Basis of Presentation and Significant Accounting Policies - Accrued Rebates and Other Accruals (Details) - USD ($) $ in Millions |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Schedule Of Accrued Liabilities [Line Items] | ||
| Accrued rebates and other accruals | $ 5,426 | $ 4,923 |
| Trade accounts receivable [Member] | ||
| Schedule Of Accrued Liabilities [Line Items] | ||
| Accrued rebates and other accruals | 1,288 | 1,352 |
| Other current liabilities [Member] | ||
| Schedule Of Accrued Liabilities [Line Items] | ||
| Accrued rebates | 3,208 | 2,674 |
| Other accruals | 531 | 512 |
| Other noncurrent liabilities [Member] | ||
| Schedule Of Accrued Liabilities [Line Items] | ||
| Accrued rebates and other accruals | $ 399 | $ 385 |