Insurance In Force (Summary Of Company's Reinsurance Agreements For U.S. Public Finance And Structured Finance And International Insurance Operations) (Detail) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Aggregate Amount Of Insured Par Outstanding Ceded To Reinsurers		$ 2,194	$ 2,700
Reinsurance Recoverables Secured By Letters Of Credit Or Trust Amount		30
Reinsurance Recoverable	[1]	6
Assured Guaranty Corp [Member]
Aggregate Amount Of Insured Par Outstanding Ceded To Reinsurers		870
Reinsurance Recoverable	[1]	2
Assured Guaranty Re Ltd [Member]
Aggregate Amount Of Insured Par Outstanding Ceded To Reinsurers		1,009
Reinsurance Recoverables Secured By Letters Of Credit Or Trust Amount		27
Reinsurance Recoverable	[1]	4
Overseas Private Investment Corporation [Member]
Aggregate Amount Of Insured Par Outstanding Ceded To Reinsurers		244
Others [Member]
Aggregate Amount Of Insured Par Outstanding Ceded To Reinsurers		71
Reinsurance Recoverables Secured By Letters Of Credit Or Trust Amount		$ 3

[1] Total reinsurance recoverable is primarily related to recoverables on unpaid losses.