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Fair Value of Financial Instruments, Assets and Equity Investements (Tables)
12 Months Ended
Dec. 31, 2017
Fair Value Disclosures [Abstract]  
Fair value and carrying value of Long-term Debt
The fair value and carrying value of our senior notes were as follows: 
 
December 31,
(Dollars in millions)
2017
 
2016
Fair Value
$
7,060

 
$
6,739

Carrying Value
7,218

 
7,028