Condensed Consolidated Statement of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 116	$ (94)
Adjustments to reconcile net income to cash provided by (used in) operating activities:
Depreciation and amortization	312	311
Unrealized/realized (gain) loss on fuel derivative instruments	(7)	2
Deferred income taxes	5	(49)
Changes in certain assets and liabilities:
Accounts and other receivables	(234)	183
Other assets	(11)	58
Accounts payable and accrued liabilities	(66)	(1,291)
Air traffic liability	599	701
Other liabilities	(122)	(132)
Cash collateral received from (provided to) derivative counterparties	38	(5)
Other, net	15	(61)
Net cash provided by (used in) operating activities	645	(377)
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(95)	(224)
Supplier Proceeds	0	300
Purchases of short-term investments	(1,324)	(1,029)
Proceeds from sales of short-term and other investments	1,218	948
Net cash used in investing activities	(201)	(5)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of long-term debt	0	500
Proceeds from term loan credit facility	0	1,000
Proceeds from revolving credit facility	0	1,000
Proceeds from Payroll Support Program loan and warrants	511	0
Proceeds from Employee stock plans	13	11
Repurchase of common stock	0	(451)
Payments of long-term debt and finance lease obligations	(67)	(78)
Payments of cash dividends	0	(188)
Other, net	7	(20)
Net cash provided by financing activities	464	1,774
NET CHANGE IN CASH AND CASH EQUIVALENTS	908	1,392
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	11,063	2,548
CASH AND CASH EQUIVALENTS AT END OF PERIOD	11,971	3,940
CASH PAYMENTS FOR:
Interest, net of amount capitalized	17	14
Income taxes	1	5
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Right-of-use assets acquired under operating leases	218	25
Assets Constructed for Others	$ 32	$ 34