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Quarterly Financial Data - Unaudited
 12 Months Ended
Dec. 31, 2018
Quaterly Financial Data Unaudited [Abstract]  
Quarterly Financial Information [Text Block]
Quarterly Financial Data—Unaudited
 
Dollars in millions
2018
 
Fourth
 
Third
 
Second
 
First
Revenues
 
$
6,206

 
$
6,147

 
$
5,878

 
$
5,624

Operating income
 
$
2,061

 
$
2,109

 
$
1,883

 
$
1,747

Net income
 
$
1,372

 
$
1,393

 
$
1,309

 
$
1,145