Income Taxes (Deferred Income Tax Liabilities and Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Liabilities
Properties, plants and equipment, and intangibles	$ 2,942	$ 4,525
Investment in joint ventures	1,923	2,442
Investment in subsidiaries	594	803
Inventory		154
Other	18	19
Total deferred tax liabilities	5,477	7,943
Deferred Tax Assets
Benefit plan accruals	314	669
Inventory	10
Asset retirement obligations and accrued environmental costs	121	211
Other financial accruals and deferrals	44	188
Loss and credit carryforwards	96	261
Other	3	1
Total deferred tax assets	588	1,330
Less: valuation allowance	28	38
Net deferred tax assets	560	1,292
Net deferred tax liabilities	$ 4,917	$ 6,651