Financial Derivative Instruments - Schedule of Fair Values by Balance Sheet Location (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fuel derivative contracts \| Prepaid expenses and other current assets
Derivatives, Fair Value [Line Items]
Gross amounts of recognized assets	$ 0	$ 22
Cash collateral deposits held from counterparties for fuel contracts	0	4
Fuel derivative contracts \| Other assets
Derivatives, Fair Value [Line Items]
Gross amounts of recognized assets	0	108
Cash collateral deposits held from counterparties for fuel contracts	0	18
Fuel derivative contracts \| Accounts and other receivables
Derivatives, Fair Value [Line Items]
Receivable from third parties for fuel contracts	0	1
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Gross amounts of recognized assets	0	130
Designated as Hedging Instrument \| Fuel derivative contracts \| Prepaid expenses and other current assets
Derivatives, Fair Value [Line Items]
Gross amounts of recognized assets	0	22
Designated as Hedging Instrument \| Fuel derivative contracts \| Other assets
Derivatives, Fair Value [Line Items]
Gross amounts of recognized assets	$ 0	$ 108

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.