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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of Asset Retirement Obligations [Table Text Block]
The following table provides asset retirement obligation activity for the years ended December 31, 2016 and 2015 (dollars in millions):
 
 
2016
 
2015
Asset retirement obligation at January 1
 
$
90

 
$
85

Accretion expense
 
10

 
9

Liabilities settled
 
(9
)
 
(8
)
Revision in estimated cash flows
 
—

 
5

Effect of foreign currency rate change
 
(2
)
 
(1
)
Asset retirement obligation at December 31
 
$
89

 
$
90