New Accounting Pronouncements - Adjustments (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle
Prepaid expenses and other current assets	$ 354		$ 310
Flight equipment	21,666		21,753
Assets constructed for others	120		1,768
Less allowance for depreciation and amortization	(9,875)		(9,731)
Operating lease right-of-use assets	1,508		0
Other assets	725		720
Total assets	26,459		26,243
Accounts payable	1,412		1,416
Accrued liabilities	1,350		1,749
Current operating lease liabilities	361		0
Current maturities of long-term debt	571		606
Long-term debt less current maturities	2,602		2,771
Deferred income taxes	2,480		2,427
Construction obligation	120		1,701
Noncurrent operating lease liabilities	1,150		0
Other noncurrent liabilities	608		650
Retained earnings	16,320		15,967
Total liabilities and stockholders' equity	$ 26,459		$ 26,243
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle
Prepaid expenses and other current assets		$ (1)
Flight equipment		(110)
Assets constructed for others		(1,669)
Less allowance for depreciation and amortization		(164)
Operating lease right-of-use assets		1,466
Other assets		(121)
Total assets		(271)
Accounts payable		(8)
Accrued liabilities		(37)
Current operating lease liabilities		355
Current maturities of long-term debt		(14)
Long-term debt less current maturities		(96)
Deferred income taxes		17
Construction obligation		(1,602)
Noncurrent operating lease liabilities		1,119
Other noncurrent liabilities		(60)
Retained earnings		55
Total liabilities and stockholders' equity		(271)
Balances Removed Under Prior Accounting | ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle
Prepaid expenses and other current assets		1
Flight equipment		0
Assets constructed for others		1,669
Less allowance for depreciation and amortization		(166)
Operating lease right-of-use assets		0
Other assets		121
Total assets		1,625
Accounts payable		8
Accrued liabilities		37
Current operating lease liabilities		0
Current maturities of long-term debt		0
Long-term debt less current maturities		0
Deferred income taxes		(17)
Construction obligation		1,602
Noncurrent operating lease liabilities		0
Other noncurrent liabilities		60
Retained earnings		(65)
Total liabilities and stockholders' equity		1,625
Balances Added Under New Lease Standard | ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle
Prepaid expenses and other current assets		0
Flight equipment		(110)
Assets constructed for others		0
Less allowance for depreciation and amortization		(2)
Operating lease right-of-use assets		1,466
Other assets		0
Total assets		1,354
Accounts payable		0
Accrued liabilities		0
Current operating lease liabilities		355
Current maturities of long-term debt		(14)
Long-term debt less current maturities		(96)
Deferred income taxes		0
Construction obligation		0
Noncurrent operating lease liabilities		1,119
Other noncurrent liabilities		0
Retained earnings		(10)
Total liabilities and stockholders' equity		$ 1,354