Income Taxes, Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred income tax assets:
Tax credit carryforwards	$ 681	$ 683
Net operating losses (NOLs)	678	582
Inventories	70	141
Compensation and employee benefit liabilities	199	213
Environmental liabilities	64	69
Other	128	156
Total deferred income tax assets	1,820	1,844
Valuation allowance	(1,223)	(1,200)
Net deferred income tax assets	597	644
Deferred income tax liabilities:
Property, plant, and equipment	4,895	4,924
Deferred turnaround costs	302	331
Inventories	269	217
Investments	171	122
Other	235	153
Total deferred income tax liabilities	5,872	5,747
Net deferred income tax liabilities	$ 5,275	$ 5,103