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	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gains (losses) on insured derivatives	$ 1,870	$ (441)	$ (607)
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]
Unrealized gains (losses) on insured derivatives	1,869	(440)	(609)
Net Realized Gains (Losses)	(547)	(2,550)	(282)
Net Gains (Losses) on Financial Instruments at Fair Value and Foreign Exchange	28	(79)	(11)
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	927	(2,702)	(1,338)
Net Gains (Losses) on Financial Instruments at Fair Value and Foreign Exchange	(6)	(90)	(3)
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	18	59	342
Variable Interest Entity [Member] | 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 Gains (Losses) on Financial Instruments at Fair Value and Foreign Exchange	(376)	230	(340)
Variable Interest Entity [Member] | 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]
Net Gains (Losses) on Financial Instruments at Fair Value and Foreign Exchange	$ (271)	$ 347	$ (395)