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Fair Value of Financial Instruments (Tables)
9 Months Ended
Sep. 30, 2017
Fair Value Disclosures [Abstract]  
Fair Value of Financial Instruments
The fair value and carrying value of our senior notes were as follows: 
(Dollars in millions)
September 30, 2017
 
December 31, 2016
Fair value
$
7,231

 
$
6,739

Carrying value
7,210

 
7,028