Financial Derivative Instruments - Fair Values by Balance Sheet Location (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Gross amounts of recognized assets	$ 234	$ 223
Gross amounts of recognized liabilities	14	0
Fuel derivative contracts \| Prepaid expenses and other current assets
Derivatives, Fair Value [Line Items]
Gross amounts of recognized assets	95	86
Gross amounts of recognized liabilities	27	15
Fuel derivative contracts \| Other assets
Derivatives, Fair Value [Line Items]
Gross amounts of recognized assets	139	137
Gross amounts of recognized liabilities	17	35
Cash collateral deposits held from counterparties for fuel contracts	17	35
Fuel derivative contracts \| Other Current Assets
Derivatives, Fair Value [Line Items]
Cash collateral deposits held from counterparties for fuel contracts	13	15
Fuel derivative contracts \| Accounts and other receivables
Derivatives, Fair Value [Line Items]
Receivable from third parties for fuel contracts	6	12
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Gross amounts of recognized assets	222	223
Gross amounts of recognized liabilities	0	0
Designated as Hedging Instrument \| Fuel derivative contracts \| Prepaid expenses and other current assets
Derivatives, Fair Value [Line Items]
Gross amounts of recognized assets	83	86
Gross amounts of recognized liabilities	0	0
Designated as Hedging Instrument \| Fuel derivative contracts \| Other assets
Derivatives, Fair Value [Line Items]
Gross amounts of recognized assets	139	137
Gross amounts of recognized liabilities	0	0
Not Designated as Hedging Instrument \| Fuel derivative contracts \| Prepaid expenses and other current assets
Derivatives, Fair Value [Line Items]
Gross amounts of recognized assets	12	0
Gross amounts of recognized liabilities	$ 14	$ 0

Derivative, Cash Receivable (Payable) On Hedge

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 5
-SubTopic 10
-Topic 815
-Publisher FASB
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-SubTopic 20
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483466/210-20-50-3

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other 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 assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 815
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
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-Name Accounting Standards Codification
-Section 55
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-22

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-7

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-SubTopic 20
-Topic 860
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481326/860-20-50-4D

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value, before 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 elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Details

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