Fair Value Disclosure (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of carrying amounts and estimated fair values of long-term debt, excluding capital lease obligations, and input level to determine fair values

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 March 31, 2018			As of 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	$	36,509	35,677	36,835	36,402