Fair Value Of Financial Instruments (Gains And Losses (Realized And Unrealized) Included In Earnings Relating To Level 3 Assets And Liabilities) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gains (losses) on insured derivatives	$ 73	$ (303)
Gain and losses (realized and unrealized) included in earnings, Total	219	383
Variable Interest Entity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	33	(27)
Significant Unobservable Inputs (Level 3) [Member] | Total Gains (Losses) Included In Earnings [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net investment income		(5)
Unrealized gains (losses) on insured derivatives	(73)	303
Realized gains (losses) and other settlements on insured derivatives	(1)	(20)
Net gains (losses) on financial instruments at fair value and foreign exchange	(16)	(36)
Net investment losses related to other-than-temporary impairments		(95)
Gain and losses (realized and unrealized) included in earnings, Total	(130)	36
Significant Unobservable Inputs (Level 3) [Member] | Change In Unrealized Gains (Losses) For The Period Included In Earnings For Assets And Liabilities Still Held [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gains (losses) on insured derivatives	(131)	286
Net gains (losses) on financial instruments at fair value and foreign exchange	(12)	(12)
Gain and losses (realized and unrealized) included in earnings, Total	(180)	161
Significant Unobservable Inputs (Level 3) [Member] | Variable Interest Entity [Member] | Total Gains (Losses) Included In Earnings [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	(40)	(111)
Significant Unobservable Inputs (Level 3) [Member] | Variable Interest Entity [Member] | Change In Unrealized Gains (Losses) For The Period Included In Earnings For Assets And Liabilities Still Held [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	$ (37)	$ (113)