Insurance [Line Items]

No definition available.

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- Definition

Percentage of financial guarantee premiums receivable related to insured transactions with non-investment grade internal ratings.

+ References

No definition available.

+ Details

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- Definition

Percentage of Premiums Receivable Related to Non Investment Grade Structured Finance Transactions

+ References

No definition available.

+ Details

Name:	ambc_PercentageofPremiumsReceivableRelatedtoNonInvestmentGradeStructuredFinanceTransactions
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Period Type:	duration

- Definition

Past due premiums on policies insuring internally rated non-investment grade obligations.

+ References

No definition available.

+ Details

Name:	ambc_PremiumsPastDueOnNonInvestmentGradeObligation
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Balance Type:	debit
Period Type:	duration

- Definition

Amount of increase (decrease) in the allowance for doubtful accounts.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the premium receivable for financial guarantee insurance contracts reported in the statement of financial position. This element primarily would consist of those financial guarantee insurance contracts which premiums are to be collected over the contract period, but may, on occasion, include premiums which are to be collected in full at inception, but which straddle a financial reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 50
-Paragraph 3
-Subparagraph (c)(1),(5)
-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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

- Definition

Amount of cash inflow from premiums received for premium receivable on financial guarantee insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 50
-Paragraph 3
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Amount of accretion of the discount for premiums receivable on financial guarantee insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 50
-Paragraph 3
-Subparagraph (c)(4)(iii)
-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of increase (decrease) in the premium receivable on financial guarantee insurance contracts from changes in the period of the contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 50
-Paragraph 3
-Subparagraph (c)(4)(i)
-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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Balance Type:	debit
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- Definition

Amount of increase (decrease) in the premiums receivable on financial guarantee insurance contracts from adjustments classified as other.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 50
-Paragraph 3
-Subparagraph (c)(4)(iv)
-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the estimated valuation allowance to reduce gross premiums receivable to net realizable value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.5)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_PremiumsReceivableAllowanceForDoubtfulAccounts
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Balance Type:	credit
Period Type:	instant

- Details

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Financial Guarantee Insurance Contracts - Summary of Gross Premium Receivable Roll-Forward (Direct and Assumed Contracts) (Detail) € in Thousands, £ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 GBP (£)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 EUR (€)	Dec. 31, 2016 GBP (£)	Dec. 31, 2015 USD ($)
Successor [Member]
Insurance [Line Items]
Premiums Receivable, Allowance for Doubtful Accounts	$ 9,331			$ 9,186
Percentage Premiums Receivable Related To Transactions With Non Investment Grade Internal Ratings	22.00%	22.00%	22.00%	25.00%	25.00%	25.00%
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Beginning premium receivable	$ 661,337			$ 831,575			$ 1,000,607
Premium receipts	81,597			77,038			(108,029)
Adjustments for changes in expected and contractual cash flows	(30,334)			(78,528)			(64,740)
Accretion of premium receivable discount	16,162			18,637			24,628
Uncollectable premiums	(141)			6,054			2,540
Other adjustments (including foreign exchange)	20,885			(39,363)			(23,431)
Ending premium receivable	$ 586,312			$ 661,337			831,575
Percentage of Premiums Receivable Related to Non Investment Grade Structured Finance Transactions	16.00%	16.00%	16.00%	16.00%	16.00%	16.00%
Premiums Past Due On Non Investment Grade Obligation	$ 500
United Kingdom, Pounds
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Beginning premium receivable	177,878		£ 144,393	$ 226,994		£ 154,135
Ending premium receivable	151,852		£ 112,342	177,878		£ 144,393	226,994
Euro Member Countries, Euro
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Beginning premium receivable	34,866	€ 33,108		43,451	€ 40,014
Ending premium receivable	$ 36,001	€ 29,976		$ 34,866	€ 33,108		$ 43,451