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, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gains (losses) on insured derivatives	$ 37	$ 838
Net gains (losses) on financial instruments at fair value and foreign exchange	30	(55)
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	37	838
Realized gains and other settlements on insured derivatives	(9)	(369)
Net gains (losses) on financial instruments at fair value and foreign exchange	18	(13)
Total revenues	49	433
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	37	30
Net gains (losses) on financial instruments at fair value and foreign exchange	20	(13)
Total revenues	61	11
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	3	(23)
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	$ 4	$ (6)