Financial Guarantee Insurance Contracts - Summary of Gross Premium Receivable Roll-Forward (Direct and Assumed Contracts) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Premiums Receivable, Gross	$ 329	$ 387
Public Finance [Member]
Premiums Receivable, Gross	159	185
Housing Revenue [Member] | Public Finance [Member]
Premiums Receivable, Gross	157	168
Surveillance Category One [Member]
Premiums Receivable, Gross	277	302
Surveillance Category One [Member] | Public Finance [Member]
Premiums Receivable, Gross	151	157
Surveillance Category One [Member] | Housing Revenue [Member] | Public Finance [Member]
Premiums Receivable, Gross	$ 149	$ 155