Financial Guarantees in Force - Summary of International Finance Guaranteed Portfolio (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 108,299,000	$ 144,734,000
International Finance [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	21,049,000	24,952,000
International Finance [Member] | United Kingdom [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	15,494,000	17,998,000
International Finance [Member] | Australia [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	1,851,000	2,168,000
International Finance [Member] | Italy [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	948,000	1,415,000
International Finance [Member] | Austria [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	737,000	841,000
International Finance [Member] | FRANCE
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	288,000	88,000
International Finance [Member] | Internationally Diversified [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	974,000	1,225,000
International Finance [Member] | Other International [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 757,000	$ 1,217,000