Recently Issued Accounting Standards - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification from other operating revenue into passenger revenue	$ 8,528	$ 8,603	$ 24,324	$ 23,696
Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification from other operating revenue into passenger revenue					$ 2,000