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Inventories (Notes)
6 Months Ended
Jun. 30, 2018
Inventory Disclosure [Abstract]  
Inventories [Text Block]
Inventories
 Crude oil and natural gas are recorded at weighted average cost and carried at the lower of cost or net realizable value. Supplies and other items consist principally of tubular goods and equipment which are valued at weighted average cost and reviewed periodically for obsolescence or impairment when market conditions indicate.
 
June 30,
 
December 31,
(In millions)
2018
 
2017
Crude oil and natural gas
$
11

 
$
9

Supplies and other items
106

 
117

Inventories
$
117

 
$
126