Financial Guarantee Insurance Contracts - Summary of Gross Premium Receivable Roll-Forward (Direct and Assumed Contracts) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Premiums Receivable, Gross	$ 290	$ 269	$ 323	$ 370
Public Finance [Member]
Premiums Receivable, Gross	140	150
Housing Revenue [Member] | Public Finance [Member]
Premiums Receivable, Gross	139	148
Surveillance Category One [Member]
Premiums Receivable, Gross	210	217
Surveillance Category One [Member] | Public Finance [Member]
Premiums Receivable, Gross	133	142
Surveillance Category One [Member] | Housing Revenue [Member] | Public Finance [Member]
Premiums Receivable, Gross	$ 131	$ 140