Fair Value Option - Gains and Losses on Other Financial Assets and Financial Liabilities at Fair Value (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Option Gains/(Losses)	$ (967)	$ (714)
Unsecured Short-Term Borrowings Including Current Portion of Unsecured Long-Term Borrowings at Fair Value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Option Gains/(Losses)	(861)	198
Unsecured Long-Term Borrowings at Fair Value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Option Gains/(Losses)	(189)	(422)
Other Liabilities and Accrued Expenses at Fair Value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Option Gains/(Losses)	187	(28)
Fair Value Option Other [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Option Gains/(Losses)	$ (104)	$ (462)