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Long-Term Debt (Details) - USD ($) $ in Millions	12 Months Ended			36 Months Ended
Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jul. 06, 2026	Feb. 12, 2018
Debt Instrument [Line Items]
Tier 2 Note Security in RMBS Litigation Settlement Proceeds					$ 1,600
Long-term debt	$ 2,230	$ 2,739
Debt Instrument, Interest Rate, Effective Percentage	8.90%
Net realized gains (losses) on extinguishment of debt	$ 33	0	$ 0
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	785
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	1,175
Paydown of Ambac Note	1,641	121	178
Long-term Debt, Maturities, Repayments of Principal after Year Five	373
Make Whole Percentage of Principal				103.00%
Reb & Warranty Subrogation Recoveries Up To	1,400
Aggregate Par Amount Reissued	$ 255
Discretionary Tier 2 Note Mandatory and Optional Redemption Percent by AAC	100.00%
Ambac Note Post Exit From Rehabilitation [Member]
Debt Instrument [Line Items]
Paydown of Ambac Note	$ (1,641)	(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	$ 333
Paid-in-Kind Interest	$ 93	66
5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	10.10%
Sitka AAC Note
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	5.70%
Debt Instrument, Redemption Price, Percentage				100.00%
Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Long-term debt	$ 2,230	2,739
Long-term Debt, Gross	2,334	2,884
Debt Instrument, Unamortized Discount (Premium), Net	(104)	(145)
Ambac Assurance Corporation [Member] \| 5.1% Junior Surplus Notes, General Account Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	0	247
Long-term Debt, Gross	0	365
Debt Instrument, Unamortized Discount (Premium), Net	0	(118)
Ambac Assurance Corporation [Member] \| Ambac Note Post Exit From Rehabilitation [Member]
Debt Instrument [Line Items]
Long-term debt	0	1,641
Long-term Debt, Gross	0	1,641
Debt Instrument, Unamortized Discount (Premium), Net	0	0
Ambac Assurance Corporation [Member] \| Tier 2 Notes [Member]
Debt Instrument [Line Items]
Long-term debt	333	306
Long-term Debt, Gross	333	306
Debt Instrument, Unamortized Discount (Premium), Net	0	0
Ambac Assurance Corporation [Member] \| 5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	729	531
Long-term Debt, Gross	785	531
Debt Instrument, Unamortized Discount (Premium), Net	(56)	0
Ambac Assurance Corporation [Member] \| Sitka AAC Note
Debt Instrument [Line Items]
Long-term debt	1,154	0
Debt Instrument, Unamortized Discount (Premium), Net	(21)	0
Debt Instrument, Face Amount	$ 1,175	0
Ambac UK [Member] \| Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	0.00%
Long-term debt	$ 15	14
Long-term Debt, Gross	41	41
Debt Instrument, Unamortized Discount (Premium), Net	$ (26)	$ (27)
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%
Consolidated Variable Interest Entities [Member]
Debt Instrument [Line Items]
Unpaid Principal Amount Of Fixed Rate Debt Accounted For Under Fair Value Option	$ 3,739	$ 3,927
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	56
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Long-term Debt, Maturities, Repayments of Principal after Year Five	$ 3,683
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] \| Sitka AAC Note
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	4.50%
London Interbank Offered Rate (LIBOR) [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest Rate on Ambac Note Post Exit From Rehabilitation	1.00%
London Interbank Offered Rate (LIBOR) [Member] \| Minimum [Member] \| Sitka AAC Note
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	0.75%
Long-term Debt [Member]
Debt Instrument [Line Items]
Gain Contingency, Unrecorded Amount	$ 1,400