Intangible Assets - Carrying Amounts of Identifiable Intangible Assets (Detail) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Goodwill And Intangible Assets Disclosure [Abstract] | ||
| Indefinite-lived intangible assets, Beginning balance | $ 17,178 | |
| Indefinite-lived intangible assets, Ending balance | 17,178 | |
| Finite-lived intangible assets, Beginning balance | 211 | |
| Finite-lived intangible assets, amortization expense | (11) | $ (25) |
| Finite-lived intangible assets, Ending balance | 200 | |
| Intangible assets, Beginning balance | 17,389 | |
| Intangible assets, Ending balance | $ 17,378 | |