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Financial Derivative Instruments - Fair Values by Balance Sheet Location (Details) - USD ($) $ in Millions | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Derivatives, Fair Value [Line Items] |  |
Gross amounts of recognized assets | $ 682 | $ 134
Gross amounts of recognized liabilities | 2 | 6
Fuel derivative contracts | Prepaid expenses and other current assets |  |
Derivatives, Fair Value [Line Items] |  |
Gross amounts of recognized assets | 338 | 13
Gross amounts of recognized liabilities | 69 | 3
Fuel derivative contracts | Other assets |  |
Derivatives, Fair Value [Line Items] |  |
Gross amounts of recognized assets | 343 | 121
Gross amounts of recognized liabilities | 93 | 31
Cash collateral deposits held from counterparties for fuel contracts - current | 93 | 31
Fuel derivative contracts | Other Current Assets |  |
Derivatives, Fair Value [Line Items] |  |
Cash collateral deposits held from counterparties for fuel contracts - current | 69 | 3
Fuel derivative contracts | Accounts and other receivables |  |
Derivatives, Fair Value [Line Items] |  |
Receivable from third parties for fuel contracts | 8 | 0
Interest rate derivatives | Other assets |  |
Derivatives, Fair Value [Line Items] |  |
Gross amounts of recognized assets | 1 | 0
Interest rate derivatives | Other noncurrent liabilities |  |
Derivatives, Fair Value [Line Items] |  |
Gross amounts of recognized liabilities | 2 | 6
Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Gross amounts of recognized assets | 666 | 130
Gross amounts of recognized liabilities | 2 | 6
Designated as Hedging Instrument | Fuel derivative contracts | Prepaid expenses and other current assets |  |
Derivatives, Fair Value [Line Items] |  |
Gross amounts of recognized assets | 322 | 9
Designated as Hedging Instrument | Fuel derivative contracts | Other assets |  |
Derivatives, Fair Value [Line Items] |  |
Gross amounts of recognized assets | 343 | 121
Designated as Hedging Instrument | Interest rate derivatives | Other assets |  |
Derivatives, Fair Value [Line Items] |  |
Gross amounts of recognized assets | 1 |
Designated as Hedging Instrument | Interest rate derivatives | Other noncurrent liabilities |  |
Derivatives, Fair Value [Line Items] |  |
Gross amounts of recognized liabilities | 2 | 6
Not Designated as Hedging Instrument | Fuel derivative contracts | Prepaid expenses and other current assets |  |
Derivatives, Fair Value [Line Items] |  |
Gross amounts of recognized assets | $ 16 | $ 4

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- 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://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 22 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 4D -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=121570589&loc=SL51823488-111719 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (a),(c) -URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5624163-113959 + Details
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