Income Taxes, Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax assets:
Tax credit carryforwards	$ 69	$ 65
Net operating losses (NOLs)	492	374
Inventories	135	93
Compensation and employee benefit liabilities	179	344
Environmental liabilities	47	69
Other	112	100
Total deferred income tax assets	1,034	1,045
Valuation allowance	(498)	(374)
Net deferred income tax assets	536	671
Deferred income tax liabilities:
Property, plant, and equipment	4,545	6,900
Deferred turnaround costs	272	450
Inventories	243	356
Investments	77	253
Other	107	73
Total deferred income tax liabilities	5,244	8,032
Net deferred income tax liabilities	$ 4,708	$ 7,361