Derivative Instruments (Narrative) (Detail) (USD $)	Mar. 31, 2013		Dec. 31, 2012
Derivative [Line Items]
Maximum amount of future guarantee payments	$ 48,500,000,000
Insured derivatives ceded under reinsurance agreements	392,000,000
Cash collateral posted derivative counterparties	262,000,000		285,000,000
Fair value of Credit Support Annex	4,000,000		4,000,000
Amount of Counterparty netting	81,000,000		90,000,000
Derivative assets, after counterparty netting	12,000,000		12,000,000
Other Assets and Other Assets - VIEs, after counterparty netting and embedded reclass	4,000,000		4,000,000
Counterparty netting	81,000,000		90,000,000
Derivative liabilities, after counterparty netting and posting of cash collateral	3,200,000,000		3,100,000,000
Medium-Term Notes And Other Investments [Member]
Derivative [Line Items]
Embedded Derivative Assets	8,000,000		8,000,000
Embedded Derivative Liabilities	37,000,000		36,000,000
Derivative Liabilities [Member]
Derivative [Line Items]
Cash collateral posted derivative counterparties	188,000,000		203,000,000
Embedded Derivative Liabilities	3,462,000,000	[1]	3,425,000,000	[2]
Other Liabilities [Member]
Derivative [Line Items]
Cash collateral posted derivative counterparties	16,000,000		16,000,000
Other Assets [Member]
Derivative [Line Items]
Cash collateral posted derivative counterparties	$ 58,000,000		$ 66,000,000

[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