Fair Value Measurements - Measured at Fair Value on a Recurring Basis (Details) - Recurring - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Fair Value
Cash equivalents	$ 5,132	$ 5,450
Restricted cash equivalents	429	635
Short-term investments	2,250	3,386
Long-term investments	1,312	1,459
Fuel hedge contracts	(14)	(18)
Level 1
Fair Value
Cash equivalents	5,132	5,450
Restricted cash equivalents	429	635
Short-term investments	681	1,376
Long-term investments	1,179	1,326
Fuel hedge contracts	0	0
Level 2
Fair Value
Cash equivalents	0	0
Restricted cash equivalents	0	0
Short-term investments	1,569	2,010
Long-term investments	36	36
Fuel hedge contracts	(14)	(18)
Level 3
Fair Value
Cash equivalents	0	0
Restricted cash equivalents	0	0
Short-term investments	0	0
Long-term investments	97	97
Fuel hedge contracts	$ 0	$ 0

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

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The aggregate value of all restricted investments.

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