Consolidated Statement of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ (3,074)	$ 2,300	$ 2,465
Adjustments to reconcile net income (loss) to cash provided by (used in) operating activities:
Depreciation and amortization	1,255	1,219	1,201
Loss on asset impairment	32	0	0
Unrealized/realized (gain) loss on fuel derivative instruments	15	0	(14)
Deferred income taxes	(716)	(55)	301
Gain on sale-leaseback transactions	(222)	0	0
Changes in certain assets and liabilities:
Accounts and other receivables	(294)	(94)	117
Other assets	415	239	(227)
Accounts payable and accrued liabilities	231	298	545
Air traffic liability	1,623	440	506
Other liabilities	(306)	(277)	0
Cash collateral received from (provided to) derivative counterparties	9	25	(15)
Other, net	(95)	(108)	14
Net cash provided by (used in) operating activities	(1,127)	3,987	4,893
Net Cash Provided by (Used in) Investing Activities [Abstract]
Capital expenditures	(515)	(1,027)	(1,922)
Supplier Proceeds	428	400	0
Proceeds from sale-leaseback transactions	815	0	0
Assets constructed for others	0	0	(54)
Purchases of short-term investments	(5,080)	(2,122)	(2,409)
Proceeds from sale of short-term and other investments	4,336	2,446	2,342
Other, net	0	0	5
Net cash used in investing activities	(16)	(303)	(2,038)
Net cash provided by (used in) financing activities
Issuance of common stock	2,294	0	0
Proceeds from issuance of long-term debt	5,622	0	0
Proceeds from term loan credit facility	3,683	0	0
Proceeds from revolving credit facility	1,000	0	0
Proceeds from convertible notes	2,300	0	0
Proceeds from Payroll support program loans and warrants	1,016	0	0
Proceeds from Employee stock plans	48	40	35
Repurchase of common stock	(451)	(2,000)	(2,000)
Reimbursement for assets constructed for others	0	0	170
Payments of long-term debt and finance lease obligations	(839)	(615)	(342)
Payments of cash dividends	(188)	(372)	(332)
Payments of terminated interest rate derivative instruments	(59)	0	0
Repayment of construction obligation	0	0	(30)
Capitalized financing items	(134)	0	0
Other, net	49	(43)	3
Net cash provided by (used in) financing activities	9,658	(2,990)	(2,496)
NET CHANGE IN CASH AND CASH EQUIVALENTS	8,515	694	359
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	2,548	1,854	1,495
CASH AND CASH EQUIVALENTS AT END OF PERIOD	11,063	2,548	1,854
CASH PAYMENTS FOR:
Interest, net of amount capitalized	212	88	107
Income taxes	19	779	327
SUPPLEMENTAL DISCLOSURE OF NONCASH TRANSACTIONS:
Assets constructed for others	145	65	171
Supplier receivables	0	428	0
Revolving Credit Facility
Net cash provided by (used in) financing activities
Payments of revolving credit facility	(1,000)	0	0
364-Day Term Loan Credit Facility
Net cash provided by (used in) financing activities
Payments of term loan credit facility	$ (3,683)	$ 0	$ 0