Financial Guarantees in Force - Summary of International Finance Guaranteed Portfolio (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 38,018	$ 46,927
International Finance [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	12,857	13,538
International Finance [Member] | United Kingdom [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	10,593	10,965
International Finance [Member] | Australia [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	382	384
International Finance [Member] | Italy [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	767	811
International Finance [Member] | Austria [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	674	712
International Finance [Member] | FRANCE
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	303	312
International Finance [Member] | Other International [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 138	$ 354