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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.

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Debt Instrument Principal Amount Subject To Reduction

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Debt Instruments Maturity Year

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Interest Rate on Ambac Note Post Exit From Rehabilitation

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One Time Interest Payment on Surplus Notes

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Paydown of Ambac Note

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Tier 2 Note Security in RMBS Litigation Settlement Proceeds

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

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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.

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

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

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Amount of unamortized debt discount (premium) and debt issuance costs.

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Gross amount of debt extinguished.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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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 after 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.

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Long-Term Debt (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
Long-Term Debt (Details) - USD ($) $ in Millions	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