Significant Accounting Policies - Information about Goodwill and Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Goodwill	$ 4,527	$ 4,527
Indefinite-lived Intangible Assets [Line Items]
Gross  Carrying Amount	2,591	2,577
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,756	1,756
Accumulated Amortization	1,544	1,495
Route authorities
Indefinite-lived Intangible Assets [Line Items]
Gross  Carrying Amount	1,020	1,020
Airport slots and gates
Indefinite-lived Intangible Assets [Line Items]
Gross  Carrying Amount	574	560
Tradenames and logos
Indefinite-lived Intangible Assets [Line Items]
Gross  Carrying Amount	593	593
Alliances
Indefinite-lived Intangible Assets [Line Items]
Gross  Carrying Amount	404	404
Frequent flyer database
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,177	1,177
Accumulated Amortization	1,008	971
Hubs
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	145	145
Accumulated Amortization	118	111
Contracts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	120	120
Accumulated Amortization	120	116
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	314	314
Accumulated Amortization	$ 298	$ 297