Insurance Contracts - Additional Information (Details) € in Millions, £ in Millions, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Jun. 30, 2023 GBP (£)	Jun. 30, 2023 EUR (€)	Mar. 31, 2023 USD ($)	Jun. 30, 2022 GBP (£)	Jun. 30, 2022 EUR (€)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Insurance [Line Items]
Reinsurance Recoverable Credit Exposure	$ 87		$ 87		$ 60
Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Rmbs Subrogation	0		0		140
Financial Guarantee Insurance Contracts, Premium Receivable	$ 253	$ 288	$ 253	$ 288	$ 254							$ 320
Estimated Future Premium Payments Weighted Average Discounted Rate	3.10%		3.10%		3.00%	3.10%	3.10%
Reinsurance Payable	$ 96		$ 96		$ 39
Weighted average period of future premiums			7 years 10 months 24 days		8 years
Uncollectable premium receivables	5		$ 5		$ 5
Reinsurance recoveries of losses included in losses and loss expenses			(45)	(14)
Subrogation recoveries, net of reinsurance	0		0		(140)
Amortization of Intangible Assets	7	13	13	28
Intangible assets	317		317		326
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,303	846	1,303	846	$ 1,305			$ 1,307			$ 974	$ 1,098
Past Due Premiums	0	0	$ 0	$ 0
Loss Reserves [Member]
Insurance [Line Items]
Weighted average risk-free rate used to discount loss reserves			3.80%	3.90%
United Kingdom, Pounds
Insurance [Line Items]
Financial Guarantee Insurance Contracts, Premium Receivable	76	91	$ 76	$ 91		£ 60			£ 74
Euro Member Countries, Euro
Insurance [Line Items]
Financial Guarantee Insurance Contracts, Premium Receivable	$ 14	$ 15	$ 14	$ 15			€ 12			€ 14