Income Taxes (Deferred Income Tax Liabilities and Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Deferred Tax Liabilities
Properties, plants and equipment, and intangibles	$ 3,074	$ 2,942
Investment in joint ventures	2,041	1,923
Investment in subsidiaries	602	594
Inventory	66	0
Other	14	18
Total deferred tax liabilities	5,797	5,477
Deferred Tax Assets
Benefit plan accruals	395	314
Asset retirement obligations and accrued environmental costs	109	121
Loss and credit carryforwards	59	96
Other financial accruals and deferrals	16	44
Inventory	0	10
Other	0	3
Total deferred tax assets	579	588
Less: valuation allowance	8	28
Net deferred tax assets	571	560
Net deferred tax liabilities	$ 5,226	$ 4,917