Fair Value Option - Gains and Losses on Other Financial Assets and Financial Liabilities at Fair Value (Detail) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2021 |
Sep. 30, 2020 |
Sep. 30, 2021 |
Sep. 30, 2020 |
|
| Fair Value, Option, Quantitative Disclosures [Line Items] | ||||
| Fair Value Option Gains/(Losses) | $ 801 | $ (701) | $ (2,782) | $ 311 |
| 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) | 875 | (406) | (935) | 1,723 |
| Unsecured Long-Term Borrowings at Fair Value [Member] | ||||
| Fair Value, Option, Quantitative Disclosures [Line Items] | ||||
| Fair Value Option Gains/(Losses) | (128) | (143) | (1,830) | (1,166) |
| Fair Value Option Other [Member] | ||||
| Fair Value, Option, Quantitative Disclosures [Line Items] | ||||
| Fair Value Option Gains/(Losses) | $ 54 | $ (152) | $ (17) | $ (246) |