Accumulated Other Comprehensive Income (Loss) - Details about AOCI Components (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Aircraft fuel	$ 9,307	$ 6,913	[1]	$ 5,813	[1]
Miscellaneous, net	76	101	[1]	11	[1]
Fuel derivative contracts | Amount Reclassified from AOCI to Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Aircraft fuel	0	2		217
Pension and Postretirement liabilities and other | Amount Reclassified from AOCI to Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Miscellaneous, net	62	58		26
Investments and other | Amount Reclassified from AOCI to Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Miscellaneous, net	$ 0	$ 0		$ (2)

[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 II, Item 8 of this report for additional information.