Inventories - Summary Of Inventories (Detail) - USD ($) $ in Millions |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Inventory Disclosure [Abstract] | ||
| Crude oil and refinery feedstocks | $ 1,777 | $ 2,056 |
| Refined products | 2,746 | 2,839 |
| Materials and supplies | 435 | 494 |
| Merchandise | 153 | 161 |
| Total | $ 5,111 | $ 5,550 |