Goodwill and other intangible assets - Intangible assets - Narrative (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Goodwill and Intangible Assets Disclosure [Abstract] | |||
| Intangible asset amortization expense | $ 1,393 | $ 1,469 | $ 1,490 |
| Estimated amortization expense - 2019 | 1,318 | ||
| Estimated amortization expense - 2020 | 1,224 | ||
| Estimated amortization expense - 2021 | 1,136 | ||
| Estimated amortization expense - 2022 | 1,063 | ||
| Estimated amortization expense - 2023 | 1,018 | ||
| Intangible assets with indefinite lives, excluding goodwill | $ 18,900 | $ 18,900 | |