Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments (Detail) - Successor [Member] - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 5,298,840	$ 4,939,325
Gross Unrealized Gains	158,969	242,962
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	71,181	32,269
Estimated Fair Value	5,386,628	5,150,018
Non - credit other - than - temporary Impairments	27,439	7,773
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	2,679,895	2,743,050
Short-Term [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	364,784	360,069
Gross Unrealized Gains	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	4	4
Estimated Fair Value	364,780	360,065
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,869,500	4,514,878
Gross Unrealized Gains	158,553	242,962
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	71,177	32,154
Estimated Fair Value	4,956,876	4,725,686
Non - credit other - than - temporary Impairments	27,439	7,773
Fixed Income Securities [Member] \| Securities Pledged as Collateral [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	64,556	64,378
Gross Unrealized Gains	416	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	111
Estimated Fair Value	64,972	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	420,465	523,019
Gross Unrealized Gains	5,217	9,769
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	6,681	6,996
Estimated Fair Value	419,001	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	1,593,457	1,382,195
Gross Unrealized Gains	11,739	12,815
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	17,618	9,416
Estimated Fair Value	1,587,578	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	104,226	126,041
Gross Unrealized Gains	1,710	3,060
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2,282	1,344
Estimated Fair Value	103,654	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	30,410	42,328
Gross Unrealized Gains	672	1,078
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	219	427
Estimated Fair Value	30,863	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	64,556	64,378
Gross Unrealized Gains	416	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	111
Estimated Fair Value	64,972	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	4,283	29,524
Gross Unrealized Gains	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2	38
Estimated Fair Value	4,281	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	1,797,616	1,557,059
Gross Unrealized Gains	116,052	167,396
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	42,185	13,500
Estimated Fair Value	1,871,483	1,710,955
Non - credit other - than - temporary Impairments	27,439	7,773
Fixed Income Securities [Member] \| Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	82,734	21,346
Gross Unrealized Gains	54	50
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	876	274
Estimated Fair Value	81,912	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	836,309	833,366
Gross Unrealized Gains	23,109	48,794
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1,314	159
Estimated Fair Value	858,104	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	5,234,284	4,874,947
Gross Unrealized Gains	158,553	242,962
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	71,181	32,158
Estimated Fair Value	5,321,656	5,085,751
Non - credit other - than - temporary Impairments	$ 27,439	$ 7,773

Non credit other than temporary impairments on investments.

No definition available.

Name:	ambc_NonCreditOtherThanTemporaryImpairmentsOnInvestments
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562

+ Details

Name:	us-gaap_AvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAmortizedCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_SuccessorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_ShortTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_FixedIncomeSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_SecuritiesPledgedAsCollateralMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MunicipalBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CollateralizedDebtObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=ambc_FixedIncomeInvestmentsAndOtherInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: