Derivative Instruments (Narrative) (Detail) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Derivative [Line Items]
Maximum amount of future guarantee payments	$ 53,100,000,000
Insured derivatives ceded under reinsurance agreements	527,000,000
Derivative assets, after counterparty netting	13,000,000	459,000,000
Derivative assets and Derivative assets - VIEs, after counterparty netting	5,000,000	452,000,000
Derivative liabilities, after counterparty netting	3,500,000,000	6,000,000,000
Fair value of derivative assets, before counterparty netting	111,000,000	552,000,000
Fair value of derivative liabilities, before counterparty netting	4,000,000,000	6,108,000,000
Cash collateral posted to derivative counter parties	327,000,000
Fair value of securities, posted to derivative counterparties	141,000,000	470,000,000
Fair value of Credit Support Annex	$ 2,000,000	$ 2,000,000