Fair Value Measurements - Total Level 3 Financial Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	$ 503,915	$ 509,779	$ 526,687
Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	154,955		144,502
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	24,289	24,732	24,046
Level 3 [Member] | Cash Instruments Assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	18,141	18,131	18,131
Level 3 [Member] | Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	6,093	6,553	5,870
Level 3 [Member] | Other Assets at Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	$ 55	$ 48	$ 45