Financial Derivative Instruments - Fair Values by Balance Sheet Location (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Derivatives, Fair Value
Gross amounts of recognized assets	$ 696	$ 134
Gross amounts offset in the balance sheet	4	6
Fuel derivative contracts \| Prepaid expenses and other current assets
Derivatives, Fair Value
Gross amounts of recognized assets	409	13
Gross amounts of recognized liabilities	80	3
Gross amounts offset in the balance sheet	80	3
Gross amounts offset in the balance sheet	80	3
Cash collateral deposits held from counterparties for fuel contracts - current	80	3
Fuel derivative contracts \| Other assets
Derivatives, Fair Value
Gross amounts of recognized assets	287	121
Gross amounts of recognized liabilities	95	31
Gross amounts offset in the balance sheet	95	31
Gross amounts offset in the balance sheet	95	31
Cash collateral deposits held from counterparties for fuel contracts - current	95	31
Fuel derivative contracts \| Accounts and other receivables
Derivatives, Fair Value
Receivable from third parties for fuel contracts	8	0
Interest rate derivatives \| Other noncurrent liabilities
Derivatives, Fair Value
Gross amounts offset in the balance sheet	0	0
Gross amounts offset in the balance sheet	4	6
Designated as Hedging Instrument
Derivatives, Fair Value
Gross amounts of recognized assets	696	130
Gross amounts offset in the balance sheet	4	6
Designated as Hedging Instrument \| Fuel derivative contracts \| Prepaid expenses and other current assets
Derivatives, Fair Value
Gross amounts of recognized assets	409	9
Designated as Hedging Instrument \| Fuel derivative contracts \| Other assets
Derivatives, Fair Value
Gross amounts of recognized assets	287	121
Designated as Hedging Instrument \| Interest rate derivatives \| Other noncurrent liabilities
Derivatives, Fair Value
Gross amounts offset in the balance sheet	4	6
Not Designated as Hedging Instrument \| Fuel derivative contracts \| Prepaid expenses and other current assets
Derivatives, Fair Value
Gross amounts of recognized assets	$ 0	$ 4

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

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Fair value of liability associated with 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.

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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.

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Fair value of asset associated with 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.

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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.

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