Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (2)	$ (1)	$ (2)	$ (1)	$ (3)	$ 2	$ 1	$ (3)
Other Comprehensive Income (Loss), Derivative, Excluded Component, Increase (Decrease), Adjustments, after Tax	0	(2)	(11)	(1)
Fuel Derivatives [Member]
Derivative [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(2)	$ (1)	(2)	$ (1)	$ (3)	$ 2	$ 1	$ (3)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	$ 1		$ 5

- Definition

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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