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Fair Value of Financial Instruments (Tables)
3 Months Ended
Mar. 31, 2018
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)
March 31, 2018
 
December 31, 2017
Fair Value
$
6,376

 
$
7,060

Carrying Value
7,319

 
7,218