Outstanding Exposure - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2026 USD ($) category	Dec. 31, 2025 USD ($)
Schedule of Insured Financial Obligations [Line Items]
Number of surveillance categories \| category	3
Loss mitigation securities	$ 800	$ 800
Aircraft residual value insurance (RVI)
Schedule of Insured Financial Obligations [Line Items]
Residual value insurance policies exposure downgraded	200	200
Net Exposure	100	100
Aircraft residual value insurance (RVI) \| BIG
Schedule of Insured Financial Obligations [Line Items]
Residual value insurance policies exposure downgraded		5
Net Exposure		$ 5
Commitment to Provide Guarantees \| Public finance
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties	1,800
Commitment to Provide Guarantees \| Structured finance
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties	$ 2,900
Minimum
Schedule of Insured Financial Obligations [Line Items]
Probability of paying more claims than being reimbursed (as a percent)	50.00%