Summary of Significant Accounting Policies - Impact of Recently Adopted Standards (Details) - USD ($) $ / shares in Units, $ 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
Income statement:
Operating revenue									$ 44,438	$ 41,138	$ 39,450
Operating expense									39,174	35,172	32,454
Non-operating expense									(113)	(466)	(643)
Income tax provision									(1,216)	(2,295)	(2,158)
Net income	$ 1,019	$ 1,322	$ 1,036	$ 557	$ 299	$ 1,159	$ 1,186	$ 561	$ 3,935	$ 3,205	$ 4,195
Diluted earnings per share (usd per share)	$ 1.49	$ 1.92	$ 1.49	$ 0.79	$ 0.42	$ 1.61	$ 1.62	$ 0.77	$ 5.67	$ 4.43	$ 5.55
Balance sheet:
Deferred income taxes, net	$ 242				$ 1,354				$ 242	$ 1,354
Other accrued and other noncurrent liabilities					4,089					4,089
Retained earnings	10,039				8,256				10,039	8,256
As Previously Reported | Recently Adopted Standards
Income statement:
Operating revenue										41,244	$ 39,639
Operating expense										35,130	32,687
Non-operating expense										(413)	(316)
Income tax provision										(2,124)	(2,263)
Net income										$ 3,577	$ 4,373
Diluted earnings per share (usd per share)										$ 4.95	$ 5.79
Balance sheet:
Deferred income taxes, net					935					$ 935
Other accrued and other noncurrent liabilities					3,969					3,969
Retained earnings					9,636					9,636
Adjustments | Recently Adopted Standards
Income statement:
Operating revenue										(106)	$ (189)
Operating expense										42	(233)
Non-operating expense										(53)	(327)
Income tax provision										(171)	105
Net income										$ (372)	$ (178)
Diluted earnings per share (usd per share)										$ (0.52)	$ (0.24)
Balance sheet:
Deferred income taxes, net					419					$ 419
Other accrued and other noncurrent liabilities					120					120
Retained earnings					(1,380)					(1,380)
Passenger
Income statement:
Operating revenue									39,755	36,947	$ 35,814
Passenger | As Previously Reported | Recently Adopted Standards
Income statement:
Operating revenue										34,819	33,777
Passenger | Adjustments | Recently Adopted Standards
Income statement:
Operating revenue										2,128	2,037
Cargo
Income statement:
Operating revenue									865	744	684
Cargo | As Previously Reported | Recently Adopted Standards
Income statement:
Operating revenue										729	668
Cargo | Adjustments | Recently Adopted Standards
Income statement:
Operating revenue										15	16
Other
Income statement:
Operating revenue									3,818	3,447	2,952
Other | As Previously Reported | Recently Adopted Standards
Income statement:
Operating revenue										5,696	5,194
Other | Adjustments | Recently Adopted Standards
Income statement:
Operating revenue										(2,249)	(2,242)
Air traffic
Income statement:
Operating revenue									34,950	32,467	31,534
Balance sheet:
Deferred revenue, current	4,661				4,364				4,661	4,364
Air traffic | As Previously Reported | Recently Adopted Standards
Balance sheet:
Deferred revenue, current					4,888					4,888
Air traffic | Adjustments | Recently Adopted Standards
Balance sheet:
Deferred revenue, current					(524)					(524)
Loyalty program
Income statement:
Operating revenue									1,459	1,269	1,110
Balance sheet:
Deferred revenue, current	2,989				2,762				2,989	2,762
Deferred revenue (current and noncurrent)	$ 6,641				6,321				$ 6,641	6,321	$ 5,922
Loyalty program | As Previously Reported | Recently Adopted Standards
Balance sheet:
Deferred revenue (current and noncurrent)					4,118					4,118
Loyalty program | Adjustments | Recently Adopted Standards
Balance sheet:
Deferred revenue (current and noncurrent)					$ 2,203					$ 2,203