Income Taxes (Income Taxes Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 11	$ 11
Unrecognized tax benefits that would impact effective income tax rate	14
Uncertain tax positions, reasonably possible increase or decrease during the next twelve months	9
Statute of limitations	0	160	$ 12
Unrecognized tax benefits income tax net penalties and interest expense (benefits)	(19)	(2)	$ 1
Interest and penalties accrued	(5)	7
Andeavor
Operating Loss Carryforwards [Line Items]
Statute of limitations		159
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Valuation allowance	2	2
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 4	7
Domestic Tax Authority | Minimum
Operating Loss Carryforwards [Line Items]
Tax years	2016
Domestic Tax Authority | Maximum
Operating Loss Carryforwards [Line Items]
Tax years	2019
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 228	11
Valuation allowance	$ 9	$ 9
State and Local Jurisdiction | Minimum
Operating Loss Carryforwards [Line Items]
Tax years	2006
State and Local Jurisdiction | Maximum
Operating Loss Carryforwards [Line Items]
Tax years	2019
CARES Act
Operating Loss Carryforwards [Line Items]
Income taxes receivable, current	$ 2,100