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Asset Retirement Obligations and Accrued Environmental Costs (Tables)
 12 Months Ended
Dec. 31, 2016
Asset Retirement Obligation and Accrual for Environmental Cost Disclosure [Abstract]  
Schedule of Asset Retirement Obligations and Accrual for Environmental Costs
Asset retirement obligations and accrued environmental costs at December 31 were:
 
 
Millions of Dollars
 
2016

 
2015

 
 
 
 
Asset retirement obligations
$
244

 
251

Accrued environmental costs
496

 
485

Total asset retirement obligations and accrued environmental costs
740

 
736

Asset retirement obligations and accrued environmental costs due within one year*
(85
)
 
(71
)
Long-term asset retirement obligations and accrued environmental costs
$
655

 
665

*Classified as a current liability on the consolidated balance sheet, under the caption “Other accruals.”
Schedule of Change in Asset Retirement Obligation
During 2016 and 2015, our overall asset retirement obligation changed as follows:
 
 
Millions of Dollars
 
2016

 
2015

 
 
 
 
Balance at January 1
$
251

 
279

Accretion of discount
9

 
9

Changes in estimates of existing obligations
10

 
(7
)
Spending on existing obligations
(15
)
 
(20
)
Property dispositions
(5
)
 
(2
)
Foreign currency translation
(6
)
 
(8
)
Balance at December 31
$
244

 
251