Pension plans - Defined benefit pension plans - Narrative (Detail) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|---|
| Defined Benefit Plan Disclosure [Line Items] | |||
| Projected benefit obligation | $ 16,922 | $ 18,824 | $ 17,750 |
| Amounts recognized in the Consolidated Balance Sheets: | |||
| Funded status reflected in assets | 510 | 1,176 | |
| Funded status reflected in liabilities | 2,473 | 2,986 | |
| Estimated future benefit payments | |||
| 2019 | 1,017 | ||
| 2020 | 986 | ||
| 2021 | 988 | ||
| 2022 | 991 | ||
| 2023 | 1,001 | ||
| 2024 - 2028 | 5,027 | ||
| Expected contribution to pension plans during the next year | 193 | ||
| Unfunded Plans [Member] | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Projected benefit obligation | $ 1,200 | $ 1,300 |