Fair Value Measurement - Narrative (Details) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2022 USD ($) Trust Security	Dec. 31, 2021
Assured IM
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Obligation to purchase debt	0.05
AGC And AGM
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Number of custodial trusts | Trust	4
Share value, amount	$ 200
Maximum amount	$ 50
Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Number of fixed maturity securities valued using model processes | Security	184
Fixed maturity securities	$ 1,000
Recurring | Level 3 | CDR | Total | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Conditional prepayment rate	2.17%	0.11%
Recurring | Level 3 | CDR | Total | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Conditional prepayment rate	3.56%	1.78%