Schedule of Severance Related Accrual (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Severance and Benefits Costs
Schedule Of Accrual Activity [Line Items]
Beginning Balance	$ 14	$ 27	$ 109
Accrual	116	37	107
Payments	(93)	(50)	(189)
Ending Balance	37	14	27
Permanently Grounded Aircraft
Schedule Of Accrual Activity [Line Items]
Beginning Balance	41	78	102
Accrual	(4)	(17)	30
Payments	(15)	(20)	(54)
Ending Balance	$ 22	$ 41	$ 78