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, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Ceded Par Outstanding	$ 3,420.0		$ 4,300.0
LOC / Trust Accounts	8
Reinsurance Recoverable	14	[1]
Reinsurance recoverables on paid losses	1
Reinsurance recoverables on unpaid losses	13
Moody's Aa3 [Member] | Assured Guaranty Corp [Member] | S&P AA- [Member]
Ceded Par Outstanding	2,437.0
Reinsurance Recoverable	14	[1]
A1 [Member] | Assured Guaranty Re Ltd [Member] | S&P AA- [Member]
Ceded Par Outstanding	506.0
LOC / Trust Accounts	5
Aaa [Member] | Overseas Private Investment Corporation [Member] | S&P AA+ [Member]
Ceded Par Outstanding	353.0
Aaa [Member] | Export Development Canada [Member] | S&P AAA [Member]
Ceded Par Outstanding	59.0
LOC / Trust Accounts	1
Moody's A2 Or Above Rating [Member] | Others [Member] | S&P A+ Or Above [Member]
Ceded Par Outstanding	65.0
LOC / Trust Accounts	$ 2

[1] Total reinsurance recoverable of $14 million comprised recoverables on paid and unpaid losses of $1 million and $13 million, respectively.