Fair Value Measurement - Narrative (Details) - Security	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Assured IM
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Obligation to purchase debt	0.05
Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Number of fixed maturity securities valued using model processes	188
Recurring | Minimum | Credit Default Swap | Level 3 | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Conditional prepayment rate (as a percent)	2.78%	0.11%
Recurring | Maximum | Credit Default Swap | Level 3 | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Conditional prepayment rate (as a percent)	5.08%	1.78%