Fair Value Measurements - Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financial assets:
Other investments	$ 290,723	$ 240,969
Other assets	9,322	12,036
Financial liabilities:
Derivative liabilities	29,887	73,459
Successor [Member]
Financial assets:
Fixed income securities	5,386,628	5,150,018
Short term investments	364,780	360,065
Successor [Member] \| Total Fair Value [Member]
Financial assets:
Other investments	302,791	349,468
Cash	27,099	73,903
Loans	5,479	5,634
Total financial assets	20,691,258	20,822,011
Financial liabilities:
Obligations under investment and repurchase agreements	100,858	161,821
Liabilities for net financial guarantees written	3,044,698	4,539,000
Long-term debt	1,318,300	1,379,864
Total financial liabilities	19,664,498	21,569,868
Successor [Member] \| Total Fair Value [Member] \| Variable Interest Entity [Member]
Financial assets:
Restricted cash	5,895	7,708
Loans	12,183,061	12,371,177
Financial liabilities:
Long-term debt	12,791,012	12,882,076
Successor [Member] \| Carrying Amount [Member]
Financial assets:
Other investments	314,934	357,016
Cash	27,099	73,903
Loans	5,499	5,714
Total financial assets	20,703,421	20,829,639
Financial liabilities:
Obligations under investment and repurchase agreements	100,358	160,079
Liabilities for net financial guarantees written	2,414,692	2,923,652
Long-term debt	1,457,996	1,273,805
Total financial liabilities	19,173,688	19,846,719
Successor [Member] \| Carrying Amount [Member] \| Variable Interest Entity [Member]
Financial assets:
Restricted cash	5,895	7,708
Loans	12,183,061	12,371,177
Financial liabilities:
Long-term debt	12,791,012	12,882,076
Successor [Member] \| Level 1 [Member]
Financial assets:
Other investments	0	0
Cash	27,099	73,903
Loans	0	0
Total financial assets	434,779	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	220	562
Successor [Member] \| Level 1 [Member] \| Variable Interest Entity [Member]
Financial assets:
Restricted cash	5,895	7,708
Loans	0	0
Financial liabilities:
Long-term debt	0	0
Successor [Member] \| Level 2 [Member]
Financial assets:
Other investments	290,723	336,013
Cash	0	0
Loans	0	0
Total financial assets	4,915,573	4,929,368
Financial liabilities:
Obligations under investment and repurchase agreements	0	0
Liabilities for net financial guarantees written	0	0
Long-term debt	139,002	0
Total financial liabilities	13,026,541	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	10,647,480	11,618,412
Successor [Member] \| Level 3 [Member]
Financial assets:
Other investments	12,068	13,455
Cash	0	0
Loans	5,479	5,634
Total financial assets	15,340,906	15,345,596
Financial liabilities:
Obligations under investment and repurchase agreements	100,858	161,821
Liabilities for net financial guarantees written	3,044,698	4,539,000
Long-term debt	1,179,298	1,379,864
Total financial liabilities	6,637,737	7,561,738
Successor [Member] \| Level 3 [Member] \| Variable Interest Entity [Member]
Financial assets:
Restricted cash	0	0
Loans	12,183,061	12,371,177
Financial liabilities:
Long-term debt	2,143,532	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	89,743	106,974
Derivative assets - interest rate swaps - liability position	0
Successor [Member] \| Interest Rate Swaps [Member] \| Carrying Amount [Member]
Financial assets:
Derivative assets	89,743	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	23,796	106,974
Derivative assets - interest rate swaps - liability position	0	0
Successor [Member] \| Interest Rate Swaps [Member] \| Level 3 [Member]
Financial assets:
Derivative assets	65,947	0
Derivative assets - interest rate swaps - liability position	0	0
Successor [Member] \| Municipal Bonds [Member] \| Total Fair Value [Member]
Financial assets:
Fixed income securities	419,001	525,792
Successor [Member] \| Municipal Bonds [Member] \| Carrying Amount [Member]
Financial assets:
Fixed income securities	419,001	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	419,001	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	1,587,578	1,385,594
Successor [Member] \| Corporate Obligations [Member] \| Total Fair Value [Member] \| Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,679,895	2,743,050
Successor [Member] \| Corporate Obligations [Member] \| Carrying Amount [Member]
Financial assets:
Fixed income securities	1,587,578	1,385,594
Successor [Member] \| Corporate Obligations [Member] \| Carrying Amount [Member] \| Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,679,895	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	1,587,578	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	2,679,895	2,743,050
Successor [Member] \| Foreign Obligations [Member] \| Total Fair Value [Member]
Financial assets:
Fixed income securities	103,654	127,757
Successor [Member] \| Foreign Obligations [Member] \| Carrying Amount [Member]
Financial assets:
Fixed income securities	103,654	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	103,654	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	30,863	42,979
Fixed income securities, pledged as collateral	64,972	64,267
Successor [Member] \| US Government Debt Securities [Member] \| Carrying Amount [Member]
Financial assets:
Fixed income securities	30,863	42,979
Fixed income securities, pledged as collateral	64,972	64,267
Successor [Member] \| US Government Debt Securities [Member] \| Level 1 [Member]
Financial assets:
Fixed income securities	30,863	42,979
Fixed income securities, pledged as collateral	64,972	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	4,281	29,486
Successor [Member] \| U.S. Agency Obligations [Member] \| Carrying Amount [Member]
Financial assets:
Fixed income securities	4,281	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	4,281	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	1,871,483	1,710,955
Successor [Member] \| Residential Mortgage-Backed Securities [Member] \| Carrying Amount [Member]
Financial assets:
Fixed income securities	1,871,483	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	1,487,694	1,516,562
Successor [Member] \| Residential Mortgage-Backed Securities [Member] \| Level 3 [Member]
Financial assets:
Fixed income securities	383,789	194,393
Successor [Member] \| Collateralized Debt Obligations [Member] \| Total Fair Value [Member]
Financial assets:
Fixed income securities	81,912	21,122
Successor [Member] \| Collateralized Debt Obligations [Member] \| Carrying Amount [Member]
Financial assets:
Fixed income securities	81,912	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	81,912	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	858,104	882,001
Successor [Member] \| Asset-backed Securities [Member] \| Carrying Amount [Member]
Financial assets:
Fixed income securities	858,104	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	858,104	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	364,780	360,065
Successor [Member] \| Short-Term [Member] \| Carrying Amount [Member]
Financial assets:
Short term investments	364,780	360,065
Successor [Member] \| Short-Term [Member] \| Level 1 [Member]
Financial assets:
Short term investments	305,950	358,190
Successor [Member] \| Short-Term [Member] \| Level 2 [Member]
Financial assets:
Short term investments	58,830	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	1,345	2,043
Successor [Member] \| Credit Derivatives [Member] \| Carrying Amount [Member]
Financial assets:
Derivative assets	1,345	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	1,345	2,043
Successor [Member] \| Other Assets [Member] \| Total Fair Value [Member]
Financial assets:
Other assets	9,322	12,036
Successor [Member] \| Other Assets [Member] \| Carrying Amount [Member]
Financial assets:
Other assets	9,322	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	9,322	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	220	562
Futures Contracts [Member] \| Successor [Member] \| Carrying Amount [Member]
Financial liabilities:
Derivative liabilities	220	562
Futures Contracts [Member] \| Successor [Member] \| Level 1 [Member]
Financial liabilities:
Derivative liabilities	220	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	(63,785)	(54,666)
Derivative liabilities	408,168	385,546
Interest Rate Swaps [Member] \| Successor [Member] \| Total Fair Value [Member] \| Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	2,065,224	2,133,268
Interest Rate Swaps [Member] \| Successor [Member] \| Carrying Amount [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	(63,785)	(54,666)
Derivative liabilities	408,168	385,546
Interest Rate Swaps [Member] \| Successor [Member] \| Carrying Amount [Member] \| Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	2,065,224	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	(63,785)	(54,666)
Derivative liabilities	270,049	243,659
Interest Rate Swaps [Member] \| Successor [Member] \| Level 2 [Member] \| Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	2,065,224	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	138,119	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	31,232	75,502
Credit Derivatives [Member] \| Successor [Member] \| Carrying Amount [Member]
Financial liabilities:
Derivative liabilities	31,232	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	31,232	75,502
Currency Swaps [Member] \| Successor [Member] \| Total Fair Value [Member] \| Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	(31,429)	66,895
Currency Swaps [Member] \| Successor [Member] \| Carrying Amount [Member] \| Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	(31,429)	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	$ (31,429)	66,895
Currency Swaps [Member] \| Successor [Member] \| Level 3 [Member] \| Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities		$ 0

Guaranteed investment agreements at fair value.

No definition available.

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- Definition

Fair value of restricted cash and cash equivalents.

+ References

No definition available.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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- Definition

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

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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-Name Accounting Standards Codification

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- Definition

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Fair value of asset associated with financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

+ References

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- Definition

Fair value portion of investments accounted under the equity method.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 25

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=35740979&loc=d3e32014-111567

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- References

No definition available.

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- References

No definition available.

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- Definition

Fair value portion of guarantee, including, but not limited to, financial standby letter of credit, fair value guarantee, guarantee of collection of scheduled contractual cash flows from financial assets, and contracts that contingently require the guarantor to make payments or perform services.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12201-110248

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- Definition

Fair value of financial and nonfinancial obligations.

+ References

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Glossary Loan

-URI http://asc.fasb.org/extlink&oid=6517073

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

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- Definition

Other investments not otherwise specified in the taxonomy.

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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)

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(f,g))

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- Definition

Other investments not otherwise specified in the taxonomy that will be realized in a short period of time, usually less than one year or the normal operating cycle, whichever is longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.5)

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-Topic 210

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-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.8)

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-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(g))

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- Definition

Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (b)(1)(i)

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6467456&loc=d3e113888-111728

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