Financial Guarantees in Force - Summary of International Finance Guaranteed Portfolio (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 28,020	$ 33,888
International Finance [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	10,756	12,054
International Finance [Member] | United Kingdom [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	9,255	9,711
International Finance [Member] | Australia [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	203	420
International Finance [Member] | Italy [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	718	803
International Finance [Member] | Austria [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	343	707
International Finance [Member] | FRANCE
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	219	277
International Finance [Member] | Other International [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	18	136
International Finance [Member] | United States [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 17,264	$ 21,834