Derivative Instruments (Narrative) (Detail) (USD $)	Dec. 31, 2012		Dec. 31, 2011
Derivative [Line Items]
Maximum amount of future guarantee payments	$ 50,900,000,000
Insured derivatives ceded under reinsurance agreements	392,000,000
Cash collateral posted derivative counterparties	285,000,000
Fair value of securities, posted to derivative counterparties			470,000,000
Fair value of Credit Support Annex	4,000,000		2,000,000
Amount of Counterparty netting	90,000,000		93,000,000
Derivative assets, after counterparty netting	12,000,000		459,000,000
Other Assets and Derivative Assets - VIEs, after counterparty netting and embedded reclass	4,000,000		452,000,000
Counterparty netting	90,000,000		93,000,000
Derivative liabilities, after counterparty netting and posting of cash collateral	3,100,000,000		6,000,000,000
Derivative Liabilities [Member]
Derivative [Line Items]
Cash collateral posted derivative counterparties	203,000,000
Fair value of derivative liabilities, before counterparty netting and posting of Cash Collateral	3,425,000,000	[1]	6,108,000,000	[2]
Other Liabilities [Member]
Derivative [Line Items]
Cash collateral posted derivative counterparties	16,000,000
Other Assets [Member]
Derivative [Line Items]
Cash collateral posted derivative counterparties	66,000,000
Medium-Term Notes And Other Investments [Member]
Derivative [Line Items]
Embedded Derivative Assets	8,000,000		7,000,000
Fair value of derivative liabilities, before counterparty netting and posting of Cash Collateral	$ 36,000,000		$ 26,000,000

[1] In accordance with the accounting guidance for derivative instruments and hedging activities, the balance sheet location of the Company's embedded derivative instruments is determined by the location of the related host contract.

[2] In accordance with the accounting guidance for derivative instruments and hedging activities, the balance sheet location of the Company's embedded derivative instruments is determined by the location of the related host contract