Financial Instruments - Investments - Unrealized Gains and Losses Related to Equity Securities - Footnotes (Details) $ in Millions |
12 Months Ended |
|---|---|
|
Dec. 31, 2018
USD ($)
| |
| New Accounting Pronouncements or Change in Accounting Principle [Line Items] | |
| Unrealized gain on equity securities | $ 477 |
| Financial Assets and Liabilities [Member] | |
| New Accounting Pronouncements or Change in Accounting Principle [Line Items] | |
| Unrealized gain on equity securities | $ 477 |