Schedule of Information Related to Amounts Recorded Related to Frequent Flyer Program (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Significant Accounting Policies [Line Items]
Cash Proceeds from Miles Sold and Earned		$ 2,343	$ 3,022	$ 2,999
Other Revenue Recognized Upon Award of Miles to Third-Party Customers	[1]	1,183	1,221	1,050
Increase in Frequent Flyer Deferred Revenue for Miles Awarded	[2]	2,025	2,050	2,173
Decrease in Advanced Purchase of Miles	[3]	$ (865)	$ (249)	$ (224)

[1] This amount represents other revenue recognized during the period from the sale of miles to third parties, representing the marketing-related deliverable services component of the sale.

[2] This amount represents the increase to Frequent flyer deferred revenue during the period.

[3] This amount represents the net decrease in the advance purchase of miles obligation due to cash payments for the sale of miles less than miles awarded to customers.