Ambac Financial (AMBC) 10-Q 11 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	8-May-15
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Trading Symbol	AMBC
Entity Registrant Name	AMBAC FINANCIAL GROUP INC
Entity Central Index Key	874501
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		45,003,680

Consolidated_Balance_Sheets

Consolidated Balance Sheets (Successor [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Assets:
Fixed income securities, at fair value (amortized cost: 2015—$4,672,886 and 2014—$4,514,878)	$4,865,750	$4,725,686
Fixed income securities pledged as collateral, at fair value (amortized cost: 2015—$64,432 and 2014—$64,378)	64,813	64,267
Short-term investments, at fair value (amortized cost: 2015—$220,980 and 2014—$360,069)	220,980	360,065
Other investments (includes 2015—$310,578 and 2014—$336,013 at fair value)	332,609	357,016
Total investments	5,484,152	5,507,034
Cash and cash equivalents	26,641	73,903
Receivable for securities	8,779	23,660
Investment income due and accrued	24,994	25,015
Premium receivables	951,999	1,000,607
Reinsurance recoverable on paid and unpaid losses	79,308	99,838
Deferred ceded premium	117,688	123,276
Subrogation recoverable	984,129	953,274
Loans	5,494	5,714
Derivative assets	113,622	109,017
Insurance intangible asset	1,347,295	1,410,920
Goodwill	514,511	514,511
Other assets	221,252	186,985
Total assets	25,386,610	25,159,864
Liabilities:
Unearned premiums	1,583,615	1,673,785
Loss and loss expense reserves	4,475,991	4,752,007
Ceded premiums payable	59,268	60,436
Obligations under investment agreements	111,967	160,079
Deferred taxes	1,905	2,079
Current taxes	2,333	5,701
Long-term debt	979,001	971,116
Accrued interest payable	322,408	304,139
Derivative liabilities	447,356	406,944
Other liabilities	56,914	63,396
Payable for securities purchased	34,559	762
Total liabilities	23,548,889	23,486,129
Stockholders’ equity:
Preferred stock, par value $0.01 per share; 20,000,000 shares authorized; issued and outstanding shares—none	0	0
Common stock, par value $0.01 per share; 130,000,000 shares authorized; issued and outstanding shares: 2015—45,006,057; 2014—45,005,932	450	450
Additional paid-in capital	189,533	189,138
Accumulated other comprehensive income	169,329	220,283
Accumulated earnings	1,204,001	989,290
Treasury stock, shares at cost: 2015—2,459; 2014—2,459	-56	-56
Total Ambac Financial Group, Inc. stockholders’ equity	1,563,257	1,399,105
Noncontrolling interest	274,464	274,630
Total stockholders’ equity	1,837,721	1,673,735
Total liabilities and stockholders’ equity	25,386,610	25,159,864
Variable Interest Entity [Member]
Variable interest entity assets:
Fixed income securities, at fair value	2,704,657	2,743,050
Restricted cash	6,219	7,708
Investment income due and accrued	3,783	1,284
Loans, at fair value	12,789,201	12,371,177
Other assets	2,886	2,891
Variable interest entity liabilities:
Accrued interest payable	5,768	3,268
Long-term debt, at fair value	13,341,902	12,882,076
Derivative liabilities	2,125,713	2,200,163
Other liabilities	$189	$178

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]
Fixed income securities, amortized cost	$4,672,886	$4,514,878
Fixed income securities pledged as collateral, amortized cost	64,432	64,378
Short-term investments, amortized cost	220,980	360,069
Other investments	$310,578	$240,969
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	45,006,057	45,005,932
Common stock, shares outstanding	45,006,057	45,005,932
Treasury stock, shares	2,459	2,459

Consolidated_Statements_of_Tot

Consolidated Statements of Total Comprehensive Income (Successor [Member], USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Successor [Member]
Revenues:
Net premiums earned	$65,718	$82,547
Net investment income:
Securities available-for-sale and short-term	63,332	68,807
Other investments	9,651	1,994
Total net investment income	72,983	70,801
Other-than-temporary impairment losses:
Total other-than-temporary impairment losses	-10,361	-10,392
Portion of other-than-temporary impairment recognized in other comprehensive income	7,242	0
Net other-than-temporary impairments	-3,119	-10,392
Net realized investment gains	54,101	16,289
Change in fair value of credit derivatives:
Realized gains and other settlements	419	775
Unrealized gains (losses)	-2,918	6,607
Net change in fair value of credit derivatives	-2,499	7,382
Derivative products	-37,774	-53,841
Net realized losses on extinguishment of debt	-93	0
Other income (expense)	-788	1,894
Income (loss) on variable interest entities	6,962	-5,542
Total revenues	155,491	109,138
Expenses:
Losses and loss (benefit)	-150,952	-140,011
Insurance intangible amortization	37,432	31,714
Underwriting and operating expenses	24,523	25,786
Interest expense	27,908	32,328
Total expenses (benefit)	-61,089	-50,183
Pre-tax income before reorganization items	216,580	159,321
Reorganization items	0	23
Pre-tax income	216,580	159,298
Provision for income taxes	1,709	3,249
Net income (loss)	214,871	156,049
Less: net (gain) loss attributable to noncontrolling interest	160	107
Net income attributable to common shareholders	214,711	155,942
Other comprehensive income (loss), after tax:
Net income (loss)	214,871	156,049
Unrealized gains (losses) on securities, net of deferred income taxes of $0	-17,448	88,722
Gains (losses) on foreign currency translation, net of deferred income taxes of $0	-33,805	4,284
Changes to postretirement benefit, net of tax of $0	-27	-204
Total other comprehensive income (loss), net of tax	-51,280	92,802
Total comprehensive income	163,591	248,851
Less: comprehensive (loss) gain attributable to the noncontrolling interest:
Net (gain) loss	160	107
Currency translation adjustments	-326	46
Total comprehensive income attributable to Ambac Financial Group, Inc.	$163,757	$248,698
Net income per share attributable to Ambac Financial Group, Inc. common shareholders:	$4.75	$3.46
Basic	$4.57	$3.31

Consolidated_Statements_of_Tot1

Consolidated Statements of Total Comprehensive Income (Parenthetical) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Successor [Member]
Unrealized (loss) gain on securities, taxes	$0	$0
Gain (loss) on foreign currency translation, taxes	0	0
Amortization of postretirement benefit, taxes	$0	$0

Consolidated_Statements_of_Sto

Consolidated Statements of Stockholders' Equity (Successor [Member], USD $)	Successor [Member]	Successor [Member]	Successor [Member]	Successor [Member]	Successor [Member]	Successor [Member]	Successor [Member]	Successor [Member]
In Thousands, unless otherwise specified	USD ($)	Retained Earnings/Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Common Stock Held in Treasury, at Cost [Member]	Noncontrolling Interest [Member]
		USD ($)	USD ($)	USD ($)	USD ($)	USD ($)	USD ($)	USD ($)
Beginning balance at Dec. 31, 2013	$978,422	$505,219	$11,661	$0	$450	$185,672	($19)	$275,439
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income	248,851	155,942	92,756	0	0	0	0	153
Stock-based compensation	1,537	0	0	0	0	1,537	0	0
Proceeds from warrant exercise	1	0	0	0	0	1	0	0
Ending balance at Mar. 31, 2014	1,228,811	661,161	104,417	0	450	187,210	-19	275,592
Beginning balance at Dec. 31, 2014	1,673,735	989,290	220,283	0	450	189,138	-56	274,630
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income	163,591	214,711	-50,954	0	0	0	0	-166
Stock-based compensation	393	0	0	0	0	393	0	0
Proceeds from warrant exercise	2	0	0	0	0	2	0	0
Ending balance at Mar. 31, 2015	$1,837,721	$1,204,001	$169,329	$0	$450	$189,533	($56)	$274,464

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Successor [Member]
Cash flows from operating activities:
Net income attributable to common shareholders	$214,711	$155,942
Net (loss) gain	-160	-107
Net income (loss)	214,871	156,049
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization	791	748
Amortization of bond premium and discount	-31,477	-27,940
Reorganization items	0	23
Share-based compensation	393	1,537
Deferred income taxes	-174	3
Current income taxes	-3,368	3,023
Unearned premiums, net	-84,582	-84,667
Losses and loss expenses, net	-197,332	-146,494
Ceded premiums payable	-1,168	-1,070
Investment income due and accrued	21	3,022
Premium receivables	48,608	34,907
Accrued interest payable	18,269	22,235
Amortization of insurance intangible assets	37,432	31,714
Net mark-to-market (gains) losses	2,918	-6,607
Net realized investment gains	-54,101	-16,289
Losses on extinguishment of debt	93	0
Other-than-temporary impairment charges	3,119	10,392
Variable interest entity activities	-6,962	5,542
Other, net	58,229	52,397
Net cash provided by operating activities	5,580	38,525
Cash flows from investing activities:
Proceeds from sales of bonds	487,462	276,555
Proceeds from matured bonds	299,715	230,290
Purchases of bonds	-919,361	-625,507
Proceeds from sales of other invested assets	36,543	36,894
Purchases of other invested assets	-10,176	-20,611
Change in short-term investments	139,085	56,016
Loans, net	220	-71
Change in swap collateral receivable	-37,239	-35,410
Other, net	779	-2,352
Net cash (used in) investing activities	-2,972	-84,196
Cash flows from financing activities:
Proceeds from warrant exercise	2	1
Payments for investment agreement draws	-49,872	0
Net cash provided by (used in) financing activities	-49,870	1
Net cash flow	-47,262	-45,670
Cash and cash equivalents at beginning of period	26,641	31,700
Cash and cash equivalents end of period	73,903	77,370
Supplemental disclosure of cash flow information:
Income taxes	4,933	0
Interest on investment agreements	88	202
Cash payments related to reorganization items:
Professional fees paid for services rendered in connection with the Chapter 11 proceeding	$0	$81

Background_and_Business_Descri

Background and Business Description	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Background and Business Description	BACKGROUND AND BUSINESS DESCRIPTION
	Ambac Financial Group, Inc. (“Ambac” or the “Company”), headquartered in New York City, is a financial services holding company incorporated in the state of Delaware on April 29, 1991.
	Ambac has two reportable business segments: Financial Guarantee and Financial Services.
	Ambac’s financial guarantee business segment is conducted through its primary operating subsidiary, Ambac Assurance Corporation (“Ambac Assurance”), and its wholly owned subsidiary, Ambac Assurance UK Limited (“Ambac UK”). 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 financial guarantee subsidiary, Everspan Financial Guarantee Corp. (“Everspan”), 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 from being able to write new business. An 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, Ambac’s liquidity, have been significantly restricted by the deterioration of Ambac Assurance’s financial condition, by the rehabilitation of the Segregated Account (as defined below) and by the terms of the Settlement Agreement, dated as of June 7, 2010 (the "Settlement Agreement"), by and among Ambac Assurance, Ambac Credit Products LLC (“ACP”), Ambac 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 terms of its Auction Market Preferred Shares, and the terms of agreements entered into with the Segregated Account. It is highly unlikely that Ambac Assurance will be able to make dividend payments to Ambac for the foreseeable future.
	Ambac’s financial services business segment is conducted through subsidiaries of Ambac Assurance, which provide financial and investment products, including investment agreements, funding conduits and interest rate swaps, principally to the clients of its financial guarantee business. Ambac Assurance insured all of the obligations of its financial services subsidiaries. These businesses are in active runoff, which is being effectuated by transaction terminations, settlements, and scheduled amortization of contracts. The Financial Services business also maintains interest rate derivatives to mitigate exposure to floating rate insured obligations in the Financial Guarantee segment.
	Ambac’s primary goal is to maximize shareholder value through executing the following key strategies:
	•	Increasing the value of its investment in Ambac Assurance by actively managing its assets and liabilities with a focus on maximizing risk-adjusted investment portfolio returns and mitigating or remediating losses on poorly performing insured transactions through executing policy commutations, pursuing recoveries of losses through litigation and the exercise of contractual and legal rights, restructuring transactions, and other means; and
	•	Selectively exploring opportunities to grow and diversify Ambac, which may include the development or acquisition of financial services businesses such as advisory, asset servicing, asset management and/or insurance.
	As part of its asset/liability management strategy, Ambac Assurance is considering the possibility of entering into transactions whereby it would monetize certain assets and/or restructure or exchange its outstanding debt and insurance obligations with the objective of ending the Segregated Account Rehabilitation Proceedings (as defined below).
	Although we are exploring new business opportunities for Ambac, no assurance can be given that we will be able to identify or execute the acquisition or development of any new business. In addition, there can be no assurance that we will be able to obtain the financial and other resources that may be required to finance the acquisition or development of any new business. 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 is speculative.
	The execution of Ambac’s strategy to increase the value of its investment in Ambac Assurance is subject to the authority of the Rehabilitator (as defined below) to control the management of the Segregated Account (as defined below). In exercising such authority, the Rehabilitator will act for the benefit of policyholders, and will not take into account the interests of Ambac. Similarly, by operation of the contracts executed in connection with the establishment, and subsequent rehabilitation, of the Segregated Account, the Rehabilitator retains rights to oversee and approve certain actions taken by or in respect of Ambac Assurance. This oversight by the Rehabilitator could impair Ambac’s ability to execute certain of its strategies. Ambac Assurance's ability to commute policies or purchase certain investments may also be limited by available liquidity.
	As a result of uncertainties associated with the aforementioned oversight by the Rehabilitator of the Segregated Account, management has concluded that there is substantial doubt about Ambac's ability to continue as a going concern. Ambac’s financial statements as of and for the and three and twelve months ending March 31, 2015 and December 31, 2014, respectively, are prepared assuming Ambac continues as a going concern and do not include any adjustment that might result from its inability to continue as a going concern.
	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 Office of the Commissioner of Insurance for the State of Wisconsin (“OCI” (which term shall be understood to refer to such office as regulator of Ambac Assurance and to refer to the Commissioner of Insurance for the State of Wisconsin as rehabilitator of the Segregated Account (the “Rehabilitator”), as the context requires)) 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 pursuant to the provisions of the Wisconsin Insurers Rehabilitation and Liquidation Act. On October 8, 2010, OCI filed a plan of rehabilitation for the Segregated Account (the “Segregated Account Rehabilitation Plan”) in the Rehabilitation Court. On June 11, 2014, the Rehabilitation Court approved amendments to the Segregated Account Rehabilitation Plan that had been proposed by the Rehabilitator, and the Segregated Account Rehabilitation Plan, as amended, became effective on June 12, 2014. Under the amended Segregated Account Rehabilitation Plan holders of permitted policy claims have received and will receive an initial interim cash payment for a portion of each policy claim (“Interim Payment”), together with the right to receive a deferred payment equal to the balance of the unpaid policy claim, as may be adjusted from time to time pursuant to the terms of the amended Segregated Account Rehabilitation Plan (“Deferred Amount”). Net par exposure as of March 31, 2015 for policies allocated to the Segregated Account was $18,052,539. Policy obligations not allocated to the Segregated Account remain in the General Account, and such policies in the General Account are not subject to and, therefore, will not be directly impacted by the Segregated Account Rehabilitation Plan.
	To pay claims and other liabilities, the Segregated Account has the ability to demand payment from time to time under an aggregate excess of loss reinsurance agreement provided by Ambac Assurance (the “Reinsurance Agreement”). In addition, certain operating and administrative costs and expenses of the Segregated Account are reimbursable by Ambac Assurance pursuant to the Cooperation Agreement, dated as of March 24, 2010, by and between the Segregated Account and Ambac Assurance, as amended (the “Cooperation Agreement”). Ambac Assurance is not obligated to make payments under the Reinsurance Agreement or Cooperation Agreement if its surplus as regards to policyholders is less than $100,000 (the “Minimum Surplus Amount”). As long as the surplus as regards to policyholders is not less than the Minimum Surplus Amount, payments by Ambac Assurance to the Segregated Account under the Reinsurance Agreement and Cooperation Agreement are not capped. At March 31, 2015, Ambac Assurance’s surplus as regards to policyholders is at the Minimum Surplus Amount and therefore $26,169 of the Segregated Account’s insurance liabilities were not assumed by Ambac Assurance under the Reinsurance Agreement. In the event that Ambac Assurance does not generate future surplus in the amount of insurance liabilities not assumed under the Reinsurance Agreement, the Segregated Account would experience a shortfall in funds available to pay its liabilities. Any such shortfall would be a consideration for the Rehabilitator in the determination of whether any changes to the Segregated Account Rehabilitation Plan (as defined below) and/or the amount of partial policy claim payments are necessary or appropriate or whether to institute general rehabilitation proceedings against Ambac Assurance.

Basis_of_Presentation_and_Sign

Basis of Presentation and Significant Accounting Policies (Notes)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES
	The Company has disclosed its significant accounting policies in Note 2. Significant Accounting Policies in the Notes to Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014. The following significant accounting policies provide an update to those included in the Company’s Annual Report on Form 10-K.
	Basis of Presentation
	The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles ("GAAP") for interim financial reporting and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and disclosures required by GAAP for annual periods. These statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Annual Report on Form 10-K for the year ended December 31, 2014. The accompanying consolidated financial statements have not been audited by an independent registered public accounting firm in accordance with the standards of the Public Company Accounting Oversight Board (U.S.), but in the opinion of management such financial statements include all adjustments, consisting only of normal recurring adjustments, necessary for the fair statement of the Company’s consolidated financial position and results of operations. All material intercompany balances and transactions have been eliminated. The results of operations for the three months ended March 31, 2015 may not be indicative of the results that may be expected for the year ending December 31, 2015. The December 31, 2014 consolidated balance sheet was derived from audited financial statements.
	The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. As additional information becomes available or actual amounts become determinable, the recorded estimates are revised and reflected in operating results.
	Reclassifications
	Certain reclassifications have been made to prior years' amounts to conform to the current year's presentation.
	Recently Adopted and Recently Issued Accounting Standards
	Adopted:
	Effective January 1, 2015, Ambac adopted ASU 2014-08, Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360) - Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity. The objective of this ASU is to limit discontinued operations reporting to disposals of components of an entity that represent strategic shifts that have (or will have) a major effect on an entity's operations and financial results. Under previous U.S. GAAP, many disposals, some of which may be routine in nature and not a change in an entity's strategy, were reported in discontinued operations. The ASU also requires certain expanded disclosures for discontinued operations and disclosure of the pre-tax profit or loss of an individually significant component of an entity that does not qualify for discontinued operations reporting. The adoption of this ASU did not have a material effect on Ambac's financial statements.
	Issued:
	In April 2015, the FASB issued ASU 2015-03, Interest - Imputation of Interest (Subtopic 835-30). This ASU simplifies the presentation of debt issuance costs by requiring that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by the amendments in this ASU. The ASU is effective for annual periods and interim periods within those annual periods beginning after December 15, 2015. Early adoption is also permitted for financial statements that have not been previously issued. Upon adoption, the ASU must be retrospectively applied to all prior periods presented. Ambac will adopt ASU 2015-02 on January 1, 2016. The adoption of this ASU is not expected to have a material impact on Ambac's financial statements.
	In May 2015, the FASB issued ASU 2015-07, Fair Value Measurement (Topic 820) - Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent). Reporting entities are permitted to use net asset value ("NAV") as a practical expedient to measure the fair value of certain investments. Under current U.S. GAAP, investments that use the NAV practical expedient to measure fair value are categorized within the fair value hierarchy as level 2 or level 3 investments depending on their redemption attributes, which has led to diversity in practice. This ASU will remove the requirement to categorize within the fair value hierarchy all investments that use the NAV practical expedient for fair value measurement purposes. Furthermore, the ASU will remove the requirement to make certain disclosures for all investments that are eligible to be measured at fair value using the NAV practical expedient. The ASU is effective for fiscal years beginning after December 15, 2015 and interim periods with those fiscal years. The ASU must be applied retrospectively to all prior periods presented. Ambac will adopt ASU 2015-07 on January 1, 2016. The adoption of this ASU is not expected to have a material impact on Ambac's financial statements.
	Basis of Presentation
	The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles ("GAAP") for interim financial reporting and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and disclosures required by GAAP for annual periods. These statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Annual Report on Form 10-K for the year ended December 31, 2014. The accompanying consolidated financial statements have not been audited by an independent registered public accounting firm in accordance with the standards of the Public Company Accounting Oversight Board (U.S.), but in the opinion of management such financial statements include all adjustments, consisting only of normal recurring adjustments, necessary for the fair statement of the Company’s consolidated financial position and results of operations. All material intercompany balances and transactions have been eliminated. The results of operations for the three months ended March 31, 2015 may not be indicative of the results that may be expected for the year ending December 31, 2015. The December 31, 2014 consolidated balance sheet was derived from audited financial statements.
	The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. As additional information becomes available or actual amounts become determinable, the recorded estimates are revised and reflected in operating results.

Special_Purpose_Entities_Inclu

Special Purpose Entities, Including Variable Interest Entities	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Special Purpose Entities, Including Variable Interest Entities	SPECIAL PURPOSE ENTITIES, INCLUDING VARIABLE INTEREST ENTITIES ("VIEs")
	Ambac, with its subsidiaries, has engaged in transactions with special purpose entities, including VIEs, in various capacities. Ambac most commonly provides financial guarantees, including credit derivative contracts, for various debt obligations issued by special purpose entities, including VIEs. Ambac has also sponsored special purpose entities that issued medium-term notes to fund the purchase of certain financial assets. Ambac is also 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. As further described in Note 1. Background and Business Description in the Notes to Consolidated Financial Statements included Part II, Item 8 in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014, 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. Ambac reports its interest in the VIE 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).
	Financial Guarantees:
	Ambac’s subsidiaries provide financial guarantees in respect of assets held or debt obligations of special purpose entities, including VIEs. Ambac’s primary variable interest exists through this financial guarantee insurance or credit derivative contract. The transaction structures provide certain financial protection to Ambac. This financial protection can take several forms; however, the most common are over-collateralization, first loss and excess spread. In the case of over-collateralization (i.e., the principal amount of the securitized assets exceeds the principal amount of the debt obligations guaranteed), the structure allows the transaction to experience defaults among the securitized assets before a default is experienced on the debt obligations that have been guaranteed by Ambac’s subsidiaries. In the case of first loss, the financial guarantee insurance policy or credit derivative contract only covers a senior layer of losses on assets held or debt issued by special purpose entities, including VIEs. The first loss with respect to the assets is either retained by the asset seller or sold off in the form of equity or mezzanine debt to other investors. In the case of excess spread, the securitized assets contributed to special purpose entities, including VIEs, generate interest cash flows that are in excess of the interest payments on the related debt; such excess cash flow is applied to redeem debt, thus creating over-collateralization. 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 loss remediation rights. These rights may enable Ambac to direct the activities of the entity that most significantly impact the entity’s economic performance.
	We determined that Ambac’s subsidiaries generally have the obligation to absorb a VIE's expected losses given that they have issued financial guarantees supporting the liabilities (and in certain cases assets). As further described below, we consolidated certain VIEs because: (i) we determined for certain transactions that experienced the aforementioned performance deterioration, that Ambac’s subsidiaries had the power, through voting rights or similar rights, to direct the activities of certain VIEs that most significantly impact the VIE’s economic performance because certain triggers had been breached in these transactions resulting in their ability to exercise certain loss remediation activities, or (ii) due to the passive nature of the VIEs’ activities, Ambac’s subsidiaries’ contingent loss remediation rights upon a breach of certain triggers in the future is considered to be the power to direct the activities that most significantly impact the VIEs’ economic performance. With respect to existing VIEs involving Ambac financial guarantees, Ambac is required to consolidate a VIE in the period that applicable triggers result in Ambac having control over the VIE’s most significant economic activities. A VIE is deconsolidated in the period that Ambac no longer has such control, which could occur in connection with insurance policies that are allocated to the Segregated Account, execution of remediation activities on the transaction or amortization of insured exposure, any of which may reduce the degree of Ambac’s control over a VIE.
	Ambac Sponsored VIEs:
	A subsidiary of Ambac transferred financial assets to two special purpose entities. The business purpose of these entities was to provide certain financial guarantee clients with funding for their debt obligations. These special purpose entities were established as separate legal entities, demonstrably distinct from Ambac and that Ambac, its affiliates or its agents could not unilaterally dissolve. The permitted activities of these entities were contractually limited to purchasing assets from Ambac, issuing MTNs to fund such purchase, executing derivative hedges and obtaining financial guarantee policies with respect to indebtedness incurred. Effective February 17, 2015, one of the special purpose entities was liquidated as it no longer had any outstanding liabilities. Ambac has not consolidated these entities because Ambac Assurance’s policies issued to these entities were allocated to the Segregated Account, thereby limiting Ambac’s control over the entities’ most significant economic activities. Ambac elected to account for its equity interest in these entities 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 these entities 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 7. Fair Value Measurements for further information on the valuation technique and inputs used to measure the fair value of Ambac’s equity interest in these entities. At March 31, 2015 and December 31, 2014 the fair value of these entities are $10,036 and $12,036, respectively, and is reported within Other assets on the Consolidated Balance Sheets.
	Since their inception, there have been 15 individual transactions with these entities, of which 3 transactions remain outstanding as of March 31, 2015. Total principal amount of debt outstanding was $457,960 and $457,960 at March 31, 2015 and December 31, 2014, respectively. In each case, Ambac sold assets to these entities. The assets are composed of utility obligations with a weighted average rating of BBB at March 31, 2015 and weighted average life of 6.8 years. The purchase by these entities of financial assets was financed through the issuance of medium-term notes (“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 entities for economic hedging purposes only. Derivative positions were established at the time MTNs were issued to purchase financial assets. As of March 31, 2015 Ambac Assurance had financial guarantee insurance policies issued for all assets, MTNs and derivative contracts owned and outstanding by the entities.
	Insurance premiums paid to Ambac Assurance by these entities 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.
	Consolidation of VIEs:
	Upon initial consolidation of a VIE, we recognize 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 VIE, we recognize 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 variable interest in a VIE generally involves one or more of the following: a financial guarantee policy issued to the VIE, a written credit derivative contract that references liabilities of the VIE or an investment in securities issued by the VIE. The impact of consolidating such VIEs on Ambac’s balance sheet is the elimination of transactions between the consolidated VIEs and Ambac’s operating subsidiaries and the inclusion of the 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. Ambac did not consolidate any VIEs solely as a result of purchases of the VIE’s debt instruments.
	As of March 31, 2015 consolidated VIE assets and liabilities relating to 14 consolidated entities were $15,506,746 and $15,473,572, respectively. As of December 31, 2014, consolidated VIE assets and liabilities relating to 15 consolidated entities were $15,126,110 and $15,085,685, respectively. Ambac is not primarily liable for, and does not guarantee all of the debt obligations issued by the VIEs. Ambac would only be required to make payments on the VIE debt obligations in the event that the issuer of such debt obligations defaults on any principal or interest due and such obligation is guaranteed by Ambac. Additionally, Ambac’s creditors 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 changes in fair value of most consolidated VIE assets and liabilities are attributable to Ambac due to Ambac’s interest through financial guarantee premium and loss payments with the VIE.
	The financial reports of certain VIEs are prepared by outside trustees and are not available within the time constraints Ambac requires to ensure the financial accuracy of the operating results. As such, the financial results of certain VIEs are consolidated on a time lag that is no longer than 90 days.
	The table below provides the fair value of fixed income securities, by asset-type, held by consolidated VIEs as of March 31, 2015 and December 31, 2014:
		March 31,		December 31,
		2015		2014
	Investments:
	Corporate obligations	$	2,704,657	$	2,743,050
	Total variable interest entity assets: fixed income securities	$	2,704,657	$	2,743,050
	The following table provides supplemental information about the loans held as assets and long-term debt associated with the VIEs for which the fair value option has been elected as of March 31, 2015 and December 31, 2014:
		Estimated fair value		Unpaid principal balance
	March 31, 2015
	Loans	$	12,789,201	$	9,675,140
	Long-term debt	13,341,902		11,299,861
	December 31, 2014
	Loans	12,371,177		10,236,695
	Long-term debt	$	12,882,076	$	11,925,499
	For the three months ended March 31, 2015, Ambac deconsolidated one VIE when the associated financial guarantee exposure matured. There was no gain or loss resulting from this deconsolidation.
	Variable Interests in Non-Consolidated VIEs
	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 March 31, 2015 and December 31, 2014:
		Carrying Value of Assets and Liabilities
		Maximum		Insurance		Insurance		Net Derivative
		Exposure		Assets (2)		Liabilities (3)		Assets (Liabilities)  (4)
		To Loss (1)
	March 31, 2015:
	Global structured finance:
	Collateralized debt obligations	$	1,297,393	$	303	$	3,889	$	(155,357	)
	Mortgage-backed—residential	18,837,405		1,037,566		2,879,199		—
	Other consumer asset-backed	4,460,126		55,219		671,303		(35,558		)
	Other commercial asset-backed	2,943,920		129,218		124,124		—
	Other	3,546,270		94,529		565,657		16,766
	Total global structured finance	31,085,114		1,316,835		4,244,172		(174,149		)
	Global public finance	30,674,652		438,852		513,664		(29,891		)
	Total	$	61,759,766	$	1,755,687	$	4,757,836	$	(204,040	)
	December 31, 2014:
	Global structured finance:
	Collateralized debt obligations	$	1,386,100	$	345	$	4,000	$	(145,565	)
	Mortgage-backed—residential	19,464,549		1,011,888		2,924,987		—
	Other consumer asset-backed	5,109,776		65,204		885,572		(36,877		)
	Other commercial asset-backed	3,119,891		135,215		128,988		—
	Other	3,801,382		97,345		599,915		18,176
	Total global structured finance	32,881,698		1,309,997		4,543,462		(164,266		)
	Global public finance	31,639,004		457,774		533,192		(22,135		)
	Total	$	64,520,702	$	1,767,771	$	5,076,654	$	(186,401	)
	-1	Maximum exposure to loss represents the maximum future payments of principal and interest on insured obligations and derivative contracts plus Deferred Amounts and accrued and unpaid interest thereon. 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 recorded in “Premium receivables” and “Subrogation recoverable” for financial guarantee contracts on Ambac’s Consolidated Balance Sheets.
	-3	Insurance liabilities represent the amount recorded in “Loss and loss expense reserves” and “Unearned premiums” for financial guarantee 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.

Comprehensive_Income

Comprehensive Income	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Comprehensive Income	COMPREHENSIVE INCOME
	The following tables detail the changes in the balances of each component of accumulated other comprehensive income for the affected periods:
		Unrealized Gains				Amortization of				Gain (Loss) on			Total
		(Losses) on				Postretirement				Foreign Currency
		Available- for				Benefit (1)				Translation (1)
		Sale Securities (1)
	Three Months Ended March 31, 2015
	Beginning Balance	$	210,693			$	10,031			$	(441	)	$	220,283
	Other comprehensive income before reclassifications	33,554				—				(33,479		)	75
	Amounts reclassified from accumulated other comprehensive income	(51,002		)		(27		)		—			(51,029		)
	Net current period other comprehensive income (loss)	(17,448		)		(27		)		(33,479		)	(50,954		)
	Balance at March 31, 2015	$	193,245			$	10,004			$	(33,920	)	$	169,329
	Three Months Ended March 31, 2014
	Beginning Balance	$	(41,910	)		$	10,847			$	42,724		$	11,661
	Other comprehensive income before reclassifications	94,622				—				4,238			98,860
	Amounts reclassified from accumulated other comprehensive income	(5,900		)		(204		)		—			(6,104		)
	Net current period other comprehensive income (loss)	88,722				(204		)		4,238			92,756
	Balance at March 31, 2014	$	46,812			$	10,643			$	46,962		$	104,417
	(1)    All amounts are net of tax and noncontrolling interest. Amounts in parentheses indicate debits.
	The following table details the significant amounts reclassified from each component of accumulated other comprehensive income for the affected periods:
			Amount Reclassified from Accumulated								Affected Line Item in the
			Other Comprehensive Income (1)
	Details about Accumulated Other		Three Months Ended March 31,								Consolidated Statement of
	Comprehensive Income Components		2015				2014				Total Comprehensive Income
	Unrealized Gains (Losses) on Available-for-Sale Securities
			$	(51,002	)		$	(5,900	)		Net realized investment gains
			—				—				Tax (expense) benefit
			$	(51,002	)		$	(5,900	)		Net of tax and noncontrolling interest (3)
	Amortization of Postretirement Benefit
	Prior service cost		$	(166	)		$	(166	)		Underwriting and operating expenses (2)
	Actuarial gains (losses)		139				(38		)		Underwriting and operating expenses (2)
			(27		)		(204		)		Total before tax
			—				—				Tax (expense) benefit
			$	(27	)		$	(204	)		Net of tax and noncontrolling interest (3)
	Total reclassifications for the period		$	(51,029	)		$	(6,104	)		Net of tax and noncontrolling interest (3)
	-1	Amounts in parentheses indicate debits to the Consolidated Statement of Comprehensive Income.
	-2	These accumulated other comprehensive income components are included in the computation of net periodic benefit cost.
	-3	Amount agrees with amount reported as reclassifications from AOCI in the disclosure about changes in AOCI balances.

Net_Income_Per_Share

Net Income Per Share	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Net Income Per Share	NET INCOME PER SHARE
	Pursuant to the Second Modified Fifth Amended Plan of Reorganization of Ambac Financial Group, Inc. (the "Reorganization Plan"), 45,000,000 shares of new common stock at par value of $0.01 per share and 5,047,138 warrants were issued. Warrants entitle such holders to acquire up to 5,047,138 shares of new common stock at an exercise price of $16.67 per share at any time on or prior to April 30, 2023. For the three months ended March 31, 2015 and 2014, 125 and 51 warrants were exercised, respectively, resulting in an issuance of 125 and 51 shares of common stock, respectively. As of March 31, 2015, Ambac had 5,039,752 warrants outstanding.
	Basic net income per share is computed by dividing net income attributable to common shareholders by the weighted-average number of common shares outstanding and vested restricted stock units. Diluted net income per share is computed by dividing net income attributable to common shareholders by the weighted-average number of common shares used for basic earnings per share plus all potential dilutive common shares outstanding during the period. All potential dilutive common shares outstanding consider common stock deliverable pursuant to warrants issued under the Reorganization Plan and unvested options, restricted stock units and performance stock units granted under employee and director compensation plans.
	The following table provides a reconciliation of the common shares used for basic net income per share to the diluted shares used for diluted net income per share:
		Three Months Ended March 31,
		2015	2014
	Weighted average number of common shares used for basic earnings per share	45,156,202	45,042,823
	Effect of potential dilutive shares:
	Warrants	1,751,798	1,998,028
	Stock options	12,841	4,891
	Restricted stock units	25,013	—
	Performance stock units	3,145	—
	Weighted average number of common shares and potential dilutive shares used for diluted earnings per share	46,948,999	47,045,742
	Stock options to purchase 110,000 shares of common stock were outstanding but not included in the computation of diluted earnings per share because they were antidilutive under the treasury stock method for the three months ended March 31, 2015.

Financial_Guarantee_Insurance_

Financial Guarantee Insurance Contracts	3 Months Ended
	Mar. 31, 2015
Insurance [Abstract]
Financial Guarantee Insurance Contracts	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:
	Gross premiums are received either upfront (typical of public finance obligations) or in installments (typical of structured finance obligations). For premiums received upfront, an unearned premium revenue (“UPR”) liability is established, which is initially recorded as the cash amount received. For installment premium transactions, a premium receivable asset and offsetting UPR liability is 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 March 31, 2015 and December 31, 2014, was 2.5% and 2.7%, respectively, and the weighted average period of future premiums used to estimate the premium receivable at March 31, 2015 and December 31, 2014, was 9.6 years and 10.1 years, respectively.
	Insured obligations consisting of homogeneous pools for which Ambac uses expected future premiums to estimate the premium receivable and UPR include residential mortgage-backed securities. 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.
	Generally, the priority for the payment of financial guarantee premiums to Ambac, as required by the bond indentures of the insured obligations, is very senior in the waterfall. Additionally, in connection with the allocation of certain liabilities to the Segregated Account, trustees and other parties are required under the Segregated Account Rehabilitation Plan and related court orders to continue to pay installment premiums, notwithstanding the Segregated Account Rehabilitation Proceedings. In evaluating the credit quality of the premium receivables, management evaluates the transaction waterfall structures and the internal ratings of the transactions underlying the premium receivables. 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. As of March 31, 2015 and December 31, 2014, approximately 32% and 32% of the premium receivables related to transactions with non-investment grade internal ratings, comprised mainly of non-investment grade RMBS and student loan transactions, which comprised 7% and 7%, of the total premium receivables at March 31, 2015 and 7% and 8%, of the total premium receivables at December 31, 2014, respectively. At March 31, 2015 and December 31, 2014, $17,082 and $17,780 respectively, of premium receivables were deemed uncollectable. Past due premiums on policies insuring non-investment grade obligations amounted to less than $500 at March 31, 2015.
	Below is the gross premium receivable roll-forward (direct and assumed contracts) for the affected periods:
		Three Months Ended March 31,
		2015			2014
	Beginning premium receivable	$	1,000,607		$	1,453,021
	Premium receipts	(27,453		)	(33,128		)
	Adjustments for changes in expected and contractual cash flows	(5,918		)	(15,062		)
	Accretion of premium receivable discount	6,282			10,370
	Uncollectable premiums	698			(1,074		)
	Other adjustments (including foreign exchange)	(22,217		)	3,987
	Ending premium receivable	$	951,999		$	1,418,114
	Similar to gross premiums, premiums ceded to reinsurers are paid either upfront or in installments. Premiums ceded to reinsurers reduce the amount of premiums earned by Ambac from its financial guarantee insurance policies.
	When a bond issue insured by Ambac Assurance has been retired, including those retirements due to refundings or calls, 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, the recognition of any remaining UPR is offset 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. Ambac’s accelerated premium revenue for retired obligations for the three months ended March 31, 2015 and 2014 was $22,852 and $25,114, respectively. 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 (a pre-refunding). 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 or a specified call date. Ambac has evaluated the provisions in certain financial guarantee insurance policies issued on legally defeased obligations and determined those insurance policies have not been legally extinguished and, therefore, premium revenue recognition has not been accelerated.
	The effect of reinsurance on premiums written and earned was as follows:
		Three months ended March 31, 2015							Three months ended March 31, 2014
		Written			Earned				Written				Earned
	Direct	$	1,062		$	71,649			$	(5,766	)		$	86,183
	Assumed	—			22				—				68
	Ceded	365			5,953				456				3,704
	Net premiums	$	697		$	65,718			$	(6,222	)		$	82,547
	The table below summarizes the future gross undiscounted premiums to be collected and future premiums earned, net of reinsurance at March 31, 2015:
		Future premiums			Future
		to be collected (1)			premiums to
					be earned net of
					reinsurance (1)
	Three months ended:
	June 30, 2015	$	22,082		$	38,127
	September 30, 2015	22,103			35,798
	December 31, 2015	21,686			33,635
	Twelve months ended:
	December 31, 2016	83,054			123,206
	December 31, 2017	76,968			110,175
	December 31, 2018	72,261			101,113
	December 31, 2019	68,564			94,047
	Five years ended:
	December 31, 2024	304,049			385,547
	December 31, 2029	254,696			272,177
	December 31, 2034	179,393			169,638
	December 31, 2039	65,595			67,126
	December 31, 2044	25,189			23,328
	December 31, 2049	9,831			9,824
	December 31, 2054	1,244			2,183
	December 31, 2059	5			3
	Total	$	1,206,720		$	1,465,927
	-1	Future premiums to be collected is undiscounted and relates to the discounted premium receivable asset recorded on Ambac's balance sheet. Future premiums to be earned, net of reinsurance relate to the unearned premium 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 described in Note 2. Basis of Presentation and Significant Accounting Principles in the Notes to Consolidated Financial Statements included in Ambac's Annual Report on Form 10-K for the year ended December 31, 2014. 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 in the future. 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 results in higher 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:
	Below are the components of the Loss and loss expense reserves liability and the Subrogation recoverable asset at March 31, 2015 and December 31, 2014:
		Unpaid Claims						Present Value of Expected
								Net Cash Flows
	Balance Sheet Line Item	Claims			Accrued			Claims and				Recoveries			Unearned			Gross Loss and
					Interest			Loss Expenses							Premium			Loss Expense
															Revenue			Reserves
	March 31, 2015:
	Loss and loss expense reserves	$	2,158,007		$	265,708		$	3,579,957			$	(1,268,916	)	$	(258,765	)	$	4,475,991
	Subrogation recoverable	774,960			103,429			175,415				(2,037,933		)	—			(984,129		)
	Totals	$	2,932,967		$	369,137		$	3,755,372			$	(3,306,849	)	$	(258,765	)	$	3,491,862
	December 31, 2014:
	Loss and loss expense reserves	$	2,172,041		$	234,802		$	3,792,133			$	(1,205,621	)	$	(241,348	)	$	4,752,007
	Subrogation recoverable	772,948			94,425			197,751				(2,018,398		)	—			(953,274		)
Totals	$	2,944,989		$	329,227		$	3,989,884			$	(3,224,019	)	$	(241,348	)	$	3,798,733
Below is the loss and loss expense reserve roll-forward, net of subrogation recoverable and reinsurance, for the affected periods:
	Three Months Ended March 31,
	2015			2014
Beginning gross loss and loss expense reserves	$	3,798,733		$	5,470,234
Less reinsurance on loss and loss expense reserves	100,355			122,357
Beginning balance of net loss and loss expense reserves	$	3,698,378		$	5,347,877
Changes in the loss and loss expense reserves due to:
Current year:
Establishment of new loss and loss expense reserves, gross of RMBS subrogation and net of reinsurance	1			151
Total current year	1			151
Prior years:
Change in previously established loss and loss expense reserves, gross of RMBS subrogation and net of reinsurance	(132,639		)	(117,692		)
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance	(104,202		)	(9,375		)
(Increase) decrease in previously established RMBS subrogation recoveries, net of reinsurance	(44,195		)	(18,331		)
Total prior years	(281,036		)	(145,398		)
Net change in net loss and loss expense reserves	(281,035		)	(145,247		)
Ending net loss and loss expense reserves	$	3,417,343		$	5,202,630
Add reinsurance on loss and loss expense reserves (1)	74,519			111,303
Ending gross loss and loss expense reserves	$	3,491,862		$	5,313,933
-1	Reinsurance recoverable reported on the Balance Sheet also includes reinsurance recoverables of previously presented loss and loss expenses of $4,789 and $139 as of March 31, 2015 and 2014, respectively.
The positive development in loss and loss expense reserves established in prior years for the three months ended March 31, 2015 was primarily due to improved performance and lower interest rates in the RMBS portfolio and the impact of commutations and lower interest rates in the student loan portfolio. The positive development in loss and loss expense reserves established in prior years for the three months ended March 31, 2014 was primarily due to improved performance of the RMBS portfolio and higher commutation probabilities for student loan exposures.
The net change in net loss and loss expense reserves are included in losses and loss expenses in the Consolidated Statement of Total Comprehensive Income. Reinsurance recoveries of losses included in losses and loss expenses in the Consolidated Statements of Total Comprehensive Income (Loss) were an expense of $20,601 and $10,559 for the three months ended March 31, 2015 and 2014, respectively.
The tables below summarize information related to policies currently included in Ambac’s loss and loss expense reserves or subrogation recoverable at March 31, 2015 and December 31, 2014. Net par exposures include capital appreciation bonds which are reported at the par amount at the time of issuance of the insurance policy. The weighted average risk-free rate used to discount loss reserves at March 31, 2015 and December 31, 2014 was 2.1% and 2.3%, respectively.
Surveillance Categories as of March 31, 2015
	I/SL			IA			II				III			IV			V			Total
Number of policies	34			21			43				66			163			3			330
Remaining weighted-average contract period (in years)	7			16			17				21			13			6			15
Gross insured contractual payments outstanding:
Principal	$	910,033		$	399,516		$	4,186,210			$	3,550,121		$	9,376,691		$	59,712		$	18,482,283
Interest	339,721			159,138			8,484,779				2,286,780			1,928,647			19,651			13,218,716
Total	$	1,249,754		$	558,654		$	12,670,989			$	5,836,901		$	11,305,338		$	79,363		$	31,700,999
Gross undiscounted claim liability (1)	$	12,901		$	6,344		$	239,113			$	1,596,918		$	6,297,440		$	79,357		$	8,232,073
Discount, gross claim liability	(644		)	(605		)	(18,502		)		(521,225		)	(712,562		)	(6,592		)	(1,260,130		)
Gross claim liability before all subrogation and before reinsurance	$	12,257		$	5,739		$	220,611			$	1,075,693		$	5,584,878		$	72,765		$	6,971,943
Less:
Gross RMBS subrogation (2)	—			—			—				—			(2,579,450		)	—			(2,579,450		)
Discount, RMBS subrogation	—			—			—				—			11,097			—			11,097
Discounted RMBS subrogation, before reinsurance	—			—			—				—			(2,568,353		)	—			(2,568,353		)
Less:
Gross other subrogation (3)	—			—			(12,388		)		(142,548		)	(646,741		)	(13,356		)	(815,033		)
Discount, other subrogation	—			—			3,474				35,608			33,795			3,660			76,537
Discounted other subrogation, before reinsurance	—			—			(8,914		)		(106,940		)	(612,946		)	(9,696		)	(738,496		)
Gross claim liability, net of all subrogation and discounts, before reinsurance	$	12,257		$	5,739		$	211,697			$	968,753		$	2,403,579		$	63,069		$	3,665,094
Less: Unearned premium revenue	(8,812		)	(2,175		)	(107,836		)		(76,061		)	(63,368		)	(513		)	(258,765		)
Plus: Loss expense reserves	—			16			2,185				7,465			75,825			42			85,533
Gross loss and loss expense reserves	$	3,445		$	3,580		$	106,046			$	900,157		$	2,416,036		$	62,598		$	3,491,862
Reinsurance recoverable reported on Balance Sheet (4)	$	1		$	910		$	2,331			$	85,082		$	(9,016	)	$	—		$	79,308
-1	Gross undiscounted claim liability includes unpaid claims, including accrued interest on Deferred Amounts, on policies allocated to the Segregated Account and Ambac's estimate of expected future claims.
-2	RMBS subrogation represents Ambac’s probability-weighted estimate of subrogation recoveries from RMBS transaction sponsors for representation and warranty ("R&W") breaches.
-3	Other subrogation primarily represents subrogation related to excess spread or other contractual cash flows on public finance and structured finance transactions, including RMBS.
-4	Reinsurance recoverable reported on Balance Sheet includes reinsurance recoverables of $74,519 related to future loss and loss expenses and $4,789 related to previously presented loss and loss expenses.
Surveillance Categories as of December 31, 2014
	I/SL			IA			II				III			IV			V			Total
Number of policies	36			26			33				69			160			1			325
Remaining weighted-average contract period (in years)	8			12			15				21			12			6			16
Gross insured contractual payments outstanding:
Principal	$	1,026,513		$	519,291		$	3,091,744			$	3,792,559		$	9,892,760		$	47		$	18,322,914
Interest	418,746			212,296			1,878,770				2,765,537			1,979,627			19			7,254,995
Total	$	1,445,259		$	731,587		$	4,970,514			$	6,558,096		$	11,872,387		$	66		$	25,577,909
Gross undiscounted claim liability (1)	$	16,360		$	11,525		$	155,488			$	2,040,402		$	6,456,139		$	60		$	8,679,974
Discount, gross claim liability	(1,147		)	(937		)	(16,438		)		(716,812		)	(774,611		)	(3		)	(1,509,948		)
Gross claim liability before all subrogation and before reinsurance	$	15,213		$	10,588		$	139,050			$	1,323,590		$	5,681,528		$	57		$	7,170,026
Less:
Gross RMBS subrogation (2)	—			—			—				—			(2,541,219		)	—			(2,541,219		)
Discount, RMBS subrogation	—			—			—				—			17,679			—			17,679
Discounted RMBS subrogation, before reinsurance	—			—			—				—			(2,523,540		)	—			(2,523,540		)
Less:
Gross other subrogation (3)	—			—			(18,034		)		(127,143		)	(647,110		)	—			(792,287		)
Discount, other subrogation	—			—			6,069				36,779			48,960			—			91,808
Discounted other subrogation, before reinsurance	—			—			(11,965		)		(90,364		)	(598,150		)	—			(700,479		)
Gross claim liability, net of all subrogation and discounts, before reinsurance	$	15,213		$	10,588		$	127,085			$	1,233,226		$	2,559,838		$	57		$	3,946,007
Less: Unearned premium revenue	(10,945		)	(3,432		)	(73,749		)		(88,332		)	(64,890		)	—			(241,348		)
Plus: Loss expense reserves	3			1,303			1,968				6,470			84,330			—			94,074
Gross loss and loss expense reserves	$	4,271		$	8,459		$	55,304			$	1,151,364		$	2,579,278		$	57		$	3,798,733
Reinsurance recoverable reported on Balance Sheet (4)	$	73		$	890		$	1,355			$	110,957		$	(13,437	)	$	—		$	99,838
-1	Gross undiscounted claim liability includes unpaid claims, including accrued interest on Deferred Amounts, on policies allocated to the Segregated Account and Ambac's estimate of expected future claims.
-2	RMBS subrogation represents Ambac’s probability-weighted estimate of subrogation recoveries from RMBS transaction sponsors for representation and warranty ("R&W") breaches.
-3	Other subrogation primarily represents subrogation related to excess spread or other contractual cash flows on public finance and structured finance transactions, including RMBS.
-4	Reinsurance recoverable reported on Balance Sheet includes reinsurance recoverables of $100,355 related to future loss and loss expenses and $(517) related to previously presented loss and loss expenses.
Ambac records estimated subrogation recoveries for breaches of representations and warranties (R&W) by sponsors of certain RMBS transactions. Prior to the June 30, 2014 reporting period, Ambac utilized the Adverse and Random Sample approaches to estimate R&W subrogation recoveries for certain RMBS transactions. For a discussion of these subrogation recovery approaches, see Note 2. Basis Of Presentation And Significant Accounting Policies in the Notes to Consolidated Financial Statements included Part II, Item 8 in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014. Beginning with the June 30, 2014 reporting period, as a result of gaining further access to loan files, the Random Sample approach has been utilized for all transactions which were previously evaluated using the Adverse Sample approach.
Ambac has recorded RMBS subrogation recoveries of $2,568,353, ($2,540,710 net of reinsurance) and $2,523,540, ($2,496,515 net of reinsurance) at March 31, 2015 and December 31, 2014, respectively. The balance of RMBS subrogation recoveries and the related claim liabilities, by estimation approach, at March 31, 2015 and December 31, 2014, are as follows:
Approach	Gross loss			Subrogation			Gross loss
	reserves before			recoveries (2)(3)			reserves after
	subrogation						subrogation
	recoveries (1)						recoveries
March 31, 2015:
Random samples (4)	$	1,899,087		$	(2,568,353	)	$	(669,266	)
December 31, 2014:
Random samples (4)	$	1,897,426		$	(2,523,540	)	$	(626,114	)
-1	Includes unpaid RMBS claims, including accrued interest on Deferred Amounts, on policies allocated to the Segregated Account.
-2	The amount of recorded subrogation recoveries related to each securitization is limited to ever-to-date paid and unpaid losses plus the present value of expected cash flows for each policy. To the extent losses have been paid but not yet fully recovered, the recorded amount of RMBS subrogation recoveries may exceed the sum of the unpaid claims and the present value of expected cash flows for a given policy. The net cash inflow for these policies is recorded as a “Subrogation recoverable” asset. For those transactions where the subrogation recovery is less than the sum of unpaid claims and the present value of expected cash flows, the net cash outflow for these policies is recorded as a “Loss and loss expense reserves” liability.
-3	The sponsor’s repurchase obligation may differ depending on the terms of the particular transaction and the status of the specific loan, such as whether it is performing or has been liquidated or charged off. The estimated subrogation recovery for these transactions is based primarily on loan level data provided through trustee reports received in the normal course of our surveillance activities or provided by the sponsor. While this data may not include all the components of the sponsor’s contractual repurchase obligation we believe it is the best information available to estimate the subrogation recovery.
-4	From time to time R&W subrogation may include estimates of potential sponsor settlements that are currently in negotiation, but have not been subject to a sampling approach. However, such estimates are not material to Ambac’s financial results and therefore are included in the Random Sample section of this table.
Below is the rollforward of RMBS subrogation, by estimation approach, for the affected periods:
	Random			Adverse			Total
	sample			sample
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2015	$	2,523,540		$	—		$	2,523,540
Changes recognized in 2015:
Changes in estimation approach	—			—			—
Impact of sponsor actions (1)	—			—			—
All other changes (2)	44,813			—			44,813
Discounted RMBS subrogation (gross of reinsurance) at March 31, 2015	$	2,568,353		$	—		$	2,568,353
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2014	$	953,825		$	1,252,773		$	2,206,598
Changes recognized in 2014:
Changes in estimation approach	—			—			—
Impact of sponsor actions (1)	—			—			—
All other changes (2)	51,789			(34,092		)	17,697
Discounted RMBS subrogation (gross of reinsurance) at March 31, 2014	$	1,005,614		$	1,218,681		$	2,224,295
-1	Sponsor actions include loan repurchases, direct payments to Ambac and other contributions.
-2	All other changes which may impact RMBS subrogation recoveries include changes in actual or projected collateral performance, changes in the creditworthiness of a sponsor, and/or the projected timing of recoveries. All other changes may also include estimates of potential sponsor settlements that are currently in negotiation but have not been subject to a sampling approach. However, such estimates are not material to Ambac’s financial results and therefore are included in the Random Sample column of this table.
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 three months ended March 31, 2015 and 2014, the insurance intangible amortization expense was $37,432 and $31,714, respectively. As of March 31, 2015 and December 31, 2014, the gross carrying value of the insurance intangible asset was $1,631,068 and $1,660,125, respectively. Accumulated amortization of the insurance intangible asset was $283,773 and $249,205, as of March 31, 2015 and December 31, 2014, respectively, resulting in a net insurance intangible asset of $1,347,295 and $1,410,920, respectively.
The estimated future amortization expense for the net insurance intangible asset is as follows:
		2015			2016			2017				2018			2019			Thereafter
Amortization expense		$	90,801		$	107,443		$	97,726			$	90,095		$	83,380		$	877,850

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	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:
	Ÿ Level 1		Quoted prices for identical instruments in active markets. Assets and liabilities classified as Level 1 include US Treasury securities, exchange traded futures contracts, variable rate demand obligations, money market funds and mutual funds.
	Ÿ 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, most financial services derivatives and most long-term debt of variable interest entities consolidated under the Consolidation Topic of the ASC. Also included are equity interests in pooled investment funds measured at fair value where the investment can be redeemed in the near term at a value based on the net asset value.
	Ÿ Level 3		Model derived valuations in which one or more significant inputs or significant value drivers are unobservable. This hierarchy requires the use of observable market data when available. Assets and liabilities classified as Level 3 include credit derivative contracts written as part of the financial guarantee business, certain financial services interest rate swap contracts, equity interests in Ambac sponsored special purpose entities and certain investments in fixed income securities. Additionally, Level 3 assets and liabilities generally include fixed income securities, loan receivables, and certain long-term debt of variable interest entities consolidated under the Consolidation Topic of the ASC.
	The following table sets forth the carrying amount and fair value of Ambac’s financial assets and liabilities as of March 31, 2015 and December 31, 2014, 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:
		Amount				Value				Level 1				Level 2				Level 3
	March 31, 2015:
	Financial assets:
	Fixed income securities:
	Municipal obligations	$	525,188			$	525,188			$	—			$	525,188			$	—
	Corporate obligations	1,609,769				1,609,769				—				1,609,769				—
	Foreign obligations	125,164				125,164				—				125,164				—
	U.S. government obligations	30,297				30,297				30,297				—				—
	U.S. agency obligations	4,427				4,427				—				4,427				—
	Residential mortgage-backed securities	1,846,477				1,846,477				—				1,583,745				262,732
	Collateralized debt obligations	88,238				88,238				—				88,238				—
	Other asset-backed securities	636,190				636,190				—				636,190				—
	Fixed income securities, pledged as collateral:
	U.S. government obligations	64,813				64,813				64,813				—				—
	Short term investments	220,980				220,980				215,207				5,773				—
	Other investments	332,609				328,187				—				310,578				17,609
	Cash and cash equivalents	26,641				26,641				26,641				—				—
	Loans	5,494				5,476				—				—				5,476
	Derivative assets:
	Credit derivatives	—				—				—				—				—
	Interest rate swaps—asset position	113,622				113,622				—				113,622				—
	Interest rate swaps—liability position	—				—				—				—				—
	Other assets	10,036				10,036				—				—				10,036
	Variable interest entity assets:
	Fixed income securities:
	Corporate obligations	2,704,657				2,704,657				—				—				2,704,657
	Restricted cash	6,219				6,219				6,219				—				—
	Loans	12,789,201				12,789,201				—				—				12,789,201
	Total financial assets	$	21,140,022			$	21,135,582			$	343,177			$	5,002,694			$	15,789,711
	Financial liabilities:
	Obligations under investment agreements	$	111,967			$	114,438			$	—			$	—			$	114,438
	Long term debt, including accrued interest	1,301,390				1,381,938				—				—				1,381,938
	Derivative liabilities:
	Credit derivatives	76,377				76,377				—				—				76,377
	Interest rate swaps—asset position	(68,481		)		(68,481		)		—				(68,481		)		—
	Interest rate swaps—liability position	438,518				438,518				—				284,694				153,824
	Futures contracts	942				942				942				—				—
	Liabilities for net financial guarantees written (1)	2,662,701				4,152,094				—				—				4,152,094
	Variable interest entity liabilities:
	Long-term debt	13,341,902				13,341,902				—				11,309,803				2,032,099
	Derivative liabilities:
	Interest rate swaps—liability position	2,081,082				2,081,082				—				2,081,082				—
	Currency swaps—liability position	44,631				44,631				—				44,631				—
	Total financial liabilities	$	19,991,029			$	21,563,441			$	942			$	13,651,729			$	7,910,770
	-1	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.
		Carrying				Total Fair				Fair Value Measurements Categorized as:
		Amount				Value				Level 1				Level 2				Level 3
	December 31, 2014:
	Financial assets:
	Fixed income securities:
	Municipal obligations	$	525,792			$	525,792			$	—			$	525,792			$	—
	Corporate obligations	1,385,594				1,385,594				—				1,381,786				3,808
	Foreign obligations	127,757				127,757				—				127,757				—
	U.S. government obligations	42,979				42,979				42,979				—				—
	U.S. agency obligations	29,486				29,486				—				29,486				—
Residential mortgage-backed securities	1,710,955				1,710,955				—				1,516,562				194,393
Collateralized debt obligations	21,122				21,122				—				21,122				—
Other asset-backed securities	882,001				882,001				—				882,001				—
Fixed income securities, pledged as collateral:
U.S. government obligations	64,267				64,267				64,267				—				—
Short term investments	360,065				360,065				358,190				1,875				—
Other investments	357,016				349,468				—				336,013				13,455
Cash and cash equivalents	73,903				73,903				73,903				—				—
Loans	5,714				5,634				—				—				5,634
Derivative assets:
Credit derivatives	2,043				2,043				—				—				2,043
Interest rate swaps—asset position	106,974				106,974				—				106,974				—
Interest rate swaps—liability position	—				—				—				—				—
Futures contracts	—				—				—				—				—
Other assets	12,036				12,036				—				—				12,036
Variable interest entity assets:
Fixed income securities:
Corporate obligations	2,743,050				2,743,050				—				—				2,743,050
Restricted cash	7,708				7,708				7,708				—				—
Loans	12,371,177				12,371,177				—				—				12,371,177
Total financial assets	$	20,829,639			$	20,822,011			$	547,047			$	4,929,368			$	15,345,596
Financial liabilities:
Obligations under investment agreements	$	160,079			$	161,821			$	—			$	—			$	161,821
Long term debt, including accrued interest	1,273,805				1,379,864				—				—				1,379,864
Derivative liabilities:
Credit derivatives	75,502				75,502				—				—				75,502
Interest rate swaps—asset position	(54,666		)		(54,666		)		—				(54,666		)		—
Interest rate swaps—liability position	385,546				385,546				—				243,659				141,887
Futures contracts	562				562				562				—				—
Other contracts	—				—				—				—				—
Liabilities for net financial guarantees written (1)	2,923,652				4,539,000				—				—				4,539,000
Variable interest entity liabilities:
Long-term debt	12,882,076				12,882,076				—				11,618,412				1,263,664
Derivative liabilities:
Interest rate swaps—liability position	2,133,268				2,133,268				—				2,133,268				—
Currency swaps—liability position	66,895				66,895				—				66,895				—
Total financial liabilities	$	19,846,719			$	21,569,868			$	562			$	14,007,568			$	7,561,738
-1	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. Because many fixed income securities do not trade on a daily basis, pricing sources apply available information through processes such as matrix pricing to calculate fair value. In those cases, the items are classified within Level 2. If quoted market prices are not available, fair value is based upon models that use, where possible, current market-based or independently-sourced market parameters. 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.
The determination of fair value for financial instruments categorized in Level 2 or 3 involves significant 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 prices for securities. 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, variable interest entity assets and liabilities and equity 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 quarterly 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 dealer quotes or alternative pricing sources with reasonable levels of price transparency. Such quotes generally consider a variety of factors, including recent trades of the same and similar securities. 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. 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. Certain investments in Ambac-wrapped securities for which projected cash flows consist solely of Deferred Amounts and interest thereon, are internally valued based upon the valuation of surplus notes. At March 31, 2015, approximately 6%, 89%, and 5% of the investment portfolio (excluding variable interest entity investments) was valued using dealer quotes, alternative pricing sources with reasonable levels of price transparency and internal valuation models, respectively. At December 31, 2014, approximately 10%, 86%, and 4% of the investment portfolio (excluding variable interest entity investments) was valued using dealer quotes, alternative pricing sources with reasonable levels of price transparency and internal valuation models, respectively.
Ambac performs various review and validation procedures to quoted and modeled prices for fixed income securities, including price variance analysis, missing and static price reviews, overall valuation analysis by senior traders 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 senior traders and finance managers.
Information about the valuation inputs for fixed income securities classified as Level 3 is included below:
Corporate obligations: These securities represent interest only strips of investment grade corporate obligations. The fair value of such securities classified as Level 3 was $0 and $3,808 at March 31, 2015 and December 31, 2014, respectively. Fair value was calculated using a discounted cash flow approach with the discount rate determined from the yields of corporate bonds from the same issuers. Significant inputs for the interest only strips valuation at December 31, 2014 include the following weighted averages:
a. Coupon rate:	0.35%
b. Maturity:	19.14 years
c. Yield:	4.93%
Residential mortgage-backed securities: These securities are guaranteed under policies that are subject to the Segregated Account Rehabilitation Plan and have projected future cash flows consisting solely of Deferred Amounts under such policies including interest thereon. The fair value of such securities classified as Level 3 was $262,732 and $194,393 at March 31, 2015 and December 31, 2014, respectively. Fair value was calculated based on the valuation of Ambac Assurance surplus notes which, under the terms of the Segregated Account Rehabilitation Plan, are to be redeemed in proportion with the payment of Deferred Amounts on or about the dates when such payments are made. Refer to Note 1.Background and Business Description and to Note 1. Background and Business Description in the Notes to Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014 for further description of the Segregated Account Rehabilitation Plan and its impact on the payment of Segregated Account policy claims and surplus note redemptions.
Other Investments:
Other investments primarily relate to investments in pooled investment funds, which are valued using the net asset value (“NAV”) per share, calculated on at least a monthly basis where NAV is the basis for determining the redemption value of the investment. These investments are classified as Level 2 as redemptions may be made in the near term (within 90 days) without significant impediments or restrictions. Ambac assesses impediments to redemption and other factors that may restrict the ability to redeem investments in the near term or at values approximating the NAV and may classify the investments as Level 3 if such factors exist. Other investments also includes Ambac's interest in a non-consolidated VIE, which is carried under the equity method. Valuation of this equity interest is internally calculated using a discounted cash flow approach and is classified as Level 3.
Derivative Instruments:
Ambac’s derivative instruments primarily comprise interest rate and credit default swaps and exchange traded futures contracts. Fair value is determined based upon market quotes from independent sources, when available. When independent quotes are not available, fair value is determined using valuation models. These valuation models require market-driven inputs, including contractual terms, credit spreads and ratings on underlying referenced obligations, yield curves and tax-exempt interest ratios. The valuation of certain 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 derivative and other liabilities. The fair value of credit derivative liabilities was reduced by $18,020 and $15,910 at March 31, 2015 and December 31, 2014, as a result of incorporating a CVA into the valuation model for these transactions. Interest rate swaps and other derivative liabilities may also require an adjustment to fair value to reflect Ambac’s credit risk. Derivative liabilities were reduced by $77,191 and $64,547 at March 31, 2015 and December 31, 2014, as a result of Ambac CVA adjustments to derivative contracts other than credit derivatives. Additional 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 derivatives and the pricing of recent terminations.
As described further below, certain valuation models require other inputs that are not readily observable in the market. The selection of a model to value a derivative depends on the contractual terms of, and specific risks inherent in the instrument as well as the availability of pricing information in the market.
For derivatives that are less complex and trade in liquid markets or may be valued primarily by reference to interest rates and yield curves that are observable and regularly quoted, such as interest rate swaps, we utilize vendor-developed models. These models provide the net present value of the derivatives based on contractual terms and observable market data. Downgrades of Ambac Assurance, as guarantor of the financial services derivatives, have increased collateral requirements and triggered termination provisions in certain interest rate swaps. Termination activity since the initial rating downgrades of Ambac Assurance provided additional information about the replacement and/or exit value of certain financial services derivatives, which has been incorporated into the fair value of these derivatives as appropriate. Generally, the need for counterparty (or Ambac) CVAs is mitigated by the existence of collateral posting agreements under which adequate collateral has been posted. 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 fair value adjustments.
For derivatives that do not trade, or trade in less liquid markets such as credit derivatives, an internal model is used because such instruments tend to be unique, contain complex or heavily modified and negotiated terms, and pricing information is not readily available in the market. Derivative fair value models and the related assumptions are continuously re-evaluated by management and enhanced, as appropriate, based on improvements in modeling techniques. Ambac has not made any significant changes to its modeling techniques or related model inputs for the periods presented.
Credit Derivatives (“CDS”):
Fair value of Ambac’s CDS is determined using internal valuation models and represents the net present value of the difference between the fees Ambac originally charged for the credit protection and our estimate of what a financial guarantor of comparable credit quality would hypothetically charge to provide the same protection at the balance sheet date. Ambac competed in the financial guarantee market, which differs from the credit markets where Ambac-insured obligations may trade. As a financial guarantor, Ambac assumes only credit risk; we do not assume other risks and costs inherent in direct ownership of the underlying reference securities. Additionally, as a result of having the ability to influence our CDS counterparty in certain investor decisions, financial guarantors generally have the ability to actively remediate the credit, potentially reducing the loss given a default. Financial guarantee contracts, including CDS, issued by Ambac and its competitors are typically priced to capture some portion of the spread that would be observed in the capital markets for the underlying (insured) obligation. Such pricing was well established by historical financial guarantee fees relative to capital market spreads as observed and executed in competitive markets, including in financial guarantee reinsurance and secondary market transactions. Because of this relationship and in the absence of severe credit deterioration, changes in the fair value of our credit default swaps will generally be less than changes in the fair value of the underlying reference obligations.
Key variables used in our valuation of substantially all of our credit derivatives include the balance of unpaid notional, expected term, fair values of the underlying reference obligations, reference obligation credit ratings, assumptions about current financial guarantee CDS fee levels relative to reference obligation spreads and the CVA applied against Ambac Assurance liabilities by market participants. Notional balances, expected remaining term and reference obligation credit ratings are monitored and determined by Ambac’s portfolio risk management group. Fair values of the underlying reference obligations are obtained from broker quotes when available, or are estimated internally. Implicit in the fair values we obtain on the underlying reference obligations are the market’s assumptions about default probabilities, default timing, correlation, recovery rates and collateral values.
Broker quotes on the reference obligations named in our CDS contracts represent an input to determine the estimated fair value of the CDS contract. Broker quotes are indicative values for the reference obligation and generally do not represent a bid for the reference instrument. Such quotes follow methodologies that are generally consistent with those used to value similar assets on the quote providers’ own books. Methodologies may differ among brokers but are understood to reflect observable trading activity (when available) and modeling that relies on empirical data and reasonable assumptions. For certain CDS contracts referencing unsecuritized pools of assets, we will obtain counterparty quotes on the credit derivative itself. Such quotes are adjusted to reflect Ambac’s own credit risk when determining the fair value of credit derivative liabilities. Third party reference obligation values or specific credit derivative quotes were used in the determination of CDS fair values related to transactions representing 86% of CDS gross par outstanding and 65% of the CDS derivative liability as of March 31, 2015.
When broker quotes for reference obligations are not available, reference obligation prices used in the valuation model are estimated internally based on available market prices or spreads for securities or indices with similar characteristics such as underlying collateral, credit rating and expected life. Internal estimates may also consider historical quotes on the reference obligation, updated for changes in market factors and security specific developments such as credit rating changes. Reference obligation prices derived internally as described above were used in the determination of CDS fair values related to transactions representing 14% of CDS gross par outstanding and 35% of the CDS derivative liability as of March 31, 2015.
Ambac’s CDS fair value calculations are adjusted for changes in our estimates of expected loss on the reference obligations and observable changes in financial guarantee market pricing. If no adjustment is considered necessary, Ambac maintains the same percentage of the credit spread (over LIBOR) demanded in the market for the reference obligation as existed at the inception of the CDS. Therefore, absent changes in expected loss on the reference obligations or financial guarantee CDS market pricing, the financial guarantee CDS fee used for a particular contract in Ambac’s fair value calculations represent a consistent percentage, period to period, of the credit spread determinable from the reference obligation value at the balance sheet date. This results in a CDS fair value balance that fluctuates in proportion with the reference obligation value.
The amount of expected loss on a reference obligation is a function of the probability that the obligation will default and severity of loss in the event of default. Ambac’s CDS transactions were all originally underwritten with extremely low expected losses. Both the reference obligation spreads and Ambac’s CDS fees at the inception of these transactions reflected these low expected losses. When reference obligations experience credit deterioration, there is an increase in the probability of default on the obligation and, therefore, an increase in expected loss. Ambac reflects the effects of changes in expected loss on the fair value of its CDS contracts by increasing the percentage of the reference obligation spread (over LIBOR) which would be captured as a CDS fee (“relative change ratio”) at the valuation date, resulting in a higher mark-to-market loss on our CDS relative to any price decline on the reference obligation. The fundamental assumption is that financial guarantee CDS fees will increase relative to reference obligation spreads as the underlying credit quality of the reference obligation deteriorates and approaches payment default. For example, if the credit spread of an underlying reference obligation was 80 basis points at the inception of a transaction and Ambac received a 20 basis point fee for issuing a CDS on that obligation, the relative change ratio, which represents the CDS fee to cash market spread Ambac would utilize in its valuation calculation, would be 25%. If the reference obligation spread increased to 100 basis points in the current reporting period, absent any observable changes in financial guarantee CDS market pricing or credit deterioration, Ambac’s current period CDS fee would be computed by multiplying the current reference obligation spread of 100 basis points by the relative change ratio of 25%, resulting in a 25 basis point fee. Thus, the model indicates we would need to receive an additional 5 basis points (25 basis points currently less the 20 basis points contractually received) for issuing a CDS in the current reporting period for this reference obligation. We would then discount the product of the notional amount of the CDS and the 5 basis point hypothetical CDS fee increase, over the weighted average life of the reference obligation to compute the current period mark-to-market loss. Using the same example, if the reference obligation spread increased to 100 basis points and there was credit deterioration as evidenced by an internal rating downgrade which increased the relative change ratio from 25% to 35%, we would estimate a 15 basis point CDS fee increase in our model (35% of 100 basis points reference obligation spread, or 35 basis points currently, less the 20 basis points contractually received). Therefore, we would record a higher mark-to-market loss based on the computations described above absent any observable changes in financial guarantee CDS market pricing.
We do not adjust the relative change ratio until an actual internal rating downgrade has occurred unless we observe new pricing on financial guarantee CDS contracts. However, because we have active surveillance procedures in place for our entire CDS portfolio, particularly for transactions at or near a below investment grade threshold, we believe it is unlikely that an internal downgrade would lag the actual credit deterioration of a transaction for any meaningful time period. The factors used to increase the relative change ratio are based on rating agency probability of default percentages determined by management to be appropriate for the relevant bond type. That is, the probability of default associated with the respective tenor and internal rating of each CDS transaction is utilized in the computation of the relative change ratio in our CDS valuation model. The new relative change ratio in the event of an internal downgrade of the reference obligation is calculated as the weighted average of: (i) a given transaction’s inception relative change ratio and (ii) a ratio of 100%. The weight given to the inception relative change ratio is 100% minus the current probability of default (the probability of non-default) and the weight given to using a 100% relative change ratio is the probability of default. For example, assume a transaction having an inception relative change ratio of 33% is downgraded to B-during the period, at which time it has an estimated remaining life of 8 years. If the estimated probability of default for an 8 year, B-rated credit of this type is 60% then the revised relative change ratio will be 73.2%. The revised relative change ratio can be calculated as 33% x (100% - 60%) + 100% x 60% =3.2%.
As noted above, reference obligation spreads incorporate market perceptions of default probability and loss severity, as well as liquidity risk and other factors. By increasing the relative change ratio in our calculations proportionally to default probabilities, Ambac incorporates into its CDS fair value the higher expected loss on the reference obligation (probability of default x loss severity), by increasing the portion of reference obligation spread that should be paid to the CDS provider.
Ambac incorporates its own credit risk into the valuation of its CDS liabilities by applying a CVA to the calculations described above. Under our methodology, determination of the CDS fair value requires estimating hypothetical financial guarantee CDS fees for a given credit at the valuation date and estimating the present value of those fees. Our approach begins with pricing in the risk of default of the reference obligation using that obligation’s credit spread. The widening of the reference obligation spread results in a mark-to-market loss to Ambac, as the credit protection seller, and a gain to the credit protection buyer because the current cost of credit protection on the reference obligation (ignoring CDS counterparty credit risk) will be greater than the amount of the actual contractual CDS fees. The Ambac CVA represents the difference between the present value of the hypothetical fees discounted at LIBOR compared to rates that incorporate Ambac credit risk. The discount rates used to determine the Ambac CVA are estimated using relevant data points, including quoted prices of securities guaranteed by Ambac Assurance which indicate the value placed by market participants on Ambac Assurance’s insurance obligations and the fair value of Ambac Assurance surplus notes. The resulting Ambac CVA, as a percentage of the CDS mark-to-market liability determined by discounting at LIBOR, was 19.1% and 17.8% as of March 31, 2015 and December 31, 2014, respectively. In instances where narrower reference obligation spreads result in a CDS asset to Ambac, those hypothetical future CDS fees are discounted at a rate which incorporates our counterparty’s credit spread (i.e. the discount rate used is LIBOR plus the current credit spread of the counterparty).
In addition, when there are sufficient numbers of new observable transactions, negotiated settlements or other market indications of a general change in market pricing trends for CDS on a given bond type, management will adjust its assumptions about the percentage of reference obligation spreads captured as CDS fees to match the current market. No such adjustments were made during the periods presented. Ambac is not transacting CDS business currently and other guarantors have stated they have exited this product. Additionally, there have been no negotiated settlements of CDS contracts during the periods presented.
Key variables which impact the “Realized gains and losses and other settlements” component of “Net change in fair value of credit derivatives” in the Consolidated Statements of Total Comprehensive Income (Loss) are the most readily observable variables since they are based solely on the CDS contractual terms and cash settlements. Those variables include premiums received and accrued and losses paid and payable on written credit derivative contracts for the appropriate accounting period. Losses paid and payable reported in “Realized gains and losses and other settlements” include those arising after a credit event that requires a payment under the contract terms has occurred or in connection with a negotiated termination of a contract. The remaining key variables described above impact the “Unrealized gains (losses)” component of “Net change in fair value of credit derivatives.”
The net notional outstanding of Ambac’s CDS contracts were $1,594,571 and $1,529,759 at March 31, 2015 and December 31, 2014, respectively. Credit derivative liabilities at March 31, 2015 and December 31, 2014 had a combined net fair value of $76,377 and $73,459, respectively, and related to underlying reference obligations that are classified as either collateralized loan obligations (“CLOs”) or Other. Information about the above described model inputs used to determine the fair value of each class of credit derivatives, including the CVA as a percentage of the gross mark-to-market liability before considering Ambac credit risk (“CVA percentage”), as of March 31, 2015 and December 31, 2014 is summarized below:
	CLOs				Other (1)
March 31, 2015:
Notional outstanding	$	466,453			$	1,069,317
Weighted average reference obligation price	99.1				86.8
Weighted average life (WAL) in years	1.5				5.8
Weighted average credit rating	AA				BBB
Weighted average relative change ratio	36.2		%		44.8		%
CVA percentage	5.21		%		19.34		%
Fair value of derivative liabilities	$	1,533			$	74,794
December 31, 2014:
Notional outstanding	$	549,923			$	921,036
Weighted average reference obligation price	98.9				86.8
Weighted average life (WAL) in years	1.8				5.7
Weighted average credit rating	AA				BBB-
Weighted average relative change ratio	35.9		%		49		%
CVA percentage	5.4		%		15.82		%
Fair value of derivative liabilities	$	2,027			$	71,104
-1	Excludes contracts for which fair values are based on credit derivative quotes rather than reference obligation quotes. Such contracts have a combined notional outstanding of $58,801, WAL of 0.9 years and liability fair value of $50 as of March 31, 2015. Other inputs to the valuation of these transactions at March 31, 2015 include weighted average quotes of less than 1% of notional, weighted average rating of A and Ambac CVA percentage of 2.02% . As of December 31, 2014, these contracts had a combined notional outstanding of $58,800, WAL of 1.2 years and liability fair value of $328. Other inputs to the valuation of these transactions at December 31, 2014 include weighted average quotes of 1% of notional, weighted average rating of A and Ambac CVA percentage of 2.21% .
Significant unobservable inputs for credit derivatives include WAL, internal credit rating, relative change ratio and CVA percentage. A longer (shorter) WAL, lower (higher) reference obligation credit rating, higher (lower) relative change ratio or lower (higher) CVA, in isolation, would result in an increase (decrease) in the fair value liability measurement. A change in an internal credit rating of a reference obligation in our model will generally result in a directionally opposite change in the relative change ratio. Also, a shorter (longer) WAL will generally correspond with a lower (higher) CVA percentage.
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.
The fair value estimate of financial guarantees is computed by utilizing cash flows calculated at the policy level. For direct and assumed contracts, net cash flows for each policy included: (i) installment premium receipts, (ii) estimated future gross claim payments, (iii) subrogation receipts, and (iv) unpaid claims on claims presented and not yet paid for policies allocated to the Segregated Account, including Deferred Amounts including interest thereon. For ceded reinsurance contracts, net cash flows for each policy included: (i) installment ceded premium payments, (ii) ceding commission receipts, (iii) ceded claim receipts, and (iv) ceded subrogation payments. For each assumed or ceded reinsurance contract, the respective undiscounted cash flow components are aggregated to determine if we are in a net asset or net liability position. U.S. GAAP requires that the nonperformance risk of a financial liability be included in the estimation of fair value, which includes considering Ambac Assurance’s own credit risk. Accordingly, for each contract in a net liability position, we estimate the fair value using internally developed discount rates and market pricing that incorporate Ambac’s own credit risk and subsequently apply a profit margin. This profit margin represents what another market participant would require to assume the financial guarantee contracts. Given the unique nature of financial guarantees there is a lack of observable market information to make this estimate. A profit margin was developed based on discussions with the third-party institutions with valuation expertise, discussions with industry participants and yields on Ambac Assurance surplus notes. The profit margin was 17% and 17% as of March 31, 2015 and December 31, 2014, respectively and is applied to the present value of contracts in a net liability position. The discount rates used for contracts in a net liability position are derived from the rates implicit in the fair value of surplus notes and guaranteed securities with future cash flows that are highly dependent upon Ambac financial guarantee payments. For each contract in a net asset position, we estimate the fair value using a discount rate that is commensurate with a hypothetical buyer’s cost of capital.
This methodology is based on management’s expectations of how a market participant would estimate net cash flows. We are aware of a number of factors that may cause such fair or exit value to differ, perhaps materially. For example, (i) since no financial guarantor with Ambac’s credit quality is writing new financial guarantee business, we do not have access to observable pricing data points; (ii) although the fair value accounting guidance for liabilities requires a company to consider the cost to completely transfer its obligation to another party of comparable credit worthiness, our primary insurance obligation is irrevocable and thus there is no established active market for transferring such obligations; and (iii) certain segments of Ambac's financial guarantees have been allocated to the Segregated Account and timing of the payments of such liabilities are at the sole discretion of the Rehabilitator.
Long-term Debt:
The fair value of surplus notes issued by Ambac Assurance and the Segregated Account and classified as long-term debt is internally estimated considering market transactions when available and internally developed discounted cash flow models.
Other Financial Assets and Liabilities:
The fair values of Ambac’s equity interest in Ambac sponsored special purpose entities (included in Other assets), Loans, and Obligations under investment agreements are estimated based upon internal valuation models that discount expected cash flows using discount rates consistent with the credit quality of the obligor after considering collateralization.
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. 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 dealer quotes or alternative pricing sources with reasonable levels of price transparency. 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. VIE debt instruments considered Level 3 include fixed rate, floating rate and zero coupon notes secured by various asset types, primarily European ABS. Information about the valuation inputs for the various VIE debt categories classified as Level 3 is as follows:
European ABS transactions: The fair value of such obligations classified as Level 3 was $1,841,412 and $1,070,439 at March 31, 2015 and December 31, 2014, respectively. 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 (Level 2) for comparable notes from the same securitization entity. Significant inputs for the valuation at March 31, 2015 and December 31, 2014 include the following weighted averages:
March 31, 2015:			December 31, 2014:
a. Coupon rate:	0.57%		a. Coupon rate:	0.30%
b. Maturity:	17.92 years		b. Maturity:	21.25 years
c. Yield:	7.30%		c. Yield:	9.52%
US Commercial ABS transaction: The fair value of such obligations classified as Level 3 was $190,687 and $193,225 at March 31, 2015 and December 31, 2014, respectively. Fair values were calculated as the sum of the present value of expected future cash flows from the underlying VIE assets plus the present value of the related Ambac financial guarantee cash flows. The discount rates applied to cash flows sourced from VIE assets were based on interest rates for similar obligations. The fair value of financial guarantee cash flows include internal estimates of future loss payments by Ambac discounted at a rate that incorporates Ambac’s own credit risk. Significant inputs for the valuation at March 31, 2015 and December 31, 2014, include the following weighted averages:
March 31, 2015:			December 31, 2014:
a. Coupon rate:	5.88%		a. Coupon rate:	5.88%
b. Maturity:	15.72 years		b. Maturity:	15.84 years
c. Yield:	7.50%		c. Yield:	7.37%
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 fair value balances at March 31, 2015 and December 31, 2014 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 the 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. Our valuation of VIE assets (fixed income securities or loans), therefore, are 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 3.5% and 4.1% at March 31, 2015 and December 31, 2014, 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:
The following tables present the changes in the Level 3 fair value category for the periods presented in 2015 and 2014. Ambac classifies financial instruments in Level 3 of the fair value hierarchy when there is reliance on at least one significant unobservable input to the valuation model. In addition to these unobservable inputs, the valuation models for Level 3 financial instruments typically also rely on a number of inputs that are readily observable either directly or indirectly. Thus, the gains and losses presented below include changes in the fair value related to both observable and unobservable inputs.
Level 3 - Financial Assets and Liabilities Accounted for at Fair Value
														VIE Assets and Liabilities
		Investments				Other				Derivatives				Investments				Loans			Long-term			Total
						assets															debt
Three Months Ended March 31, 2015:
Balance, beginning of period		$	198,201			$	12,036			$	(215,346	)		$	2,743,050			$	12,371,177		$	(1,263,664	)	$	13,845,454
Total gains/(losses) realized and unrealized:
Included in earnings		5,729				(295		)		(13,921		)		92,120				1,110,927			(839,998		)	354,562
Included in other comprehensive income		(5,706		)		—				—				(130,513		)		(562,621		)	67,625			(631,215		)
Purchases		84,504				—				—				—				—			—			84,504
Issuances		—				—				—				—				—			—			—
Sales		—				—				—				—				—			—			—
Settlements		(19,996		)		(1,705		)		(934		)		—				(130,282		)	3,938			(148,979		)
Transfers into Level 3		—				—				—				—				—			—			—
Transfers out of Level 3		—				—				—				—				—			—			—
Balance, end of period		$	262,732			$	10,036			$	(230,201	)		$	2,704,657			$	12,789,201		$	(2,032,099	)	$	13,504,326
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		$	—			$	(295	)		$	(14,364	)		$	92,120			$	1,110,927		$	(839,998	)	$	348,390
Three Months Ended March 31, 2014:
Balance, beginning of period		$	67,783			$	13,384			$	(186,934	)		$	2,475,182			$	13,398,895		$	(1,514,605	)	$	14,253,705
Total gains/(losses) realized and unrealized:
Included in earnings		419				(262		)		(14,249		)		55,745				321,847			(190,962		)	172,538
Included in other comprehensive income		(217		)		—				—				15,835				79,802			(8,621		)	86,799
Purchases		—				—				—				—				70,000			—			70,000
Issuances		—				—				—				—				—			—			—
Sales		—				—				—				—				—			—			—
Settlements		(854		)		—				(1,299		)		—				(601,092		)	429,794			(173,451		)
Transfers into Level 3		—				—				—				—				—			—			—
Transfers out of Level 3		(208		)		—				—				—				—			—			(208		)
Balance, end of period		$	66,923			$	13,122			$	(202,482	)		$	2,546,762			$	13,269,452		$	(1,284,394	)	$	14,409,383
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		$	—			$	(262	)		$	(15,024	)		$	55,745			$	316,714		$	(187,824	)	$	169,349
The tables below provide roll-forward information by class of investments and derivatives measured using significant unobservable inputs.
Level 3 - Investments by Class:
		Collateralized				Other Asset				Corporate				U.S. Agency				Non-Agency			Total
		Debt				Backed				Obligations				Obligations				RMBS			Investments
		Obligations				Securities
Three Months Ended March 31, 2015:
Balance, beginning of period		$	—			$	—			$	3,808			$	—			$	194,393		$	198,201
Total gains/(losses) realized and unrealized:
Included in earnings		—				—				(19		)		—				5,748			5,729
Included in other comprehensive income		—				—				(286		)		—				(5,420		)	(5,706		)
Purchases		—				—				—				—				84,504			84,504
Issuances		—				—				—				—				—			—
Sales		—				—				—				—				—			—
Settlements		—				—				(3,503		)		—				(16,493		)	(19,996		)
Transfers into Level 3		—				—				—				—				—			—
Transfers out of Level 3		—				—				—				—				—			—
Balance, end of period		$	—			$	—			$	—			$	—			$	262,732		$	262,732
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		$	—			$	—			$	—			$	—			$	—		$	—
Three Months Ended March 31, 2014:
Balance, beginning of period		$	—			$	64,073			$	3,502			$	208			$	—		$	67,783
Total gains/(losses) realized and unrealized:
Included in earnings		—				443				(24		)		—				—			419
Included in other comprehensive income		—				(295		)		78				—				—			(217		)
Purchases		—				—				—				—				—			—
Issuances		—				—				—				—				—			—
Sales		—				—				—				—				—			—
Settlements		—				(854		)		—				—				—			(854		)
Transfers into Level 3		—				—				—				—				—			—
Transfers out of Level 3		$	—			$	—			$	—			$	(208	)		$	—		$	(208	)
Balance, end of period		$	—			$	63,367			$	3,556			$	—			$	—		$	66,923
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:
		Interest				Credit				Total
		Rate Swaps				Derivatives				Derivatives
Three Months Ended March 31, 2015:
Balance, beginning of period		$	(141,887	)		$	(73,459	)		$	(215,346	)
Total gains/(losses) realized and unrealized:
Included in earnings		(11,422		)		(2,499		)		(13,921		)
Included in other comprehensive income		—				—				—
Purchases		—				—				—
Issuances		—				—				—
Sales		—				—				—
Settlements		(515		)		(419		)		(934		)
Transfers into Level 3		—				—				—
Transfers out of Level 3		—				—				—
Balance, end of period		$	(153,824	)		$	(76,377	)		$	(230,201	)
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		$	(11,422	)		$	(2,942	)		$	(14,364	)
Three Months Ended March 31, 2014:
Balance, beginning of period		$	(92,612	)		$	(94,322	)		$	(186,934	)
Total gains/(losses) realized and unrealized:
Included in earnings		(21,631		)		7,382				(14,249		)
Included in other comprehensive income		—				—				—
Purchases		—				—				—
Issuances		—				—				—
Sales		—				—				—
Settlements		(524		)		(775		)		(1,299		)
Transfers into Level 3		—				—				—
Transfers out of Level 3		—				—				—
Balance, end of period		$	(114,767	)		$	(87,715	)		$	(202,482	)
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		$	(21,631	)		$	6,607			$	(15,024	)
Invested assets and VIE long-term debt are transferred into Level 3 when internal valuation models that include significant unobservable inputs are used to estimate fair value. All such securities that have internally modeled fair values have been classified as Level 3. Derivative instruments are transferred into Level 3 when the use of unobservable inputs becomes significant to the overall valuation. All transfers out of Level 3 represent transfers between Level 3 and Level 2 for the periods presented. 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				Realized				Unrealized				Derivative				Income			Other
		investment				gains or				gains or				products				(loss) on			income
		income				(losses) and				(losses) on				revenues				variable			or (loss)
						other				credit				(interest rate				interest
						settlements				derivative				swaps)				entities
						on credit				contracts
						derivative
						contracts
Three Months Ended March 31, 2015:
Total gains or losses included in earnings for the period		$	5,729			$	419			$	(2,918	)		$	(11,422	)		$	363,049		$	(295	)
Changes in unrealized gains or losses relating to the assets and liabilities still held at the reporting date		—				—				(2,942		)		(11,422		)		363,049			(295		)
Three Months Ended March 31, 2014:
Total gains or losses included in earnings for the period		$	419			$	775			$	6,607			$	(21,631	)		$	186,630		$	(262	)
Changes in unrealized gains or losses relating to the assets and liabilities still held at the reporting date		—				—				6,607				(21,631		)		184,635			(262		)

Investments

Investments	3 Months Ended
	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Investments	INVESTMENTS
	Ambac’s invested assets are primarily comprised of fixed income securities classified as available-for-sale and equity interests in pooled investment funds. Such equity interests in the form of common stock or in-substance common stock are classified as trading securities.
	The amortized cost and estimated fair value of available-for-sale investments, excluding VIE investments, at March 31, 2015 and December 31, 2014 were as follows:
			Amortized			Gross			Gross		Estimated		Non-credit  other-
			Cost			Unrealized			Unrealized		Fair Value		than-temporary
						Gains			Losses				Impairments (1)
	March 31, 2015
	Fixed income securities:
	Municipal obligations		$	517,256		$	12,136		$	4,204	$	525,188	$	—
	Corporate obligations		1,588,962			24,097			3,290		1,609,769		—
	Foreign obligations		123,601			4,038			2,475		125,164		—
	U.S. government obligations		28,983			1,418			104		30,297		—
	U.S. agency obligations		4,438			—			11		4,427		—
	Residential mortgage-backed securities		1,705,246			159,388			18,157		1,846,477		9,844
	Collateralized debt obligations		88,569			102			433		88,238		—
	Other asset-backed securities		615,831			21,048			689		636,190		—
			4,672,886			222,227			29,363		4,865,750		9,844
	Short-term		220,980			—			—		220,980		—
			4,893,866			222,227			29,363		5,086,730		9,844
	Fixed income securities pledged as collateral:
	U.S. government obligations		64,432			381			—		64,813		—
	Total collateralized investments		64,432			381			—		64,813		—
	Total available-for-sale investments		$	4,958,298		$	222,608		$	29,363	$	5,151,543	$	9,844
	December 31, 2014
	Fixed income securities:
	Municipal obligations		$	523,019		$	9,769		$	6,996	$	525,792	$	—
	Corporate obligations		1,382,195			12,815			9,416		1,385,594		—
	Foreign obligations		126,041			3,060			1,344		127,757		—
	U.S. government obligations		42,328			1,078			427		42,979		—
	U.S. agency obligations		29,524			—			38		29,486		—
	Residential mortgage-backed securities		1,557,059			167,396			13,500		1,710,955		7,773
	Collateralized debt obligations		21,346			50			274		21,122		—
	Other asset-backed securities		833,366			48,794			159		882,001		—
			4,514,878			242,962			32,154		4,725,686		7,773
	Short-term		360,069			—			4		360,065		—
			4,874,947			242,962			32,158		5,085,751		7,773
	Fixed income securities pledged as collateral:
	U.S. government obligations		64,378			—			111		64,267		—
	Total collateralized investments		64,378			—			111		64,267		—
	Total available-for-sale investments		$	4,939,325		$	242,962		$	32,269	$	5,150,018	$	7,773
	-1	Represents the amount of non-credit other-than-temporary impairment losses remaining in accumulated other comprehensive loss on securities that also had a credit impairment. These losses are included in gross unrealized losses as of March 31, 2015 and December 31, 2014.
	The amortized cost and estimated fair value of available-for-sale investments, excluding VIE investments, at March 31, 2015, by contractual maturity, were as follows:
			Amortized			Estimated
			Cost			Fair Value
	Due in one year or less		$	413,150		$	413,291
	Due after one year through five years		927,630			935,442
	Due after five years through ten years		994,286			1,013,939
	Due after ten years		213,586			217,966
			2,548,652			2,580,638
	Residential mortgage-backed securities		1,705,246			1,846,477
	Collateralized debt obligations		88,569			88,238
	Other asset-backed securities		615,831			636,190
	Total		$	4,958,298		$	5,151,543
	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:
	The following table shows gross unrealized losses and fair values of Ambac’s available-for-sale investments, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position, at March 31, 2015 and December 31, 2014:
			Less Than 12 Months						12 Months or More				Total
			Fair Value			Gross			Fair Value		Gross		Fair Value		Gross
						Unrealized					Unrealized				Unrealized
						Loss					Loss				Loss
	March 31, 2015
	Fixed income securities:
	Municipal obligations		$	46,461		$	412		$	119,412	$	3,792	$	165,873	$	4,204
	Corporate obligations		278,044			2,081			81,739		1,209		359,783		3,290
Foreign government obligations		32,206			1,864			8,900		611		41,106		2,475
U.S. government obligations		1,661			2			10,814		102		12,475		104
U.S. agency obligations		—			—			4,359		11		4,359		11
Residential mortgage-backed securities		547,706			17,336			10,266		821		557,972		18,157
Collateralized debt obligations		63,834			289			4,434		144		68,268		433
Other asset-backed securities		163,243			687			68		2		163,311		689
		1,133,155			22,671			239,992		6,692		1,373,147		29,363
Short-term		—			—			—		—		—		—
		1,133,155			22,671			239,992		6,692		1,373,147		29,363
Fixed income securities, pledged as collateral:
U. S. government obligations		—			—			—		—		—		—
Total collateralized investments		—			—			—		—		—		—
Total temporarily impaired securities		$	1,133,155		$	22,671		$	239,992	$	6,692	$	1,373,147	$	29,363
		Less Than 12 Months						12 Months or More				Total
		Fair Value			Gross			Fair Value		Gross		Fair Value		Gross
					Unrealized					Unrealized				Unrealized
					Loss					Loss				Loss
December 31, 2014:
Fixed income securities:
Municipal obligations		$	77,788		$	1,244		$	135,076	$	5,752	$	212,864	$	6,996
Corporate obligations		453,504			4,998			172,045		4,418		625,549		9,416
Foreign government obligations		20,827			748			14,277		596		35,104		1,344
U.S. government obligations		7,223			154			14,735		273		21,958		427
U.S. agency obligations		25,039			2			4,378		36		29,417		38
Residential mortgage-backed securities		413,203			12,391			10,076		1,109		423,279		13,500
Collateralized debt obligations		5,012			274			—		—		5,012		274
Other asset-backed securities		248,823			155			68		4		248,891		159
		1,251,419			19,966			350,655		12,188		1,602,074		32,154
Short-term		8,803			4			—		—		8,803		4
		1,260,222			19,970			350,655		12,188		1,610,877		32,158
Fixed income securities, pledged as collateral:
U. S. government obligations		64,267			111			—		—		64,267		111
Total collateralized investments		64,267			111			—		—		64,267		111
Total temporarily impaired securities		$	1,324,489		$	20,081		$	350,655	$	12,188	$	1,675,144	$	32,269
Management has determined that the unrealized losses reflected in the tables above are temporary in nature as of March 31, 2015 and December 31, 2014 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) management has no 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. 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, trading securities plus the scheduled maturities and interest payments from the remaining securities in the portfolio. 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. 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. In the liquidity assessment described above, 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. Projected interest receipts on securities pledged as collateral generally belong to Ambac and are considered to be sources of available liquidity from the investment portfolio.
As of March 31, 2015, for securities that have indications of possible other-than-temporary impairment but which management does not intend to sell and will not more likely than not be required to sell, management compared 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 were discounted at the effective interest rate implicit in the security at the date of acquisition (or Fresh Start Reporting Date of April 30, 2013 for securities purchased prior to that date) or for debt securities that are beneficial interests in securitized financial assets, at a rate equal to the current yield used to accrete the beneficial interest. For floating rate securities, future cash flows and the discount rate used were 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 March 31, 2015, $613,511 of the total fair value and $20,130 of the unrealized loss related to below investment grade securities and non-rated securities. Of the securities that were in a gross unrealized loss position at December 31, 2014, $473,656 of the total fair value and $16,001 of the unrealized loss related to below investment grade securities and non-rated securities. With respect to Ambac-wrapped securities guaranteed under policies that have been allocated to the Segregated Account, 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, including interest on Deferred Amounts. Ambac estimates the timing of such claim payment receipts but the actual timing of such amounts are at the sole discretion of the Rehabilitator. Further modifications to the Segregated Account Rehabilitation Plan or to the rules and guidelines promulgated thereunder, orders from the Rehabilitation Court or actions by the Rehabilitator with respect to the form, amount and timing of satisfying permitted policy claims, or making payments on Deferred Amounts or surplus notes, may have a material effect on the fair value of Ambac-wrapped securities and future recognition of other-than-temporary impairments. Refer to Note 1.Background and Business Description and to Note 1. Background and Business Description in the Notes to Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014 for information relating to the amended Segregated Account Rehabilitation Plan. 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, including Ambac's intention to sell securities and ability to hold temporarily impaired securities until recovery. If that judgment changes, Ambac may ultimately record a charge for other-than-temporary impairment in future periods.
Municipal and corporate obligations
The gross unrealized losses on municipal and corporate obligations as of March 31, 2015 are primarily the result of the increase in interest rates since the Fresh Start Reporting Date of April 30, 2013. These securities are primarily fixed-rate securities with an investment grade credit rating. Management believes that the timely receipt of all principal and interest on these positions is probable.
Residential mortgage-backed securities
Of the $18,157 of unrealized losses on residential mortgage-backed securities, $16,631 is attributable to Ambac-wrapped securities. The unrealized loss on these securities is primarily the result of discount accretion, which has exceeded the increase in fair value since the Fresh Start Reporting Date of April 30, 2013. As part of the quarterly impairment review process, management estimates expected future cash flows from residential mortgage-backed securities. This approach includes the utilization of market accepted software models in conjunction with detailed data of the historical performance of the collateral pools, which assists in the determination of assumptions such as defaults, severity and voluntary prepayment rates that are largely driven by home price forecasts as well as other macro-economic factors.  Additionally, for Ambac-wrapped securities that are allocated to the Segregated Account, expected future cash flows include assumptions about the timing of Ambac Assurance claim payments, including interest on Deferred Amounts, although the actual timing of such payments are at the sole discretion of the Rehabilitator. These assumptions are used to project future cash flows for each security. Management considered this analysis in making our determination that a credit loss has not occurred at March 31, 2015 on these transactions.
Realized Gains and Losses and Other-Than-Temporary Impairments:
The following table details amounts included in net realized gains and other-than-temporary impairments included in earnings for the affected periods:
		Three Months Ended March 31,
		2015			2014
Gross realized gains on securities		$	50,654		$	19,576
Gross realized losses on securities		(3,737		)	(1,128		)
Foreign exchange gains (losses)		7,184			(2,159		)
Net realized gains		$	54,101		$	16,289
Net other-than-temporary impairments (1)		$	(3,119	)	$	(10,392	)
-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 Ambac will be required to sell before recovery of the amortized cost basis.
Since commencement of the Segregated Account Rehabilitation Proceedings, changes in the estimated timing of claim payments have resulted in adverse changes in projected cash flows on certain impaired Ambac-wrapped securities. Such changes in estimated claim payments on Ambac-wrapped securities contributed to net other-than-temporary impairments for the periods presented in the table above. Further changes to the timing of estimated claim payments could result in additional other-than-temporary impairment charges in the future. Ambac’s other-than-temporary impairments for 2014 also relate to the company’s intent to sell certain securities that were in an unrealized loss position as of March 31, 2014. Future changes in our estimated liquidity needs could result in a determination that Ambac no longer has the ability to hold additional 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 March 31, 2015 and 2014 for which a portion of an other-than-temporary impairment was recognized in other comprehensive income:
		Credit
		Impairment
Balance at January 1, 2015		$	14,062
Additions for credit impairments recognized on:
Securities not previously impaired		1,660
Securities previously impaired		1,457
Reductions for credit impairments previously recognized on:
Securities that matured or were sold during the period		—
Balance at March 31, 2015		$	17,179
Balance at January 1, 2014		$	1,182
Additions for credit impairments recognized on:
Securities not previously impaired		4,767
Securities previously impaired		—
Reductions for credit impairments previously recognized on:
Securities that matured or were sold during the period		—
Balance at March 31, 2014		$	5,949
Counterparty Collateral, Deposits with Regulators and Other Restrictions:
Ambac routinely pledges and receives collateral related to certain business lines and/or transactions. The following is a description of those arrangements by collateral source:
-1	Cash and securities held in Ambac’s investment portfolio—Ambac pledges assets it holds in its investment portfolio to investment agreement and derivative counterparties. Securities pledged to investment agreement counterparties may not then be re-pledged to another entity. Ambac’s counterparties under derivative agreements have the right to pledge or rehypothecate the securities and as such, these pledged securities are separately classified on the Consolidated Balance Sheets as “Fixed income securities pledged as collateral, at fair value”.
-2	Cash and securities pledged to Ambac under derivative agreements—Ambac may re-pledge securities it holds from certain derivative counterparties to other derivative counterparties in accordance with its rights and obligations under those agreements.
The following table presents (i) the sources of collateral either received from various counterparties where Ambac is permitted to sell or re-pledge the collateral or collateral held directly in the investment portfolio and (ii) how that collateral was pledged to various investment agreement, derivative and repurchase agreement counterparties at March 31, 2015 and December 31, 2014:
		Fair Value of Cash			Fair Value of Cash			Fair Value of Cash
		and Underlying			and Securities			and Securities
		Securities			Pledged to			Pledged to
					Investment			Derivative
					Agreement			Counterparties
					Counterparties
March 31, 2015:
Sources of Collateral:
Cash and securities pledged directly from the investment portfolio		$	368,979		$	108,469		$	260,510
December 31, 2014:
Sources of Collateral:
Cash and securities pledged directly from the investment portfolio		$	379,423		$	156,916		$	222,507
Securities carried at $6,842 and $6,790 at March 31, 2015 and December 31, 2014, respectively, were deposited by Ambac Assurance and Everspan with governmental authorities or designated custodian banks as required by laws affecting insurance companies.
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) because the insurance cannot be legally separated from the underlying security by the insurer. 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 March 31, 2015 and December 31, 2014, respectively:
		Municipal			Corporate			Mortgage		Total		Weighted
		obligations			obligations			and asset-				Average
								backed				Underlying
								securities				Rating (1)
March 31, 2015:
Ambac Assurance Corporation (2)		$	54,124		$	—		$	2,078,084	$	2,132,208	CCC-
Assured Guaranty Municipal Corporation		121,519			—			—		121,519		A
National Public Finance Guarantee Corporation		64,693			—			—		64,693		A-
MBIA Insurance Corporation		—			32,265			—		32,265		A+
Total		$	240,336		$	32,265		$	2,078,084	$	2,350,685	CCC
December 31, 2014:
Ambac Assurance Corporation (2)		$	53,164		$	—		$	2,146,555	$	2,199,719	CCC-
Assured Guaranty Municipal Corporation		119,492			—			—		119,492		A
National Public Finance Guarantee Corporation		67,895			—			—		67,895		A-
MBIA Insurance Corporation		—			32,460			—		32,460		A+
Total		$	240,551		$	32,460		$	2,146,555	$	2,419,566	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 $51,395 at March 31, 2015 and December 31, 2014, insured by Ambac UK.
Investment Income:
Net investment income was comprised of the following for the affected periods:
		Three Months Ended March 31,
		2015			2014
Fixed income securities		$	65,585		$	71,231
Short-term investments		42			57
Loans		132			117
Investment expense		(2,427		)	(2,598		)
Securities available-for-sale and short-term		63,332			68,807
Other investments		9,651			1,994
Total net investment income		$	72,983		$	70,801
Net investment income from Other investments primarily represents changes in fair value on securities classified as trading or under the fair value option. The portion of net unrealized gains related to such securities still held at the end of each period is as follows:
		Three Months Ended March 31,
		2015			2014
Net gains recognized during the period on trading securities		$	7,819		$	1,994
Less: net gains (losses) recognized during the reporting period on trading securities sold during the period		1,564			(455		)
Unrealized gains recognized during the reporting period on trading securities still held at the reporting date		$	6,255		$	2,449

Derivative_Instruments

Derivative Instruments	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	.    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 March 31, 2015 and December 31, 2014:
		Gross				Gross				Net Amounts		Gross		Net Amount
		Amounts of				Amounts				of Assets/		Amount of
		Recognized				Offset in the				Liabilities		Collateral
		Assets /				Consolidated				Presented		Received /
		Liabilities				Balance Sheet				in the		Pledged Not
										Consolidated		Offset in the
										Balance Sheet		Consolidated
												Balance Sheet
	March 31, 2015:
	Derivative Assets:
	Credit derivatives	$	—			$	—			$	—	$	—	$	—
	Interest rate swaps	182,103				68,481				113,622		—		113,622
	Total non-VIE derivative assets	$	182,103			$	68,481			$	113,622	$	—	$	113,622
	Derivative Liabilities:
	Credit derivatives	$	76,377			$	—			$	76,377	$	—	$	76,377
	Interest rate swaps	438,518				68,481				370,037		196,039		173,998
	Futures contracts	942				—				942		942		—
	Total non-VIE derivative liabilities	$	515,837			$	68,481			$	447,356	$	196,981	$	250,375
	Variable Interest Entities:
	Interest rate swaps	$	2,081,082			$	—			$	2,081,082	$	—	$	2,081,082
	Currency swaps	44,631				—				44,631		—		44,631
	Total VIE derivative liabilities	$	2,125,713			$	—			$	2,125,713	$	—	$	2,125,713
	December 31, 2014:
	Derivative Assets:
	Credit derivatives	$	2,043			$	—			$	2,043	$	—	$	2,043
	Interest rate swaps	161,640				54,666				106,974		—		106,974
	Total non-VIE derivative assets	$	163,683			$	54,666			$	109,017	$	—	$	109,017
	Derivative Liabilities:
	Credit derivatives	$	75,502			$	—			$	75,502	$	—	$	75,502
	Interest rate swaps	385,546				54,666				330,880		169,573		161,307
	Futures contracts	562				—				562		562		—
	Total non-VIE derivative liabilities	$	461,610			$	54,666			$	406,944	$	170,135	$	236,809
	Variable Interest Entities:
	Interest rate swaps	$	2,133,268			$	—			$	2,133,268	$	—	$	2,133,268
	Currency swaps	66,895				—				66,895		—		66,895
	Total VIE derivative liabilities	$	2,200,163			$	—			$	2,200,163	$	—	$	2,200,163
	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 $195,697 and $158,240 as of March 31, 2015 and December 31, 2014, respectively. There were no amounts held representing an obligation to return cash collateral as of March 31, 2015 and December 31, 2014.
	The following tables summarize the location and amount of gains and losses of derivative contracts in the Consolidated Statements of Total Comprehensive Income for the three months ended March 31, 2015 and 2014:
		Location of Gain or (Loss) Recognized in		Amount of Gain or (Loss) Recognized in Consolidated Statement of Total Comprehensive Income
		Consolidated Statements of Total Comprehensive Income		Three Months Ended March 31,
				2015				2014
	Financial Guarantee:
	Credit derivatives	Net change in fair value of credit derivatives		$	(2,499	)		$	7,382
	Financial Services derivatives products:
	Interest rate swaps	Derivative products		(35,547		)		(51,849		)
	Futures contracts	Derivative products		(2,227		)		(1,992		)
	Total Financial Services derivative products			(37,774		)		(53,841		)
	Variable Interest Entities:
	Currency swaps	Income (loss) on variable interest entities		22,264				5,408
	Interest rate swaps	Income (loss) on variable interest entities		52,186				(77,792		)
	Total Variable Interest Entities			74,450				(72,384		)
	Total derivative contracts			$	34,177			$	(118,843	)
	Financial Guarantee 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. Upon a credit event, Ambac is generally required to make payments equal to the difference between the scheduled debt service payment and the actual payment made by the issuer. Substantially all of Ambac’s credit derivative contracts relate to structured finance transactions. Credit derivatives issued are insured by Ambac Assurance. None of the outstanding credit derivative transactions at March 31, 2015 include ratings based collateral-posting triggers or otherwise require Ambac to post collateral regardless of Ambac’s ratings or the size of the mark to market exposure to Ambac.
	Our remaining outstanding credit derivatives were written on a “pay-as-you-go” basis. Similar to an 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. Independent rating agencies may have assigned different ratings on the credits in Ambac’s portfolio than Ambac’s internal ratings. The following tables summarize the gross principal notional outstanding for CDS contracts, by Ambac rating, for each major category as of March 31, 2015 and December 31, 2014:
		CLO				Other				Total
	Ambac Rating - March 31, 2015:
	AAA	$	—			$	—			$	—
	AA	466,453				303,860				770,313
	A	—				43,160				43,160
	BBB (1)	—				515,578				515,578
Below investment grade (2)	—				265,520				265,520
Total	$	466,453			$	1,128,118			$	1,594,571
Ambac Rating - December 31, 2014:
AAA	$	—			$	—			$	—
AA	549,923				217,680				767,603
A	—				43,160				43,160
BBB  (1)	—				448,249				448,249
Below investment grade (2)	—				270,747				270,747
Total	$	549,923			$	979,836			$	1,529,759
-1	BBB internal ratings reflect bonds which are of medium grade credit quality with adequate capacity to pay interest and repay principal. Certain protective elements and margins may weaken under adverse economic conditions and changing circumstances. These bonds are more likely than higher rated bonds to exhibit unreliable protection levels over all cycles.
-2	Below investment grade internal ratings reflect bonds which are of speculative grade credit quality with the adequacy of future margin levels for payment of interest and repayment of principal potentially adversely affected by major ongoing uncertainties or exposure to adverse conditions.
The tables below summarize information by major category as of March 31, 2015 and December 31, 2014:
	CLO				Other				Total
March 31, 2015:
Number of CDS transactions	5				10				15
Remaining expected weighted-average life of obligations (in years)	1.5				5.6				4.4
Gross principal notional outstanding	$	466,453			$	1,128,118			$	1,594,571
Net derivative liabilities at fair value	$	1,533			$	74,844			$	76,377
December 31, 2014:
Number of CDS transactions	6				10				16
Remaining expected weighted-average life of obligations (in years)	1.8				5.4				4.1
Gross principal notional outstanding	$	549,923			$	979,836			$	1,529,759
Net derivative liabilities at fair value	$	2,027			$	71,432			$	73,459
The maximum potential amount of future payments under Ambac’s credit derivative contracts is generally the gross principal notional outstanding amount included in the above table plus future interest payments payable by the derivative reference obligations. Since Ambac’s credit derivatives typically reference obligations of or assets held by special purpose entities that meet the definition of a VIE, the amount of maximum potential future payments for credit derivatives is included in the table in Note 3. Special Purpose Entities.
Changes in fair value of Ambac’s credit derivative contracts are accounted for at fair value since they do not qualify for the financial guarantee scope exception under the Derivatives and Hedging Topic of the ASC. Changes in fair value are recorded in “Net change in fair value of credit derivatives” on the Consolidated Statements of Total Comprehensive Income (Loss). Although CDS contracts are accounted for at fair value, they are surveilled similar to non-derivative financial guarantee contracts. As with financial guarantee insurance policies, Ambac’s risk group tracks credit migration of CDS contracts’ reference obligations from period to period.
Adversely classified credits are assigned risk classifications by the risk group. As of March 31, 2015, there are four CDS contracts on Ambac’s adversely classified credit listing, with a net derivative liability fair value of $61,338 and gross notional principal outstanding of $265,520. As of December 31, 2014, there were four CDS contracts on Ambac’s adversely classified credit listing, with a net derivative liability fair value of $60,729 and total notional principal outstanding of $270,747.
Financial Services Derivative Products:
Ambac, through its subsidiary Ambac Financial Services (“AFS”), provides interest rate and currency swaps to states, municipalities and their authorities, asset-backed issuers and other entities in connection with their financings. AFS manages its interest rate swaps business with the goal of retaining some basis risk and excess interest rate sensitivity as an economic hedge against the effects of rising interest rates elsewhere in the Company, including on Ambac’s financial guarantee exposures. As of March 31, 2015 and December 31, 2014 the notional amounts of AFS’s trading derivative products are as follows:
	Notional
Type of derivative	March 31,				December 31,
	2015				2014
Interest rate swaps—receive-fixed/pay-variable	$	760,808			$	782,904
Interest rate swaps—pay-fixed/receive-variable	1,465,871				1,479,650
Interest rate swaps—basis swaps	55,800				55,800
Futures contracts	60,000				80,000
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 March 31, 2015 and December 31, 2014 are as follows:
	Notional
Type of VIE derivative	March 31,				December 31,
	2015				2014
Interest rate swaps—receive-fixed/pay-variable	$	1,629,458			$	1,710,344
Interest rate swaps—pay-fixed/receive-variable	3,003,021				3,152,090
Currency swaps	690,386				724,656
Credit derivatives	16,249				18,278
Contingent Features in Derivatives Related to Ambac Credit Risk
Ambac’s interest rate swaps with professional swap-dealer counterparties and certain front-end counterparties 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 March 31, 2015 and December 31, 2014, the net liability fair value of all derivative instruments with contingent features linked to Ambac’s own credit risk was $107,213 and $92,869, respectively, related to which Ambac had posted assets as collateral with a fair value of $136,810 and $118,844, 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 contracts terminated on March 31, 2015, settlement of collateral balances and net derivative liabilities would result in a net receipt of cash and/or securities by Ambac. If counterparties elect to exercise their right to terminate, the actual termination payment amounts will be determined in accordance with derivative contract terms, which may result in amounts that differ from market values as reported in Ambac’s financial statements.

Income_Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES
	Ambac files a consolidated Federal income tax return with its subsidiaries. Ambac and its subsidiaries also file separate or combined income tax returns in various states, local and foreign jurisdictions. The following are the major jurisdictions in which Ambac and its affiliates operate and the earliest tax years subject to examination:
	Jurisdiction	Tax Year
	United States	2010
	New York State	2011
	New York City	2011
	United Kingdom	2009
	Italy	2009
	As of March 31, 2015 Ambac had loss carryforwards totaling $5,225,954. This includes carryforwards of $133,626 relating to U.S. capital losses, $182,059 of Ambac UK loss carryforwards, and an ordinary U. S. federal net operating tax carryforward of approximately $4,910,269, which, if not utilized, will begin expiring in 2029, and will fully expire in 2034.
	The tax effects of temporary differences that give rise to significant portions of the deferred tax liabilities and deferred tax assets at March 31, 2015 and December 31, 2014 are presented below:
		March 31,			December 31,
		2015			2014
	Deferred tax liabilities:
	Insurance intangible	$	471,553		$	493,822
	Variable interest entities	11,611			14,149
	Investments	141,208			138,072
	Unearned premiums and credit fees	101,647			104,589
	Other	33,763			33,835
	Total deferred tax liabilities	759,782			784,467
	Deferred tax assets:
	Net operating loss and capital carryforward	1,829,084			1,890,551
	Loss reserves	146,429			185,881
	Compensation	5,469			5,276
	AMT Credits	11,899			10,359
	Other	9,539			9,539
	Sub total deferred tax assets	2,002,420			2,101,606
	Valuation allowance	1,244,543			1,319,218
	Total deferred tax assets	757,877			782,388
	Net deferred tax asset (liability)	(1,905		)	(2,079		)
	In accordance with the Income Tax Topic of the ASC, a valuation allowance is recognized if, based on the weight of available evidence, it is more-likely-than-not that some, or all, of the deferred tax asset will not be realized. As a result of the risks and uncertainties associated with future operating results, management believes it is more likely than not that the Company will not generate sufficient taxable income to recover the deferred tax operating asset and therefore has a full valuation allowance.

Commitments_and_Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES
	The following commitments and contingencies provide an update of those discussed in Note 18: Commitments and Contingencies in the Notes to Consolidated Financial Statements included Part II, Item 8 in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014, and should be read in conjunction with the complete descriptions provided in the aforementioned Form 10-K.
	The Segregated Account and Wisconsin Rehabilitation Proceeding
	On March 18, 2015, the Rehabilitator filed a motion to confirm and declare the reimbursement amounts due with respect to cash claim payments made by Ambac Assurance and the Segregated Account on a certain policy. Objections to the motion were due on April 27, 2015, but no objection was filed. On May 1, 2015, the Rehabilitation Court granted the Rehabilitator’s motion.
	Litigation Against Ambac
	County of Alameda et al. v. Ambac Assurance Corporation et al. (Superior Court of the State of California, County of San Francisco, second amended complaint filed on or about August 23, 2011); Contra Costa County et al. v. Ambac Assurance Corporation et al. (Superior Court of the State of California, County of San Francisco, third amended complaint filed on or about October 21, 2011); The Olympic Club v. Ambac Assurance Corporation et al. (Superior Court of the State of California, County of San Francisco, fourth amended complaint filed on or about October 21, 2011). Ambac Assurance and the other Bond Insurer Defendants filed a demurrer seeking dismissal of the current amended complaints on September 21, 2011, which was denied on October 20, 2011. On December 2, 2011, Ambac Assurance and the other Bond Insurer Defendants filed a special motion to strike the current amended complaints under California’s Anti-SLAPP statute (Calif. Code of Civ. Proc. Section 425.16). A hearing on the motion was held on March 23, 2012. On May 1, 2012, the Court ruled that the complaints were governed by the Anti-SLAPP statute to the extent they alleged conspiracy to influence the rating agencies’ rating methodologies, but not to the extent that the complaints alleged false or misleading statements or nondisclosures. After oral argument on March 21, 2013, the court dismissed claims related to the conspiracy branch of the complaint under the California Antitrust Law (the Cartwright Act) and after oral argument on April 22, 2013 denied defendants’ motion to dismiss claims under the California Unfair Competition Law. The court entered an order to this effect on July 9, 2013. On September 9, 2013, plaintiffs filed a notice of appeal of the July 9th order and on September 30, 2013, Ambac Assurance filed a notice of cross-appeal. On September 9, 2013, the parties filed motions for attorneys’ fees in connection with the portions of the Anti-SLAPP motions on which they were successful. The court denied plaintiffs’ motion for fees from the bench on November 8, 2013. On March 26, 2014, the court granted the defendants’ motions for attorneys’ fees awarding Ambac Assurance approximately $207. On July 7, 2014, plaintiffs filed a notice of appeal from the court’s decision awarding attorneys’ fees to Ambac Assurance and the other defendants. This appeal was dismissed on December 19, 2014. Plaintiffs have filed a motion to reinstate the appeal, stating that it should only have been dismissed as against one defendant with whom plaintiffs settled. Ambac did not oppose that motion, which was granted on January 29, 2015. Also on July 7, 2014, the Bond Insurer Defendants filed their appellate brief appealing the July 9th Order. Plaintiffs’ opposition to the Bond Insurer Defendants’ appellate brief and plaintiffs’ affirmative brief on their cross-motion were filed on November 5, 2014. The defendants’ brief in opposition to plaintiffs’ appeal and in further support of their cross-appeal was filed on February 3, 2015. Plaintiffs’ reply brief in further support of their appeal was filed on April 24, 2015. The appeal is now fully briefed and awaiting scheduling of oral argument.
	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. Ambac Assurance has been made aware that a transaction participant has directed a bond trustee to employ a different waterfall interpretation in a RMBS transaction, which may lead to the commencement of legal action. 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.
	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 Ambac which are probable and reasonably estimable, and management's estimated range of loss for such matters, are not material to the operating results or financial position of the Company. For the litigation matters Ambac 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 but, 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 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.
	Ambac Assurance Corporation v. Adelanto Public Utility Authority (United States District Court, Southern District of New York, filed on June 1, 2009). On December 23, 2014, the parties entered into a Judgment Satisfaction and Release Agreement to resolve the matter and in April 2015, when the Agreement became fully effective, the parties dismissed the Authority’s appeal to the Court of Appeals for the Second Circuit and the portion of the action that remained in the District Court and filed instruments of satisfaction of Ambac’s judgment against the Authority in the Southern District of New York and the Central District of California.
	Erste Europäische Pfandbriefund Kommunalkreditbank AG In Luxemburg and Ambac Assurance Corporation v. City of San Bernardino, California (United States Bankruptcy Court, Central District of California, Riverside Division, filed on January 7, 2015). On March 13, 2015, the City filed a motion to dismiss the complaint, which Ambac Assurance opposed. A hearing on the motion is currently scheduled for May 11, 2015.
	In connection with Ambac Assurance’s efforts to seek redress for breaches of representations and warranties and fraud related to the information provided by both the underwriters and the sponsors of various transactions and for failure to comply with the obligation by the sponsors to repurchase ineligible loans, Ambac Assurance has filed various lawsuits:
	•	Ambac Assurance Corporation v. EMC Mortgage LLC (formerly known as EMC Mortgage Corporation), J.P. Morgan Securities, Inc. (formerly known as Bear, Stearns & Co. Inc.), and JP Morgan Chase Bank, N.A. (Supreme Court of the State of New York, County of New York, filed February 17, 2011). On December 18, 2014, defendants filed a motion for partial summary judgment seeking to dismiss the plaintiffs’ claim for fraudulent inducement arguing that as a matter of law, plaintiffs cannot prove justifiable reliance. Ambac Assurance has opposed the motion, which is fully briefed. No decision has been issued.
	•	Ambac Assurance Corporation and The Segregated Account of Ambac Assurance Corporation v. Countrywide Securities Corp., Countrywide Financial Corp. (a.k.a. Bank of America Home Loans) and Bank of America Corp. (Supreme Court of the State of New York, County of New York, filed on September 28, 2010). On May 1, 2015, Ambac Assurance filed a motion for partial summary judgment. Defendants also each filed motions for summary judgment, which Ambac Assurance intends to oppose.
	•	Ambac Assurance Corporation and The Segregated Account of Ambac Assurance Corporation v. Nomura Credit & Capital, Inc. and Nomura Holding America Inc. (Supreme Court of the State of New York, County of New York, filed on April 15, 2013). On September 22, 2014, plaintiffs filed an amended complaint alleging claims for fraudulent inducement, material breach of contract and for the repurchase of loans that breach representations and warranties under the contracts, as well as damages. On October 31, 2014 defendants filed a motion to strike the amended complaint. Ambac Assurance opposed that motion and at the court’s recommendation also filed a cross motion for leave to amend the complaint on November 14, 2014, which the defendants opposed. Defendants also filed a motion to dismiss the fraudulent inducement claim, which Ambac Assurance opposed. All motions are fully briefed. The court heard oral argument on the defendants’ motion to dismiss the fraudulent inducement claim on April 14, 2015. No decision has been issued on any of the outstanding motions.
	•	The Segregated Account of Ambac Assurance Corporation and Ambac Assurance Corporation v. Countrywide Home Loans, Inc. (Wisconsin Circuit Court for Dane County, filed on December 30, 2014). Ambac Assurance alleges a claim for fraudulent inducement in connection with Ambac Assurance’s issuance of insurance policies relating to five residential mortgage-backed securitizations that are not the subject of Ambac Assurance’s previously filed lawsuit against the same defendant. Defendant filed a motion to dismiss the complaint on February 20, 2015, which Ambac Assurance opposed. The motion is fully briefed. No decision has been issued.
	•	Ambac Assurance Corporation and the Segregated Account of Ambac Assurance Corporation v. Countrywide Home Loans, Inc., Countrywide Securities Corp., Countrywide Financial Corp., and Bank of America Corp. (Supreme Court of the State of New York, County of New York, filed on December 30, 2014). Ambac Assurance alleges a claim for fraudulent inducement in connection with Ambac Assurance’s issuance of insurance policies relating to eight residential mortgage-backed securitizations that are not the subject of Ambac Assurance’s previously filed lawsuits against the same defendants. On February 20, 2015, the Countrywide defendants filed a motion to dismiss the complaint, which Bank of America joined on February 23, 2015. Ambac Assurance opposed the motion. Defendants’ reply is due on May 18, 2015.

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Segment Information	SEGMENT INFORMATION
	Ambac has two reportable business segments, as follows: (i) Financial Guarantee, which provides financial guarantees (including credit derivatives) for public finance, structured finance and international obligations; and (ii) Financial Services, which provides investment agreements, funding conduits, interest rate swaps, principally to clients of the financial guarantee business. Ambac’s reportable business segments are strategic business units that offer different products and services. They are managed separately because each business required different marketing strategies, personnel skill sets and technology.
	Ambac Assurance guarantees the swap and investment agreement obligations of its Financial Services subsidiaries. Additionally, Ambac Assurance provides loans to the Financial Services businesses. Inter-segment revenues include the premiums and investment income earned under those agreements. Such premiums are determined as if they were premiums paid by third parties, that is, at current market prices.
	Information provided below for unaffiliated “Corporate and Other” primarily relates to investment income on Ambac's investment portfolio. Equity in net income of investees accounted for by the equity method relates to the Owner Trust Certificate received when Ambac deposited its Segregated Account junior surplus note into a Trust (see Note 1. Background and Business Description in the Notes to Consolidated Financial Statements included Part II, Item 8 in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014 for further information relating to the sale by Ambac of a junior surplus note issued to it by the Segregated Account). Inter-segment for "Corporate and Other" relates to amounts received by Ambac under the Mediation Agreement dated September 21, 2011 (as more fully described in Note 1. Background and Business Description in the Notes to Consolidated Financial Statements included Part II, Item 8 in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014), including accrual of interest on the junior surplus notes issued by the Segregated Account prior to Ambac's deposit into a Trust.
	The following table is a summary of financial information by reportable business segment for the affected periods:
			Financial			Financial			Corporate			Inter-segment			Consolidated
			Guarantee			Services			and Other			Eliminations
	Three Months Ended March 31, 2015:
	Revenues:
	Unaffiliated customers (1)		$	191,814		$	(37,708	)	$	357		$	—		$	154,463
	Equity in net income of investees accounted for by equity method		—			—			1,028			—			1,028
	Inter-segment		257			(230		)	(27		)	—			—
	Total revenues before expenses and reorganization items		192,071			(37,938		)	1,358			—			155,491
	Pre-tax income (loss) from continuing operations:
	Unaffiliated customers (1)(2)(3)		256,005			(38,580		)	(1,873		)	—			215,552
	Equity in net income of investees accounted for by equity method		—			—			1,028			—			1,028
	Inter-segment		(539		)	(312		)	851			—			—
	Pre-tax income (loss) from continuing operations		255,466			(38,892		)	6			—			216,580
	Total assets as of March 31, 2015		24,672,977			431,445			282,188			—			25,386,610
	Net investment income		71,470			128			1,385			—			72,983
	Insurance intangible amortization		37,432			—			—			—			37,432
	Interest expense		27,585			323			—			—			27,908
	Three Months Ended March 31, 2014:
	Revenues:
	Unaffiliated customers (1)		$	162,553		$	(53,438	)	$	23		$	—		$	109,138
	Equity in net income of investees accounted for by equity method		—			—			—			—			—
	Inter-segment		375			(75		)	8,635			(8,935		)	—
	Total revenues before expenses and reorganization items		162,928			(53,513		)	8,658			(8,935		)	109,138
	Pre-tax income (loss) from continuing operations:
	Unaffiliated customers (1) (2) (3)		217,158			(54,450		)	(3,410		)	—			159,298
	Equity in net income of investees accounted for by equity method		—			—			—			$	—		—
	Inter-segment		(9,157		)	(454		)	9,611			—			—
	Pre-tax income (loss) from continuing operations		208,001			(54,904		)	6,201			—			159,298
	Total assets as of March 31, 2014		26,535,119			534,256			44,873			—			27,114,248
	Net investment income		70,384			394			23			—			70,801
	Insurance intangible amortization		31,714			—			—			—			31,714
	Interest expense		31,881			447			—			—			32,328
	-1	Included in both revenues from unaffiliated customers and in pre-tax income (loss) from continuing operations from unaffiliated customers is net investment income.
	-2	Included in pre-tax income (loss) from continuing operations from unaffiliated customers is interest expense.
	-3	Included in pre-tax income (loss) from continuing operations from unaffiliated customers is amortization of intangible asset arising from financial guarantee contracts that were set to fair value upon adoption of Fresh Start on April 30, 2013.
	The following table summarizes gross premiums written, net premiums earned and the net change in fair value of credit derivatives included in the Financial Guarantee segment by location of risk for the affected periods:
			Three Months Ended March 31, 2015									Three Months Ended March 31, 2014
			Gross			Net			Net Change in			Gross			Net		Net Change in
			Premiums			Premiums			Fair Value of			Premiums			Premiums		Fair Value of
			Written			Earned			Credit			Written			Earned		Credit
									Derivatives								Derivatives
	United States		$	(2,366	)	$	52,739		$	3,958		$	(699	)	$	56,758	$	6,581
	United Kingdom		9,174			7,582			—			(6,166		)	20,635		—
	Other international		(5,746		)	5,397			(6,457		)	1,099			5,154		801
	Total		$	1,062		$	65,718		$	(2,499	)	$	(5,766	)	$	82,547	$	7,382

Basis_of_Presentation_and_Sign1

Basis of Presentation and Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies [Text Block]	BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES
	The Company has disclosed its significant accounting policies in Note 2. Significant Accounting Policies in the Notes to Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014. The following significant accounting policies provide an update to those included in the Company’s Annual Report on Form 10-K.
	Basis of Presentation
	The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles ("GAAP") for interim financial reporting and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and disclosures required by GAAP for annual periods. These statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Annual Report on Form 10-K for the year ended December 31, 2014. The accompanying consolidated financial statements have not been audited by an independent registered public accounting firm in accordance with the standards of the Public Company Accounting Oversight Board (U.S.), but in the opinion of management such financial statements include all adjustments, consisting only of normal recurring adjustments, necessary for the fair statement of the Company’s consolidated financial position and results of operations. All material intercompany balances and transactions have been eliminated. The results of operations for the three months ended March 31, 2015 may not be indicative of the results that may be expected for the year ending December 31, 2015. The December 31, 2014 consolidated balance sheet was derived from audited financial statements.
	The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. As additional information becomes available or actual amounts become determinable, the recorded estimates are revised and reflected in operating results.
	Reclassifications
	Certain reclassifications have been made to prior years' amounts to conform to the current year's presentation.
	Recently Adopted and Recently Issued Accounting Standards
	Adopted:
	Effective January 1, 2015, Ambac adopted ASU 2014-08, Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360) - Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity. The objective of this ASU is to limit discontinued operations reporting to disposals of components of an entity that represent strategic shifts that have (or will have) a major effect on an entity's operations and financial results. Under previous U.S. GAAP, many disposals, some of which may be routine in nature and not a change in an entity's strategy, were reported in discontinued operations. The ASU also requires certain expanded disclosures for discontinued operations and disclosure of the pre-tax profit or loss of an individually significant component of an entity that does not qualify for discontinued operations reporting. The adoption of this ASU did not have a material effect on Ambac's financial statements.
	Issued:
	In April 2015, the FASB issued ASU 2015-03, Interest - Imputation of Interest (Subtopic 835-30). This ASU simplifies the presentation of debt issuance costs by requiring that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by the amendments in this ASU. The ASU is effective for annual periods and interim periods within those annual periods beginning after December 15, 2015. Early adoption is also permitted for financial statements that have not been previously issued. Upon adoption, the ASU must be retrospectively applied to all prior periods presented. Ambac will adopt ASU 2015-02 on January 1, 2016. The adoption of this ASU is not expected to have a material impact on Ambac's financial statements.
	In May 2015, the FASB issued ASU 2015-07, Fair Value Measurement (Topic 820) - Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent). Reporting entities are permitted to use net asset value ("NAV") as a practical expedient to measure the fair value of certain investments. Under current U.S. GAAP, investments that use the NAV practical expedient to measure fair value are categorized within the fair value hierarchy as level 2 or level 3 investments depending on their redemption attributes, which has led to diversity in practice. This ASU will remove the requirement to categorize within the fair value hierarchy all investments that use the NAV practical expedient for fair value measurement purposes. Furthermore, the ASU will remove the requirement to make certain disclosures for all investments that are eligible to be measured at fair value using the NAV practical expedient. The ASU is effective for fiscal years beginning after December 15, 2015 and interim periods with those fiscal years. The ASU must be applied retrospectively to all prior periods presented. Ambac will adopt ASU 2015-07 on January 1, 2016. The adoption of this ASU is not expected to have a material impact on Ambac's financial statements.
	Basis of Presentation
	The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles ("GAAP") for interim financial reporting and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and disclosures required by GAAP for annual periods. These statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Annual Report on Form 10-K for the year ended December 31, 2014. The accompanying consolidated financial statements have not been audited by an independent registered public accounting firm in accordance with the standards of the Public Company Accounting Oversight Board (U.S.), but in the opinion of management such financial statements include all adjustments, consisting only of normal recurring adjustments, necessary for the fair statement of the Company’s consolidated financial position and results of operations. All material intercompany balances and transactions have been eliminated. The results of operations for the three months ended March 31, 2015 may not be indicative of the results that may be expected for the year ending December 31, 2015. The December 31, 2014 consolidated balance sheet was derived from audited financial statements.
	The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. As additional information becomes available or actual amounts become determinable, the recorded estimates are revised and reflected in operating results.
Reclassifications	Reclassifications
	Certain reclassifications have been made to prior years' amounts to conform to the current year's presentation.
New Accounting Pronouncements, Policy [Policy Text Block]	Recently Adopted and Recently Issued Accounting Standards
	Adopted:
	Effective January 1, 2015, Ambac adopted ASU 2014-08, Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360) - Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity. The objective of this ASU is to limit discontinued operations reporting to disposals of components of an entity that represent strategic shifts that have (or will have) a major effect on an entity's operations and financial results. Under previous U.S. GAAP, many disposals, some of which may be routine in nature and not a change in an entity's strategy, were reported in discontinued operations. The ASU also requires certain expanded disclosures for discontinued operations and disclosure of the pre-tax profit or loss of an individually significant component of an entity that does not qualify for discontinued operations reporting. The adoption of this ASU did not have a material effect on Ambac's financial statements.
	Issued:
	In April 2015, the FASB issued ASU 2015-03, Interest - Imputation of Interest (Subtopic 835-30). This ASU simplifies the presentation of debt issuance costs by requiring that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by the amendments in this ASU. The ASU is effective for annual periods and interim periods within those annual periods beginning after December 15, 2015. Early adoption is also permitted for financial statements that have not been previously issued. Upon adoption, the ASU must be retrospectively applied to all prior periods presented. Ambac will adopt ASU 2015-02 on January 1, 2016. The adoption of this ASU is not expected to have a material impact on Ambac's financial statements.
	In May 2015, the FASB issued ASU 2015-07, Fair Value Measurement (Topic 820) - Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent). Reporting entities are permitted to use net asset value ("NAV") as a practical expedient to measure the fair value of certain investments. Under current U.S. GAAP, investments that use the NAV practical expedient to measure fair value are categorized within the fair value hierarchy as level 2 or level 3 investments depending on their redemption attributes, which has led to diversity in practice. This ASU will remove the requirement to categorize within the fair value hierarchy all investments that use the NAV practical expedient for fair value measurement purposes. Furthermore, the ASU will remove the requirement to make certain disclosures for all investments that are eligible to be measured at fair value using the NAV practical expedient. The ASU is effective for fiscal years beginning after December 15, 2015 and interim periods with those fiscal years. The ASU must be applied retrospectively to all prior periods presented. Ambac will adopt ASU 2015-07 on January 1, 2016. The adoption of this ASU is not expected to have a material impact on Ambac's financial statements.

Special_Purpose_Entities_Inclu1

Special Purpose Entities, Including Variable Interest Entities (Tables)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Summary of Fair Value of Fixed Income Securities, by Asset-Type, Held by Consolidated Variable Interest Entities	The table below provides the fair value of fixed income securities, by asset-type, held by consolidated VIEs as of March 31, 2015 and December 31, 2014:
		March 31,		December 31,
		2015		2014
	Investments:
	Corporate obligations	$	2,704,657	$	2,743,050
	Total variable interest entity assets: fixed income securities	$	2,704,657	$	2,743,050
Supplemental Information about Loans Held as Assets and Long-Term Debt Associated with Consolidated Variable Interest Entities	The following table provides supplemental information about the loans held as assets and long-term debt associated with the VIEs for which the fair value option has been elected as of March 31, 2015 and December 31, 2014:
		Estimated fair value		Unpaid principal balance
	March 31, 2015
	Loans	$	12,789,201	$	9,675,140
	Long-term debt	13,341,902		11,299,861
	December 31, 2014
	Loans	12,371,177		10,236,695
	Long-term debt	$	12,882,076	$	11,925,499
Summary of Carrying Amount of Assets, Liabilities and Maximum Exposure to Loss of Ambac's Variable Interests in Non-Consolidated Variable Interest Entities	The following table displays the carrying amount of the assets, liabilities and maximum exposure to loss of Ambac’s variable interests in non-consolidated VIEs resulting from financial guarantee and derivative contracts by major underlying asset classes, as of March 31, 2015 and December 31, 2014:
		Carrying Value of Assets and Liabilities
		Maximum		Insurance		Insurance		Net Derivative
		Exposure		Assets (2)		Liabilities (3)		Assets (Liabilities)  (4)
		To Loss (1)
	March 31, 2015:
	Global structured finance:
	Collateralized debt obligations	$	1,297,393	$	303	$	3,889	$	(155,357	)
	Mortgage-backed—residential	18,837,405		1,037,566		2,879,199		—
	Other consumer asset-backed	4,460,126		55,219		671,303		(35,558		)
	Other commercial asset-backed	2,943,920		129,218		124,124		—
	Other	3,546,270		94,529		565,657		16,766
	Total global structured finance	31,085,114		1,316,835		4,244,172		(174,149		)
	Global public finance	30,674,652		438,852		513,664		(29,891		)
	Total	$	61,759,766	$	1,755,687	$	4,757,836	$	(204,040	)
	December 31, 2014:
	Global structured finance:
	Collateralized debt obligations	$	1,386,100	$	345	$	4,000	$	(145,565	)
	Mortgage-backed—residential	19,464,549		1,011,888		2,924,987		—
	Other consumer asset-backed	5,109,776		65,204		885,572		(36,877		)
	Other commercial asset-backed	3,119,891		135,215		128,988		—
	Other	3,801,382		97,345		599,915		18,176
	Total global structured finance	32,881,698		1,309,997		4,543,462		(164,266		)
	Global public finance	31,639,004		457,774		533,192		(22,135		)
	Total	$	64,520,702	$	1,767,771	$	5,076,654	$	(186,401	)
	-1	Maximum exposure to loss represents the maximum future payments of principal and interest on insured obligations and derivative contracts plus Deferred Amounts and accrued and unpaid interest thereon. 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 recorded in “Premium receivables” and “Subrogation recoverable” for financial guarantee contracts on Ambac’s Consolidated Balance Sheets.
	-3	Insurance liabilities represent the amount recorded in “Loss and loss expense reserves” and “Unearned premiums” for financial guarantee 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.

Comprehensive_Income_Tables

Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income	The following tables detail the changes in the balances of each component of accumulated other comprehensive income for the affected periods:
		Unrealized Gains				Amortization of				Gain (Loss) on			Total
		(Losses) on				Postretirement				Foreign Currency
		Available- for				Benefit (1)				Translation (1)
		Sale Securities (1)
	Three Months Ended March 31, 2015
	Beginning Balance	$	210,693			$	10,031			$	(441	)	$	220,283
	Other comprehensive income before reclassifications	33,554				—				(33,479		)	75
	Amounts reclassified from accumulated other comprehensive income	(51,002		)		(27		)		—			(51,029		)
	Net current period other comprehensive income (loss)	(17,448		)		(27		)		(33,479		)	(50,954		)
	Balance at March 31, 2015	$	193,245			$	10,004			$	(33,920	)	$	169,329
	Three Months Ended March 31, 2014
	Beginning Balance	$	(41,910	)		$	10,847			$	42,724		$	11,661
	Other comprehensive income before reclassifications	94,622				—				4,238			98,860
	Amounts reclassified from accumulated other comprehensive income	(5,900		)		(204		)		—			(6,104		)
	Net current period other comprehensive income (loss)	88,722				(204		)		4,238			92,756
	Balance at March 31, 2014	$	46,812			$	10,643			$	46,962		$	104,417
	(1)    All amounts are net of tax and noncontrolling interest. Amounts in parentheses indicate debits.
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:
			Amount Reclassified from Accumulated								Affected Line Item in the
			Other Comprehensive Income (1)
	Details about Accumulated Other		Three Months Ended March 31,								Consolidated Statement of
	Comprehensive Income Components		2015				2014				Total Comprehensive Income
	Unrealized Gains (Losses) on Available-for-Sale Securities
			$	(51,002	)		$	(5,900	)		Net realized investment gains
			—				—				Tax (expense) benefit
			$	(51,002	)		$	(5,900	)		Net of tax and noncontrolling interest (3)
	Amortization of Postretirement Benefit
	Prior service cost		$	(166	)		$	(166	)		Underwriting and operating expenses (2)
	Actuarial gains (losses)		139				(38		)		Underwriting and operating expenses (2)
			(27		)		(204		)		Total before tax
			—				—				Tax (expense) benefit
			$	(27	)		$	(204	)		Net of tax and noncontrolling interest (3)
	Total reclassifications for the period		$	(51,029	)		$	(6,104	)		Net of tax and noncontrolling interest (3)
	-1	Amounts in parentheses indicate debits to the Consolidated Statement of Comprehensive Income.
	-2	These accumulated other comprehensive income components are included in the computation of net periodic benefit cost.
	-3	Amount agrees with amount reported as reclassifications from AOCI in the disclosure about changes in AOCI balances.

Net_Income_Per_Share_Tables

Net Income Per Share (Tables)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Reconciliation of Common Shares Used for Basic and Diluted Earnings Per Share	The following table provides a reconciliation of the common shares used for basic net income per share to the diluted shares used for diluted net income per share:
		Three Months Ended March 31,
		2015	2014
	Weighted average number of common shares used for basic earnings per share	45,156,202	45,042,823
	Effect of potential dilutive shares:
	Warrants	1,751,798	1,998,028
	Stock options	12,841	4,891
	Restricted stock units	25,013	—
	Performance stock units	3,145	—
	Weighted average number of common shares and potential dilutive shares used for diluted earnings per share	46,948,999	47,045,742

Financial_Guarantee_Insurance_1

Financial Guarantee Insurance Contracts (Tables)	3 Months Ended
	Mar. 31, 2015
Insurance [Line Items]
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 March 31, 2015 and December 31, 2014:
		Unpaid Claims						Present Value of Expected
								Net Cash Flows
	Balance Sheet Line Item	Claims			Accrued			Claims and				Recoveries			Unearned			Gross Loss and
					Interest			Loss Expenses							Premium			Loss Expense
															Revenue			Reserves
	March 31, 2015:
	Loss and loss expense reserves	$	2,158,007		$	265,708		$	3,579,957			$	(1,268,916	)	$	(258,765	)	$	4,475,991
	Subrogation recoverable	774,960			103,429			175,415				(2,037,933		)	—			(984,129		)
	Totals	$	2,932,967		$	369,137		$	3,755,372			$	(3,306,849	)	$	(258,765	)	$	3,491,862
	December 31, 2014:
	Loss and loss expense reserves	$	2,172,041		$	234,802		$	3,792,133			$	(1,205,621	)	$	(241,348	)	$	4,752,007
	Subrogation recoverable	772,948			94,425			197,751				(2,018,398		)	—			(953,274		)
	Totals	$	2,944,989		$	329,227		$	3,989,884			$	(3,224,019	)	$	(241,348	)	$	3,798,733
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:
		Three Months Ended March 31,
		2015			2014
	Beginning premium receivable	$	1,000,607		$	1,453,021
	Premium receipts	(27,453		)	(33,128		)
	Adjustments for changes in expected and contractual cash flows	(5,918		)	(15,062		)
	Accretion of premium receivable discount	6,282			10,370
	Uncollectable premiums	698			(1,074		)
	Other adjustments (including foreign exchange)	(22,217		)	3,987
	Ending premium receivable	$	951,999		$	1,418,114
Effect of Reinsurance on Premiums Written and Earned	The effect of reinsurance on premiums written and earned was as follows:
		Three months ended March 31, 2015							Three months ended March 31, 2014
		Written			Earned				Written				Earned
	Direct	$	1,062		$	71,649			$	(5,766	)		$	86,183
	Assumed	—			22				—				68
	Ceded	365			5,953				456				3,704
	Net premiums	$	697		$	65,718			$	(6,222	)		$	82,547
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 March 31, 2015:
		Future premiums			Future
		to be collected (1)			premiums to
					be earned net of
					reinsurance (1)
	Three months ended:
	June 30, 2015	$	22,082		$	38,127
	September 30, 2015	22,103			35,798
	December 31, 2015	21,686			33,635
	Twelve months ended:
	December 31, 2016	83,054			123,206
	December 31, 2017	76,968			110,175
	December 31, 2018	72,261			101,113
	December 31, 2019	68,564			94,047
	Five years ended:
	December 31, 2024	304,049			385,547
	December 31, 2029	254,696			272,177
	December 31, 2034	179,393			169,638
	December 31, 2039	65,595			67,126
	December 31, 2044	25,189			23,328
	December 31, 2049	9,831			9,824
	December 31, 2054	1,244			2,183
	December 31, 2059	5			3
	Total	$	1,206,720		$	1,465,927
	-1	Future premiums to be collected is undiscounted and relates to the discounted premium receivable asset recorded on Ambac's balance sheet. Future premiums to be earned, net of reinsurance relate to the unearned premium 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 described in Note 2. Basis of Presentation and Significant Accounting Principles in the Notes to Consolidated Financial Statements included in Ambac's Annual Report on Form 10-K for the year ended December 31, 2014. 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 in the future. 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 results in higher 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.
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:
		Three Months Ended March 31,
		2015			2014
	Beginning gross loss and loss expense reserves	$	3,798,733		$	5,470,234
	Less reinsurance on loss and loss expense reserves	100,355			122,357
	Beginning balance of net loss and loss expense reserves	$	3,698,378		$	5,347,877
	Changes in the loss and loss expense reserves due to:
	Current year:
	Establishment of new loss and loss expense reserves, gross of RMBS subrogation and net of reinsurance	1			151
	Total current year	1			151
	Prior years:
	Change in previously established loss and loss expense reserves, gross of RMBS subrogation and net of reinsurance	(132,639		)	(117,692		)
	Claim and loss expense (payments) recoveries, net of subrogation and reinsurance	(104,202		)	(9,375		)
	(Increase) decrease in previously established RMBS subrogation recoveries, net of reinsurance	(44,195		)	(18,331		)
	Total prior years	(281,036		)	(145,398		)
	Net change in net loss and loss expense reserves	(281,035		)	(145,247		)
	Ending net loss and loss expense reserves	$	3,417,343		$	5,202,630
	Add reinsurance on loss and loss expense reserves (1)	74,519			111,303
	Ending gross loss and loss expense reserves	$	3,491,862		$	5,313,933
	-1	Reinsurance recoverable reported on the Balance Sheet also includes reinsurance recoverables of previously presented loss and loss expenses of $4,789 and $139 as of March 31, 2015 and 2014, respectively.
Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable	The tables below summarize information related to policies currently included in Ambac’s loss and loss expense reserves or subrogation recoverable at March 31, 2015 and December 31, 2014. Net par exposures include capital appreciation bonds which are reported at the par amount at the time of issuance of the insurance policy. The weighted average risk-free rate used to discount loss reserves at March 31, 2015 and December 31, 2014 was 2.1% and 2.3%, respectively.
	Surveillance Categories as of March 31, 2015
		I/SL			IA			II				III			IV			V			Total
	Number of policies	34			21			43				66			163			3			330
	Remaining weighted-average contract period (in years)	7			16			17				21			13			6			15
	Gross insured contractual payments outstanding:
	Principal	$	910,033		$	399,516		$	4,186,210			$	3,550,121		$	9,376,691		$	59,712		$	18,482,283
	Interest	339,721			159,138			8,484,779				2,286,780			1,928,647			19,651			13,218,716
	Total	$	1,249,754		$	558,654		$	12,670,989			$	5,836,901		$	11,305,338		$	79,363		$	31,700,999
	Gross undiscounted claim liability (1)	$	12,901		$	6,344		$	239,113			$	1,596,918		$	6,297,440		$	79,357		$	8,232,073
	Discount, gross claim liability	(644		)	(605		)	(18,502		)		(521,225		)	(712,562		)	(6,592		)	(1,260,130		)
	Gross claim liability before all subrogation and before reinsurance	$	12,257		$	5,739		$	220,611			$	1,075,693		$	5,584,878		$	72,765		$	6,971,943
	Less:
	Gross RMBS subrogation (2)	—			—			—				—			(2,579,450		)	—			(2,579,450		)
	Discount, RMBS subrogation	—			—			—				—			11,097			—			11,097
	Discounted RMBS subrogation, before reinsurance	—			—			—				—			(2,568,353		)	—			(2,568,353		)
	Less:
	Gross other subrogation (3)	—			—			(12,388		)		(142,548		)	(646,741		)	(13,356		)	(815,033		)
	Discount, other subrogation	—			—			3,474				35,608			33,795			3,660			76,537
	Discounted other subrogation, before reinsurance	—			—			(8,914		)		(106,940		)	(612,946		)	(9,696		)	(738,496		)
	Gross claim liability, net of all subrogation and discounts, before reinsurance	$	12,257		$	5,739		$	211,697			$	968,753		$	2,403,579		$	63,069		$	3,665,094
	Less: Unearned premium revenue	(8,812		)	(2,175		)	(107,836		)		(76,061		)	(63,368		)	(513		)	(258,765		)
	Plus: Loss expense reserves	—			16			2,185				7,465			75,825			42			85,533
	Gross loss and loss expense reserves	$	3,445		$	3,580		$	106,046			$	900,157		$	2,416,036		$	62,598		$	3,491,862
	Reinsurance recoverable reported on Balance Sheet (4)	$	1		$	910		$	2,331			$	85,082		$	(9,016	)	$	—		$	79,308
	-1	Gross undiscounted claim liability includes unpaid claims, including accrued interest on Deferred Amounts, on policies allocated to the Segregated Account and Ambac's estimate of expected future claims.
	-2	RMBS subrogation represents Ambac’s probability-weighted estimate of subrogation recoveries from RMBS transaction sponsors for representation and warranty ("R&W") breaches.
	-3	Other subrogation primarily represents subrogation related to excess spread or other contractual cash flows on public finance and structured finance transactions, including RMBS.
	-4	Reinsurance recoverable reported on Balance Sheet includes reinsurance recoverables of $74,519 related to future loss and loss expenses and $4,789 related to previously presented loss and loss expenses.
	Surveillance Categories as of December 31, 2014
		I/SL			IA			II				III			IV			V			Total
	Number of policies	36			26			33				69			160			1			325
	Remaining weighted-average contract period (in years)	8			12			15				21			12			6			16
	Gross insured contractual payments outstanding:
	Principal	$	1,026,513		$	519,291		$	3,091,744			$	3,792,559		$	9,892,760		$	47		$	18,322,914
	Interest	418,746			212,296			1,878,770				2,765,537			1,979,627			19			7,254,995
	Total	$	1,445,259		$	731,587		$	4,970,514			$	6,558,096		$	11,872,387		$	66		$	25,577,909
	Gross undiscounted claim liability (1)	$	16,360		$	11,525		$	155,488			$	2,040,402		$	6,456,139		$	60		$	8,679,974
	Discount, gross claim liability	(1,147		)	(937		)	(16,438		)		(716,812		)	(774,611		)	(3		)	(1,509,948		)
	Gross claim liability before all subrogation and before reinsurance	$	15,213		$	10,588		$	139,050			$	1,323,590		$	5,681,528		$	57		$	7,170,026
	Less:
	Gross RMBS subrogation (2)	—			—			—				—			(2,541,219		)	—			(2,541,219		)
	Discount, RMBS subrogation	—			—			—				—			17,679			—			17,679
	Discounted RMBS subrogation, before reinsurance	—			—			—				—			(2,523,540		)	—			(2,523,540		)
	Less:
	Gross other subrogation (3)	—			—			(18,034		)		(127,143		)	(647,110		)	—			(792,287		)
	Discount, other subrogation	—			—			6,069				36,779			48,960			—			91,808
	Discounted other subrogation, before reinsurance	—			—			(11,965		)		(90,364		)	(598,150		)	—			(700,479		)
	Gross claim liability, net of all subrogation and discounts, before reinsurance	$	15,213		$	10,588		$	127,085			$	1,233,226		$	2,559,838		$	57		$	3,946,007
	Less: Unearned premium revenue	(10,945		)	(3,432		)	(73,749		)		(88,332		)	(64,890		)	—			(241,348		)
	Plus: Loss expense reserves	3			1,303			1,968				6,470			84,330			—			94,074
	Gross loss and loss expense reserves	$	4,271		$	8,459		$	55,304			$	1,151,364		$	2,579,278		$	57		$	3,798,733
	Reinsurance recoverable reported on Balance Sheet (4)	$	73		$	890		$	1,355			$	110,957		$	(13,437	)	$	—		$	99,838
	-1	Gross undiscounted claim liability includes unpaid claims, including accrued interest on Deferred Amounts, on policies allocated to the Segregated Account and Ambac's estimate of expected future claims.
	-2	RMBS subrogation represents Ambac’s probability-weighted estimate of subrogation recoveries from RMBS transaction sponsors for representation and warranty ("R&W") breaches.
	-3	Other subrogation primarily represents subrogation related to excess spread or other contractual cash flows on public finance and structured finance transactions, including RMBS.
	-4	Reinsurance recoverable reported on Balance Sheet includes reinsurance recoverables of $100,355 related to future loss and loss expenses and $(517) related to previously presented loss and loss expenses.
Summary of Balance of Subrogation Recoveries and Related Claim Liabilities, by Estimation Approach	The balance of RMBS subrogation recoveries and the related claim liabilities, by estimation approach, at March 31, 2015 and December 31, 2014, are as follows:
	Approach	Gross loss			Subrogation			Gross loss
		reserves before			recoveries (2)(3)			reserves after
		subrogation						subrogation
		recoveries (1)						recoveries
	March 31, 2015:
	Random samples (4)	$	1,899,087		$	(2,568,353	)	$	(669,266	)
	December 31, 2014:
	Random samples (4)	$	1,897,426		$	(2,523,540	)	$	(626,114	)
	-1	Includes unpaid RMBS claims, including accrued interest on Deferred Amounts, on policies allocated to the Segregated Account.
	-2	The amount of recorded subrogation recoveries related to each securitization is limited to ever-to-date paid and unpaid losses plus the present value of expected cash flows for each policy. To the extent losses have been paid but not yet fully recovered, the recorded amount of RMBS subrogation recoveries may exceed the sum of the unpaid claims and the present value of expected cash flows for a given policy. The net cash inflow for these policies is recorded as a “Subrogation recoverable” asset. For those transactions where the subrogation recovery is less than the sum of unpaid claims and the present value of expected cash flows, the net cash outflow for these policies is recorded as a “Loss and loss expense reserves” liability.
	-3	The sponsor’s repurchase obligation may differ depending on the terms of the particular transaction and the status of the specific loan, such as whether it is performing or has been liquidated or charged off. The estimated subrogation recovery for these transactions is based primarily on loan level data provided through trustee reports received in the normal course of our surveillance activities or provided by the sponsor. While this data may not include all the components of the sponsor’s contractual repurchase obligation we believe it is the best information available to estimate the subrogation recovery.
	-4	From time to time R&W subrogation may include estimates of potential sponsor settlements that are currently in negotiation, but have not been subject to a sampling approach. However, such estimates are not material to Ambac’s financial results and therefore are included in the Random Sample section of this table.
Summary of Rollforward of RMBS Subrogation, by Estimation Approach	Below is the rollforward of RMBS subrogation, by estimation approach, for the affected periods:
		Random			Adverse			Total
		sample			sample
	Discounted RMBS subrogation (gross of reinsurance) at January 1, 2015	$	2,523,540		$	—		$	2,523,540
	Changes recognized in 2015:
	Changes in estimation approach	—			—			—
	Impact of sponsor actions (1)	—			—			—
	All other changes (2)	44,813			—			44,813
	Discounted RMBS subrogation (gross of reinsurance) at March 31, 2015	$	2,568,353		$	—		$	2,568,353
	Discounted RMBS subrogation (gross of reinsurance) at January 1, 2014	$	953,825		$	1,252,773		$	2,206,598
	Changes recognized in 2014:
	Changes in estimation approach	—			—			—
	Impact of sponsor actions (1)	—			—			—
	All other changes (2)	51,789			(34,092		)	17,697
	Discounted RMBS subrogation (gross of reinsurance) at March 31, 2014	$	1,005,614		$	1,218,681		$	2,224,295
	-1	Sponsor actions include loan repurchases, direct payments to Ambac and other contributions.
	-2	All other changes which may impact RMBS subrogation recoveries include changes in actual or projected collateral performance, changes in the creditworthiness of a sponsor, and/or the projected timing of recoveries. All other changes may also include estimates of potential sponsor settlements that are currently in negotiation but have not been subject to a sampling approach. However, such estimates are not material to Ambac’s financial results and therefore are included in the Random Sample column of 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:
			2015			2016			2017				2018			2019			Thereafter
	Amortization expense		$	90,801		$	107,443		$	97,726			$	90,095		$	83,380		$	877,850

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
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 March 31, 2015 and December 31, 2014, 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:
		Amount				Value				Level 1				Level 2				Level 3
	March 31, 2015:
	Financial assets:
	Fixed income securities:
	Municipal obligations	$	525,188			$	525,188			$	—			$	525,188			$	—
	Corporate obligations	1,609,769				1,609,769				—				1,609,769				—
	Foreign obligations	125,164				125,164				—				125,164				—
	U.S. government obligations	30,297				30,297				30,297				—				—
	U.S. agency obligations	4,427				4,427				—				4,427				—
	Residential mortgage-backed securities	1,846,477				1,846,477				—				1,583,745				262,732
	Collateralized debt obligations	88,238				88,238				—				88,238				—
	Other asset-backed securities	636,190				636,190				—				636,190				—
	Fixed income securities, pledged as collateral:
	U.S. government obligations	64,813				64,813				64,813				—				—
	Short term investments	220,980				220,980				215,207				5,773				—
	Other investments	332,609				328,187				—				310,578				17,609
	Cash and cash equivalents	26,641				26,641				26,641				—				—
	Loans	5,494				5,476				—				—				5,476
	Derivative assets:
	Credit derivatives	—				—				—				—				—
	Interest rate swaps—asset position	113,622				113,622				—				113,622				—
	Interest rate swaps—liability position	—				—				—				—				—
	Other assets	10,036				10,036				—				—				10,036
	Variable interest entity assets:
	Fixed income securities:
	Corporate obligations	2,704,657				2,704,657				—				—				2,704,657
	Restricted cash	6,219				6,219				6,219				—				—
	Loans	12,789,201				12,789,201				—				—				12,789,201
	Total financial assets	$	21,140,022			$	21,135,582			$	343,177			$	5,002,694			$	15,789,711
	Financial liabilities:
	Obligations under investment agreements	$	111,967			$	114,438			$	—			$	—			$	114,438
	Long term debt, including accrued interest	1,301,390				1,381,938				—				—				1,381,938
	Derivative liabilities:
	Credit derivatives	76,377				76,377				—				—				76,377
	Interest rate swaps—asset position	(68,481		)		(68,481		)		—				(68,481		)		—
	Interest rate swaps—liability position	438,518				438,518				—				284,694				153,824
	Futures contracts	942				942				942				—				—
	Liabilities for net financial guarantees written (1)	2,662,701				4,152,094				—				—				4,152,094
	Variable interest entity liabilities:
	Long-term debt	13,341,902				13,341,902				—				11,309,803				2,032,099
	Derivative liabilities:
	Interest rate swaps—liability position	2,081,082				2,081,082				—				2,081,082				—
	Currency swaps—liability position	44,631				44,631				—				44,631				—
	Total financial liabilities	$	19,991,029			$	21,563,441			$	942			$	13,651,729			$	7,910,770
	-1	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.
		Carrying				Total Fair				Fair Value Measurements Categorized as:
		Amount				Value				Level 1				Level 2				Level 3
	December 31, 2014:
	Financial assets:
	Fixed income securities:
	Municipal obligations	$	525,792			$	525,792			$	—			$	525,792			$	—
	Corporate obligations	1,385,594				1,385,594				—				1,381,786				3,808
	Foreign obligations	127,757				127,757				—				127,757				—
	U.S. government obligations	42,979				42,979				42,979				—				—
	U.S. agency obligations	29,486				29,486				—				29,486				—
	Residential mortgage-backed securities	1,710,955				1,710,955				—				1,516,562				194,393
	Collateralized debt obligations	21,122				21,122				—				21,122				—
	Other asset-backed securities	882,001				882,001				—				882,001				—
	Fixed income securities, pledged as collateral:
	U.S. government obligations	64,267				64,267				64,267				—				—
	Short term investments	360,065				360,065				358,190				1,875				—
	Other investments	357,016				349,468				—				336,013				13,455
Cash and cash equivalents	73,903				73,903				73,903				—				—
Loans	5,714				5,634				—				—				5,634
Derivative assets:
Credit derivatives	2,043				2,043				—				—				2,043
Interest rate swaps—asset position	106,974				106,974				—				106,974				—
Interest rate swaps—liability position	—				—				—				—				—
Futures contracts	—				—				—				—				—
Other assets	12,036				12,036				—				—				12,036
Variable interest entity assets:
Fixed income securities:
Corporate obligations	2,743,050				2,743,050				—				—				2,743,050
Restricted cash	7,708				7,708				7,708				—				—
Loans	12,371,177				12,371,177				—				—				12,371,177
Total financial assets	$	20,829,639			$	20,822,011			$	547,047			$	4,929,368			$	15,345,596
Financial liabilities:
Obligations under investment agreements	$	160,079			$	161,821			$	—			$	—			$	161,821
Long term debt, including accrued interest	1,273,805				1,379,864				—				—				1,379,864
Derivative liabilities:
Credit derivatives	75,502				75,502				—				—				75,502
Interest rate swaps—asset position	(54,666		)		(54,666		)		—				(54,666		)		—
Interest rate swaps—liability position	385,546				385,546				—				243,659				141,887
Futures contracts	562				562				562				—				—
Other contracts	—				—				—				—				—
Liabilities for net financial guarantees written (1)	2,923,652				4,539,000				—				—				4,539,000
Variable interest entity liabilities:
Long-term debt	12,882,076				12,882,076				—				11,618,412				1,263,664
Derivative liabilities:
Interest rate swaps—liability position	2,133,268				2,133,268				—				2,133,268				—
Currency swaps—liability position	66,895				66,895				—				66,895				—
Total financial liabilities	$	19,846,719			$	21,569,868			$	562			$	14,007,568			$	7,561,738
-1	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.
Information about Valuation Inputs for Variable Interest Entity Assets and Liabilities Classified as Level 3	Information about the above described model inputs used to determine the fair value of each class of credit derivatives, including the CVA as a percentage of the gross mark-to-market liability before considering Ambac credit risk (“CVA percentage”), as of March 31, 2015 and December 31, 2014 is summarized below:
		CLOs				Other (1)
	March 31, 2015:
	Notional outstanding	$	466,453			$	1,069,317
	Weighted average reference obligation price	99.1				86.8
	Weighted average life (WAL) in years	1.5				5.8
	Weighted average credit rating	AA				BBB
	Weighted average relative change ratio	36.2		%		44.8		%
	CVA percentage	5.21		%		19.34		%
	Fair value of derivative liabilities	$	1,533			$	74,794
	December 31, 2014:
	Notional outstanding	$	549,923			$	921,036
	Weighted average reference obligation price	98.9				86.8
	Weighted average life (WAL) in years	1.8				5.7
	Weighted average credit rating	AA				BBB-
	Weighted average relative change ratio	35.9		%		49		%
	CVA percentage	5.4		%		15.82		%
	Fair value of derivative liabilities	$	2,027			$	71,104
	-1	Excludes contracts for which fair values are based on credit derivative quotes rather than reference obligation quotes. Such contracts have a combined notional outstanding of $58,801, WAL of 0.9 years and liability fair value of $50 as of March 31, 2015. Other inputs to the valuation of these transactions at March 31, 2015 include weighted average quotes of less than 1% of notional, weighted average rating of A and Ambac CVA percentage of 2.02% . As of December 31, 2014, these contracts had a combined notional outstanding of $58,800, WAL of 1.2 years and liability fair value of $328. Other inputs to the valuation of these transactions at December 31, 2014 include weighted average quotes of 1% of notional, weighted average rating of A and Ambac CVA percentage of 2.21% .
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 2015 and 2014. Ambac classifies financial instruments in Level 3 of the fair value hierarchy when there is reliance on at least one significant unobservable input to the valuation model. In addition to these unobservable inputs, the valuation models for Level 3 financial instruments typically also rely on a number of inputs that are readily observable either directly or indirectly. Thus, the gains and losses presented below include changes in the fair value related to both observable and unobservable inputs.
	Level 3 - Financial Assets and Liabilities Accounted for at Fair Value
															VIE Assets and Liabilities
			Investments				Other				Derivatives				Investments				Loans			Long-term			Total
							assets															debt
	Three Months Ended March 31, 2015:
	Balance, beginning of period		$	198,201			$	12,036			$	(215,346	)		$	2,743,050			$	12,371,177		$	(1,263,664	)	$	13,845,454
	Total gains/(losses) realized and unrealized:
	Included in earnings		5,729				(295		)		(13,921		)		92,120				1,110,927			(839,998		)	354,562
	Included in other comprehensive income		(5,706		)		—				—				(130,513		)		(562,621		)	67,625			(631,215		)
	Purchases		84,504				—				—				—				—			—			84,504
	Issuances		—				—				—				—				—			—			—
	Sales		—				—				—				—				—			—			—
	Settlements		(19,996		)		(1,705		)		(934		)		—				(130,282		)	3,938			(148,979		)
	Transfers into Level 3		—				—				—				—				—			—			—
	Transfers out of Level 3		—				—				—				—				—			—			—
	Balance, end of period		$	262,732			$	10,036			$	(230,201	)		$	2,704,657			$	12,789,201		$	(2,032,099	)	$	13,504,326
	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		$	—			$	(295	)		$	(14,364	)		$	92,120			$	1,110,927		$	(839,998	)	$	348,390
	Three Months Ended March 31, 2014:
	Balance, beginning of period		$	67,783			$	13,384			$	(186,934	)		$	2,475,182			$	13,398,895		$	(1,514,605	)	$	14,253,705
	Total gains/(losses) realized and unrealized:
	Included in earnings		419				(262		)		(14,249		)		55,745				321,847			(190,962		)	172,538
	Included in other comprehensive income		(217		)		—				—				15,835				79,802			(8,621		)	86,799
	Purchases		—				—				—				—				70,000			—			70,000
	Issuances		—				—				—				—				—			—			—
	Sales		—				—				—				—				—			—			—
	Settlements		(854		)		—				(1,299		)		—				(601,092		)	429,794			(173,451		)
	Transfers into Level 3		—				—				—				—				—			—			—
	Transfers out of Level 3		(208		)		—				—				—				—			—			(208		)
	Balance, end of period		$	66,923			$	13,122			$	(202,482	)		$	2,546,762			$	13,269,452		$	(1,284,394	)	$	14,409,383
	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		$	—			$	(262	)		$	(15,024	)		$	55,745			$	316,714		$	(187,824	)	$	169,349
	The tables below provide roll-forward information by class of investments and derivatives measured using significant unobservable inputs.
	Level 3 - Investments by Class:
			Collateralized				Other Asset				Corporate				U.S. Agency				Non-Agency			Total
			Debt				Backed				Obligations				Obligations				RMBS			Investments
			Obligations				Securities
	Three Months Ended March 31, 2015:
	Balance, beginning of period		$	—			$	—			$	3,808			$	—			$	194,393		$	198,201
	Total gains/(losses) realized and unrealized:
	Included in earnings		—				—				(19		)		—				5,748			5,729
	Included in other comprehensive income		—				—				(286		)		—				(5,420		)	(5,706		)
	Purchases		—				—				—				—				84,504			84,504
	Issuances		—				—				—				—				—			—
	Sales		—				—				—				—				—			—
	Settlements		—				—				(3,503		)		—				(16,493		)	(19,996		)
	Transfers into Level 3		—				—				—				—				—			—
	Transfers out of Level 3		—				—				—				—				—			—
	Balance, end of period		$	—			$	—			$	—			$	—			$	262,732		$	262,732
	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		$	—			$	—			$	—			$	—			$	—		$	—
	Three Months Ended March 31, 2014:
	Balance, beginning of period		$	—			$	64,073			$	3,502			$	208			$	—		$	67,783
	Total gains/(losses) realized and unrealized:
	Included in earnings		—				443				(24		)		—				—			419
	Included in other comprehensive income		—				(295		)		78				—				—			(217		)
	Purchases		—				—				—				—				—			—
	Issuances		—				—				—				—				—			—
	Sales		—				—				—				—				—			—
	Settlements		—				(854		)		—				—				—			(854		)
	Transfers into Level 3		—				—				—				—				—			—
	Transfers out of Level 3		$	—			$	—			$	—			$	(208	)		$	—		$	(208	)
	Balance, end of period		$	—			$	63,367			$	3,556			$	—			$	—		$	66,923
	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:
			Interest				Credit				Total
Rate Swaps			Derivatives				Derivatives
Three Months Ended March 31, 2015:
Balance, beginning of period		$	(141,887	)		$	(73,459	)		$	(215,346	)
Total gains/(losses) realized and unrealized:
Included in earnings		(11,422		)		(2,499		)		(13,921		)
Included in other comprehensive income		—				—				—
Purchases		—				—				—
Issuances		—				—				—
Sales		—				—				—
Settlements		(515		)		(419		)		(934		)
Transfers into Level 3		—				—				—
Transfers out of Level 3		—				—				—
Balance, end of period		$	(153,824	)		$	(76,377	)		$	(230,201	)
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		$	(11,422	)		$	(2,942	)		$	(14,364	)
Three Months Ended March 31, 2014:
Balance, beginning of period		$	(92,612	)		$	(94,322	)		$	(186,934	)
Total gains/(losses) realized and unrealized:
Included in earnings		(21,631		)		7,382				(14,249		)
Included in other comprehensive income		—				—				—
Purchases		—				—				—
Issuances		—				—				—
Sales		—				—				—
Settlements		(524		)		(775		)		(1,299		)
Transfers into Level 3		—				—				—
Transfers out of Level 3		—				—				—
Balance, end of period		$	(114,767	)		$	(87,715	)		$	(202,482	)
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		$	(21,631	)		$	6,607			$	(15,024	)
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				Realized				Unrealized				Derivative				Income			Other
			investment				gains or				gains or				products				(loss) on			income
			income				(losses) and				(losses) on				revenues				variable			or (loss)
							other				credit				(interest rate				interest
							settlements				derivative				swaps)				entities
							on credit				contracts
							derivative
							contracts
	Three Months Ended March 31, 2015:
	Total gains or losses included in earnings for the period		$	5,729			$	419			$	(2,918	)		$	(11,422	)		$	363,049		$	(295	)
	Changes in unrealized gains or losses relating to the assets and liabilities still held at the reporting date		—				—				(2,942		)		(11,422		)		363,049			(295		)
	Three Months Ended March 31, 2014:
	Total gains or losses included in earnings for the period		$	419			$	775			$	6,607			$	(21,631	)		$	186,630		$	(262	)
	Changes in unrealized gains or losses relating to the assets and liabilities still held at the reporting date		—				—				6,607				(21,631		)		184,635			(262		)

Investments_Tables

Investments (Tables)	3 Months Ended
	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments	The amortized cost and estimated fair value of available-for-sale investments, excluding VIE investments, at March 31, 2015 and December 31, 2014 were as follows:
			Amortized			Gross			Gross		Estimated		Non-credit  other-
			Cost			Unrealized			Unrealized		Fair Value		than-temporary
						Gains			Losses				Impairments (1)
	March 31, 2015
	Fixed income securities:
	Municipal obligations		$	517,256		$	12,136		$	4,204	$	525,188	$	—
	Corporate obligations		1,588,962			24,097			3,290		1,609,769		—
	Foreign obligations		123,601			4,038			2,475		125,164		—
	U.S. government obligations		28,983			1,418			104		30,297		—
	U.S. agency obligations		4,438			—			11		4,427		—
	Residential mortgage-backed securities		1,705,246			159,388			18,157		1,846,477		9,844
	Collateralized debt obligations		88,569			102			433		88,238		—
	Other asset-backed securities		615,831			21,048			689		636,190		—
			4,672,886			222,227			29,363		4,865,750		9,844
	Short-term		220,980			—			—		220,980		—
			4,893,866			222,227			29,363		5,086,730		9,844
	Fixed income securities pledged as collateral:
	U.S. government obligations		64,432			381			—		64,813		—
	Total collateralized investments		64,432			381			—		64,813		—
	Total available-for-sale investments		$	4,958,298		$	222,608		$	29,363	$	5,151,543	$	9,844
	December 31, 2014
	Fixed income securities:
	Municipal obligations		$	523,019		$	9,769		$	6,996	$	525,792	$	—
	Corporate obligations		1,382,195			12,815			9,416		1,385,594		—
	Foreign obligations		126,041			3,060			1,344		127,757		—
	U.S. government obligations		42,328			1,078			427		42,979		—
	U.S. agency obligations		29,524			—			38		29,486		—
	Residential mortgage-backed securities		1,557,059			167,396			13,500		1,710,955		7,773
	Collateralized debt obligations		21,346			50			274		21,122		—
	Other asset-backed securities		833,366			48,794			159		882,001		—
			4,514,878			242,962			32,154		4,725,686		7,773
	Short-term		360,069			—			4		360,065		—
			4,874,947			242,962			32,158		5,085,751		7,773
	Fixed income securities pledged as collateral:
	U.S. government obligations		64,378			—			111		64,267		—
	Total collateralized investments		64,378			—			111		64,267		—
	Total available-for-sale investments		$	4,939,325		$	242,962		$	32,269	$	5,150,018	$	7,773
	-1	Represents the amount of non-credit other-than-temporary impairment losses remaining in accumulated other comprehensive loss on securities that also had a credit impairment. These losses are included in gross unrealized losses as of March 31, 2015 and December 31, 2014.
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 March 31, 2015, by contractual maturity, were as follows:
			Amortized			Estimated
			Cost			Fair Value
	Due in one year or less		$	413,150		$	413,291
	Due after one year through five years		927,630			935,442
	Due after five years through ten years		994,286			1,013,939
	Due after ten years		213,586			217,966
			2,548,652			2,580,638
	Residential mortgage-backed securities		1,705,246			1,846,477
	Collateralized debt obligations		88,569			88,238
	Other asset-backed securities		615,831			636,190
	Total		$	4,958,298		$	5,151,543
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, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position, at March 31, 2015 and December 31, 2014:
			Less Than 12 Months						12 Months or More				Total
			Fair Value			Gross			Fair Value		Gross		Fair Value		Gross
						Unrealized					Unrealized				Unrealized
						Loss					Loss				Loss
	March 31, 2015
	Fixed income securities:
	Municipal obligations		$	46,461		$	412		$	119,412	$	3,792	$	165,873	$	4,204
	Corporate obligations		278,044			2,081			81,739		1,209		359,783		3,290
	Foreign government obligations		32,206			1,864			8,900		611		41,106		2,475
	U.S. government obligations		1,661			2			10,814		102		12,475		104
	U.S. agency obligations		—			—			4,359		11		4,359		11
	Residential mortgage-backed securities		547,706			17,336			10,266		821		557,972		18,157
	Collateralized debt obligations		63,834			289			4,434		144		68,268		433
	Other asset-backed securities		163,243			687			68		2		163,311		689
			1,133,155			22,671			239,992		6,692		1,373,147		29,363
	Short-term		—			—			—		—		—		—
			1,133,155			22,671			239,992		6,692		1,373,147		29,363
	Fixed income securities, pledged as collateral:
	U. S. government obligations		—			—			—		—		—		—
	Total collateralized investments		—			—			—		—		—		—
	Total temporarily impaired securities		$	1,133,155		$	22,671		$	239,992	$	6,692	$	1,373,147	$	29,363
			Less Than 12 Months						12 Months or More				Total
			Fair Value			Gross			Fair Value		Gross		Fair Value		Gross
						Unrealized					Unrealized				Unrealized
						Loss					Loss				Loss
	December 31, 2014:
	Fixed income securities:
	Municipal obligations		$	77,788		$	1,244		$	135,076	$	5,752	$	212,864	$	6,996
	Corporate obligations		453,504			4,998			172,045		4,418		625,549		9,416
	Foreign government obligations		20,827			748			14,277		596		35,104		1,344
	U.S. government obligations		7,223			154			14,735		273		21,958		427
	U.S. agency obligations		25,039			2			4,378		36		29,417		38
	Residential mortgage-backed securities		413,203			12,391			10,076		1,109		423,279		13,500
	Collateralized debt obligations		5,012			274			—		—		5,012		274
	Other asset-backed securities		248,823			155			68		4		248,891		159
			1,251,419			19,966			350,655		12,188		1,602,074		32,154
	Short-term		8,803			4			—		—		8,803		4
			1,260,222			19,970			350,655		12,188		1,610,877		32,158
	Fixed income securities, pledged as collateral:
	U. S. government obligations		64,267			111			—		—		64,267		111
	Total collateralized investments		64,267			111			—		—		64,267		111
	Total temporarily impaired securities		$	1,324,489		$	20,081		$	350,655	$	12,188	$	1,675,144	$	32,269
Summary of Amounts Included in Net Realized (Losses) Gains and Other-Than-Temporary Impairments	The following table details amounts included in net realized gains and other-than-temporary impairments included in earnings for the affected periods:
			Three Months Ended March 31,
			2015			2014
	Gross realized gains on securities		$	50,654		$	19,576
	Gross realized losses on securities		(3,737		)	(1,128		)
	Foreign exchange gains (losses)		7,184			(2,159		)
	Net realized gains		$	54,101		$	16,289
	Net other-than-temporary impairments (1)		$	(3,119	)	$	(10,392	)
	-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 Ambac will be required to sell before recovery of the amortized cost basis.
Summary of Roll-Forward of Ambac's Cumulative Credit Losses on Debt Securities for Which Portion of Other-than-Temporary Impairment was Recognized in Other Comprehensive Income	The following table presents a roll-forward of Ambac’s cumulative credit losses on debt securities held as of March 31, 2015 and 2014 for which a portion of an other-than-temporary impairment was recognized in other comprehensive income:
			Credit
			Impairment
	Balance at January 1, 2015		$	14,062
	Additions for credit impairments recognized on:
	Securities not previously impaired		1,660
	Securities previously impaired		1,457
	Reductions for credit impairments previously recognized on:
	Securities that matured or were sold during the period		—
	Balance at March 31, 2015		$	17,179
	Balance at January 1, 2014		$	1,182
	Additions for credit impairments recognized on:
	Securities not previously impaired		4,767
	Securities previously impaired		—
	Reductions for credit impairments previously recognized on:
	Securities that matured or were sold during the period		—
	Balance at March 31, 2014		$	5,949
Summary of Sources of Collateral Received and Various Investment Agreement in which Collateral Pledged	The following table presents (i) the sources of collateral either received from various counterparties where Ambac is permitted to sell or re-pledge the collateral or collateral held directly in the investment portfolio and (ii) how that collateral was pledged to various investment agreement, derivative and repurchase agreement counterparties at March 31, 2015 and December 31, 2014:
			Fair Value of Cash			Fair Value of Cash			Fair Value of Cash
			and Underlying			and Securities			and Securities
			Securities			Pledged to			Pledged to
						Investment			Derivative
						Agreement			Counterparties
						Counterparties
	March 31, 2015:
	Sources of Collateral:
	Cash and securities pledged directly from the investment portfolio		$	368,979		$	108,469		$	260,510
	December 31, 2014:
	Sources of Collateral:
	Cash and securities pledged directly from the investment portfolio		$	379,423		$	156,916		$	222,507
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 March 31, 2015 and December 31, 2014, respectively:
			Municipal			Corporate			Mortgage		Total		Weighted
			obligations			obligations			and asset-				Average
									backed				Underlying
									securities				Rating (1)
	March 31, 2015:
	Ambac Assurance Corporation (2)		$	54,124		$	—		$	2,078,084	$	2,132,208	CCC-
	Assured Guaranty Municipal Corporation		121,519			—			—		121,519		A
	National Public Finance Guarantee Corporation		64,693			—			—		64,693		A-
	MBIA Insurance Corporation		—			32,265			—		32,265		A+
	Total		$	240,336		$	32,265		$	2,078,084	$	2,350,685	CCC
	December 31, 2014:
	Ambac Assurance Corporation (2)		$	53,164		$	—		$	2,146,555	$	2,199,719	CCC-
	Assured Guaranty Municipal Corporation		119,492			—			—		119,492		A
	National Public Finance Guarantee Corporation		67,895			—			—		67,895		A-
	MBIA Insurance Corporation		—			32,460			—		32,460		A+
	Total		$	240,551		$	32,460		$	2,146,555	$	2,419,566	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 $51,395 at March 31, 2015 and December 31, 2014, insured by Ambac UK.
Summary of Net Investment Income	Net investment income was comprised of the following for the affected periods:
			Three Months Ended March 31,
			2015			2014
	Fixed income securities		$	65,585		$	71,231
	Short-term investments		42			57
	Loans		132			117
	Investment expense		(2,427		)	(2,598		)
	Securities available-for-sale and short-term		63,332			68,807
	Other investments		9,651			1,994
	Total net investment income		$	72,983		$	70,801
	Net investment income from Other investments primarily represents changes in fair value on securities classified as trading or under the fair value option. The portion of net unrealized gains related to such securities still held at the end of each period is as follows:
			Three Months Ended March 31,
			2015			2014
	Net gains recognized during the period on trading securities		$	7,819		$	1,994
	Less: net gains (losses) recognized during the reporting period on trading securities sold during the period		1,564			(455		)
	Unrealized gains recognized during the reporting period on trading securities still held at the reporting date		$	6,255		$	2,449

Derivative_Instruments_Tables

Derivative Instruments (Tables)	3 Months Ended
	Mar. 31, 2015
Summary of Gross Fair Values of Individual Derivative Instruments	The following tables summarize the gross fair values of individual derivative instruments and the impact of legal rights of offset as reported in the Consolidated Balance Sheets as of March 31, 2015 and December 31, 2014:
		Gross				Gross				Net Amounts		Gross		Net Amount
		Amounts of				Amounts				of Assets/		Amount of
		Recognized				Offset in the				Liabilities		Collateral
		Assets /				Consolidated				Presented		Received /
		Liabilities				Balance Sheet				in the		Pledged Not
										Consolidated		Offset in the
										Balance Sheet		Consolidated
												Balance Sheet
	March 31, 2015:
	Derivative Assets:
	Credit derivatives	$	—			$	—			$	—	$	—	$	—
	Interest rate swaps	182,103				68,481				113,622		—		113,622
	Total non-VIE derivative assets	$	182,103			$	68,481			$	113,622	$	—	$	113,622
	Derivative Liabilities:
	Credit derivatives	$	76,377			$	—			$	76,377	$	—	$	76,377
	Interest rate swaps	438,518				68,481				370,037		196,039		173,998
	Futures contracts	942				—				942		942		—
	Total non-VIE derivative liabilities	$	515,837			$	68,481			$	447,356	$	196,981	$	250,375
	Variable Interest Entities:
	Interest rate swaps	$	2,081,082			$	—			$	2,081,082	$	—	$	2,081,082
	Currency swaps	44,631				—				44,631		—		44,631
	Total VIE derivative liabilities	$	2,125,713			$	—			$	2,125,713	$	—	$	2,125,713
	December 31, 2014:
	Derivative Assets:
	Credit derivatives	$	2,043			$	—			$	2,043	$	—	$	2,043
	Interest rate swaps	161,640				54,666				106,974		—		106,974
	Total non-VIE derivative assets	$	163,683			$	54,666			$	109,017	$	—	$	109,017
	Derivative Liabilities:
	Credit derivatives	$	75,502			$	—			$	75,502	$	—	$	75,502
	Interest rate swaps	385,546				54,666				330,880		169,573		161,307
	Futures contracts	562				—				562		562		—
	Total non-VIE derivative liabilities	$	461,610			$	54,666			$	406,944	$	170,135	$	236,809
	Variable Interest Entities:
	Interest rate swaps	$	2,133,268			$	—			$	2,133,268	$	—	$	2,133,268
	Currency swaps	66,895				—				66,895		—		66,895
	Total VIE derivative liabilities	$	2,200,163			$	—			$	2,200,163	$	—	$	2,200,163
Summary of Location and Amount of Gains and Losses of Derivative Contracts	There were no amounts held representing an obligation to return cash collateral as of March 31, 2015 and December 31, 2014.
	The following tables summarize the location and amount of gains and losses of derivative contracts in the Consolidated Statements of Total Comprehensive Income for the three months ended March 31, 2015 and 2014:
		Location of Gain or (Loss) Recognized in		Amount of Gain or (Loss) Recognized in Consolidated Statement of Total Comprehensive Income
		Consolidated Statements of Total Comprehensive Income		Three Months Ended March 31,
				2015				2014
	Financial Guarantee:
	Credit derivatives	Net change in fair value of credit derivatives		$	(2,499	)		$	7,382
	Financial Services derivatives products:
	Interest rate swaps	Derivative products		(35,547		)		(51,849		)
	Futures contracts	Derivative products		(2,227		)		(1,992		)
	Total Financial Services derivative products			(37,774		)		(53,841		)
	Variable Interest Entities:
	Currency swaps	Income (loss) on variable interest entities		22,264				5,408
	Interest rate swaps	Income (loss) on variable interest entities		52,186				(77,792		)
	Total Variable Interest Entities			74,450				(72,384		)
	Total derivative contracts			$	34,177			$	(118,843	)
Summary of Gross Principal Notional Outstanding for CDS Contracts	The following tables summarize the gross principal notional outstanding for CDS contracts, by Ambac rating, for each major category as of March 31, 2015 and December 31, 2014:
		CLO				Other				Total
	Ambac Rating - March 31, 2015:
	AAA	$	—			$	—			$	—
	AA	466,453				303,860				770,313
	A	—				43,160				43,160
	BBB (1)	—				515,578				515,578
	Below investment grade (2)	—				265,520				265,520
	Total	$	466,453			$	1,128,118			$	1,594,571
	Ambac Rating - December 31, 2014:
	AAA	$	—			$	—			$	—
	AA	549,923				217,680				767,603
	A	—				43,160				43,160
	BBB  (1)	—				448,249				448,249
	Below investment grade (2)	—				270,747				270,747
	Total	$	549,923			$	979,836			$	1,529,759
	-1	BBB internal ratings reflect bonds which are of medium grade credit quality with adequate capacity to pay interest and repay principal. Certain protective elements and margins may weaken under adverse economic conditions and changing circumstances. These bonds are more likely than higher rated bonds to exhibit unreliable protection levels over all cycles.
	-2	Below investment grade internal ratings reflect bonds which are of speculative grade credit quality with the adequacy of future margin levels for payment of interest and repayment of principal potentially adversely affected by major ongoing uncertainties or exposure to adverse conditions.
Summarize Information by Major Category of CDS Contracts	The tables below summarize information by major category as of March 31, 2015 and December 31, 2014:
		CLO				Other				Total
	March 31, 2015:
	Number of CDS transactions	5				10				15
	Remaining expected weighted-average life of obligations (in years)	1.5				5.6				4.4
	Gross principal notional outstanding	$	466,453			$	1,128,118			$	1,594,571
	Net derivative liabilities at fair value	$	1,533			$	74,844			$	76,377
	December 31, 2014:
	Number of CDS transactions	6				10				16
	Remaining expected weighted-average life of obligations (in years)	1.8				5.4				4.1
	Gross principal notional outstanding	$	549,923			$	979,836			$	1,529,759
	Net derivative liabilities at fair value	$	2,027			$	71,432			$	73,459
Summary of Notional Amounts of AFS's Trading Derivative Products	As of March 31, 2015 and December 31, 2014 the notional amounts of AFS’s trading derivative products are as follows:
		Notional
	Type of derivative	March 31,				December 31,
		2015				2014
	Interest rate swaps—receive-fixed/pay-variable	$	760,808			$	782,904
	Interest rate swaps—pay-fixed/receive-variable	1,465,871				1,479,650
	Interest rate swaps—basis swaps	55,800				55,800
	Futures contracts	60,000				80,000
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 March 31, 2015 and December 31, 2014 are as follows:
		Notional
	Type of VIE derivative	March 31,				December 31,
		2015				2014
	Interest rate swaps—receive-fixed/pay-variable	$	1,629,458			$	1,710,344
	Interest rate swaps—pay-fixed/receive-variable	3,003,021				3,152,090
	Currency swaps	690,386				724,656
	Credit derivatives	16,249				18,278

Income_Taxes_Tables

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Major Jurisdictions	The following are the major jurisdictions in which Ambac and its affiliates operate and the earliest tax years subject to examination:
	Jurisdiction	Tax Year
	United States	2010
	New York State	2011
	New York City	2011
	United Kingdom	2009
	Italy	2009
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 March 31, 2015 and December 31, 2014 are presented below:
		March 31,			December 31,
		2015			2014
	Deferred tax liabilities:
	Insurance intangible	$	471,553		$	493,822
	Variable interest entities	11,611			14,149
	Investments	141,208			138,072
	Unearned premiums and credit fees	101,647			104,589
	Other	33,763			33,835
	Total deferred tax liabilities	759,782			784,467
	Deferred tax assets:
	Net operating loss and capital carryforward	1,829,084			1,890,551
	Loss reserves	146,429			185,881
	Compensation	5,469			5,276
	AMT Credits	11,899			10,359
	Other	9,539			9,539
	Sub total deferred tax assets	2,002,420			2,101,606
	Valuation allowance	1,244,543			1,319,218
	Total deferred tax assets	757,877			782,388
	Net deferred tax asset (liability)	(1,905		)	(2,079		)

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Summary of Financial Information by Reportable Segment	The following table is a summary of financial information by reportable business segment for the affected periods:
			Financial			Financial			Corporate			Inter-segment			Consolidated
			Guarantee			Services			and Other			Eliminations
	Three Months Ended March 31, 2015:
	Revenues:
	Unaffiliated customers (1)		$	191,814		$	(37,708	)	$	357		$	—		$	154,463
	Equity in net income of investees accounted for by equity method		—			—			1,028			—			1,028
	Inter-segment		257			(230		)	(27		)	—			—
	Total revenues before expenses and reorganization items		192,071			(37,938		)	1,358			—			155,491
	Pre-tax income (loss) from continuing operations:
	Unaffiliated customers (1)(2)(3)		256,005			(38,580		)	(1,873		)	—			215,552
	Equity in net income of investees accounted for by equity method		—			—			1,028			—			1,028
	Inter-segment		(539		)	(312		)	851			—			—
	Pre-tax income (loss) from continuing operations		255,466			(38,892		)	6			—			216,580
	Total assets as of March 31, 2015		24,672,977			431,445			282,188			—			25,386,610
	Net investment income		71,470			128			1,385			—			72,983
	Insurance intangible amortization		37,432			—			—			—			37,432
	Interest expense		27,585			323			—			—			27,908
	Three Months Ended March 31, 2014:
	Revenues:
	Unaffiliated customers (1)		$	162,553		$	(53,438	)	$	23		$	—		$	109,138
	Equity in net income of investees accounted for by equity method		—			—			—			—			—
	Inter-segment		375			(75		)	8,635			(8,935		)	—
	Total revenues before expenses and reorganization items		162,928			(53,513		)	8,658			(8,935		)	109,138
	Pre-tax income (loss) from continuing operations:
	Unaffiliated customers (1) (2) (3)		217,158			(54,450		)	(3,410		)	—			159,298
	Equity in net income of investees accounted for by equity method		—			—			—			$	—		—
	Inter-segment		(9,157		)	(454		)	9,611			—			—
	Pre-tax income (loss) from continuing operations		208,001			(54,904		)	6,201			—			159,298
	Total assets as of March 31, 2014		26,535,119			534,256			44,873			—			27,114,248
	Net investment income		70,384			394			23			—			70,801
	Insurance intangible amortization		31,714			—			—			—			31,714
	Interest expense		31,881			447			—			—			32,328
	-1	Included in both revenues from unaffiliated customers and in pre-tax income (loss) from continuing operations from unaffiliated customers is net investment income.
	-2	Included in pre-tax income (loss) from continuing operations from unaffiliated customers is interest expense.
	-3	Included in pre-tax income (loss) from continuing operations from unaffiliated customers is amortization of intangible asset arising from financial guarantee contracts that were set to fair value upon adoption of Fresh Start on April 30, 2013.
Schedule of Gross Premiums Written, Net Premiums Earned and Net Change in Fair Value of Credit Derivatives	The following table summarizes gross premiums written, net premiums earned and the net change in fair value of credit derivatives included in the Financial Guarantee segment by location of risk for the affected periods:
			Three Months Ended March 31, 2015									Three Months Ended March 31, 2014
			Gross			Net			Net Change in			Gross			Net		Net Change in
			Premiums			Premiums			Fair Value of			Premiums			Premiums		Fair Value of
			Written			Earned			Credit			Written			Earned		Credit
									Derivatives								Derivatives
	United States		$	(2,366	)	$	52,739		$	3,958		$	(699	)	$	56,758	$	6,581
	United Kingdom		9,174			7,582			—			(6,166		)	20,635		—
	Other international		(5,746		)	5,397			(6,457		)	1,099			5,154		801
	Total		$	1,062		$	65,718		$	(2,499	)	$	(5,766	)	$	82,547	$	7,382

Background_and_Business_Descri1

Background and Business Description - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Apr. 30, 2013
	Segment
Background And Basis Of Presentation [Line Items]
Entity Incorporation, Date of Incorporation	29-Apr-91
Number of reportable segments	2
Investment Warrants Expiration Date		30-Apr-23
Payment of permitted policy claim (percent)		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	45,006,057	45,005,932
Warrants Distributed In Bankruptcy			5,047,138
Warrants issued exercise price			$16.67
Ambac Assurance [Member]
Background And Basis Of Presentation [Line Items]
Net par exposure for policies allocated to the Segregated Account	$18,052,539,000
Minimum surplus amount	100,000,000
Segregated Account [Member]
Background And Basis Of Presentation [Line Items]
Insurance Liabilities Not Assumed	$26,169,000
Successor [Member]
Background And Basis Of Presentation [Line Items]
Common stock, shares issued			45,000,000
Warrants Distributed In Bankruptcy			5,047,138

Basis_of_Presentation_and_Sign2

Basis of Presentation and Significant Accounting Policies (Details) (USD $)	3 Months Ended		12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Goodwill [Roll Forward]
Currency Translation, Weighted Average Risk Free Discount Rate	2.50%		2.70%
Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount	$22,852	$25,114
Financial Guarantee Insurance Contracts, Premium Received over Contract Period, Premium Receivable, Weighted Average Collection Period	9 years 7 months 6 days		10 years 1 month 6 days
Successor [Member]
Goodwill [Roll Forward]
Beginning balance	514,511
Ending balance	514,511
Reorganization items	$0	$23

Basis_of_Presentation_and_Sign3

Basis of Presentation and Significant Accounting Policies Additional Information (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Apr. 30, 2013
Finite-Lived Intangible Assets [Line Items]
Common Stock, Par or Stated Value Per Share	$0.01	$0.01	$0.01
Entity Incorporation, Date of Incorporation	29-Apr-91
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	45,006,057	45,005,932
Warrant Exercised During Period Shares	125

Special_Purpose_Entities_Inclu2

Special Purpose Entities, Including Variable Interest Entities - Additional Information (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Variable Interest Entities [Line Items]
Fair value of special purpose entities	10,036	$12,036
Consolidated VIE assets	15,506,746	15,126,110
Consolidated VIE liabilities	15,473,572	15,085,685
Asset-Backed Securities and Utility Obligations [Member]
Variable Interest Entities [Line Items]
Weighted average life	6 years 9 months 12 days
Average rating of assets held by sponsored special purpose entities	BBB
Sponsored Variable Interest Entities [Member]
Variable Interest Entities [Line Items]
Number of individual transactions with special purpose entities	15
Number of transactions outstanding with special purpose entities	3
Total principal amount of debt outstanding	457,960	$457,960
Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number of consolidated Variable Interest Entities	14	15

Special_Purpose_Entities_Inclu3

Special Purpose Entities, Including Variable Interest Entities - Summary of Fair Value of Fixed Income Securities, by Asset-Type, Held by Consolidated Variable Interest Entities (Detail) (Successor [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Investments:
Fixed income securities	$5,151,543	$5,150,018
Variable Interest Entities [Member]
Investments:
Fixed income securities	2,704,657	2,743,050
Corporate Obligations [Member]
Investments:
Fixed income securities	$2,704,657	$2,743,050

Special_Purpose_Entities_Inclu4

Special Purpose Entities, Including Variable Interest Entities - Supplemental Information about Loans Held as Assets and Long-Term Debt Associated with Consolidated Variable Interest Entities (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Variable Interest Entities [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	$15,473,572	$15,085,685
Variable Interest Entities [Member] | Successor [Member]
Variable Interest Entities [Line Items]
Loans, Estimated fair value	12,789,201	12,371,177
Long-term debt, Estimated fair value	13,341,902	12,882,076
Loans, Unpaid principal balance	9,675,140	10,236,695
Long-term debt, Unpaid principal balance	$11,299,861	$11,925,499

Special_Purpose_Entities_Inclu5

Special Purpose Entities, Including Variable Interest Entities - Summary of Carrying Amount of Assets, Liabilities and Maximum Exposure to Loss of Ambac's Variable Interests in Non-Consolidated Variable Interest Entities (Detail) (Variable Interest Entity [Member], Successor [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	$61,759,766
Insurance Assets	1,755,687
Insurance Liabilities	4,757,836
Derivative Liabilities	-204,040
Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	31,085,114
Insurance Assets	1,316,835
Insurance Liabilities	4,244,172
Derivative Liabilities	-174,149
Global Public Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	30,674,652	31,639,004
Insurance Assets	438,852	457,774
Insurance Liabilities	513,664	533,192
Derivative Liabilities	-29,891	-22,135
Collateralized Debt Obligations [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	1,297,393	1,386,100
Insurance Assets	303	345
Insurance Liabilities	3,889	4,000
Derivative Liabilities	-155,357	-145,565
Residential Mortgage-Backed Securities [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	18,837,405	19,464,549
Insurance Assets	1,037,566	1,011,888
Insurance Liabilities	2,879,199	2,924,987
Other Consumer Asset-Backed [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	4,460,126	5,109,776
Insurance Assets	55,219	65,204
Insurance Liabilities	671,303	885,572
Derivative Liabilities	-35,558	-36,877
Other Commercial Asset-Backed [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	2,943,920	3,119,891
Insurance Assets	129,218	135,215
Insurance Liabilities	124,124	128,988
Derivative Liabilities	0	0
Other [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	3,546,270	3,801,382
Insurance Assets	94,529	97,345
Insurance Liabilities	565,657	599,915
Derivative Liabilities	$16,766	$18,176

Comprehensive_Income_Schedule_

Comprehensive Income - Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income (Detail) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$220,283	$11,661
Other comprehensive income before reclassifications	75	98,860
Amounts reclassified from accumulated other comprehensive income	-51,029	-6,104
Net current period other comprehensive income	-50,954	92,756
Ending Balance	169,329	104,417
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	210,693	-41,910
Other comprehensive income before reclassifications	33,554	94,622
Amounts reclassified from accumulated other comprehensive income	-51,002	-5,900
Net current period other comprehensive income	-17,448	88,722
Ending Balance	193,245	46,812
Other Postretirement Benefit Plan, Defined Benefit [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	10,031	10,847
Other comprehensive income before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	-27	-204
Net current period other comprehensive income	-27	-204
Ending Balance	10,004	10,643
Accumulated Translation Adjustment [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	-441	42,724
Other comprehensive income before reclassifications	-33,479	4,238
Amounts reclassified from accumulated other comprehensive income	0	0
Net current period other comprehensive income	-33,479	4,238
Ending Balance	($33,920)	$46,962

Comprehensive_Income_Schedule_1

Comprehensive Income - Schedule of Amounts Reclassed Out of Each Component of Accumulated Other Comprehensive Income (Detail) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	($1,709)	($3,249)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	-51,029	-6,104
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized investment gains	-51,002	-5,900
Net of tax and noncontrolling interest	-51,002	-5,900
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	-51,002	-5,900
Other Postretirement Benefit Plan, Defined Benefit [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	-27	-204
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax and noncontrolling interest	-51,029	-6,104
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	0	0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	0	0
Prior service cost	-166	-166
Actuarial gains (losses)	139	-38
Total before tax	-27	-204
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	($27)	($204)

Net_Income_Per_Share_Additiona

Net Income Per Share - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Apr. 30, 2013
Schedule Of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	110,000
Number of new common stock issued	45,006,057	45,005,932
Par value of common stock issued	$0.01	$0.01	$0.01
Class of Warrant or Right, Number of Securities Called by Warrants or Rights			5,047,138
Exercise price of common stock			$16.67
Investment Warrants Expiration Date		30-Apr-23
Warrant exercised	125
Common stock shares issued	125
Warrants outstanding	5,039,752
Successor [Member]
Schedule Of Earnings Per Share [Line Items]
Number of new common stock issued			45,000,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights			5,047,138

Net_Income_Per_Share_Reconcili

Net Income Per Share - Reconciliation of Common Shares Used for Basic and Diluted Earnings Per Share (Detail)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Effect of potential dilutive shares:
Anti-dilutive shares excluded from reconciliation	110,000
Successor [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of common shares used for basic earnings per share	45,156,202	45,042,823
Effect of potential dilutive shares:
Weighted average number of common shares and potential dilutive shares used for diluted earnings per share	46,948,999	47,045,742
Successor [Member] | Restricted Stock Units (RSUs) [Member]
Effect of potential dilutive shares:
Effect of potential dilutive shares	25,013	0
Successor [Member] | Performance Shares [Member]
Effect of potential dilutive shares:
Effect of potential dilutive shares	3,145	0
Successor [Member] | Warrants [Member]
Effect of potential dilutive shares:
Effect of potential dilutive shares	1,751,798	1,998,028
Successor [Member] | Employee Stock Option [Member]
Effect of potential dilutive shares:
Effect of potential dilutive shares	12,841	4,891

Financial_Guarantee_Insurance_2

Financial Guarantee Insurance Contracts - Additional Information (Detail) (USD $)	3 Months Ended			12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Insurance [Line Items]
Estimated Future Premium Payments Weighted Average Discounted Rate	2.50%	2.70%		2.70%
Weighted average period of future premiums	9 years 7 months 6 days			10 years 1 month 6 days
Transactions with non-investment grade internal ratings	32.00%	32.00%
Non-investment grade RMBS on total premiums receivable	7.00%	7.00%
Percentage of student loan transactions on total premium receivables	7.00%	8.00%
Uncollectable premium receivables	$17,082	$17,780		$17,780
Past due premiums on policies insuring non-investment grade obligations amount	500
Accelerated premium revenue for retired obligations	22,852		25,114
Losses and loss expense reserves ceded to reinsurers	74,519	100,355		100,355
Subrogation recoveries	2,568,353	2,523,540		2,523,540
Subrogation recoveries, net of reinsurance	2,540,710	2,496,515		2,496,515
Accumulated amortization on insurance intangible asset	283,773	249,205		249,205
Successor [Member]
Insurance [Line Items]
Reinsurance Payable	59,268	60,436		60,436
Reinsurance recoveries of losses included in losses and loss expenses	20,601		10,559
Losses and loss expense reserves ceded to reinsurers	74,519	100,355	111,303	100,355	122,357
Intangible amortization expense	37,432		31,714
Insurance intangible asset	1,347,295	1,410,920		1,410,920
Successor [Member] | Insurance Intangible Asset [Member]
Insurance [Line Items]
Intangible amortization expense	$37,432		$31,714
Loss Reserves [Member]
Insurance [Line Items]
Weighted average risk-free rate used to discount loss reserves	2.10%			2.30%

Financial_Guarantee_Insurance_3

Financial Guarantee Insurance Contracts - Summary of Gross Premium Receivable Roll-Forward (Direct and Assumed Contracts) (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Insurance [Line Items]
Percentage Premiums Receivable Related To Transactions With Non Investment Grade Internal Ratings	32.00%	32.00%
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Percentage Of Premiums Receivable Related To Non Investment Grade Rmbs Transactions	7.00%	7.00%
Percentage Of Premiums Receivable Related To Student Loan Transactions	7.00%	8.00%
Premiums Receivable, Allowance for Doubtful Accounts	$17,082	$17,780
Premiums Past Due On Non Investment Grade Obligation	500
Successor [Member]
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Beginning premium receivable	1,000,607		1,453,021
Premium receipts	-27,453		-33,128
Adjustments for changes in expected and contractual cash flows	-5,918		-15,062
Accretion of premium receivable discount	6,282		10,370
Uncollectable premiums	698		-1,074
Other adjustments (including foreign exchange)	-22,217		3,987
Ending premium receivable	$951,999		$1,418,114

Financial_Guarantee_Insurance_4

Financial Guarantee Insurance Contracts - Effect of Reinsurance on Premiums Written and Earned (Detail) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Successor [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Premiums Written	$1,062	($5,766)
Assumed Reinsurance Premiums Written	0	0
Ceded Reinsurance Premiums Written	365	456
Premiums written, net of reinsurance	-697	6,222
Direct Premiums Earned	71,649	86,183
Assumed Reinsurance Premiums Earned	22	68
Ceded Reinsurance Premiums Earned	5,953	3,704
Reinsurance on premiums earned, Net	$65,718	$82,547

Financial_Guarantee_Insurance_5

Financial Guarantee Insurance Contracts - Summarized Future Gross Undiscounted Premiums Expected to be Collected, and Future Expected Premiums Earned, Net of Reinsurance (Detail) (USD $)	Mar. 31, 2015
In Thousands, unless otherwise specified
Insurance [Abstract]
Future premiums expected to be collected, June 30. 2015	$22,082
Future premiums expected to be collected, September 30, 2015	22,103
Future premiums expected to be collected, December 31, 2015	21,686
Future premiums expected to be collected, December 31, 2016	83,054
Future premiums expected to be collected, December 31, 2017	76,968
Future premiums expected to be collected, December 31, 2018	72,261
Future premiums expected to be collected, December 31, 2019	68,564
Future premiums expected to be collected, December 31, 2024	304,049
Future premiums expected to be collected, December 31, 2029	254,696
Future premiums expected to be collected, December 31, 2034	179,393
Future premiums expected to be collected, December 31, 2039	65,595
Future premiums expected to be collected, December 31, 2044	25,189
Future premiums expected to be collected, December 31, 2049	9,831
Future premiums expected to be collected, December 31, 2054	1,244
Future premiums expected to be collected, December 31, 2059	5
Future premiums expected to be collected, Total	1,206,720
Future expected premiums to be earned, net of reinsurance, June 30, 2015	38,127
Future expected premiums to be earned, net of reinsurance, September 30, 2015	35,798
Future expected premiums to be earned, net of reinsurance, December 31, 2015	33,635
Future expected premiums to be earned, net of reinsurance, December 31, 2016	123,206
Future expected premiums to be earned, net of reinsurance, December 31, 2017	110,175
Future expected premiums to be earned, net of reinsurance, December 31, 2018	101,113
Future expected premiums to be earned, net of reinsurance, December 31, 2019	94,047
Future expected premiums to be earned, net of reinsurance, December 31, 2024	385,547
Future expected premiums to be earned, net of reinsurance, December 31, 2029	272,177
Future expected premiums to be earned, net of reinsurance, December 31, 2034	169,638
Future expected premiums to be earned, net of reinsurance, December 31, 2039	67,126
Future expected premiums to be earned, net of reinsurance, December 31, 2044	23,328
Future expected premiums to be earned, net of reinsurance, December 31, 2049	9,824
Future expected premiums to be earned, net of reinsurance, December 31, 2054	2,183
Future expected premiums to be earned, net of reinsurance, December 31, 2059	3
Future expected premiums to be earned, net of reinsurance, Total	$1,465,927

Financial_Guarantee_Insurance_6

Financial Guarantee Insurance Contracts Financial Guarantee Insurance Contracts - Components of Loss and Loss Expense Reserves and Subrogation Recoverable (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$4,789	($517)	$139
Loss Reserves Ceded To Reinsurers	74,519		100,355
Successor [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss Reserves Ceded To Reinsurers	74,519	111,303	100,355	122,357
Policyholder Benefits and Claims Incurred, Ceded	-20,601	-10,559
Liability for Unpaid Claims and Claims Adjustment Expense, Net	3,417,343	5,202,630	3,698,378	5,347,877
Loss and loss expense reserves	4,475,991		4,752,007
Subrogation recoverable	-984,129		-953,274
Claim liability reported on Balance Sheet, before reinsurance	3,491,862		3,798,733
Successor [Member] | Unpaid Claims-Claims [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	2,158,007		2,172,041
Subrogation recoverable	774,960		772,948
Claim liability reported on Balance Sheet, before reinsurance	2,932,967		2,944,989
Successor [Member] | Unpaid Claims-Accrued Interest [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	265,708		234,802
Subrogation recoverable	103,429		94,425
Claim liability reported on Balance Sheet, before reinsurance	369,137		329,227
Successor [Member] | 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	3,579,957		3,792,133
Subrogation recoverable	175,415		197,751
Claim liability reported on Balance Sheet, before reinsurance	3,755,372		3,989,884
Successor [Member] | 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	-1,268,916		-1,205,621
Subrogation recoverable	-2,037,933		-2,018,398
Claim liability reported on Balance Sheet, before reinsurance	-3,306,849		-3,224,019
Successor [Member] | Unearned Premium Reserve [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	-258,765		-241,348
Subrogation recoverable	0		0
Claim liability reported on Balance Sheet, before reinsurance	($258,765)		($241,348)

Financial_Guarantee_Insurance_7

Financial Guarantee Insurance Contracts - Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Loss And Loss Adjustment Expense Reserves [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$4,789	($517)	$139
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Less reinsurance on loss and loss expense reserves			100,355
Prior years:
Add reinsurance on loss and loss expense reserves	74,519		100,355
Successor [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Policyholder Benefits and Claims Incurred, Ceded	-20,601	-10,559
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross loss and loss expense reserves	3,798,733	5,470,234
Less reinsurance on loss and loss expense reserves	100,355	122,357
Beginning balance of net loss and loss expense reserves	3,698,378	5,347,877
Current year:
ambc_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsCurrentYear	1	151
Total current year	1	151
Prior years:
Change in previously established loss and loss expense reserves, gross of RMBS subrogation and net of reinsurance	-132,639	-117,692
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance	104,202	9,375
Change in previously established RMBS subrogation recoveries, net of reinsurance	-44,195	-18,331
Liability For Unpaid Claims And Claims Adjustment Expense Change In Loss Reserves Prior Year	-281,036	-145,398
Net change in loss and loss expense reserves	-281,035	-145,247
Liability for Unpaid Claims and Claims Adjustment Expense, Net	3,417,343	5,202,630
Add reinsurance on loss and loss expense reserves	74,519	111,303
Ending gross loss and loss expense reserves	$3,491,862	$5,313,933

Financial_Guarantee_Insurance_8

Financial Guarantee Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Detail) (Successor [Member], USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
	Policies	Policies
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	330	325
Remaining weighted-average contract period (in years)	15 years	16 years
Gross insured contractual payments outstanding:
Principal	$18,482,283	$18,322,914
Interest	13,218,716	7,254,995
Total	31,700,999	25,577,909
Gross undiscounted claim liability	8,232,073	8,679,974
Discount, gross claim liability	1,260,130	1,509,948
Gross claim liability before all subrogation and before reinsurance	6,971,943	7,170,026
Less:
Gross RMBS subrogation	-2,579,450	-2,541,219
Discount, RMBS subrogation	11,097	17,679
Discounted RMBS subrogation, before reinsurance	-2,568,353	-2,523,540	-2,224,295	-2,206,598
Less:
Gross other subrogation	-815,033	-792,287
Discount, other subrogation	76,537	91,808
Discounted other subrogation, before reinsurance	-738,496	-700,479
Gross claim liability, net of all subrogation and discounts, before reinsurance	3,665,094	3,946,007
Less: Unearned premium reserves	-258,765	-241,348
Plus: Loss adjustment expenses reserves	85,533	94,074
Claim liability reported on Balance Sheet, before reinsurance	3,491,862	3,798,733
Reinsurance recoverable reported on Balance Sheet	79,308	99,838
I/SL [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	34	36
Remaining weighted-average contract period (in years)	7 years	8 years
Gross insured contractual payments outstanding:
Principal	910,033	1,026,513
Interest	339,721	418,746
Total	1,249,754	1,445,259
Gross undiscounted claim liability	12,901	16,360
Discount, gross claim liability	644	1,147
Gross claim liability before all subrogation and before reinsurance	12,257	15,213
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	0	0
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	12,257	15,213
Less: Unearned premium reserves	-8,812	-10,945
Plus: Loss adjustment expenses reserves	0	3
Claim liability reported on Balance Sheet, before reinsurance	3,445	4,271
Reinsurance recoverable reported on Balance Sheet	1	73
IA [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	21	26
Remaining weighted-average contract period (in years)	16 years	12 years
Gross insured contractual payments outstanding:
Principal	399,516	519,291
Interest	159,138	212,296
Total	558,654	731,587
Gross undiscounted claim liability	6,344	11,525
Discount, gross claim liability	605	937
Gross claim liability before all subrogation and before reinsurance	5,739	10,588
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	0	0
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	5,739	10,588
Less: Unearned premium reserves	-2,175	-3,432
Plus: Loss adjustment expenses reserves	16	1,303
Claim liability reported on Balance Sheet, before reinsurance	3,580	8,459
Reinsurance recoverable reported on Balance Sheet	910	890
II [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	43	33
Remaining weighted-average contract period (in years)	17 years	15 years
Gross insured contractual payments outstanding:
Principal	4,186,210	3,091,744
Interest	8,484,779	1,878,770
Total	12,670,989	4,970,514
Gross undiscounted claim liability	239,113	155,488
Discount, gross claim liability	18,502	16,438
Gross claim liability before all subrogation and before reinsurance	220,611	139,050
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	-12,388	-18,034
Discount, other subrogation	3,474	6,069
Discounted other subrogation, before reinsurance	-8,914	-11,965
Gross claim liability, net of all subrogation and discounts, before reinsurance	211,697	127,085
Less: Unearned premium reserves	-107,836	-73,749
Plus: Loss adjustment expenses reserves	2,185	1,968
Claim liability reported on Balance Sheet, before reinsurance	106,046	55,304
Reinsurance recoverable reported on Balance Sheet	2,331	1,355
III [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	66	69
Remaining weighted-average contract period (in years)	21 years	21 years
Gross insured contractual payments outstanding:
Principal	3,550,121	3,792,559
Interest	2,286,780	2,765,537
Total	5,836,901	6,558,096
Gross undiscounted claim liability	1,596,918	2,040,402
Discount, gross claim liability	521,225	716,812
Gross claim liability before all subrogation and before reinsurance	1,075,693	1,323,590
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	-142,548	-127,143
Discount, other subrogation	35,608	36,779
Discounted other subrogation, before reinsurance	-106,940	-90,364
Gross claim liability, net of all subrogation and discounts, before reinsurance	968,753	1,233,226
Less: Unearned premium reserves	-76,061	-88,332
Plus: Loss adjustment expenses reserves	7,465	6,470
Claim liability reported on Balance Sheet, before reinsurance	900,157	1,151,364
Reinsurance recoverable reported on Balance Sheet	85,082	110,957
IV [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	163	160
Remaining weighted-average contract period (in years)	13 years	12 years
Gross insured contractual payments outstanding:
Principal	9,376,691	9,892,760
Interest	1,928,647	1,979,627
Total	11,305,338	11,872,387
Gross undiscounted claim liability	6,297,440	6,456,139
Discount, gross claim liability	712,562	774,611
Gross claim liability before all subrogation and before reinsurance	5,584,878	5,681,528
Less:
Gross RMBS subrogation	-2,579,450	-2,541,219
Discount, RMBS subrogation	11,097	17,679
Discounted RMBS subrogation, before reinsurance	-2,568,353	-2,523,540
Less:
Gross other subrogation	-646,741	-647,110
Discount, other subrogation	33,795	48,960
Discounted other subrogation, before reinsurance	-612,946	-598,150
Gross claim liability, net of all subrogation and discounts, before reinsurance	2,403,579	2,559,838
Less: Unearned premium reserves	-63,368	-64,890
Plus: Loss adjustment expenses reserves	75,825	84,330
Claim liability reported on Balance Sheet, before reinsurance	2,416,036	2,579,278
Reinsurance recoverable reported on Balance Sheet	-9,016	-13,437
V [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	3	1
Remaining weighted-average contract period (in years)	6 years	6 years
Gross insured contractual payments outstanding:
Principal	59,712	47
Interest	19,651	19
Total	79,363	66
Gross undiscounted claim liability	79,357	60
Discount, gross claim liability	6,592	3
Gross claim liability before all subrogation and before reinsurance	72,765	57
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	-13,356	0
Discount, other subrogation	3,660	0
Discounted other subrogation, before reinsurance	-9,696	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	63,069	57
Less: Unearned premium reserves	-513	0
Plus: Loss adjustment expenses reserves	42	0
Claim liability reported on Balance Sheet, before reinsurance	62,598	57
Reinsurance recoverable reported on Balance Sheet	$0	$0

Financial_Guarantee_Insurance_9

Financial Guarantee Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Parenthetical) (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	$74,519	$100,355
Ceded Loss And Loss Expenses Paid Not Yet Recovered	4,789	139	-517
Successor [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	74,519	100,355	111,303	122,357
Loss and loss expense reserves	4,475,991	4,752,007
Subrogation recoverable	-984,129	-953,274
Liability for Claims	$3,491,862	$3,798,733	$5,313,933	$5,470,234

Recovered_Sheet1

Financial Guarantee Insurance Contracts - Summary of Balance of RMBS Subrogation Recoveries and Related Claim Liabilities, by Estimation Approach (Detail) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Subrogation recoveries	$2,568,353	$2,224,295	$2,523,540	$2,206,598
Changes in Estimation Approach In Rmbs Subrogation	0	0
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation	0	0
Other Changes Rmbs Subrogation	44,813	17,697
Random Samples [Member]
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Gross loss reserve before subrogation recoveries	1,899,087		1,897,426
Subrogation recoveries	2,568,353		2,523,540
Gross loss reserve after subrogation recoveries	-669,266		-626,114
Adverse Samples [Member]
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Subrogation recoveries	0	1,218,681	0	1,252,773
Changes in Estimation Approach In Rmbs Subrogation	0	0
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation	0	0
Other Changes Rmbs Subrogation	0	-34,092
Random Samples [Member]
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Subrogation recoveries	2,568,353	1,005,614	2,523,540	953,825
Changes in Estimation Approach In Rmbs Subrogation	0	0
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation	0	0
Other Changes Rmbs Subrogation	$44,813	$51,789

Recovered_Sheet2

Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	$2,523,540	$2,206,598
Changes recognized
Changes in Estimation Approach In Rmbs Subrogation	0	0
Impact of sponsor actions	0	0
Other Changes Rmbs Subrogation	44,813	17,697
Discounted RMBS subrogation (gross of reinsurance), ending balance	2,568,353	2,224,295
Random Samples [Member]
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	2,523,540	953,825
Changes recognized
Changes in Estimation Approach In Rmbs Subrogation	0	0
Impact of sponsor actions	0	0
Other Changes Rmbs Subrogation	44,813	51,789
Discounted RMBS subrogation (gross of reinsurance), ending balance	2,568,353	1,005,614
Adverse Samples [Member]
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	0	1,252,773
Changes recognized
Changes in Estimation Approach In Rmbs Subrogation	0	0
Impact of sponsor actions	0	0
Other Changes Rmbs Subrogation	0	-34,092
Discounted RMBS subrogation (gross of reinsurance), ending balance	$0	$1,218,681

Recovered_Sheet3

Financial Guarantee Insurance Contracts Financial Guarantee Insurance Contracts - Summary of Percentage Ceded to Reinsurers and Reinsurance Recoverable and Rating Levels (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Insurance [Abstract]
Loss Reserves Ceded To Reinsurers	$74,519	$100,355
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$4,789	$139	($517)

Recovered_Sheet4

Financial Guarantee Insurance Contracts - Estimated Future Amortization Expense for Insurance Intangible Asset (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Amortization Of Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$1,631,068		$1,660,125
Accumulated amortization on insurance intangible asset	283,773		249,205
2015	90,801
2016	107,443
2017	97,726
2018	90,095
2019	83,380
Thereafter	877,850
Successor [Member]
Amortization Of Intangible Assets [Line Items]
Amortization of insurance intangible assets	37,432	31,714
Successor [Member] | Insurance Asset [Member]
Amortization Of Intangible Assets [Line Items]
Amortization of insurance intangible assets	$37,432	$31,714

Fair_Value_Measurements_Summar

Fair Value Measurements - Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Financial assets:
Other investments	$310,578	$240,969
Other assets	10,036	12,036
Financial liabilities:
Derivative liabilities	76,377	73,459
Successor [Member]
Financial assets:
Fixed income securities	5,151,543	5,150,018
Short term investments	220,980	360,065
Successor [Member] | Total Fair Value [Member]
Financial assets:
Other investments	328,187	349,468
Cash	26,641	73,903
Loans	5,476	5,634
Total financial assets	21,135,582	20,822,011
Financial liabilities:
Obligations under investment and repurchase agreements	114,438	161,821
Liabilities for net financial guarantees written	4,152,094	4,539,000
Long-term debt	1,381,938	1,379,864
Total financial liabilities	21,563,441	21,569,868
Successor [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	6,219	7,708
Loans	12,789,201	12,371,177
Financial liabilities:
Long-term debt	13,341,902	12,882,076
Successor [Member] | Carrying Amount [Member]
Financial assets:
Other investments	332,609	357,016
Cash	26,641	73,903
Loans	5,494	5,714
Total financial assets	21,140,022	20,829,639
Financial liabilities:
Obligations under investment and repurchase agreements	111,967	160,079
Liabilities for net financial guarantees written	2,662,701	2,923,652
Long-term debt	1,301,390	1,273,805
Total financial liabilities	19,991,029	19,846,719
Successor [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	6,219	7,708
Loans	12,789,201	12,371,177
Financial liabilities:
Long-term debt	13,341,902	12,882,076
Successor [Member] | Level 1 [Member]
Financial assets:
Other investments	0	0
Cash	26,641	73,903
Loans	0	0
Total financial assets	343,177	547,047
Financial liabilities:
Obligations under investment and repurchase agreements	0	0
Liabilities for net financial guarantees written	0	0
Long-term debt	0	0
Total financial liabilities	942	562
Successor [Member] | Level 1 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	6,219	7,708
Loans	0	0
Financial liabilities:
Long-term debt	0	0
Successor [Member] | Level 2 [Member]
Financial assets:
Other investments	310,578	336,013
Cash	0	0
Loans	0	0
Total financial assets	5,002,694	4,929,368
Financial liabilities:
Obligations under investment and repurchase agreements	0	0
Liabilities for net financial guarantees written	0	0
Long-term debt	0	0
Total financial liabilities	13,651,729	14,007,568
Successor [Member] | Level 2 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	0	0
Loans	0	0
Financial liabilities:
Long-term debt	11,309,803	11,618,412
Successor [Member] | Level 3 [Member]
Financial assets:
Other investments	17,609	13,455
Cash	0	0
Loans	5,476	5,634
Total financial assets	15,789,711	15,345,596
Financial liabilities:
Obligations under investment and repurchase agreements	114,438	161,821
Liabilities for net financial guarantees written	4,152,094	4,539,000
Long-term debt	1,381,938	1,379,864
Total financial liabilities	7,910,770	7,561,738
Successor [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	0	0
Loans	12,789,201	12,371,177
Financial liabilities:
Long-term debt	2,032,099	1,263,664
Successor [Member] | Level 3 [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0
Successor [Member] | Interest Rate Swaps [Member] | Total Fair Value [Member]
Financial assets:
Derivative assets	113,622	106,974
Derivative assets - interest rate swaps - liability position	0
Successor [Member] | Interest Rate Swaps [Member] | Carrying Amount [Member]
Financial assets:
Derivative assets	113,622	106,974
Derivative assets - interest rate swaps - liability position	0
Successor [Member] | Interest Rate Swaps [Member] | Level 1 [Member]
Financial assets:
Derivative assets	0	0
Derivative assets - interest rate swaps - liability position	0	0
Successor [Member] | Interest Rate Swaps [Member] | Level 2 [Member]
Financial assets:
Derivative assets	113,622	106,974
Derivative assets - interest rate swaps - liability position	0	0
Successor [Member] | Interest Rate Swaps [Member] | Level 3 [Member]
Financial assets:
Derivative assets	0	0
Derivative assets - interest rate swaps - liability position	0	0
Successor [Member] | Municipal Bonds [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	525,188	525,792
Successor [Member] | Municipal Bonds [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	525,188	525,792
Successor [Member] | Municipal Bonds [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Municipal Bonds [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	525,188	525,792
Successor [Member] | Municipal Bonds [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Corporate Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	1,609,769	1,385,594
Successor [Member] | Corporate Obligations [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,704,657	2,743,050
Successor [Member] | Corporate Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	1,609,769	1,385,594
Successor [Member] | Corporate Obligations [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,704,657	2,743,050
Successor [Member] | Corporate Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Corporate Obligations [Member] | Level 1 [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Corporate Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	1,609,769	1,381,786
Successor [Member] | Corporate Obligations [Member] | Level 2 [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Corporate Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	3,808
Successor [Member] | Corporate Obligations [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,704,657	2,743,050
Successor [Member] | Foreign Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	125,164	127,757
Successor [Member] | Foreign Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	125,164	127,757
Successor [Member] | Foreign Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Foreign Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	125,164	127,757
Successor [Member] | Foreign Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | US Government Debt Securities [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	30,297	42,979
Fixed income securities, pledged as collateral	64,813	64,267
Successor [Member] | US Government Debt Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	30,297	42,979
Fixed income securities, pledged as collateral	64,813	64,267
Successor [Member] | US Government Debt Securities [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	30,297	42,979
Fixed income securities, pledged as collateral	64,813	64,267
Successor [Member] | US Government Debt Securities [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	0	0
Fixed income securities, pledged as collateral	0	0
Successor [Member] | US Government Debt Securities [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Fixed income securities, pledged as collateral	0	0
Successor [Member] | U.S. Agency Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	4,427	29,486
Successor [Member] | U.S. Agency Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	4,427	29,486
Successor [Member] | U.S. Agency Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | U.S. Agency Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	4,427	29,486
Successor [Member] | U.S. Agency Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	1,846,477	1,710,955
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	1,846,477	1,710,955
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	1,583,745	1,516,562
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	262,732	194,393
Successor [Member] | Collateralized Debt Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	88,238	21,122
Successor [Member] | Collateralized Debt Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	88,238	21,122
Successor [Member] | Collateralized Debt Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Collateralized Debt Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	88,238	21,122
Successor [Member] | Collateralized Debt Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Asset-backed Securities [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	636,190	882,001
Successor [Member] | Asset-backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	636,190	882,001
Successor [Member] | Asset-backed Securities [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Asset-backed Securities [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	636,190	882,001
Successor [Member] | Asset-backed Securities [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Short-Term [Member] | Total Fair Value [Member]
Financial assets:
Short term investments	220,980	360,065
Successor [Member] | Short-Term [Member] | Carrying Amount [Member]
Financial assets:
Short term investments	220,980	360,065
Successor [Member] | Short-Term [Member] | Level 1 [Member]
Financial assets:
Short term investments	215,207	358,190
Successor [Member] | Short-Term [Member] | Level 2 [Member]
Financial assets:
Short term investments	5,773	1,875
Successor [Member] | Short-Term [Member] | Level 3 [Member]
Financial assets:
Short term investments	0	0
Successor [Member] | Credit Derivatives [Member] | Total Fair Value [Member]
Financial assets:
Derivative assets	0	2,043
Successor [Member] | Credit Derivatives [Member] | Carrying Amount [Member]
Financial assets:
Derivative assets	0	2,043
Successor [Member] | Credit Derivatives [Member] | Level 1 [Member]
Financial assets:
Derivative assets	0	0
Successor [Member] | Credit Derivatives [Member] | Level 2 [Member]
Financial assets:
Derivative assets	0	0
Successor [Member] | Credit Derivatives [Member] | Level 3 [Member]
Financial assets:
Derivative assets	0	2,043
Successor [Member] | Other Assets [Member] | Total Fair Value [Member]
Financial assets:
Other assets	10,036	12,036
Successor [Member] | Other Assets [Member] | Carrying Amount [Member]
Financial assets:
Other assets	10,036	12,036
Successor [Member] | Other Assets [Member] | Level 1 [Member]
Financial assets:
Other assets	0	0
Successor [Member] | Other Assets [Member] | Level 2 [Member]
Financial assets:
Other assets	0	0
Successor [Member] | Other Assets [Member] | Level 3 [Member]
Financial assets:
Other assets	10,036	12,036
Successor [Member] | Futures Contracts [Member] | Total Fair Value [Member]
Financial assets:
Derivative assets		0
Successor [Member] | Futures Contracts [Member] | Carrying Amount [Member]
Financial assets:
Derivative assets		0
Successor [Member] | Futures Contracts [Member] | Level 1 [Member]
Financial assets:
Derivative assets		0
Successor [Member] | Futures Contracts [Member] | Level 2 [Member]
Financial assets:
Derivative assets		0
Successor [Member] | Futures Contracts [Member] | Level 3 [Member]
Financial assets:
Derivative assets		0
Other Contracts [Member] | Successor [Member] | Total Fair Value [Member]
Financial liabilities:
Derivative liabilities		0
Other Contracts [Member] | Successor [Member] | Carrying Amount [Member]
Financial liabilities:
Derivative liabilities		0
Other Contracts [Member] | Successor [Member] | Level 1 [Member]
Financial liabilities:
Derivative liabilities		0
Other Contracts [Member] | Successor [Member] | Level 2 [Member]
Financial liabilities:
Derivative liabilities		0
Other Contracts [Member] | Successor [Member] | Level 3 [Member]
Financial liabilities:
Derivative liabilities		0
Futures Contracts [Member] | Successor [Member] | Total Fair Value [Member]
Financial liabilities:
Derivative liabilities	942	562
Futures Contracts [Member] | Successor [Member] | Carrying Amount [Member]
Financial liabilities:
Derivative liabilities	942	562
Futures Contracts [Member] | Successor [Member] | Level 1 [Member]
Financial liabilities:
Derivative liabilities	942	562
Futures Contracts [Member] | Successor [Member] | Level 2 [Member]
Financial liabilities:
Derivative liabilities	0	0
Futures Contracts [Member] | Successor [Member] | Level 3 [Member]
Financial liabilities:
Derivative liabilities	0	0
Interest Rate Swaps [Member] | Successor [Member] | Total Fair Value [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	-68,481	-54,666
Derivative liabilities	438,518	385,546
Interest Rate Swaps [Member] | Successor [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	2,081,082	2,133,268
Interest Rate Swaps [Member] | Successor [Member] | Carrying Amount [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	-68,481	-54,666
Derivative liabilities	438,518	385,546
Interest Rate Swaps [Member] | Successor [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	2,081,082	2,133,268
Interest Rate Swaps [Member] | Successor [Member] | Level 1 [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	0	0
Derivative liabilities	0	0
Interest Rate Swaps [Member] | Successor [Member] | Level 1 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Interest Rate Swaps [Member] | Successor [Member] | Level 2 [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	-68,481	-54,666
Derivative liabilities	284,694	243,659
Interest Rate Swaps [Member] | Successor [Member] | Level 2 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	2,081,082	2,133,268
Interest Rate Swaps [Member] | Successor [Member] | Level 3 [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	0	0
Derivative liabilities	153,824	141,887
Interest Rate Swaps [Member] | Successor [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Credit Derivatives [Member] | Successor [Member] | Total Fair Value [Member]
Financial liabilities:
Derivative liabilities	76,377	75,502
Credit Derivatives [Member] | Successor [Member] | Carrying Amount [Member]
Financial liabilities:
Derivative liabilities	76,377	75,502
Credit Derivatives [Member] | Successor [Member] | Level 1 [Member]
Financial liabilities:
Derivative liabilities	0	0
Credit Derivatives [Member] | Successor [Member] | Level 2 [Member]
Financial liabilities:
Derivative liabilities	0	0
Credit Derivatives [Member] | Successor [Member] | Level 3 [Member]
Financial liabilities:
Derivative liabilities	76,377	75,502
Currency Swaps [Member] | Successor [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	44,631	66,895
Currency Swaps [Member] | Successor [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	44,631	66,895
Currency Swaps [Member] | Successor [Member] | Level 1 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Currency Swaps [Member] | Successor [Member] | Level 2 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	44,631	66,895
Currency Swaps [Member] | Successor [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities		$0

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Credit valuation adjustment included in fair value of credit derivative liabilities	$18,020	$15,910
Credit valuation adjustment included in fair value of derivative liabilities other than credit derivatives	77,191	64,547
Percentage of CDS gross par outstanding used in the determination of CDS fair values	86.00%
Percentage of CDS derivative liability used in the determination of CDS fair values	65.00%
Percentage of CDS gross par outstanding using internally estimated reference obligation prices in determination of fair value	14.00%
Percentage of CDS liability using internally estimated reference obligation prices in determination of fair value	35.00%
Additional basis point fee need to receive for issuing a CDS on obligation	0.05%
Additional basis points fee increase on change of reference obligation spread	0.15%
Revised relative change ratio of CDS fee to cash market spread	73.20%
Estimated remaining life	8 years
Notional outstanding	1,594,571	1,529,759
Derivative liabilities	76,377	73,459
Percentage of profit margin	17.00%	17.00%
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs	2.50%	2.70%
Credit Derivatives [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
CVA percentage	19.10%	17.80%
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	1,841,412	1,070,439
US Commercial ABS Transaction [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	190,687	193,225
Minimum [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Basis point fee received for issuing a CDS on reference obligation base fee	0.20%
Credit spread of reference obligation of a base transaction	0.80%
Relative change ratio of CDS fee to cash market spread	25.00%
Maximum [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Basis point fee received for issuing a CDS on reference obligation hypothetical fee	0.25%
Relative change ratio of CDS fee to cash market spread	35.00%
Credit spread of reference obligation of revised transaction	1.00%
Internal Credit Rating [Member] | Minimum [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Revised relative change ratio of CDS fee to cash market spread	33.00%
Internal Credit Rating [Member] | Maximum [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Full relative change ratio of CDS fee to cash market spread	100.00%
Successor [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available-for-sale Securities	5,151,543	5,150,018
Successor [Member] | 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	6.00%	10.00%
Percentage of investment portfolio valued using external pricing services	89.00%	86.00%
Percentage of investment portfolio valued using internal valuation models	5.00%	4.00%
Successor [Member] | U.S. Agency Obligations [Member] | Level 3 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available-for-sale Securities	0	0
Successor [Member] | Asset-backed Securities [Member] | Level 3 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available-for-sale Securities	0	0
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Level 3 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available-for-sale Securities	262,732	194,393
Successor [Member] | Corporate Obligations [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Coupon rate	0.35%
Fair Value Inputs Maturity	19 years 1 month 21 days
Fair Value Inputs Yield	4.93%
Successor [Member] | Corporate Obligations [Member] | Level 3 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available-for-sale Securities	0	3,808
Successor [Member] | Collateralized Debt Obligations [Member] | Level 3 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available-for-sale Securities	0	0
Variable Interest Entities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs	3.50%	4.10%
Other Contracts [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fair Value Input Weighted Average Credit Derivative Quote As Percentage Of Notional	1.00%	1.00%
Fair Value Input Weighted Average Credit Rating	A	A
CVA percentage	2.02%	2.21%
Notional outstanding	58,801	58,800
Fair Value Input Weighted Average Life	0 years 11 months	1 year 2 months 12 days
Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member] | Corporate Obligations [Member] | Level 3 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Available-for-sale Securities	$2,704,657	$2,743,050
Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member] | European ABS Transactions [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Coupon rate	0.57%	0.30%
Fair Value Inputs Maturity	17 years 11 months	21 years 2 months 30 days
Fair Value Inputs Yield	7.30%	9.52%
Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member] | US Commercial ABS Transaction [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Coupon rate	5.88%	5.88%
Fair Value Inputs Maturity	15 years 8 months 20 days	15 years 10 months 4 days
Fair Value Inputs Yield	7.50%	7.37%

Fair_Value_Measurements_Inform

Fair Value Measurements - Information about Valuation Inputs for Fixed Income Securities Classified as Level 3 (Detail) (Successor [Member])	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Corporate Obligations [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate	0.35%
Fair Value Inputs Maturity	19 years 1 month 21 days
Yield	4.93%
Variable Interest Entity, Primary Beneficiary [Member] | United States Transactions [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate	5.88%	5.88%
Fair Value Inputs Maturity	15 years 8 months 20 days	15 years 10 months 4 days
Yield	7.50%	7.37%
Variable Interest Entity, Primary Beneficiary [Member] | European Transactions [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate	0.57%	0.30%
Fair Value Inputs Maturity	17 years 11 months	21 years 2 months 30 days
Yield	7.30%	9.52%

Fair_Value_Measurements_Summar1

Fair Value Measurements - Summary of Information about Described Model Inputs Used to Determine Fair Value of Each Class of Credit Derivatives (Detail) (USD $)	3 Months Ended	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding	$1,594,571	$1,529,759
Successor [Member] | CLO [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding	466,453	549,923
Weighted average reference obligation price	$99.10	$98.90
Weighted average life (WAL) in years	1 year 6 months	1 year 9 months
Weighted average credit rating	AA	AA
Weighted average relative change ratio	36.20%	35.90%
CVA percentage	5.21%	5.40%
Fair value of derivative liabilities	1,533	2,027
Successor [Member] | Other [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding	1,069,317	921,036
Weighted average reference obligation price	$86.80	$86.80
Weighted average life (WAL) in years	5 years 9 months	5 years 8 months
Weighted average credit rating	BBB	BBB-
Weighted average relative change ratio	44.80%	49.00%
CVA percentage	19.34%	15.82%
Fair value of derivative liabilities	$74,794	$71,104

Fair_Value_Measurements_Summar2

Fair Value Measurements - Summary of Information about Described Model Inputs Used to Determine Fair Value of Each Class of Credit Derivatives (Parenthetical) (Detail) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Notional outstanding	$1,594,571	$1,529,759
Other Contracts [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Notional outstanding	58,801	58,800
Weighted average life (WAL) in years	0 years 11 months	1 year 2 months 12 days
Weighted average quotes	1.00%	1.00%
CVA percentage	2.02%	2.21%
Weighted average credit rating	A	A
Fair value of derivative liabilities	$50	$328

Fair_Value_Measurements_Inform1

Fair Value Measurements - Information about Valuation Inputs for Variable Interest Entity Assets and Liabilities Classified as Level 3 (Detail) (Fair Value, Inputs, Level 3 [Member], Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	$13,504,326	$14,409,383	$13,845,454	$14,253,705
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	354,562	172,538
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	-631,215	86,799
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	84,504	70,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	148,979	173,451
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	208
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	348,390	169,349
Investments [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	262,732	66,923	198,201	67,783
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	5,729	419
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	-5,706	-217
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	84,504	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	19,996	854
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	208
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	0	0
Other Assets [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	10,036	13,122	12,036	13,384
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	-295	-262
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	1,705	0
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
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	-295	-262
Variable Interest Entity, Primary Beneficiary [Member] | Loans Receivable [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	12,789,201	13,269,452	12,371,177	13,398,895
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,110,927	321,847
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	-562,621	79,802
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	70,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	130,282	601,092
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
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	1,110,927	316,714
Variable Interest Entity, Primary Beneficiary [Member] | Corporate Debt Securities [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	2,704,657	2,546,762	2,743,050	2,475,182
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	92,120	55,745
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	-130,513	15,835
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability 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
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	92,120	55,745
Variable Interest Entity, Primary Beneficiary [Member] | Long-term Debt [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	-2,032,099	-1,284,394	-1,263,664	-1,514,605
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	-839,998	-190,962
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	67,625	-8,621
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	-3,938	-429,794
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
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	($839,998)	($187,824)

Fair_Value_Measurements_Summar3

Fair Value Measurements - Summary of Changes in Level 3 Fair Value Category (Detail) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Investment by Class [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$198,201	$67,783
Included in earnings	5,729	419
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	-5,706	-217
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	84,504
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	-19,996	-854
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		-208
Balance, end of period	262,732	66,923
Derivatives by Class [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	-215,346	-186,934
Included in earnings	-13,921	-14,249
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	-934	-1,299
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
Balance, end of period	-230,201	-202,482
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	14,364	15,024
Credit Derivative [Member] | Derivatives by Class [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	-73,459	-94,322
Included in earnings	-2,499	7,382
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	-419	-775
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
Balance, end of period	-76,377	-87,715
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	2,942	-6,607
Interest Rate Swaps [Member] | Derivatives by Class [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	-141,887	-92,612
Included in earnings	-11,422	-21,631
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	-515	-524
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
Balance, end of period	-153,824	-114,767
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	11,422	21,631
Residential Mortgage-Backed Securities [Member] | Investment by Class [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	194,393	0
Included in earnings	5,748	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	-5,420
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	84,504
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	-16,493	0
Balance, end of period	262,732
Collateralized Debt Obligations [Member] | Investment by Class [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	0	0
Included in earnings	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0
Asset-backed Securities [Member] | Investment by Class [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	0	64,073
Included in earnings	0	443
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	-295
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	-854
Balance, end of period	0	63,367
Corporate Obligations [Member] | Investment by Class [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	3,808	3,502
Included in earnings	-19	-24
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	-286	78
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	-3,503
Balance, end of period	0	3,556
US Government Agencies Debt Securities [Member] | Investment by Class [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	0	208
Included in earnings	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three		-208
Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	13,845,454	14,253,705
Included in earnings	354,562	172,538
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	-631,215	86,799
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	84,504	70,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	148,979	173,451
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	208
Balance, end of period	13,504,326	14,409,383
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	-348,390	-169,349
Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	-215,346	-186,934
Included in earnings	-13,921	-14,249
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	934	1,299
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
Balance, end of period	-230,201	-202,482
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	14,364	15,024
Level 3 [Member] | Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	198,201	67,783
Included in earnings	5,729	419
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	-5,706	-217
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	84,504	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	19,996	854
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	208
Balance, end of period	262,732	66,923
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
Level 3 [Member] | Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	12,036	13,384
Included in earnings	-295	-262
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	1,705	0
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
Balance, end of period	10,036	13,122
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	$295	$262

Fair_Value_Measurements_Summar4

Fair Value Measurements - Summary of Gains and Losses (Realized and Unrealized) Relating to Level 3 Assets and Liabilities Included in Earnings (Detail) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Net Investment Income [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings for the period	$5,729	$419
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	0	0
Realized Gains Or (Losses) and Other Settlements On Credit Derivative Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings for the period	419	775
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	0	0
Unrealized Gains Or (Losses) On Credit Derivative Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings for the period	-2,918	6,607
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	-2,942	6,607
Interest Rate Swaps [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings for the period	-11,422	-21,631
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	-11,422	-21,631
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	363,049	186,630
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	363,049	184,635
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	-295	-262
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held	($295)	($262)

Investments_Summary_of_Amortiz

Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments (Detail) (Successor [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$4,958,298	$4,939,325
Gross Unrealized Gains	222,608	242,962
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	29,363	32,269
Estimated Fair Value	5,151,543	5,150,018
Non - credit other - than - temporary Impairments	9,844	7,773
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	2,704,657	2,743,050
Short-Term [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	220,980	360,069
Gross Unrealized Gains	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	4
Estimated Fair Value	220,980	360,065
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,672,886	4,514,878
Gross Unrealized Gains	222,227	242,962
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	29,363	32,154
Estimated Fair Value	4,865,750	4,725,686
Non - credit other - than - temporary Impairments	9,844	7,773
Fixed Income Securities [Member] | Securities Pledged as Collateral [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	64,432	64,378
Gross Unrealized Gains	381	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	111
Estimated Fair Value	64,813	64,267
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	517,256	523,019
Gross Unrealized Gains	12,136	9,769
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	4,204	6,996
Estimated Fair Value	525,188	525,792
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,588,962	1,382,195
Gross Unrealized Gains	24,097	12,815
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	3,290	9,416
Estimated Fair Value	1,609,769	1,385,594
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] | Foreign Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	123,601	126,041
Gross Unrealized Gains	4,038	3,060
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2,475	1,344
Estimated Fair Value	125,164	127,757
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	28,983	42,328
Gross Unrealized Gains	1,418	1,078
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	104	427
Estimated Fair Value	30,297	42,979
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] | U.S. Government Obligations [Member] | Securities Pledged as Collateral [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	64,432	64,378
Gross Unrealized Gains	381	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	111
Estimated Fair Value	64,813	64,267
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] | U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,438	29,524
Gross Unrealized Gains	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	11	38
Estimated Fair Value	4,427	29,486
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,705,246	1,557,059
Gross Unrealized Gains	159,388	167,396
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	18,157	13,500
Estimated Fair Value	1,846,477	1,710,955
Non - credit other - than - temporary Impairments	9,844	7,773
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	88,569	21,346
Gross Unrealized Gains	102	50
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	433	274
Estimated Fair Value	88,238	21,122
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] | Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	615,831	833,366
Gross Unrealized Gains	21,048	48,794
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	689	159
Estimated Fair Value	636,190	882,001
Non - credit other - than - temporary Impairments	0	0
Fixed Income Investments And Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,893,866	4,874,947
Gross Unrealized Gains	222,227	242,962
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	29,363	32,158
Estimated Fair Value	5,086,730	5,085,751
Non - credit other - than - temporary Impairments	$9,844	$7,773

Investments_Summary_of_Amortiz1

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) (Successor [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Due in one year or less	$413,150
Amortized Cost, Due after one year through five years	927,630
Amortized Cost, Due after five years through ten years	994,286
Amortized Cost, Due after ten years	213,586
Amortized Cost, Total	2,548,652
Amortized Cost	4,958,298	4,939,325
Estimated Fair Value, Due in one year or less	413,291
Estimated Fair Value, Due after one year through five years	935,442
Estimated Fair Value, Due after five years through ten years	1,013,939
Estimated Fair Value, Due after ten years	217,966
Estimated Fair Value due, Total	2,580,638
Fixed income securities	5,151,543	5,150,018
Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,672,886	4,514,878
Fixed income securities	4,865,750	4,725,686
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,705,246	1,557,059
Fixed income securities	1,846,477	1,710,955
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	88,569	21,346
Fixed income securities	88,238	21,122
Fixed Income Securities [Member] | Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	615,831	833,366
Fixed income securities	$636,190	$882,001

Investments_Summary_of_Gross_U

Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Detail) (Successor [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$1,133,155	$1,324,489
Less than 12 Months, Gross Unrealized Loss	22,671	20,081
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	239,992	350,655
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	6,692	12,188
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,373,147	1,675,144
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	29,363	32,269
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		77,788
Less than 12 Months, Gross Unrealized Loss		1,244
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		135,076
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments		5,752
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		453,504
Less than 12 Months, Gross Unrealized Loss		4,998
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		172,045
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments		4,418
Foreign Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		20,827
Less than 12 Months, Gross Unrealized Loss		748
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		14,277
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments		596
U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		7,223
Less than 12 Months, Gross Unrealized Loss		154
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		14,735
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments		273
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		25,039
Less than 12 Months, Gross Unrealized Loss		2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		4,378
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments		36
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		413,203
Less than 12 Months, Gross Unrealized Loss		12,391
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		10,076
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments		1,109
Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		5,012
Less than 12 Months, Gross Unrealized Loss		274
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments		0
Other Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		248,823
Less than 12 Months, Gross Unrealized Loss		155
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		68
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments		4
Short-Term [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	8,803
Less than 12 Months, Gross Unrealized Loss	0	4
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	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	0	8,803
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	4
Fixed Income Investments And Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,133,155	1,260,222
Less than 12 Months, Gross Unrealized Loss	22,671	19,970
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	239,992	350,655
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	6,692	12,188
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,373,147	1,610,877
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	29,363	32,158
Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,133,155	1,251,419
Less than 12 Months, Gross Unrealized Loss	22,671	19,966
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	239,992	350,655
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	6,692	12,188
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,373,147	1,602,074
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	29,363	32,154
Fixed Income Securities [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	46,461
Less than 12 Months, Gross Unrealized Loss	412
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	119,412
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	3,792
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	165,873	212,864
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	4,204	6,996
Fixed Income Securities [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	278,044
Less than 12 Months, Gross Unrealized Loss	2,081
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	81,739
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	1,209
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	359,783	625,549
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	3,290	9,416
Fixed Income Securities [Member] | Foreign Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	32,206
Less than 12 Months, Gross Unrealized Loss	1,864
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	8,900
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	611
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	41,106	35,104
Fixed Income Securities [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,661
Less than 12 Months, Gross Unrealized Loss	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	10,814
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	102
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	12,475	21,958
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	104	427
Fixed Income Securities [Member] | U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0
Less than 12 Months, Gross Unrealized Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	4,359
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	11
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	4,359	29,417
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	11	38
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	547,706
Less than 12 Months, Gross Unrealized Loss	17,336
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	10,266
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	821
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	557,972	423,279
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	18,157	13,500
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	63,834
Less than 12 Months, Gross Unrealized Loss	289
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	4,434
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	144
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	68,268	5,012
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	433	274
Fixed Income Securities [Member] | Other Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	163,243
Less than 12 Months, Gross Unrealized Loss	687
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	68
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	163,311	248,891
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	689	159
Fixed Income Securities [Member] | Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2,475	1,344
Securities Pledged as Collateral [Member] | Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	64,267
Less than 12 Months, Gross Unrealized Loss	0	111
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	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	0	64,267
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	111
Securities Pledged as Collateral [Member] | Fixed Income Securities [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	64,267
Less than 12 Months, Gross Unrealized Loss	0	111
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	0	64,267
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	111
Securities Pledged as Collateral [Member] | Securities Pledged as Collateral [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$0	$0

Investments_Additional_Informa

Investments - Additional Information (Detail) (USD $)	12 Months Ended	3 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Investment [Line Items]
Payment of permitted policy claim (percent)	25.00%
Future payment of permitted policy claim (percent)	45.00%
Securities fair value	$6,790	$6,842
Successor [Member]
Investment [Line Items]
Unrealized losses on securities	20,081	22,671
Other investments		9,651	1,994
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	32,269	29,363
Below Investment Grade Securities and Non-Rated Securities [Member] | Successor [Member]
Investment [Line Items]
Fair value of below investment grade securities and non-rated securities	473,656	613,511
Gross unrealized loss	16,001	20,130
Residential Mortgage-Backed Securities [Member] | Successor [Member]
Investment [Line Items]
Unrealized losses on securities	12,391
Ambac Wrapped Securities [Member] | Successor [Member]
Investment [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments		16,631
Asset-backed Securities [Member] | Successor [Member]
Investment [Line Items]
Unrealized losses on securities	155
Gains (losses) on securities held as of reporting date [Member] | Successor [Member]
Investment [Line Items]
Other investments		6,255	2,449
National Century Financial Enterprises, Inc. [Member]
Investment [Line Items]
Cash recoveries	$35	$0

Investments_Summary_of_Amounts

Investments - Summary of Amounts Included in Net Realized (Losses) Gains and Other-Than-Temporary Impairments (Detail) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Successor [Member]
Investment [Line Items]
Gross realized gains on securities	$50,654	$19,576
Gross realized losses on securities	-3,737	-1,128
Foreign exchange (losses) gains	7,184	-2,159
Net realized (losses) gains	54,101	16,289
Net other-than-temporary impairments	($3,119)	($10,392)

Investments_Summary_of_RollFor

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) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Successor [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance at beginning	$14,062	$1,182
Additions for credit impairments recognized on:
Securities not previously impaired	1,660	4,767
Securities previously impaired	1,457
Reductions for credit impairments previously recognized on:
Securities that matured or were sold during the period	0	0
Balance at end	$17,179	$5,949

Investments_Summary_of_Sources

Investments - Summary of Sources of Collateral Received and Various Investment Agreement in which Collateral Pledged (Detail) (Successor [Member], Cash and Securities Pledged Directly from Investment Portfolio [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Successor [Member] | Cash and Securities Pledged Directly from Investment Portfolio [Member]
Investment [Line Items]
Fair Value of Cash and Underlying Securities	$368,979	$379,423
Fair Value of Cash and Securities Pledged to Investment and Repurchase Agreement Counterparties	108,469	156,916
Fair Value of Cash and Securities Pledged to Derivative Counterparties	$260,510	$222,507

Investments_Summary_of_Fair_Va

Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Detail) (Successor [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Standard & Poor's, CCC- Rating [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	$2,132,208	$2,199,719
Standard & Poor's, A Rating [Member] | Assured Guaranty Municipal Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	121,519	119,492
Standard & Poor's, A- Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	64,693	67,895
Standard & Poor's, A+ Rating [Member] | MBIA Insurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	32,265	32,460
Standard & Poor's, CCC Rating [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	2,350,685	2,419,566
Municipal Bonds [Member] | Standard & Poor's, CCC- Rating [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	54,124	53,164
Municipal Bonds [Member] | Standard & Poor's, A Rating [Member] | Assured Guaranty Municipal Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	121,519	119,492
Municipal Bonds [Member] | Standard & Poor's, A- Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	64,693	67,895
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	240,336	240,551
Corporate Debt Securities [Member] | Standard & Poor's, A Rating [Member] | Assured Guaranty Municipal Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0	0
Corporate Debt Securities [Member] | Standard & Poor's, A- Rating [Member] | National Public Finance Guarantee Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	0	0
Corporate Debt Securities [Member] | Standard & Poor's, A+ Rating [Member] | MBIA Insurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	32,265	32,460
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	32,265	32,460
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, CCC- Rating [Member] | Ambac Assurance Corporation [Member]
Investment [Line Items]
Fair value of securities that include benefit of guarantees provided by financial guarantors	2,078,084	2,146,555
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	$2,078,084	$2,146,555

Investments_Summary_of_Fair_Va1

Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Parenthetical) (Detail) (Ambac UK [Member], USD $)	Mar. 31, 2015
In Thousands, unless otherwise specified
Ambac UK [Member]
Investment [Line Items]
Asset-backed securities fair value	$51,395

Investments_Summary_of_Net_Inv

Investments - Summary of Net Investment Income (Detail) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$7,819	$1,994
Trading Securities, Realized Gain (Loss)	1,564	-455
Fixed income securities	65,585	71,231
Short-term investments	42	57
Loans	132	117
Investment expense	-2,427	-2,598
Securities available-for-sale and short-term	63,332	68,807
Other investments	9,651	1,994
Total net investment income	72,983	70,801
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Other investments	$6,255	$2,449

Derivative_Instruments_Summary

Derivative Instruments - Summary of Gross Fair Values of Individual Derivative Instruments (Detail) (Successor [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets, Derivative Assets	$182,103	$163,683
Gross Amounts of Recognized Liabilities, Derivative Liabilities	515,837	461,610
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	68,481	54,666
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	68,481	54,666
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	113,622	109,017
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	447,356	406,944
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Assets	0	0
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities	196,981	170,135
Net Amount, Derivative Assets	113,622	109,017
Net Amount, Derivative Liabilities	250,375	236,809
Variable Interest Entities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Liabilities, Derivative Liabilities	2,125,713	2,200,163
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	0	0
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	2,125,713	2,200,163
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities	0	0
Net Amount, Derivative Liabilities	2,125,713	2,200,163
Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets, Derivative Assets	182,103	161,640
Gross Amounts of Recognized Liabilities, Derivative Liabilities	438,518	385,546
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	68,481	54,666
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	68,481	54,666
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	113,622	106,974
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	370,037	330,880
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities	196,039	169,573
Net Amount, Derivative Assets	113,622	106,974
Net Amount, Derivative Liabilities	173,998	161,307
Interest Rate Swaps [Member] | Variable Interest Entities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Liabilities, Derivative Liabilities	2,081,082	2,133,268
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	2,081,082	2,133,268
Net Amount, Derivative Liabilities	2,081,082	2,133,268
Futures Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Liabilities, Derivative Liabilities	942
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	0
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	942
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities	942
Net Amount, Derivative Liabilities	0
Credit Derivatives [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets, Derivative Assets	0	2,043
Gross Amounts of Recognized Liabilities, Derivative Liabilities	76,377	75,502
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	0	0
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	0	2,043
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	76,377	75,502
Net Amount, Derivative Assets	0	2,043
Net Amount, Derivative Liabilities	76,377	75,502
Currency Swaps [Member] | Variable Interest Entities [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Liabilities, Derivative Liabilities	44,631	66,895
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	44,631	66,895
Net Amount, Derivative Liabilities	$44,631	$66,895

Derivative_Instruments_Additio

Derivative Instruments - Additional Information (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Value of right to reclaim cash collateral and posted margin, recorded in "Other assets"	$195,697,000	$158,240,000
Value of obligation to return cash collateral, recorded in "Other liabilities"	0	0
Net liability fair value of all derivative instruments linked to Ambac's own credit risk	107,213,000	92,869,000
Fair value of posted assets as collateral	136,810,000	118,844,000
Credit Derivatives [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Number of credit derivative contracts	4	4
Net liability fair value of credit derivative contracts	61,338,000	60,729,000
Notional value of credit derivative contracts	$265,520,000	$270,747,000

Derivative_Instruments_Summary1

Derivative Instruments - Summary of Location and Amount of Gains and Losses of Derivative Contracts (Detail) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Derivative instruments, gain (loss) recognized in income, net, Total	$34,177	($118,843)
Net Change in Fair Value of Credit Derivatives [Member] | Credit Derivatives [Member] | Financial Guarantee [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Derivative instruments, gain (loss) recognized in income, net, Total	-2,499	7,382
Derivative Products [Member] | Financial Services Derivatives Products [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Derivative instruments, gain (loss) recognized in income, net, Total	-37,774	-53,841
Derivative Products [Member] | Interest Rate Swaps [Member] | Financial Services Derivatives Products [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Derivative instruments, gain (loss) recognized in income, net, Total	-35,547	-51,849
Derivative Products [Member] | Futures Contracts [Member] | Financial Services Derivatives Products [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Derivative instruments, gain (loss) recognized in income, net, Total	-2,227	-1,992
Income Loss On Variable Interest Entities [Member] | Variable Interest Entity [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Derivative instruments, gain (loss) recognized in income, net, Total	74,450	-72,384
Income Loss On Variable Interest Entities [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Derivative instruments, gain (loss) recognized in income, net, Total	52,186	-77,792
Income Loss On Variable Interest Entities [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Derivative instruments, gain (loss) recognized in income, net, Total	$22,264	$5,408

Derivative_Instruments_Summary2

Derivative Instruments - Summary of Gross Principal Notional Outstanding for CDS Contracts (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Ambac Rating
Notional outstanding	$1,594,571	$1,529,759
Other Derivatives [Member] | Successor [Member]
Ambac Rating
Notional outstanding	1,594,571	1,529,759
Other Derivatives [Member] | Successor [Member] | AAA Rating [Member]
Ambac Rating
Notional outstanding	0	0
Other Derivatives [Member] | Successor [Member] | AA Rating [Member]
Ambac Rating
Notional outstanding	770,313	767,603
Other Derivatives [Member] | Successor [Member] | A Rating [Member]
Ambac Rating
Notional outstanding	43,160	43,160
Other Derivatives [Member] | Successor [Member] | BBB Rating [Member]
Ambac Rating
Notional outstanding	515,578	448,249
Other Derivatives [Member] | Successor [Member] | Below Investment Grade Rating [Member]
Ambac Rating
Notional outstanding	265,520	270,747
CLO [Member] | Successor [Member]
Ambac Rating
Notional outstanding	466,453	549,923
CLO [Member] | Other Derivatives [Member] | Successor [Member]
Ambac Rating
Notional outstanding	466,453	549,923
CLO [Member] | Other Derivatives [Member] | Successor [Member] | AAA Rating [Member]
Ambac Rating
Notional outstanding	0	0
CLO [Member] | Other Derivatives [Member] | Successor [Member] | AA Rating [Member]
Ambac Rating
Notional outstanding	466,453	549,923
CLO [Member] | Other Derivatives [Member] | Successor [Member] | A Rating [Member] [Member]
Ambac Rating
Notional outstanding	0	0
Other [Member] | Successor [Member]
Ambac Rating
Notional outstanding	1,128,118	979,836
Other [Member] | Other Derivatives [Member] | Successor [Member]
Ambac Rating
Notional outstanding	1,128,118	979,836
Other [Member] | Other Derivatives [Member] | Successor [Member] | AAA Rating [Member]
Ambac Rating
Notional outstanding	0	0
Other [Member] | Other Derivatives [Member] | Successor [Member] | AA Rating [Member]
Ambac Rating
Notional outstanding	303,860	217,680
Other [Member] | Other Derivatives [Member] | Successor [Member] | A Rating [Member]
Ambac Rating
Notional outstanding	43,160	43,160
Other [Member] | Other Derivatives [Member] | Successor [Member] | BBB Rating [Member]
Ambac Rating
Notional outstanding	515,578	448,249
Other [Member] | Other Derivatives [Member] | Successor [Member] | Below Investment Grade Rating [Member]
Ambac Rating
Notional outstanding	$265,520	$270,747

Derivative_Instruments_Summari

Derivative Instruments - Summarize Information by Major Category of CDS Contracts (Detail) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
	Transactions	Transactions
Summary of information by major category of CDS contracts
Gross principal notional outstanding	1,594,571	1,529,759
Successor [Member]
Summary of information by major category of CDS contracts
Number of CDS transactions	15	16
Remaining expected weighted-average life of obligations (in years)	4 years 4 months 20 days	4 years 1 month 12 days
CLO [Member] | Successor [Member]
Summary of information by major category of CDS contracts
Number of CDS transactions	5	6
Remaining expected weighted-average life of obligations (in years)	1 year 6 months 1 day	1 year 9 months 18 days
Gross principal notional outstanding	466,453	549,923
CLO [Member] | Successor [Member] | Credit Derivatives [Member]
Summary of information by major category of CDS contracts
Net derivative liabilities at fair value	1,533	2,027
Other [Member] | Successor [Member]
Summary of information by major category of CDS contracts
Number of CDS transactions	10	10
Remaining expected weighted-average life of obligations (in years)	5 years 7 months 1 day	5 years 5 months 2 days
Gross principal notional outstanding	1,128,118	979,836
Other [Member] | Successor [Member] | Credit Derivatives [Member]
Summary of information by major category of CDS contracts
Net derivative liabilities at fair value	74,844	71,432

Derivative_Instruments_Summary3

Derivative Instruments - Summary of Notional Amounts of AFS's Trading Derivative Products (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	$1,594,571	$1,529,759
AFS [Member] | Successor [Member] | Interest Rate Swaps [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	760,808	782,904
AFS [Member] | Successor [Member] | Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	1,465,871	1,479,650
AFS [Member] | Successor [Member] | Interest Rate Swaps-Basis Swaps [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	55,800	55,800
AFS [Member] | Successor [Member] | Futures Contracts [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	$60,000	$80,000

Derivative_Instruments_Summary4

Derivative Instruments - Summary of Notional for VIE Derivatives Outstanding (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	$1,594,571	$1,529,759
Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member] | Interest Rate Swaps [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	1,629,458	1,710,344
Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member] | Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	3,003,021	3,152,090
Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member] | Currency Swaps [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	690,386	724,656
Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member] | Credit Derivatives [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	$16,249	$18,278

LongTerm_Debt_Details

Long-Term Debt (Details) (Successor [Member], USD $)	3 Months Ended		12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term debt	$979,001		971,116
Net realized losses on extinguishment of debt	($93)	$0
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%		5.10%
Debt Instruments Maturity Year	2020		2020
5.1% Surplus Notes, Segregated Account, Due 2020 [Member] | Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.10%		5.10%
Debt Instruments Maturity Year	2020		2020
5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member] | Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.10%		5.10%
Debt Instruments Maturity Year	2020		2020

Income_Taxes_Major_Jurisdictio

Income Taxes - Major Jurisdictions (Detail)	3 Months Ended
	Mar. 31, 2015
United States [Member]
Income Tax Contingency [Line Items]
Tax Year	2010
New York State [Member]
Income Tax Contingency [Line Items]
Tax Year	2011
New York City [Member]
Income Tax Contingency [Line Items]
Tax Year	2011
United Kingdom [Member]
Income Tax Contingency [Line Items]
Tax Year	2009
Italy [Member]
Income Tax Contingency [Line Items]
Tax Year	2009

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015
Tax Credit Carryforward [Line Items]
NOL allocated amount	$5,225,954
Operating tax carryforward expiration year start	2029
Operating tax carryforward expiration year end	2034
U. S. Federal Net Operating Tax [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	4,910,269
United States [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	133,626
United Kingdom [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	$182,059

Income_Taxes_Significant_Porti

Income Taxes - Significant Portions of Deferred Tax Liabilities and Deferred Tax Assets (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Deferred tax liabilities:
Insurance intangible	$471,553	$493,822
Variable interest entities	11,611	14,149
Investments	141,208	138,072
Unearned premiums and credit fees	101,647	104,589
Other	33,763	33,835
Total deferred tax liabilities	759,782	784,467
Deferred tax assets:
Net operating loss and capital carryforward	1,829,084	1,890,551
Loss reserves	146,429	185,881
Compensation	5,469	5,276
AMT Credits	11,899	10,359
Other	9,539	9,539
Sub total deferred tax assets	2,002,420	2,101,606
Valuation allowance	1,244,543	1,319,218
Total deferred tax assets	757,877	782,388
Net deferred tax asset (liability)	($1,905)	($2,079)

Income_Taxes_Income_Taxes_Prov

Income Taxes Income Taxes - Provision for Income Taxes Charged To Income From Continuing Operations (Details) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Successor [Member]
Provision for Income Taxes [Line Items]
Income tax expense (benefit)	$1,709	$3,249

Income_Taxes_Income_Taxes_Effe

Income Taxes Income Taxes - Effect of Income Taxes on Net Income and Stockholders' Equity (Details) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Successor [Member]
Income Tax Expense (Benefit) [Roll Forward]
Income tax expense (benefit)	$1,709	$3,249
Income tax expense (benefit)	$1,709	$3,249

Income_Taxes_Income_Taxes_Effe1

Income Taxes Income Taxes - Effective Tax Rates Differing From Prevailing Federal Corporate Income Tax Rates (Details) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Successor [Member]
Reconciliation of Effective Tax Rates [Line Items]
Provision for income taxes	$1,709	$3,249

Income_Taxes_Income_Taxes_NOL_

Income Taxes Income Taxes - NOL Usage Table (Details) (USD $)	Mar. 31, 2015
In Thousands, unless otherwise specified
Net Income Loss Reconciliation [Line Items]
NOL allocated amount	$5,225,954

Commitments_and_Contingencies_

Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
Loss Contingencies [Line Items]
Number of RMBS Trustees Filing Suit	5
Litigation Settlement, Expense	$207

Segment_Information_Additional

Segment Information - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015
	Segment
Segment Reporting [Abstract]
Number of reportable segments	2

Segment_Information_Summary_of

Segment Information - Summary of Financial Information by Reportable Segment (Detail) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Revenues:
Total revenues before expenses and reorganization items	$155,491	$109,138
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	216,580	159,298
Total assets	25,386,610	27,114,248	25,159,864
Net investment income	72,983	70,801
Amortization of insurance intangible assets	37,432	31,714
Interest expense	27,908	32,328
Reorganization items	0	23
Unaffiliated Customers [Member]
Revenues:
Total revenues before expenses and reorganization items	154,463	109,138
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	215,552	159,298
Equity Method Investee [Member]
Revenues:
Total revenues before expenses and reorganization items	1,028	0
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	1,028	0
Intersegment [Member]
Revenues:
Total revenues before expenses and reorganization items	0	0
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	0	0
Financial Guarantee [Member]
Revenues:
Total revenues before expenses and reorganization items	192,071	162,928
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	255,466	208,001
Total assets	24,672,977	26,535,119
Net investment income	71,470	70,384
Amortization of insurance intangible assets	37,432	31,714
Interest expense	27,585	31,881
Financial Guarantee [Member] | Unaffiliated Customers [Member]
Revenues:
Total revenues before expenses and reorganization items	191,814	162,553
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	256,005	217,158
Financial Guarantee [Member] | Equity Method Investee [Member]
Revenues:
Total revenues before expenses and reorganization items	0	0
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	0	0
Financial Guarantee [Member] | Intersegment [Member]
Revenues:
Total revenues before expenses and reorganization items	257	375
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	-539	-9,157
Financial Services [Member]
Revenues:
Total revenues before expenses and reorganization items	-37,938	-53,513
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	-38,892	-54,904
Total assets	431,445	534,256
Net investment income	128	394
Amortization of insurance intangible assets	0	0
Interest expense	323	447
Financial Services [Member] | Unaffiliated Customers [Member]
Revenues:
Total revenues before expenses and reorganization items	-37,708	-53,438
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	-38,580	-54,450
Financial Services [Member] | Equity Method Investee [Member]
Revenues:
Total revenues before expenses and reorganization items	0	0
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	0	0
Financial Services [Member] | Intersegment [Member]
Revenues:
Total revenues before expenses and reorganization items	-230	-75
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	-312	-454
Corporate and Other [Member]
Revenues:
Total revenues before expenses and reorganization items	1,358	8,658
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	6	6,201
Total assets	282,188	44,873
Net investment income	1,385	23
Amortization of insurance intangible assets	0	0
Interest expense	0	0
Corporate and Other [Member] | Unaffiliated Customers [Member]
Revenues:
Total revenues before expenses and reorganization items	357	23
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	-1,873	-3,410
Corporate and Other [Member] | Equity Method Investee [Member]
Revenues:
Total revenues before expenses and reorganization items	1,028	0
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	1,028	0
Corporate and Other [Member] | Intersegment [Member]
Revenues:
Total revenues before expenses and reorganization items	-27	8,635
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	851	9,611
Inter-segment Eliminations [Member] | Intersegment [Member]
Revenues:
Total revenues before expenses and reorganization items	0	-8,935
Inter-segment Eliminations [Member] | Inter-segment Eliminations [Member]
Revenues:
Total revenues before expenses and reorganization items	0	-8,935
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	0	0
Total assets	0	0
Net investment income	0	0
Amortization of insurance intangible assets	0	0
Interest expense	0	0
Inter-segment Eliminations [Member] | Inter-segment Eliminations [Member] | Unaffiliated Customers [Member]
Revenues:
Total revenues before expenses and reorganization items	0	0
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	0	0
Inter-segment Eliminations [Member] | Inter-segment Eliminations [Member] | Equity Method Investee [Member]
Revenues:
Total revenues before expenses and reorganization items	0	0
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	0	0
Inter-segment Eliminations [Member] | Inter-segment Eliminations [Member] | Intersegment [Member]
Pre-tax income (loss) from continuing operations:
Pre-tax (loss) income from continuing operations	$0	$0

Segment_Information_Schedule_o

Segment Information - Schedule of Gross Premiums Written, Net Premiums Earned and Net Change in Fair Value of Credit Derivatives (Detail) (Successor [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Gross Premiums Written	$1,062	($5,766)
Net premiums earned	65,718	82,547
Net Change In Fair Value Of Credit Derivatives	-2,499	7,382
Reportable Geographical Components [Member] | United States [Member]
Segment Reporting Information [Line Items]
Gross Premiums Written	-2,366	-699
Net premiums earned	52,739	56,758
Net Change In Fair Value Of Credit Derivatives	3,958	6,581
Reportable Geographical Components [Member] | United Kingdom [Member]
Segment Reporting Information [Line Items]
Gross Premiums Written	9,174	-6,166
Net premiums earned	7,582	20,635
Net Change In Fair Value Of Credit Derivatives	0	0
Reportable Geographical Components [Member] | Other International [Member]
Segment Reporting Information [Line Items]
Gross Premiums Written	-5,746	1,099
Net premiums earned	5,397	5,154
Net Change In Fair Value Of Credit Derivatives	($6,457)	$801