Variable Interest Entities Special Purpose Entities, including Variable Interest Entities - Summary of Assets and Liabilities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2022 USD ($) Entity	Dec. 31, 2021 USD ($)	Dec. 31, 2021 USD ($) Entity	Dec. 31, 2020 USD ($)
Available-for-sale Securities, Amortized Cost Basis	$ 2,041	$ 2,041	$ 2,140	$ 2,140
Available-for-sale Securities	1,966	1,966
Restricted Cash	14	14	5	5	$ 13
Derivative assets	27	27	76	76
Other assets	84	84	68	68
Assets	7,973	7,973	12,303	12,303
Accrued interest payable	427	427	576	576
Long-term debt	639	639	2,230	2,230
Derivative liabilities	38	38	95	95
Other liabilities	163	163	133	133
Liabilities	6,647	6,647	11,187	11,187
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	106	106	16	16
Variable Interest Entity [Member]
Available-for-sale Securities	1,967	1,967	3,455	3,455
Restricted Cash	17	17	2	2	$ 2
Loans, at fair value	1,829	1,829	2,718	2,718
Derivative assets	239	239	38	38
Other assets	2	2	2	2
Assets	4,054	4,054	6,216	6,216
Long-term Debt	2,788	2,788	4,056	4,056
Long-term Debt, at par less amortized discount	319	319	160	160
Long-term debt	3,107	3,107	4,216	4,216
Derivative liabilities	1,048	1,048	1,940	1,940
Other liabilities	5	5	0	0
Liabilities	4,160	4,160	6,156	6,156
Loans, Unpaid principal balance	1,977	1,977	2,363	2,363
Long-term debt, Unpaid principal balance	3,064	3,064	3,579	3,579
Variable Interest Entity [Member] | Ambac UK [Member]
Available-for-sale Securities	1,828	1,828	3,320	3,320
Restricted Cash	1	1	1	1
Loans, at fair value	1,829	1,829	2,718	2,718
Derivative assets	239	239	38	38
Other assets	0	0	0	0
Assets	3,896	3,896	6,077	6,077
Long-term Debt	2,788	2,788	4,056	4,056
Long-term Debt, at par less amortized discount	0	0	0	0
Long-term debt	2,788	2,788	4,056	4,056
Derivative liabilities	1,048	1,048	1,940	1,940
Other liabilities	0	0	0	0
Liabilities	3,836	3,836	5,996	5,996
Variable Interest Entity [Member] | Ambac Assurance [Member]
Available-for-sale Securities	139	139	136	136
Restricted Cash	16	16	1	1
Loans, at fair value	0	0	0	0
Derivative assets	0	0	0	0
Other assets	2	2	2	2
Assets	157	157	139	139
Long-term Debt	0	0	0	0
Long-term Debt, at par less amortized discount	319	319	160	160
Long-term debt	319	319	160	160
Derivative liabilities	0	0	0	0
Other liabilities	5	5	0	0
Liabilities	324	324	160	160
Variable Interest Entity [Member] | Corporate Debt Securities [Member]
Available-for-sale Securities	1,828	1,828	3,320	3,320
Variable Interest Entity [Member] | Corporate Debt Securities [Member] | Ambac UK [Member]
Available-for-sale Securities	1,828	1,828	3,320	3,320
Variable Interest Entity [Member] | Corporate Debt Securities [Member] | Ambac Assurance [Member]
Available-for-sale Securities	0	0	0	0
Variable Interest Entity [Member] | Municipal Bonds [Member]
Available-for-sale Securities, Amortized Cost Basis	99	99	106	106
Available-for-sale Securities	96	96	136	136
Debt Securities, Trading	43	43	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(4)	(4)
Variable Interest Entity [Member] | Municipal Bonds [Member] | Ambac UK [Member]
Available-for-sale Securities	0	0	0	0
Debt Securities, Trading	0	0	0	0
Variable Interest Entity [Member] | Municipal Bonds [Member] | Ambac Assurance [Member]
Available-for-sale Securities	96	96	136	136
Debt Securities, Trading	$ 43	$ 43	$ 0	$ 0
Consolidated Entities [Member]
Number of consolidated Variable Interest Entities	3	9	0	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		4		1