Financial Guarantee Insurance Contracts Earned Premiums by Geographic Location (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Premiums Earned, Net, Financial Guarantee Insurance Contracts	$ 15	$ 10	$ 36	$ 46
United States [Member] \| Reportable Geographical Components [Member]
Premiums Earned, Net, Financial Guarantee Insurance Contracts	9	11	24	44
United Kingdom [Member] \| Reportable Geographical Components [Member]
Premiums Earned, Net, Financial Guarantee Insurance Contracts	7	4	15	13
Other International [Member] \| Reportable Geographical Components [Member]
Premiums Earned, Net, Financial Guarantee Insurance Contracts	$ (1)	$ (4)	$ (2)	$ (11)

Amount, after premiums ceded to other entities and premiums assumed by the entity, of financial guarantee premiums earned.

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