Schedule of Severance Related Accrual (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Severance and Benefits Costs
Schedule Of Accrual Activity [Line Items]
Beginning Balance	$ 37	$ 14
Accrual	14	37
Payments	(19)	(23)
Ending Balance	32	28
Permanently Grounded Aircraft
Schedule Of Accrual Activity [Line Items]
Beginning Balance	22	41
Payments	(1)	(1)
Ending Balance	$ 21	$ 40