Leases Capital Leases, Balance Sheet, Assets by Major Class, Net (Details) $ in Millions		12 Months Ended
		Dec. 31, 2018 USD ($) aircraft Years	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) aircraft
Capital Leased Assets
2019		$ 111
2020		109
2021		105
2022		100
2023		97
Thereafter		335
Total minimum lease payments		857
Less amount representing interest		126
Present value of minimum lease payments (a)	[1]	731
Less current portion		85
Long-term portion		$ 646
Operating Leased Assets [Line Items]
Capital Leased Assets, Number of Units | aircraft		72
2019		$ 348
2020		357		$ 78
2021		244		41
2022		172		17
2023		146		7
Thereafter		474
Total minimum lease payments		1,741
2019		256
2020		279
2021		203
2022		155
2023		139
Thereafter		473
Total minimum lease payments		1,505
Lease Incentive Obligation Excluded		114
Rental expense for operating leases		$ 935	$ 939
Property Subject to or Available for Operating Lease, Number of Units | Years		51
Subleases
2019		$ (92)
2020		(78)
2021		(41)
2022		(17)
2023		(7)
Thereafter		(1)
Total minimum lease payments		$ (236)
Capital Leased Assets [Line Items]
Capital Leased Assets, Number of Units | aircraft		72
2019		$ 348
2020		357		78
2021		244		41
2022		172		17
2023		146		$ 7
Thereafter		474
Total minimum lease payments		1,741
2019		256
2020		279
2021		203
2022		155
2023		139
Thereafter		473
Total minimum lease payments		1,505
Lease Incentive Obligation Excluded		114
Rental expense for operating leases		$ 935	$ 939
Property Subject to or Available for Operating Lease, Number of Units | Years		51
Property Available for Operating Lease [Member]
Operating Leased Assets [Line Items]
Property Subject to or Available for Operating Lease, Number of Units | aircraft		124
Capital Leased Assets [Line Items]
Property Subject to or Available for Operating Lease, Number of Units | aircraft		124
B-717-200
Operating Leased Assets [Line Items]
Property Subject to or Available for Operating Lease, Number of Units | aircraft		73		65
Capital Leased Assets [Line Items]
Property Subject to or Available for Operating Lease, Number of Units | aircraft		73		65

[1] Excludes lease incentive obligation of $114 million.