Fair Value Measurements - Schedule of Fair Value Measurements on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Net Asset (Liability)
Long-term investments	$ 1,367	$ 1,099
Recurring
Fair Value, Net Asset (Liability)
Cash equivalents	4,669	586
Restricted cash equivalents	494	847
Long-term investments	1,367	1,099
Recurring \| Fuel hedge contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	8	1
Recurring \| Interest rate contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	25	61
Recurring \| Foreign currency exchange contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	14	6
Recurring \| Level 1
Fair Value, Net Asset (Liability)
Cash equivalents	4,669	586
Restricted cash equivalents	494	847
Long-term investments	908	881
Recurring \| Level 1 \| Fuel hedge contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	(5)	(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	459	218
Recurring \| Level 2 \| Fuel hedge contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	13	2
Recurring \| Level 2 \| Interest rate contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	25	61
Recurring \| Level 2 \| Foreign currency exchange contracts
Fair Value, Net Asset (Liability)
Hedge derivatives, net	$ 14	$ 6

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.

No definition available.

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- Definition

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=117331979&loc=d3e41228-113958

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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- References

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- Definition

The aggregate value of all restricted investments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-12C.9(c))
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611225-123010

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-12.6(c))
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611133-123010

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