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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of Change in Asset Retirement Obligation
Asset retirement obligations primarily consist of estimated costs to remove, dismantle and restore land or seabed at the end of oil and gas production operations. Changes in asset retirement obligations for the periods ended December 31 were as follows:
(In millions)
2018
 
2017
Beginning balance
$
1,483

 
$
1,652

Incurred liabilities, including acquisitions
21

 
25

Settled liabilities, including dispositions
(117
)
 
(50
)
Accretion expense (included in depreciation, depletion and amortization)
70

 
85

Revisions of estimates
(204
)
 
(227
)
Held for sale(a)
(108
)
 
(2
)
Ending balance(b)
$
1,145

 
$
1,483