Recently Issued Accounting Standards - Impact of the Adoption of the New Lease Standard on the Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Receivables, less allowance for doubtful accounts	$ 1,617	$ 1,426	[1]
Prepaid expenses and other	725	733	[1]
Flight equipment, owned and finance leases	34,413	32,599	[1]
Other property and equipment, owned and finance leases	7,626	6,889	[1]
Accumulated depreciation and amortization, owned and finance leases	(14,153)	(13,266)	[1]
Operating lease right-of-use assets	4,937	5,262	[1]
Current maturities of finance leases	92	123	[1]
Current maturities of operating leases	778	719	[1]
Other current liabilities	574	553	[1]
Long-term obligations under finance leases	186	224	[1]
Long-term obligations under operating leases	4,941	5,276	[1]
Deferred income taxes	1,594	828	[1]
Other long-term liabilities	981	1,010	[1]
Retained earnings	$ 9,075	6,715	[1]
As Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Receivables, less allowance for doubtful accounts		1,346
Prepaid expenses and other		913
Flight equipment, owned and finance leases		32,636
Other property and equipment, owned and finance leases		7,930
Accumulated depreciation and amortization, owned and finance leases		(13,414)
Operating lease right-of-use assets		0
Current maturities of finance leases		149
Current maturities of operating leases		0
Other current liabilities		619
Long-term obligations under finance leases		1,134
Long-term obligations under operating leases		0
Deferred income taxes		814
Other long-term liabilities		1,832
Retained earnings		6,668
New Lease Standard | Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Receivables, less allowance for doubtful accounts		80
Prepaid expenses and other		(180)
Flight equipment, owned and finance leases		(37)
Other property and equipment, owned and finance leases		(1,041)
Accumulated depreciation and amortization, owned and finance leases		148
Operating lease right-of-use assets		5,262
Current maturities of finance leases		(26)
Current maturities of operating leases		719
Other current liabilities		(66)
Long-term obligations under finance leases		(910)
Long-term obligations under operating leases		5,276
Deferred income taxes		14
Other long-term liabilities		(822)
Retained earnings		$ 47

[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 I, Item 1 of this report for additional information.