Supplemental Financial Information - Accrued Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018		Dec. 31, 2017
Accrued Liabilities, Current [Abstract]
ProfitSharing and savings plans	$ 132		$ 579
Aircraft and other lease related obligations	39		40
Permanently grounded aircraft liability current	14	[1]	34
Vacation pay	372		365
Union Bonuses	95		83
Health	95		100
Workers compensation	173		172
Property and income taxes	56		57
Other	158		270
Accrued liabilities	$ 1,134		$ 1,700

[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 first quarter 2018 decrease was primarily related to contractual rent obligations paid.