Fair Value Of Financial Instruments (Realized And Unrealized Gains And Losses Included In Earnings Pertaining To Level 3 Assets And Liabilities) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gains (losses) on insured derivatives	$ 157	$ 903	$ 1,777
Net gains (losses) on financial instruments at fair value and foreign exchange	63	78	69
Net investment losses related to other-than-temporary impairments	(13)	(15)
Fair Value Inputs Level 3 [Member] | Total Gains Losses Included In Earnings [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gains (losses) on insured derivatives	159	903	1,778
Realized gains and other settlements on insured derivatives	(28)	(445)	(1,548)
Net gains (losses) on financial instruments at fair value and foreign exchange	39	18	(37)
Net investment losses related to other-than-temporary impairments			0
Total revenues	193	444	353
Fair Value Inputs Level 3 [Member] | Change In Unrealized Gains Losses For 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	145	20	(87)
Net gains (losses) on financial instruments at fair value and foreign exchange	42	12	(12)
Total revenues	206	52	161
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [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	23	(32)	160
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member] | Change In Unrealized Gains Losses For 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	$ 19	$ 20	$ 260