Fair Value Option - Gains and Losses on Other Financial Assets and Financial Liabilities at Fair Value (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| Fair Value, Option, Quantitative Disclosures [Line Items] | |||
| Fair Value Option Gains/(Losses) | $ (3,161) | $ (9,499) | $ 2,677 |
| 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) | 206 | (3,365) | 1,443 |
| Unsecured Long-Term Borrowings at Fair Value [Member] | |||
| Fair Value, Option, Quantitative Disclosures [Line Items] | |||
| Fair Value Option Gains/(Losses) | (2,804) | (5,251) | 926 |
| Fair Value Option Other [Member] | |||
| Fair Value, Option, Quantitative Disclosures [Line Items] | |||
| Fair Value Option Gains/(Losses) | $ (563) | $ (883) | $ 308 |