) (690 ) — (731 ) Transfers into Level 3 — — — — — — — Transfers out of Level 3 — — — — — — — Deconsolidation of VIEs — — — — (851 ) 223 (627 ) Balance, end of period $ 72 $ 3 $ 66 $ 2,957 $ 3,108 $ — $ 6,207 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 $ — $ (2 ) $ 25 $ 138 $ 215 $ — $ 376 (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 Year Ended December 31, 2018 Investments Other Derivatives Investments Loans Long-term Total Balance, beginning of period $ 809 $ 6 $ 61 $ 2,914 $ 11,529 $ (2,758 ) $ 12,561 Total gains/(losses) realized and unrealized: Included in earnings 36 (1 ) (9 ) 16 (201 ) 189 30 Included in other comprehensive income (53 ) — — (158 ) (470 ) 91 (590 ) Purchases — — — — — — — Issuances — — — — — — — Sales — — — — — — — Settlements (714 ) — (6 ) (35 ) (624 ) 23 (1,356 ) Transfers out of Level 3 (5 ) — — — — — (5 ) Deconsolidations of VIEs — — — — (5,946 ) 2,237 (3,709 ) Balance, end of period $ 72 $ 5 $ 46 $ 2,737 $ 4,288 $ (217 ) $ 6,930 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 ) $ (10 ) $ 16 $ (63 ) $ 47 $ (11 ) Level-3 Financial Assets and Liabilities Accounted for at Fair Value VIE Assets and Liabilities Year Ended December 31, 2017 Investments Other Derivatives Investments Loans Long-term Total Balance, beginning of period $ 763 $ 7 $ (100 ) $ 2,623 $ 10,659 $ (2,582 ) $ 11,369 Total gains/(losses) realized and unrealized: Included in earnings 65 (1 ) 63 71 550 35 783 Included in other comprehensive income 6 — — 253 1,004 (254 ) 1,010 Purchases 36 — — — — — 36 Issuances — — — — — — — Sales (79 ) — — — — — (79 ) Settlements (30 ) — 98 (33 ) (684 ) 44 (605 ) Transfers into Level 3 48 — — — — — 48 Balance, end of period $ 809 $ 6 $ 61 $ 2,914 $ 11,529 $ (2,758 ) $ 12,561 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 ) $ 9 $ 71 $ 547 $ 37 $ 662 The tables below provide roll-forward information by class of investments and derivatives measured using si gnificant unobservable inputs. Level-3 Investments by Class 2019 2018 Year Ended December 31, Other Asset Non-Agency RMBS Total Other Asset Non-Agency RMBS Total Balance, beginning of period $ 72 $ — $ 72 $ 73 $ 736 $ 809 Total gains/(losses) realized and unrealized: Included in earnings 2 — 2 1 35 36 Included in other comprehensive income — — — (1 ) (52 ) (53 ) Purchases — — — — — — Issuances — — — — — — Sales — — — — — — Settlements (2 ) — (2 ) (1 ) (713 ) (714 ) Transfers out of Level 3 — — — — (5 ) (5 ) Balance, end of period $ 72 $ — $ 72 $ 72 $ — $ 72 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 $ — $ — $ — $ — $ — $ — Level-3 Investments by Class Year Ended December 31, 2017 Other Asset Non-Agency RMBS Total Balance, beginning of period $ 66 $ 697 $ 763 Total gains/(losses) realized and unrealized: Included in earnings 1 64 65 Included in other comprehensive income 6 — 6 Purchases — 36 36 Issuances — — — Sales — (79 ) (79 ) Settlements (1 ) (29 ) (30 ) Transfers into Level 3 — 48 48 Balance, end of period $ 73 $ 736 $ 809 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 $ — $ — $ — Level-3 Derivatives by Class 2019 2018 Year Ended December 31, Interest Credit Total Interest Credit Total Balance, beginning of period $ 47 $ (1 ) $ 46 $ 61 $ (1 ) $ 61 Total gains/(losses) realized and unrealized: Included in earnings 24 2 25 (9 ) (1 ) (9 ) Purchases — — — — — — Issuances — — — — — — Sales — — — — — — Settlements (4 ) — (5 ) (5 ) — (6 ) Balance, end of period $ 67 $ — $ 66 $ 47 $ (1 ) $ 46 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 $ 25 $ (9 ) $ (1 ) $ (10 ) Level-3 Derivatives by Class Year Ended December 31, 2017 Interest Credit Total Balance, beginning of period $ (85 ) $ (15 ) $ (100 ) Total gains/(losses) realized and unrealized: Included in earnings 46 16 63 Purchases — — — Issuances — — — Sales — — — Settlements 100 (2 ) 98 Balance, end of period $ 61 $ (1 ) $ 61 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 $ 7 $ 2 $ 9 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. Non-agency RMBS securities transferred from Level 2 into Level 3 in 2017 were investments in Ambac-wrapped RMBS securities for which projected cash flows consisted solely of Deferred Amounts and interest thereon. These invested assets were internally valued as management either could not obtain or could not corroborate the reasonableness of third party quotes. Non-agency RMBS transferred out of Level 3 into Level 2 in 2018 consisted of an Ambac-insured re-REMIC collateralized by distressed mortgage-backed securities. Derivative instruments are transferred into Level 3 when the use of unobservable inputs becomes significant to the overall valuation. There were no transfers of derivative instruments into or out of Level 3 in the periods disclosed. There were no transfers between Level 1 and Level 2 for the periods presented. All transfers between fair value hierarchy Levels 1, 2, and 3 are recognized at the beginning of each accounting period. 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 Investment Income Net Gains Income (Loss) on Variable Interest Entities Other Year Ended December 31, 2019 Total gains (losses) included in earnings for the period $ 2 $ 25 $ 410 $ (2 ) Changes in unrealized gains (losses) relating to financial instruments still held at the reporting date — 25 353 (2 ) Year Ended December 31, 2018 Total gains (losses) included in earnings for the period $ 36 $ (9 ) $ 4 $ (1 ) Changes in unrealized gains (losses) relating to financial instruments still held at the reporting date — (10 ) — (1 ) Year Ended December 31, 2017 Total gains (losses) included in earnings for the period $ 65 $ 63 $ 656 $ (1 ) Changes in unrealized gains (losses) relating to financial instruments still held at the reporting date — 9 655 (1 )

Investments

Investments	12 Months Ended
	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Investments	10. 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 Ambac's equity interest in an unconsolidated trust created in connection with its sale of Segregated Account junior surplus notes on August 28, 2014. Fixed Income Securities The amortized cost and estimated fair value of available-for-sale fixed income investments, excluding VIE investments, at December 31, 2019 and 2018 were as follows: Amortized Gross Gross Estimated Non-Credit Other- (1) December 31, 2019 Fixed income securities: Municipal obligations $ 194 $ 22 $ — $ 215 $ — Corporate obligations (2) 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 $ — December 31, 2018 Fixed income securities: Municipal obligations $ 883 $ 14 $ 17 $ 880 $ — Corporate obligations (2) 1,289 6 17 1,278 — Foreign obligations 30 — — 31 — U.S. government obligations 94 1 1 94 — Residential mortgage-backed securities 222 38 1 259 — Collateralized debt obligations 133 — 2 131 — Other asset-backed securities 370 73 1 442 — 3,021 133 38 3,116 — Short-term 430 — — 430 — Total available-for-sale investments $ 3,451 $ 133 $ 38 $ 3,546 $ — (1) 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 as of December 31, 2019 and 2018 . (2) Includes Ambac's holdings of the secured notes issued by Ambac LSNI in connection with the Rehabilitation Exit Transactions. The amortized cost and estimated fair value of available-for-sale investments, excluding VIE investments, at December 31, 2019 , by contractual maturity, were as follows: Amortized Estimated Due in one year or less $ 749 $ 749 Due after one year through five years 1,157 1,173 Due after five years through ten years 477 501 Due after ten years 145 160 2,528 2,583 Residential mortgage-backed securities 200 248 Commercial mortgage-backed securities 49 50 Collateralized debt obligations 147 146 Other asset-backed securities 263 287 Total $ 3,187 $ 3,314 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, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position, at December 31, 2019 and 2018 : 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 temporarily impaired securities $ 401 $ 4 $ 88 $ 1 $ 489 $ 5 Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross December 31, 2018 Fixed income securities: Municipal obligations $ 538 $ 16 $ 29 $ 1 $ 566 $ 17 Corporate obligations 307 9 190 9 497 17 Foreign obligations 1 — 5 — 6 — U.S. government obligations 6 — 58 — 64 1 Residential mortgage-backed securities 35 1 — — 35 1 Collateralized debt obligations 124 2 — — 124 2 Other asset-backed securities 14 — 77 1 91 1 1,024 27 360 11 1,384 38 Short-term 115 — — — 115 — Total temporarily impaired securities $ 1,139 $ 27 $ 360 $ 11 $ 1,499 $ 38 Management has determined that the unrealized losses reflected in the tables above are temporary in nature as of December 31, 2019 and 2018 based upon (i) no unexpected principal and interest payment defaults on these securities; (ii) analysis of the creditworthiness of the issuer and financial guarantor, as applicable, and analysis of projected defaults on the underlying collateral; (iii) no management intent to sell these investments in debt securities; and (iv) it is not more likely than not that Ambac will be required to sell these debt securities before the anticipated recovery of its amortized cost basis. To the extent that securities that management intends to sell are in an unrealized loss position, they would have already been considered other-than-temporarily impaired with the amortized cost written down to fair value. The assessment under (iv) is based on a comparison of future available liquidity from the investment portfolio against the projected net cash outflow from operating activities and debt service. For purposes of this assessment, available liquidity from the investment portfolio is comprised of the fair value of securities for which management has asserted its intent to sell, the fair value of other securities that are available for sale and in an unrealized gain position, highly liquid pooled fund investments plus the scheduled maturities and interest payments from the remaining securities in the portfolio. Principal payments on securities pledged as collateral are not considered to be available for other liquidity needs until the collateralized positions are projected to be settled. Because the above-described assessment indicates that future available liquidity exceeds projected net cash outflow, it is not more likely than not that we would be required to sell securities in an unrealized loss position before the recovery of their amortized cost basis. For securities that have indications of possible other-than-temporary impairment but for which management does not intend to sell and will not more likely than not be required to sell, management compares the present value of cash flows expected to be collected to the amortized cost basis of the securities to assess whether the amortized cost will be recovered. Cash flows are discounted at the effective interest rate implicit in the security. For debt securities that are beneficial interests in securitized financial assets, the effective interest rate is the current yield used to accrete the beneficial interest. For floating rate securities, future cash flows and the discount rate used are both adjusted to reflect changes in the index rate applicable to each security as of the evaluation date. Of the securities that were in a gross unrealized loss position at December 31, 2019 , $29 of the total fair value and $0 of the unrealized loss related to below investment grade and non-rated securities. Of the securities that were in a gross unrealized loss position at December 31, 2018 , $660 of the total fair value and $18 of the unrealized loss related to below investment grade and non-rated securities. The remainder of gross unrealized losses as of December 31, 2019 , are primarily on investment grade fixed-rate securities purchased during periods of lower interest rates. Management believes that the timely receipt of all principal and interest on these positions is probable . 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 the factors noted above. If that judgment changes, Ambac may ultimately record a charge for other-than-temporary impairment in future periods. Future changes in our estimated liquidity needs could result in a determination that Ambac no longer has the ability to hold securities that are in an unrealized loss position, which could also result in additional other-than-temporary impairment charges. Realized Gains and Losses and Other-Than-Temporary Impairments The following table details amounts included in net realized gains (losses) and other-than-temporary impairments included in earnings for the affected periods: Year Ended December 31, 2019 2018 2017 Gross realized gains on securities $ 64 $ 111 $ 29 Gross realized losses on securities (5 ) (7 ) (19 ) Foreign exchange (losses) gains 22 7 (5 ) Net realized gains (losses) $ 81 $ 111 $ 5 Net other-than-temporary impairments (1) $ — $ (3 ) $ (20 ) (1) Other-than-temporary impairments exclude impairment amounts recorded in other comprehensive income under ASC Paragraph 320-10-65-1, which comprise non-credit related amounts on securities that are credit impaired but 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. During the Segregated Account Rehabilitation Proceedings, changes in the estimated timing of claim payments on Ambac insured securities contributed to net other-than-temporary impairments for the year ended December 31, 2017 presented in the table above. Future changes in our estimated liquidity needs could result in a determination that Ambac no longer has the ability to hold securities that are in an unrealized loss position, which could result in additional other-than-temporary impairment charges. The following table presents a roll-forward of Ambac’s cumulative credit losses on debt securities held as of December 31, 2019 , 2018 and 2017 for which a portion of an other-than-temporary impairment was recognized in other comprehensive income: Year Ended December 31, 2019 2018 2017 Balance, beginning of period 12 67 52 Additions for credit impairments recognized on: Securities not previously impaired — 1 3 Securities previously impaired — — 12 Reductions for credit impairments previously recognized on: Securities that matured or were sold during the period (1 ) (56 ) — Balance, end of period 12 12 67 Counterparty Collateral, Deposits with Regulators and Other Restrictions Ambac routinely pledges and receives collateral related to certain transactions. Cash, cash equivalents and securities held directly in Ambac’s investment portfolio with a fair value of $85 and $103 at December 31, 2019 and 2018 , 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 “Short-term investments pledged as collateral, at fair value”. Refer to Note 11. Derivative Instruments for further information on cash collateral. There was no cash or securities received from other counterparties that were re-pledged by Ambac. Securities carried at $6 and $6 at December 31, 2019 and 2018 , 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 December 31, 2019 were deposited as security in connection with a letter of credit issued for an office lease. Securities carried at $197 and $210 at December 31, 2019 and 2018 , 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 redemption of the Secured Notes held by Ambac Assurance. The amount of such proceeds held by Ambac Assurance was $55 and $19 at December 31, 2019 and 2018 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, including the value of the financial guarantee, and weighted-average underlying rating, excluding the financial guarantee, of the insured securities at December 31, 2019 and 2018 , respectively: Municipal Corporate (3) Mortgage Total Weighted (1) (3) December 31, 2019: Ambac Assurance Corporation (2) $ 176 $ 535 $ 442 $ 1,153 B- National Public Finance Guarantee Corporation 11 — — 11 BBB- Total $ 187 $ 535 $ 442 $ 1,164 B- December 31, 2018: Ambac Assurance Corporation (2) $ 833 $ 656 $ 599 $ 2,089 CCC National Public Finance Guarantee Corporation 16 — — 16 BBB- Total $ 849 $ 656 $ 599 $ 2,105 CCC (1) Ratings are based on the lower of Standard & Poor’s or Moody’s rating. If unavailable, Ambac’s internal rating is used. (2) Includes asset-backed securities with a fair value of $0 and $145 at December 31, 2019 and 2018 , respectively, insured by Ambac UK. (3) Represents Ambac's holdings of secured notes issued by Ambac LSNI in connection with the Rehabilitation Exit Transactions. Ambac LSNI secured notes are insured by Ambac Assurance and are excluded from the calculation of weighted average underlying rating. 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 at December 31, 2019 of $41 to private credit funds and $48 to a hedge fund. Class of Funds December 31, 2019 2018 Redemption Frequency Redemption Notice Period Real estate properties (1) $ 16 $ 16 quarterly 10 business days Hedge funds (2) 65 — quarterly 90 days High yield and leveraged loans (3) (8) 176 114 daily 0 - 30 days Private credit (4) 51 84 quarterly 180 days if permitted Insurance-linked investments (5) 3 29 fully redeemed none Equity market investments (6) (8) 55 44 daily 0 days Investment grade floating rate income (7) 66 63 weekly 0 days Total equity investments in pooled funds $ 432 $ 351 (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 within structured credit markets, including mortgage-backed securities, commercial real estate securities and loans, CLOs, REITs and asset backed securities. (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 includes investments in a range of instruments that include funds that have diversified exposure to global equity market returns through holdings of market index funds . (7) This class of funds includes investments in high quality floating rate debt securities including ABS and corporate floating rate notes (FRNs) as well as ultra-short term bonds and money market instruments. (8) High yield and leveraged loans products include $81 at December 31, 2019 and $27 at December 31, 2018 and equity market investments include $55 at December 31, 2019 and $44 at December 31, 2018 that have readily determinable fair values priced through pricing vendors. Ambac also holds an equity interest in an unconsolidated trust created in connection with the 2014 sale of Segregated Account junior surplus notes that is accounted for under the equity method. Investment Income Net investment income was comprised of the following for the affected periods: Year Ended December 31, 2019 2018 2017 Fixed income securities $ 183 $ 265 $ 337 Short-term investments 17 11 8 Loans 1 1 1 Investment expense (6 ) (7 ) (8 ) Securities available-for-sale and short-term 196 271 338 Other investments 32 2 23 Total net investment income $ 227 $ 273 $ 361 Net investment income from Other investments primarily represents changes in fair value on securities classified as trading or 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: Year Ended December 31, 2019 2018 2017 Net gains (losses) recognized during the period on trading securities $ 24 $ (3 ) $ 18 Less: net gains (losses) recognized during the reporting period on trading securities sold during the period 7 1 5 Unrealized gains (losses) recognized during the reporting period on trading securities still held at the reporting date $ 17 $ (4 ) $ 13

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	11. 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 December 31, 2019 and 2018 . Gross Gross Net Amounts Gross Amount Net Amount December 31, 2019: Derivative Assets: Interest rate swaps $ 75 $ — $ 75 $ — $ 75 Total non-VIE derivative assets $ 75 $ — $ 75 $ — $ 75 Derivative Liabilities: Credit derivatives $ — $ — $ — $ — $ — 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 Gross Gross Net Amounts Gross Amount Net Amount December 31, 2018: Derivative Assets: Interest rate swaps $ 60 $ — $ 59 $ — $ 59 Total non-VIE derivative assets $ 60 $ — $ 59 $ — $ 59 Derivative Liabilities: Credit derivatives $ 1 $ — $ 1 $ — $ 1 Interest rate swaps 72 — 72 67 5 Futures contracts 3 — 3 3 — Total non-VIE derivative liabilities $ 77 $ — $ 77 $ 71 $ 6 Variable Interest Entities Derivative Assets: Currency swaps $ 66 $ — $ 66 $ — $ 66 Total VIE derivative assets $ 66 $ — $ 66 $ — $ 66 Variable Interest Entities Derivative Liabilities: Interest rate swaps $ 1,712 $ — $ 1,712 $ — $ 1,712 Total VIE derivative liabilities $ 1,712 $ — $ 1,712 $ — $ 1,712 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 Consolidated Balance Sheets. The amounts representing the right to reclaim cash collateral and posted margin, recorded in “Other assets” were $36 and $103 as of December 31, 2019 and 2018 , respectively. There were no amounts held representing an obligation to return cash collateral as of December 31, 2019 and 2018 . The following tables summarize the location and amount of gains and losses of derivative contracts in the Consolidated Statements of Total Comprehensive Income (Loss) for the years ended December 31, 2019, 2018 and 2017 : Location of Gain (Loss) Recognized Amount of Gain (Loss) Recognized in Consolidated Statement of Total Comprehensive Income (Loss) – 2019 2018 2017 Non-VIE derivatives: Futures contracts Net gains (losses) on derivative contracts (45 ) 7 11 Interest rate swaps Net gains (losses) on derivative contracts (6 ) 1 49 Credit derivatives Net gains (losses) on derivative contracts 2 (1 ) 16 Total non-VIE derivatives (50 ) 7 76 Variable Interest Entities: Interest rate swaps Income (loss) on variable interest entities (20 ) 493 (127 ) Currency swaps Income (loss) on variable interest entities (12 ) 11 (26 ) Total Variable Interest Entities (32 ) 505 (152 ) Total derivative contracts $ (82 ) $ 512 $ (76 ) 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. None of the outstanding credit derivative transactions at December 31, 2019 , 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. The portfolio of our credit derivatives were written on a “pay-as-you-go” basis. Similar to insurance policy execution, 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 CDS contracts was $280 and $295 as of December 31, 2019 and 2018 , 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 and US Treasury futures contracts 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 December 31, 2019 and 2018 , the notional amounts of AFS's derivatives are as follows: Notional - December 31, Type of Derivative 2019 2018 Interest rate swaps—pay-fixed/receive-variable $ 1,261 $ 1,122 US Treasury futures contracts—short 755 1,760 Interest rate swaps—receive-fixed/pay-variable 332 493 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 December 31, 2019 and 2018 , are as follows: Notional - December 31, Type of VIE Derivative 2019 2018 Interest rate swaps—receive-fixed/pay-variable $ 1,194 $ 1,400 Interest rate swaps—pay-fixed/receive-variable 1,176 1,177 Currency swaps 329 345 Credit derivatives 9 10 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 certain 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 December 31, 2019 and 2018 , the net liability fair value of derivative instruments with contingent features linked to Ambac’s own credit risk was $89 and $67 , respectively, related to which Ambac had posted cash, cash equivalents and securities as collateral with a fair value of $109 and $84 , respectively. All such ratings-based contingent features have been triggered as requiring maximum collateral levels to be posted by Ambac while preserving counterparties’ rights to terminate the contracts. Assuming all such contracts terminated at fair value on December 31, 2019 , 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 fair values as reported in Ambac’s financial statements.

Loans (Notes)

Loans (Notes)	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Loans	12. LOANS Loans had been extended: (i) by VIEs which are consolidated by Ambac under ASC Topic 810 as a result of Ambac’s financial guarantees of the VIEs’ note liabilities and/or assets and (ii) to certain institutions in connection with various transactions. Loans extended by consolidated VIEs are generally carried at fair value on the Consolidated Balance Sheets. See Note 3. Variable Interest Entities for further information about VIEs for which the assets and liabilities are carried at fair value. Other loans had an outstanding principal balance of $19 and $19 at December 31, 2019 and 2018 , respectively. The effective interest rate on these loans ranged from 6.51% to 7.35% and 6.51% to 8.60% at December 31, 2019 and 2018 , respectively. The maturity date of these loans ranged from June 2026 to December 2046 as of December 31, 2019 . Collectability of these loans is evaluated on an ongoing basis; no loan has been considered impaired and as such no loan impairments have been recorded as of December 31, 2019 and 2018

Long-Term Debt (Notes)

Long-Term Debt (Notes)	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Long-term Debt	13. LONG-TERM DEBT Long-term debt outstanding, excluding VIE long-term debt, was as follows: December 31, 2019 2018 Par Value Unamortized Discount Carrying Value Par Value Unamortized Discount Carrying Value Ambac Assurance: 5.1% surplus notes $ 531 $ (14 ) $ 517 $ 531 $ (44 ) $ 487 5.1% junior surplus notes 365 (113 ) 252 367 (117 ) 250 Ambac note 1,763 — 1,763 1,940 — 1,940 Tier 2 notes 281 (4 ) 278 259 (7 ) 252 Ambac UK debt 41 (28 ) 13 — — — Long-term debt $ 2,980 $ (159 ) $ 2,822 $ 3,096 $ (167 ) $ 2,929 Aggregated annual maturities of non-VIE long-term debt obligations (based on scheduled maturity dates as further discussed below) are as follows: 2020 $ 531 2021 — 2022 — 2023 1,763 2024 — Thereafter 687 Total $ 2,980 Surplus Notes Ambac Assurance surplus notes, with a par amount of $531 and $531 at December 31, 2019 and 2018 , respectively, have a scheduled maturity of June 7, 2020. The retirement of certain notes as part of the Rehabilitation Exit Transactions in 2018 resulted in gains of $3 for the year ended December 31, 2018 , recognized in Net realized gains (losses) on extinguishment of debt on the Consolidated Statements of Total Comprehensive Income. Surplus notes outstanding are recorded at their fair value at the date of issuance. The discount on surplus notes is accreted into income using the effective interest method based on projected cash flows at the date of issuance. The weighted average imputed interest rate on surplus notes outstanding as of December 31, 2019 is 10.1% . All payments of principal and interest on these surplus notes are subject to the prior approval of the OCI. Since the issuance of the surplus notes in 2010, OCI has declined to approve regular payments of interest on surplus notes, although the OCI has permitted exceptional payments in connection with (a) increasing the percentage of deferred policy payments of the Segregated Account of Ambac Assurance from 25% to 45% in 2014 and (b) a one-time payment of approximately six months of interest on the surplus notes (other than junior surplus notes) outstanding immediately after consummation of the Rehabilitation Exit Transactions in 2018 in the amount of $14 , of which $3 was received by AFG for surplus notes that it owned and that are considered extinguished for accounting purposes. Ambac Assurance may not receive approval from OCI to make payments as and when scheduled, including the payment of the surplus notes on their scheduled maturity date of June 7, 2020. If the OCI does not approve the making of any payment of principal of or interest on surplus notes on the scheduled payment date or scheduled maturity date thereof, the scheduled payment date or scheduled maturity date, as the case may be, shall be extended until OCI grants approval to make the payment. Interest will accrue, compounded on each anniversary of the original scheduled payment date or scheduled maturity date, on any unpaid principal or interest through the actual date of payment at 5.1% per annum. Refer to Note 1. Background and Business Description for further discussion of both the Rehabilitation Exit Transactions and the AMPS Exchange. Junior Surplus Notes The junior surplus notes have a par value of $365 and $367 at December 31, 2019 and 2018 , respectively. Pursuant to the Second Amended Plan of Rehabilitation, Ambac Assurance became the obligor under the junior surplus notes (originally issued by the Segregated Account) as of February 12, 2018. These junior surplus notes have a scheduled maturity of June 7, 2020, subject to the following restrictions. Principal and interest payments on these junior surplus notes cannot be made until all Ambac Assurance surplus notes (other than junior surplus notes) are paid in full and after all of Ambac Assurance's future and existing senior indebtedness, policy and other priority claims have been paid in full. All payments of principal and interest on these junior surplus notes are subject to the prior approval of the OCI. If the OCI does not approve the payment of principal of or interest on the junior surplus notes, such interest will accrue and compound annually until paid. No such approval has been sought or obtained to pay interest on junior surplus notes since their issuance. • Par value at December 31, 2019 and 2018 includes $15 and $17 , respectively, of junior surplus notes issued in connection with a settlement agreement (the “OSS Settlement Agreement”) entered into among Ambac, Ambac Assurance, the Segregated Account and One State Street, LLC (“OSS”) with respect to the termination of Ambac’s office lease with OSS. A portion of the principal balance of the originally issued notes were eligible to be reduced based on rents paid to OSS by Ambac Assurance after December 31, 2015. Par value of these junior surplus notes was reduced by $2 and $4 during the years ended December 31, 2019 and 2018 , respectively, as rent payments were made by Ambac Assurance. As of December 31, 2019 , there was no remaining balance of the junior surplus notes that can be reduced on rents paid by Ambac Assurance. These junior surplus notes were recorded at their fair value at the date of issuance. The discount on these notes are currently being accreted into income using the effective interest method at an imputed interest rate of 19.5% . • Par value at December 31, 2019 and 2018 includes $350 of a junior surplus note originally issued to AFG pursuant to AFG's Chapter 11 Reorganization Plan in accordance with the Mediation Agreement dated September 21, 2011, among AFG, Ambac Assurance, the Segregated Account, the Rehabilitator, the OCI and the Official Committee of Unsecured Creditors of AFG, and that AFG sold to a Trust on August 28, 2014. This junior surplus note was recorded at a discount to par based on its fair value on August 28, 2014. Ambac is accreting the discount on this junior surplus note into earnings using the effective interest method, based on an imputed interest rate of 8.4% . Ambac Note The Ambac Note, issued in connection with the Rehabilitation Exit Transactions on February 12, 2018, as more fully described in Note 1. Background and Business Description , has a par value of $1,763 and $1,940 at December 31, 2019 and 2018 , respectively, and has a legal maturity of February 12, 2023. Interest on the Ambac Note is payable quarterly (on the last day of each quarter beginning with June 30, 2018) at an annual rate of 3-month U.S. Dollar LIBOR + 5.00% , subject to a 1.00% LIBOR floor. During the years ended December 31, 2019 and 2018 , $178 and $214 par value of the Ambac Note was redeemed, respectively. The maturity date for the Ambac Note is the earlier of (x) February 12, 2023, and (y) if the Secured Notes are then outstanding, the date that is five business days prior to the date for which OCI has approved the repayment of the outstanding principal amount of the surplus notes (other than junior surplus notes) issued by Ambac Assurance. Promptly, and in any event within four business days after the receipt (whether directly or indirectly) of any representation and warranty subrogation recoveries, Ambac Assurance shall (i) apply an amount (the “Mandatory Redemption Amount”) equal to the lesser of (a) the amount of representation and warranty subrogation recoveries up to $1,400 and (b) all outstanding principal and accrued and unpaid interest on the Ambac Note to redeem the Ambac Note, in whole or in part, as applicable; provided, that any non-cash representation and warranty subrogation recoveries shall be deemed to be received upon the receipt of the applicable appraisal. • The portion of the Ambac Note issued in connection with the exchange of surplus notes ("Ambac Note A") was accounted for as a debt modification since the creditors before and after the exchange remained the same and the change in terms was not considered substantial. A substantial change is considered to be a change in cash flows of equal to or greater than 10%, and because the change in cash flows was less than 10%, debt modification accounting is appropriate. Under debt modification accounting, Ambac Note A was recorded at a discount to par based on the carrying value of the surplus notes less the cash consideration paid. Furthermore, no gain or loss was recorded on the surplus note exchange and a new effective interest rate was established based on the cash flows of Ambac Note A. Any consideration paid directly related to the issuance of Ambac Note A was expensed as incurred. • The portion of the Ambac Note issued in connection with the exchange of Deferred Amounts ("Ambac Note B") was recorded at fair value. The Deferred Amount exchange was accounted for as an extinguishment of the Deferred Amounts with the gain reflected as a benefit to loss and loss expenses. Any consideration paid directly related to the issuance of Ambac Note B was capitalized and amortized as part of the effective yield calculation. The aggregate discount on the entire Ambac Note (portions A and B) was accreted into earnings from the date of issuance through September 30, 2018 using the effective interest method, based on an imputed interest rate of 7.6% . Refer to Note 1. Background and Business Description for further discussion of the Rehabilitation Exit Transactions in connection with which the Ambac Note was issued. Refer to the discussion under "Counterparty Collateral, Deposits with Regulators and Other Restrictions" in Note 10. Investments for further information on security and collateral related to the Ambac Note and the Secured Notes issued by Ambac LSNI. Tier 2 Notes The Tier 2 Notes, issued in connection with the Rehabilitation Exit Transactions on February 12, 2018, with a par value of $281 and $259 (including paid-in-kind interest of $41 and $19 ) at December 31, 2019 and 2018 , respectively, have a legal maturity of February 12, 2055. Interest on the Tier 2 Notes is at an annual rate of 8.50% . Other than upon payment of principal at redemption or maturity, interest payments will not be made in cash on interest payment dates and shall be paid-in-kind and compounded on the last day of each calendar quarter. The Tier 2 Notes were recorded at a discount to par as any consideration paid that was directly related to the issuance of the Tier 2 Notes was capitalized and is part of the effective yield calculation. Ambac is accreting the discount on the Tier 2 Notes into earnings using the effective interest method, based on an imputed interest rate of 9.9% . The Tier 2 Notes are subject to mandatory redemption upon: (i) receipt of representation and warranty subrogation recoveries in excess of $1,600 ("Tier 2 Net Proceeds") and (ii) payment of principal or interest on Ambac Assurance surplus notes (other than junior surplus notes). Promptly, and in any event within five business days after the receipt (whether directly or indirectly) of Tier 2 Net Proceeds, Ambac Assurance shall deposit an amount equal to the Tier 2 Net Proceeds to a collateral account, provided, that any non-cash representation and warranty subrogation recoveries shall be deemed to be received upon the receipt of the applicable appraisal of the consideration received by Ambac Assurance. Similarly, within five business dates after a surplus note payment (other than in connection with the Rehabilitation Exit Transactions), Ambac Assurance shall deposit an amount based on the percentage of surplus notes paid applied to the outstanding balance of the Tier 2 Notes to a collateral account. In both cases, the amount deposited shall not be in excess of the amount required to redeem all outstanding Tier 2 Notes. Also, such amounts shall be used to initiate a redemption on the initial call date for the Tier 2 Notes or, if the initial call date has occurred, promptly following the receipt of the Tier 2 Net Proceeds or surplus note payment. The Tier 2 Notes may also be redeemed, in whole or in part, at the option of Ambac Assurance. Both mandatory and optional redemptions may be made at a price equal to 100% of the aggregate principal amount redeemed, plus accrued and unpaid interest, if any, plus a make-whole premium. Make-whole premiums are calculated based on future interest payments through the contractual call date ("Initial Call Date"). The Initial Call Date at issuance of December 17, 2020, extends ratably beginning the first anniversary of issuance to September 17, 2021 by the second anniversary, and to March 17, 2022 by the third anniversary of issuance. There are no extensions of the Initial Call Date beyond March 17, 2022. The Initial Call Date for redemptions is determined based on the date the applicable amounts are deposited to the collateral account. Ambac UK Debt The Ambac UK debt, issued in connection with the Ballantyne commutation on June 18, 2019 has a par value of $41 at December 31, 2019 , and a legal maturity of May 2, 2036. Interest on the Ambac UK debt is at an annual rate of 0.00% . The Ambac UK debt was recorded at its fair value at the date of issuance. The discount on the debt is currently being accreted into income using the effective interest method at an imputed interest rate of 7.4% . Variable Interest Entities, Long-term Debt The variable interest entity notes were issued by consolidated VIEs. Ambac is the primary beneficiary of the VIEs as a result of providing financial guarantees on certain of the variable interest obligations. Consequently, Ambac has consolidated these variable interest entity notes and all other assets and liabilities of the VIEs. Ambac is not primarily liable for the debt obligations of these entities. Ambac would only be required to make payments on these debt obligations in the event that the issuer defaults on any principal or interest due and to the extent such obligations are guaranteed by Ambac. The total unpaid principal amount of outstanding long-term debt associated with VIEs consolidated as a result of the financial guarantee provided by Ambac was $3,990 and $4,553 as of December 31, 2019 and 2018 , respectively. As of December 31, 2019 and 2018 , the ranges of final maturity dates of the outstanding long-term debt associated with these VIEs were December 2025 to August 2054 as of December 31, 2019 , and September 2019 to December 2047 as of December 31, 2018 . As of December 31, 2019 and 2018 , the interest rates on these VIEs’ long-term debt ranged from 0.00% to 7.93% and from 1.36% to 7.93% , respectively. Aggregated annual maturities of VIE long-term debt following December 31, 2019 are: 2020 - $0 ; 2021 - $0 ; 2022 - $0 ; 2023 - $0 ; 2024 - $0 ; Thereafter- $3,990 .

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	14. INCOME TAXES AFG files a consolidated Federal income tax return with its subsidiaries. Ambac also files separate or combined income tax returns in various states, local and foreign jurisdictions. The following are the major jurisdictions in which Ambac operates and the earliest tax years subject to examination: Jurisdiction Tax Year United States 2010 New York State 2013 New York City 2015 United Kingdom 2016 Italy 2015 Consolidated Pretax Income (Loss) U.S. and foreign components of pre-tax income (loss) were as follows: Year Ended December 31, 2019 2018 2017 U.S. $ (174 ) $ 264 $ (451 ) Foreign (9 ) 8 167 Total $ (183 ) $ 273 $ (284 ) Provision (Benefit) for Income Taxes The components of the provision (benefit) for income taxes were as follows: Year Ended December 31, 2019 2018 2017 Current taxes U. S. federal $ — $ (2 ) $ (30 ) U.S. state and local (3 ) 2 2 Foreign 37 (1 ) 41 Total current taxes 34 — 13 Deferred taxes Foreign (1 ) 5 31 Total deferred taxes $ (1 ) $ 5 $ 31 Provision for income taxes $ 32 $ 5 $ 44 The total effect of income taxes on net income and stockholders’ equity for the years ended December 31, 2019, 2018 and 2017 is as follows: Year Ended December 31, 2019 2018 2017 Total income taxes charged to net income $ 32 $ 5 $ 44 Income taxes charged (credited) to stockholders’ equity: Unrealized gains (losses) on investment securities 14 12 (31 ) Unrealized gains (losses) on foreign currency translations — — 26 Valuation allowance to equity (23 ) (9 ) 5 Total charged to stockholders’ equity: (8 ) 3 — Total effect of income taxes $ 24 $ 8 $ 44 Reconciliation of U.S. Federal Statutory Income Tax Rate to Actual Income Tax Rate The tax provisions in the accompanying Consolidated Statements of Total Comprehensive Loss reflect effective tax rates differing from prevailing Federal corporate income tax rates. The following is a reconciliation of these differences: 2019 2018 2017 Year Ended December 31, Amount % Amount % Amount % Tax on income from continuing operations at statutory rate $ (38 ) 21.0 % $ 57 21.0 % $ (99 ) 35.0 % Changes in expected tax resulting from: Tax-exempt interest (3 ) 1.8 % (7 ) (2.5 )% (6 ) 2.1 % Foreign taxes 40 (22.1 )% 10 3.9 % (18 ) 6.2 % Substantiation adjustment 28 (15.3 )% (60 ) (22.0 )% 36 (12.7 )% Valuation allowance 8 (4.4 )% 5 1.9 % 128 (44.9 )% Change in Tax Law — — % (2 ) (0.7 )% 2 (0.7 )% Other, net (2 ) 1.3 % 1 0.4 % 2 (0.7 )% Tax expense on income from continuing operations $ 32 (17.7 )% $ 5 2.0 % $ 44 (15.7 )% Unrecognized Tax Positions A reconciliation of the beginning and ending amounts of material unrecognized tax benefits for 2019 , 2018 and 2017 is as follows: Year Ended December 31, 2019 2018 2017 Balance, beginning of period $ — $ — $ — Increases related to prior year tax positions — — — Decreases related to prior year tax positions — — — Balance, end of period $ — $ — $ — Included in these balances at December 31, 2019 , 2018 and 2017 are $0 , $0 and $0 , respectively, of unrecognized tax benefits that, if recognized, would affect the effective tax rate. During the years ended December 31, 2019 , 2018 and 2017 , Ambac recognized interest of approximately $0 , $0 and $0 , respectively. Ambac had approximately $0 , $0 and $0 , for the payment of interest accrued at December 31, 2019 , 2018 and 2017 , respectively. Deferred Income Taxes The tax effects of temporary differences that give rise to significant portions of the deferred tax liabilities and deferred tax assets at December 31, 2019 and 2018 , are presented below: December 31, 2019 2018 Deferred tax liabilities: Insurance intangible $ 90 $ 151 Variable interest entities 12 19 Investments 32 26 Unearned premiums and credit fees 42 48 Other 8 8 Total deferred tax liabilities 183 252 Deferred tax assets: Net operating loss and capital carryforward 742 719 Loss reserves 148 227 Debentures 29 23 Compensation 7 10 Other 1 2 Subtotal deferred tax assets 927 980 Valuation allowance 777 768 Total deferred tax assets 151 212 Net deferred tax liability $ 32 $ 40 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. With respect to Ambac's domestic subsidiaries subject to U.S. tax, 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 taxable income to recover the deferred tax asset and therefore maintains a full valuation allowance. The remaining net deferred tax liability of $32 is attributable to Ambac U.K. NOL Usage Pursuant to the 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 Percentage 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% Any net operating loss carryforwards ("NOLs") generated by Ambac Assurance after September 30, 2011, are utilized prior to any Allocated NOLs for which Tolling Payments will be due. Through December 31, 2018 , Ambac Assurance generated cumulative taxable income of $1,508 , utilizing all post September 30, 2011, NOLs. For the year ended December 31, 2019 , Ambac Assurance generated an NOL of $143 , that will need to be utilized before any new Tolling Payments will be generated. Of the credits available to offset the first $5 of payments due under each of the NOL usage Tiers A, B, and C, Ambac Assurance has fully utilized the combined $10 of Tier A and Tier B credits. Through December 31, 2019 , Ambac Assurance utilized all of the $479 Tier A NOL and $1,029 of the $1,057 Tier B NOL resulting in Tolling Payments, net of applicable credits, of $147 , of which $119 was paid to AFG through December 31, 2019 . 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 $28 payment by June 1, 2018. AFG has also agreed to continue to defer the Tolling Payment for the use of net operating losses by Ambac Assurance until such time as OCI consent to the 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 AFG. As of December 31, 2019 , Ambac had U.S. federal net operating loss tax carryforwards of approximately $3,535 , which, if not utilized, will begin expiring in 2029 , and will fully expire in 2040 . The remaining balance of the NOL allocated to Ambac Assurance was $2,285 and Ambac was $1,250 .

Employment Benefit Plans (Notes

Employment Benefit Plans (Notes)	12 Months Ended
	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Compensation and Employee Benefit Plans [Text Block]	15. EMPLOYMENT BENEFIT PLANS Postretirement Health Care and Other Benefits Ambac provides postretirement and postemployment / severance benefits, including health and life benefits for certain employees who meet certain age and service requirements. None of the plans are currently funded. Postretirement and postemployment benefits expenses, including severance benefits paid, were $3 , $1 and $5 for the years ended December 31, 2019, 2018 and 2017 , respectively. Effective August 1, 2005, new employees were not eligible for postretirement benefits. The current postretirement benefit requires retirees to purchase their own medical insurance policy with a portion of their premium being reimbursed by Ambac. The unfunded accumulated postretirement benefit obligation was $8 as of December 31, 2019 . The assumed health care cost trend rates range from 5.3% in 2020 , decreasing ratably to 4.5% in 2028 . Increasing the assumed health care cost trend rate by one percentage point in each future year would increase the accumulated postretirement benefit obligation at December 31, 2019 , by less than a million dollars and the 2019 benefit expense by less than a million dollars . Decreasing the assumed health care cost trend rate by one percentage point in each future year would decrease the accumulated postretirement benefit obligation at December 31, 2019 by less than a million dollars and the 2019 benefit expense by less than a million dollars . The following table sets forth projected benefit payments from Ambac’s postretirement plan over the next ten years for current retirees: 2020 $ — 2021 — 2022 — 2023 — 2024 1 2025-2029 3 Total $ 5 The discount rate used in determining the projected benefit obligations for the postretirement plan is selected by reference to a pension liability index with similar duration to that of the benefit plan. The rates used for the projected plan benefit obligations at the measurement date for December 31, 2019 and 2018 , were 3.00% and 4.00% , respectively. Savings Incentive Plan Substantially all employees of Ambac Assurance are covered by a defined contribution plan (the “Savings Incentive Plan”). Ambac Assurance makes employer matching contributions equal 100% of the employees’ contributions, up to 3% of such participants’ compensation, as defined in the plan, plus 50% of contributions up to an additional 2% of compensation, subject to limits set by the Internal Revenue Code. The total cost of the Savings Incentive Plan was $1 , $1 and $1 for the years December 31, 2019, 2018 and 2017 , respectively. Incentive Compensation - Stock Units and Cash Incentive compensation is a key component of our compensation strategy. Our incentive compensation awards generally have two components: short term incentive compensation awards ("STIP") and long term incentive plan awards ("LTIP"). Annual decisions with regard to incentive compensation are generally made in the first quarter of each year and are based on Company performance and individual and business unit performance of the previous year. For all employees, an allocation of incentive compensation is made between STIP and LTIP awards. Employees, directors and consultants of Ambac are eligible to participate in Ambac’s 2013 Incentive Compensation Plan (“2013 Plan”) subject to the discretion of the compensation committee of Ambac’s Board of Directors. The 2013 Plan provides for incentives and rewards that are valued or determined by reference to Ambac common stock as currently traded on the New York Stock Exchange. There are 4,000,000 shares of Ambac’s common stock authorized for awards under the 2013 Plan of which 1,383,489 shares are available for future grant as of December 31, 2019 . Shares available for future grant are reduced by the maximum number of shares that could be issued pursuant to granted performance awards. The number of shares available for future issuance considering the target number of shares instead of the maximum number of shares related to performance awards is 2,079,181 . In March 2014, Ambac developed the LTIP as a sub-plan of the 2013 Plan. The LTIP is intended to be an annual program that allows for both cash and equity performance awards to certain US employees. In 2015, Ambac UK 's Board of Directors adopted a long term incentive plan which provides cash based performance awards to Ambac UK employees. Cash based compensation expense related to performance awards granted to Ambac UK employees was $5 , $1 and $2 for the years ended December 31, 2019, 2018 and 2017 , respectively. The amount of stock-based compensation expense and corresponding after-tax expense are as follows: Year Ended December 31, 2019 2018 2017 Stock options $ — $ — $ — Restricted stock units 4 6 2 Performance awards (1) (2) 8 6 3 Total stock-based compensation $ 12 $ 12 $ 4 Total stock-based compensation (after-tax) $ 12 $ 12 $ 4 (1) Represents expense related to performance stock unit portion of performance awards. Certain performance awards are in the form of cash. Cash based compensation expense related to performance awards granted to US employees was $0 , $1 and $2 for the years ended December 31, 2019, 2018 and 2017 , respectively. (2) A performance award issued to Ambac's former Chief Executive Officer in the form of performance stock units was expensed during 2018. Stock Options Stock options were awarded in 2013 to directors that had an expiry term of seven years from the grant date, subject to earlier expiration upon the recipient's departure from the Company. The Company intends to use Treasury shares first and then, if necessary, issue new shares to satisfy stock option exercises. A summary of stock option activity for 2019 is as follows: Shares Weighted Average Exercise Price Aggregate Intrinsic Value Weighted Average Remaining Contractual Life (in years) Outstanding at beginning of period 16,667 $ 20.63 Granted — — Exercised — — Forfeited or expired — — Outstanding at end of period 16,667 $ 20.63 $ — 0.97 Exercisable 16,667 $ 20.63 $ — 0.97 All stock options granted were fully vested as of December 31, 2019 . Total unrecognized compensation costs related to unvested stock options granted were $0 as of December 31, 2019 . No stock options were exercised during the years ended December 31, 2019 , 2018 and 2017 , respectively. Restricted Stock Units (“RSUs”) RSUs have been awarded to certain employees for a portion of their STIP compensation, LTIP compensation and special awards for exceptional performance. Generally, the STIP and special awards vest upon grant, but settlement is deferred (other than for employment tax withholdings) into two equal installments generally on the first and second anniversary date of the grant. The LTIP awards generally vest in equal installments over a three year period. Such vesting is expressly conditioned upon the respective employees continued service with Ambac through the applicable vesting date. RSUs are awarded annually to directors and vest on the last day of April of the following year. These RSUs will not settle until the respective director’s termination from the board of directors or, if earlier, upon a change in control. All RSUs provide for accelerated vesting upon a change in control, death or disability or involuntary removal other than for cause (not including removal pursuant to a shareholder vote at a regularly scheduled annual meeting of shareholders). Upon termination (other than for cause), the unvested RSUs shall partially vest as of the date of such termination in an amount equal to the number of then outstanding unvested RSUs multiplied by a fraction, the numerator of which shall be the number of calendar days which have lapsed since the grant date and the denominator of which shall be the total number of calendar days of the original vesting period. As of December 31, 2019 , 702,579 RSUs remained outstanding, of which (i) 248,942 units required future service as a condition to the delivery of the underlying shares of common stock and (ii) 453,637 units do not require future service and are deferred for future settlement. As of December 31, 2018 , 645,028 RSUs remained outstanding, of which (i) 209,093 units required future service as a condition to the delivery of the underlying shares of common stock,and (ii) 435,935 units did not require future service and were deferred for future settlement. A summary of RSU activity for 2019 is as follows: Shares Weighted Average Grant Date Fair Value Outstanding at beginning of period 645,028 $ 17.17 Granted 248,861 19.75 Delivered or returned to plan (1) (189,832 ) 16.76 Forfeited (1,478 ) 20.11 Outstanding at end of period 702,579 $ 18.19 (1) When restricted stock unit awards issued by Ambac become taxable compensation to employees, shares may be withheld to cover the employee’s withholding taxes. For the year ended December 31, 2019 , Ambac purchased 72,977 of shares from employees that settled restricted stock units to meet the required tax withholdings. Ambac’s closing share price on the grant date was used to estimate the fair value of the service condition based RSU on the grant date. The weighted average grant date fair value of RSUs granted during 2019 , 2018 and 2017 was $19.75 , $16.35 and $20.22 , respectively. As of December 31, 2019 , there was $2 of total unrecognized compensation costs related to unvested RSUs granted. These costs are expected to be recognized over a weighted average period of 1.7 years . The fair value for RSUs vested and delivered during the year ended December 31, 2019, 2018 and 2017 was $4 , $1 and $3 , respectively. Performance Stock Awards ("PSUs") Performance awards granted vest in 3 years and actual awards will be based on performance at both AFG and Ambac Assurance. Actual awards can payout 0% to 220% of the number of units granted. Under currently outstanding award agreements, performance will be evaluated as follows: • AFG performance will be evaluated relative to cumulative earnings before interest, taxes, depreciation and amortization over the vesting period (exclusive of Ambac Assurance and its subsidiaries' earnings), which is intended to reward participants for generating pre-tax income. • Ambac Assurance performance will be evaluated according to changes in Ambac Assurance's assets relative to its insurance and financial obligations, which is intended to reward participants for increases in the relative value of Ambac Assurance, as well as reductions in watch list and adversely classified credits, which is intended to reward participants for de-risking the insured portfolio. • In 2019, a relative Total Shareholder Return modifier was added as an additional metric with respect to the LTIP award payouts. The modifier will cause the payout at the end of the performance period to be increased or decreased by 10% if AFG's stock performance compared to a peer group is at or above the 75 th percentile or at or below the 25 th percentile, respectively . These performance metrics are subject to change by the Compensation Committee of the Board of Directors as Ambac's business evolves. Other than voluntary termination or involuntary termination for cause, and provided that the participant meets certain minimum service requirements, the performance awards are subject to either partial or accelerated vesting. The current performance awards shall be settled within 75 days after the end of the performance period, including those with partial or accelerated vesting. In 2015, a performance award was granted to the former Chief Executive Officer. This award vested on February 12, 2018, upon the emergence of the Segregated Account from rehabilitation. A summary of PSU activity for 2019 is as follows: Shares Weighted Average Grant Date Fair Value Outstanding at beginning of period 516,999 $ 17.02 Granted (1) 230,391 19.17 Delivered (2) (166,353 ) 15.52 Forfeited (1) (8,151 ) 18.11 Performance adjustment (3) 77,326 15.52 Outstanding at end of period 650,212 $ 17.98 (1) Represents performance share units at 100% of units granted for LTIP Awards. (2) Reflects the number of performance shares attributable to the performance goals attained over the completed performance period and for which service conditions have been met. When performance stock unit awards issued by Ambac become taxable compensation to employees, shares may be withheld to cover the employee’s withholding taxes. For the year ended December 31, 2019 , Ambac purchased 64,086 of shares from employees that settled performance based restricted stock units to meet the required tax withholdings. (3) Represents the increase (decrease) in shares issued for awards granted in 2016 based upon the attainment of performance metrics at the end of the performance period. As of December 31, 2019 , there was $6 of total unrecognized compensation costs related to the PSU portion of unvested performance awards, which are expected to be recognized over a weighted average period of 1.6 years

Leases (Notes)

Leases (Notes)	12 Months Ended
	Dec. 31, 2019
Leases of Lessee Disclosure [Text Block]	16. LEASES Ambac adopted the New Lease Standard, as defined and further described in Note 2. Basis of Presentation and Significant Accounting Policies . Ambac is the lessee and lessor for certain lease agreements further described below. Lessee information Ambac is the lessee in operating leases of corporate offices, a data center and equipment. Our leases, in effect at December 31, 2019 , have remaining lease terms ranging from less than 1 year to 11 years. Our data center lease has an automatic renewal of one-year unless either party elects to terminate by providing 120 days notice prior to the renewal. This renewal feature is not recognized in the lease liability or right-of-use asset as it is not reasonably certain we will elect to renew. No other leases contain extension or termination provisions. Lease costs are included in operating expenses on the Consolidated Statement of Total Comprehensive Income (Loss). The components of lease costs, net of sub-lessor income, is as follows: Year Ended December 31, 2019 Operating lease cost $ 7 Variable lease cost — Sublease income (1 ) Total lease cost $ 7 Ambac is required to make variable lease payments under certain leases which primarily related to variable costs of the lessor. Such costs include taxes, insurance, maintenance and electricity and are less than a million dollars for the year ended December 31, 2019. Supplemental information related to leases is as follows: Year Ended December 31, 2019 Cash paid for amounts included in the measurement of operating lease liabilities $ 6 Right-of-use assets obtained in exchange for operating lease liabilities (non-cash) (1) 30 (1) Includes right-of-use assets of $14 for the year ended December 31, 2019 for leases which existed prior to the New Lease Standard implementation date of January 1, 2019. Supplemental balance sheet information related to leases is as follows: December 31, 2019 Operating leases: Operating lease right of use assets $ 25 Operating lease liabilities 29 Weighted average remaining lease term: Operating leases 9.9 years Weighted average discount rate: Operating leases 7.9 % Operating lease right of use assets and operating lease liabilities are included in Other assets and Other liabilities, respectively, on the consolidated balance sheet. Future undiscounted lease payments, gross of sublease receipts, to be made are as follows: As of December 31, 2019 Operating Leases 2020 $ 4 2021 4 2022 4 2023 4 2024 4 Thereafter 22 Total lease payments 42 Less: imputed interest (13 ) Total $ 29 Lessor information Ambac is the lessor in one operating sublease of corporate office space which has a remaining term of 10.0 years . There are no extension or termination provisions. Future undiscounted lease payments to be received are as follows: As of December 31, 2019 Operating Leases 2020 $ 1 2021 1 2022 1 2023 1 2024 1 Thereafter 6 Total lease receipts $ 12

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	17. COMMITMENTS AND CONTINGENCIES Litigation Against Ambac Monterey Bay Military Housing, LLC, et al. v. Ambac Assurance Corporation, et al. (United States District Court, Northern District of California, San Jose Division, Case No. 17-cv-04992-BLF, filed August 28, 2017). Plaintiffs, the corporate developers of various military housing projects, filed an amended complaint on October 27, 2017 against Ambac Assurance, a former employee of Ambac Assurance, and certain unaffiliated persons and entities, asserting claims for (i) violation of 18 U.S.C §§ 1962(c) and 1962(d) (civil Racketeer Influenced and Corrupt Organizations Act (“RICO”) and conspiracy to commit civil RICO), (ii) breach of fiduciary duty, (iii) aiding and abetting breach of fiduciary duty, (iv) fraudulent misrepresentation, (v) fraudulent concealment and (vi) conspiracy to commit fraud. The claims relate to bonds and debt certificates (insured by Ambac Assurance) that were issued to finance the renovation and construction of housing at certain military bases. Plaintiffs allege that defendants secretly conspired to overcharge plaintiffs for the financing of the projects and directed the excess profits to themselves. Plaintiffs allege defendants generated these excess profits by supposedly charging inflated interest rates, manipulating “shadow ratings,” charging unnecessary fees, and hiding evidence of their alleged wrongdoing. Plaintiffs seek, among other things, compensatory damages, disgorgement of profits and fees, punitive damages, trebled damages and attorneys’ fees. Ambac and the other defendants filed motions to dismiss the amended complaint on November 13, 2017. On July 17, 2018, the court granted Ambac Assurance’s and the other defendants’ motion to dismiss the first amended complaint without prejudice. On December 17, 2018, Plaintiffs filed a second amended complaint. On February 15, 2019, Ambac and the other defendants filed a motion to dismiss the second amended complaint. On September 26, 2019, the court issued a decision denying defendants’ motion to dismiss and sua sponte reconsidering its previous denial of defendants’ motion to transfer venue to the Southern District of New York (“SDNY”). On October 4, 2019, the case was transferred to the SDNY. On October 10, 2019, the defendants filed motions in the SDNY to vacate or reconsider the decision by the Northern District of California on the defendants’ motion to dismiss. On October 24, 2019, plaintiffs filed their brief in opposition to defendants' motions to vacate or reconsider, and on October 31, 2019, defendants filed their reply briefs in further support of their motions. On November 20, 2019, the court ordered that the defendants’ answers to the second amended complaint would be due seven days after the court issues a decision on their motions. 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”). The team of mediators designated in the Commonwealth’s restructuring cases (the “Mediation Team”) has recommended this case be stayed while the Oversight Board attempts to confirm the Amended POA. The District Court has not yet ruled on this recommendation. Financial Oversight and Management Board for Puerto Rico, et al. v. Ambac Assurance Corporation, et al. (United States District Court, District of Puerto Rico, No. 19-ap-00363, filed May 20, 2019). On May 20, 2019, the Oversight Board, together with the Committee, as Plaintiffs, filed an adversary proceeding against certain parties that filed proofs of claim on account of bonds issued by the Puerto Rico Highways and Transportation Authority ("PRHTA"), including Ambac Assurance. The complaint seeks declarations that the PRHTA bonds are only secured by revenues on deposit with the PRHTA Fiscal Agent and that PRHTA bondholders have no security interest in any other property of PRHTA or the Commonwealth, and in the alternative, to the extent such other security interests exist, the complaint seeks to avoid other security interests that holders of PRHTA bonds may have. On June 14, 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. On December 19, 2019, the District Court ordered that this matter will remain stayed pending further order of the District Court pursuant to the Oversight Board’s initiation of a separate adversary proceeding concerning PRHTA bonds (No. 20-ap-00005, discussed below). 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 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. Briefing on motions to dismiss is expected to conclude on May 13, 2020, and a hearing is scheduled for June 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. Briefing on motions to dismiss is expected to conclude on May 13, 2020, and a hearing is scheduled for June 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 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. Briefing on motions to dismiss is expected to conclude on May 13, 2020, and a hearing is scheduled for June 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. Briefing on motions to dismiss is expected to conclude on May 13, 2020, and a hearing is scheduled for June 2020. 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. Plaintiffs seek a number of judicial determinations, including that the Owner Trustee and Administrator are required to follow the NC Owners’ issuer orders and cause the invoices of certain retained professional advisors to be paid from the assets of the Trusts as Owner Trustee expenses and Administrator expenses. Plaintiffs also seek a declaration that, with respect to the Trusts, the Owner Trustee does not owe fiduciary or extracontractual duties to any party except the NC Owners. Finally, Plaintiffs request their costs and attorney’s fees incurred in connection with this action. On January 21, 2020, the presiding Vice Chancellor entered an order consolidating the action with previously filed litigation relating to the Trusts. On January 31, 2020, Plaintiffs filed an amended complaint containing an expanded list of requested judicial determinations. On February 13, 2020, Ambac Assurance, the Owner Trustee, the Indenture Trustee, and other parties filed declaratory judgment counterclaims. 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 Assured Guaranty Corp., Assured Guaranty Municipal Corp., and Ambac Assurance Corporation v. Alejandro Garcia Padilla, et al. (United States District Court, District of Puerto Rico No. 3:16-cv-01037, filed January 7, 2016). Ambac Assurance, along with co-plaintiffs Assured Guaranty Corp. and Assured Guaranty Municipal Corp., filed a complaint for declaratory and injunctive relief to protect its rights against the illegal clawback of certain revenue by the Commonwealth of Puerto Rico. Defendants moved to dismiss on January 29, 2016. On October 4, 2016, the court denied the Defendants’ motions to dismiss. On October 14, 2016, Defendants filed a Notice of Automatic Stay, asserting that Plaintiffs’ claims have been rendered moot and further asserting that the case was automatically stayed under section 405 of the Puerto Rico Oversight, Management and Economic Stability Act ("PROMESA"). On October 28, 2016, Plaintiffs informed the court that neither party was currently challenging the stay, and expressly reserved their right to seek to lift the stay at any time. Plaintiffs also objected to Defendants’ assertion that the case should be dismissed as moot. PROMESA’s litigation stay expired on May 2, 2017. On May 3, 2017, the Oversight Board filed a petition to adjust the Commonwealth’s debts under Title III of PROMESA, resulting in an automatic stay of litigation against the Commonwealth. On May 17, 2017, the court issued an order staying this case until further order of the court. Ambac Assurance Corporation v. Puerto Rico Highways and Transportation Authority (United States District Court, District of Puerto Rico, No. 16-cv-1893, filed May 10, 2016). Ambac Assurance filed a complaint against the Puerto Rico Highways and Transportation Authority ("PRHTA") on May 10, 2016, alleging breach of fiduciary duty and breach of contract in connection with PRHTA’s extension of an existing toll road concession agreement. The complaint alleges that it was inappropriate for PRHTA to enter into the extension agreement in its current state of financial distress because PRHTA has no control over, and is unlikely to receive, the proceeds of the transaction. Ambac Assurance also filed related motions seeking the appointment of a provisional receiver for PRHTA and expedited discovery. On May 21, 2017, the Oversight Board filed a petition to adjust PRHTA’s debts under Title III of PROMESA, resulting in an automatic stay of litigation against PRHTA. On May 24, 2017, the court issued an order staying this case until further order of the court. Lex Claims, LLC et al. v. Alejandro Garcia Padilla et al. (United States District Court, District of Puerto Rico, No. 16-2374, filed July 20, 2016). On October 7, 2016, certain General Obligation bondholder Plaintiffs in an action to which Ambac Assurance was not then a party filed a motion for leave to amend an existing complaint, adding the Puerto Rico Sales Tax Financing Corporation ("COFINA"), COFINA’s executive director, and the trustee for the COFINA bonds as Defendants, and asserting numerous claims that challenged the legal validity of the COFINA structure and seek injunctive relief requiring the sales and use tax proceeds securing COFINA’s bonds to be transferred to the Puerto Rico Treasury. On February 17, 2017, the court permitted Ambac Assurance to intervene. On May 3, 2017, a petition under Title III of PROMESA was filed on behalf of the Commonwealth of Puerto Rico, and on May 5, 2017, a petition under Title III of PROMESA was filed on behalf of COFINA, resulting in an automatic stay of litigation against the Commonwealth and COFINA (respectively). On May 17, 2017, the court issued an order staying this case until further order of the court. On October 19, 2018, the Oversight Board filed (i) a disclosure statement and a plan of adjustment for COFINA (the “COFINA Plan”) in the COFINA Title III case incorporating a resolution of the dispute between the Commonwealth and COFINA concerning entitlement to sales and use taxes (the “Commonwealth-COFINA Dispute”), and (ii) a motion under Bankruptcy Rule 9019 in the Commonwealth Title III case for approval of the settlement of the Commonwealth-COFINA Dispute (the “9019 Motion”). On February 4, 2019 the District Court granted the 9019 Motion and confirmed the COFINA Plan, which resolves the dispute in this case. The COFINA Plan became effective on February 12, 2019. Following confirmation of the COFINA Plan, several parties filed notices of appeal of the District Court’s confirmation order. On April 12, 2019, the Oversight Board and the Puerto Rico Fiscal Agency and Financial Advisory Authority ("AAFAF") moved to dismiss these appeals as equitably moot because the COFINA Plan has been consummated. On August 7 and October 4, 2019, the First Circuit denied the motions to dismiss, but without prejudice to reconsideration of the mootness issue by the panel that decides the appeals. Briefing on the merits of the appeals is ongoing before the First Circuit. Ambac Assurance Corporation v. Puerto Rico, et al. (United States District Court, District of Puerto Rico, No. 17-1567, filed May 2, 2017). On May 2, 2017, Ambac Assurance filed a complaint seeking a declaration that the Commonwealth’s Fiscal and Economic Growth Plan (the "FEGP") and a recently enacted statute called the “Fiscal Plan Compliance Law” are unconstitutional and unlawful because they violate the Contracts, Takings, and Due Process Clauses of the U.S. Constitution, are preempted by PROMESA, and are unlawful transfers of property from COFINA to the Commonwealth in violation of PROMESA. On May 3, 2017, a petition under Title III of PROMESA was filed on behalf of the Commonwealth of Puerto Rico, and on May 5, 2017, a petition under Title III of PROMESA was filed on behalf of COFINA, resulting in an automatic stay of litigation against COFINA. On May 17, 2017, the court issued an order staying this case until further order of the court. On February 4, 2019, the District Court granted the 9019 Motion and confirmed the COFINA Plan. The COFINA Plan became effective on February 12, 2019. Following confirmation of the COFINA Plan, several parties filed notices of appeal of the District Court’s confirmation order. Ambac Assurance anticipates that this case will be voluntarily dismissed given the effectiveness of the COFINA Plan. Ambac Assurance Corporation v. Puerto Rico, et al. (United States District Court, District of Puerto Rico, No. 17-1568, filed May 2, 2017). On May 2, 2017, Ambac Assurance filed a complaint alleging that various moratorium laws and executive orders enacted by the Commonwealth to claw back funds from PRIFA, PRHTA, and PRCCDA bonds violate the Contracts, Takings, and Due Process Clauses of the U.S. Constitution, are preempted by PROMESA, and unlawfully transfer PRHTA, PRCCDA, and PRIFA property to the Commonwealth. On May 3, 2017, a petition under Title III of PROMESA was filed on behalf of the Commonwealth of Puerto Rico and on May 21, 2017, a petition under Title III of PROMESA was filed on behalf of PRHTA, resulting in an automatic stay of litigation against the Commonwealth and PRHTA (respectively). On May 17, 2017, the court issued an order staying this case until further order of the court. Ambac Assurance Corporation v. U.S. Department of Treasury et al. (United States District Court, District of Columbia, No. 17-809, filed May 2, 2017). On May 2, 2017, Ambac Assurance filed a complaint against the U.S. Department of Treasury and Steven Mnuchin, in his official capacity as Secretary of the Treasury, alleging that Puerto Rico’s ongoing diversion of rum taxes from PRIFA violates the Contracts, Takings, and Due Process Clauses of the U.S. Constitution, and seeking an equitable lien on all rum taxes possessed by the U.S. Treasury, and an injunction preventing their transfer to the Commonwealth. On May 3, 2017, a petition under Title III of PROMESA was filed on behalf of the Commonwealth of Puerto Rico. On May 24, 2017, the Oversight Board filed a statement requesting that the court take notice of the stay resulting from the Commonwealth’s Title III filing. On May 25, 2017, the court issued an order staying this case as a result of the Title III proceedings. Ambac Assurance Corporation v. Bank of New York Mellon (United States District Court, Southern District of New York. No. 1:17-cv-03804, filed May 2, 2017). On May 2, 2017, Ambac Assurance filed a complaint in New York State Supreme Court, New York County, against the trustee for the COFINA bonds, Bank of New York Mellon ("BNY"), alleging breach of fiduciary, contractual, and other duties for failing to adequately and appropriately protect the holders of certain Ambac Assurance-insured senior COFINA bonds. On May 19, 2017, BNY filed a notice of removal of this action from New York state court to the United States District Court for the Southern District of New York. On May 30, 2017, the United States District Court for the District of Puerto Rico entered an order in an adversary proceeding brought by BNY (No. 1:17-ap-00133) staying this litigation pending further order of the court. The COFINA Plan became effective on February 12, 2019, and, pursuant to the District Court’s confirmation order, this litigation is permitted to continue, with Ambac’s claims against BNYM being limited to those for gross negligence, willful misconduct and intentional fraud. Following confirmation of the COFINA Plan, several parties filed notices of appeal of the District Court’s confirmation order to the First Circuit Court of Appeals. On April 12, 2019, the Oversight Board and AAFAF moved to dismiss these appeals as equitably moot because the COFINA Plan has been consummated. On August 7 and October 4, 2019, the First Circuit denied the motions to dismiss, but without prejudice to reconsideration of the mootness issue by the panel that decides the appeals. Briefing on the merits of the appeals is ongoing before the First Circuit. Bank of New York Mellon v. COFINA, et al. (United States District Court, District of Puerto Rico, No. 1:17-ap-00133, filed May 16, 2017). On May 16, 2017, BNY filed an interpleader action styled as an adversary proceeding against COFINA and certain creditors of COFINA, including Ambac Assurance, that have made competing claims of entitlement to funds held by BNY in order to determine the parties’ respective entitlements to the funds. BNY also sought a release of liability in association with the COFINA funds in its possession.. On September 27, 2018, the court terminated competing motions for summary judgment without prejudice in light of the pending agreement in principle between the agent for COFINA and the agent for the Commonwealth in adversary proceeding no. 1:17-ap-00257 (the “Commonwealth-COFINA Dispute,” discussed below). On October 19, 2018, the Oversight Board filed (i) a disclosure statement and the COFINA Plan in the COFINA Title III case incorporating a resolution of the Commonwealth-COFINA Dispute, and (ii) the 9019 Motion in the Commonwealth Title III case for approval of the settlement of the Commonwealth-COFINA Dispute. On February 4, 2019 the District Court granted the 9019 Motion and confirmed the COFINA Plan, which resolves the dispute in this case. The COFINA Plan became effective on February 12, 2019. Following confirmation of the COFINA Plan, several parties filed notices of appeal of the District Court’s confirmation order to the First Circuit Court of Appeals. On February 20, 2019, on the joint motion of BNY and COFINA, the District Court dismissed this case with prejudice. On April 12, 2019, the Oversight Board and AAFAF moved to dismiss these appeals as equitably moot because the COFINA Plan has been consummated. On August 7 and October 4, 2019, the First Circuit denied the motions to dismiss, but without prejudice to reconsideration of the mootness issue by the panel that decides the appeals. Briefing on the merits of the appeals is ongoing before the First Circuit. Ambac Assurance Corporation v. Puerto Rico, et al. (United States District Court, District of Puerto Rico, No. 1:17-ap-00159, filed June 8, 2017). On June 8, 2017, Ambac Assurance filed an adversary complaint in the Commonwealth’s Title III case against the Commonwealth, PRHTA, the Oversight Board, AAFAF, and other Commonwealth government officers. Ambac Assurance challenges the Commonwealth’s clawback of funds from the PRIFA, PRHTA, and PRCCDA bonds under the Contracts, Takings, and Due Process Clauses of the U.S. Constitution and under PROMESA. The complaint further seeks a declaration that revenues pledged to the PRHTA bonds are “special revenues” under Sections 922 and 928 of the Bankruptcy Code, and an injunction compelling Defendants to remit the pledged special revenues to PRHTA for payment of the PRHTA bonds. On July 7, 2017, Ambac Assurance filed an amended complaint that added an additional claim for relief: a declaration that the funds held in the PRHTA reserve accounts are property of the PRHTA bondholders. On July 28, 2017, Defendants moved to dismiss Ambac Assurance’s complaint, which Ambac Assurance opposed. On February 27, 2018, the District Court granted Defendants’ motion to dismiss. On March 9, 2018, Ambac Assurance appealed this ruling to the First Circuit Court of Appeals. On June 24, 2019, the First Circuit affirmed the District Court's dismissal of Ambac Assurance's claims for relief on the grounds that PROMESA deprives courts of jurisdiction to review the Oversight Board's certification determinations, and that PROMESA prohibits the Title III court from interfering with the political or governmental powers of the Commonwealth or the Commonwealth's property or revenues. On January 13, 2020, the Supreme Court of the United States denied Ambac Assurance’s petition for certiorari. Official Committee of Unsecured Creditors v. Whyte (United States District Court, District of Puerto Rico, No. 1:17-ap-00257, filed September 8, 2017) (the Commonwealth-COFINA Dispute). On August 10, 2017, the court approved a stipulation between the Oversight Board, the Commonwealth, COFINA, and certain creditor parties, including Ambac Assurance, to resolve the Commonwealth-COFINA Dispute regarding entitlement to sales and use taxes. The stipulation provided that separate agents for COFINA and the Commonwealth would litigate the dispute while preserving the ability of interested parties, to participate in the litigation. On September 8, 2017, the Commonwealth Agent filed an adversary proceeding against the COFINA Agent challenging the COFINA structure on various grounds. The Commonwealth Agent filed a revised complaint on October 25, 2017, making technical corrections to the original complaint. Ambac Assurance made a motion to intervene in this action, which the court granted on November 21, 2017. The Commonwealth Agent filed an amended complaint on January 16, 2018, largely re-stating its original causes of action to fall within the parameters of the dispute set by the court. After extensive motion practice, on September 27, 2018, the court terminated competing summary judgment motions without prejudice in light of a pending agreement in principle between the Commonwealth Agent and COFINA Agent. On October 19, 2018, the Oversight Board filed (i) a disclosure statement and the COFINA Plan in the COFINA Title III case incorporating a resolution of the Commonwealth-COFINA Dispute, and (ii) the 9019 Motion in the Commonwealth Title III case for approval of the settlement of the Commonwealth-COFINA Dispute. On February 4, 2019, the District Court granted the 9019 Motion and confirmed the COFINA Plan, which resolves the dispute in this case. The COFINA Plan became effective on February 12, 2019. On February 21, 2019, on the joint motion of the agents for the Commonwealth and COFINA, the Oversight Board, AAFAF, and all participating interested parties, the District Court dismissed this case with prejudice. Following confirmation of the COFINA Plan, several parties filed notices of appeal of the District Court’s confirmation order to the First Circuit Court of Appeals. On April 12, 2019, the Oversight Board and AAFAF moved to dismiss these appeals as equitably moot because the COFINA Plan has been consummated. On August 7 and October 4, 2019, the First Circuit denied the motions to dismiss, but without prejudice to reconsideration of the mootness issue by the panel that decides the appeals. Briefing on the merits of the appeals is ongoing before the First Circuit. 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. Certain intervenor-defendants filed counterclaims for declarations to this effect, and a motion for judgment on the pleadings. 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 June 27, 2019, the Oversight Board moved to stay this adversar

Quarterly Information (unaudite

Quarterly Information (unaudited) (Notes)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Data [Abstract]
Quarterly Financial Information (unaudited)	2019 Quarters 2018 Quarters First Second Third Fourth First Second Third Fourth Gross premiums written $ 3 $ (21 ) $ (13 ) $ 2 $ 4 $ (1 ) $ (23 ) $ (5 ) Net premiums earned 28 8 10 20 31 26 26 29 Net investment income 55 86 45 42 110 67 58 37 Net other than temporary impairment losses — — — — — (1 ) — (2 ) Net realized investment gains (losses) 17 36 18 9 5 47 30 29 Net gains (losses) on derivative contracts (16 ) (35 ) (10 ) 12 25 9 18 (45 ) Net realized gains (losses) on extinguishment of debt — — — — 3 — — — Other income (loss) 1 (9 ) 141 1 (1 ) 2 1 2 Income (loss) on Variable Interest Entities 16 3 11 7 1 1 2 — Losses and loss expenses (benefit) 12 (133 ) 37 97 (247 ) 33 34 (42 ) Insurance intangible amortization 36 226 17 15 29 23 26 29 Operating expenses 25 29 26 23 36 26 28 21 Interest expense 68 67 67 66 48 62 66 66 Pre-tax income (loss) (41 ) (100 ) 69 (111 ) 308 6 (20 ) (22 ) Net income (loss) (43 ) (128 ) 66 (110 ) 306 4 (22 ) (20 ) Net income (loss) attributable to Common Stockholders $ (43 ) $ (128 ) $ 66 $ (110 ) $ 306 $ 4 $ (104 ) $ (20 ) Net income (loss) per share: Basic $ (0.94 ) $ (2.79 ) $ 1.44 $ (2.40 ) $ 6.72 $ 0.09 $ (2.27 ) $ (0.45 ) Diluted $ (0.94 ) $ (2.79 ) $ 1.41 $ (2.40 ) $ 6.70 $ 0.09 $ (2.27 ) $ (0.45 )

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Disclosure [Table Text Block]	Operating Leases Ambac adopted the New Lease Standard as further described below in this Note 2. A contract contains a lease if it conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Ambac's evaluation of whether certain contracts contain leases may require judgment regarding what party controls the asset and whether the asset is physically distinct. Ambac is the lessee in leases which are classified as operating leases that recognize a single lease cost, calculated so that the cost is allocated over the lease term generally on a straight-line basis over the lease term within operating expenses in the Consolidated Statements of Total Comprehensive Income (Loss). The lease term commences on the earlier of the date when we become legally obligated for the rent payments or the date on which we take possession of the property. For such operating leases, Ambac recognizes a right-of-use asset ("ROU") and a lease liability, initially measured at the present value of the lease payments, on the later of the adoption date or lease commencement date. The discount rate used to initially measure the right of use assets and lease liabilities was based on Ambac's estimated secured borrowing rate. The Ambac Note, more fully described in Note 1. Background and Business Description was a significant data point in estimating this rate. For contracts where Ambac is the lessee, we have elected the short-term lease recognition exemption for all leases that qualify. For those leases that qualify for that exemption, we will not recognize ROU assets or lease liabilities. For all contracts where Ambac is the lessee and lessor we have also elected the practical expedient to not separate lease and non-lease components.
Noncontrolling Interest Policy [Policy Text Block]	Noncontrolling Interest At December 31, 2019 and 2018 , Ambac Assurance had 5,501 and 4,115 shares of issued and outstanding AMPS with a liquidation preference of $138 and $103 (reported as noncontrolling interest of $60 and $41 on Ambac's balance sheet), respectively. The auction occurs every 28 days and the dividend rate has continuously been reset at the maximum rate of one-month LIBOR plus 200 basis points. Under the terms of the AMPS, dividends may not be paid on the common stock of Ambac Assurance unless all accrued and unpaid dividends on the AMPS for the then current dividend period have been paid, provided, that dividends on the common stock may be made at all times for the purpose of, and only in such amounts as are necessary for, enabling AFG (i) to service its indebtedness for borrowed money as such payments become due or (ii) to pay its operating expenses. If dividends are paid on the common stock as provided in the prior sentence, dividends on the AMPS become cumulative until the date that all accumulated and unpaid dividends have been paid on the AMPS. Ambac Assurance has not paid dividends on its AMPS since 2010.
Consolidation	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. Refer to 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.
Unconsolidated Financial Information	AFG Unconsolidated Financial Information Financial information of AFG is presented in Schedule II to this Form 10-K as of December 31, 2019 and 2018 and for the years ended December 31, 2019, 2018 and 2017 . Investments in subsidiaries are accounted for using the equity method of accounting in Schedule II.
Investments	Investments The Investments - Debt Securities Topic of the ASC requires that all debt instruments be classified in Ambac’s Consolidated Balance Sheets according to their purpose and, depending on that classification, be carried at either cost or fair market value. Ambac’s non-VIE debt investment portfolio is accounted for on a trade-date basis and consists primarily of investments in fixed income securities that are considered available-for-sale as defined by the Investments - Debt Securities Topic of the ASC. Available-for-sale debt securities are reported in the financial statements at fair value with unrealized gains and losses, net of deferred taxes, reflected in Accumulated Other Comprehensive Income (Loss) in Stockholders’ Equity and computed using amortized cost as the basis. For purposes of computing amortized cost, premiums and discounts are accounted for using the effective interest method over a future term of the security. For structured debt securities with a large underlying pool of homogenous loans, such as mortgage-backed and asset-backed securities, premiums and discounts are adjusted for the effects of actual and anticipated prepayments. For other fixed income securities, such as corporate and municipal bonds, discounts were amortized or accreted over the remaining term of the securities. Ambac adopted ASU 2017-08, Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20) - Premium Amortization on Purchased Callable Debt Securities, on January 1, 2019. ASU 2017-08 shortened the amortization period for the premium on callable debt securities to the earliest call date. Under previous GAAP, Ambac generally amortized the premium over the contractual life (i.e. maturity) of the debt security and if that debt security was called, we would record a loss equal to the unamortized premium. Ambac’s non-VIE investment portfolio also includes equity interests in pooled investment funds which are accounted for in accordance with the Investments - Equity Securities Topic of the ASC and reported as Other investments on the Consolidated Balance Sheet with income reported through Net investment income on the Statement of Total Comprehensive Income (Loss). Equity interests in the form of common stock or in-substance common stock are classified as trading securities and reported at fair value while limited partner interests in such funds are reported using the equity method. Fair value is based primarily on quotes obtained from independent market sources. When quotes are not available or cannot be reasonably corroborated, valuation models are used to estimate fair value. These models include estimates, made by management, which utilize current market information. The quotes received or modeled valuations could differ materially from amounts that would actually be realized in the market. Realized gains and losses on the sale of investments are determined on the basis of specific identification. VIE investments in fixed income securities are carried at fair value as they are either considered as available for sale securities or under the fair value option election. For additional information about VIE investments, including fair value by asset-type, see Note 3. Variable Interest Entities . Ambac has a formal impairment review process for fixed income available-for-sale securities in its investment portfolio. Ambac conducts a review each quarter to identify and evaluate investments that have indications of impairment that may be other than temporary in accordance with the Investments - Debt Securities Topic of the ASC. Factors considered to identify and assess securities for other than temporary impairment include: (i) fair values that have declined by 20% or more below amortized cost; (ii) market values that have declined by 5% or more but less than 20% below amortized cost for a continuous period of at least six months; (iii) recent downgrades by rating agencies; (iv) the financial condition of the issuer and financial guarantor, as applicable, and an analysis of projected defaults on the underlying collateral; (v) whether scheduled interest payments are past due; (vi) whether Ambac has the intent to sell the security; and (vii) whether it is more likely than not that Ambac will be required to sell a security before the anticipated recovery of its amortized cost basis. If we believe a decline in the fair value of a particular investment is temporary, we record the decline as an unrealized loss net of tax in Accumulated Other Comprehensive Income (Loss) in Stockholders’ Equity on our Consolidated Balance Sheets. If management either: (i) has the intent to sell its investment in a debt security or (ii) determines that the Company more likely than not will be required to sell the debt security before its anticipated recovery of the amortized cost basis less any current period credit impairment, then an other-than-temporary impairment charge is recognized in earnings, with the amortized cost of the security being written-down to fair value. If these conditions are not met, but it is determined that a credit loss exists, the credit impairment loss is recognized in earnings, and the other-than-temporary amount related to all other factors is recognized in other comprehensive income. For fixed income securities that have other-than-temporary impairments in a period, the previous amortized cost of the security less the amount of the other-than-temporary impairment recorded through earnings becomes the investment’s new amortized cost basis. Ambac accretes the new amortized cost basis to par or to the estimated future cash flows to be recovered over the expected remaining life of the security. The evaluation of securities for impairment is a quantitative and qualitative process, which is subject to risks and uncertainties and is intended to determine whether, and to what extent, declines in the fair value of investments should be recognized in current period earnings. The risks and uncertainties include changes in general economic conditions, the issuer’s or guarantor’s financial condition and/or future prospects, the impact of regulatory actions on the investment portfolio, the performance of the underlying collateral, the effects of changes in interest rates or credit spreads and the expected recovery period. With respect to Ambac insured securities owned, future cash flows used to measure credit impairment represents the sum of (i) the bond’s intrinsic cash flows and (ii) the estimated Ambac Assurance claim payments. Prior to the discharge and settlement of the Segregated Account's claim obligations on February 12, 2018, the estimate of Ambac's Segregated Account claim payments, including interest on Deferred Amounts, was an important consideration in the evaluation of other than temporary impairment as such payments were at the sole discretion of the Rehabilitator. Refer to Note 1. Background and Business Description for more information on the Segregated Account and the Segregated Account Rehabilitation Proceedings. 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 the factors noted above. If that judgment changes, Ambac may ultimately record a charge for other-than-temporary impairment in future periods.
Net Premiums Earned	Net Premiums Gross premiums were received either upfront or in installments. For premiums received upfront, an unearned premium revenue (“UPR”) liability was established, which was initially recorded as the cash amount received. For installment premium transactions, a premium receivable asset and offsetting UPR liability was initially established in an amount equal to: (i) the present value of future contractual premiums due (the “contractual” method) or (ii) if the underlying insured obligation is a homogenous pool of assets which are contractually prepayable, the present value of premiums to be collected over the expected life of the transaction (the “expected” method). An appropriate risk-free rate corresponding to the weighted average life of each policy and currency is used to discount the future premiums contractually due or expected to be collected. For example, U.S. dollar exposures are discounted using U.S. Treasury rates while exposures denominated in a foreign currency are discounted using the appropriate risk-free rate for the respective currency. The weighted average risk-free rate at December 31, 2019 and 2018 , was 2.4% . and 2.7% , respectively, and the weighted average period of future premiums used to estimate the premium receivable at December 31, 2019 and 2018 , was 8.5 and 8.7 years , respectively. Insured obligations consisting of homogeneous pools for which Ambac uses expected future premiums to estimate the premium receivable include residential mortgage-backed securities ("RMBS"). As prepayment assumptions change for homogenous pool transactions, or if there is an actual prepayment for a “contractual” method installment transaction, the related premium receivable and UPR are adjusted in equal and offsetting amounts with no immediate effect on earnings using new premium cash flows and the then current risk-free rate corresponding to the initial weighted average life of the related policy. For both upfront and installment premium policies, premium revenues are earned over the life of the financial guarantee contract in proportion to the insured principal amount outstanding at each reporting date (referred to as the level-yield method). For installment paying policies, the premium receivable discount, equating to the difference between the undiscounted future installment premiums and the present value of future installment premiums, is accreted as premiums earned in proportion to the premium receivable balance at each reporting date. Additionally, the Company evaluates whether any premiums receivable are uncollectible at each balance sheet date and records an allowance for policies with a premium receivable impairment based on our expectation. Similar to gross premiums, premiums ceded to reinsurers were paid either upfront or in installments. For premiums paid upfront, a deferred ceded premium asset was established which is initially recorded as the cash amount paid. For installment premiums, a ceded premiums payable liability and offsetting deferred ceded premium asset were initially established in an amount equal to: i) the present value of future contractual premiums due or ii) if the underlying insured obligation is a homogenous pool of assets, the present value of expected premiums to be paid over the life of the transaction. An appropriate risk-free rate corresponding to the weighted average life of each policy and exposure currency is used to discount the future premiums contractually due or expected to be collected. Premiums ceded to reinsurers reduce the amount of premiums earned by Ambac from its financial guarantee insurance policies. For both upfront and installment premiums, ceded premiums written are primarily recognized in earnings in proportion to and at the same time as the related gross premium revenue is recognized. For premiums paid to reinsurers on an installment basis, Ambac records the present value of future ceding commissions as an offset to ceded premiums payable, using the same assumptions noted above for installment premiums. When a bond issue insured by Ambac has been retired early, typically due to an issuer call, any remaining UPR is recognized at that time to the extent the financial guarantee contract is legally extinguished, causing accelerated premium revenue. For installment premium paying transactions, we offset the recognition of any remaining UPR by the reduction of the related premium receivable to zero (as it will not be collected as a result of the retirement), which may cause negative accelerated premium revenue. Certain obligations insured by Ambac have been legally defeased whereby government securities are purchased by the issuer with the proceeds of a new bond issuance, or less frequently with other funds of the issuer, and held in escrow. The principal and interest received from the escrowed securities are then used to retire the Ambac-insured obligations at a future date either to their maturity date (a refunding) or a specified call date (a pre-refunding). Ambac has evaluated the provisions in policies issued on these obligations and determined those insurance policies have not been legally extinguished. For policies with refunding securities, premium revenue recognition is not impacted as the escrowed maturity date is the same as the previous legal maturity date. For policies with pre-refunding securities, the maturity date of the pre-refunded security has been shortened from its previous legal maturity. Although premium revenue recognition has not been accelerated in the period of the pre-refunding, it results in an increase in the rate at which the policy's remaining UPR is to be recognized.
Loans	Loans Loans are reported at either their outstanding principal balance less unamortized discount or at fair value. • Loans not held by consolidated VIEs are reported at their outstanding principal balance less unamortized discount and are reported within Other assets on the Consolidated Balance Sheet. Interest income is earned using the effective interest method based upon interest accrued on the unpaid principal balance adjusted for accretion of discounts. A loan is considered impaired when, based on the financial condition of the borrower, it is probable that Ambac will be unable to collect all principal and interest due according to the contractual terms of the loan agreement. •
Derivative Contracts	Derivative Contracts The Company has entered into derivative contracts both for trading purposes and to hedge certain economic risks inherent in its financial asset and liability portfolios. None of Ambac’s derivative contracts are designated as hedges under the Derivatives and Hedging Topic of the ASC. Ambac's derivatives consist primarily of interest rate swaps and futures contracts. • Ambac maintains a portfolio consisting primarily of interest rate swaps and futures contracts to economically hedge interest rate risk in the financial guarantee and investment portfolios. This portfolio also includes legacy interest rate swaps with asset-backed securitization issuers, states, municipalities and their authorities which were written in connection with their financings. Changes in fair value of these interest rate derivatives are recorded, along with changes in fair value of Ambac's remaining credit derivatives, within Net gains (losses) on derivative contracts on the Consolidated Statements of Total Comprehensive Income (Loss). • VIEs consolidated under the Consolidation Topic of the ASC entered into derivative contracts to meet specified purposes within their securitization structure. Changes in fair value of consolidated VIE derivatives are included within Income (loss) on variable interest entities on the Consolidated Statements of Total Comprehensive Income (Loss). All derivatives are recorded on the Consolidated Balance Sheets at fair value on a gross basis; assets and liabilities are netted by counterparty only when a legal right of offset exists. Variation payments on centrally cleared swaps and futures contracts are considered settlements of the associated derivative balances and are reflected as a reduction to derivative liabilities or assets on the Consolidated Balance Sheets. For other derivatives, Ambac has determined that the amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral may not be used to offset amounts due under the derivative instruments in the normal course of settlement. Therefore, such amounts are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement and are included in "Other assets" on the Consolidated Balance Sheets. Refer to Note 11. Derivative Instruments for further discussion of the Company’s use of derivative instruments and their impact of the consolidated financial statements. Refer to Note 9. Fair Value Measurements for further description of the methodologies used to determine the fair value of derivative contracts, including model inputs and assumptions where applicable.
Intangible Assets	Insurance Intangible Asset Upon Ambac's emergence from bankruptcy in 2013, an insurance intangible asset was recorded which represented the difference between the fair value and aggregate carrying value of the financial guarantee insurance and reinsurance assets and liabilities. The carrying values of our financial guarantee insurance and reinsurance contracts continue to be reported and measured in accordance with their existing accounting policies. Pursuant to the Financial Services-Insurance Topic of the ASC, the insurance intangible is to be measured on a basis consistent with the related financial guarantee insurance and reinsurance contracts. The insurance intangible asset is amortized using a level-yield method based on par exposure of the related financial guarantee insurance or reinsurance contracts and is applied to groups of contracts with similar characteristics.
Restricted Cash	Restricted Cash Cash that we do not have the right to use for general purposes is recorded as restricted cash in our consolidated balance sheets. Restricted cash includes (i) consolidated variable interest entity cash restricted to support the obligations of the consolidated VIEs and (ii) cash held by Ambac Assurance received from its investment in Secured Notes and pledged for the benefit of holders of Secured Notes (other than Ambac Assurance).
Loss Reserves	Loss and Loss Expenses The loss and loss expense reserve (“loss reserve”) policy relates only to Ambac’s non-derivative insurance business for insurance policies issued to beneficiaries, including VIEs, for which we do not consolidate the VIE. Losses and loss expenses are based upon estimates of the ultimate aggregate losses inherent in the non-derivative financial guarantee portfolio as of the reporting date. The policy for derivative contracts is discussed in the “Derivative Contracts” section above. A loss reserve is recorded on the balance sheet on a policy-by-policy basis based upon the present value ("PV") of expected net claim cash outflows or expected net recovery cash inflows, discounted at risk-free rates. The estimate for future net cash flows consider the likelihood of all possible outcomes that may occur from missed principal and/or interest payments on the insured obligation. This estimate also considers future recoveries related to breaches of contractual representations and warranties by RMBS transaction sponsors, remediation strategies, excess spread and other contractual cash flows on public finance and structured finance transactions (including RMBS). Ambac’s approach to resolving disputes involving contractual breaches by transaction sponsors or other third parties has included negotiations and/or pursuing litigation. Ambac does not estimate recoveries for litigations where its sole claim is for fraudulent inducement, since any remedies under such claims would be non-contractual. • Net claim cash outflow policies represent contracts where the PV of expected cash outflows are greater than the PV of expected recovery cash inflows. For such policies, a “Loss and loss expense reserves” liability is recorded for the excess of the PV of expected net claim cash outflows over the unearned premium revenue. • Net recovery cash inflow policies represent contracts where the PV of expected recovery cash inflows are greater than the PV of expected claim cash outflows. For such policies, a “Subrogation recoverable” asset is recorded. The evaluation process for determining expected losses is subject to certain judgments based on our assumptions regarding the probability of default by the issuer of the insured security, probability of settlement outcomes (which may include commutation settlements, refinancing and/or other settlement outcomes) and expected severity of credits for each insurance contract. Ambac’s loss reserves are based on management’s ongoing review of the financial guarantee credit portfolio. Active surveillance of the insured portfolio enables Ambac’s Risk Management Group ("RMG") to track credit migration of insured obligations from period to period and update internal classifications and credit ratings for each transaction. Non-adversely classified credits are assigned a Class I rating while adversely classified credits are assigned a rating of Class IA through Class V. The criteria for an exposure to be assigned an adversely classified credit rating includes the deterioration of an issuer’s financial condition, underperformance of the underlying collateral (for collateral dependent transactions such as mortgage-backed or student loan securitizations), poor performance by the servicer of the underlying collateral and other adverse economic events or trends. The servicer of the underlying collateral of an insured securitization transaction is a consideration in assessing credit quality because the servicer’s performance can directly impact the performance of the related issue. For example, a servicer of a mortgage-backed securitization that does not remain current in its collection efforts could cause an increase in the delinquency and the potential for default of the underlying obligation. Similarly, loss severities increase when a servicer does not effectively handle loss mitigation activities such as (i) the advancing of delinquent principal and interest and of default related expenses which are deemed to be recoverable by the servicer, (ii) pursuit of loan charge-offs which maximize cash flows from the mortgage loan pool and (iii) foreclosure and real estate owned disposition strategies and timelines. All credits are assigned risk classifications by RMG using the following guidelines: CLASS I - “Fully Performing - Meets Ambac Criteria with Remote Probability of Claim” - Credits that demonstrate adequate security and structural protection with a strong capacity to pay interest, repay principal and perform as underwritten. Factors supporting debt service payment and performance are considered unlikely to change and any such change would not have a negative impact upon the fundamental credit quality. Through ongoing surveillance, Ambac may also designate Class I credits into one or more of the following categories: • Survey List - credits that may lack information or demonstrate a weakness but further deterioration is not expected. • Watch List - credits that demonstrate the potential for future material adverse development due to such factors as long-term uncertainty about a particular sector, a certain structural element or concern related to the issuer or transaction or the overall financial and economic sustainability. CLASS IA - “Potential Problem with Risks to be Dimensioned” - Credits that are fully current and monetary default or claims-payment are not anticipated. The payor’s or issuer’s financial condition may be deteriorating or the credits may lack adequate collateral. A structured financing may also evidence weakness in its fundamental credit quality as evidenced by its under-performance relative to its modeled projections at underwriting, issues related to the servicer’s ability to perform or questions about the structural integrity of the transaction. While certain of these credits may still retain an investment grade rating, they usually have experienced or are vulnerable to a ratings downgrade. Further investigation is required to dimension and correct any deficiencies. A complete legal review of documents may be required. An action plan should be developed with triggers for future classification changes upward or downward. CLASS II - “Substandard Requiring Intervention” - Credits whose fundamental credit quality has deteriorated to the point that timely payment of debt service may be jeopardized by adversely developing trends of a financial, economic, structural, managerial or political nature. No claim payment is currently foreseen but the probability of loss or claim payment over the life of the transaction is now existent (generally 10% or greater probability). Class II credits may be border-line or below investment grade (BBB- to B). Prompt and sustained action must be taken to execute a comprehensive loss mitigation plan and correct deficiencies. CLASS III - “Doubtful with Clear Potential for Loss” - Credits whose fundamental credit quality has deteriorated to the point that timely payment of debt service has been or will be jeopardized by adverse trends of a financial, economic, structural, managerial or political nature which, in the absence of positive change or corrective action, are likely to result in a loss. The probability of monetary default or claims paying over the life of the transaction is generally 50% or greater. Full exercise of all available remedial actions is required to avert or minimize losses. Class III credits will generally be rated below investment grade (B to CCC). CLASS IV - “Imminent Default or Defaulted” - Monetary default or claim payments have occurred or are expected imminently. Class IV credits are generally rated D. CLASS V - “Fully Reserved” - The credit has defaulted and payments have occurred. The claim payments are scheduled and known, reserves have been established to fully cover such claims, and no claim volatility is expected. The population of credits evaluated in Ambac’s loss reserve process are: (i) all adversely classified credits (Class IA through V) and ii) non-adversely classified credits which had an internal Ambac rating downgrade since the transaction’s inception. One of two approaches is then utilized to estimate losses to ultimately determine if a loss reserve should be established. The first approach is a statistical expected loss approach, which considers the likelihood of all possible outcomes. The “base case” statistical expected loss is the product of: (i) the par outstanding on the credit; (ii) internally developed default information (taking into consideration internal ratings and average life of an obligation); (iii) internally developed loss severities; and (iv) a discount factor. The loss severities and default information are based on rating agency information, are specific to each bond type and are established and approved by senior RMG officers. For certain credit exposures, Ambac’s additional monitoring, loss remediation efforts and probabilities of potential settlement outcomes may provide information relevant to adjust this estimate of “base case” statistical expected losses. Analysts may accept the “base case” statistical expected loss as the best estimate of expected loss or assign multiple probability weighted scenarios to determine an adjusted statistical expected loss that better reflects management’s view of a given transaction’s expected losses, as well as the potential for additional remediation activities (e.g., commutations). The second approach entails the use of cash-flow based models to estimate expected losses (future claims, net of potential recoveries, expected to be paid to the holder of the insured financial obligation). Ambac’s RMG group will consider the likelihood of all possible outcomes and develop appropriate cash flow scenarios. This approach can include the utilization of internal or third party models and tools to project future losses and resultant claim payment estimates. We utilize cash flow models for RMBS, student loan, Puerto Rico and other exposures. RMBS and student loan models use historical performance of the collateral pools in order to then derive future performance characteristics, such as default and voluntary prepayment rates, which in turn determine projected future claim payments. In other cases, such as many public finance exposures, including our Puerto Rico exposures, we do not specifically forecast resources available to pay debt service in the cash flow model itself. Rather, we consider the issuers’ overall ability and willingness to pay, including the fiscal, economic, legal and political framework. In this approach, a probability-weighted expected loss estimate is developed based on assigning probabilities to multiple claim payment scenarios and applying an appropriate discount factor. Additionally, we assign a probability to the issuer’s ability to refinance an insured issue, Ambac’s ability to execute a potential settlement (i.e., commutation) of the insurance policy, including the impact on future installment premiums, and/or other restructuring scenarios. The commutation scenarios and the related probabilities of occurrence vary by transaction, depending on our view of the likelihood of negotiating such a transaction with issuers and/or investors. The discount factor applied to the statistical expected loss approach is based on a risk-free discount rate corresponding to the remaining expected weighted-average life of the exposure and the exposure currency. For the cash flow scenario approach, discount factors are applied based on a risk-free discount rate term structure and correspond to the date of each respective cash flow payment or recovery and the exposure currency. Discount factors are updated for the current risk-free rate each reporting period. Ambac establishes loss expense reserves based on our estimate of expected net cash outflows for loss expenses, such as legal and consulting costs. Below we provide further details of our loss reserve models for both RMBS and student loan exposures: RMBS Expected Loss Estimate Ambac insures RMBS transactions collateralized by first-lien mortgages. Ambac has also insured RMBS transactions collateralized predominantly by second-lien mortgage loans such as closed-end seconds and home equity lines of credit. A second-lien mortgage loan is a type of loan in which the borrower uses the equity in their home as collateral and the second-lien loan is subordinate to the first-lien loan outstanding on the home. Borrowers are obligated to make monthly payments on both their first and second-lien loans. If the borrower defaults on the payments due under these loans and the property is subsequently liquidated, the liquidation proceeds are first utilized to pay off the first-lien loan (as well as other costs) and any remaining funds are applied to pay off the second-lien loan. As a result of this subordinate position to the first-lien loan, second-lien loans may carry a significantly higher severity in the event of a loss, approaching or exceeding 100%. Ambac primarily utilizes a cash flow model (“RMBS cash flow model”) to develop estimates of projected losses for both our first and second lien transactions. First, the RMBS cash flow model projects collateral performance utilizing: (i) the transaction’s underlying loans' characteristics and status, (ii) projected home price appreciation (“HPA”) and (iii) projected interest rates. Depending in the amount of collateral information available for each transaction, we project such performance either at the loan-level or the deal-level. In the absence of specific loan-level information, the deal-level approach evaluates a loan pool as if it were a single loan, selecting certain aggregated deal-level characteristics to then perform a series of statistical analyses. The deal-level approach projects performance using a roll-rate that evaluates the possible future state of a loan based on its current status and three variables: average FICO (credit score), average current consolidated loan to value ratio (“CLTV”) and an overall quality indicator. Projected servicer-level behavior may also have an impact on transaction performance. We source HPA projections from a market accepted vendor and interest rate projections are developed from market sources. We use three HPA projection scenarios to develop a base case as well as stress and upside cases. The highest probability is assigned to the base case, with lower probabilities to the stress and upside cases. For the liabilities of the transaction which we insure, we generally utilize waterfall projections generated from a tool provided by a market accepted vendor. This waterfall tool allows us to capture the impact of each transaction’s specific structure (e.g., the waterfall priority of payments, triggers, redemption priority) to generate our specific projected claims profile in the base, upside and downside scenarios. On a monthly basis, we compare monthly claims submitted against the trustees’ reports, waterfall projections and our understanding of the transactions’ structures to identify and resolve discrepancies. We also review the vendor’s published waterfall revisions to identify significant discrepancies. Resolving discrepancies is challenging and may take place over an extended period of time. Moreover, transaction documents are subject to interpretation, and our interpretation or that of the vendor and as reflected in our loss reserves may prove to be incorrect and/or not consistent with trustees directing cash flows in the future. In some cases, we may utilize an alternative waterfall structure when our legal and commercial analysis of the transaction’s payment structure differs from the vendor’s waterfall structure. In our experience, market performance and model characteristics change and therefore need to be updated and reflected in our models through time. As such, we conduct regular reviews of current models, alternative models and the overall approach to loss estimation. RMBS Representation and Warranty Subrogation Recoveries Ambac records, as a component of its loss reserve estimate, subrogation recoveries related to securitized loans in RMBS transactions that breached certain representations and warranties described herein. Generally, the sponsor of an RMBS transaction provided representations and warranties with respect to the securitized loans, including representations and warranties with respect to loan characteristics, the absence of borrower fraud in the underlying loan pools and other misconduct in the origination process and attesting to the compliance of loans with the prevailing underwriting policies. In such cases, the sponsor of the transaction is contractually obligated to repurchase, cure or substitute collateral for any loan that breaches the representations or warranties. Ambac or its counsel engaged consultants with significant mortgage underwriting experience to review the underwriting documentation for mortgage loans underlying certain insured RMBS transactions which exhibited exceptionally poor performance. Factors which Ambac believes to be indicative of poor performance include (i) high levels of early payment defaults, (ii) significant numbers of loan liquidations or charge-offs and resulting high levels of losses and (iii) rapid elimination of credit protections inherent in the transactions’ structures. With respect to item (ii), “loan liquidations” refers to loans for which the servicer has liquidated the related collateral and the securitization has realized losses on the loan; “charge-offs” refers to loans which have been written off as uncollectible by the servicer, generating no recoveries to the securitization, and may also refer to the unrecovered balance of liquidated loans. In either case, the servicer has taken actions to recover against the collateral, and the securitization has incurred losses to the extent such actions did not result in full repayment of the borrower’s obligations. Generally, subsequent to the forensic exercise of examining loan files to ascertain whether the loans conformed to the representations and warranties, we submit nonconforming loans for repurchase to the contractual counterparty bearing the repurchase obligation, which is typically the transaction sponsor. To effect a repurchase, depending on the transaction, the sponsor is obligated to repurchase the loan at (a) for loans which have not been liquidated or charged off, either (i) the current unpaid principal balance of the loan, (ii) the current unpaid principal balance plus accrued unpaid interest, or (iii) the current unpaid principal balance plus accrued interest plus unreimbursed servicer advances/expenses and/or trustee expenses resulting from the breach of representations and warranties that trigger the repurchase, and (b) for loans that have already been liquidated or charged-off, the amount of the realized loss (which in certain cases may exclude accrued unpaid interest). In cases where loans are repurchased by a sponsor, the effect is typically to offset current period losses and then to increase the over-collateralization of the securitization, depending on the extent of loan repurchases and the structure of the securitization. Specifically, the repurchase price is paid by the sponsor to the securitization trust which holds the loan. The cash becomes an asset of the trust, replacing the loan that was repurchased by the sponsor. On a monthly basis the cash received related to loan repurchases by the sponsor is aggregated with cash collections from the underlying mortgages and applied in accordance with the trust indenture payment waterfall. This payment waterfall typically includes principal and interest payments to the note holders, various expenses of the trust and reimbursements to Ambac, as financial guarantor, for previously paid claims. Notwithstanding the reimbursement of previous claim payments, to the extent there continues to be insufficient cash in the waterfall in the current month to make scheduled principal and interest payments to the note holders, Ambac is required to make additional claim payments to cover this shortfall. Ambac may also receive payments directly from transaction sponsors in settlement of their repurchase obligations pursuant to negotiated settlement agreements or otherwise as a result of related litigation. While the obligation by sponsors to repurchase loans with material breaches is clear, generally the sponsors have not honored those obligations without actual or threatened litigation. Ambac has utilized the results of the above described loan file examinations to make demands for loan repurchases from sponsors or their successors and, in certain instances, as a part of the basis for litigation. Ambac’s approach to resolving these disputes has included negotiating with individual sponsors at the transaction level and in some cases at the individual loan level and has resulted in the repurchase of some loans. Ambac has initiated and will continue to pursue lawsuits seeking compliance with the repurchase obligations in the securitization documents. Ambac has performed the above-mentioned, detailed examinations on a variety of second-lien and first-lien transactions that have experienced exceptionally poor performance. However, the loan file examinations and related estimated recoveries we have reviewed and recorded to date have been limited to only those transactions whose sponsors (or their successors) are subsidiaries of large financial institutions, all of which carry an investment grade rating from at least one nationally recognized rating agency, or are otherwise deemed to have the financial wherewithal to live up to their repurchase obligations. While our contractual recourse is generally to the sponsor/subsidiary, rather than to the parent, each of these large institutions has significant financial resources and may have an ongoing interest in mortgage finance, and we therefore believe that the financial institution/parent would ultimately assume financial responsibility for these obligations if the sponsor/subsidiary is unable to honor its contractual obligations or pay a judgment that we may obtain in litigation. Additionally, in the case of successor institutions, we are not aware of any provisions that explicitly preclude or limit the successors’ ability to honor the obligations of the original sponsor. Certain successor financial institutions have made significant payments to certain claimants to settle breaches of representations and warranties perpetrated by sponsors that have been acquired by such financial institutions. For example, Ambac received a significant payment in 2016 from JP Morgan to settle RMBS-related litigation. As a result of these factors, we do not make significant adjustments to our estimated subrogation recoveries with respect to the credit risk of these sponsors or their successors. Our ability to realize RMBS R&W subrogation recoveries is subject to significant uncertainty, including risks inherent in litigation; collectability of such amounts from counterparties (and/or their respective parents and affiliates); timing of receipt of any such recoveries; intervention by OCI, which could impede our ability to take actions required to realize such recoveries; and uncertainty inherent in the assumptions used in estimating such recoveries. Failure to realize RMBS R&W subrogation recoveries for any reason or the realization of RMBS R&W subrogation recoveries materially below the amount recorded on Ambac's consolidated balance sheet would have a material adverse effect on our results of operations and financial condition and may result in adverse consequences such as impairing the ability of Ambac Assurance to honor its financial obligations; the initiation of rehabilitation proceedings against Ambac Assurance; decreased likelihood of Ambac Assurance delivering value to Ambac, through dividends or otherwise; and a significant drop in the value of securities issued and/or insured by Ambac or Ambac Assurance. The approach used to estimate RMBS R&W subrogation recoveries is based on obtaining loan files from the original pool and conducting loan file re-underwriting to derive a breach rate to be extrapolated to determine an estimated repurchase obligation. We limit the estimated repurchase obligation by ever-to-date incurred losses. Multiple probability-weighted scenarios are developed by applying various realization factors to the estimated repurchase obligation. The realization factors in these scenarios reflect Ambac’s own assumptions about the likelihood of outcomes based on all the information available to it including, but not limited to, (i) discussions with external legal counsel and their views on ultimate settlement and/or litigation outcomes, (ii) assessment of the strength of the specific case and (iii) experience in settling similar claims. The probability weightings are developed based on the unique facts and circumstances for each transaction. The sum of these probability-weighted scenarios represents the undiscounted RMBS R&W subrogation recovery, which is then discounted using a factor derived from a risk-free discount rate term structure that corresponds to the estimated date of each respective recovery. Student Loan Expected Loss Estimate The student loan insured portfolio consists of credits collateralized by private student loans. The calculation of loss reserves for our student loan portfolio involves evaluating numerous factors that can impact ultimate losses. The factor which contributes the greatest degree of uncertainty in ascertaining appropriate loss reserves is the long final legal maturity date of the insured bonds. Most of the student loan bonds which we insure were issued with original terms of 20 to 40 years until final maturity. Since our policy covers timely interest and ultimate principal payment, our loss projections must make assumptions for many factors covering a long time horizon. Key assumptions that will impact ultimate losses include, but are not limited to, the following: collateral performance (which is highly correlated to the economic environment); interest rates; operating risks associated with the issuer, servicers, special servicers, and administrators; investor appetite for tendering or commuting insured obligations and; as applicable, Ambac’s ability and willingness to commute policies. In addition, we consider in our student loan loss projections the potential impact, if any, of proposed or final regulatory actions or orders, including by the Consumer Financial Protection Bureau ("CFPB"), affecting our insured transactions. In evaluating our student loan portfolio, our losses are projected using a cash flow modeling approach. In order to project collateral performance under the cash flow approach, we use a default projection tool that constructs lifetime cohort default curves based on loan and deal-level historical performance data. To determine ultimate losses on the transactions, the cohort default curves are used to extrapolate future default behavior. Additionally, a regression-based model is used to estimate recoveries on defaulted loans. This regression-based recovery forecast is grounded in deal-level performance data. For the liabilities of the transaction which we insure, the transaction losses are then incorporated into a waterfall tool to develop loss estimates for our exposures in various base, upside and downside scenarios. We develop and assign probabilities to multiple cash flow scenarios based on each transaction’s unique characteristics. Probabilities assigned are based on available data related to the credit, information from contact with the issuer (if applicable), and any economic or market information that may impact the outcomes of the various scenarios being evaluated. Our base case usually projects deal performance out to maturity using expected loss assumptions. As appropriate, we also develop other cases that incorporate various upside and downside scenarios that may include changes to defaults and recoveries.
Debt, Policy	Long-Term Debt Long-term debt issued by Ambac is carried at par value less unamortized discount. Accrued interest and discount accretion on long-term debt is reported as Interest expense on the Consolidated Statements of Total Comprehensive Income (Loss). To the extent Ambac repurchases or redeems its long-term debt, such repurchases or redemptions may be settled for an amount different than the carrying value of the obligation. Any difference between the payment and carrying value of the obligation is reported in Net realized gains (losses) on extinguishment of debt on the Consolidated Statements of Total Comprehensive Income (Loss). For long-term debt issued by consolidated VIEs in which Ambac's variable interest arises from financial guarantees written by Ambac's subsidiaries ("FG VIEs"), we may elect to use the fair value option on an instrument by instrument basis. When the fair value option is elected, changes in the fair value of the FG VIEs' long-term debt is reported within Income (loss) on variable interest entities in the Consolidated Statements of Total Comprehensive Income (Loss), except for the portion of the total change in fair value of financial liabilities caused by changes in the instrument- specific credit risk which is presented separately in Other comprehensive income (loss). In cases where the fair value option has not been elected, the FG VIEs' long-term debt is carried at par less unamortized discount, with interest expense reported within Income (loss) on variable interest entities in the Consolidated Statements of Total Comprehensive Income (Loss).
Long Term Incentive and Stock Compensation Plan	Incentive Compensation Incentive compensation is a key component of our compensation strategy. Incentive compensation has two components: short term incentive compensation (consisting of an annual cash bonus and awards of deferred stock units for certain officers) and long term incentive plan awards (consisting of cash awards and restricted and performance stock units). Annual decisions with regard to incentive compensation are generally made in the first quarter of each year and are based on the prior year's performance for the Company, the employee and the employee's business unit. The Ambac 2013 Incentive Compensation Plan (the “Equity Plan”) provides for the granting of stock options, restricted stock, stock appreciation rights, restricted and performance units and other awards that are valued or determined by reference to Ambac's common stock to employees and directors. In March 2014, Ambac developed a long term incentive compensation plan (“LTIP”) as a sub-plan of the 2013 Plan. This LTIP allows for both cash and equity awards to US employees. Ambac recognizes compensation costs for all equity classified awards granted at fair value and records forfeitures for unvested shares only when they occur. The types of equity awards granted to employees are as follows: • Deferred stock units granted vest upon grant and will settle and convert to Ambac common stock annually over a two-year period ( 50% on the first anniversary of the grant date and 50% on the second anniversary of the grant date). The fair value of these grants is recognized as compensation expense on the date of grant since no future service is required. • Restricted stock units granted only require future service and accordingly the respective fair value is recognized as compensation expense over the relevant service period. • Performance stock units granted require both future service and achieving specified performance targets to vest and accordingly compensation costs are only recognized when the achievement of the performance conditions are considered probable. Once deemed probable, such compensation costs are recognized as compensation expense over the relevant service period. Compensation costs are initially based on the probable outcome of the performance conditions and adjusted for subsequent changes in the estimated or actual outcome each reporting period as necessary. Changes in the estimated or actual outcome of a performance condition are recognized by reflecting a retrospective adjustment to compensation cost in the current period. In 2015, Ambac UK's Board of Directors adopted a long term incentive plan which provides cash based performance awards to Ambac UK employees. Compensation costs are initially based on the probable outcome of the performance conditions and adjusted for subsequent changes in the estimated or actual outcome each reporting period as necessary.
Postretirement and Postemployment Benefits	Postretirement and Postemployment Benefits Ambac provides postretirement and postemployment benefits, including health and life benefits covering employees who meet certain age and service requirements. Ambac accounts for these benefits under the accrual method of accounting. Amounts related to the postretirement health benefits liability are established and charged to expense based on actuarial determinations.
Depreciation and Amortization	Depreciation and Amortization Depreciation of furniture and fixtures, certain information technology development costs and electronic data processing equipment is charged over the estimated useful lives of the respective assets, ranging from three to five years, using the straight-line method. Amortization of leasehold improvements is charged over the remaining term of the respective operating lease using the straight-line method.
Foreign Currency	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 Ambac'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 Ambac’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 (Loss) in Stockholders' Equity. Functional currencies 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 $12 , $(7) and $21 for the years ended December 31, 2019, 2018 and 2017 , of which $22 , $7 , and $(5) relate to investments, classified in Net realized investment gains (losses), $(10) , $2 , and $(2) relate to the remeasurement of premiums receivable, and $(1) , $(15) , and $29 relate to the remeasurement of loss reserves, classified in Loss and loss expenses, respectively. Foreign currency transaction 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.
Income Taxes	Income Taxes Ambac files a consolidated U.S. Federal income tax return with its subsidiaries. Ambac UK files tax returns in both the United Kingdom and Italy (for its Milan branch). Current tax assets and liabilities are recognized for taxes refundable or payable for the current year. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on current and deferred tax assets and liabilities of a change in tax rates is recognized in the period that includes the enactment date. In December 2017, the Tax Cut and Jobs Act ("TCJA") was enacted that introduced significant changes that impact U.S. corporate tax rates, business-related exclusions, and deductions and credits effective January 1, 2018. As such, we incorporated the effects of the TCJA in our current and deferred tax evaluation for the year ended December 31, 2017. The Income Taxes Topic of the ASC requires that companies assess whether valuation allowances should be established against their deferred tax assets based on the consideration of all available evidence using a ‘more likely than not” standard. In making such judgments, significant weight is given to evidence that can be objectively verified. The level of deferred tax asset recognition is influenced by management’s assessment of future profitability, which depends on the existence of sufficient taxable income within the carry forward periods available under the tax law.
Net Income Per Share	Net Income Per Share 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 employee and director compensation plans.
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.
Adoption of New Accounting Standards	Recently Adopted Accounting Standards Effective January 1, 2019 , Ambac adopted the following accounting standards: Equity-linked Instruments with Down Round Features In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260) and Derivatives and Hedging (Topic 815) - Accounting for Certain Financial Instruments with Down Round Features . Equity-linked instruments, such as warrants and convertible instruments may contain down round features that result in the strike price being reduced on the basis of the pricing of future equity offerings. Under the ASU, a down round feature will no longer require a freestanding equity-linked instrument (or embedded conversion option) to be classified as a liability that is remeasured at fair value through the income statement (i.e. marked-to-market). However, other features of the equity-linked instrument (or embedded conversion option) must still be evaluated to determine whether liability or equity classification is appropriate. Equity classified instruments are not marked-to-market. For earnings per share ("EPS") reporting, the ASU requires companies to recognize the effect of the down round feature only when it is triggered by treating it as a dividend and as a reduction of income available to common stockholders in basic EPS. Adoption of this ASU did not impact Ambac's financial statements. Premium Amortization on Callable Debt Securities In March 2017, the FASB issued ASU 2017-08, Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20) - Premium Amortization on Purchased Callable Debt Securities . The ASU shortens the amortization period for the premium on callable debt securities to the earliest call date. Under previous GAAP, a reporting entity generally amortized the premium as a yield adjustment over the contractual life (i.e. maturity) of the debt security and if that debt security is called, the entity would record a loss equal to the unamortized premium. The ASU does not change the accounting for callable debt securities held at a discount, which will continue to be amortized to maturity. Adoption of this ASU did not have a consequential impact on Ambac's financial statements. Leases In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) . This ASU was subsequently amended by ASU 2018-01, Land Easement Practical Expedient; ASU 2018-10, Codification Improvements to Topic 842; ASU 2018-11 , Targeted Improvements; ASU 2018-20, Narrow-Scope Improvements for Lessors; and ASU 2019-01 , Leases (Topic 842): Codification Improvements (collectively the "New Lease Standard") . The primary difference between previous GAAP and the New Lease Standard is the recognition of lease assets and lease liabilities for those leases classified as operating leases with a term longer than 12 months. For those operating leases, a lessee is required to: 1) recognize a right-of-use asset ("ROU") and a lease liability, initially measured at the present value of the lease payments, on the balance sheet, 2) recognize a single lease cost, calculated so that the cost is allocated over the lease term generally on a straight-line basis and 3) classify all cash payments within operating activities in the statement of cash flows. For leases classified as finance leases under the New Lease Standard, the balance sheet presentation and expense recognition pattern is similar to capital leases under previous GAAP. Under the transition guidance, a reporting entity must use a modified retrospective approach and may choose to initially apply the New Lease Standard either at (1) the beginning of the earliest comparative period presented, which is January 1, 2017 or (2) its effective date, which is January 1, 2019. If a reporting entity chooses the first option it must recast its comparative period financial statements and provide disclosures for those comparative periods. Ambac chose the second option and initially applied the New Lease Standard on January 1, 2019. Consequently financial information and disclosures were not provided for dates and periods prior to January 1, 2019. There are a number of optional practical expedients that were elected at transition. We elected the package of practical expedients, which permitted us not to reassess under the new standard our prior conclusions about lease identification, lease classification and initial direct costs. We also elected the hindsight practical expedient allowing us to use the benefit of hindsight in determining the probability of exercising any lessee options to extend or terminate the lease, or purchase the underlying asset. We did not use the practical expedient pertaining to land easements as it was not applicable to Ambac. The new new lease standard did not have a material effect on our financial statements. The most significant effects related to (1) the recognition of new ROU assets and lease liabilities on our balance sheet for our office and equipment operating leases of approximately $15 at transition and (2) providing significant new disclosures about our leasing activities. See Note 16. Leases for further information.

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies Recently Adopted and Recently Issued Accounting Standards (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
New Accounting Pronouncements, Policy [Policy Text Block]	Recently Adopted Accounting Standards Effective January 1, 2019 , Ambac adopted the following accounting standards: Equity-linked Instruments with Down Round Features In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260) and Derivatives and Hedging (Topic 815) - Accounting for Certain Financial Instruments with Down Round Features . Equity-linked instruments, such as warrants and convertible instruments may contain down round features that result in the strike price being reduced on the basis of the pricing of future equity offerings. Under the ASU, a down round feature will no longer require a freestanding equity-linked instrument (or embedded conversion option) to be classified as a liability that is remeasured at fair value through the income statement (i.e. marked-to-market). However, other features of the equity-linked instrument (or embedded conversion option) must still be evaluated to determine whether liability or equity classification is appropriate. Equity classified instruments are not marked-to-market. For earnings per share ("EPS") reporting, the ASU requires companies to recognize the effect of the down round feature only when it is triggered by treating it as a dividend and as a reduction of income available to common stockholders in basic EPS. Adoption of this ASU did not impact Ambac's financial statements. Premium Amortization on Callable Debt Securities In March 2017, the FASB issued ASU 2017-08, Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20) - Premium Amortization on Purchased Callable Debt Securities . The ASU shortens the amortization period for the premium on callable debt securities to the earliest call date. Under previous GAAP, a reporting entity generally amortized the premium as a yield adjustment over the contractual life (i.e. maturity) of the debt security and if that debt security is called, the entity would record a loss equal to the unamortized premium. The ASU does not change the accounting for callable debt securities held at a discount, which will continue to be amortized to maturity. Adoption of this ASU did not have a consequential impact on Ambac's financial statements. Leases In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) . This ASU was subsequently amended by ASU 2018-01, Land Easement Practical Expedient; ASU 2018-10, Codification Improvements to Topic 842; ASU 2018-11 , Targeted Improvements; ASU 2018-20, Narrow-Scope Improvements for Lessors; and ASU 2019-01 , Leases (Topic 842): Codification Improvements (collectively the "New Lease Standard") . The primary difference between previous GAAP and the New Lease Standard is the recognition of lease assets and lease liabilities for those leases classified as operating leases with a term longer than 12 months. For those operating leases, a lessee is required to: 1) recognize a right-of-use asset ("ROU") and a lease liability, initially measured at the present value of the lease payments, on the balance sheet, 2) recognize a single lease cost, calculated so that the cost is allocated over the lease term generally on a straight-line basis and 3) classify all cash payments within operating activities in the statement of cash flows. For leases classified as finance leases under the New Lease Standard, the balance sheet presentation and expense recognition pattern is similar to capital leases under previous GAAP. Under the transition guidance, a reporting entity must use a modified retrospective approach and may choose to initially apply the New Lease Standard either at (1) the beginning of the earliest comparative period presented, which is January 1, 2017 or (2) its effective date, which is January 1, 2019. If a reporting entity chooses the first option it must recast its comparative period financial statements and provide disclosures for those comparative periods. Ambac chose the second option and initially applied the New Lease Standard on January 1, 2019. Consequently financial information and disclosures were not provided for dates and periods prior to January 1, 2019. There are a number of optional practical expedients that were elected at transition. We elected the package of practical expedients, which permitted us not to reassess under the new standard our prior conclusions about lease identification, lease classification and initial direct costs. We also elected the hindsight practical expedient allowing us to use the benefit of hindsight in determining the probability of exercising any lessee options to extend or terminate the lease, or purchase the underlying asset. We did not use the practical expedient pertaining to land easements as it was not applicable to Ambac. The new new lease standard did not have a material effect on our financial statements. The most significant effects related to (1) the recognition of new ROU assets and lease liabilities on our balance sheet for our office and equipment operating leases of approximately $15 at transition and (2) providing significant new disclosures about our leasing activities. See Note 16. Leases for further information.
Basis of Presentation and Significant Accounting Policies [Text Block]	2. BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES Ambac’s consolidated financial statements have been prepared on the basis of U.S. generally accepted accounting principles (“GAAP”). The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, expenses and disclosures. Such estimates that are particularly susceptible to change are used in connection with certain fair value measurements, valuation of loss reserves for non-derivative insurance policies and the valuation allowance on the deferred tax asset, any of which individually could be material. 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. Refer to 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. AFG Unconsolidated Financial Information Financial information of AFG is presented in Schedule II to this Form 10-K as of December 31, 2019 and 2018 and for the years ended December 31, 2019, 2018 and 2017 . Investments in subsidiaries are accounted for using the equity method of accounting in Schedule II. Investments The Investments - Debt Securities Topic of the ASC requires that all debt instruments be classified in Ambac’s Consolidated Balance Sheets according to their purpose and, depending on that classification, be carried at either cost or fair market value. Ambac’s non-VIE debt investment portfolio is accounted for on a trade-date basis and consists primarily of investments in fixed income securities that are considered available-for-sale as defined by the Investments - Debt Securities Topic of the ASC. Available-for-sale debt securities are reported in the financial statements at fair value with unrealized gains and losses, net of deferred taxes, reflected in Accumulated Other Comprehensive Income (Loss) in Stockholders’ Equity and computed using amortized cost as the basis. For purposes of computing amortized cost, premiums and discounts are accounted for using the effective interest method over a future term of the security. For structured debt securities with a large underlying pool of homogenous loans, such as mortgage-backed and asset-backed securities, premiums and discounts are adjusted for the effects of actual and anticipated prepayments. For other fixed income securities, such as corporate and municipal bonds, discounts were amortized or accreted over the remaining term of the securities. Ambac adopted ASU 2017-08, Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20) - Premium Amortization on Purchased Callable Debt Securities, on January 1, 2019. ASU 2017-08 shortened the amortization period for the premium on callable debt securities to the earliest call date. Under previous GAAP, Ambac generally amortized the premium over the contractual life (i.e. maturity) of the debt security and if that debt security was called, we would record a loss equal to the unamortized premium. Ambac’s non-VIE investment portfolio also includes equity interests in pooled investment funds which are accounted for in accordance with the Investments - Equity Securities Topic of the ASC and reported as Other investments on the Consolidated Balance Sheet with income reported through Net investment income on the Statement of Total Comprehensive Income (Loss). Equity interests in the form of common stock or in-substance common stock are classified as trading securities and reported at fair value while limited partner interests in such funds are reported using the equity method. Fair value is based primarily on quotes obtained from independent market sources. When quotes are not available or cannot be reasonably corroborated, valuation models are used to estimate fair value. These models include estimates, made by management, which utilize current market information. The quotes received or modeled valuations could differ materially from amounts that would actually be realized in the market. Realized gains and losses on the sale of investments are determined on the basis of specific identification. VIE investments in fixed income securities are carried at fair value as they are either considered as available for sale securities or under the fair value option election. For additional information about VIE investments, including fair value by asset-type, see Note 3. Variable Interest Entities . Ambac has a formal impairment review process for fixed income available-for-sale securities in its investment portfolio. Ambac conducts a review each quarter to identify and evaluate investments that have indications of impairment that may be other than temporary in accordance with the Investments - Debt Securities Topic of the ASC. Factors considered to identify and assess securities for other than temporary impairment include: (i) fair values that have declined by 20% or more below amortized cost; (ii) market values that have declined by 5% or more but less than 20% below amortized cost for a continuous period of at least six months; (iii) recent downgrades by rating agencies; (iv) the financial condition of the issuer and financial guarantor, as applicable, and an analysis of projected defaults on the underlying collateral; (v) whether scheduled interest payments are past due; (vi) whether Ambac has the intent to sell the security; and (vii) whether it is more likely than not that Ambac will be required to sell a security before the anticipated recovery of its amortized cost basis. If we believe a decline in the fair value of a particular investment is temporary, we record the decline as an unrealized loss net of tax in Accumulated Other Comprehensive Income (Loss) in Stockholders’ Equity on our Consolidated Balance Sheets. If management either: (i) has the intent to sell its investment in a debt security or (ii) determines that the Company more likely than not will be required to sell the debt security before its anticipated recovery of the amortized cost basis less any current period credit impairment, then an other-than-temporary impairment charge is recognized in earnings, with the amortized cost of the security being written-down to fair value. If these conditions are not met, but it is determined that a credit loss exists, the credit impairment loss is recognized in earnings, and the other-than-temporary amount related to all other factors is recognized in other comprehensive income. For fixed income securities that have other-than-temporary impairments in a period, the previous amortized cost of the security less the amount of the other-than-temporary impairment recorded through earnings becomes the investment’s new amortized cost basis. Ambac accretes the new amortized cost basis to par or to the estimated future cash flows to be recovered over the expected remaining life of the security. The evaluation of securities for impairment is a quantitative and qualitative process, which is subject to risks and uncertainties and is intended to determine whether, and to what extent, declines in the fair value of investments should be recognized in current period earnings. The risks and uncertainties include changes in general economic conditions, the issuer’s or guarantor’s financial condition and/or future prospects, the impact of regulatory actions on the investment portfolio, the performance of the underlying collateral, the effects of changes in interest rates or credit spreads and the expected recovery period. With respect to Ambac insured securities owned, future cash flows used to measure credit impairment represents the sum of (i) the bond’s intrinsic cash flows and (ii) the estimated Ambac Assurance claim payments. Prior to the discharge and settlement of the Segregated Account's claim obligations on February 12, 2018, the estimate of Ambac's Segregated Account claim payments, including interest on Deferred Amounts, was an important consideration in the evaluation of other than temporary impairment as such payments were at the sole discretion of the Rehabilitator. Refer to Note 1. Background and Business Description for more information on the Segregated Account and the Segregated Account Rehabilitation Proceedings. 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 the factors noted above. If that judgment changes, Ambac may ultimately record a charge for other-than-temporary impairment in future periods. Net Premiums Gross premiums were received either upfront or in installments. For premiums received upfront, an unearned premium revenue (“UPR”) liability was established, which was initially recorded as the cash amount received. For installment premium transactions, a premium receivable asset and offsetting UPR liability was initially established in an amount equal to: (i) the present value of future contractual premiums due (the “contractual” method) or (ii) if the underlying insured obligation is a homogenous pool of assets which are contractually prepayable, the present value of premiums to be collected over the expected life of the transaction (the “expected” method). An appropriate risk-free rate corresponding to the weighted average life of each policy and currency is used to discount the future premiums contractually due or expected to be collected. For example, U.S. dollar exposures are discounted using U.S. Treasury rates while exposures denominated in a foreign currency are discounted using the appropriate risk-free rate for the respective currency. The weighted average risk-free rate at December 31, 2019 and 2018 , was 2.4% . and 2.7% , respectively, and the weighted average period of future premiums used to estimate the premium receivable at December 31, 2019 and 2018 , was 8.5 and 8.7 years , respectively. Insured obligations consisting of homogeneous pools for which Ambac uses expected future premiums to estimate the premium receivable include residential mortgage-backed securities ("RMBS"). As prepayment assumptions change for homogenous pool transactions, or if there is an actual prepayment for a “contractual” method installment transaction, the related premium receivable and UPR are adjusted in equal and offsetting amounts with no immediate effect on earnings using new premium cash flows and the then current risk-free rate corresponding to the initial weighted average life of the related policy. For both upfront and installment premium policies, premium revenues are earned over the life of the financial guarantee contract in proportion to the insured principal amount outstanding at each reporting date (referred to as the level-yield method). For installment paying policies, the premium receivable discount, equating to the difference between the undiscounted future installment premiums and the present value of future installment premiums, is accreted as premiums earned in proportion to the premium receivable balance at each reporting date. Additionally, the Company evaluates whether any premiums receivable are uncollectible at each balance sheet date and records an allowance for policies with a premium receivable impairment based on our expectation. Similar to gross premiums, premiums ceded to reinsurers were paid either upfront or in installments. For premiums paid upfront, a deferred ceded premium asset was established which is initially recorded as the cash amount paid. For installment premiums, a ceded premiums payable liability and offsetting deferred ceded premium asset were initially established in an amount equal to: i) the present value of future contractual premiums due or ii) if the underlying insured obligation is a homogenous pool of assets, the present value of expected premiums to be paid over the life of the transaction. An appropriate risk-free rate corresponding to the weighted average life of each policy and exposure currency is used to discount the future premiums contractually due or expected to be collected. Premiums ceded to reinsurers reduce the amount of premiums earned by Ambac from its financial guarantee insurance policies. For both upfront and installment premiums, ceded premiums written are primarily recognized in earnings in proportion to and at the same time as the related gross premium revenue is recognized. For premiums paid to reinsurers on an installment basis, Ambac records the present value of future ceding commissions as an offset to ceded premiums payable, using the same assumptions noted above for installment premiums. When a bond issue insured by Ambac has been retired early, typically due to an issuer call, any remaining UPR is recognized at that time to the extent the financial guarantee contract is legally extinguished, causing accelerated premium revenue. For installment premium paying transactions, we offset the recognition of any remaining UPR by the reduction of the related premium receivable to zero (as it will not be collected as a result of the retirement), which may cause negative accelerated premium revenue. Certain obligations insured by Ambac have been legally defeased whereby government securities are purchased by the issuer with the proceeds of a new bond issuance, or less frequently with other funds of the issuer, and held in escrow. The principal and interest received from the escrowed securities are then used to retire the Ambac-insured obligations at a future date either to their maturity date (a refunding) or a specified call date (a pre-refunding). Ambac has evaluated the provisions in policies issued on these obligations and determined those insurance policies have not been legally extinguished. For policies with refunding securities, premium revenue recognition is not impacted as the escrowed maturity date is the same as the previous legal maturity date. For policies with pre-refunding securities, the maturity date of the pre-refunded security has been shortened from its previous legal maturity. Although premium revenue recognition has not been accelerated in the period of the pre-refunding, it results in an increase in the rate at which the policy's remaining UPR is to be recognized. Loans Loans are reported at either their outstanding principal balance less unamortized discount or at fair value. • Loans not held by consolidated VIEs are reported at their outstanding principal balance less unamortized discount and are reported within Other assets on the Consolidated Balance Sheet. Interest income is earned using the effective interest method based upon interest accrued on the unpaid principal balance adjusted for accretion of discounts. A loan is considered impaired when, based on the financial condition of the borrower, it is probable that Ambac will be unable to collect all principal and interest due according to the contractual terms of the loan agreement. • Loans held by VIEs consolidated as required under the Consolidation Topic of the ASC are carried at fair value under the fair value option election with changes in fair value recorded in Income (loss) on variable interest entities on the Consolidated Statements of Total Comprehensive Income (Loss). Such loans are reported as Loans, at fair value within the Variable interest entity assets section of the Consolidated Balance Sheet. Derivative Contracts The Company has entered into derivative contracts both for trading purposes and to hedge certain economic risks inherent in its financial asset and liability portfolios. None of Ambac’s derivative contracts are designated as hedges under the Derivatives and Hedging Topic of the ASC. Ambac's derivatives consist primarily of interest rate swaps and futures contracts. • Ambac maintains a portfolio consisting primarily of interest rate swaps and futures contracts to economically hedge interest rate risk in the financial guarantee and investment portfolios. This portfolio also includes legacy interest rate swaps with asset-backed securitization issuers, states, municipalities and their authorities which were written in connection with their financings. Changes in fair value of these interest rate derivatives are recorded, along with changes in fair value of Ambac's remaining credit derivatives, within Net gains (losses) on derivative contracts on the Consolidated Statements of Total Comprehensive Income (Loss). • VIEs consolidated under the Consolidation Topic of the ASC entered into derivative contracts to meet specified purposes within their securitization structure. Changes in fair value of consolidated VIE derivatives are included within Income (loss) on variable interest entities on the Consolidated Statements of Total Comprehensive Income (Loss). All derivatives are recorded on the Consolidated Balance Sheets at fair value on a gross basis; assets and liabilities are netted by counterparty only when a legal right of offset exists. Variation payments on centrally cleared swaps and futures contracts are considered settlements of the associated derivative balances and are reflected as a reduction to derivative liabilities or assets on the Consolidated Balance Sheets. For other derivatives, Ambac has determined that the amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral may not be used to offset amounts due under the derivative instruments in the normal course of settlement. Therefore, such amounts are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement and are included in "Other assets" on the Consolidated Balance Sheets. Refer to Note 11. Derivative Instruments for further discussion of the Company’s use of derivative instruments and their impact of the consolidated financial statements. Refer to Note 9. Fair Value Measurements for further description of the methodologies used to determine the fair value of derivative contracts, including model inputs and assumptions where applicable. Insurance Intangible Asset Upon Ambac's emergence from bankruptcy in 2013, an insurance intangible asset was recorded which represented the difference between the fair value and aggregate carrying value of the financial guarantee insurance and reinsurance assets and liabilities. The carrying values of our financial guarantee insurance and reinsurance contracts continue to be reported and measured in accordance with their existing accounting policies. Pursuant to the Financial Services-Insurance Topic of the ASC, the insurance intangible is to be measured on a basis consistent with the related financial guarantee insurance and reinsurance contracts. The insurance intangible asset is amortized using a level-yield method based on par exposure of the related financial guarantee insurance or reinsurance contracts and is applied to groups of contracts with similar characteristics. Restricted Cash Cash that we do not have the right to use for general purposes is recorded as restricted cash in our consolidated balance sheets. Restricted cash includes (i) consolidated variable interest entity cash restricted to support the obligations of the consolidated VIEs and (ii) cash held by Ambac Assurance received from its investment in Secured Notes and pledged for the benefit of holders of Secured Notes (other than Ambac Assurance). Loss and Loss Expenses The loss and loss expense reserve (“loss reserve”) policy relates only to Ambac’s non-derivative insurance business for insurance policies issued to beneficiaries, including VIEs, for which we do not consolidate the VIE. Losses and loss expenses are based upon estimates of the ultimate aggregate losses inherent in the non-derivative financial guarantee portfolio as of the reporting date. The policy for derivative contracts is discussed in the “Derivative Contracts” section above. A loss reserve is recorded on the balance sheet on a policy-by-policy basis based upon the present value ("PV") of expected net claim cash outflows or expected net recovery cash inflows, discounted at risk-free rates. The estimate for future net cash flows consider the likelihood of all possible outcomes that may occur from missed principal and/or interest payments on the insured obligation. This estimate also considers future recoveries related to breaches of contractual representations and warranties by RMBS transaction sponsors, remediation strategies, excess spread and other contractual cash flows on public finance and structured finance transactions (including RMBS). Ambac’s approach to resolving disputes involving contractual breaches by transaction sponsors or other third parties has included negotiations and/or pursuing litigation. Ambac does not estimate recoveries for litigations where its sole claim is for fraudulent inducement, since any remedies under such claims would be non-contractual. • Net claim cash outflow policies represent contracts where the PV of expected cash outflows are greater than the PV of expected recovery cash inflows. For such policies, a “Loss and loss expense reserves” liability is recorded for the excess of the PV of expected net claim cash outflows over the unearned premium revenue. • Net recovery cash inflow policies represent contracts where the PV of expected recovery cash inflows are greater than the PV of expected claim cash outflows. For such policies, a “Subrogation recoverable” asset is recorded. The evaluation process for determining expected losses is subject to certain judgments based on our assumptions regarding the probability of default by the issuer of the insured security, probability of settlement outcomes (which may include commutation settlements, refinancing and/or other settlement outcomes) and expected severity of credits for each insurance contract. Ambac’s loss reserves are based on management’s ongoing review of the financial guarantee credit portfolio. Active surveillance of the insured portfolio enables Ambac’s Risk Management Group ("RMG") to track credit migration of insured obligations from period to period and update internal classifications and credit ratings for each transaction. Non-adversely classified credits are assigned a Class I rating while adversely classified credits are assigned a rating of Class IA through Class V. The criteria for an exposure to be assigned an adversely classified credit rating includes the deterioration of an issuer’s financial condition, underperformance of the underlying collateral (for collateral dependent transactions such as mortgage-backed or student loan securitizations), poor performance by the servicer of the underlying collateral and other adverse economic events or trends. The servicer of the underlying collateral of an insured securitization transaction is a consideration in assessing credit quality because the servicer’s performance can directly impact the performance of the related issue. For example, a servicer of a mortgage-backed securitization that does not remain current in its collection efforts could cause an increase in the delinquency and the potential for default of the underlying obligation. Similarly, loss severities increase when a servicer does not effectively handle loss mitigation activities such as (i) the advancing of delinquent principal and interest and of default related expenses which are deemed to be recoverable by the servicer, (ii) pursuit of loan charge-offs which maximize cash flows from the mortgage loan pool and (iii) foreclosure and real estate owned disposition strategies and timelines. All credits are assigned risk classifications by RMG using the following guidelines: CLASS I - “Fully Performing - Meets Ambac Criteria with Remote Probability of Claim” - Credits that demonstrate adequate security and structural protection with a strong capacity to pay interest, repay principal and perform as underwritten. Factors supporting debt service payment and performance are considered unlikely to change and any such change would not have a negative impact upon the fundamental credit quality. Through ongoing surveillance, Ambac may also designate Class I credits into one or more of the following categories: • Survey List - credits that may lack information or demonstrate a weakness but further deterioration is not expected. • Watch List - credits that demonstrate the potential for future material adverse development due to such factors as long-term uncertainty about a particular sector, a certain structural element or concern related to the issuer or transaction or the overall financial and economic sustainability. CLASS IA - “Potential Problem with Risks to be Dimensioned” - Credits that are fully current and monetary default or claims-payment are not anticipated. The payor’s or issuer’s financial condition may be deteriorating or the credits may lack adequate collateral. A structured financing may also evidence weakness in its fundamental credit quality as evidenced by its under-performance relative to its modeled projections at underwriting, issues related to the servicer’s ability to perform or questions about the structural integrity of the transaction. While certain of these credits may still retain an investment grade rating, they usually have experienced or are vulnerable to a ratings downgrade. Further investigation is required to dimension and correct any deficiencies. A complete legal review of documents may be required. An action plan should be developed with triggers for future classification changes upward or downward. CLASS II - “Substandard Requiring Intervention” - Credits whose fundamental credit quality has deteriorated to the point that timely payment of debt service may be jeopardized by adversely developing trends of a financial, economic, structural, managerial or political nature. No claim payment is currently foreseen but the probability of loss or claim payment over the life of the transaction is now existent (generally 10% or greater probability). Class II credits may be border-line or below investment grade (BBB- to B). Prompt and sustained action must be taken to execute a comprehensive loss mitigation plan and correct deficiencies. CLASS III - “Doubtful with Clear Potential for Loss” - Credits whose fundamental credit quality has deteriorated to the point that timely payment of debt service has been or will be jeopardized by adverse trends of a financial, economic, structural, managerial or political nature which, in the absence of positive change or corrective action, are likely to result in a loss. The probability of monetary default or claims paying over the life of the transaction is generally 50% or greater. Full exercise of all available remedial actions is required to avert or minimize losses. Class III credits will generally be rated below investment grade (B to CCC). CLASS IV - “Imminent Default or Defaulted” - Monetary default or claim payments have occurred or are expected imminently. Class IV credits are generally rated D. CLASS V - “Fully Reserved” - The credit has defaulted and payments have occurred. The claim payments are scheduled and known, reserves have been established to fully cover such claims, and no claim volatility is expected. The population of credits evaluated in Ambac’s loss reserve process are: (i) all adversely classified credits (Class IA through V) and ii) non-adversely classified credits which had an internal Ambac rating downgrade since the transaction’s inception. One of two approaches is then utilized to estimate losses to ultimately determine if a loss reserve should be established. The first approach is a statistical expected loss approach, which considers the likelihood of all possible outcomes. The “base case” statistical expected loss is the product of: (i) the par outstanding on the credit; (ii) internally developed default information (taking into consideration internal ratings and average life of an obligation); (iii) internally developed loss severities; and (iv) a discount factor. The loss severities and default information are based on rating agency information, are specific to each bond type and are established and approved by senior RMG officers. For certain credit exposures, Ambac’s additional monitoring, loss remediation efforts and probabilities of potential settlement outcomes may provide information relevant to adjust this estimate of “base case” statistical expected losses. Analysts may accept the “base case” statistical expected loss as the best estimate of expected loss or assign multiple probability weighted scenarios to determine an adjusted statistical expected loss that better reflects management’s view of a given transaction’s expected losses, as well as the potential for additional remediation activities (e.g., commutations). The second approach entails the use of cash-flow based models to estimate expected losses (future claims, net of potential recoveries, expected to be paid to the holder of the insured financial obligation). Ambac’s RMG group will consider the likelihood of all possible outcomes and develop appropriate cash flow scenarios. This approach can include the utilization of internal or third party models and tools to project future losses and resultant claim payment estimates. We utilize cash flow models for RMBS, student loan, Puerto Rico and other exposures. RMBS and student loan models use historical performance of the collateral pools in order to then derive future performance characteristics, such as default and voluntary prepayment rates, which in turn determine projected future claim payments. In other cases, such as many public finance exposures, including our Puerto Rico exposures, we do not specifically forecast resources available to pay debt service in the cash flow model itself. Rather, we consider the issuers’ overall ability and willingness to pay, including the fiscal, economic, legal and political framework. In this approach, a probability-weighted expected loss estimate is developed based on assigning probabilities to multiple claim payment scenarios and applying an appropriate discount factor. Additionally, we assign a probability to the issuer’s ability to refinance an insured issue, Ambac’s ability to execute a potential settlement (i.e., commutation) of the insurance policy, including the impact on future installment premiums, and/or other restructuring scenarios. The commutation scenarios and the related probabilities of occurrence vary by transaction, depending on our view of the likelihood of negotiating such a transaction with issuers and/or investors. The discount

Basis of Presentation and Sig_4

Basis of Presentation and Significant Accounting Policies Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2019
Schedule of Cash Flow Supplemental Information [Line Items]
Schedule of Supplemental Cash Flow Information [Table Text Block]	Supplemental Disclosure of Cash Flow Information Year Ended December 31, 2019 2018 2017 Cash paid during the period for: Income taxes $ 21 $ 35 $ 40 Interest on long-term debt and investment agreements 143 232 39 Non-cash financing activities: Increase in long-term debt in exchange for AMPS — 187 — Decrease in long-term debt as a result of an exchange for investment securities — — 55 Rehabilitation exit transaction discharge of all Deferred Amounts and cancellation of certain General Account Surplus Notes — 1,919 — December 31, 2019 2018 2017 Reconciliation of cash, cash equivalents, and restricted cash reported within the Consolidated Balance Sheets to the Consolidated Statements of Cash Flow: Cash and cash equivalents $ 24 $ 63 $ 624 Restricted cash 55 19 — Variable Interest Entity Restricted cash 2 1 1 Total cash, cash equivalents, and restricted cash shown on the Consolidated Statements of Cash Flows 81 83 625
Cash Flow, Supplemental Disclosures [Text Block]	Supplemental information related to leases is as follows: Year Ended December 31, 2019 Cash paid for amounts included in the measurement of operating lease liabilities $ 6 Right-of-use assets obtained in exchange for operating lease liabilities (non-cash) (1) 30 (1) Includes right-of-use assets of $14 for the year ended December 31, 2019 for leases which existed prior to the New Lease Standard implementation date of January 1, 2019.

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	12 Months Ended
	Dec. 31, 2019
Variable Interest Entity Not Primary Beneficiary Table [Line Items]
Schedule of Variable Interest Entities Assets and Liabilities [Table Text Block]	The following schedule details the components of Income (loss) on variable interest entities for the affected periods: Year ended December 31, 2019 2018 2017 Net change in fair value of VIE assets and liabilities reported under the fair value option $ 13 $ 3 $ 20 Less: Credit risk changes of fair value option long-term debt reported through other comprehensive income (loss) — (1 ) — Net change in fair value of VIE assets and liabilities reported in earnings 14 2 20 Investment income on available-for-sale securities 10 — — Net realized investment gains (losses) on available-for-sale securities 13 — — Interest expense on long-term debt carried at par less unamortized cost (11 ) — — 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 $ 38 $ 3 $ 20
Variable Interest Entity Not Primary Beneficiary Table [Table Text Block]	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 December 31, 2019 and 2018 : Carrying Value of Assets and Liabilities Maximum (1) Insurance (2) Insurance (3) Net Derivative (4) 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 December 31, 2018: Global structured finance: Collateralized debt obligations $ 10 $ — $ — $ — Mortgage-backed—residential 6,713 1,859 547 — Other consumer asset-backed 1,701 15 238 — Other commercial asset-backed 873 21 12 — Other 2,123 53 301 7 Total global structured finance 11,420 1,949 1,098 7 Global public finance 24,146 309 335 (1 ) Total $ 35,566 $ 2,258 $ 1,434 $ 6 (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.
Components of VIE Gain (Loss) [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: December 31, 2019 2018 ASSETS: Ambac UK Ambac Assurance Total VIEs Ambac UK Ambac Assurance Total VIEs Fixed income securities, at fair value: Corporate obligations, fair value option $ 2,957 $ — $ 2,957 $ 2,737 $ — $ 2,737 Municipal obligations, available-for-sale (1) — 164 164 — — — Total FG VIE fixed income securities, at fair value 2,957 164 3,121 2,737 — 2,737 Restricted cash 1 1 2 1 — 1 Loans, at fair value (2) 3,108 — 3,108 4,288 — 4,288 Derivative assets 52 — 52 66 — 66 Other assets 1 2 3 1 — 1 Total FG VIE assets $ 6,119 $ 167 $ 6,286 $ 7,093 $ — $ 7,093 LIABILITIES: Accrued interest payable $ 1 $ — $ 1 $ 1 $ — $ 1 Long-term debt: Long-term debt, at fair value (3) 4,351 — 4,351 5,269 — 5,269 Long-term debt, at par less unamortized discount — 203 203 — — — Total long-term debt 4,351 203 4,554 5,269 — 5,269 Derivative liabilities 1,657 — 1,657 1,712 — 1,712 Total FG VIE liabilities $ 6,009 $ 203 $ 6,212 $ 6,981 $ — $ 6,981 Number of FG VIEs consolidated 6 1 7 7 — 7 (1) Available-for-sale securities consist of municipal obligations with an amortized cost basis of $139 and aggregate gross unrealized gains and (losses) of $25 at December 31, 2019 . All such securities had contractual maturities due after ten years as of December 31, 2019 . (2) The unpaid principal balances of loan assets carried at fair value were $2,618 as of December 31, 2019 and $3,418 as of December 31, 2018 . (3) The unpaid principal balances of long-term debt carried at fair value were $3,800 as of December 31, 2019 and $4,553 as of December 31, 2018 .

Comprehensive Income (Tables)

Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2019
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 (loss) 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 Year Ended December 31, 2019: Beginning Balance $ 86 $ 9 $ (142 ) $ (2 ) $ (49 ) Other comprehensive income (loss)before reclassifications 142 1 26 — 168 Amounts reclassified from accumulated other comprehensive income (loss) (76 ) (1 ) — — (78 ) Net current period other comprehensive income (loss) 65 (1 ) 26 — 91 Balance at December 31, 2019 $ 151 $ 8 $ (116 ) $ (2 ) $ 42 Year ended December 31, 2018: Beginning Balance $ 31 $ 11 $ (94 ) $ — $ (52 ) Adjustments to opening balance, net of taxes (3) — — — (3 ) (3 ) Adjusted balance, beginning of period 31 11 (94 ) (3 ) (55 ) Other comprehensive income before reclassifications 136 (1 ) (48 ) — 87 Amounts reclassified from accumulated other comprehensive income (81 ) (1 ) — 1 (81 ) Net current period other comprehensive income (loss) 55 (2 ) (48 ) 1 6 Balance at December 31, 2018 $ 86 $ 9 $ (142 ) $ (2 ) $ (49 ) (1) All amounts are net of tax and noncontrolling interest. Amounts in parentheses indicate reductions to Accumulated Other Comprehensive Income. (2) Represents the ch anges in fair value attributable to instrument-specific credit risk of liabilities for which the fair value option is elected. (3) Beginning in 2018, credit risk changes of fair value option liabilities are reflected as a component of Accumulated Other Comprehensive Income pursuant to the adoption of ASU 2016-01. Refer to Note 2. Basis of Presentation and Significant Accounting Policies for further information regarding this change.
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 for the affected periods: Details about Accumulated Other Comprehensive Income Components Amount Reclassified from Accumulated Affected Line Item in the Consolidated Statement of Total Comprehensive Income Year Ended December 31, 2019 2018 Unrealized Gains (Losses) on Available-for-Sale Securities $ (81 ) $ (82 ) Net realized investment gains (loses) 4 1 Provision for income taxes $ (76 ) $ (81 ) Net of tax and noncontrolling interest Amortization of Postretirement Benefit Prior service cost $ (1 ) $ (1 ) Other income Actuarial gains (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 $ — $ 1 Credit risk changes of fair value option liabilities — — Provision for income taxes — 1 Net of tax and noncontrolling interest Total reclassifications for the period $ (78 ) $ (81 ) Net of tax and noncontrolling interest

Net Income Per Share (Tables)

Net Income Per Share (Tables)	12 Months Ended
	Dec. 31, 2019
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: Year Ended December 31, 2019 2018 2017 Basic weighted average shares outstanding 45,954,908 45,665,883 45,367,932 Effect of potential dilutive shares (1) : Warrants — 441,104 — Stock options — — — Restricted stock units — 77,572 — Performance stock units (2) — 375,276 — Diluted weighted average shares outstanding 45,954,908 46,559,835 45,367,932 Anti-dilutive shares excluded from the above reconciliation Stock options 16,667 16,667 126,667 Warrants 4,877,783 — 4,053,670 Restricted stock units 249,263 — 68,654 Performance stock units (2) 872,258 — 322,943 (1) For the years ended December 31, 2019 and 2017 , 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 Guarantees in Force_2

Financial Guarantees in Force (Tables)	12 Months Ended
	Dec. 31, 2019
Guarantees [Abstract]
Schedule of Financial Guarantee Insurance In Force By Bond Type	As of December 31, 2019 and 2018 , the guarantee portfolio was diversified by type of guaranteed bond as shown in the following table: Net Par Outstanding December 31, 2019 2018 Public Finance: Housing revenue (1) $ 5,991 $ 6,159 Lease and tax-backed revenue 5,102 7,565 General obligation 3,011 4,214 Higher education 885 1,168 Transportation revenue 855 1,754 Utility revenue 768 1,178 Other 1,041 1,404 Total Public Finance 17,653 23,442 Structured Finance: Mortgage-backed and home equity 4,423 5,510 Investor-owned utilities 1,675 1,754 Student loan 769 934 Structured Insurance 395 1,365 Asset-backed and other 246 384 Total Structured Finance 7,508 9,947 International Finance: Sovereign/sub-sovereign 5,264 5,250 Investor-owned and public utilities 4,436 4,499 Asset-backed and other 1,625 2,176 Transportation 1,532 1,613 Total International Finance 12,857 13,538 Total $ 38,018 $ 46,927 (1) Includes $5,654 and $5,759 of Military Housing net par at December 31, 2019 and 2018 , respectively.
Schedule of International Financial Guarantee Insurance In Force Portfolio By Location Of Risk	As of December 31, 2019 and 2018 , the International Finance guaranteed portfolio by location of risk was as outlined in the table below: Net Par Outstanding December 31, 2019 2018 United Kingdom $ 10,593 $ 10,965 Italy 767 811 Austria 674 712 Australia 382 384 France 303 312 Other international (1) 138 354 Total International Finance $ 12,857 $ 13,538 (1) Other international may include components of U.S. exposure.

Financial Guarantee Insurance_2

Financial Guarantee Insurance Contracts (Tables)	12 Months Ended
	Dec. 31, 2019
Insurance [Line Items]
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: Year Ended December 31, 2019 2018 2017 United States $ 55 $ 88 $ 134 United Kingdom 17 19 33 Other international (6 ) 5 8 Total $ 66 $ 111 $ 175
Summary of Gross Premium Receivable Roll-Forward (Direct and Assumed Contracts)	Below is the gross premium receivable roll-forward (direct and assumed contracts) for the affected periods: Year Ended December 31, 2019 2018 2017 Beginning premium receivable $ 495 $ 586 $ 661 Premium receipts (48 ) (56 ) (82 ) Adjustments for changes in expected and contractual cash flows (1) (38 ) (42 ) (30 ) Accretion of premium receivable discount 11 15 16 Deconsolidation of certain VIEs 3 — — Changes to uncollectable premiums (2 ) 2 — Other adjustments (including foreign exchange) (6 ) (10 ) 21 Ending premium receivable (2) $ 416 $ 495 $ 586 (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. At December 31, 2019, 2018 and 2017 premium receivables include British Pounds of $129 ( £97 ), $131 ( £103 ) and $152 ( £112 ), respectively, and Euros of $26 ( €23 ), $31 ( €27 ) and $36 ( €30 ), respectively.
Schedule Of Reinsurance Recoverable And Provision By Category Of Reinsurer [Table Text Block]	The following table represents the percentage ceded to reinsurers and unsecured reinsurance recoverable at December 31, 2019 . Reinsurers Percentage Ceded Par Net Unsecured Reinsurance Recoverable (1) Assured Guaranty Re Ltd 47% $ — Build America Mutual Assurance Company (2) 42 36 Assured Guaranty Corporation 8 5 Sompo Japan Nipponkoa Insurance, Inc. 3 — Total 100% $ 41 (1) Represents reinsurance recoverables on paid and unpaid losses and deferred ceded premiums, net of ceded premium payables due to reinsurers, letters of credit, and collateral posted for the benefit of Ambac Assurance. (2) Build America Mutual Assurance Company has an S&P rating of AA.
Effect of Reinsurance on Premiums Written and Earned	The effect of reinsurance on premiums written and earned was as follows: Year Ended December 31, Direct Assumed Ceded (1) Net Premiums 2019: Written $ (28 ) $ — $ 31 $ (60 ) Earned 75 — 10 66 2018: Written $ (24 ) $ — $ 17 $ (41 ) Earned 119 — 8 111 2017: Written $ (14 ) $ — $ (2 ) $ (12 ) Earned 190 — 15 175 (1) Includes ceded premium activity related to the execution of reinsurance transactions in the years ended December 31, 2019 and 2018.
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 December 31, 2019 : Future Premiums Collected (1) Future to be Earned Net of (2) Three months ended: March 31, 2020 $ 14 $ 10 June 30, 2020 11 10 September 30, 2020 10 10 December 31, 2020 9 10 Twelve months ended: December 31, 2021 37 36 December 31, 2022 36 34 December 31, 2023 34 32 December 31, 2024 33 30 Five years ended: December 31, 2029 143 124 December 31, 2034 102 82 December 31, 2039 47 38 December 31, 2044 22 14 December 31, 2049 9 5 December 31, 2054 1 1 Total $ 508 $ 436 (1) Future premiums to be collected are undiscounted 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 . This results in a different premium receivable balance than if expected lives were considered. If installment paying policies are retired or prepay early, premiums reflected in the premium receivable asset and amounts reported in the above table for such policies may not be collected. Future premiums to be earned also considers the use of contractual lives for many bond types which do not have homogeneous pools of underlying collateral, which may result in different unearned premium than if expected lives were considered. If those bonds types are retired early, premium earnings may be negative in the period of call or refinancing.
Schedule of Loss And Loss Expense Reserves And Subrogation Recoverable Table [Table Text Block]	Below are the components of the Loss and loss expense reserves liability and the Subrogation recoverable asset at December 31, 2019 and 2018 : Present Value of Expected Unearned Gross Loss and Balance Sheet Line Item Claims and Recoveries December 31, 2019: Loss and loss expense reserves $ 1,835 $ (233 ) $ (54 ) $ 1,548 Subrogation recoverable 131 (2,160 ) — (2,029 ) Totals $ 1,966 $ (2,394 ) $ (54 ) $ (482 ) December 31, 2018: Loss and loss expense reserves $ 2,246 $ (314 ) $ (107 ) $ 1,826 Subrogation recoverable 176 (2,109 ) — (1,933 ) Totals $ 2,422 $ (2,422 ) $ (107 ) $ (107 )
Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance	Below is the loss and loss expense reserve roll-forward, net of subrogation recoverable and reinsurance, for the affected periods. Year Ended December 31, 2019 2018 2017 Beginning gross loss and loss expense reserves $ (107 ) $ 4,114 $ 3,696 Reinsurance recoverable 23 41 31 Beginning balance of net loss and loss expense reserves (130 ) 4,073 3,665 Losses and loss expenses (benefit) incurred: Current year 1 5 6 Prior years (1) 12 (228 ) 507 Total (2)(3) 13 (224 ) 513 Loss and loss expenses (recovered) paid: Current year — — 1 Prior years (1) 318 3,963 133 Total 318 3,964 134 Foreign exchange effect (1 ) (15 ) 29 Ending net loss and loss expense reserves (436 ) (130 ) 4,073 Impact of VIE consolidation (72 ) — — Reinsurance recoverable (4) 26 23 41 Ending gross loss and loss expense reserves (482 ) (107 ) 4,114 (1) 2018 loss and loss expenses (recovered) paid includes the settlement of Deferred Amounts and Interest Accrued on Deferred Amounts in the amount of $3,000 and $857 , respectively in connection with the Rehabilitation Exit Transactions through a combination of cash, surplus notes and secured notes. 2018 loss and loss expenses incurred includes a $288 loss and loss expense benefit on these settled Deferred Amounts. (2) Total losses and loss expenses (benefit) includes $(7) , $(2) and $20 for the years ended December 31, 2019, 2018 and 2017 , respectively, related to ceded reinsurance. (3) Ambac records the impact of estimated recoveries related to securitized loans in RMBS transactions that breached certain representations and warranties within losses and loss expenses (benefit). The losses and loss expense (benefit) incurred associated with changes in estimated representation and warranty recoveries for the year ended December 31, 2019, 2018 and 2017 was $42 , $62 and $72 , respectively. (4) 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 $0 , $1 and $0 as of December 31, 2019, 2018 and 2017 , 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	tables below summarize information related to policies currently included in Ambac’s loss and loss expense reserves or subrogation recoverable at December 31, 2019 and 2018 . 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 December 31, 2019 and 2018 was 2.1% and 2.8% , respectively. 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 representation and warranty ("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. Surveillance Categories as of December 31, 2018 I IA II III IV V Total Number of policies 21 28 18 16 145 3 231 Remaining weighted-average contract period (in years) (1) 9 19 9 22 14 3 16 Gross insured contractual payments outstanding: Principal $ 917 $ 708 $ 623 $ 1,705 $ 5,407 $ 43 $ 9,403 Interest 488 632 293 6,979 2,178 13 10,583 Total $ 1,404 $ 1,340 $ 916 $ 8,685 $ 7,585 $ 57 $ 19,986 Gross undiscounted claim liability $ 4 $ 64 $ 36 $ 992 $ 2,296 $ 57 $ 3,448 Discount, gross claim liability — (13 ) (3 ) (434 ) (638 ) (4 ) (1,092 ) Gross claim liability before all subrogation and before reinsurance $ 4 $ 51 $ 33 $ 558 $ 1,658 $ 52 $ 2,356 Less: Gross RMBS subrogation (2) $ — $ — $ — $ — $ (1,810 ) $ — $ (1,810 ) Discount, RMBS subrogation — — — — 39 — 39 Discounted RMBS subrogation, before reinsurance — — — — (1,771 ) — (1,771 ) Less: Gross other subrogation (3) — (11 ) — (137 ) (625 ) (13 ) (785 ) Discount, other subrogation — 7 — 67 55 4 133 Discounted other subrogation, before reinsurance — (3 ) — (70 ) (570 ) (9 ) (652 ) Gross claim liability, net of all subrogation and discounts, before reinsurance $ 4 $ 47 $ 33 $ 489 $ (682 ) $ 43 $ (66 ) Less: Unearned premium revenue $ (1 ) $ (10 ) $ (5 ) $ (36 ) $ (54 ) $ — $ (107 ) Plus: Loss expense reserves 1 4 3 (6 ) 63 — 66 Gross loss and loss expense reserves $ 4 $ 41 $ 30 $ 446 $ (672 ) $ 43 $ (107 ) Reinsurance recoverable reported on Balance Sheet (4) $ — $ 7 $ 4 $ 26 $ (15 ) $ — $ 23 (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 $23 related to future loss and loss expenses and $1 related to presented loss and loss expenses and subrogation.
Summary of Rollforward of RMBS Subrogation, by Estimation Approach	w is the rollforward of RMBS R&W subrogation for the affected periods: Year ended December 31, 2019 2018 2017 Discounted RMBS subrogation recovery (gross of reinsurance) at beginning of year $ 1,771 $ 1,834 $ 1,907 All other changes (1) (43 ) (64 ) (73 ) Discounted RMBS subrogation recovery (gross of reinsurance) at end of year $ 1,727 $ 1,771 $ 1,834 (1) All other changes which may impact RMBS R&W subrogation recoveries include changes in actual or projected collateral performance, changes in the creditworthiness of a sponsor and the projected timing of recoveries. All other changes may also include estimates of potential sponsor settlements that may not have been subject to a sampling approach or have been executed, but the settlement amounts have not yet been received. Those that have not been subject to a sampling approach are not material to Ambac’s financial results and therefore are included in this table.
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 $ 45 2021 39 2022 36 2023 33 2024 30 Thereafter 244 (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 as described in Note 2. Basis of Presentation and Significant Accounting Policies . 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 from the amounts provided in the table above. (2) The weighted-average amortizations period is 7.6 years .

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
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 December 31, 2019 and 2018 , 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: Level 1 Level 2 Level 3 December 31, 2019: 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, 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 Carrying Total Fair Fair Value Measurements Categorized as: Level 1 Level 2 Level 3 December 31, 2018: Financial assets: Fixed income securities: Municipal obligations $ 880 $ 880 $ — $ 880 $ — Corporate obligations 1,278 1,278 — 1,278 — Foreign obligations 31 31 30 1 — U.S. government obligations 94 94 94 — — Residential mortgage-backed securities 259 259 — 259 — Collateralized debt obligations 131 131 — 131 — Other asset-backed securities 442 442 — 370 72 Short term investments 430 430 305 125 — Other investments (1) 391 367 71 — 16 Cash and cash equivalents and restricted cash 82 82 53 30 — Derivative assets: Interest rate swaps—asset position 59 59 — 12 47 Other assets - equity in sponsored VIE 5 5 — — 5 Other assets-loans 10 12 — — 12 Variable interest entity assets: Fixed income securities: Corporate obligations 2,737 2,737 — — 2,737 Restricted cash 1 1 1 — — Loans 4,288 4,288 — — 4,288 Derivative assets; Currency swaps-asset position 66 66 — 66 — Total financial assets $ 11,186 $ 11,164 $ 554 $ 3,153 $ 7,177 Financial liabilities: Long term debt, including accrued interest $ 3,305 $ 3,260 $ — $ 2,909 $ 351 Derivative liabilities: Credit derivatives 1 1 — — 1 Interest rate swaps—liability position 72 72 — 72 — Futures contracts 3 3 3 — Liabilities for net financial guarantees written (2) (718 ) 559 — — 559 Variable interest entity liabilities: Long-term debt (includes $5,269 at fair value) 5,269 5,269 — 5,052 217 Derivative liabilities: Interest rate swaps—liability position 1,712 1,712 — 1,712 — Total financial liabilities $ 9,644 $ 10,876 3 9,745 1,128 (1) Excluded from the fair value measurement categories in the table above are investment funds of $296 and $280 as of December 31, 2019 and 2018 , respectively, which are measured using NAV per share 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 2019 , 2018 and 2017. 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 Year Ended December 31, 2019 Investments Other (1) Derivatives Investments Loans Long-term Total Balance, beginning of period $ 72 $ 5 $ 46 $ 2,737 $ 4,288 $ (217 ) $ 6,930 Total gains/(losses) realized and unrealized: Included in earnings 2 (2 ) 25 138 287 (15 ) 436 Included in other comprehensive income — — — 116 74 8 199 Purchases — — — — — — — Issuances — — — — — — — Sales — — — — — — — Settlements (2 ) — (5 ) (35 ) (690 ) — (731 ) Transfers into Level 3 — — — — — — — Transfers out of Level 3 — — — — — — — Deconsolidation of VIEs — — — — (851 ) 223 (627 ) Balance, end of period $ 72 $ 3 $ 66 $ 2,957 $ 3,108 $ — $ 6,207 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 $ — $ (2 ) $ 25 $ 138 $ 215 $ — $ 376 (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 Year Ended December 31, 2018 Investments Other Derivatives Investments Loans Long-term Total Balance, beginning of period $ 809 $ 6 $ 61 $ 2,914 $ 11,529 $ (2,758 ) $ 12,561 Total gains/(losses) realized and unrealized: Included in earnings 36 (1 ) (9 ) 16 (201 ) 189 30 Included in other comprehensive income (53 ) — — (158 ) (470 ) 91 (590 ) Purchases — — — — — — — Issuances — — — — — — — Sales — — — — — — — Settlements (714 ) — (6 ) (35 ) (624 ) 23 (1,356 ) Transfers out of Level 3 (5 ) — — — — — (5 ) Deconsolidations of VIEs — — — — (5,946 ) 2,237 (3,709 ) Balance, end of period $ 72 $ 5 $ 46 $ 2,737 $ 4,288 $ (217 ) $ 6,930 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 ) $ (10 ) $ 16 $ (63 ) $ 47 $ (11 ) Level-3 Financial Assets and Liabilities Accounted for at Fair Value VIE Assets and Liabilities Year Ended December 31, 2017 Investments Other Derivatives Investments Loans Long-term Total Balance, beginning of period $ 763 $ 7 $ (100 ) $ 2,623 $ 10,659 $ (2,582 ) $ 11,369 Total gains/(losses) realized and unrealized: Included in earnings 65 (1 ) 63 71 550 35 783 Included in other comprehensive income 6 — — 253 1,004 (254 ) 1,010 Purchases 36 — — — — — 36 Issuances — — — — — — — Sales (79 ) — — — — — (79 ) Settlements (30 ) — 98 (33 ) (684 ) 44 (605 ) Transfers into Level 3 48 — — — — — 48 Balance, end of period $ 809 $ 6 $ 61 $ 2,914 $ 11,529 $ (2,758 ) $ 12,561 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 ) $ 9 $ 71 $ 547 $ 37 $ 662 The tables below provide roll-forward information by class of investments and derivatives measured using si gnificant unobservable inputs. Level-3 Investments by Class 2019 2018 Year Ended December 31, Other Asset Non-Agency RMBS Total Other Asset Non-Agency RMBS Total Balance, beginning of period $ 72 $ — $ 72 $ 73 $ 736 $ 809 Total gains/(losses) realized and unrealized: Included in earnings 2 — 2 1 35 36 Included in other comprehensive income — — — (1 ) (52 ) (53 ) Purchases — — — — — — Issuances — — — — — — Sales — — — — — — Settlements (2 ) — (2 ) (1 ) (713 ) (714 ) Transfers out of Level 3 — — — — (5 ) (5 ) Balance, end of period $ 72 $ — $ 72 $ 72 $ — $ 72 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 $ — $ — $ — $ — $ — $ — Level-3 Investments by Class Year Ended December 31, 2017 Other Asset Non-Agency RMBS Total Balance, beginning of period $ 66 $ 697 $ 763 Total gains/(losses) realized and unrealized: Included in earnings 1 64 65 Included in other comprehensive income 6 — 6 Purchases — 36 36 Issuances — — — Sales — (79 ) (79 ) Settlements (1 ) (29 ) (30 ) Transfers into Level 3 — 48 48 Balance, end of period $ 73 $ 736 $ 809 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 $ — $ — $ — Level-3 Derivatives by Class 2019 2018 Year Ended December 31, Interest Credit Total Interest Credit Total Balance, beginning of period $ 47 $ (1 ) $ 46 $ 61 $ (1 ) $ 61 Total gains/(losses) realized and unrealized: Included in earnings 24 2 25 (9 ) (1 ) (9 ) Purchases — — — — — — Issuances — — — — — — Sales — — — — — — Settlements (4 ) — (5 ) (5 ) — (6 ) Balance, end of period $ 67 $ — $ 66 $ 47 $ (1 ) $ 46 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 $ 25 $ (9 ) $ (1 ) $ (10 ) Level-3 Derivatives by Class Year Ended December 31, 2017 Interest Credit Total Balance, beginning of period $ (85 ) $ (15 ) $ (100 ) Total gains/(losses) realized and unrealized: Included in earnings 46 16 63 Purchases — — — Issuances — — — Sales — — — Settlements 100 (2 ) 98 Balance, end of period $ 61 $ (1 ) $ 61 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 $ 7 $ 2 $ 9
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 Investment Income Net Gains Income (Loss) on Variable Interest Entities Other Year Ended December 31, 2019 Total gains (losses) included in earnings for the period $ 2 $ 25 $ 410 $ (2 ) Changes in unrealized gains (losses) relating to financial instruments still held at the reporting date — 25 353 (2 ) Year Ended December 31, 2018 Total gains (losses) included in earnings for the period $ 36 $ (9 ) $ 4 $ (1 ) Changes in unrealized gains (losses) relating to financial instruments still held at the reporting date — (10 ) — (1 ) Year Ended December 31, 2017 Total gains (losses) included in earnings for the period $ 65 $ 63 $ 656 $ (1 ) Changes in unrealized gains (losses) relating to financial instruments still held at the reporting date — 9 655 (1 )

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Equity Method Investments [Table Text Block]	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 at December 31, 2019 of $41 to private credit funds and $48 to a hedge fund. Class of Funds December 31, 2019 2018 Redemption Frequency Redemption Notice Period Real estate properties (1) $ 16 $ 16 quarterly 10 business days Hedge funds (2) 65 — quarterly 90 days High yield and leveraged loans (3) (8) 176 114 daily 0 - 30 days Private credit (4) 51 84 quarterly 180 days if permitted Insurance-linked investments (5) 3 29 fully redeemed none Equity market investments (6) (8) 55 44 daily 0 days Investment grade floating rate income (7) 66 63 weekly 0 days Total equity investments in pooled funds $ 432 $ 351 (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 within structured credit markets, including mortgage-backed securities, commercial real estate securities and loans, CLOs, REITs and asset backed securities. (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 includes investments in a range of instruments that include funds that have diversified exposure to global equity market returns through holdings of market index funds . (7) This class of funds includes investments in high quality floating rate debt securities including ABS and corporate floating rate notes (FRNs) as well as ultra-short term bonds and money market instruments. (8) High yield and leveraged loans products include $81 at December 31, 2019 and $27 at December 31, 2018 and equity market investments include $55 at December 31, 2019 and $44 at December 31, 2018 that have readily determinable fair values priced through pricing vendors.
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 fixed income investments, excluding VIE investments, at December 31, 2019 and 2018 were as follows: Amortized Gross Gross Estimated Non-Credit Other- (1) December 31, 2019 Fixed income securities: Municipal obligations $ 194 $ 22 $ — $ 215 $ — Corporate obligations (2) 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 $ — December 31, 2018 Fixed income securities: Municipal obligations $ 883 $ 14 $ 17 $ 880 $ — Corporate obligations (2) 1,289 6 17 1,278 — Foreign obligations 30 — — 31 — U.S. government obligations 94 1 1 94 — Residential mortgage-backed securities 222 38 1 259 — Collateralized debt obligations 133 — 2 131 — Other asset-backed securities 370 73 1 442 — 3,021 133 38 3,116 — Short-term 430 — — 430 — Total available-for-sale investments $ 3,451 $ 133 $ 38 $ 3,546 $ — (1) 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 as of December 31, 2019 and 2018 .
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 December 31, 2019 , by contractual maturity, were as follows: Amortized Estimated Due in one year or less $ 749 $ 749 Due after one year through five years 1,157 1,173 Due after five years through ten years 477 501 Due after ten years 145 160 2,528 2,583 Residential mortgage-backed securities 200 248 Commercial mortgage-backed securities 49 50 Collateralized debt obligations 147 146 Other asset-backed securities 263 287 Total $ 3,187 $ 3,314
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, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position, at December 31, 2019 and 2018 : 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 temporarily impaired securities $ 401 $ 4 $ 88 $ 1 $ 489 $ 5 Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross December 31, 2018 Fixed income securities: Municipal obligations $ 538 $ 16 $ 29 $ 1 $ 566 $ 17 Corporate obligations 307 9 190 9 497 17 Foreign obligations 1 — 5 — 6 — U.S. government obligations 6 — 58 — 64 1 Residential mortgage-backed securities 35 1 — — 35 1 Collateralized debt obligations 124 2 — — 124 2 Other asset-backed securities 14 — 77 1 91 1 1,024 27 360 11 1,384 38 Short-term 115 — — — 115 — Total temporarily impaired securities $ 1,139 $ 27 $ 360 $ 11 $ 1,499 $ 38
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 other-than-temporary impairments included in earnings for the affected periods: Year Ended December 31, 2019 2018 2017 Gross realized gains on securities $ 64 $ 111 $ 29 Gross realized losses on securities (5 ) (7 ) (19 ) Foreign exchange (losses) gains 22 7 (5 ) Net realized gains (losses) $ 81 $ 111 $ 5 Net other-than-temporary impairments (1) $ — $ (3 ) $ (20 ) (1) Other-than-temporary impairments exclude impairment amounts recorded in other comprehensive income under ASC Paragraph 320-10-65-1, which comprise non-credit related amounts on securities that are credit impaired but 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.
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	Year Ended December 31, 2019 2018 2017 Balance, beginning of period 12 67 52 Additions for credit impairments recognized on: Securities not previously impaired — 1 3 Securities previously impaired — — 12 Reductions for credit impairments previously recognized on: Securities that matured or were sold during the period (1 ) (56 ) — Balance, end of period 12 12 67
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, including the value of the financial guarantee, and weighted-average underlying rating, excluding the financial guarantee, of the insured securities at December 31, 2019 and 2018 , respectively: Municipal Corporate (3) Mortgage Total Weighted (1) (3) December 31, 2019: Ambac Assurance Corporation (2) $ 176 $ 535 $ 442 $ 1,153 B- National Public Finance Guarantee Corporation 11 — — 11 BBB- Total $ 187 $ 535 $ 442 $ 1,164 B- December 31, 2018: Ambac Assurance Corporation (2) $ 833 $ 656 $ 599 $ 2,089 CCC National Public Finance Guarantee Corporation 16 — — 16 BBB- Total $ 849 $ 656 $ 599 $ 2,105 CCC (1) Ratings are based on the lower of Standard & Poor’s or Moody’s rating. If unavailable, Ambac’s internal rating is used. (2) Includes asset-backed securities with a fair value of $0 and $145 at December 31, 2019 and 2018 , respectively, insured by Ambac UK. (3) Represents Ambac's holdings of secured notes issued by Ambac LSNI in connection with the Rehabilitation Exit Transactions. Ambac LSNI secured notes are insured by Ambac Assurance and are excluded from the calculation of weighted average underlying rating.
Summary of Net Investment Income	Net investment income was comprised of the following for the affected periods: Year Ended December 31, 2019 2018 2017 Fixed income securities $ 183 $ 265 $ 337 Short-term investments 17 11 8 Loans 1 1 1 Investment expense (6 ) (7 ) (8 ) Securities available-for-sale and short-term 196 271 338 Other investments 32 2 23 Total net investment income $ 227 $ 273 $ 361 Net investment income from Other investments primarily represents changes in fair value on securities classified as trading or 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: Year Ended December 31, 2019 2018 2017 Net gains (losses) recognized during the period on trading securities $ 24 $ (3 ) $ 18 Less: net gains (losses) recognized during the reporting period on trading securities sold during the period 7 1 5 Unrealized gains (losses) recognized during the reporting period on trading securities still held at the reporting date $ 17 $ (4 ) $ 13

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2019
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]	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 December 31, 2019 and 2018 . Gross Gross Net Amounts Gross Amount Net Amount December 31, 2019: Derivative Assets: Interest rate swaps $ 75 $ — $ 75 $ — $ 75 Total non-VIE derivative assets $ 75 $ — $ 75 $ — $ 75 Derivative Liabilities: Credit derivatives $ — $ — $ — $ — $ — 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 Gross Gross Net Amounts Gross Amount Net Amount December 31, 2018: Derivative Assets: Interest rate swaps $ 60 $ — $ 59 $ — $ 59 Total non-VIE derivative assets $ 60 $ — $ 59 $ — $ 59 Derivative Liabilities: Credit derivatives $ 1 $ — $ 1 $ — $ 1 Interest rate swaps 72 — 72 67 5 Futures contracts 3 — 3 3 — Total non-VIE derivative liabilities $ 77 $ — $ 77 $ 71 $ 6 Variable Interest Entities Derivative Assets: Currency swaps $ 66 $ — $ 66 $ — $ 66 Total VIE derivative assets $ 66 $ — $ 66 $ — $ 66 Variable Interest Entities Derivative Liabilities: Interest rate swaps $ 1,712 $ — $ 1,712 $ — $ 1,712 Total VIE derivative liabilities $ 1,712 $ — $ 1,712 $ — $ 1,712
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 Consolidated Statements of Total Comprehensive Income (Loss) for the years ended December 31, 2019, 2018 and 2017 : Location of Gain (Loss) Recognized Amount of Gain (Loss) Recognized in Consolidated Statement of Total Comprehensive Income (Loss) – 2019 2018 2017 Non-VIE derivatives: Futures contracts Net gains (losses) on derivative contracts (45 ) 7 11 Interest rate swaps Net gains (losses) on derivative contracts (6 ) 1 49 Credit derivatives Net gains (losses) on derivative contracts 2 (1 ) 16 Total non-VIE derivatives (50 ) 7 76 Variable Interest Entities: Interest rate swaps Income (loss) on variable interest entities (20 ) 493 (127 ) Currency swaps Income (loss) on variable interest entities (12 ) 11 (26 ) Total Variable Interest Entities (32 ) 505 (152 ) Total derivative contracts $ (82 ) $ 512 $ (76 )
Summary of Notional Amounts of AFS's Trading Derivative Products	As of December 31, 2019 and 2018 , the notional amounts of AFS's derivatives are as follows: Notional - December 31, Type of Derivative 2019 2018 Interest rate swaps—pay-fixed/receive-variable $ 1,261 $ 1,122 US Treasury futures contracts—short 755 1,760 Interest rate swaps—receive-fixed/pay-variable 332 493
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member]
Summary of Notional Amounts of AFS's Trading Derivative Products	The notional for VIE derivatives outstanding as of December 31, 2019 and 2018 , are as follows: Notional - December 31, Type of VIE Derivative 2019 2018 Interest rate swaps—receive-fixed/pay-variable $ 1,194 $ 1,400 Interest rate swaps—pay-fixed/receive-variable 1,176 1,177 Currency swaps 329 345 Credit derivatives 9 10

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2019
Debt Instrument [Line Items]
Schedule of Maturities of Long-term Debt [Table Text Block]	Aggregated annual maturities of non-VIE long-term debt obligations (based on scheduled maturity dates as further discussed below) are as follows: 2020 $ 531 2021 — 2022 — 2023 1,763 2024 — Thereafter 687 Total $ 2,980
Schedule of Long-term Debt Instruments	Long-term debt outstanding, excluding VIE long-term debt, was as follows: December 31, 2019 2018 Par Value Unamortized Discount Carrying Value Par Value Unamortized Discount Carrying Value Ambac Assurance: 5.1% surplus notes $ 531 $ (14 ) $ 517 $ 531 $ (44 ) $ 487 5.1% junior surplus notes 365 (113 ) 252 367 (117 ) 250 Ambac note 1,763 — 1,763 1,940 — 1,940 Tier 2 notes 281 (4 ) 278 259 (7 ) 252 Ambac UK debt 41 (28 ) 13 — — — Long-term debt $ 2,980 $ (159 ) $ 2,822 $ 3,096 $ (167 ) $ 2,929

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Major Jurisdictions	The following are the major jurisdictions in which Ambac operates and the earliest tax years subject to examination: Jurisdiction Tax Year United States 2010 New York State 2013 New York City 2015 United Kingdom 2016 Italy 2015
Significant Portions of Deferred Tax Liabilities and Deferred Tax Assets	The tax effects of temporary differences that give rise to significant portions of the deferred tax liabilities and deferred tax assets at December 31, 2019 and 2018 , are presented below: December 31, 2019 2018 Deferred tax liabilities: Insurance intangible $ 90 $ 151 Variable interest entities 12 19 Investments 32 26 Unearned premiums and credit fees 42 48 Other 8 8 Total deferred tax liabilities 183 252 Deferred tax assets: Net operating loss and capital carryforward 742 719 Loss reserves 148 227 Debentures 29 23 Compensation 7 10 Other 1 2 Subtotal deferred tax assets 927 980 Valuation allowance 777 768 Total deferred tax assets 151 212 Net deferred tax liability $ 32 $ 40
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: Year Ended December 31, 2019 2018 2017 U.S. $ (174 ) $ 264 $ (451 ) Foreign (9 ) 8 167 Total $ (183 ) $ 273 $ (284 )
Schedule of Components of Income Tax Expense (Benefit)	he components of the provision (benefit) for income taxes were as follows: Year Ended December 31, 2019 2018 2017 Current taxes U. S. federal $ — $ (2 ) $ (30 ) U.S. state and local (3 ) 2 2 Foreign 37 (1 ) 41 Total current taxes 34 — 13 Deferred taxes Foreign (1 ) 5 31 Total deferred taxes $ (1 ) $ 5 $ 31 Provision for income taxes $ 32 $ 5 $ 44
Schedule Of Income Taxes Charged Credited Directly To Equity	The total effect of income taxes on net income and stockholders’ equity for the years ended December 31, 2019, 2018 and 2017 is as follows: Year Ended December 31, 2019 2018 2017 Total income taxes charged to net income $ 32 $ 5 $ 44 Income taxes charged (credited) to stockholders’ equity: Unrealized gains (losses) on investment securities 14 12 (31 ) Unrealized gains (losses) on foreign currency translations — — 26 Valuation allowance to equity (23 ) (9 ) 5 Total charged to stockholders’ equity: (8 ) 3 — Total effect of income taxes $ 24 $ 8 $ 44
Schedule of Effective Income Tax Rate Reconciliation	The tax provisions in the accompanying Consolidated Statements of Total Comprehensive Loss reflect effective tax rates differing from prevailing Federal corporate income tax rates. The following is a reconciliation of these differences: 2019 2018 2017 Year Ended December 31, Amount % Amount % Amount % Tax on income from continuing operations at statutory rate $ (38 ) 21.0 % $ 57 21.0 % $ (99 ) 35.0 % Changes in expected tax resulting from: Tax-exempt interest (3 ) 1.8 % (7 ) (2.5 )% (6 ) 2.1 % Foreign taxes 40 (22.1 )% 10 3.9 % (18 ) 6.2 % Substantiation adjustment 28 (15.3 )% (60 ) (22.0 )% 36 (12.7 )% Valuation allowance 8 (4.4 )% 5 1.9 % 128 (44.9 )% Change in Tax Law — — % (2 ) (0.7 )% 2 (0.7 )% Other, net (2 ) 1.3 % 1 0.4 % 2 (0.7 )% Tax expense on income from continuing operations $ 32 (17.7 )% $ 5 2.0 % $ 44 (15.7 )%
Schedule of Unrecognized Tax Benefits Roll Forward	A reconciliation of the beginning and ending amounts of material unrecognized tax benefits for 2019 , 2018 and 2017 is as follows: Year Ended December 31, 2019 2018 2017 Balance, beginning of period $ — $ — $ — Increases related to prior year tax positions — — — Decreases related to prior year tax positions — — — Balance, end of period $ — $ — $ —
Schedule of Net Operating Loss And Tax Credit Carryovers	Pursuant to the 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 Percentage 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%

Employment Benefit Plans (Table

Employment Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2019
Postemployment Benefits [Abstract]
Schedule of Expected Benefit Payments [Table Text Block]	The following table sets forth projected benefit payments from Ambac’s postretirement plan over the next ten years for current retirees: 2020 $ — 2021 — 2022 — 2023 — 2024 1 2025-2029 3 Total $ 5
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable [Table Text Block]	The amount of stock-based compensation expense and corresponding after-tax expense are as follows: Year Ended December 31, 2019 2018 2017 Stock options $ — $ — $ — Restricted stock units 4 6 2 Performance awards (1) (2) 8 6 3 Total stock-based compensation $ 12 $ 12 $ 4 Total stock-based compensation (after-tax) $ 12 $ 12 $ 4 (1) Represents expense related to performance stock unit portion of performance awards. Certain performance awards are in the form of cash. Cash based compensation expense related to performance awards granted to US employees was $0 , $1 and $2 for the years ended December 31, 2019, 2018 and 2017 , respectively. (2) A performance award issued to Ambac's former Chief Executive Officer in the form of performance stock units was expensed during 2018.
Share-based Payment Arrangement, Option, Activity [Table Text Block]	A summary of stock option activity for 2019 is as follows: Shares Weighted Average Exercise Price Aggregate Intrinsic Value Weighted Average Remaining Contractual Life (in years) Outstanding at beginning of period 16,667 $ 20.63 Granted — — Exercised — — Forfeited or expired — — Outstanding at end of period 16,667 $ 20.63 $ — 0.97 Exercisable 16,667 $ 20.63 $ — 0.97
Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]	A summary of RSU activity for 2019 is as follows: Shares Weighted Average Grant Date Fair Value Outstanding at beginning of period 645,028 $ 17.17 Granted 248,861 19.75 Delivered or returned to plan (1) (189,832 ) 16.76 Forfeited (1,478 ) 20.11 Outstanding at end of period 702,579 $ 18.19 (1) When restricted stock unit awards issued by Ambac become taxable compensation to employees, shares may be withheld to cover the employee’s withholding taxes. For the year ended December 31, 2019 , Ambac purchased 72,977 of shares from employees that settled restricted stock units to meet the required tax withholdings.
Schedule of Nonvested Performance-based Units Activity [Table Text Block]	A summary of PSU activity for 2019 is as follows: Shares Weighted Average Grant Date Fair Value Outstanding at beginning of period 516,999 $ 17.02 Granted (1) 230,391 19.17 Delivered (2) (166,353 ) 15.52 Forfeited (1) (8,151 ) 18.11 Performance adjustment (3) 77,326 15.52 Outstanding at end of period 650,212 $ 17.98 (1) Represents performance share units at 100% of units granted for LTIP Awards. (2) Reflects the number of performance shares attributable to the performance goals attained over the completed performance period and for which service conditions have been met. When performance stock unit awards issued by Ambac become taxable compensation to employees, shares may be withheld to cover the employee’s withholding taxes. For the year ended December 31, 2019 , Ambac purchased 64,086 of shares from employees that settled performance based restricted stock units to meet the required tax withholdings. (3) Represents the increase (decrease) in shares issued for awards granted in 2016 based upon the attainment of performance metrics at the end of the performance period.

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Lessor, Operating Lease, Payments to be Received, Maturity [Table Text Block]	Future undiscounted lease payments to be received are as follows: As of December 31, 2019 Operating Leases 2020 $ 1 2021 1 2022 1 2023 1 2024 1 Thereafter 6 Total lease receipts $ 12
Schedule of Capital Leased Assets [Table Text Block]	Supplemental balance sheet information related to leases is as follows: December 31, 2019 Operating leases: Operating lease right of use assets $ 25 Operating lease liabilities 29 Weighted average remaining lease term: Operating leases 9.9 years Weighted average discount rate: Operating leases 7.9 %
Lease, Cost [Table Text Block]	The components of lease costs, net of sub-lessor income, is as follows: Year Ended December 31, 2019 Operating lease cost $ 7 Variable lease cost — Sublease income (1 ) Total lease cost $ 7
Cash Flow, Supplemental Disclosures [Text Block]	Supplemental information related to leases is as follows: Year Ended December 31, 2019 Cash paid for amounts included in the measurement of operating lease liabilities $ 6 Right-of-use assets obtained in exchange for operating lease liabilities (non-cash) (1) 30 (1) Includes right-of-use assets of $14 for the year ended December 31, 2019 for leases which existed prior to the New Lease Standard implementation date of January 1, 2019.
Lessee, Operating Lease, Liability, Maturity [Table Text Block]	Future undiscounted lease payments, gross of sublease receipts, to be made are as follows: As of December 31, 2019 Operating Leases 2020 $ 4 2021 4 2022 4 2023 4 2024 4 Thereafter 22 Total lease payments 42 Less: imputed interest (13 ) Total $ 29

Quarterly Information (unaudi_2

Quarterly Information (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Data [Abstract]
Quarterly Financial Information (unaudited)	2019 Quarters 2018 Quarters First Second Third Fourth First Second Third Fourth Gross premiums written $ 3 $ (21 ) $ (13 ) $ 2 $ 4 $ (1 ) $ (23 ) $ (5 ) Net premiums earned 28 8 10 20 31 26 26 29 Net investment income 55 86 45 42 110 67 58 37 Net other than temporary impairment losses — — — — — (1 ) — (2 ) Net realized investment gains (losses) 17 36 18 9 5 47 30 29 Net gains (losses) on derivative contracts (16 ) (35 ) (10 ) 12 25 9 18 (45 ) Net realized gains (losses) on extinguishment of debt — — — — 3 — — — Other income (loss) 1 (9 ) 141 1 (1 ) 2 1 2 Income (loss) on Variable Interest Entities 16 3 11 7 1 1 2 — Losses and loss expenses (benefit) 12 (133 ) 37 97 (247 ) 33 34 (42 ) Insurance intangible amortization 36 226 17 15 29 23 26 29 Operating expenses 25 29 26 23 36 26 28 21 Interest expense 68 67 67 66 48 62 66 66 Pre-tax income (loss) (41 ) (100 ) 69 (111 ) 308 6 (20 ) (22 ) Net income (loss) (43 ) (128 ) 66 (110 ) 306 4 (22 ) (20 ) Net income (loss) attributable to Common Stockholders $ (43 ) $ (128 ) $ 66 $ (110 ) $ 306 $ 4 $ (104 ) $ (20 ) Net income (loss) per share: Basic $ (0.94 ) $ (2.79 ) $ 1.44 $ (2.40 ) $ 6.72 $ 0.09 $ (2.27 ) $ (0.45 ) Diluted $ (0.94 ) $ (2.79 ) $ 1.41 $ (2.40 ) $ 6.70 $ 0.09 $ (2.27 ) $ (0.45 )
Schedule of Quarterly Financial Information	18. QUARTERLY INFORMATION (Unaudited) 2019 Quarters 2018 Quarters First Second Third Fourth First Second Third Fourth Gross premiums written $ 3 $ (21 ) $ (13 ) $ 2 $ 4 $ (1 ) $ (23 ) $ (5 ) Net premiums earned 28 8 10 20 31 26 26 29 Net investment income 55 86 45 42 110 67 58 37 Net other than temporary impairment losses — — — — — (1 ) — (2 ) Net realized investment gains (losses) 17 36 18 9 5 47 30 29 Net gains (losses) on derivative contracts (16 ) (35 ) (10 ) 12 25 9 18 (45 ) Net realized gains (losses) on extinguishment of debt — — — — 3 — — — Other income (loss) 1 (9 ) 141 1 (1 ) 2 1 2 Income (loss) on Variable Interest Entities 16 3 11 7 1 1 2 — Losses and loss expenses (benefit) 12 (133 ) 37 97 (247 ) 33 34 (42 ) Insurance intangible amortization 36 226 17 15 29 23 26 29 Operating expenses 25 29 26 23 36 26 28 21 Interest expense 68 67 67 66 48 62 66 66 Pre-tax income (loss) (41 ) (100 ) 69 (111 ) 308 6 (20 ) (22 ) Net income (loss) (43 ) (128 ) 66 (110 ) 306 4 (22 ) (20 ) Net income (loss) attributable to Common Stockholders $ (43 ) $ (128 ) $ 66 $ (110 ) $ 306 $ 4 $ (104 ) $ (20 ) Net income (loss) per share: Basic $ (0.94 ) $ (2.79 ) $ 1.44 $ (2.40 ) $ 6.72 $ 0.09 $ (2.27 ) $ (0.45 ) Diluted $ (0.94 ) $ (2.79 ) $ 1.41 $ (2.40 ) $ 6.70 $ 0.09 $ (2.27 ) $ (0.45 )

Background and Business Descr_2

Background and Business Description - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2014	Feb. 12, 2018	May 01, 2013	Apr. 30, 2013
Background And Basis Of Presentation [Line Items]
Entity Incorporation, Date of Incorporation	Apr. 29, 1991
Minimum surplus amount	$ 100
Amount of Senior Surplus Notes Outstanding on June 8, 2020			25.00%
Tier 2 Notes					$ 240
Tier 2 Note Security in RMBS Litigation Settlement Proceeds					$ 1,600
Common stock, shares authorized	130,000,000	130,000,000
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01					$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common stock, shares issued	45,571,743	45,365,170
Class of Warrant or Right, Exercise Price of Warrants or Rights						$ 16.67
Junior surplus note of Ambac Assurance Segregated Account						$ 350
Common Stock Voting Restrictions				10.00%
Common Stock Voting Restriction Less One Vote				10.00%
Common Stock Transfer Restrictions				5.00%
Common Stock Additional Transfer Restrictions				5.00%
Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount	$ 10	$ 32	$ 64
Ambac UK [Member]
Background And Basis Of Presentation [Line Items]
Total Benefit Related to Ballantyne Settlement			$ 145

Background and Business Descr_3

Background and Business Description Rehabilitation Exit Support Agreement (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2014	Dec. 31, 2018	Jun. 30, 2018	Feb. 12, 2018	Dec. 31, 2017	May 01, 2013	Apr. 30, 2013
Preferred Stock, Shares Outstanding	0		0
Entity Incorporation, Date of Incorporation	Apr. 29, 1991
satisfaction and discharge of segregated account deferred amounts					$ 3,857,000,000
Cancellation of Surplus Notes Principal					552,000,000
Cancellation of Surplus Notes Accrued Interest					257,000,000
Amount of Senior Surplus Notes Outstanding on June 8, 2020						25.00%
Common stock, shares authorized	130,000,000		130,000,000
Common Stock, Par or Stated Value Per Share	$ 0.01		$ 0.01					$ 0.01
Preferred stock, shares authorized	20,000,000		20,000,000
Preferred Stock, Par or Stated Value Per Share	$ 0.01		$ 0.01
Common stock, shares issued	45,571,743		45,365,170
Class of Warrant or Right, Exercise Price of Warrants or Rights							$ 16.67
Common Stock Voting Restrictions		10.00%
Common Stock Voting Restriction Less One Vote		10.00%
Common Stock Transfer Restrictions		5.00%
Common Stock Additional Transfer Restrictions		5.00%
Minimum surplus amount	$ 100,000,000
Stockholders' Equity Attributable to Noncontrolling Interest	60,000,000		$ 41,000,000	$ 264,000,000
Market Value of Secured Note Collateral	$ 197,000,000		$ 210,000,000
Ambac Assurance Corporation [Member]
Preferred Stock, Shares Outstanding	5,501		4,115	26,411
Preferred Stock, Liquidation Preference, Value	$ 138,000,000		$ 103,000,000	$ 660,000,000
Ambac Assurance [Member]
Secured Notes Received from Ambac LSNI					644,000,000
Ambac [Member] | Deferred Payment Obligation [Member]
One Dollar Outstanding					1
Discount Amount					0.09
Payment Amount in New Secured Notes					0.91
AFG [Member]
Amount of Remaining Senior Suplus Notes						$ 60,000,000
Secured Notes Received from Ambac LSNI					125,000,000
Ambac LSNI Secured Note [Domain]
AMBAC LSNI Secured Note					$ 2,154,000,000
5.1% Surplus Notes, General Account, Due 2020 [Member] | Ambac Assurance Corporation [Member]
Debt Instrument, Interest Rate, Stated Percentage					5.10%
Deferred Payment Obligation [Member]
Discount Amount					$ 0.065
Surplus Notes [Member]
Cash Payment Amount					0.40
Payment Amount in New Secured Notes					0.41
Payment Amount in Existing Surplus Notes					$ 0.125
Long-term Debt [Member]
Gain Contingency, Unrecorded Amount	$ 1,400,000,000

Background and Business Descr_4

Background and Business Description Tier 2 Commitment (Details) $ in Millions	Feb. 12, 2018USD ($)
Tier 2 Note Security in RMBS Litigation Settlement Proceeds	$ 1,600

Background and Business Descr_5

Background and Business Description AMPS Exchange (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)	Aug. 03, 2018USD ($)$ / sharesshares	Jun. 30, 2018USD ($)shares	May 01, 2013$ / shares
Preferred Stock, Shares Issued | shares	0	0
Stockholders' Equity Attributable to Noncontrolling Interest	$ 60,000	$ 41,000			$ 264,000
AMPS Liquidation Preference Value Per Share | $ / shares				$ 25,000
AMPS Exchange Surplus Notes Issued Per Share | $ / shares				$ 13,875
AMPS Exchange Shares Tendered | shares				22,096
AMPS Exchange Cash Paid Per Share | $ / shares				$ 500
AMPS Exchange Warrants Issued Per Share | $ / shares				$ 37.3076
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 16.67
AMPS Exchange Percent Acquired				0.844
AMPS Exchange Shares Acquired | shares				22,296
AMPS Exchange Aggregated Liquidation Preference				$ 557,000
AMPS Exchange Nominal Discount				227,000
AMPS Exchange Nominal Discount at Fair Value				253,000
AMPS Exchange Total Surplus Notes Issued				213,000
AMPS Exchange Interest Included in Surplus Notes Issued				$ 98,000
AMPS Exchange Total Warrants Issued				824,307
AMPS Exchange Cash Paid	0	11,000
AMPS Exchange Loss Based on Carry Value	$ 0	$ 82,000	$ 0
Preferred Stock, Shares Outstanding | shares	0	0
Ambac Assurance Corporation [Member]
Preferred Stock, Shares Issued | shares	1,386
Preferred Stock, Liquidation Preference, Value	$ 138,000	$ 103,000			$ 660,000
Preferred Stock, Shares Outstanding | shares	5,501	4,115			26,411
AFG [Member]
AMPS Exchange Aggregated Liquidation Preference				$ 35,000

Basis of Presentation and Sig_5

Basis of Presentation and Significant Accounting Policies Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014	Aug. 03, 2018	May 01, 2013	Apr. 30, 2013
Finite-Lived Intangible Assets [Line Items]
Operating Lease, Liability	$ 29	$ 29	$ 15
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			0
Income Taxes Paid		$ 21	$ 35	$ 40
AMPS Exchange Carrying Value of Surplus Notes Issued							$ 187
Decrease in long-term debt as a result of an exchange for investment securities				$ 55
Common Stock Voting Restrictions						10.00%
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01	$ 0.01						$ 0.01
Entity Incorporation, Date of Incorporation		Apr. 29, 1991
Preferred stock, shares authorized	20,000,000	20,000,000	20,000,000
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01	$ 0.01
Common stock, shares issued	45,571,743	45,571,743	45,365,170
Warrant Exercised During Period Shares	0			194	0
Junior surplus note of Ambac Assurance Segregated Account								$ 350
Common Stock Transfer Restrictions						5.00%
Common Stock Additional Transfer Restrictions						5.00%
Non Cash Impact of Rehabilitation Exit Transaction			$ 1,919
Cash and cash equivalents	$ 24	$ 24	63	$ 624
Restricted Cash	55	55	19
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	81	$ 81	83	625	$ 96
Minimum [Member] | Furniture and Fixtures [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		3 years
Maximum [Member] | Furniture and Fixtures [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		5 years
Long-term Debt [Member]
Finite-Lived Intangible Assets [Line Items]
Interest Paid, Including Capitalized Interest, Operating and Investing Activities		$ 143	232	39
Accounting Standards Update 2016-01 [Member] | AOCI Attributable to Parent [Member]
Finite-Lived Intangible Assets [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			(3)
Accounting Standards Update 2016-01 [Member] | Retained Earnings [Member]
Finite-Lived Intangible Assets [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			3
Variable Interest Entity, Primary Beneficiary [Member]
Finite-Lived Intangible Assets [Line Items]
Restricted Cash	$ 2	$ 2	$ 1	$ 1

Basis of Presentation and Sig_6

Basis of Presentation and Significant Accounting Policies FX gain (loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Foreign Currency Transaction Gain (Loss), before Tax	$ 12	$ (7)	$ 21
Premiums Receivable [Member]
Foreign Currency Transaction Gain (Loss), before Tax	(10)	2	(2)
Lossandlossreserves [Member]
Foreign Currency Transaction Gain (Loss), before Tax	(1)	(15)	29
Gain (Loss) on Investments [Member]
Foreign Currency Transaction Gain (Loss), before Tax	$ 22	$ 7	$ (5)

Basis of Presentation and Sig_7

Basis of Presentation and Significant Accounting Policies Goodwill (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 0

Basis of Presentation and Sig_8

Basis of Presentation and Significant Accounting Policies Noncontrolling Interest (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)shares	Jun. 30, 2018USD ($)shares
Stockholders' Equity Attributable to Noncontrolling Interest | $	$ 60	$ 41	$ 264
Preferred Stock, Shares Outstanding | shares	0	0
Ambac Assurance Corporation [Member]
Preferred Stock, Shares Outstanding | shares	5,501	4,115	26,411
Preferred Stock, Liquidation Preference, Value | $	$ 138	$ 103	$ 660
London Interbank Offered Rate (LIBOR) [Member]
Dividend Rate on Auction Rate Preferred Shares	200

Basis of Presentation and Sig_9

Basis of Presentation and Significant Accounting Policies Incentive Compensation (Details)	12 Months Ended
	Dec. 31, 2018
Twelve Months from Award Date [Domain]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	50.00%
Twenty Four Months from Award Date [Domain]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	50.00%

Basis of Presentation and Si_10

Basis of Presentation and Significant Accounting Policies Adoption of New Accounting Standards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Operating Lease, Liability	$ 15	$ 29
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 0

Basis of Presentation and Si_11

Basis of Presentation and Significant Accounting Policies Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Aug. 03, 2018	Dec. 31, 2016
Income Taxes Paid	$ 21	$ 35	$ 40
AMPS Exchange Carrying Value of Surplus Notes Issued				$ 187
Decrease in long-term debt as a result of an exchange for investment securities			55
Non Cash Impact of Rehabilitation Exit Transaction		1,919
Cash and cash equivalents	24	63	624
Restricted Cash	55	19
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	81	83	625		$ 96
Long-term Debt [Member]
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	143	232	39
Variable Interest Entity, Primary Beneficiary [Member]
Restricted Cash	$ 2	$ 1	$ 1

Variable Interest Entities - Ad

Variable Interest Entities - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)Entity	Dec. 31, 2018USD ($)Entity	Dec. 31, 2017USD ($)	Feb. 12, 2018USD ($)
Variable Interest Entities [Line Items]
Fixed income securities, amortized cost	$ 3,187	$ 3,451
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	132	133
satisfaction and discharge of segregated account deferred amounts				$ 3,000
satisfaction and discharge of segregated account deferred interest amounts				857
Available-for-sale Securities	3,314
Restricted Cash	55	19
Fair value of special purpose entities	3	5
Variable Interest Entity, Consolidated, Carrying Amount, Assets	292
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	364
Equity Method Investments	46	40
Loans, Unpaid principal balance		19	$ 19
Other Investments	478	391
Deconsolidated VIE Assets	1,233
Deconsolidated VIE Liabilities	1,230
Long-term debt	2,822	2,929
Derivative assets	75	59
Other assets	95	138
Assets	13,320	14,589
Accrued interest payable	441	376
Derivative liabilities	90	77
Other liabilities	93	64
Liabilities	$ 11,783	12,956
Asset-Backed Securities and Utility Obligations [Member]
Variable Interest Entities [Line Items]
Weighted average life	1 year 1 month 6 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	$ 403	393
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Available-for-sale Securities	3,121	2,737
Restricted Cash	2	1	$ 1
Long-term Debt, Fair Value	4,351	5,269
Long-term debt	4,554	5,269
Financing Receivable, after Allowance for Credit Loss	3,108	4,288
Derivative assets	52	66
Other assets	3	1
Assets	6,286	7,093
Accrued interest payable	1	1
Long-term Debt, at par less amortized discount	203	0
Derivative liabilities	1,657	1,712
Liabilities	$ 6,212	$ 6,981
Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number of DeConsolidated Variable Interest Entities	1	4	1
Number of consolidated Variable Interest Entities | Entity	7	7
Ambac UK [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Available-for-sale Securities	$ 2,957	$ 2,737
Restricted Cash	1	1
Long-term Debt, Fair Value	4,351	5,269
Long-term debt	4,351	5,269
Financing Receivable, after Allowance for Credit Loss	3,108	4,288
Derivative assets	52	66
Other assets	1	1
Assets	6,119	7,093
Accrued interest payable	1	1
Long-term Debt, at par less amortized discount	0	0
Derivative liabilities	1,657	1,712
Liabilities	$ 6,009	$ 6,981
Ambac UK [Member] | Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number of consolidated Variable Interest Entities | Entity	6	7
Ambac Assurance [Member]
Variable Interest Entities [Line Items]
Secured Notes Received from Ambac LSNI				644
Unsettled Amounts Secured Notes from LSNI	$ 55	$ 19
Ambac Assurance [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Available-for-sale Securities	164	0
Restricted Cash	1	0
Long-term Debt, Fair Value	0	0
Long-term debt	203	0
Financing Receivable, after Allowance for Credit Loss	0	0
Derivative assets	0	0
Other assets	2	0
Assets	167	0
Accrued interest payable	0	0
Long-term Debt, at par less amortized discount	203	0
Derivative liabilities	0	0
Liabilities	$ 203	$ 0
Ambac Assurance [Member] | Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number of consolidated Variable Interest Entities | Entity	1	0
AFG [Member]
Variable Interest Entities [Line Items]
Secured Notes Received from Ambac LSNI				$ 125
Corporate Debt Securities [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Available-for-sale Securities	$ 2,957	$ 2,737
Corporate Debt Securities [Member] | Ambac UK [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Available-for-sale Securities	2,957	2,737
Corporate Debt Securities [Member] | Ambac Assurance [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Available-for-sale Securities	0	0
Municipal Bonds [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Fixed income securities, amortized cost	139
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	25
Available-for-sale Securities	164	0
Municipal Bonds [Member] | Ambac UK [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Available-for-sale Securities	0	0
Municipal Bonds [Member] | Ambac Assurance [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Available-for-sale Securities	$ 164	$ 0

Variable Interest Entities - Su

Variable Interest Entities - Summary of Fair Value of Fixed Income Securities, by Asset-Type, Held by Consolidated Variable Interest Entities (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entities [Line Items]
Variable Interest Entity Nonconsolidated Carrying Amount Insurance Assets	$ 2,247	$ 2,258
Variable Interest Entity Nonconsolidated Carrying Amount Insurance Liabilities	1,083	1,434
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	31,506	$ 35,566
Investments:
Variable Interest Entity Nonconsolidated Carrying Amount Derivative Net Assets Or Liabilities	$ 7

Variable Interest Entities - _2

Variable Interest Entities - Supplemental Information about Loans Held as Assets and Long-Term Debt Associated with Consolidated Variable Interest Entities (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entities [Line Items]
Loans, Unpaid principal balance		$ 19	$ 19
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	$ 364
Variable Interest Entities [Member]
Variable Interest Entities [Line Items]
Loans, Unpaid principal balance	2,618	3,418
Long-term debt, Unpaid principal balance	$ 3,800	$ 4,553

Variable Interest Entities - _3

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 (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	$ 31,506	$ 35,566
Insurance Assets	2,247	2,258
Insurance Liabilities	1,083	1,434
Derivative Liabilities	7
Variable Interest Entity [Member]
Variable Interest Entities [Line Items]
Derivative Liabilities		6
Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	8,165	11,420
Insurance Assets	1,961	1,949
Insurance Liabilities	762	1,098
Derivative Liabilities	8	7
Global Structured Finance [Member] | Collateralized Debt Obligations [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss		10
Insurance Assets		0
Insurance Liabilities		0
Derivative Liabilities		0
Global Structured Finance [Member] | Residential Mortgage-Backed Securities [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	5,373	6,713
Insurance Assets	1,913	1,859
Insurance Liabilities	523	547
Derivative Liabilities	0	0
Global Structured Finance [Member] | Other Consumer Asset-Backed [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	1,373	1,701
Insurance Assets	31	15
Insurance Liabilities	216	238
Derivative Liabilities	0	0
Global Structured Finance [Member] | Other Commercial Asset-Backed [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	314	873
Insurance Assets	9	21
Insurance Liabilities	6	12
Derivative Liabilities	0	0
Global Structured Finance [Member] | Other Debt Obligations [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	1,107	2,123
Insurance Assets	7	53
Insurance Liabilities	18	301
Derivative Liabilities	8	7
Global Public Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	23,341	24,146
Insurance Assets	287	309
Insurance Liabilities	321	335
Derivative Liabilities	$ 0	$ (1)

Variable Interest Entities Vari

Variable Interest Entities Variable Interest Entity - Change in Fair Value of Assets and Liabilities (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Deconsolidated VIE Assets	$ 1,233								$ 1,233
Fixed income securities, amortized cost	3,187				$ 3,451				3,187	$ 3,451
Long-term debt	2,822				2,929				2,822	2,929
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	132				133				132	133
Loans, Unpaid principal balance					19					19	$ 19
Variable Interest Entity Change in Fair Value of Assets and Liabilities									13	3	20
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, before Tax											0
Realized Investment Gains (Losses)	9	$ 18	$ 36	$ 17	29	$ 30	$ 47	$ 5	81	112	5
Variable Interest Entity, Initial Consolidation, Gain (Loss)									15	0	0
Variable Interest Entities Deconsolidation Gain Loss									(2)	2	0
Variable Interest Entity, Measure of Activity, Income or Loss before Tax									38	3	20
Variable Interest Entity, Consolidated, Carrying Amount, Assets	292								292
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	364								364
Deconsolidated VIE Liabilities	1,230								1,230
Variable Interest Entity, Primary Beneficiary [Member]
Long-term debt	4,554				5,269				4,554	5,269
Interest Expense, Long-term Debt									(11)	0	0
Other Expenses									(1)	0	0
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member]
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, before Tax									0	(1)
Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure [Member]
Loans, Unpaid principal balance	2,618				3,418				2,618	3,418
Long-term debt, Unpaid principal balance	$ 3,800				$ 4,553				3,800	4,553
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, before Tax									14	2	20
Available-for-sale Securities [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Gross Investment Income, Operating									10	0	0
Realized Investment Gains (Losses)									$ 13	$ 0	$ 0
Consolidated Entities [Member]
Number of DeConsolidated Variable Interest Entities									1	4	1

Variable Interest Entities Va_2

Variable Interest Entities Variabile Interest Entities - Carry Value of Secured Notes from LSNI (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Long-term debt	$ 2,822	$ 2,929
Ambac [Member]
Carry Value Secured Notes from LSNI	535	656
Ambac Assurance Corporation [Member]
Long-term debt	2,822	2,929
Ambac Note Post Exit From Rehabilitation [Member] | Ambac Assurance Corporation [Member]
Long-term debt	$ 1,763	$ 1,940

Comprehensive Income - Schedule

Comprehensive Income - Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Restated			$ (55)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets			(3)
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ (49)	$ (52)
Other comprehensive income before reclassifications	(168)	(87)
Amounts reclassified from accumulated other comprehensive income	(78)	(81)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		0
Income Tax Expense (Benefit)	(32)	(5)	(44)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	91	6
Ending Balance	42	(49)	(52)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	86	31
Other comprehensive income before reclassifications	(142)	(136)
Amounts reclassified from accumulated other comprehensive income	(76)	(81)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	65	55
Ending Balance	151	86	31
Accumulated Translation Adjustment [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(142)	(94)
Other comprehensive income before reclassifications	(26)	48
Amounts reclassified from accumulated other comprehensive income	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	26	(48)
Ending Balance	(116)	(142)	(94)
Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets			(3)
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(2)	(3)
Other comprehensive income before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	0	1
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0	1
Ending Balance	(2)	(2)	(3)
Other Postretirement Benefits Plan [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	9	11
Other comprehensive income before reclassifications	(1)	1
Amounts reclassified from accumulated other comprehensive income	(1)	(1)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(1)	(2)
Ending Balance	$ 8	$ 9	$ 11

Comprehensive Income - Schedu_2

Comprehensive Income - Schedule of Amounts Reclassed Out of Each Component of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	$ (32)	$ (5)	$ (44)
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(78)	(81)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized investment gains	(81)	(82)
Net of tax and noncontrolling interest	(76)	(81)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(76)	(81)
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		1
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	1
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, before Tax	0	1
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax and noncontrolling interest	(78)	(81)
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)	(4)	(1)
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
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	(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
Prior service cost	(1)	(1)
Actuarial gains (losses)	0	0
Total before tax	(1)	(1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ (1)	$ (1)

Net Income Per Share - Addition

Net Income Per Share - Additional Information (Detail) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended		18 Months Ended
	Dec. 31, 2019$ / sharesshares	Dec. 31, 2017shares	Dec. 31, 2016shares	Dec. 31, 2016USD ($)$ / sharesshares	Mar. 31, 2019USD ($)	Dec. 31, 2018$ / sharesshares	Aug. 03, 2018$ / shares	Nov. 02, 2016USD ($)	Jun. 30, 2015USD ($)	May 01, 2013$ / shares	Apr. 30, 2013$ / shares
Schedule Of Earnings Per Share [Line Items]
Common Stock, Shares, Outstanding	45,555,400					45,336,278
Class of Warrant or Right, Outstanding	4,877,783
Number of new common stock issued	45,571,743					45,365,170
Par value of common stock issued | $ / shares	$ 0.01					$ 0.01					$ 0.01
Exercise price of common stock | $ / shares										$ 16.67
Warrant exercised	0	194	0
Stock Issued During Period, Shares, New Issues	0	194	0
First Warrant Buyback Authorization Dollars | $									$ 10
Payments for Repurchase of Warrants | $				$ 8
Warrants Repurchased Average Cost per Warrant | $ / shares				$ 8.21
SecondWarrantBuyBackAuthorizedDollars | $								$ 10
Warrants Purchased Shares				985,331
RemainingWarrantBuyBackAuthorizedDollars | $					$ 12
AMPS Exchange Total Warrants Issued							824,307
AMPS Exchange Total Warrants Issued Cost Per Share | $ / shares							$ 9.72

Net Income Per Share - Reconcil

Net Income Per Share - Reconciliation of Common Shares Used for Basic and Diluted Earnings Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of common shares and potential dilutive shares used for diluted earnings per share		45,954,908	46,559,835	45,367,932
Weighted Average Number of Shares Outstanding, Basic		45,954,908	45,665,883	45,367,932
Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	4,877,783	0	4,053,670
Effect of potential dilutive shares:
Effect of potential dilutive shares	0	441,104
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	126,667
Effect of potential dilutive shares:
Effect of potential dilutive shares	0	0
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	249,263	0	68,654
Effect of potential dilutive shares:
Effect of potential dilutive shares	0	77,572
Performance Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	872,258	0	322,943
Effect of potential dilutive shares:
Effect of potential dilutive shares	0	375,276
Warrant [Member]
Effect of potential dilutive shares:
Effect of potential dilutive shares			0
Share-based Payment Arrangement, Option [Member]
Effect of potential dilutive shares:
Effect of potential dilutive shares			0
Performance Shares [Member]
Effect of potential dilutive shares:
Effect of potential dilutive shares			0
Restricted Stock Units (RSUs) [Member]
Effect of potential dilutive shares:
Effect of potential dilutive shares			0

Financial Guarantees in Force -

Financial Guarantees in Force - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Guarantor Obligations [Line Items]
Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount	$ 10	$ 32	$ 64
Gross par amount of financial guarantees outstanding	43,908	52,055
Net par amount of financial guarantees	38,018	46,927
Gross financial guarantees in force	69,826	87,543
Net financial guarantees in force	$ 58,245	$ 77,972
Highest single insured risk of aggregate net par amount guaranteed		2.70%
California [Member]
Guarantor Obligations [Line Items]
Aggregate net par amounts in force	6.70%
NEW JERSEY
Guarantor Obligations [Line Items]
Aggregate net par amounts in force	6.30%
NEW YORK
Guarantor Obligations [Line Items]
Aggregate net par amounts in force	6.10%
No other state [Member] | Maximum [Member]
Guarantor Obligations [Line Items]
Aggregate net par amounts in force	5.00%
Public Finance [Member]
Guarantor Obligations [Line Items]
Net par amount of financial guarantees	$ 17,653	$ 23,442
Public Finance [Member] | Housing Revenue [Member]
Guarantor Obligations [Line Items]
Net par amount of financial guarantees	5,991	6,159
Military Housing [Domain] | Public Finance [Member] | Housing Revenue [Member]
Guarantor Obligations [Line Items]
Net par amount of financial guarantees	$ 5,654	$ 5,759

Financial Guarantees in Force_3

Financial Guarantees in Force - Summary of Financial Guarantee Portfolio Diversification by Type of Guaranteed Bond (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 38,018	$ 46,927
Public Finance [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	17,653	23,442
Public Finance [Member] | Lease and Tax-backed Revenue [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	5,102	7,565
Public Finance [Member] | General Obligation [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	3,011	4,214
Public Finance [Member] | Utility Revenue [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	768	1,178
Public Finance [Member] | Higher Education [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	885	1,168
Public Finance [Member] | Housing Revenue [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	5,991	6,159
Public Finance [Member] | Other [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	1,041	1,404
Public Finance [Member] | Transportation [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	855	1,754
Structured Finance [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	7,508	9,947
Structured Finance [Member] | Mortgage-backed and Home Equity [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	4,423	5,510
Structured Finance [Member] | Investor-owned Utilities [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	1,675	1,754
Structured Finance [Member] | Structured Insurance [Domain]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	395	1,365
Structured Finance [Member] | Student Loan [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	769	934
Structured Finance [Member] | Asset Backed and Other [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	246	384
International Finance [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	12,857	13,538
International Finance [Member] | Asset Backed and Other [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	1,625	2,176
International Finance [Member] | Investor-owned and Public Utilities [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	4,436	4,499
International Finance [Member] | Sovereign/Sub-sovereign [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	5,264	5,250
International Finance [Member] | Transportation [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 1,532	$ 1,613

Financial Guarantees in Force_4

Financial Guarantees in Force - Summary of International Finance Guaranteed Portfolio (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 38,018	$ 46,927
International Finance [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	12,857	13,538
International Finance [Member] | United Kingdom [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	10,593	10,965
International Finance [Member] | Australia [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	382	384
International Finance [Member] | Italy [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	767	811
International Finance [Member] | Austria [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	674	712
International Finance [Member] | FRANCE
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	303	312
International Finance [Member] | Other International [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 138	$ 354

Financial Guarantee Insurance_3

Financial Guarantee Insurance Contracts - Additional Information (Detail) £ in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2019GBP (£)	Feb. 12, 2019	Dec. 31, 2018GBP (£)	Dec. 31, 2017GBP (£)	Dec. 31, 2016USD ($)
Insurance [Line Items]
Net par amount of financial guarantees	$ 38,018				$ 46,927				$ 38,018	$ 46,927
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,536				$ 1,633				1,536	$ 1,633	$ 1,645					$ 1,978
Stockholders Equity After Possible Increase in Domestic Public Finance Loss Reserves	536								536
Possible Increase in Domestic Public Finance Loss Reserves	$ 1,000								$ 1,000
Estimated Future Premium Payments Weighted Average Discounted Rate	2.40%				2.70%				2.40%	2.70%		2.40%		2.70%
Financial Guarantee Insurance Contracts, Premium Receivable	$ 416				$ 495				$ 416	$ 495	586					661
Amount Of Insured Par Outstanding Ceded To Reinsurer	2,746								$ 2,746
Ceded Principal Outstanding Major Reinsurer Percentage									6.30%
Financial Guarantee Gross Outstanding Principal Assumed From Third Parties	219				219				$ 219	219
Deferred Ceded Premiums And Reinsurance Recoverables	109								109
Reinsurance Payable	29				33				$ 29	$ 33
Weighted average period of future premiums									8 years 6 months	8 years 8 months 12 days
Uncollectable premium receivables	9				7				$ 9	$ 7
Accelerated premium revenue for retired obligations									10	32	64
Reinsurance recoveries of losses included in losses and loss expenses									(7)	(2)	20
Losses and loss expense reserves ceded to reinsurers	26				23				26	23	41					$ 31
Subrogation recoveries, net of reinsurance	(1,702)				(1,744)				(1,702)	(1,744)
Intangible amortization expense	15	$ 17	$ 226	$ 36	29	$ 26	$ 23	$ 29	295	107	151
Intangible Assets, Gross (Excluding Goodwill)	1,273				1,552				1,273	1,552
Finite-Lived Intangible Assets, Accumulated Amortization	847				833				847	833
Insurance intangible asset	427				719				427	719
Letters of Credit Outstanding, Amount	124								124
Financial Guarantee Outstanding Principal Ceded To Third Parties	5,890								5,890
Public Finance Puerto Rico Net Par Outstanding	1,123								1,123
Percent Cash & New COFINA Bonds Allocated Under POA													93.00%
Ambac Assurance Remaining Policy Obligations	101								101
Insurance Intangible Asset [Member]
Insurance [Line Items]
Intangible amortization expense									$ 295	$ 107	151
Loss Reserves [Member]
Insurance [Line Items]
Weighted average risk-free rate used to discount loss reserves									2.10%	2.80%
United Kingdom, Pounds
Insurance [Line Items]
Financial Guarantee Insurance Contracts, Premium Receivable	129				131				$ 129	$ 131	152	£ 97		£ 103	£ 112
Ambac UK [Member]
Insurance [Line Items]
Total Benefit Related to Ballantyne Settlement											$ 145
Commonwealth of Puerto Rico [Member]
Insurance [Line Items]
Domestic Public Finance Losses									250
Public Finance [Member]
Insurance [Line Items]
Net par amount of financial guarantees	17,653				23,442				17,653	23,442
Housing Revenue [Member] | Public Finance [Member]
Insurance [Line Items]
Net par amount of financial guarantees	5,991				6,159				5,991	6,159
Housing Revenue [Member] | Military Housing [Domain] | Public Finance [Member]
Insurance [Line Items]
Net par amount of financial guarantees	$ 5,654				$ 5,759				$ 5,654	$ 5,759

Financial Guarantee Insurance_4

Financial Guarantee Insurance Contracts - Summary of Gross Premium Receivable Roll-Forward (Direct and Assumed Contracts) (Detail) € in Millions, £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2019EUR (€)	Dec. 31, 2019GBP (£)	Dec. 31, 2018USD ($)	Dec. 31, 2018EUR (€)	Dec. 31, 2018GBP (£)	Dec. 31, 2017USD ($)
Insurance [Line Items]
Premium Receivable, Allowance for Credit Loss	$ 9			$ 7
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Beginning premium receivable	495			586			$ 661
Premium receipts	48			56			(82)
Adjustments for changes in expected and contractual cash flows	(38)			(42)			(30)
Accretion of premium receivable discount	11			15			16
Financial Guarantee Insurance Contracts, Premium Receivable, Deconsolidation of VIE	3
Uncollectable premiums	(2)			2			0
Other adjustments (including foreign exchange)	(6)			(10)			21
Ending premium receivable	416			495			586
United Kingdom, Pounds
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Beginning premium receivable	131		£ 103	152		£ 112
Ending premium receivable	129		£ 97	131		£ 103	152
Euro Member Countries, Euro
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Beginning premium receivable	31	€ 27		36	€ 30
Ending premium receivable	$ 26	€ 23		$ 31	€ 27		$ 36

Financial Guarantee Insurance_5

Financial Guarantee Insurance Contracts - Effect of Reinsurance on Premiums Written and Earned (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Written									$ 28	$ 24	$ 14
Assumed Reinsurance Premiums Written									0	0	0
Ceded Reinsurance Premiums Written									(31)	(17)	2
Premiums written, net of reinsurance									60	41	12
Direct Premiums Earned									75	119	190
Premiums Earned, Net									66	111	175
Assumed Reinsurance Premiums Earned									0	0	0
Ceded Reinsurance Premiums Earned									10	8	15
Reinsurance on premiums earned, Net	$ 20	$ 10	$ 8	$ 28	$ 29	$ 26	$ 26	$ 31	$ 66	$ 111	$ 175

Financial Guarantee Insurance_6

Financial Guarantee Insurance Contracts - Summarized Future Gross Undiscounted Premiums Expected to be Collected, and Future Expected Premiums Earned, Net of Reinsurance (Detail) $ in Millions	Dec. 31, 2019USD ($)
Future premiums expected to be collected, March 31, 2018	$ 14
Future premiums expected to be collected, June 30. 2018	11
Future premiums expected to be collected, September 30, 2018	10
Future premiums expected to be collected, December 31, 2018	9
Future premiums expected to be collected, December 31, 2019	37
Future premiums expected to be collected, December 31, 2020	36
Future premiums expected to be collected, December 31, 2021	34
Future premiums expected to be collected, December 31, 2022	33
Future premiums expected to be collected, December 31, 2027	143
Future premiums expected to be collected, December 31, 2032	102
Future premiums expected to be collected, December 31, 2037	47
Future premiums expected to be collected, December 31, 2042	22
Future premiums expected to be collected, December 31, 2047	9
Future premiums expected to be collected, December 31, 2052	1
Future premiums expected to be collected, Total	508
Future expected premium to be earned, net of reinsurance, March 31, 2018	10
Future expected premiums to be earned, net of reinsurance, June 30, 2018	10
Future expected premiums to be earned, net of reinsurance, September 30, 2018	10
Future expected premiums to be earned, net of reinsurance, December 31, 2018	10
Future expected premiums to be earned, net of reinsurance, December 31, 2019	36
Future expected premiums to be earned, net of reinsurance, December 31, 2020	34
Future expected premiums to be earned, net of reinsurance, December 31, 2021	32
Future expected premiums to be earned, net of reinsurance, December 31, 2022	30
Future expected premiums to be earned, net of reinsurance, December 31, 2027	124
Future expected premiums to be earned, net of reinsurance, December 31, 2032	82
Future expected premiums to be earned, net of reinsurance, December 31, 2037	38
Future expected premiums to be earned, net of reinsurance, December 31, 2042	14
Future expected premiums to be earned, net of reinsurance, December 31, 2047	5
Future expected premiums to be earned, net of reinsurance, December 31, 2052	1
Future expected premiums to be earned, net of reinsurance, Total	$ 436

Financial Guarantee Insurance_7

Financial Guarantee Insurance Contracts Financial Guarantee Insurance Contracts - Components of Loss and Loss Expense Reserves and Subrogation Recoverable (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Policyholder Benefits and Claims Incurred, Ceded	$ 7	$ 2	$ (20)
Liability for Unpaid Claims and Claims Adjustment Expense, Net	(436)	(130)	$ 4,073	$ 3,665
Loss and loss expense reserves	1,548	1,826
Subrogation recoverable	(2,029)	(1,933)
Claim liability reported on Balance Sheet, before reinsurance	(482)	(107)
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	1,835	2,246
Subrogation recoverable	131	176
Claim liability reported on Balance Sheet, before reinsurance	1,966	2,422
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	(233)	(314)
Subrogation recoverable	(2,160)	(2,109)
Claim liability reported on Balance Sheet, before reinsurance	(2,394)	(2,422)
Unearned Premium Reserve [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	(54)	(107)
Subrogation recoverable	0	0
Claim liability reported on Balance Sheet, before reinsurance	$ (54)	$ (107)

Financial Guarantee Insurance_8

Financial Guarantee Insurance Contracts - Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Feb. 12, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss And Loss Adjustment Expense Reserves [Line Items]
Impact of VIE Consolidation on Gross Loss and Loss Reserves				$ (72)
Liability for Unpaid Claims and Claims Adjustment Expense, Foreign Currency Translation Gain (Loss)	$ (1)	$ (15)	$ 29
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	13	(224)	513
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation				(1,727)	$ (1,771)
Policyholder Benefits and Claims Incurred, Ceded	7	2	(20)
Net Incurred RMBS Subrogation Recoveries	(42)	(62)	(72)
satisfaction and discharge of segregated account deferred amounts						$ 3,000
satisfaction and discharge of segregated account deferred interest amounts						857
Loss and Loss Expense Benefit on Settled Deferred Amounts						$ 288
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross loss and loss expense reserves	(107)	4,114	3,696
Less reinsurance on loss and loss expense reserves	23	41	31
Beginning balance of net loss and loss expense reserves	(130)	4,073	3,665
Current year:
Claim and loss expense payments, net of subrogation and reinsurance	0	0	(1)
Prior years:
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance	(318)	(3,963)	(133)
Liability for Unpaid Claims and Claims Adjustment Expense, Net	(130)	4,073	3,665	(436)	(130)		$ 4,073	$ 3,665
Add reinsurance on loss and loss expense reserves	26	23	41
Ending gross loss and loss expense reserves	(482)	(107)	4,114
Balance Of Rmbs Subrogation Recoveries Net Of Reinsurance				(1,702)	(1,744)
Current Year Claims and Claims Adjustment Expense	1	5	6
Prior Year Claims and Claims Adjustment Expense	12	(228)	507
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	$ 318	$ 3,964	$ 134
Random Samples [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation				$ (1,727)	$ (1,771)		$ (1,834)	$ (1,907)

Financial Guarantee Insurance_9

Financial Guarantee Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)Policies	Dec. 31, 2018USD ($)Policies
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	221	231
Remaining weighted-average contract period (in years)	15 years	16 years
Gross insured contractual payments outstanding:
Principal	$ 6,168	$ 9,403
Interest	3,029	10,583
Total	9,197	19,986
Gross undiscounted claim liability	2,434	3,448
Discount, gross claim liability	541	1,092
Gross claim liability before all subrogation and before reinsurance	1,893	2,356
Less:
Gross RMBS subrogation	(1,777)	(1,810)
Discount, RMBS subrogation	49	39
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	(1,727)	(1,771)
Less:
Gross other subrogation	(720)	(785)
Discount, other subrogation	53	133
Discounted other subrogation, before reinsurance	(666)	(652)
Gross claim liability, net of all subrogation and discounts, before reinsurance	(501)	(66)
Less: Unearned premium reserves	(54)	(107)
Plus: Loss adjustment expenses reserves	73	66
Claim liability reported on Balance Sheet, before reinsurance	(482)	(107)
Reinsurance recoverable reported on Balance Sheet	$ 26	$ 23
Surveillance Category One [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	34	21
Remaining weighted-average contract period (in years)	8 years	9 years
Gross insured contractual payments outstanding:
Principal	$ 668	$ 917
Interest	340	488
Total	1,007	1,404
Gross undiscounted claim liability	2	4
Discount, gross claim liability	0	0
Gross claim liability before all subrogation and before reinsurance	2	4
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	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	2	4
Less: Unearned premium reserves	(1)	(1)
Plus: Loss adjustment expenses reserves	1	1
Claim liability reported on Balance Sheet, before reinsurance	1	4
Reinsurance recoverable reported on Balance Sheet	$ 0	$ 0
IA [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	18	28
Remaining weighted-average contract period (in years)	21 years	19 years
Gross insured contractual payments outstanding:
Principal	$ 510	$ 708
Interest	507	632
Total	1,016	1,340
Gross undiscounted claim liability	44	64
Discount, gross claim liability	5	13
Gross claim liability before all subrogation and before reinsurance	39	51
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	0	0
Less:
Gross other subrogation	0	(11)
Discount, other subrogation	0	7
Discounted other subrogation, before reinsurance	0	(3)
Gross claim liability, net of all subrogation and discounts, before reinsurance	39	47
Less: Unearned premium reserves	(9)	(10)
Plus: Loss adjustment expenses reserves	1	4
Claim liability reported on Balance Sheet, before reinsurance	30	41
Reinsurance recoverable reported on Balance Sheet	$ 6	$ 7
II [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	11	18
Remaining weighted-average contract period (in years)	9 years	9 years
Gross insured contractual payments outstanding:
Principal	$ 277	$ 623
Interest	128	293
Total	404	916
Gross undiscounted claim liability	21	36
Discount, gross claim liability	1	3
Gross claim liability before all subrogation and before reinsurance	20	33
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	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	20	33
Less: Unearned premium reserves	(1)	(5)
Plus: Loss adjustment expenses reserves	1	3
Claim liability reported on Balance Sheet, before reinsurance	20	30
Reinsurance recoverable reported on Balance Sheet	$ 7	$ 4
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)	17 years	22 years
Gross insured contractual payments outstanding:
Principal	$ 857	$ 1,705
Interest	366	6,979
Total	1,223	8,685
Gross undiscounted claim liability	541	992
Discount, gross claim liability	152	434
Gross claim liability before all subrogation and before reinsurance	389	558
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	0	0
Less:
Gross other subrogation	(41)	(137)
Discount, other subrogation	4	67
Discounted other subrogation, before reinsurance	(37)	(70)
Gross claim liability, net of all subrogation and discounts, before reinsurance	353	489
Less: Unearned premium reserves	(7)	(36)
Plus: Loss adjustment expenses reserves	4	(6)
Claim liability reported on Balance Sheet, before reinsurance	349	446
Reinsurance recoverable reported on Balance Sheet	$ 24	$ 26
IV [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	139	145
Remaining weighted-average contract period (in years)	14 years	14 years
Gross insured contractual payments outstanding:
Principal	$ 3,819	$ 5,407
Interest	1,678	2,178
Total	5,498	7,585
Gross undiscounted claim liability	1,778	2,296
Discount, gross claim liability	381	638
Gross claim liability before all subrogation and before reinsurance	1,397	1,658
Less:
Gross RMBS subrogation	(1,777)	(1,810)
Discount, RMBS subrogation	49	39
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	(1,727)	(1,771)
Less:
Gross other subrogation	(666)	(625)
Discount, other subrogation	47	55
Discounted other subrogation, before reinsurance	(620)	(570)
Gross claim liability, net of all subrogation and discounts, before reinsurance	(950)	(682)
Less: Unearned premium reserves	(35)	(54)
Plus: Loss adjustment expenses reserves	67	63
Claim liability reported on Balance Sheet, before reinsurance	(918)	(672)
Reinsurance recoverable reported on Balance Sheet	$ (10)	$ (15)
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)	3 years	3 years
Gross insured contractual payments outstanding:
Principal	$ 37	$ 43
Interest	11	13
Total	48	57
Gross undiscounted claim liability	48	57
Discount, gross claim liability	2	4
Gross claim liability before all subrogation and before reinsurance	46	52
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	0	0
Less:
Gross other subrogation	(13)	(13)
Discount, other subrogation	3	4
Discounted other subrogation, before reinsurance	(10)	(9)
Gross claim liability, net of all subrogation and discounts, before reinsurance	36	43
Less: Unearned premium reserves	0	0
Plus: Loss adjustment expenses reserves	0	0
Claim liability reported on Balance Sheet, before reinsurance	36	43
Reinsurance recoverable reported on Balance Sheet	$ 0	$ 0

Financial Guarantee Insuranc_10

Financial Guarantee Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Detail2) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	$ 1,727	$ 1,771
Loss Reserves Ceded To Reinsurers	26	23	$ 41	$ 31
Loss and loss expense reserves	1,548	1,826
Subrogation recoverable	(2,029)	(1,933)
Liability for Claims	(482)	(107)	$ 4,114	$ 3,696
Surveillance Category One [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	0	0
Surveillance Category Onea [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	0	0
Surveillance Category Two [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	0	0
Surveillance Category Three [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	0	0
Surveillance Category Four [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	1,727	1,771
Surveillance Category Five [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	$ 0	$ 0

Financial Guarantee Insuranc_11

Financial Guarantee Insurance Contracts - Summary of Balance of RMBS Subrogation Recoveries and Related Claim Liabilities, by Estimation Approach (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Subrogation recoveries	$ 1,727	$ 1,771
Random Samples [Member]
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Subrogation recoveries	1,727	1,771	$ 1,834	$ 1,907
Other Changes Rmbs Subrogation	$ (43)	$ (64)	$ (73)

Financial Guarantee Insuranc_12

Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	$ 1,771
Changes recognized
Discounted RMBS subrogation (gross of reinsurance), ending balance	1,727	$ 1,771
Random Samples [Member]
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	1,771	1,834	$ 1,907
Changes recognized
Other Changes Rmbs Subrogation	(43)	(64)	(73)
Discounted RMBS subrogation (gross of reinsurance), ending balance	$ 1,727	$ 1,771	$ 1,834

Financial Guarantee Insuranc_13

Financial Guarantee Insurance Contracts - Estimated Future Amortization Expense for Insurance Intangible Asset (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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	$ 15	$ 17	$ 226	$ 36	$ 29	$ 26	$ 23	$ 29	$ 295	$ 107	$ 151
Intangible Assets, Gross (Excluding Goodwill)	1,273				$ 1,552				1,273	1,552
Insurance Asset [Member]
Amortization Of Intangible Assets [Line Items]
Amortization of insurance intangible assets									295	$ 107	$ 151
Insurance Intangible Asset [Member]
Amortization Of Intangible Assets [Line Items]
2018	45								45
2019	39								39
2020	36								36
2021	33								33
2022	30								30
Thereafter	$ 244								$ 244

Financial Guarantee Insurance -

Financial Guarantee Insurance - Summary of Percentage Ceded to Reinsurers and Reinsurance Recoverable and Rating Levels (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Percentage ceded Par	100.00%
Net unsecured reinsurance recoverable	$ 41
Assured Guaranty Re Ltd [Member]
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Percentage ceded Par	47.00%
Net unsecured reinsurance recoverable	$ 0
Sompo Japan Nipponkoa Holdings, Inc [Member]
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Percentage ceded Par	3.00%
Net unsecured reinsurance recoverable	$ 0
Assured Guaranty Corporation [Member]
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Percentage ceded Par	8.00%
Net unsecured reinsurance recoverable	$ 5
Build America Mutual Assurance Company [Domain]
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Percentage ceded Par	42.00%
Net unsecured reinsurance recoverable	$ 36

Financial Guarantee Insuranc_14

Financial Guarantee Insurance Contracts Financial Guarantee Insurance Contracts Earned Premiums by Geographic Location (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Premiums Earned, Net, Financial Guarantee Insurance Contracts	$ 20	$ 10	$ 8	$ 28	$ 29	$ 26	$ 26	$ 31	$ 66	$ 111	$ 175
Reportable Geographical Components [Member] | UNITED STATES
Premiums Earned, Net, Financial Guarantee Insurance Contracts									55	88	134
Reportable Geographical Components [Member] | UNITED KINGDOM
Premiums Earned, Net, Financial Guarantee Insurance Contracts									17	19	33
Reportable Geographical Components [Member] | Other International [Member]
Premiums Earned, Net, Financial Guarantee Insurance Contracts									$ (6)	$ 5	$ 8

Insurance Regulatory Restrict_2

Insurance Regulatory Restrictions Additional Details (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Average Annual Rate Of Return	5.43%	5.87%
Prescribed Discount Rate Percentage	5.10%
Statutory Accounting Practices, Statutory Capital and Surplus Required	$ 100
REDUCTION TO GROSS PAID-IN AND CONNTRIBUTED SURPLUS	$ 3,433
Statutory Accounting Practices, Statutory Capital and Surplus Required Pursuant to AMPS Exchange		$ 75
Quarterly Dividend Increase Limitation Percentage	15.00%
Percentage Of Policy Holders Surplus	10.00%
Minimum [Member]
Settlement Agreement Annual Restricted Payment Amount	$ 5
Maximum [Member]
Settlement Agreement Annual Restricted Payment Amount	8
Ambac Assurance [Member]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	1,088	1,152
Ambac Assurance [Member] | Prescribed Or Permitted Additional Accounting Practices [Member]
Statutory Accounting Practices, Prescribed Practice, Amount	$ (12)	$ (42)
5.1 % Surplus Notes Due 2020 [Member] | Ambac Assurance Corporation [Member]
Debt Instrument, Interest Rate, Stated Percentage		5.10%	5.10%

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial assets:
Debt Securities, Available-for-sale	$ 3,314,000
Short term investments	653,000	$ 430,000
Other Investments	478,000	391,000
Derivative assets	75,000	60,000
Other assets	3,000	5,000
Financial liabilities:
Derivative liabilities	90,000	77,000
Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	3,121,000	2,737,000
Loans, at fair value	3,108,000	4,288,000
Derivative assets	52,000	66,000
Financial liabilities:
Derivative liabilities	1,657,000	1,712,000
Long-term Debt	4,351,000	5,269,000
Short-term Investments [Member]
Financial assets:
Debt Securities, Available-for-sale	653,000	430,000
Available-for-sale Securities	737,000
Corporate Debt Securities [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	2,957,000	2,737,000
Municipal Bonds [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	164,000	0
Carrying Amount [Member]
Financial assets:
Cash	79,000	82,000
Loans	10,000	10,000
Other assets	3,000	5,000
Total financial assets	10,242,000	11,186,000
Financial liabilities:
Liabilities for net financial guarantees written	(863,000)	(718,000)
Long-term Debt	3,262,000	3,305,000
Total financial liabilities	8,699,000	9,644,000
Carrying Amount [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	2,000	1,000
Loans, at fair value	3,108,000	4,288,000
Financial liabilities:
Long-term Debt	4,554,000	5,269,000
Carrying Amount [Member] | Other Debt Obligations [Member]
Financial assets:
Other Investments	478,000	391,000
Carrying Amount [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	653,000	430,000
Carrying Amount [Member] | Other Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities		1,000
Carrying Amount [Member] | Corporate Debt Securities [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	2,957,000	2,737,000
Carrying Amount [Member] | Municipal Bonds [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	164,000
Carrying Amount [Member] | Interest Rate Swaps [Member]
Financial liabilities:
Derivative liabilities	89,000	72,000
Carrying Amount [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	1,657,000	1,712,000
Carrying Amount [Member] | Futures Contracts [Member]
Financial liabilities:
Derivative liabilities		3,000
Carrying Amount [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	52,000	66,000
Total Fair Value [Member]
Financial assets:
Cash	79,000	82,000
Other Assets [Member] | Carrying Amount [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	75,000	59,000
Fair Value Measured at Net Asset Value Per Share [Member]
Financial assets:
Other Investments	296,000	280,000
Level 1 [Member]
Financial assets:
Cash	70,000	53,000
Total financial assets	1,091,000	554,000
Financial liabilities:
Liabilities for net financial guarantees written	0	0
Long-term Debt	0	0
Total financial liabilities	0	3,000
Level 1 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	2,000	1,000
Loans	0	0
Financial liabilities:
Long-term Debt	0	0
Level 1 [Member] | Other Debt Obligations [Member]
Financial assets:
Other Investments	136,000	71,000
Level 1 [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	598,000	305,000
Level 1 [Member] | Equity Method Investments [Member]
Financial assets:
Other assets	0	0
Level 1 [Member] | Other Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities		0
Level 1 [Member] | Corporate Debt Securities [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Level 1 [Member] | Municipal Bonds [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	0
Level 1 [Member] | Interest Rate Swaps [Member]
Financial liabilities:
Derivative liabilities	0	0
Level 1 [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Level 1 [Member] | Futures Contracts [Member]
Financial liabilities:
Derivative liabilities		3,000
Level 1 [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	0	0
Level 1 [Member] | Loans Receivable [Member]
Financial assets:
Loans	0	0
Level 1 [Member] | Other Assets [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	0	0
Level 2 [Member]
Financial assets:
Cash	9,000	30,000
Total financial assets	2,593,000	3,153,000
Financial liabilities:
Liabilities for net financial guarantees written	0	0
Long-term Debt	2,829,000	2,909,000
Total financial liabilities	8,983,000	9,745,000
Level 2 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	0	0
Loans	0	0
Financial liabilities:
Long-term Debt	4,408,000	5,052,000
Level 2 [Member] | Other Debt Obligations [Member]
Financial assets:
Other Investments	0	0
Level 2 [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	55,000	125,000
Level 2 [Member] | Equity Method Investments [Member]
Financial assets:
Other assets	0	0
Level 2 [Member] | Other Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities		0
Level 2 [Member] | Corporate Debt Securities [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Level 2 [Member] | Municipal Bonds [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	164,000
Level 2 [Member] | Interest Rate Swaps [Member]
Financial liabilities:
Derivative liabilities	89,000	72,000
Level 2 [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	1,657,000	1,712,000
Level 2 [Member] | Futures Contracts [Member]
Financial liabilities:
Derivative liabilities		0
Level 2 [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	52,000	66,000
Level 2 [Member] | Loans Receivable [Member]
Financial assets:
Loans	0	0
Level 2 [Member] | Other Assets [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	8,000	12,000
Level 3 [Member]
Financial assets:
Cash	0	0
Total financial assets	6,281,000	7,177,000
Financial liabilities:
Liabilities for net financial guarantees written	284,000	559,000
Long-term Debt	445,000	351,000
Total financial liabilities	889,000	1,128,000
Level 3 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	0	0
Loans	3,108,000	4,288,000
Financial liabilities:
Long-term Debt	159,000	217,000
Level 3 [Member] | Other Debt Obligations [Member]
Financial assets:
Other Investments	61,000	16,000
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	3,000	5,000
Level 3 [Member] | Other Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities		1,000
Level 3 [Member] | Corporate Debt Securities [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	2,957,000	2,737,000
Level 3 [Member] | Municipal Bonds [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	0
Level 3 [Member] | Interest Rate Swaps [Member]
Financial liabilities:
Derivative liabilities	0	0
Level 3 [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Level 3 [Member] | Futures Contracts [Member]
Financial liabilities:
Derivative liabilities
Level 3 [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	0	0
Level 3 [Member] | Loans Receivable [Member]
Financial assets:
Loans	13,000	12,000
Level 3 [Member] | Other Assets [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	67,000	47,000
Commercial Mortgage Backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	50,000
Municipal Bonds [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	215,000	880,000
Corporate Debt Securities [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	1,430,000	1,278,000
Debt Security, Government, Non-US [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	44,000	31,000
US Government Debt Securities [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	156,000	94,000
Residential Mortgage-Backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	248,000	259,000
Collateralized Debt Obligations [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	146,000	131,000
Asset-backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	287,000	442,000
Fair Value, Recurring [Member]
Financial assets:
Total financial assets	10,260,000	11,164,000
Financial liabilities:
Liabilities for net financial guarantees written	284,000	559,000
Long-term Debt	3,274,000	3,260,000
Total financial liabilities	9,872,000	10,876,000
Fair Value, Recurring [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	2,000	1,000
Loans	3,108,000	4,288,000
Financial liabilities:
Long-term Debt	4,567,000	5,269,000
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	50,000
Fair Value, Recurring [Member] | Other Debt Obligations [Member]
Financial assets:
Other Investments	493,000	367,000
Fair Value, Recurring [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	653,000	430,000
Fair Value, Recurring [Member] | Equity Method Investments [Member]
Financial assets:
Other assets	3,000	5,000
Fair Value, Recurring [Member] | Other Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities		1,000
Fair Value, Recurring [Member] | Asset-backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	287,000	442,000
Fair Value, Recurring [Member] | Collateralized Debt Obligations [Member]
Financial assets:
Debt Securities, Available-for-sale	146,000	131,000
Fair Value, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	248,000	259,000
Fair Value, Recurring [Member] | US Government Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	156,000	94,000
Fair Value, Recurring [Member] | Debt Security, Government, Non-US [Member]
Financial assets:
Debt Securities, Available-for-sale	44,000	31,000
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	1,430,000	1,278,000
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	2,957,000	2,737,000
Fair Value, Recurring [Member] | Municipal Bonds [Member]
Financial assets:
Debt Securities, Available-for-sale	215,000	880,000
Fair Value, Recurring [Member] | Municipal Bonds [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	164,000
Fair Value, Recurring [Member] | Interest Rate Swaps [Member]
Financial liabilities:
Derivative liabilities	89,000	72,000
Fair Value, Recurring [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	1,657,000	1,712,000
Fair Value, Recurring [Member] | Futures Contracts [Member]
Financial liabilities:
Derivative liabilities		3,000
Fair Value, Recurring [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	52,000	66,000
Fair Value, Recurring [Member] | Loans Receivable [Member]
Financial assets:
Loans	13,000	12,000
Fair Value, Recurring [Member] | Other Assets [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	75,000	59,000
Fair Value, Recurring [Member] | Level 1 [Member] | Commercial Mortgage Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0
Fair Value, Recurring [Member] | Level 1 [Member] | Asset-backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Collateralized Debt Obligations [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Residential Mortgage-Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | US Government Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	156,000	94,000
Fair Value, Recurring [Member] | Level 1 [Member] | Debt Security, Government, Non-US [Member]
Financial assets:
Debt Securities, Available-for-sale	44,000	30,000
Fair Value, Recurring [Member] | Level 1 [Member] | Corporate Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Municipal Bonds [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 2 [Member] | Commercial Mortgage Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	50,000
Fair Value, Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	215,000	370,000
Fair Value, Recurring [Member] | Level 2 [Member] | Collateralized Debt Obligations [Member]
Financial assets:
Debt Securities, Available-for-sale	146,000	131,000
Fair Value, Recurring [Member] | Level 2 [Member] | Residential Mortgage-Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	248,000	259,000
Fair Value, Recurring [Member] | Level 2 [Member] | US Government Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 2 [Member] | Debt Security, Government, Non-US [Member]
Financial assets:
Debt Securities, Available-for-sale	0	1,000
Fair Value, Recurring [Member] | Level 2 [Member] | Corporate Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	1,430,000	1,278,000
Fair Value, Recurring [Member] | Level 2 [Member] | Municipal Bonds [Member]
Financial assets:
Debt Securities, Available-for-sale	215,000	880,000
Fair Value, Recurring [Member] | Level 3 [Member] | Commercial Mortgage Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0
Fair Value, Recurring [Member] | Level 3 [Member] | Asset-backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	72,000	72,000
Fair Value, Recurring [Member] | Level 3 [Member] | Collateralized Debt Obligations [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Residential Mortgage-Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | US Government Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Debt Security, Government, Non-US [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Corporate Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Municipal Bonds [Member]
Financial assets:
Debt Securities, Available-for-sale	0	$ 0
Collateral Pledged [Member] | Short-term Investments [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	85,000
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Short-term Investments [Member]
Financial assets:
Debt Securities, Available-for-sale	85,000
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 1 [Member] | Short-term Investments [Member]
Financial assets:
Debt Securities, Available-for-sale	85,000
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 2 [Member] | Short-term Investments [Member]
Financial assets:
Debt Securities, Available-for-sale	0
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 3 [Member] | Short-term Investments [Member]
Financial assets:
Debt Securities, Available-for-sale	$ 0

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other Investments	$ 478		$ 391
Credit valuation adjustment included in fair value of credit derivative liabilities	0		0
Fair value of derivative liabilities	89
Derivative liabilities	$ 90		$ 77
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs	2.40%		2.70%
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%		8.00%
Asset-backed Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Coupon rate	5.97%		5.97%
European ABS Transactions [Member] | Level 3 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fair value of consolidated VIE debt obligations valued using unobservable inputs by asset class	$ 0		$ 217
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%		90.00%
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fair value of derivative liabilities	$ 0
Derivative liabilities	$ 1,657		$ 1,712
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs	2.70%		3.10%
Variable Interest Entity, Primary Beneficiary [Member] | European ABS Transactions [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Coupon rate			2.20%
Real Estate [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other Investments	$ 16		$ 16
Hedge Funds, Multi-strategy [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other Investments		$ 65	0
Interest Rate Contract [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other Investments	176		114
Illiquid Investments [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other Investments	$ 51		84
Other Credit Derivatives [Member] | Level 3 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Derivative liabilities			$ 1

Fair Value Measurements - Infor

Fair Value Measurements - Information about Valuation Inputs for Fixed Income Securities Classified as Level 3 (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other Investments	$ 478	$ 391
Debt Securities, Available-for-sale	$ 3,314
Asset-backed Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Coupon rate	5.97%	5.97%
Fair Value Inputs Maturity	15 years 6 months 29 days	16 years 3 months 14 days
Yield	11.75%	12.00%
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Debt Securities, Available-for-sale	$ 3,121	$ 2,737
Variable Interest Entity, Primary Beneficiary [Member] | European Transactions [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Coupon rate		2.20%
Fair Value Inputs Maturity		18 years 11 months 4 days
Yield		3.18%
Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other Investments	16	$ 16
Hedge Funds, Multi-strategy [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other Investments		0	$ 65
Interest Rate Contract [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other Investments	176	114
Illiquid Investments [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other Investments	51	84
Fair Value, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Debt Securities, Available-for-sale	248	259
Fair Value, Recurring [Member] | Residential Mortgage-Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Debt Securities, Available-for-sale	$ 0	$ 0

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 (Detail) $ in Millions	Dec. 31, 2019USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair value of derivative liabilities	$ 89

Fair Value Measurements - Sum_3

Fair Value Measurements - Summary of Information about Described Model Inputs Used to Determine Fair Value of Each Class of Credit Derivatives (Detail2) $ in Millions	Dec. 31, 2019USD ($)
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair value of derivative liabilities	$ 89

Fair Value Measurements - Inf_2

Fair Value Measurements - Information about Valuation Inputs for Variable Interest Entity Assets and Liabilities Classified as Level 3 (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Estimated Future Premium Payments Weighted Average Discounted Rate	2.40%	2.70%
Asset-backed Securities [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Inputs Coupon Rate	5.97%	5.97%
Fair Value Inputs Maturity	15 years 6 months 29 days	16 years 3 months 14 days
Fair Value Inputs Yield	11.75%	12.00%
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 Deconsolidation Of Vies	$ 627		$ 3,709
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 Deconsolidation Of Vies	0		0
Fair Value, Inputs, Level 3 [Member] | European ABS Transactions [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Of Consolidated Variable Interest Entity Debt Obligations Valued Using Unobservable Inputs By Asset Class	0	$ 217
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 Deconsolidation Of Vies	0		0
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 Deconsolidation Of Vies	0		0
Loan Origination Commitments [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 Deconsolidation Of Vies	851		5,946
Long-term Debt [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 Deconsolidation Of Vies	(223)		(2,237)
Investment Contracts [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 Deconsolidation Of Vies	$ 0		0
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			$ 655
Estimated Future Premium Payments Weighted Average Discounted Rate	2.70%	3.10%
Variable Interest Entity, Primary Beneficiary [Member] | European ABS Transactions [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Inputs Coupon Rate		2.20%
Fair Value Inputs Maturity		18 years 11 months 4 days
Fair Value Inputs Yield		3.18%

Fair Value Measurements - Sum_4

Fair Value Measurements - Summary of Changes in Level 3 Fair Value Category (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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 Value	$ 72	$ 72	$ 809	$ 763
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	0	(53)	6
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	2	36	65
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	36
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	(79)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(2)	(714)	(30)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			48
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0	5
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	0	0	0
Credit Derivatives [Member] | Credit Derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0	0
Other Credit Derivatives [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 Value	0	(1)	(1)	(15)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			16
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	2	(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0	(2)
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	(2)
Interest Rate Swaps [Member] | Interest Rate Swaps [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 Value	67	47	61	(85)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			46
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	24	(9)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(4)	(5)	100
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)	9	(7)
Residential Mortgage-Backed Securities [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 Value		0	736	697
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)		(52)	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings			64
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0	36
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0	(79)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(713)	(29)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			48
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3			5
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		0	0
Non-Agency RMBS [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 Value	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	0	35
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0
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	0
Asset-backed Securities [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 Value	72	72	73	66
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	0	(1)	6
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	2	1	1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(2)	(1)	(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0	0
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	0	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 Value	66	46	61	(100)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			63
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	25	(9)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(5)	(6)	98
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	(25)	10	(9)
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 Value	6,207	6,930	12,561	11,369
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	436		783
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)			1,010
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	199	(590)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings		30
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	36
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	(79)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(731)	(1,356)	(605)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0		48
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	5
Deconsolidation of VIEs	627		3,709
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	(376)	11	(662)
Level 3 [Member] | Investments Contract [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Deconsolidation of VIEs	0		0
Level 3 [Member] | Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Deconsolidation of VIEs	851		5,946
Level 3 [Member] | Long-term Debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Deconsolidation of VIEs	(223)		(2,237)
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 Value	72	72	809	763
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	2		65
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)			6
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	0	(53)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings		36
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	36
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	(79)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(2)	(714)	(30)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0		48
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	5
Deconsolidation of VIEs	0		0
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	0	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 Value	3	5	6	7
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	(2)		(1)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)			0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings		(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0
Deconsolidation of VIEs	0		0
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	2	1	1
Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Deconsolidation of VIEs	0		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 Value	66	46	61	(100)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	25
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)			0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			63
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings		(9)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(5)	(6)	98
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0
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	(25)	10	(9)
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Long-term Debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	8	91	(254)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	(23)	(44)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three	0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three	0	0
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	0	(47)	(37)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	0	(217)	(2,758)	(2,582)
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Loans Receivable [Member] | Loans [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 Value	3,108	4,288	11,529	10,659
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	287		550
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)			1,004
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	74	(470)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		189	35
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	(15)	(201)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(690)	(624)	(684)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0
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	(215)	63	(547)
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Corporate Debt Securities [Member] | Investments Contract [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 Value	2,957	2,737	2,914	$ 2,623
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	138		71
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)			253
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	116	(158)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings		16
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(35)	(35)	(33)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0
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	$ (138)	$ (16)	$ (71)

Fair Value Measurements - Sum_5

Fair Value Measurements - Summary of Gains and Losses (Realized and Unrealized) Relating to Level 3 Assets and Liabilities Included in Earnings (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings for the period			$ 656
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			655
Net Investment Income [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, Gain (Loss) Included in Earnings	$ 2	$ 36	65
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	0	0	0
Derivative Contract [Domain]
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, Gain (Loss) Included in Earnings	25	(9)	63
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	25	(10)	9
Income Loss On Variable Interest Entities [Member] | Variable Interest Entity [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings for the period	410	4
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	353	0
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	(2)	(1)	(1)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	$ (2)	$ (1)	$ (1)

Investments - Summary of Amorti

Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 3,187	$ 3,451
Gross Unrealized Gains	132	133
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	5	38
Available-for-sale Securities, Current	3,314	3,546
Estimated Fair Value	3,314
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0	0
Below Investment Grade Securities and Non-Rated Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Below Investment Grade Securities And Non Rated Securities Continuous Unrealized Loss Position Aggregate Losses	0	18
Below Investment Grade Securities And Non Rated Securities Continuous Unrealized Loss Position Fair Value	29	660
Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	653	430
Gross Unrealized Gains	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Estimated Fair Value	653	430
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0	0
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,450	3,021
Gross Unrealized Gains	132	133
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	5	38
Estimated Fair Value	2,577	3,116
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0	0
Fixed Income Securities [Member] | Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	194	883
Gross Unrealized Gains	22	14
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	17
Estimated Fair Value	215	880
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0	0
Fixed Income Securities [Member] | Corporate Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,396	1,289
Gross Unrealized Gains	36	6
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2	17
Estimated Fair Value	1,430	1,278
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0	0
Fixed Income Securities [Member] | Debt Security, Government, Non-US [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	44	30
Gross Unrealized Gains	1	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Estimated Fair Value	44	31
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0	0
Fixed Income Securities [Member] | U.S. Government Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	157	94
Gross Unrealized Gains	2	1
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2	1
Estimated Fair Value	156	94
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0	0
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	200	222
Gross Unrealized Gains	47	38
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	1
Estimated Fair Value	248	259
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0	0
Fixed Income Securities [Member] | Collateralized Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	49
Gross Unrealized Gains	1
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0
Estimated Fair Value	50
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	147	133
Gross Unrealized Gains	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1	2
Estimated Fair Value	146	131
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0	0
Fixed Income Securities [Member] | Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	263	370
Gross Unrealized Gains	24	73
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	1
Estimated Fair Value	287	442
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0	0
Fixed Income Investments And Other Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,103
Gross Unrealized Gains	132
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	5
Estimated Fair Value	3,230
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0
Collateral Pledged [Member] | Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	85	0
Gross Unrealized Gains	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0
Estimated Fair Value	85	$ 0
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0
Collateral Pledged [Member] | Fixed Income Securities [Member] | Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	85
Gross Unrealized Gains	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0
Estimated Fair Value	85
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities	0
Asset Pledged as Collateral [Member] | Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 85

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 (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost, Due in one year or less	$ 749
Amortized Cost, Due after one year through five years	1,157
Amortized Cost, Due after five years through ten years	477
Amortized Cost, Due after ten years	145
Amortized Cost, Total	2,528
Fixed income securities, amortized cost	3,187	$ 3,451
Estimated Fair Value, Due in one year or less	749
Estimated Fair Value, Due after one year through five years	1,173
Estimated Fair Value, Due after five years through ten years	501
Estimated Fair Value, Due after ten years	160
Estimated Fair Value due, Total	2,583
Debt Securities, Available-for-sale	3,314
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, amortized cost	2,450	3,021
Debt Securities, Available-for-sale	2,577	3,116
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, amortized cost	200	222
Debt Securities, Available-for-sale	248	259
Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, amortized cost	49
Debt Securities, Available-for-sale	50
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, amortized cost	147	133
Debt Securities, Available-for-sale	146	131
Fixed Income Securities [Member] | Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, amortized cost	263	370
Debt Securities, Available-for-sale	$ 287	$ 442

Investments - Summary of Gross

Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 401	$ 1,139
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	27
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	88	360
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	1	11
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	489	1,499
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	5	38
Below Investment Grade Securities and Non-Rated Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Below Investment Grade Securities And Non Rated Securities Continuous Unrealized Loss Position Fair Value	29	660
Below Investment Grade Securities And Non Rated Securities Continuous Unrealized Loss Position Aggregate Losses	0	18
Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	201	115
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
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	201	115
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Fixed Income Investments And Other Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	5
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	200	1,024
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	27
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	88	360
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	1	11
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	288	1,384
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	5	38
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	13	538
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	16
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	10	29
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	0	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	23	566
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	17
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	36	6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2	58
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	38	64
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2	1
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	63	307
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	5	190
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	0	9
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	68	497
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2	17
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	20	1
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	5
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	20	6
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
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	5	35
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	5	35
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	1
Fixed Income Securities [Member] | Collateralized 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
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	7
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	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	124
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	63	0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	1	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	116	124
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1	2
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	2	14
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	7	77
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	0	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	10	91
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	$ 1
Collateral Pledged [Member] | Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0
Collateral Pledged [Member] | Fixed Income Securities [Member] | Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	$ 0

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Other Investments	$ 478		$ 391
Securities fair value	6		6
Market Value of Secured Note Collateral	197		210
Real Estate [Member]
Investment [Line Items]
Other Investments	16		16
Hedge Funds, Multi-strategy [Member]
Investment [Line Items]
Other Investments		$ 65	0
Interest Rate Contract [Member]
Investment [Line Items]
Other Investments	176		114
Illiquid Investments [Member]
Investment [Line Items]
Other Investments	51		84
Insurance Linked [Member]
Investment [Line Items]
Other Investments	3		29
Equity [Member]
Investment [Line Items]
Other Investments	55		44
Credit Index Product [Member]
Investment [Line Items]
Other Investments	66		63
Equity investments in pooled funds [Member]
Investment [Line Items]
Other Investments	432			$ 351
Reported Value Measurement [Member] | Interest Rate Contract [Member]
Investment [Line Items]
Other Investments	81		27
Priced Through Pricing Vendors [Member] | Equity [Member]
Investment [Line Items]
Other Investments	55		44
Investment Portfolio [Member]
Investment [Line Items]
Fair Value of Cash and Securities Pledged to Derivative Counterparties	85		103
Ambac Assurance [Member]
Investment [Line Items]
Unsettled Amounts Secured Notes from LSNI	55		$ 19
Commitments [Member] | Partnership Interest [Member]
Investment [Line Items]
Other Investments	41
Commitments [Member] | Capital of Dislocations [Member]
Investment [Line Items]
Other Investments	$ 48

Investments - Summary of Amount

Investments - Summary of Amounts Included in Net Realized (Losses) Gains and Other-Than-Temporary Impairments (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Gross realized gains on securities									$ 64	$ 111	$ 29
Gross realized losses on securities									(5)	(7)	(19)
Foreign exchange (losses) gains									12	(7)	21
Net realized (losses) gains									81	111	5
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	$ 0	$ 0	$ 0	$ 0	$ (2)	$ 0	$ (1)	$ 0	0	(3)	(20)
Gain (Loss) on Investments [Member]
Investment [Line Items]
Foreign exchange (losses) gains									$ 22	$ 7	$ (5)

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 (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance at beginning	$ 12	$ 67	$ 52
Additions for credit impairments recognized on:
Securities not previously impaired	0	1	3
Securities previously impaired		0	12
Reductions for credit impairments previously recognized on:
Securities that matured or were sold during the period	(1)	(56)	0
Balance at end	$ 12	$ 12	$ 67

Investments - Summary of Source

Investments - Summary of Sources of Collateral Received and Various Investment Agreement in which Collateral Pledged (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Fair Value Of Securities Deposited With Governmental Authorities	$ 6	$ 6
Market Value of Secured Note Collateral	$ 197	$ 210

Investments - Summary of Fair V

Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Standard & Poor's, B- Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	$ 1,164
Standard & Poor's, CCC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		$ 2,105
Municipal Bonds [Member] | Standard & Poor's, B- Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	187
Municipal Bonds [Member] | Standard & Poor's, CCC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		849
Corporate Debt Securities [Member] | Standard & Poor's, B- Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	535
Corporate Debt Securities [Member] | Standard & Poor's, CCC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		656
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, B- Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	442
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, CCC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		599
National Public Finance Guarantee Corporation [Member] | Standard & Poor's, BBB- Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	11	16
National Public Finance Guarantee Corporation [Member] | Standard & Poor's, BBB- Rating [Member] | Municipal Bonds [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	11	16
National Public Finance Guarantee Corporation [Member] | Standard & Poor's, BBB- Rating [Member] | Corporate Debt Securities [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0	0
Ambac Assurance Corporation [Member] | Standard & Poor's, CCC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		2,089
Ambac Assurance Corporation [Member] | Standard & Poor's, CCC Rating [Member] | Municipal Bonds [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		833
Ambac Assurance Corporation [Member] | Standard & Poor's, CCC Rating [Member] | Corporate Debt Securities [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		656
Ambac Assurance Corporation [Member] | Standard & Poor's, CCC Rating [Member] | Mortgage and Asset-Backed Securities [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors		$ 599
Ambac Assurance Corporation [Member] | Standard & Poor's, B- Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	1,153
Ambac Assurance Corporation [Member] | Standard & Poor's, B- Rating [Member] | Municipal Bonds [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	176
Ambac Assurance Corporation [Member] | Standard & Poor's, B- Rating [Member] | Corporate Debt Securities [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	535
Ambac Assurance Corporation [Member] | Standard & Poor's, B- Rating [Member] | Mortgage and Asset-Backed Securities [Member]
Investment [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 (Detail2) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Ambac UK [Member]
Investment [Line Items]
Asset-backed securities fair value	$ 145	$ 0

Investments - Summary of Net In

Investments - Summary of Net Investment Income (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities										$ 24	$ (3)	$ 18
Trading Securities, Realized Gain (Loss)										7	1	5
Fixed income securities										265	337
Investment expense									$ (6)	(7)	(8)
Securities available-for-sale and short-term									196	271	338
Net investment income	$ 42	$ 45	$ 86	$ 55	$ 37	$ 58	$ 67	$ 110	227	273	361
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Other Investments Income										17	(4)	$ 13
Available-for-sale Securities [Member]
Investment [Line Items]
Fixed income securities									183
Short-term Investments [Member]
Investment [Line Items]
Fixed income securities									17	11	8
Financing Receivable [Member]
Investment [Line Items]
Fixed income securities									1	1	1
Other Investments [Member]
Investment [Line Items]
Fixed income securities									$ 32	$ 2	$ 23

Derivative Instruments - Summar

Derivative Instruments - Summary of Gross Fair Values of Individual Derivative Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 75	$ 60
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	75	59
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	90	77
Derivative Liabilities Gross Amount Of Collateral Cash And Securities Pledged Not Offset		71
Fair value of derivative liabilities	89
Net Amount, Derivative Assets	75	59
Net Amount, Derivative Liabilities	1	6
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0	0
Derivative Liability, Fair Value, Gross Liability	90	77
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Variable Interest Entity, Primary Beneficiary [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	52	66
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	52	66
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	1,657	1,712
Derivative Liabilities Gross Amount Of Collateral Cash And Securities Pledged Not Offset		0
Fair value of derivative liabilities	0
Net Amount, Derivative Assets	52	66
Net Amount, Derivative Liabilities	1,657	1,712
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0	0
Derivative Liability, Fair Value, Gross Liability	1,657	1,712
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Other Credit Derivatives [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	0	1
Net Amount, Derivative Liabilities	0	1
Derivative Liability, Fair Value, Gross Liability	0	1
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	75	60
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	75	59
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	90	72
Fair value of derivative liabilities	89	67
Net Amount, Derivative Assets	75	59
Net Amount, Derivative Liabilities	1	5
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		0
Derivative Liability, Fair Value, Gross Liability	89	72
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Interest Rate Swaps [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	1,657	1,712
Net Amount, Derivative Liabilities	1,657	1,712
Derivative Liability, Fair Value, Gross Liability	1,657	1,712
Future [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities		3
Fair value of derivative liabilities		3
Net Amount, Derivative Liabilities		0
Derivative Liability, Fair Value, Gross Liability		3
Derivative Liability, Fair Value, Amount Offset Against Collateral		0
Currency Swaps [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	52	66
Derivative Asset, Fair Value, Amount Offset Against Collateral	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	52	66
Net Amount, Derivative Assets	$ 52	66
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		$ 0

Derivative Instruments - Additi

Derivative Instruments - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative, Net Liability Position, Aggregate Fair Value		$ 89	$ 67
Derivative, Collateral, Right to Reclaim Cash	$ 36	103
Collateral Already Posted, Aggregate Fair Value		109	$ 84
Variable Interest Entity, Primary Beneficiary [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	1,194	1,400
Variable Interest Entity, Primary Beneficiary [Member] | Interest Rate Swap One [Member]
Derivative [Line Items]
Derivative, Notional Amount	1,176	1,177
Variable Interest Entity, Primary Beneficiary [Member] | Currency Swaps [Member]
Derivative [Line Items]
Derivative, Notional Amount	329	345
Variable Interest Entity, Primary Beneficiary [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative, Notional Amount	9	10
AFS [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	332	493
AFS [Member] | Interest Rate Swap One [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 1,261	$ 1,122

Derivative Instruments - Summ_2

Derivative Instruments - Summary of Location and Amount of Gains and Losses of Derivative Contracts (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]
Unrealized Gain (Loss) on Derivatives									$ 1	$ (1)	$ 15
Derivative, Gain (Loss) on Derivative, Net	$ 12	$ (10)	$ (35)	$ (16)	$ (45)	$ 18	$ 9	$ 25	(50)	7	76
Derivative, Gain (Loss) on Derivatives, Total Net									(82)	512	(76)
Net gains (losses) on derivative contracts [Domain] | Credit Derivatives [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net									2	(1)	16
Net gains (losses) on derivative contracts [Domain] | Interest Rate Swaps [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net									(6)	1	49
Net gains (losses) on derivative contracts [Domain] | Futures Contracts [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net									(45)	7	11
Income Loss On Variable Interest Entities [Member] | Variable Interest Entity [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net									(32)	505	(152)
Income Loss On Variable Interest Entities [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net									(20)	493	(127)
Income Loss On Variable Interest Entities [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Gain (Loss) on Derivative, Net									$ (12)	$ 11	$ (26)

Derivative Instruments - Summ_3

Derivative Instruments - Summarize Information by Major Category of CDS Contracts (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Summary of information by major category of CDS contracts
Net derivative liabilities at fair value	$ 89
AA Rating [Member] | Other Credit Derivatives [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative, Notional Amount	$ 280	$ 295

Derivative Instruments - Summ_4

Derivative Instruments - Summary of Notional Amounts of AFS's Trading Derivative Products (Detail) - AFS [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Interest Rate Swaps [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative, Notional Amount	$ 332	$ 493
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, Notional Amount	$ 1,261	$ 1,122

Derivative Instruments - Summ_5

Derivative Instruments - Summary of Notional for VIE Derivatives Outstanding (Detail) - Variable Interest Entity, Primary Beneficiary [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Interest Rate Swaps [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative, Notional Amount	$ 1,194	$ 1,400
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, Notional Amount	1,176	1,177
Currency Swaps [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative, Notional Amount	329	345
Other Credit Derivatives [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative, Notional Amount	$ 9	$ 10

Loans (Details)

Loans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, Unpaid principal balance	$ 19	$ 19
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate On Term Loan		6.51%
Loan Maturity Date	Jun. 30, 2026
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate On Term Loan	7.35%	8.60%
Loan Maturity Date	Dec. 15, 2046

Long-Term Debt (Details)

Long-Term Debt (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Aug. 03, 2018	Feb. 12, 2018	May 01, 2013
Debt Instrument [Line Items]
Tier 2 Note Security in RMBS Litigation Settlement Proceeds													$ 1,600
Long-term debt	$ 2,822				$ 2,929				$ 2,822	$ 2,929
One Time Interest Payment on Surplus Notes													$ 14
Junior surplus note of Ambac Assurance Segregated Account														$ 350
AMPS Exchange Total Surplus Notes Issued												$ 213
Net realized gains (losses) on extinguishment of debt	0	$ 0	$ 0	$ 0	0	$ 0	$ 0	$ 3	0	3	$ 5
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	531								531
Long-term Debt, Maturities, Repayments of Principal in Year Two	0								0
Long-term Debt, Maturities, Repayments of Principal in Year Three	0								0
Long-term Debt, Maturities, Repayments of Principal in Year Four	1,763								1,763
Long-term Debt, Maturities, Repayments of Principal in Year Five	0								0
Paydown of Ambac Note									178	214
Long-term Debt, Maturities, Repayments of Principal after Year Five	$ 687								$ 687
Ambac Note Post Exit From Rehabilitation [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	7.60%								7.60%
Paydown of Ambac Note									$ (178)	(214)
Tier 2 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	8.50%								8.50%
Debt Instrument, Interest Rate, Effective Percentage	9.90%								9.90%
Debt Instrument, Face Amount	$ 281								$ 281
Paid-in-Kind Interest									$ 41	19
5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	10.10%								10.10%
Net realized gains (losses) on extinguishment of debt										3
5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	19.50%								19.50%
One State Street [Member] | 5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 15				17				$ 15	17
Debt Instrument Principal Amount Subject To Repurchase	$ 0								0
Extinguishment of Debt, Amount									$ 2	4
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member] | 5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	8.40%								8.40%
Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Long-term debt	$ 2,822				2,929				$ 2,822	2,929
Long-term Debt, Gross	2,980				3,096				2,980	3,096
Debt Instrument, Unamortized Discount (Premium), Net	(159)				(167)				(159)	(167)
Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes, General Account Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	252				250				252	250
Long-term Debt, Gross	365				367				365	367
Debt Instrument, Unamortized Discount (Premium), Net	(113)				(117)				(113)	(117)
Ambac Assurance Corporation [Member] | Ambac Note Post Exit From Rehabilitation [Member]
Debt Instrument [Line Items]
Long-term debt	1,763				1,940				1,763	1,940
Long-term Debt, Gross	1,763				1,940				1,763	1,940
Debt Instrument, Unamortized Discount (Premium), Net	0				0				0	0
Ambac Assurance Corporation [Member] | Tier 2 Notes [Member]
Debt Instrument [Line Items]
Long-term debt	278				252				278	252
Long-term Debt, Gross	281				259				281	259
Debt Instrument, Unamortized Discount (Premium), Net	(4)				(7)				(4)	(7)
Ambac Assurance Corporation [Member] | 5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	517				487				517	487
Long-term Debt, Gross	531				531				531	531
Debt Instrument, Unamortized Discount (Premium), Net	$ (14)				(44)				$ (14)	(44)
Ambac UK [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	0.00%								0.00%
Long-term debt	$ 13				0				$ 13	0
Long-term Debt, Gross	41				0				41	0
Debt Instrument, Unamortized Discount (Premium), Net	$ (28)				$ 0				$ (28)	$ 0
Debt Instrument, Interest Rate, Effective Percentage	7.40%								7.40%
Variable Interest Entities [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage											6.65%
5.1% Junior Surplus Notes Due 2020 [Member] | Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					5.10%					5.10%	5.10%
Debt Instruments Maturity Year										2020	2020
5.1 % Surplus Notes Due 2020 [Member] | Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					5.10%					5.10%	5.10%
Debt Instruments Maturity Year										2020	2020
5.1% Surplus Notes, General Account, Due 2020 [Member] | Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage													5.10%
Consolidated Variable Interest Entities [Member]
Debt Instrument [Line Items]
Unpaid Principal Amount Of Fixed Rate Debt Accounted For Under Fair Value Option	$ 3,990				$ 4,553				$ 3,990	$ 4,553
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	0								0
Long-term Debt, Maturities, Repayments of Principal in Year Two	0								0
Long-term Debt, Maturities, Repayments of Principal in Year Three	0								0
Long-term Debt, Maturities, Repayments of Principal in Year Four	0								0
Long-term Debt, Maturities, Repayments of Principal in Year Five	0								0
Long-term Debt, Maturities, Repayments of Principal after Year Five	$ 3,990								$ 3,990
Consolidated Variable Interest Entities [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	0.00%				1.36%				0.00%	1.36%
Consolidated Variable Interest Entities [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	7.93%				7.93%				7.93%	7.93%
London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest Rate on Ambac Note Post Exit From Rehabilitation									5.00%
London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate on Ambac Note Post Exit From Rehabilitation									1.00%
Ambac [Member]
Debt Instrument [Line Items]
One Time Interest Payment on Surplus Notes													$ 3
Long-term Debt [Member]
Debt Instrument [Line Items]
Gain Contingency, Unrecorded Amount	$ 1,400								$ 1,400

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2011
Tax Credit Carryforward [Line Items]
Deferred Tax Liabilities, Net	$ 32,000		$ 40,000
Tolling Payment Payable to AFG	147,000
Impact of AMT Repeal on Current Taxes		$ 29,581
Impact of new Tax Law on Deferred Taxes		31,418
Net Impact of New Tax Law		1,886
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	0	$ 0	$ 0
NOL allocated amount	3,535,000			$ 3,650,000
AFG [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	1,250,000
U. S. Federal Net Operating Tax [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	$ 3,535,000
Minimum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2029
Minimum [Member] | AFG [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
Maximum [Member] | AFG [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 1, 2034

Income Taxes - Significant Port

Income Taxes - Significant Portions of Deferred Tax Liabilities and Deferred Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Deferred Tax Assets, Net of Valuation Allowance	$ 151	$ 212
Deferred tax assets:
Net operating loss and capital carryforward	742	719
Loss reserves	148	227
Deferred Tax Assets, Debentures	29	23
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation	7	10
Other	1	2
Sub total deferred tax assets	927	980
Valuation allowance	777	768
Insurance intangible	90	151
Variable interest entities	12	19
Investments	32	26
Unearned premiums and credit fees	42	48
Other	8	8
Deferred Tax Liabilities, Gross, Noncurrent	183	252
Deferred Tax Liabilities, Net	$ 32	$ 40

Income Taxes Income Taxes - Pro

Income Taxes Income Taxes - Provision for Income Taxes Charged To Income From Continuing Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Provision for Income Taxes [Line Items]
Current Federal Tax Expense (Benefit)	$ 0	$ (2)	$ (30)
Current Income Tax Expense (Benefit)	34	0	13
Deferred Income Tax Expense (Benefit)	(1)	5	31
Income tax expense (benefit)	32	5	44
Deferred Foreign Income Tax Expense (Benefit)	(1)	5	31
Current State and Local Tax Expense (Benefit)	(3)	2	2
Current Foreign Tax Expense (Benefit)	$ 37	$ (1)	$ 41

Income Taxes Income Taxes - Eff

Income Taxes Income Taxes - Effect of Income Taxes on Net Income and Stockholders' Equity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Expense (Benefit) [Roll Forward]
Income tax expense (benefit)	$ 32	$ 5	$ 44
Net Unrealized Losses On Securities Tax Effect	14	12	(31)
Valuation Allowances And Reserves Charged To Equity	(23)	(9)	(5)
Income Tax Effects Allocated Directly to Equity	(8)	3	0
Unrealized Loss on FX Tax Effect	0	0	26
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, Tax			0
Income Tax Effects Allocated Directly to Equity, Other	$ 24	$ 8	$ 44

Income Taxes Income Taxes - E_2

Income Taxes Income Taxes - Effective Tax Rates Differing From Prevailing Federal Corporate Income Tax Rates (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Effective Tax Rates [Line Items]
Tax on income from continuing operations at statutory rate									$ (38)	$ 57	$ (99)
Tax on income from continuing operations at statutory rate,tax rate									21.00%	21.00%	35.00%
Tax-exempt interest									$ (3)	$ (7)	$ (6)
Tax-exempt interest, tax rate									1.80%	(2.50%)	2.10%
Derivative, Gain (Loss) on Derivative, Net	$ 12	$ (10)	$ (35)	$ (16)	$ (45)	$ 18	$ 9	$ 25	$ (50)	$ 7	$ 76
Valuation allowance									$ 8	$ 5	$ 128
Valuation allowance, tax rate									(4.40%)	1.90%	(44.90%)
Foreign taxes									$ 40	$ 10	$ (18)
Foreign taxes, tax rate									(22.10%)	3.90%	6.20%
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Amount									$ 28	$ (60)	$ 36
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent									(15.30%)	(22.00%)	(12.70%)
Other, net									$ (2)	$ 1	$ 2
Other, net, tax rate									1.30%	0.40%	(0.70%)
Income tax expense (benefit)									$ 32	$ 5	$ 44
Effective Income Tax Rate Reconciliation, Percent									(17.70%)	2.00%	(15.70%)
Income Tax Reconciliation Tax Bankruptcy Adjustments									$ 0	$ (2)	$ 2
Effective income Tax Reconciliation Tax Bankruptcy Adjustments									0.00%	(0.70%)	(0.70%)
Variable Interest Entity, Primary Beneficiary [Member] | Income Loss On Variable Interest Entities [Member]
Reconciliation of Effective Tax Rates [Line Items]
Derivative, Gain (Loss) on Derivative, Net									$ (32)	$ 505	$ (152)
Variable Interest Entity, Primary Beneficiary [Member] | Currency Swaps [Member] | Income Loss On Variable Interest Entities [Member]
Reconciliation of Effective Tax Rates [Line Items]
Derivative, Gain (Loss) on Derivative, Net									(12)	11	(26)
Variable Interest Entity, Primary Beneficiary [Member] | Interest Rate Swaps [Member] | Income Loss On Variable Interest Entities [Member]
Reconciliation of Effective Tax Rates [Line Items]
Derivative, Gain (Loss) on Derivative, Net									$ (20)	$ 493	$ (127)

Income Taxes Income Taxes - Rec

Income Taxes Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits [Line Items]
AACNetTaxableIncomeFromTierB	$ 1,029
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	0	$ 0	$ 0
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Unrecognized Tax Benefits	0	0	0
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	0	0	0
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	0	0	0
Unrecognized Tax Benefits	0	0	0
UnrecognizedTaxBenefitsInterestOnIncomeTaxesPaid	$ 0	$ 0	$ 0

Income Taxes Income Taxes - NOL

Income Taxes Income Taxes - NOL Usage Table (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended			87 Months Ended
	Sep. 30, 2011	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018
Net Income Loss Reconciliation [Line Items]
Impact of AMT Repeal on Current Taxes				$ 29,581
Change in Impact of AMT Repeal on Current Taxes			$ 1,902
AMT Related to Filing of 2017 Tax Return				5,536
AMT Receivable Resulting from TCJA			$ 37,019		$ 37,019
Impact of new Tax Law on Deferred Taxes				31,418
Net Impact of New Tax Law				$ 1,886
AMT Installment Payment End Date			Dec. 31, 2021
AACNetTaxableIncome					$ 1,508,000
Operating Loss Generated in Current Year		$ 143,000
TierABCCredit		(5,000)
TierABCredit		(10,000)
NOL allocated amount	$ 3,650,000	3,535,000
Tolling Payment to AFG		119,000
Tolling Payment Payable to AFG Outstanding Amount		28,000
Tolling Payment Payable to AFG		147,000
AACNetTaxableIncomeFromTierB		$ 1,029,000
Tier C Tolling Payment Payable to IRS		12.50%
Tier D Tolling Payments Payable to IRS		17.50%
Ambac Assurance [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		$ 2,285,000
Percentage Of Notional Federal Tax Liability	25.00%
AFG [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		1,250,000
Tier A [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		$ 479,000
NOL applicable percentage		15.00%
Tier B [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		$ 1,057,000
NOL applicable percentage		40.00%
Tier C [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		$ 1,057,000
NOL applicable percentage		10.00%
Tier D [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		$ 1,057,000
NOL applicable percentage		15.00%
Minimum [Member]
Net Income Loss Reconciliation [Line Items]
Operating Loss Carryforwards, Expiration Date		Dec. 31, 2029
Minimum [Member] | Ambac Assurance [Member]
Net Income Loss Reconciliation [Line Items]
Operating Loss Carryforwards, Expiration Date		Dec. 31, 2029
Minimum [Member] | AFG [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
Maximum [Member] | Ambac Assurance [Member]
Net Income Loss Reconciliation [Line Items]
Operating Loss Carryforwards, Expiration Date		Dec. 31, 2040
Maximum [Member] | AFG [Member]
Net Income Loss Reconciliation [Line Items]
Operating Loss Carryforwards, Expiration Date		Jan. 1, 2034

Income Taxes Schedule of Income

Income Taxes Schedule of Income Before Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Income Before Income Tax, Domestic and Foreign [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Domestic									$ (174)	$ 264	$ (451)
Income (Loss) from Continuing Operations before Income Taxes, Foreign									(9)	8	167
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	$ (111)	$ 69	$ (100)	$ (41)	$ (22)	$ (20)	$ 6	$ 308	$ (183)	$ 273	$ (284)

Income Taxes Impact of New Tax

Income Taxes Impact of New Tax Legislation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
AMT Receivable Resulting from TCJA	$ 37,019
Change in Impact of AMT Repeal on Current Taxes	$ 1,902
AMT Installment Payment End Date	Dec. 31, 2021
Impact of AMT Repeal on Current Taxes		$ 29,581
AMT Related to Filing of 2017 Tax Return		$ 5,536

Employment Benefit Plans Postre

Employment Benefit Plans Postretirement Health Care and Other Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Postemployment Benefits, Period Expense	$ 3	$ 1	$ 5
Unfunded Accumulated Postretirement Benefit Obligations Determined By Company	$ 8
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.00%	4.00%
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	$ 0
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	0
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	0
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	0
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	1
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	3
Defined Benefit Plan, Benefit Obligation	$ 5
Maximum [Member]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year	5.30%
Minimum [Member]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year	4.50%

Employment Benefit Plans Saving

Employment Benefit Plans Savings Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	3.00%
Defined Contribution Plan, Cost	$ 1	$ 1	$ 1
Minimum [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	100.00%
Maximum [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	50.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	2.00%

Employment Benefit Plans Stock

Employment Benefit Plans Stock Compensation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based compensation expense [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	4,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,383,489
Share Based Compensation Arrangement Shares Available for Future Issuance at Target	2,079,181
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		$ 0
Share-based Payment Arrangement, Expense	$ 12	12	$ 4
Total stock-based compensation (after-tax)	12	12	4
Other Labor-related Expenses	0	1	2
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	0	0	0
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	4	6	2
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	8	6	3
Ambac UK [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Other Labor-related Expenses	5	1	$ 2
Retained Earnings [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	$ 0	$ 0

Employment Benefit Plans Stoc_2

Employment Benefit Plans Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	7 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	16,667	16,667
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 20.63	$ 20.63
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	29 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	16,667
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	$ 20.63
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	29 days
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount	$ 0

Employment Benefit Plans Restri

Employment Benefit Plans Restricted Stock Units (Details)	12 Months Ended
	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payment, Tax Withholding, Share-based Payment Arrangement | $	$ 3,000,000	$ 1,000,000	$ 1,000,000
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Restricted Stock Units Vested Number	453,637	435,935
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	209,093
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	248,942	209,093
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payment, Tax Withholding, Share-based Payment Arrangement | $	$ 72,977
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	645,028
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	248,861
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	189,832
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(1,478)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	702,579	645,028
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ / shares	$ 17.17
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares	19.75	$ 16.35	$ 20.22
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value | $ / shares	16.76
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value | $ / shares	20.11
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ / shares	$ 18.19	$ 17.17
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized | $	$ 2,000,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	1 year 8 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value | $	$ 4,000,000	$ 1,000,000	$ 3,000,000
Annual Bonus and Special Awards [Domain] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSU Award Vesting Period	2
Long-term Incentive Compensation [Domain] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSU Award Vesting Period	3

Employment Benefit Plans Perfor

Employment Benefit Plans Performance Units (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		$ 0
Total Shareholder Return Modifier	10.00%
Payment, Tax Withholding, Share-based Payment Arrangement	$ 3,000,000	$ 1,000,000	$ 1,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	209,093
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	248,942	209,093
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Shareholder Return Modifier	2500.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Shareholder Return Modifier	7500.00%
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PSUUnrecognizedCompensationYearstoGo	1 year 7 months 6 days
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
PerformanceAwardsSettlementPeriod	75 days
Target Units	100.00%
Payment, Tax Withholding, Share-based Payment Arrangement	$ 64,086
PerformanceStockUnitsUnrecognizedCompensationExpense	$ 6,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	516,999
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	230,391
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(166,353)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(8,151)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	650,212	516,999
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 17.02
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	19.17
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	15.52
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	18.11
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 17.98	$ 17.02
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Period Increase (Decrease)	77,326
ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsIncrease(Decrease)WeightedAverageGrantDateFairValue	$ 15.52
Performance Shares [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	0.00%
Performance Shares [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	220.00%
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PSUUnrecognizedCompensationYearstoGo	1 year 8 months 12 days
Payment, Tax Withholding, Share-based Payment Arrangement	$ 72,977
PerformanceStockUnitsUnrecognizedCompensationExpense	$ 2,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	645,028
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	248,861
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	189,832
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(1,478)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	702,579	645,028
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 17.17
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	19.75	$ 16.35	$ 20.22
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	16.76
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	20.11
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 18.19	$ 17.17

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	Dec. 31, 2019USD ($)
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments, Due Thereafter	$ 6

Quarterly Information (unaudi_3

Quarterly Information (unaudited) Quarterly Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Gross Premiums Written	$ 2,000	$ 13,000	$ 21,000	$ 3,000	$ 5,000	$ 23,000	$ 1,000	$ 4,000
Premiums Earned, Net, Financial Guarantee Insurance Contracts	20,000	10,000	8,000	28,000	29,000	26,000	26,000	31,000	$ 66,000	$ 111,000	$ 175,000
Net Investment Income	42,000	45,000	86,000	55,000	37,000	58,000	67,000	110,000	227,000	273,000	361,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	0	0	0	(2,000)	0	(1,000)	0	0	(3,000)	(20,000)
Realized Investment Gains (Losses)	9,000	18,000	36,000	17,000	29,000	30,000	47,000	5,000	81,000	112,000	5,000
Derivative, Gain (Loss) on Derivative, Net	12,000	(10,000)	(35,000)	(16,000)	(45,000)	18,000	9,000	25,000	(50,000)	7,000	76,000
Net realized gains (losses) on extinguishment of debt	0	0	0	0	0	0	0	3,000	0	3,000	5,000
Other income	1,000	141,000	(9,000)	1,000	2,000	1,000	2,000	(1,000)	134,000	5,000	0
Variable Interest Entity, Measure of Activity, Operating Income or Loss	7,000	11,000	3,000	16,000	0	2,000	1,000	1,000	38,000	3,000	20,000
Policyholder Benefits and Claims Incurred, Net, Financial Guarantee	(97,000)	(37,000)	133,000	(12,000)	42,000	(34,000)	(33,000)	(247,000)	(13,000)	224,000	(513,000)
Amortization of insurance intangible assets	15,000	17,000	226,000	36,000	29,000	26,000	23,000	29,000	295,000	107,000	151,000
Other Underwriting Expense	23,000	26,000	29,000	25,000	21,000	28,000	26,000	36,000	103,000	112,000	122,000
Interest Expense, Debt	66,000	67,000	67,000	68,000	66,000	66,000	62,000	48,000	269,000	242,000	120,000
Pre-tax (loss) income from continuing operations	(111,000)	69,000	(100,000)	(41,000)	(22,000)	(20,000)	6,000	308,000	(183,000)	273,000	(284,000)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(110,000)	66,000	(128,000)	(43,000)	(20,000)	(22,000)	4,000	306,000	(216,000)	267,000	(329,000)
Net Income (Loss) Attributable to Parent	$ (110,000)	$ 66,000	$ (128,000)	$ (43,000)	$ (20,000)	$ (104,000)	$ 4,000	$ 306,000	$ (216,000)	$ 186,000	$ (329,000)
Earnings Per Share, Basic	$ (2.40)	$ 1.44	$ (2.79)	$ (0.94)	$ (0.45)	$ (2.27)	$ 0.09	$ 6.72	$ (4.69)	$ 4.07	$ (7.25)
Earnings Per Share, Diluted	$ (2.40)	$ 1.41	$ (2.79)	$ (0.94)	$ (0.45)	$ (2.27)	$ 0.09	$ 6.70	$ (4.69)	$ 3.99	$ (7.25)

Schedule I - Summary Of Investm

Schedule I - Summary Of Investments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Cost	$ 3,575
Investments	3,792	$ 3,937
Other Investments and Securities, at Cost	388
Other Investments	478	$ 391
U.S. Government Obligations [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities	156
Short-term Investments [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	737
Available-for-sale Securities	737
U S Government Obligations [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Cost	157
Fixed Income Securities [Member] | Municipal Bonds [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	194
Available-for-sale Securities	215
Fixed Income Securities [Member] | Corporate Debt Securities [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,396
Available-for-sale Securities	1,430
Fixed Income Securities [Member] | Debt Security, Government, Non-US [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	44
Available-for-sale Securities	44
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	200
Available-for-sale Securities	248
Fixed Income Securities [Member] | Collateralized Mortgage Backed Securities [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	49
Available-for-sale Securities	50
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	147
Available-for-sale Securities	146
Fixed Income Securities [Member] | Asset-backed Securities [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	263
Available-for-sale Securities	287
Fair Value Measurement [Domain]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Investments	3,807
Other Investments	$ 493

Schedule II - Condensed Financi

Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 01, 2013
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock, shares issued	45,571,743	45,365,170
Treasury stock, shares	16,343	28,892
Common Stock, Shares, Outstanding	45,555,400	45,336,278
Assets:
Debt Securities, Available-for-sale	$ 3,314
Junior surplus note of Ambac Assurance Segregated Account					$ 350
Short-term investments, at cost (approximates fair value)	3,187	$ 3,451
Other Investments	478	391
Total investments	3,792	3,937
Other assets	95	138
Total assets	13,320	14,589
Tolling Payment Payable to AFG	28	44
Liabilities:
Total liabilities	11,783	12,956
Stockholders' equity (deficit):
Preferred stock	0	0
Common stock	0	0
Additional paid-in capital	232	219
Accumulated other comprehensive income (loss)	42	(49)	$ (52)
Retained earnings	1,203	1,421
Common stock held in treasury at cost	0	0
Total Ambac Financial Group, Inc. stockholders’ equity	1,477	1,592
Total liabilities and stockholders’ equity	13,320	14,589
Ambac Financial Group, Inc Parent Company Only [Member]
Assets:
Short-term investments, at cost (approximates fair value)	71	151
Other Investments	46	40
Total investments	434	381
Cash	9	15
Investment in subsidiaries	993	1,148
Investment income due and accrued	1	1
Current taxes receivable	30	44
Other assets	11	3
Total assets	1,478	1,593
Liabilities:
Accounts payable and other liabilities	2	1
Total liabilities	2	1
Stockholders' equity (deficit):
Preferred stock	0	0
Common stock	0	0
Additional paid-in capital	232	219
Accumulated other comprehensive income (loss)	42	(49)
Retained earnings	1,203	1,421
Common stock held in treasury at cost	0	0
Total Ambac Financial Group, Inc. stockholders’ equity	1,477	1,592	$ 1,381	$ 1,714
Total liabilities and stockholders’ equity	1,478	1,593
Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	653	430
Short-term investments, at cost (approximates fair value)	653	430
Short-term Investments [Member] | Ambac Financial Group, Inc Parent Company Only [Member]
Assets:
Short-term investments, at cost (approximates fair value)	318	193
Fixed Income Securities [Member]
Assets:
Debt Securities, Available-for-sale	2,577	3,116
Short-term investments, at cost (approximates fair value)	2,450	3,021
Fixed Income Securities [Member] | Ambac Financial Group, Inc Parent Company Only [Member]
Assets:
Debt Securities, Available-for-sale	$ 70	$ 148

Schedule II - Condensed Finan_2

Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statement of Total Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Income Statements, Captions [Line Items]
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, Tax											$ 0
Revenues:
Other income	$ 1,000	$ 141,000	$ (9,000)	$ 1,000	$ 2,000	$ 1,000	$ 2,000	$ (1,000)	$ 134,000	$ 5,000	0
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	0	0	0	(2,000)	0	(1,000)	0	0	(3,000)	(20,000)
Net realized investment gains	(9,000)	(18,000)	(36,000)	(17,000)	(29,000)	(30,000)	(47,000)	(5,000)	(81,000)	(112,000)	(5,000)
Total revenues									496,000	511,000	622,000
Expenses:
Pre-tax income (loss)	(111,000)	69,000	(100,000)	(41,000)	(22,000)	(20,000)	6,000	308,000	(183,000)	273,000	(284,000)
Income tax expense (benefit)									(32,000)	(5,000)	(44,000)
Net income (loss) attributable to common stockholders	(110,000)	66,000	(128,000)	(43,000)	(20,000)	(104,000)	4,000	306,000	(216,000)	186,000	(329,000)
Other comprehensive income, after tax:
Net income (loss)	$ (110,000)	$ 66,000	$ (128,000)	$ (43,000)	$ (20,000)	$ (22,000)	$ 4,000	$ 306,000	(216,000)	267,000	(329,000)
Unrealized gains (losses) on securities, net of deferred income taxes of $0									65,000	55,000	(82,000)
Gains (losses) on foreign currency translation, net of income tax provision (benefit) of $0, $0 and $0									26,000	(48,000)	74,000
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, after Tax									0	1,000	0
Total other comprehensive income (loss), net of income tax									91,000	6,000	(7,000)
Total comprehensive income (loss) attributable to common stockholders									(125,000)	192,000	(335,000)
Ambac Financial Group, Inc Parent Company Only [Member]
Condensed Income Statements, Captions [Line Items]
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax									(8,000)	2,000	0
Other Comprehensive Income (Loss), Foreign Currency Translation Gain (Loss) Arising During Period, Tax									0	0	0
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, Tax									0	0
Revenues:
Investment income									19,000	28,000	24,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net									(2,000)	(1,000)	(1,000)
Net realized investment gains									(1,000)	1,000	7,000
Total revenues									18,000	26,000	17,000
Expenses:
Operating Expenses									16,000	8,000	4,000
Total expenses									16,000	8,000	4,000
Pre-tax income (loss)									2,000	17,000	13,000
Income tax expense (benefit)									5,000	11,000	29,000
Income before equity in undistributed net income (loss) of subsidiaries									(7,000)	(28,000)	(43,000)
Equity in undistributed net income (loss) of subsidiaries									(223,000)	157,000	(371,000)
Net income (loss) attributable to common stockholders									(216,000)	186,000	(329,000)
Other comprehensive income, after tax:
Net income (loss)									(216,000)	186,000	(329,000)
Unrealized gains (losses) on securities, net of deferred income taxes of $0									65,000	55,000	(82,000)
Gains (losses) on foreign currency translation, net of income tax provision (benefit) of $0, $0 and $0									26,000	(48,000)	74,000
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, after Tax									0	1,000	0
Changes to postretirement benefit, net of tax									(1,000)	(2,000)	1,000
Total other comprehensive income (loss), net of income tax									91,000	6,000	(7,000)
Total comprehensive income (loss) attributable to common stockholders									(125,000)	192,000	(335,000)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Tax Effect									$ 0	$ 0	$ 0

Schedule II - Condensed Finan_3

Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statements of Stockholders' Equity (Detail) - USD ($) $ in Millions	12 Months Ended			18 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	$ (125)	$ 274	$ (335)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		0
Stock-based compensation	(12)	(12)	(4)
Issuance of common stock	(3)	(1)	(2)
Payments for Repurchase of Warrants				$ 8
AMPS Impact on Stockholders Equity	19	(297)
Ending balance	1,536	1,633	1,645	1,978
Stockholders' Equity Attributable to Parent	1,477	1,592
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	(216)	267	(329)
Stock-based compensation	0	0
Issuance of common stock	(3)	(1)	(2)
AMPS Impact on Stockholders Equity	0	(82)
Ending balance	1,203	1,421	1,234	1,558
AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	91	6	(7)
Stock-based compensation	0	0
Issuance of common stock	0	0
AMPS Impact on Stockholders Equity	0	0
Ending balance	42	(49)	(52)	(39)
Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	0	0	0
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		0
Stock-based compensation	0	0
Issuance of common stock	0	0
AMPS Impact on Stockholders Equity	0	0
Ending balance	0	0	0	0
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	0	0	0
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		0
Stock-based compensation	0	0
Issuance of common stock	0	0
AMPS Impact on Stockholders Equity	0	0
Ending balance	0	0	0	0
Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	0	0	0
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		0
Stock-based compensation	(12)	(12)	(4)
Issuance of common stock	0	0
AMPS Impact on Stockholders Equity	0	8
Ending balance	232	219	200	195
Common Stock Held in Treasury, at Cost [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	0	0	0
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		0
Stock-based compensation	0	0
Issuance of common stock	0	0	0
AMPS Impact on Stockholders Equity	0	0
Ending balance	0	0	0	0
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	0	0	0
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		0
Stock-based compensation	0	0
Issuance of common stock	0	0	0
AMPS Impact on Stockholders Equity	19	(223)
Ending balance	60	41	264	264
Ambac Financial Group, Inc Parent Company Only [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	(125)	192	(335)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		0
Stock-based compensation	(12)	(12)	(4)
Issuance of common stock	(3)	(1)	(2)
AMPS Impact on Stockholders Equity		8
Stockholders' Equity Attributable to Parent	1,477	1,592	1,381	1,714
Ambac Financial Group, Inc Parent Company Only [Member] | Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	(216)	186	(329)
Issuance of common stock	(3)	(1)	(2)
Stockholders' Equity Attributable to Parent	1,203	1,421	1,234	1,558
Ambac Financial Group, Inc Parent Company Only [Member] | AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	91	6	(7)
Stockholders' Equity Attributable to Parent	42	(49)	(52)	(39)
Ambac Financial Group, Inc Parent Company Only [Member] | Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity Attributable to Parent	0	0	0	0
Ambac Financial Group, Inc Parent Company Only [Member] | Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity Attributable to Parent	0	0	0	0
Ambac Financial Group, Inc Parent Company Only [Member] | Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	(12)	(12)	(4)
AMPS Impact on Stockholders Equity		8
Stockholders' Equity Attributable to Parent	232	219	200	195
Ambac Financial Group, Inc Parent Company Only [Member] | Common Stock Held in Treasury, at Cost [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation		0
Issuance of common stock	0	0	0
Stockholders' Equity Attributable to Parent	$ 0	0	0	$ 0
Accounting Standards Update 2016-01 [Member] | Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		3
Accounting Standards Update 2016-01 [Member] | AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		(3)
Accounting Standards Update 2016-01 [Member] | Parent [Member] | Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		3
Accounting Standards Update 2016-01 [Member] | Parent [Member] | AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		$ (3)
Accounting Standards Update 2018-02 [Domain] | Ambac Financial Group, Inc Parent Company Only [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			0
Accounting Standards Update 2018-02 [Domain] | Ambac Financial Group, Inc Parent Company Only [Member] | Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			7
Accounting Standards Update 2018-02 [Domain] | Ambac Financial Group, Inc Parent Company Only [Member] | AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			$ (7)

Schedule II - Condensed Finan_4

Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended			18 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 03, 2018
Condensed Cash Flow Statements, Captions [Line Items]
AMPS Exchange Dollar Value Warrants Issued													$ 8,000
Cash flows from operating activities:
Net income (loss)	$ (110,000)	$ 66,000	$ (128,000)	$ (43,000)	$ (20,000)	$ (22,000)	$ 4,000	$ 306,000	$ (216,000)	$ 267,000	$ (329,000)
Adjustments to reconcile net income loss to net cash used in operating activities:
Accretion (Amortization) of Discounts and Premiums, Investments									(63,000)	(137,000)	(183,000)
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	0	0	0	2,000	0	1,000	0	0	3,000	20,000
Net realized investment gains	(9,000)	$ (18,000)	$ (36,000)	(17,000)	(29,000)	$ (30,000)	$ (47,000)	(5,000)	(81,000)	(112,000)	(5,000)
Decrease in current income taxes payable									35,000	(35,000)	(26,000)
Share-based compensation									12,000	12,000	4,000
Other, net									80,000	67,000	22,000
Net cash used in operating activities									(311,000)	(1,543,000)	(221,000)
Cash flows from investing activities:
Proceeds from matured bonds									379,000	432,000	814,000
Purchases of bonds									(959,000)	(528,000)	(2,054,000)
Change in short-term investments									(218,000)	127,000	(127,000)
Proceeds from Sale and Maturity of Other Investments									81,000	159,000	350,000
Payments for (Proceeds from) Other Investing Activities									(2,000)	0	(17,000)
Net cash provided by investing activities									1,000,000	1,588,000	1,163,000
AMPS Proceeds									19,000
Cash flows from financing activities:
Payments for Repurchase of Warrants												$ 8,000
AMPS Exchange Cash Paid									0	(11,000)
Net Cash Provided by (Used in) Financing Activities									(691,000)	(585,000)	(412,000)
Cash and Cash Equivalents, Period Increase (Decrease)									(2,000)	(541,000)	529,000
Cash and cash equivalents at beginning of period				63,000				624,000	63,000	624,000
Cash and cash equivalents end of period	24,000				63,000				24,000	63,000	624,000
Cash paid during the period for:
Income taxes									21,000	35,000	40,000
Ambac Financial Group, Inc Parent Company Only [Member]
Cash flows from operating activities:
Net income (loss)									(216,000)	186,000	(329,000)
Adjustments to reconcile net income loss to net cash used in operating activities:
Equity in undistributed net (income) loss of non-debtor subsidiaries									223,000	(157,000)	371,000
Accretion (Amortization) of Discounts and Premiums, Investments									(6,000)	(7,000)	(17,000)
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net									2,000	1,000	1,000
Net realized investment gains									(1,000)	1,000	7,000
Decrease in current income taxes payable									15,000	(15,000)	(1,000)
Share-based compensation									12,000	12,000	4,000
Decrease in other assets									(8,000)	12,000	(11,000)
Other, net									(6,000)	0	(10,000)
Net cash used in operating activities									16,000	32,000	16,000
Cash flows from investing activities:
Proceeds from matured bonds									86,000	230,000	187,000
Purchases of bonds									(2,000)	(137,000)	(196,000)
Change in short-term investments									(125,000)	(123,000)	(3,000)
Net cash provided by investing activities									(22,000)	(21,000)	(44,000)
Cash flows from financing activities:
AMPS Exchange Cash Paid									0
Cash and Cash Equivalents, Period Increase (Decrease)									(6,000)	11,000	(28,000)
Cash and cash equivalents at beginning of period				$ 15,000				$ 4,000	15,000	4,000	32,000
Cash and cash equivalents end of period	$ 9,000				$ 15,000				9,000	15,000	4,000	$ 32,000
Cash paid during the period for:
Income taxes									1,000	4,000	1,000
Parent [Member]
Cash flows from investing activities:
Proceeds from Sale and Maturity of Other Investments									0	25,000	(35,000)
Payments for (Proceeds from) Other Investing Activities									0	(5,000)	3,000
AMPS Proceeds									$ 19,000
Cash flows from financing activities:
AMPS Exchange Cash Paid										$ (11,000)	$ 0

Schedule II - Condensed Finan_5

Schedule II - Condensed Financial Information of Registrant (Parent Company Only) Schedule II - Condensed Financial Information of Registrant - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019
Entity Incorporation, Date of Incorporation	Apr. 29, 1991

Schedule II - Condensed Finan_6

Schedule II - Condensed Financial Information of Registrant (Parent Company Only) Schedule II - Condensed Financial Information of Registrant - Income Taxes (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended	87 Months Ended
	Sep. 30, 2011	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards	$ 3,650	$ 3,535
AACNetTaxableIncome			$ 1,508
Operating Loss Generated in Current Year		143
AACNetTaxableIncomeFromTierB		1,029
Tolling Payment Payable to AFG		147
Tolling Payment to AFG		119
TierABCCredit		(5)
TierABCredit		(10)
Tolling Payment Payable to AFG Outstanding Amount		$ 28
Minimum [Member]
Operating Loss Carryforwards, Expiration Date		Dec. 31, 2029
Maximum [Member]
Operating Loss Carryforwards, Expiration Date		Dec. 31, 2040
AFG [Member]
Operating Loss Carryforwards		$ 1,250
AFG [Member] | Minimum [Member]
Operating Loss Carryforwards, Expiration Date		Dec. 31, 2029
AFG [Member] | Maximum [Member]
Operating Loss Carryforwards, Expiration Date		Jan. 1, 2034
Ambac Assurance [Member]
Operating Loss Carryforwards		$ 2,285
Percentage Of Notional Federal Tax Liability	25.00%
Ambac Assurance [Member] | Minimum [Member]
Operating Loss Carryforwards, Expiration Date		Dec. 31, 2029
Ambac Assurance [Member] | Maximum [Member]
Operating Loss Carryforwards, Expiration Date		Dec. 31, 2040
Tier B [Member]
Operating Loss Carryforwards		$ 1,057

Schedule IV - Reinsurance (Deta

Schedule IV - Reinsurance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Direct Premiums Written	$ (28)	$ (24)	$ (14)
Ceded Premiums Written	31	17	(2)
Assumed Premiums Written	0	0	0
Premiums Written, Net	$ (60)	$ (41)	$ (12)
Percentage of Amount Assumed to Net		0.00%	0.00%