Inventory, Linefill and Base Gas and Long-term Inventory (Details) bbl in Thousands, Mcf in Thousands, $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2020 USD ($)	Sep. 30, 2020 USD ($) $ / bbl $ / Mcf bbl Mcf	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) $ / bbl $ / Mcf bbl Mcf
Inventory by category
Inventory		$ 683		$ 604
Linefill and base gas		966		981
Long-term inventory		120		182
Total		1,769		$ 1,767
Charge related to the write-down of inventory	$ 233	$ 233	$ 11
Charge related to the write-down of inventory, long-term inventory	$ 40
Crude oil
Inventory by category
Inventory, Volumes (in barrels) | bbl		15,332		8,613
Linefill and base gas, Volumes (in barrels or in Mcf) | bbl		14,496		14,316
Long-term inventory, Volumes (in barrels) | bbl		2,773		2,598
Inventory		$ 449		$ 450
Linefill and base gas		813		826
Long-term inventory		$ 102		$ 152
Inventory (Price/Unit of measure) | $ / bbl		29.29		52.25
Linefill and base gas (Price/Unit of measure) | $ / bbl		56.08		57.70
Long-term inventory (Price/Unit of measure) | $ / bbl		36.78		58.51
NGL
Inventory by category
Inventory, Volumes (in barrels) | bbl		16,144		7,574
Linefill and base gas, Volumes (in barrels or in Mcf) | bbl		1,642		1,701
Long-term inventory, Volumes (in barrels) | bbl		1,354		1,707
Inventory		$ 226		$ 142
Linefill and base gas		43		47
Long-term inventory		$ 18		$ 30
Inventory (Price/Unit of measure) | $ / bbl		14.00		18.75
Linefill and base gas (Price/Unit of measure) | $ / bbl		26.19		27.63
Long-term inventory (Price/Unit of measure) | $ / bbl		13.29		17.57
Natural gas
Inventory by category
Linefill and base gas, Volumes (in barrels or in Mcf) | Mcf		25,576		24,976
Linefill and base gas		$ 110		$ 108
Linefill and base gas (Price/Unit of measure) | $ / Mcf		4.30		4.32
Other
Inventory by category
Inventory		$ 8		$ 12