Pension plans - Net periodic pension expense (Detail) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Components of net periodic pension expense | |||
| Service cost | $ 271 | $ 273 | $ 282 |
| Interest cost | 593 | 635 | 691 |
| Expected return on plan assets | (988) | (939) | (908) |
| Amortization of actuarial losses and other | 188 | 157 | 148 |
| Net periodic pension expense | $ 64 | $ 126 | $ 213 |