Schedule I - Summary Of Investments (Details) - Successor [Member] - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	$ 6,351,348
Investments	6,500,215	$ 5,644,720
Available-for-sale Securities, Amortized Cost Basis	5,931,045	5,283,157
Available-for-sale Securities	6,049,908	5,334,120
Other Investments and Securities, at Cost	420,303
Other investments	450,307	310,600
Corporate Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities	2,622,566	2,588,556
U.S. Government Obligations [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities	101,091
Residential Mortgage-Backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities, Amortized Cost Basis	2,284,425
Available-for-sale Securities	2,351,595
Collateralized Debt Obligations [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities, Amortized Cost Basis	113,650
Available-for-sale Securities	113,923
Asset-backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities, Amortized Cost Basis	778,383
Available-for-sale Securities	828,783
Short-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities, Amortized Cost Basis	430,827	225,789
Available-for-sale Securities	430,788	225,789
U S Government Obligations [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	98,565
Fixed Income Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities, Amortized Cost Basis	5,435,385	4,992,756
Available-for-sale Securities	5,554,215	5,043,776
Fixed Income Securities [Member] \| Municipal Bonds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities, Amortized Cost Basis	376,064	424,048
Available-for-sale Securities	374,368	420,770
Fixed Income Securities [Member] \| Corporate Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,803,136	1,610,912
Available-for-sale Securities	1,802,165	1,593,669
Fixed Income Securities [Member] \| Foreign Government Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities, Amortized Cost Basis	41,932	96,638
Available-for-sale Securities	43,135	96,306
Fixed Income Securities [Member] \| U.S. Agency Obligations [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities, Amortized Cost Basis	4,063	4,239
Available-for-sale Securities	4,060	4,212
Fixed Income Securities [Member] \| Residential Mortgage-Backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities, Amortized Cost Basis	2,284,425	1,942,285
Available-for-sale Securities	2,351,595	1,977,338
Fixed Income Securities [Member] \| Collateralized Debt Obligations [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities, Amortized Cost Basis	113,650	85,706
Available-for-sale Securities	113,923	84,267
Fixed Income Securities [Member] \| Asset-backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Available-for-sale Securities, Amortized Cost Basis	778,383	802,842
Available-for-sale Securities	$ 828,783	$ 840,527

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

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

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

+ Details

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

- Definition

Sum of the carrying amounts as of the balance sheet date of all investments.

+ References

+ Details

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

- Definition

Other investments not otherwise specified in the taxonomy.

+ 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 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(f,g))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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

- Definition

Includes other investments and securities that are not at fair value as of the balance sheet date and those that are not accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph a
-Subparagraph 1(g)
-Article 7

+ Details

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

- Definition

This item represents the original cost of the entity's investments including investments in equity securities and, as to fixed maturities, original cost reduced by repayments and adjusted for amortization of premiums or accrual of discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15)
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611379-123010

+ Details

Name:	us-gaap_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesCost
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_SummaryOfInvestmentsOtherThanInvestmentsInRelatedPartiesReportableDataLineItems
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=ambc_U.S.GovernmentObligationsMember
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_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_ShortTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=ambc_USGovernmentObligationsMember
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_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_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: