Derivative Instruments (Narrative) (Detail) (USD $)	Jun. 30, 2013		Dec. 31, 2012
Derivative [Line Items]
Maximum amount of future guarantee payments	$ 27,500,000,000
Insured derivatives ceded under reinsurance agreements	72,000,000
Cash collateral posted to derivative counterparties	223,000,000		285,000,000
Fair value of Credit Support Annex	3,000,000		4,000,000
Amount of counterparty netting	59,000,000		90,000,000
Derivative assets, after counterparty netting	12,000,000		12,000,000
Other assets and derivative assets - VIEs, after counterparty netting and embedded reclass	4,000,000		4,000,000
Counterparty netting	59,000,000		90,000,000
Derivative liabilities, after counterparty netting and posting of cash collateral	1,700,000,000		3,100,000,000
Derivative Liabilities [Member]
Derivative [Line Items]
Cash collateral posted to derivative counterparties	151,000,000		203,000,000
Embedded derivative liabilities	1,913,000,000	[1]	3,425,000,000	[1]
Other Liabilities [Member]
Derivative [Line Items]
Cash collateral posted to derivative counterparties	16,000,000		16,000,000
Other Assets [Member]
Derivative [Line Items]
Cash collateral posted to derivative counterparties	56,000,000		66,000,000
Medium Term Notes And Other Investments [Member]
Derivative [Line Items]
Embedded derivative assets	8,000,000		8,000,000
Embedded derivative liabilities	$ 30,000,000		$ 36,000,000

[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 determinedby the location of the related host contract.