Variable Interest Entities Special Purpose Entities, including Variable Interest Entities - Summary of Assets and Liabilities (Details) $ in Millions	Mar. 31, 2022 USD ($) Entity	Dec. 31, 2021 USD ($) Entity	Mar. 31, 2021 USD ($)
Debt Securities, Available-for-sale, Amortized Cost	$ 2,005
Fixed maturity securities, at fair value	2,036
Restricted Cash	7	$ 5	$ 16
Derivative assets	55	76
Other assets	94	68
Total assets	11,531	12,303	12,840
Interest Payable	593	576
Long-term debt	2,242	2,230
Derivative Liability	76	95
Other Liabilities	135	133
Liabilities	10,538	11,187
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	73	141
Ambac Assurance Corporation [Member] | Sitka AAC Note
Long-term debt	1,155	1,154
Variable Interest Entity, Primary Beneficiary [Member]
Fixed maturity securities, at fair value	3,364	3,455
Restricted Cash	49	2	$ 2
Financing Receivable, after Allowance for Credit Loss	2,469	2,718
Derivative assets	42	38
Other assets	1	2
Total assets	5,925	6,216
Long-term debt	3,701	4,056
Long-term Debt, at par less amortized discount	422	160
Long-term debt	4,124	4,216
Derivative Liability	1,866	1,940
Other Liabilities	3	0
Liabilities	5,993	6,156
Variable Interest Entity, Primary Beneficiary [Member] | Corporate Debt Securities [Member]
Fixed maturity securities, at fair value	3,131	3,320
Variable Interest Entity, Primary Beneficiary [Member] | Municipal Bonds [Member]
Debt Securities, Available-for-sale, Amortized Cost	103	106
Fixed maturity securities, at fair value	119	136
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	17	29
Variable Interest Entity, Primary Beneficiary [Member] | US States and Political Subdivisions Debt Securities
Fixed maturity securities, at fair value	114	0
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member]
Fixed maturity securities, at fair value	3,131	3,320
Restricted Cash	1	1
Financing Receivable, after Allowance for Credit Loss	2,469	2,718
Derivative assets	42	38
Other assets	0	0
Total assets	5,643	6,077
Long-term debt	3,701	4,056
Long-term Debt, at par less amortized discount	0	0
Long-term debt	3,701	4,056
Derivative Liability	1,866	1,940
Other Liabilities	0	0
Liabilities	5,568	5,996
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member] | Corporate Debt Securities [Member]
Fixed maturity securities, at fair value	3,131	3,320
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member] | Municipal Bonds [Member]
Fixed maturity securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member] | US States and Political Subdivisions Debt Securities
Fixed maturity securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Ambac Assurance [Member]
Fixed maturity securities, at fair value	233	136
Restricted Cash	48	1
Financing Receivable, after Allowance for Credit Loss	0	0
Derivative assets	0	0
Other assets	1	2
Total assets	283	139
Long-term debt	0	0
Long-term Debt, at par less amortized discount	422	160
Long-term debt	422	160
Derivative Liability	0	0
Other Liabilities	3	0
Liabilities	426	160
Variable Interest Entity, Primary Beneficiary [Member] | Ambac Assurance [Member] | Corporate Debt Securities [Member]
Fixed maturity securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Ambac Assurance [Member] | Municipal Bonds [Member]
Fixed maturity securities, at fair value	119	136
Variable Interest Entity, Primary Beneficiary [Member] | Ambac Assurance [Member] | US States and Political Subdivisions Debt Securities
Fixed maturity securities, at fair value	$ 114	$ 0
Consolidated Entities [Member]
Number Of Consolidated Variable Interest Entities | Entity	8	6
Consolidated Entities [Member] | Ambac UK [Member]
Number Of Consolidated Variable Interest Entities | Entity	5	5
Consolidated Entities [Member] | Ambac Assurance [Member]
Number Of Consolidated Variable Interest Entities | Entity	3	1