Supplemental Financial Information - Other Non-Current Liabilities (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Other Liabilities, Noncurrent [Abstract]
Postretirement obligation		$ 294	$ 275
Non-current lease-related obligations		56	85
Permanently grounded aircraft liability noncurrent	[1]	0	13
Other deferred compensation		260	237
Other		116	76
Other noncurrent liabilities		748	707
Other Noncurrent Liabilities
Other Liabilities, Noncurrent [Abstract]
Derivative contracts		$ 22	$ 21

[1] These amounts represent the current and noncurrent portion of the Company's cease-use liability recorded as a result of the Company grounding its remaining leased Boeing 737-300 aircraft in 2017. The decrease was primarily related to contractual rent obligations paid.