Fair Value Of Financial Instruments (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Percentage of level 3 assets at fair value in total assets measured at fair value value	12.00%	30.00%
Percentage of level 3 liabilities at fair value in total liabilities measured at fair value	65.00%	41.00%
Cumulative changes in instrument-specific credit risk of liabilities elected under the fair value option	$ (156)	$ (19)	$ (128)	$ (61)
Instrument-specific credit risk of liabilities measured at fair value, net [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cumulative changes in instrument-specific credit risk of liabilities elected under the fair value option	(110)	$ 0	$ 0	$ 0
Loss on instrument-specific credit risk recognized in earnings	$ 97

Amount, after tax, of reclassification adjustment from accumulated other comprehensive income (loss) for unrealized gain (loss) from increase (decrease) in instrument-specific credit risk, realized upon derecognition of financial liability measured under fair value option.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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