Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		Jan. 01, 2018	Jan. 01, 2017
Summary Of Significant Accounting Policies [Line Items]
Revenue	$ 10,491	$ 11,003	$ 10,777	$ 9,032	$ 9,451	$ 9,899	$ 10,008	$ 8,426	$ 41,303	$ 37,784	[1]	$ 36,558	[1]
Period of member account inactivity at which miles expire									18 months
Carrying value of computer software	$ 359				$ 345				$ 359	345
Residual value	10.00%								10.00%
Advertising expense									$ 211	217		220
Reclassification to retained earnings upon adoption of accounting standard															$ (14)
Retained Earnings (Accumulated Deficit)
Summary Of Significant Accounting Policies [Line Items]
Reclassification to retained earnings upon adoption of accounting standard														$ 6	$ (14)
ASU 2016-01 | Retained Earnings (Accumulated Deficit)
Summary Of Significant Accounting Policies [Line Items]
Reclassification to retained earnings upon adoption of accounting standard														$ 6
Minimum
Summary Of Significant Accounting Policies [Line Items]
Frequent flier program expiration period									1 year
Maximum
Summary Of Significant Accounting Policies [Line Items]
Frequent flier program expiration period									8 years
Aircraft Seats | Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life									10 years
Aircraft Seats | Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life									15 years
Aircraft and Aircraft Spare Parts
Summary Of Significant Accounting Policies [Line Items]
Residual value	10.00%								10.00%
Computer Software
Summary Of Significant Accounting Policies [Line Items]
Depreciation expense									$ 122	117		108
Computer Software | Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life									5 years
Computer Software | Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life									15 years
Passenger Revenue
Summary Of Significant Accounting Policies [Line Items]
Ancillary fees									$ 2,200	2,000		1,900
Passenger Revenue
Summary Of Significant Accounting Policies [Line Items]
Revenue									37,706	34,460	[1]	33,429	[1]
Other Operating Revenue
Summary Of Significant Accounting Policies [Line Items]
Revenue									2,360	2,210	[1]	2,195	[1]
Other Operating Revenue | Chase and Other Partner Agreements
Summary Of Significant Accounting Policies [Line Items]
Revenue									2,000	1,800		$ 1,700
Transportation Advance Ticket Arrangement | Passenger Revenue
Summary Of Significant Accounting Policies [Line Items]
Revenue									$ 3,100	$ 2,900

[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.