Schedule of Adoption of ASC 606 and Expected Impact - Statements of Consolidated Operations (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Passenger revenue	$ 8,149	$ 7,653	[1]
Cargo	293	238	[1]
Other operating revenue	590	535	[1]
Total operating revenue	9,032	8,426	[1]
Salaries and related costs	2,726	2,636	[1]
Distribution expenses	342	319	[1]
Other operating expenses	1,398	1,309	[1]
Total operating expenses	8,756	8,106	[1]
Operating income	276	320	[1]
Interest expense	(176)	(162)	[1]
Miscellaneous, net	48	(42)	[1]
Total nonoperating expense, net	(92)	(170)	[1]
Income before income taxes	184	150	[1]
Income tax expense	37	51	[1]
Net income	$ 147	$ 99	[1]
Earnings per share, basic and diluted	$ 0.52	$ 0.32	[1]
ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Passenger revenue		$ 7,653
Cargo		238
Other operating revenue		535
Total operating revenue		8,426
Salaries and related costs		2,636
Distribution expenses		319
Other operating expenses		1,309
Total operating expenses		8,106
Operating income		320
Interest expense		(162)
Miscellaneous, net		(42)
Total nonoperating expense, net		(170)
Income before income taxes		150
Income tax expense		51
Net income		$ 99
Earnings per share, basic and diluted		$ 0.32
Scenario, Previously Reported | ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Passenger revenue		$ 7,174
Cargo		220
Other operating revenue		1,026
Total operating revenue		8,420
Salaries and related costs		2,661
Distribution expenses		307
Other operating expenses		1,332
Total operating expenses		8,142
Operating income		278
Interest expense		(150)
Miscellaneous, net		(17)
Total nonoperating expense, net		(133)
Income before income taxes		145
Income tax expense		49
Net income		$ 96
Earnings per share, basic and diluted		$ 0.31
Adjustment | ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Passenger revenue		$ 479
Cargo		18
Other operating revenue		(491)
Total operating revenue		6
Distribution expenses		12
Other operating expenses		(23)
Total operating expenses		(11)
Operating income		17
Interest expense		(12)
Total nonoperating expense, net		(12)
Income before income taxes		5
Income tax expense		2
Net income		$ 3
Earnings per share, basic and diluted		$ 0.01
New Retirement Standard Adjustments | ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Salaries and related costs		$ (25)
Total operating expenses		(25)
Operating income		25
Miscellaneous, net		(25)
Total nonoperating expense, net		$ (25)

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) and Accounting Standards Update No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.