Summary of Accounting Policies (Variable Interest Entities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Total assets	$ 10,909	$ 9,476
Property, Plant and Equipment, Net	$ 3,939	3,713
Variable Interest Entity, Primary Beneficiary [Member]
Schedule of Investments [Line Items]
Ownership percentage	50.00%
Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule of Investments [Line Items]
Maximum exposure to loss	$ 267	113
Fairway Methanol LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Schedule of Investments [Line Items]
Total assets	666	722
Property, Plant and Equipment, Net	$ 592	$ 622