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Financial Guarantee Insurance Contracts (Tables) | 12 Months Ended
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Dec. 31, 2019
Insurance [Line Items] |
Schedule of Revenue from External Customers Attributed to Foreign Countries by Geographic Area [Table Text Block] | The following table summarizes net premiums earned by location of risk:
Year Ended December 31, |  | 2019 |  | 2018 |  | 2017
United States |  | $ | 55 |  |  | $ | 88 |  |  | $ | 134 |
United Kingdom |  | 17 |  |  | 19 |  |  | 33 |
Other international |  | (6 | ) |  | 5 |  |  | 8 |
Total |  | $ | 66 |  |  | $ | 111 |  |  | $ | 175 |
Summary of Gross Premium Receivable Roll-Forward (Direct and Assumed Contracts) | Below is the gross premium receivable roll-forward (direct and assumed contracts) for the affected periods:
Year Ended December 31, | 2019 |  | 2018 |  | 2017
Beginning premium receivable | $ | 495 |  |  | $ | 586 |  |  | $ | 661 |
Premium receipts | (48 | ) |  | (56 | ) |  | (82 | )
Adjustments for changes in expected and contractual cash flows (1) | (38 | ) |  | (42 | ) |  | (30 | )
Accretion of premium receivable discount | 11 |  |  | 15 |  |  | 16 |
Deconsolidation of certain VIEs | 3 |  |  | — |  |  | — |
Changes to uncollectable premiums | (2 | ) |  | 2 |  |  | — |
Other adjustments (including foreign exchange) | (6 | ) |  | (10 | ) |  | 21 |
Ending premium receivable (2) | $ | 416 |  |  | $ | 495 |  |  | $ | 586 |
(1) | Adjustments for changes in expected and contractual cash flows primarily due to reductions in insured exposure as a result of early policy terminations and unscheduled principal paydowns.
(2) Premium receivable includes premiums to be received in foreign denominated currencies most notably in British Pounds and Euros. At December 31, 2019, 2018 and 2017 premium receivables include British Pounds of $129 (£97), $131 (£103) and $152 (£112), respectively, and Euros of $26 (€23), $31 (€27) and $36 (€30), respectively.
Schedule Of Reinsurance Recoverable And Provision By Category Of Reinsurer [Table Text Block] | The following table represents the percentage ceded to reinsurers and unsecured reinsurance recoverable at December 31, 2019.
Reinsurers |  | Percentage Ceded Par |  | Net Unsecured Reinsurance Recoverable (1)
Assured Guaranty Re Ltd |  | 47% |  | $ | — |
Build America Mutual Assurance Company (2) |  | 42 |  | 36 |
Assured Guaranty Corporation |  | 8 |  | 5 |
Sompo Japan Nipponkoa Insurance, Inc. |  | 3 |  | — |
Total |  | 100% |  | $ | 41 |
(1) | Represents reinsurance recoverables on paid and unpaid losses and deferred ceded premiums, net of ceded premium payables due to reinsurers, letters of credit, and collateral posted for the benefit of Ambac Assurance.
(2) Build America Mutual Assurance Company has an S&P rating of AA.
Effect of Reinsurance on Premiums Written and Earned | The effect of reinsurance on premiums written and earned was as follows:
Year Ended December 31, | Direct |  | Assumed |  | Ceded (1) |  | Net Premiums
2019: |  |  |  |  |  |  |
Written | $ | (28 | ) |  | $ | — |  |  | $ | 31 |  |  | $ | (60 | )
Earned | 75 |  |  | — |  |  | 10 |  |  | 66 |
2018: |  |  |  |  |  |  |
Written | $ | (24 | ) |  | $ | — |  |  | $ | 17 |  |  | $ | (41 | )
Earned | 119 |  |  | — |  |  | 8 |  |  | 111 |
2017: |  |  |  |  |  |  |
Written | $ | (14 | ) |  | $ | — |  |  | $ | (2 | ) |  | $ | (12 | )
Earned | 190 |  |  | — |  |  | 15 |  |  | 175 |
(1) Includes ceded premium activity related to the execution of reinsurance transactions in the years ended December 31, 2019 and 2018.
Summarized Future Gross Undiscounted Premiums Expected to be Collected and Future Expected Premiums Earned, Net of Reinsurance | The table below summarizes the future gross undiscounted premiums to be collected and future premiums earned, net of reinsurance at December 31, 2019:
| Future Premiums to be Collected (1) |  | Future Premiums to be Earned Net of Reinsurance (2)
Three months ended: |  |  |
March 31, 2020 | $ | 14 |  |  | $ | 10 |
June 30, 2020 | 11 |  |  | 10 |
September 30, 2020 | 10 |  |  | 10 |
December 31, 2020 | 9 |  |  | 10 |
Twelve months ended: |  |  |
December 31, 2021 | 37 |  |  | 36 |
December 31, 2022 | 36 |  |  | 34 |
December 31, 2023 | 34 |  |  | 32 |
December 31, 2024 | 33 |  |  | 30 |
Five years ended: |  |  |
December 31, 2029 | 143 |  |  | 124 |
December 31, 2034 | 102 |  |  | 82 |
December 31, 2039 | 47 |  |  | 38 |
December 31, 2044 | 22 |  |  | 14 |
December 31, 2049 | 9 |  |  | 5 |
December 31, 2054 | 1 |  |  | 1 |
Total | $ | 508 |  |  | $ | 436 |
(1) | Future premiums to be collected are undiscounted and are used to derive the discounted premium receivable asset recorded on Ambac's balance sheet.
(2) Future premiums to be earned, net of reinsurance relate to the unearned premiums liability and deferred ceded premium asset recorded on Ambac’s balance sheet. The use of contractual lives for many bond types which do not have homogeneous pools of underlying collateral is required in the calculation of the premium receivable as further described in Note 2. Basis of Presentation and Significant Accounting Policies. This results in a different premium receivable balance than if expected lives were considered. If installment paying policies are retired or prepay early, premiums reflected in the premium receivable asset and amounts reported in the above table for such policies may not be collected. Future premiums to be earned also considers the use of contractual lives for many bond types which do not have homogeneous pools of underlying collateral, which may result in different unearned premium than if expected lives were considered. If those bonds types are retired early, premium earnings may be negative in the period of call or refinancing.
Schedule of Loss And Loss Expense Reserves And Subrogation Recoverable Table [Table Text Block] | Below are the components of the Loss and loss expense reserves liability and the Subrogation recoverable asset at December 31, 2019 and 2018:
| Present Value of Expected Net Cash Flows |  | Unearned Premium Revenue |  | Gross Loss and Loss Expense Reserves
Balance Sheet Line Item | Claims and Loss Expenses |  | Recoveries |  |
December 31, 2019: |  |  |  |  |  |  |
Loss and loss expense reserves | $ | 1,835 |  |  | $ | (233 | ) |  | $ | (54 | ) |  | $ | 1,548 |
Subrogation recoverable | 131 |  |  | (2,160 | ) |  | — |  |  | (2,029 | )
Totals | $ | 1,966 |  |  | $ | (2,394 | ) |  | $ | (54 | ) |  | $ | (482 | )
December 31, 2018: |  |  |  |  |  |  |
Loss and loss expense reserves | $ | 2,246 |  |  | $ | (314 | ) |  | $ | (107 | ) |  | $ | 1,826 |
Subrogation recoverable | 176 |  |  | (2,109 | ) |  | — |  |  | (1,933 | )
Totals | $ | 2,422 |  |  | $ | (2,422 | ) |  | $ | (107 | ) |  | $ | (107 | )
Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance | Below is the loss and loss expense reserve roll-forward, net of subrogation recoverable and reinsurance, for the affected periods.
Year Ended December 31, | 2019 |  | 2018 |  | 2017
Beginning gross loss and loss expense reserves | $ | (107 | ) |  | $ | 4,114 |  |  | $ | 3,696 |
Reinsurance recoverable | 23 |  |  | 41 |  |  | 31 |
Beginning balance of net loss and loss expense reserves | (130 | ) |  | 4,073 |  |  | 3,665 |
Losses and loss expenses (benefit) incurred: |  |  |  |  |
Current year | 1 |  |  | 5 |  |  | 6 |
Prior years (1) | 12 |  |  | (228 | ) |  | 507 |
Total (2)(3) | 13 |  |  | (224 | ) |  | 513 |
Loss and loss expenses (recovered) paid: |  |  |  |  |
Current year | — |  |  | — |  |  | 1 |
Prior years (1) | 318 |  |  | 3,963 |  |  | 133 |
Total | 318 |  |  | 3,964 |  |  | 134 |
Foreign exchange effect | (1 | ) |  | (15 | ) |  | 29 |
Ending net loss and loss expense reserves | (436 | ) |  | (130 | ) |  | 4,073 |
Impact of VIE consolidation | (72 | ) |  | — |  |  | — |
Reinsurance recoverable (4) | 26 |  |  | 23 |  |  | 41 |
Ending gross loss and loss expense reserves | (482 | ) |  | (107 | ) |  | 4,114 |
(1) | 2018 loss and loss expenses (recovered) paid includes the settlement of Deferred Amounts and Interest Accrued on Deferred Amounts in the amount of $3,000 and $857, respectively in connection with the Rehabilitation Exit Transactions through a combination of cash, surplus notes and secured notes. 2018 loss and loss expenses incurred includes a $288 loss and loss expense benefit on these settled Deferred Amounts.
(2) | Total losses and loss expenses (benefit) includes $(7), $(2) and $20 for the years ended December 31, 2019, 2018 and 2017, respectively, related to ceded reinsurance.
(3) | Ambac records the impact of estimated recoveries related to securitized loans in RMBS transactions that breached certain representations and warranties within losses and loss expenses (benefit). The losses and loss expense (benefit) incurred associated with changes in estimated representation and warranty recoveries for the year ended December 31, 2019, 2018 and 2017 was $42, $62 and $72, respectively.
(4) Represents reinsurance recoverable on future loss and loss expenses. Additionally, the Balance Sheet line "Reinsurance recoverable on paid and unpaid losses" includes reinsurance recoverables (payables) of $0, $1 and $0 as of December 31, 2019, 2018 and 2017, respectively, related to previously presented loss and loss expenses and subrogation.
Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable | tables below summarize information related to policies currently included in Ambac’s loss and loss expense reserves or subrogation recoverable at December 31, 2019 and 2018. Gross par exposures include capital appreciation bonds which are reported at the par amount at the time of issuance of the insurance policy as opposed to the current accreted value of the bond. The weighted average risk-free rate used to discount loss reserves at December 31, 2019 and 2018 was 2.1% and 2.8%, respectively.
|  | Surveillance Categories as of December 31, 2019
|  | I |  | IA |  | II |  | III |  | IV |  | V |  | Total
Number of policies |  | 34 |  |  | 18 |  |  | 11 |  |  | 16 |  |  | 139 |  |  | 3 |  |  | 221 |
Remaining weighted-average contract period (in years) (1) |  | 8 |  |  | 21 |  |  | 9 |  |  | 17 |  |  | 14 |  |  | 3 |  |  | 15 |
Gross insured contractual payments outstanding: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal |  | $ | 668 |  |  | $ | 510 |  |  | $ | 277 |  |  | $ | 857 |  |  | $ | 3,819 |  |  | $ | 37 |  |  | $ | 6,168 |
Interest |  | 340 |  |  | 507 |  |  | 128 |  |  | 366 |  |  | 1,678 |  |  | 11 |  |  | 3,029 |
Total |  | $ | 1,007 |  |  | $ | 1,016 |  |  | $ | 404 |  |  | $ | 1,223 |  |  | $ | 5,498 |  |  | $ | 48 |  |  | $ | 9,197 |
Gross undiscounted claim liability |  | $ | 2 |  |  | $ | 44 |  |  | $ | 21 |  |  | $ | 541 |  |  | $ | 1,778 |  |  | $ | 48 |  |  | $ | 2,434 |
Discount, gross claim liability |  | — |  |  | (5 | ) |  | (1 | ) |  | (152 | ) |  | (381 | ) |  | (2 | ) |  | (541 | )
Gross claim liability before all subrogation and before reinsurance |  | $ | 2 |  |  | $ | 39 |  |  | $ | 20 |  |  | $ | 389 |  |  | $ | 1,397 |  |  | $ | 46 |  |  | $ | 1,893 |
Less: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross RMBS subrogation (2) |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | (1,777 | ) |  | $ | — |  |  | $ | (1,777 | )
Discount, RMBS subrogation |  | — |  |  | — |  |  | — |  |  | — |  |  | 49 |  |  | — |  |  | 49 |
Discounted RMBS subrogation, before reinsurance |  | — |  |  | — |  |  | — |  |  | — |  |  | (1,727 | ) |  | — |  |  | (1,727 | )
Less: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross other subrogation (3) |  | — |  |  | — |  |  | — |  |  | (41 | ) |  | (666 | ) |  | (13 | ) |  | (720 | )
Discount, other subrogation |  | — |  |  | — |  |  | — |  |  | 4 |  |  | 47 |  |  | 3 |  |  | 53 |
Discounted other subrogation, before reinsurance |  | — |  |  | — |  |  | — |  |  | (37 | ) |  | (620 | ) |  | (10 | ) |  | (666 | )
Gross claim liability, net of all subrogation and discounts, before reinsurance |  | $ | 2 |  |  | $ | 39 |  |  | $ | 20 |  |  | $ | 353 |  |  | $ | (950 | ) |  | $ | 36 |  |  | $ | (501 | )
Less: Unearned premium revenue |  | $ | (1 | ) |  | $ | (9 | ) |  | $ | (1 | ) |  | $ | (7 | ) |  | $ | (35 | ) |  | $ | — |  |  | $ | (54 | )
Plus: Loss expense reserves |  | 1 |  |  | 1 |  |  | 1 |  |  | 4 |  |  | 67 |  |  | — |  |  | 73 |
Gross loss and loss expense reserves |  | $ | 1 |  |  | $ | 30 |  |  | $ | 20 |  |  | $ | 349 |  |  | $ | (918 | ) |  | $ | 36 |  |  | $ | (482 | )
Reinsurance recoverable reported on Balance Sheet (4) |  | $ | — |  |  | $ | 6 |  |  | $ | 7 |  |  | $ | 24 |  |  | $ | (10 | ) |  | $ | — |  |  | $ | 26 |
(1) | Remaining weighted-average contract period is weighted based on projected gross claims over the lives of the respective policies.
(2) | RMBS subrogation represents Ambac’s estimate of subrogation recoveries from RMBS transaction sponsors for representation and warranty ("R&W") breaches.
(3) | Other subrogation represents subrogation related to excess spread and other contractual cash flows on public finance and structured finance transactions including RMBS.
(4) | Reinsurance recoverable reported on Balance Sheet includes reinsurance recoverables of $26 related to future loss and loss expenses and $0 related to presented loss and loss expenses and subrogation.
|  | Surveillance Categories as of December 31, 2018
|  | I |  | IA |  | II |  | III |  | IV |  | V |  | Total
Number of policies |  | 21 |  |  | 28 |  |  | 18 |  |  | 16 |  |  | 145 |  |  | 3 |  |  | 231 |
Remaining weighted-average contract period (in years) (1) |  | 9 |  |  | 19 |  |  | 9 |  |  | 22 |  |  | 14 |  |  | 3 |  |  | 16 |
Gross insured contractual payments outstanding: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal |  | $ | 917 |  |  | $ | 708 |  |  | $ | 623 |  |  | $ | 1,705 |  |  | $ | 5,407 |  |  | $ | 43 |  |  | $ | 9,403 |
Interest |  | 488 |  |  | 632 |  |  | 293 |  |  | 6,979 |  |  | 2,178 |  |  | 13 |  |  | 10,583 |
Total |  | $ | 1,404 |  |  | $ | 1,340 |  |  | $ | 916 |  |  | $ | 8,685 |  |  | $ | 7,585 |  |  | $ | 57 |  |  | $ | 19,986 |
Gross undiscounted claim liability |  | $ | 4 |  |  | $ | 64 |  |  | $ | 36 |  |  | $ | 992 |  |  | $ | 2,296 |  |  | $ | 57 |  |  | $ | 3,448 |
Discount, gross claim liability |  | — |  |  | (13 | ) |  | (3 | ) |  | (434 | ) |  | (638 | ) |  | (4 | ) |  | (1,092 | )
Gross claim liability before all subrogation and before reinsurance |  | $ | 4 |  |  | $ | 51 |  |  | $ | 33 |  |  | $ | 558 |  |  | $ | 1,658 |  |  | $ | 52 |  |  | $ | 2,356 |
Less: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross RMBS subrogation (2) |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | (1,810 | ) |  | $ | — |  |  | $ | (1,810 | )
Discount, RMBS subrogation |  | — |  |  | — |  |  | — |  |  | — |  |  | 39 |  |  | — |  |  | 39 |
Discounted RMBS subrogation, before reinsurance |  | — |  |  | — |  |  | — |  |  | — |  |  | (1,771 | ) |  | — |  |  | (1,771 | )
Less: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross other subrogation (3) |  | — |  |  | (11 | ) |  | — |  |  | (137 | ) |  | (625 | ) |  | (13 | ) |  | (785 | )
Discount, other subrogation |  | — |  |  | 7 |  |  | — |  |  | 67 |  |  | 55 |  |  | 4 |  |  | 133 |
Discounted other subrogation, before reinsurance |  | — |  |  | (3 | ) |  | — |  |  | (70 | ) |  | (570 | ) |  | (9 | ) |  | (652 | )
Gross claim liability, net of all subrogation and discounts, before reinsurance |  | $ | 4 |  |  | $ | 47 |  |  | $ | 33 |  |  | $ | 489 |  |  | $ | (682 | ) |  | $ | 43 |  |  | $ | (66 | )
Less: Unearned premium revenue |  | $ | (1 | ) |  | $ | (10 | ) |  | $ | (5 | ) |  | $ | (36 | ) |  | $ | (54 | ) |  | $ | — |  |  | $ | (107 | )
Plus: Loss expense reserves |  | 1 |  |  | 4 |  |  | 3 |  |  | (6 | ) |  | 63 |  |  | — |  |  | 66 |
Gross loss and loss expense reserves |  | $ | 4 |  |  | $ | 41 |  |  | $ | 30 |  |  | $ | 446 |  |  | $ | (672 | ) |  | $ | 43 |  |  | $ | (107 | )
Reinsurance recoverable reported on Balance Sheet (4) |  | $ | — |  |  | $ | 7 |  |  | $ | 4 |  |  | $ | 26 |  |  | $ | (15 | ) |  | $ | — |  |  | $ | 23 |
(1) | Remaining weighted-average contract period is weighted based on projected gross claims over the lives of the respective policies.
(2) | RMBS subrogation represents Ambac's estimate of subrogation recoveries from RMBS transaction sponsors for R&W breaches.
(3) | Other subrogation represents subrogation related to excess spread and other contractual cash flows on public finance and structured finance transactions, including RMBS.
(4) Reinsurance recoverable reported on Balance Sheet includes reinsurance recoverables of $23 related to future loss and loss expenses and $1 related to presented loss and loss expenses and subrogation.
Summary of Rollforward of RMBS Subrogation, by Estimation Approach | w is the rollforward of RMBS R&W subrogation for the affected periods:
Year ended December 31, | 2019 |  | 2018 |  | 2017
Discounted RMBS subrogation recovery (gross of reinsurance) at beginning of year | $ | 1,771 |  |  | $ | 1,834 |  |  | $ | 1,907 |
All other changes (1) | (43 | ) |  | (64 | ) |  | (73 | )
Discounted RMBS subrogation recovery (gross of reinsurance) at end of year | $ | 1,727 |  |  | $ | 1,771 |  |  | $ | 1,834 |
(1) All other changes which may impact RMBS R&W subrogation recoveries include changes in actual or projected collateral performance, changes in the creditworthiness of a sponsor and the projected timing of recoveries. All other changes may also include estimates of potential sponsor settlements that may not have been subject to a sampling approach or have been executed, but the settlement amounts have not yet been received. Those that have not been subject to a sampling approach are not material to Ambac’s financial results and therefore are included in this table.
Insurance Intangible Asset [Member] |
Insurance [Line Items] |
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] | The estimated future amortization expense for the net insurance intangible asset is as follows:
Amortization expense (1) (2) |
2020 | $ | 45 |
2021 | 39 |
2022 | 36 |
2023 | 33 |
2024 | 30 |
Thereafter | 244 |
(1) | The insurance intangible asset will be amortized using a level-yield method based on par exposure of the related financial guarantee insurance or reinsurance contracts as described in Note 2. Basis of Presentation and Significant Accounting Policies. Future amortization considers the use of contractual lives for many bond types which do not have homogeneous pools of underlying collateral. Actual maturities will differ from contractual maturities because borrowers may have the right to call or prepay certain obligations. If those bonds types are retired early, amortization expense may differ in the period of call or refinancing from the amounts provided in the table above.
(2) The weighted-average amortizations period is 7.6 years.

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- Definition Tabular disclosure of insured financial obligations with credit deterioration related to the claim liability on financial guarantee insurance contracts as of the end of each annual and interim reporting period detailing, at a minimum, the following for each surveillance category or grouping used to track and monitor the entity's insured financial obligations: (1) number of issued and outstanding financial guarantee insurance contracts; (2) remaining weighted average contract period; (3) insured contractual payments outstanding, segregating principal and interest; (4) gross claim liability; (5) gross potential recoveries; (6) net discount of both the claim liability and potential recoveries; (7) net claim liability; (8) reinsurance recoverable; and (9) unearned premium revenue. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 55 -Paragraph 34 -URI http://asc.fasb.org/extlink&oid=99379334&loc=SL5751140-161288 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 9 -Subparagraph (a)(5), (b)(1) -URI http://asc.fasb.org/extlink&oid=99382878&loc=SL5749324-161292 + Details
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- Definition Tabular disclosure of the activity in the reserve for settling insured claims and expenses incurred in the claims settlement process for the period. The estimated liability includes the amount of money that will be required for future payments of (a) claims that have been reported to the insurer, (b) claims related to insured events that have occurred but that have not been reported to the insurer as of the date the liability is estimated, and (c) claim adjustment expenses. Claim adjustment expenses include costs incurred in the claim settlement process such as legal fees; outside adjuster fees; and costs to record, process, and adjust claims. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
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- Definition Tabular disclosure of the names of foreign countries from which revenue is material and the amount of revenue from external customers attributed to those countries. An entity may also provide subtotals of geographic information about groups of countries. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 41 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e9038-108599 + Details
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