Long-Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jul. 06, 2021
Debt Instrument [Line Items]
Long-term debt	$ 508	$ 639
Debt Instrument, Interest Rate, Effective Percentage	6.60%
Net realized gains on extinguishment of debt	$ 0	81	$ 33
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	519
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	0
Paydown of Ambac Note			1,641
Long-term Debt, Maturities, Repayments of Principal after Year Five	41
5.1% Junior Surplus Notes, General Account Due 2020 Plus Accrued Interest	$ 475
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	$ 0
Paid-in-Kind Interest	0	49
5.1% Junior Surplus Notes, General Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Issued, Principal			280
Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Long-term debt	508	639
Long-term Debt, Gross	560	706
Debt Instrument, Unamortized Discount (Premium), Net	(52)	(67)
Ambac Assurance Corporation [Member] | 5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	491	477
Long-term Debt, Gross	519	519
Debt Instrument, Unamortized Discount (Premium), Net	(28)	(42)
Ambac Assurance Corporation [Member] | Tier 2 Notes [Member]
Debt Instrument [Line Items]
Long-term debt	0	146
Long-term Debt, Gross	0	146
Debt Instrument, Unamortized Discount (Premium), Net	0	0
Ambac Assurance Corporation [Member] | Sitka AAC Note
Debt Instrument [Line Items]
Net realized gains on extinguishment of debt	$ 53
Ambac UK [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	0.00%
Long-term debt	$ 17	16
Long-term Debt, Gross	41	41
Debt Instrument, Unamortized Discount (Premium), Net	$ (24)	(25)
Debt Instrument, Interest Rate, Effective Percentage	7.40%
Sitka Holdings, LLC | LIBOR + 4.5% Senor Secured Notes Due 2026
Debt Instrument [Line Items]
Debt Instrument, Face Amount				$ 1,175
5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Net realized gains on extinguishment of debt		134
Debt Instrument, Repurchased During Period	$ 266
5.1% Junior Surplus Notes, General Account Due 2020 [Member]
Debt Instrument [Line Items]
Net realized gains on extinguishment of debt			$ 33
Consolidated Variable Interest Entities [Member]
Debt Instrument [Line Items]
Unpaid Principal Amount Of Fixed Rate Debt Accounted For Under Fair Value Option	3,655	$ 3,388
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	0
Long-term Debt, Maturities, Repayments of Principal after Year Five	$ 3,655
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	22.20%	7.93%
London Interbank Offered Rate (LIBOR) [Member] | LIBOR + 4.5% Senor Secured Notes Due 2026
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				4.50%