Pension plans - Defined contribution pension plans - Narrative (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Defined Contribution Plan [Abstract] | |||
| Contributions to defined contribution plans | $ 1,009 | $ 1,001 | $ 912 |