Operating Revenues (Revenues Disaggregated) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	$ 241	$ 263	$ 508	$ 565
Pipelines
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	97	117	208	226
Terminals
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	33	39	76	79
Storage, processing and other revenues
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	$ 111	$ 107	$ 224	$ 260