Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Period over which miles are expected to be redeemed									P2Y
Revenue	$ 10,888	$ 11,380	$ 11,402	$ 9,589	$ 10,491	$ 11,003	$ 10,777	$ 9,032	$ 43,259	$ 41,303	[1]	$ 37,784	[1]
Carrying value of computer software	422				$ 359				422	359
Amortization expense									60	67		79
Projected amortization expense in 2020	55								55
Projected amortization expense in 2021	50								50
Projected amortization expense in 2022	40								40
Projected amortization expense in 2023	37								37
Projected amortization expense in 2024	$ 32								32
Advertising expense									$ 212	211		217
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									9 years
Computer software
Summary Of Significant Accounting Policies [Line Items]
Depreciation expense									$ 135	122		117
Advance Ticket Sales
Summary Of Significant Accounting Policies [Line Items]
Passenger revenue included in advance ticket sales recognized									3,400	3,100
Ancillary Fees Recorded within Passenger Revenues
Summary Of Significant Accounting Policies [Line Items]
Revenue									2,400	2,200		2,000
Other Operating Revenue
Summary Of Significant Accounting Policies [Line Items]
Revenue									2,455	2,360	[1]	2,210	[1]
Other Operating Revenue | Chase and Other Partner Agreements
Summary Of Significant Accounting Policies [Line Items]
Revenue									$ 2,000	2,000		$ 1,800
One-time payment										$ 50

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2016-02, Leases (Topic 842). See Note 1 to the financial statements contained in Part II, Item 8 of this report for additional information.