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Fixed Assets
 12 Months Ended
Dec. 31, 2017
Property, Plant and Equipment [Abstract]  
Fixed Assets
FIXED ASSETS
(dollars in millions)
Estimated
Useful Lives

2017

2016
Land
 

$
412


$
392

Buildings and improvements
12-40 years

5,727


5,180

Machinery, tools and equipment
3-20 years

13,476


12,471

Other, including assets under construction
 

1,749


1,426

 
 

21,364


19,469

Accumulated depreciation
 

(11,178
)

(10,311
)
 
 

$
10,186


$
9,158


Depreciation expense was $1,178 million in 2017, $1,105 million in 2016 and $1,068 million in 2015.