Impairment	12 Months Ended
Dec. 31, 2018
Asset Impairment Charges [Abstract]
Impairment	13. Impairment 2017: In the third quarter, we recognized a pre-tax charge of $2,503 million ($550 million after income taxes) to impair the carrying value of our interests in Norway based on an anticipated sale of the asset, which closed in the fourth quarter of 2017. See Note 3, Dispositions. In the fourth quarter, we recognized pre-tax impairment charges to reduce the carrying value of our interests in the Stampede Field by $1,095 million ($1,095 million after income taxes), and the Tubular Bells Field by $605 million ($605 million after income taxes) primarily as a result of a lower long-term crude oil price outlook. The Stampede Field had significant capitalized exploration and appraisal costs that were incurred on a 100% working interest basis on the Pony discovery prior to unitizing into the Stampede project. The fourth quarter impairment charges were based on a total fair value estimate of approximately $1.1 billion that was determined using internal projected discounted cash flows. The determination of projected discounted cash flows depended on estimates of oil and gas reserves, future prices, operating costs, capital expenditures, discount rate and timing of future net cash flows. 2016: We recorded a pre-tax impairment charge of $67 million ($21 million after income taxes and noncontrolling interest) to impair older specification rail cars in our Midstream segment based on estimated salvage values, which approximated fair value. Each of the valuation methods used in the determination of the impairment charges above represent Level 3 fair value measurements.

Impairment

12 Months Ended

Dec. 31, 2018

13. Impairment

2017: In the third quarter, we recognized a pre-tax charge of $2,503 million ($550 million after income taxes) to impair the carrying value of our interests in Norway based on an anticipated sale of the asset, which closed in the fourth quarter of 2017. See Note 3, Dispositions. In the fourth quarter, we recognized pre-tax impairment charges to reduce the carrying value of our interests in the Stampede Field by $1,095 million ($1,095 million after income taxes), and the Tubular Bells Field by $605 million ($605 million after income taxes) primarily as a result of a lower long-term crude oil price outlook. The Stampede Field had significant capitalized exploration and appraisal costs that were incurred on a 100% working interest basis on the Pony discovery prior to unitizing into the Stampede project. The fourth quarter impairment charges were based on a total fair value estimate of approximately $1.1 billion that was determined using internal projected discounted cash flows. The determination of projected discounted cash flows depended on estimates of oil and gas reserves, future prices, operating costs, capital expenditures, discount rate and timing of future net cash flows.

2016: We recorded a pre-tax impairment charge of $67 million ($21 million after income taxes and noncontrolling interest) to impair older specification rail cars in our Midstream segment based on estimated salvage values, which approximated fair value.

Each of the valuation methods used in the determination of the impairment charges above represent Level 3 fair value measurements.