Contingencies and Commitments - Narrative (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Commitments and Contingencies Disclosure [Abstract] | |||
| Operating leases, rent expense | $ 1,649 | $ 1,579 | $ 1,573 |
| Purchase commitments - 2019 | 15,700 | ||
| Purchase commitments - 2020 | 4,500 | ||
| Purchase commitments - 2021 | 3,700 | ||
| Purchase commitments - 2022 | 3,200 | ||
| Purchase commitments - 2023 | 2,900 | ||
| Purchase commitments - After 2023 | 17,300 | ||
| Estimated cost to acquire certain equity ownership interests of less than wholly-owned subsidiaries | $ 5,600 | ||