Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated other comprehensive income (loss), net of taxes
Accumulated gains (losses), beginning balance	$ 2	$ (3)	$ 0
Reclassification into earnings, Tax	5	1	0
Reclassifications into earnings	9	4	1
Change in fair value	(11)	1	(4)
Change in fair value, tax	(5)	0	(2)
Accumulated gains (losses), ending balance	0	2	(3)
Aircraft Fuel Derivatives
Accumulated other comprehensive income (loss), net of taxes
Accumulated gains (losses), beginning balance	2	(3)	0
Reclassifications into earnings	9	4	1
Change in fair value	(11)	1	(4)
Accumulated gains (losses), ending balance	0	$ 2	$ (3)
Other comprehensive income (loss), cash flow hedge, reclassification for discontinuance, before tax	$ 5

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount, after reclassification, of tax expense (benefit) for gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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Amount of tax expense (benefit) for reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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Amount, before tax, of reclassification from accumulated other comprehensive income (AOCI) for gain (loss) from discontinuance of cash flow hedge included in assessment of hedge effectiveness.

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Amount after tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Amount after tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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