Financial Derivative Instruments and Risk Management (Details) bbl in Thousands, $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2020 USD ($) bbl	Dec. 31, 2019 USD ($) bbl
Derivative [Line Items]
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	$ 3	$ (2)
Fuel Derivatives [Member]
Derivative [Line Items]
Longest remaining term, cash flow hedge (months)	6 months	6 months
Barrels Of Fuel Covered Under Derivative Contracts \| bbl	1,220	2,112
Derivative, Collateral, Right to Reclaim Cash	$ 0	$ 0
Fuel [Member] \| Call Option [Member]
Derivative [Line Items]
Percentage Fuel Hedged - Third Quarter Current Year	19.00%
Percentage Fuel Hedged - Fourth Quarter Second Year	20.00%
Fair Value, Recurring [Member]
Derivative [Line Items]
Derivative Asset	$ 0	8
Fair Value, Inputs, Level 1 [Member] \| Fair Value, Recurring [Member]
Derivative [Line Items]
Derivative Asset	0	0
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Recurring [Member]
Derivative [Line Items]
Derivative Asset	$ 0	$ 8

Barrels of fuel covered under derivative contracts as of the end of the period.

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Percentage Fuel Hedged - Fourth Quarter Current Year

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Percentage Fuel Hedged - Third Quarter Current Year

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- Definition

Fair value, after the 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 not subject to a master netting arrangement and not elected to be offset.

+ References

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- Definition

Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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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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Maximum period the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The estimated net amount of unrealized gains or losses on price risk cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

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