Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis - Footnotes (Details) - USD ($) $ in Millions |
Dec. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Recurring [Member] | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Long-term equity securities held in trust | $ 190 | $ 176 |