Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of fair value of liabilities measured on a recurring basis

The following table presents the carrying amounts and estimated fair values of our long-term debt, excluding capital lease and other obligations, as well as the input level used to determine the fair values indicated below:

		As of			As of
		March 31, 2018			December 31, 2017
	Input Level	Carrying Amount		Fair Value	Carrying Amount	Fair Value
		(Dollars in millions)
Liabilities-Long-term debt, excluding capital lease and other obligations	2	$	10,704	10,435	10,711	10,528