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Summary of Significant Accounting Policies (Tables)
12 Months Ended
Dec. 31, 2017
Accounting Policies [Abstract]  
Research and Development
($ in millions)
2017

 
2016

 
2015

Research and development – total

$474

 

$479

 

$484

Less depreciation on research facilities
21

 
20

 
18

Research and development, net

$453

 

$459

 

$466