Aggregate payment to repurchase surplus notes.

No definition available.

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

- Definition

Aggregate principal amount of surplus notes that may be repurchased at a discount under call option agreements.

+ References

No definition available.

+ Details

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

- Definition

Debt Instruments Maturity Year

+ References

No definition available.

+ Details

Name:	ambc_DebtInstrumentsMaturityYear
Namespace Prefix:	ambc_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Principal amount of surplus notes for which repurchase approval was declined by the insurance regulator.

+ References

No definition available.

+ Details

Name:	ambc_SurplusNoteRepurchaseAmountNotApproved
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Unpaid Principal Amount Of Fixed Rate Debt Accounted For Under Fair Value Option

+ References

No definition available.

+ Details

Name:	ambc_UnpaidPrincipalAmountOfFixedRateDebtAccountedForUnderFairValueOption
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

+ Details

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

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

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

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

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

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Definition

Face (par) amount of the original debt instrument that was repurchased.

+ References

No definition available.

+ Details

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

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 50

-Section 40

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6850294&loc=d3e12317-112629

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 50

-Section 40

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6850294&loc=d3e12355-112629

+ Details

Name:	us-gaap_GainsLossesOnExtinguishmentOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 7

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20, 22

-Article 5

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 3

-Subparagraph (SX 210.12-04.(a))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Details

Name:	us-gaap_CounterpartyNameAxis=ambc_Ambc_NonconsolidatedVIETrustMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CounterpartyNameAxis=ambc_OneStateStreetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=ambc_A5.1JuniorSurplusNotesSegregatedAccountDue2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=ambc_A5.1SurplusNotesGeneralAccountDue2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=ambc_A5.1SurplusNotesSegregatedAccountDue2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=ambc_ConsolidatedVariableInterestEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term Debt (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			4 Months Ended	3 Months Ended				8 Months Ended
	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2012	Apr. 30, 2013	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2012
Debt Instrument [Line Items]
Debt Instrument Principal Amount Subject To Repurchase			$ 939,179
Surplus Note Repurchase Amount Not Approved	150,000
5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		10.50%			10.50%
Debt Instrument, Repurchased Face Amount			789,179
Net realized losses on extinguishment of debt		71,590	177,745
Debt Instrument, Face Amount	1,210,821	893,300			893,300				1,210,821
5.1% Surplus Notes, Segregated Account, Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		10.50%			10.50%
Aggregate Payment To Repurchase Surplus Notes										188,446
Net realized losses on extinguishment of debt		3,134
Debt Instrument, Face Amount	53,000	39,102			39,102				53,000
5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		19.50%			19.50%
Debt Instrument, Face Amount	28,039	378,039			378,039	350,000			28,039
One State Street [Member] \| 5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		28,039			28,039
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member] \| 5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		8.40%			8.40%
Predecessor [Member]
Debt Instrument [Line Items]
Long-term debt				155,271
Net realized losses on extinguishment of debt			(177,580)	0
Predecessor [Member] \| 5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage				53.90%
Predecessor [Member] \| 5.1% Surplus Notes, Segregated Account, Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage				52.80%
Predecessor [Member] \| 5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage				58.30%
Successor [Member]
Debt Instrument [Line Items]
Long-term debt	963,178	971,116		940,313	971,116				963,178
Net realized losses on extinguishment of debt		(74,724)			(74,724)	0	0	0	0
Successor [Member] \| Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Long-term debt	963,178	971,116			971,116				963,178
Successor [Member] \| Ambac Assurance Corporation [Member] \| 5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	909,186	696,330			696,330				909,186
Successor [Member] \| Ambac Assurance Corporation [Member] \| 5.1% Surplus Notes, Segregated Account, Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	39,797	30,479			30,479				39,797
Successor [Member] \| Ambac Assurance Corporation [Member] \| 5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	14,195	244,307			244,307				14,195
Successor [Member] \| Variable Interest Entities [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.65%								6.65%
Long-term debt	14,091,753	12,882,076			12,882,076				14,091,753
Successor [Member] \| 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%			5.10%
Debt Instruments Maturity Year	2020	2020
Successor [Member] \| 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%			5.10%
Debt Instruments Maturity Year	2020	2020
Successor [Member] \| 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%			5.10%
Debt Instruments Maturity Year	2020	2020
Consolidated Variable Interest Entities [Member]
Debt Instrument [Line Items]
Unpaid Principal Amount Of Fixed Rate Debt Accounted For Under Fair Value Option	14,251,771	11,925,499			11,925,499				14,251,771
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months		77,920			77,920
Long-term Debt, Maturities, Repayments of Principal in Year Two		0			0
Long-term Debt, Maturities, Repayments of Principal in Year Three		0			0
Long-term Debt, Maturities, Repayments of Principal in Year Four		162,939			162,939
Long-term Debt, Maturities, Repayments of Principal in Year Five		$ 393,235			$ 393,235
Consolidated Variable Interest Entities [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	0.50%	0.69%			0.69%				0.50%
Consolidated Variable Interest Entities [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	13.00%	13.00%			13.00%				13.00%