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Long-Term Debt (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Aug. 03, 2018 | Feb. 12, 2018 | May 01, 2013
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tier 2 Note Security in RMBS Litigation Settlement Proceeds |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,600 |
Long-term debt | $ 2,822 |  |  |  | $ 2,929 |  |  |  | $ 2,822 | $ 2,929 |  |  |  |
One Time Interest Payment on Surplus Notes |  |  |  |  |  |  |  |  |  |  |  |  | $ 14 |
Junior surplus note of Ambac Assurance Segregated Account |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 350
AMPS Exchange Total Surplus Notes Issued |  |  |  |  |  |  |  |  |  |  |  | $ 213 |  |
Net realized gains (losses) on extinguishment of debt | 0 | $ 0 | $ 0 | $ 0 | 0 | $ 0 | $ 0 | $ 3 | 0 | 3 | $ 5 |  |  |
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months | 531 |  |  |  |  |  |  |  | 531 |  |  |  |  |
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 | 1,763 |  |  |  |  |  |  |  | 1,763 |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Year Five | 0 |  |  |  |  |  |  |  | 0 |  |  |  |  |
Paydown of Ambac Note |  |  |  |  |  |  |  |  | 178 | 214 |  |  |  |
Long-term Debt, Maturities, Repayments of Principal after Year Five | $ 687 |  |  |  |  |  |  |  | $ 687 |  |  |  |  |
Ambac Note Post Exit From Rehabilitation [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 7.60% |  |  |  |  |  |  |  | 7.60% |  |  |  |  |
Paydown of Ambac Note |  |  |  |  |  |  |  |  | $ (178) | (214) |  |  |  |
Tier 2 Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 8.50% |  |  |  |  |  |  |  | 8.50% |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 9.90% |  |  |  |  |  |  |  | 9.90% |  |  |  |  |
Debt Instrument, Face Amount | $ 281 |  |  |  |  |  |  |  | $ 281 |  |  |  |  |
Paid-in-Kind Interest |  |  |  |  |  |  |  |  | $ 41 | 19 |  |  |  |
5.1% Surplus Notes, General Account, Due 2020 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 10.10% |  |  |  |  |  |  |  | 10.10% |  |  |  |  |
Net realized gains (losses) on extinguishment of debt |  |  |  |  |  |  |  |  |  | 3 |  |  |  |
5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 19.50% |  |  |  |  |  |  |  | 19.50% |  |  |  |  |
One State Street [Member] | 5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | $ 15 |  |  |  | 17 |  |  |  | $ 15 | 17 |  |  |  |
Debt Instrument Principal Amount Subject To Repurchase | $ 0 |  |  |  |  |  |  |  | 0 |  |  |  |  |
Extinguishment of Debt, Amount |  |  |  |  |  |  |  |  | $ 2 | 4 |  |  |  |
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% |  |  |  |  |
Ambac Assurance Corporation [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | $ 2,822 |  |  |  | 2,929 |  |  |  | $ 2,822 | 2,929 |  |  |  |
Long-term Debt, Gross | 2,980 |  |  |  | 3,096 |  |  |  | 2,980 | 3,096 |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net | (159) |  |  |  | (167) |  |  |  | (159) | (167) |  |  |  |
Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes, General Account Due 2020 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | 252 |  |  |  | 250 |  |  |  | 252 | 250 |  |  |  |
Long-term Debt, Gross | 365 |  |  |  | 367 |  |  |  | 365 | 367 |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net | (113) |  |  |  | (117) |  |  |  | (113) | (117) |  |  |  |
Ambac Assurance Corporation [Member] | Ambac Note Post Exit From Rehabilitation [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | 1,763 |  |  |  | 1,940 |  |  |  | 1,763 | 1,940 |  |  |  |
Long-term Debt, Gross | 1,763 |  |  |  | 1,940 |  |  |  | 1,763 | 1,940 |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net | 0 |  |  |  | 0 |  |  |  | 0 | 0 |  |  |  |
Ambac Assurance Corporation [Member] | Tier 2 Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | 278 |  |  |  | 252 |  |  |  | 278 | 252 |  |  |  |
Long-term Debt, Gross | 281 |  |  |  | 259 |  |  |  | 281 | 259 |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net | (4) |  |  |  | (7) |  |  |  | (4) | (7) |  |  |  |
Ambac Assurance Corporation [Member] | 5.1% Surplus Notes, General Account, Due 2020 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | 517 |  |  |  | 487 |  |  |  | 517 | 487 |  |  |  |
Long-term Debt, Gross | 531 |  |  |  | 531 |  |  |  | 531 | 531 |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net | $ (14) |  |  |  | (44) |  |  |  | $ (14) | (44) |  |  |  |
Ambac UK [Member] | Secured Debt [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 0.00% |  |  |  |  |  |  |  | 0.00% |  |  |  |  |
Long-term debt | $ 13 |  |  |  | 0 |  |  |  | $ 13 | 0 |  |  |  |
Long-term Debt, Gross | 41 |  |  |  | 0 |  |  |  | 41 | 0 |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net | $ (28) |  |  |  | $ 0 |  |  |  | $ (28) | $ 0 |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 7.40% |  |  |  |  |  |  |  | 7.40% |  |  |  |  |
Variable Interest Entities [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  |  |  |  | 6.65% |  |  |
5.1% Junior Surplus Notes 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 |  |  |
5.1 % Surplus Notes 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 |  |  |
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% |
Consolidated Variable Interest Entities [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unpaid Principal Amount Of Fixed Rate Debt Accounted For Under Fair Value Option | $ 3,990 |  |  |  | $ 4,553 |  |  |  | $ 3,990 | $ 4,553 |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months | 0 |  |  |  |  |  |  |  | 0 |  |  |  |  |
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 | 0 |  |  |  |  |  |  |  | 0 |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Year Five | 0 |  |  |  |  |  |  |  | 0 |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal after Year Five | $ 3,990 |  |  |  |  |  |  |  | $ 3,990 |  |  |  |  |
Consolidated Variable Interest Entities [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 0.00% |  |  |  | 1.36% |  |  |  | 0.00% | 1.36% |  |  |  |
Consolidated Variable Interest Entities [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 7.93% |  |  |  | 7.93% |  |  |  | 7.93% | 7.93% |  |  |  |
London Interbank Offered Rate (LIBOR) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest Rate on Ambac Note Post Exit From Rehabilitation |  |  |  |  |  |  |  |  | 5.00% |  |  |  |  |
London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest Rate on Ambac Note Post Exit From Rehabilitation |  |  |  |  |  |  |  |  | 1.00% |  |  |  |  |
Ambac [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
One Time Interest Payment on Surplus Notes |  |  |  |  |  |  |  |  |  |  |  |  | $ 3 |
Long-term Debt [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain Contingency, Unrecorded Amount | $ 1,400 |  |  |  |  |  |  |  | $ 1,400 |  |  |  |  |

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- Definition Junior Surplus Notes issued by the Segregated Account of Ambac Assurance to Ambac upon Ambac's emergence from bankruptcy. These Junior Surplus notes will be includable in surplus for statutory accounting purposes as prescribed or permitted by state laws and regulations. + References No definition available. + Details
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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -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=119400593&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -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 4: http://fasb.org/us-gaap/role/ref/legacyRef -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 + Details
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