Fair Value Measurements (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Net Asset (Liability)
Long-term investments	$ 1,384	$ 1,099
Recurring
Fair Value, Net Asset (Liability)
Cash equivalents	8,225	586
Restricted cash equivalents	452	847
Long-term investments	1,384	1,099
Recurring \| U.S. Government securities
Fair Value, Net Asset (Liability)
Short-term investments	4,302
Recurring \| Fuel hedge contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	(6)	1
Recurring \| Interest rate contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	26	61
Recurring \| Foreign currency exchange contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	6	6
Recurring \| Level 1
Fair Value, Net Asset (Liability)
Cash equivalents	8,225	586
Restricted cash equivalents	452	847
Long-term investments	924	881
Recurring \| Level 1 \| U.S. Government securities
Fair Value, Net Asset (Liability)
Short-term investments	4,244
Recurring \| Level 1 \| Fuel hedge contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	0	(1)
Recurring \| Level 1 \| Interest rate contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	0	0
Recurring \| Level 1 \| Foreign currency exchange contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	0	0
Recurring \| Level 2
Fair Value, Net Asset (Liability)
Cash equivalents	0	0
Restricted cash equivalents	0	0
Long-term investments	226	218
Recurring \| Level 2 \| U.S. Government securities
Fair Value, Net Asset (Liability)
Short-term investments	58
Recurring \| Level 2 \| Fuel hedge contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	(6)	2
Recurring \| Level 2 \| Interest rate contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	26	61
Recurring \| Level 2 \| Foreign currency exchange contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	6	$ 6
Recurring \| Level 3
Fair Value, Net Asset (Liability)
Cash equivalents	0
Restricted cash equivalents	0
Long-term investments	234
Recurring \| Level 3 \| U.S. Government securities
Fair Value, Net Asset (Liability)
Short-term investments	0
Recurring \| Level 3 \| Fuel hedge contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	0
Recurring \| Level 3 \| Interest rate contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	0
Recurring \| Level 3 \| Foreign currency exchange contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	$ 0

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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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The aggregate value of all restricted investments.

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