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Long-Term Debt (Details) - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Jan. 19, 2021 | 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 |  | $ 2,739 | $ 2,822 |  |  |  |  |
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 | $ 3 |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months |  | 531 |  |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Year Two |  | 0 |  |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Year Three |  | 1,641 |  |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Year Four |  | 0 |  |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Year Five |  | 0 |  |  |  |  |  |
Paydown of Ambac Note |  | 121 | 178 | $ 214 |  |  |  |
Long-term Debt, Maturities, Repayments of Principal after Year Five |  | $ 712 |  |  |  |  |  |
Ambac Note Post Exit From Rehabilitation [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 7.60% |  |  |  |  |  |
Paydown of Ambac Note |  | $ (121) | (178) |  |  |  |  |
Tier 2 Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 8.50% |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 9.90% |  |  |  |  |  |
Debt Instrument, Face Amount |  | $ 306 |  |  |  |  |  |
Paid-in-Kind Interest |  | $ 66 | 41 |  |  |  |  |
5.1% Surplus Notes, General Account, Due 2020 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 10.10% |  |  |  |  |  |
5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 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 | 15 |  |  |  |  |
Debt Instrument Principal Amount Subject To Repurchase |  | 0 |  |  |  |  |  |
Extinguishment of Debt, Amount | $ 2 | $ 0 |  |  |  |  |  |
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% |  |  |  |  |  |
Ambac Assurance Corporation [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt |  | $ 2,739 | 2,822 |  |  |  |  |
Long-term Debt, Gross |  | 2,884 | 2,980 |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  | (145) | (159) |  |  |  |  |
Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes, General Account Due 2020 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt |  | 247 | 252 |  |  |  |  |
Long-term Debt, Gross |  | 365 | 365 |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  | (118) | (113) |  |  |  |  |
Ambac Assurance Corporation [Member] | Ambac Note Post Exit From Rehabilitation [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt |  | 1,641 | 1,763 |  |  |  |  |
Long-term Debt, Gross |  | 1,641 | 1,763 |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  | 0 | 0 |  |  |  |  |
Ambac Assurance Corporation [Member] | Tier 2 Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt |  | 306 | 278 |  |  |  |  |
Long-term Debt, Gross |  | 306 | 281 |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  | 0 | (4) |  |  |  |  |
Ambac Assurance Corporation [Member] | 5.1% Surplus Notes, General Account, Due 2020 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term debt |  | 531 | 517 |  |  |  |  |
Long-term Debt, Gross |  | 531 | 531 |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  | $ 0 | (14) |  |  |  |  |
Ambac Assurance Corporation [Member] | 5.1% Surplus Notes, General Account, Due 2020 [Member] | Corolla Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt Issued in Exchange Transaction |  |  |  |  | $ 267 |  |  |
Ambac Assurance Corporation [Member] | 5.1% Surplus Notes, General Account, Due 2020 [Member] | Corolla Notes and Lease Reducing |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt Issued in Exchange Transaction |  |  |  |  | $ 279 |  |  |
Ambac UK [Member] | Secured Debt [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 0.00% |  |  |  |  |  |
Long-term debt |  | $ 14 | 13 |  |  |  |  |
Long-term Debt, Gross |  | 41 | 41 |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  | $ (27) | $ (28) |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 7.40% |  |  |  |  |  |
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% |  |  |  |  |
5.1 % Surplus Notes Due 2020 [Member] | Ambac Assurance Corporation [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 5.10% | 5.10% |  |  |  |  |
5.1 % Surplus Notes Due 2020 [Member] | Ambac Assurance Corporation [Member] | Corolla Notes |  |  |  |  |  |  |  |
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 |  | $ 3,927 | $ 3,990 |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months |  | 0 |  |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Year Two |  | 0 |  |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Year Three |  | 0 |  |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Year Four |  | 0 |  |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal in Year Five |  | 83 |  |  |  |  |  |
Long-term Debt, Maturities, Repayments of Principal after Year Five |  | $ 3,844 |  |  |  |  |  |
Consolidated Variable Interest Entities [Member] | Minimum [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 0.00% | 0.00% |  |  |  |  |
Consolidated Variable Interest Entities [Member] | Maximum [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 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 |  |  |  |  |  |

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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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