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Leases - Components of Lease Cost (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Lessee, Lease, Description [Line Items]      
Short-term lease cost $ 1 $ 1 $ 4
Variable lease cost 1,406 1,260 1,377
Finance lease cost:      
Amortization of lease liabilities 112 113 116
Interest on lease liabilities 19 22 26
Total net finance lease cost 131 135 142
Sublease income 41 78 97
Aircraft      
Lessee, Lease, Description [Line Items]      
Operating lease cost 204 216 182
Other      
Lessee, Lease, Description [Line Items]      
Operating lease cost $ 81 $ 89 $ 89