Financial Instruments - Investments - Unrealized Gains and Losses Related to Equity Securities (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Financial Instruments [Abstract] | |||
| Net gains recognized during the period on investments in equity securities | $ 454 | $ 586 | $ 224 |
| Less: Net gains recognized during the period on equity securities sold during the period | (25) | (109) | |
| Net unrealized gains during the reporting period on equity securities still held at the reporting date | $ 429 | $ 477 | |