Financial Guaranty Variable Interest Entities and Consolidated Investment Vehicles - Schedule of Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Sep. 30, 2023
Variable Interest Entity [Line Items]
Assets	$ 16,843	$ 11,944
Liabilities	11,551	6,643
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles
Variable Interest Entity [Line Items]
Liabilities	4,625	4
Variable Interest Entity, Primary Beneficiary | CLO obligations of CFEs | Consolidated Investment Vehicles
Variable Interest Entity [Line Items]
Liabilities	4,090	0
Variable Interest Entity, Primary Beneficiary | Warehouse financing debt | Consolidated Investment Vehicles
Variable Interest Entity [Line Items]
Liabilities	313	0
Variable Interest Entity, Primary Beneficiary | Due to brokers and counterparties | Consolidated Investment Vehicles
Variable Interest Entity [Line Items]
Liabilities	112	4
Variable Interest Entity, Primary Beneficiary | Other liabilities | Consolidated Investment Vehicles
Variable Interest Entity [Line Items]
Liabilities	110	0
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles
Variable Interest Entity [Line Items]
Assets	5,493	330
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles | Fund investments: | Equity securities and warrants
Variable Interest Entity [Line Items]
Assets	434	79
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles | Fund investments: | Structured products
Variable Interest Entity [Line Items]
Assets	128	239
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles | Fund investments: | Corporate securities
Variable Interest Entity [Line Items]
Assets	96	0
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles | CLOs and CLO warehouse assets: | Loans in CLOs and CLO warehouses, FVO
Variable Interest Entity [Line Items]
Assets	4,570	0
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles | CLOs and CLO warehouse assets: | Short-term investments
Variable Interest Entity [Line Items]
Assets	135	0
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles | Investments in AssuredIM Funds and Other Affiliated Entities
Variable Interest Entity [Line Items]
Assets	392
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles | Cash and cash equivalents | Fund investments:
Variable Interest Entity [Line Items]
Assets	59	7
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles | Cash and cash equivalents | CLOs and CLO warehouse assets:
Variable Interest Entity [Line Items]
Assets	38	0
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles | Other assets | Fund investments:
Variable Interest Entity [Line Items]
Assets	1	5
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles | Due from brokers and counterparties | CLOs and CLO warehouse assets:
Variable Interest Entity [Line Items]
Assets	$ 32	$ 0
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles | CLO obligations of CFEs
Variable Interest Entity [Line Items]
CLO's weighted average maturity	6 years 2 months 12 days
CLO's weighted average interest rate	5.30%
Variable Interest Entity, Primary Beneficiary | Consolidated Investment Vehicles | Warehouse financing debt
Variable Interest Entity [Line Items]
CLO's weighted average maturity	1 year 10 months 24 days
CLO's weighted average interest rate	4.50%
Voting Interest Entity | Consolidated Investment Vehicles
Variable Interest Entity [Line Items]
Liabilities	$ 1
Voting Interest Entity | Consolidated Investment Vehicles | Investments
Variable Interest Entity [Line Items]
Assets	$ 58