AOCI - Schedule of AOCI Components (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2019
Fuel derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 42	$ (56)
Changes in fair value	(71)	16
Ending Balance	(31)	(31)
Interest rate derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(14)	0
Changes in fair value	(20)	(35)
Reclassification to earnings	(1)	(2)
Ending Balance	(33)	(33)
Defined Benefit Plan Items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	58	58
Changes in fair value	0	0
Reclassification to earnings	0	0
Ending Balance	58	58
Other comprehensive income other changes net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	39	25
Changes in fair value	6	20
Reclassification to earnings	0	0
Ending Balance	45	45
Deferred Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(29)	(7)
Changes in fair value	20	0
Reclassification to earnings	0	(2)
Ending Balance	(9)	(9)
AOCI Including Portion Attributable to Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	96	20
Changes in fair value	(65)	1
Reclassification to earnings	(1)	9
Ending Balance	30	30
Reclassification out of Accumulated Other Comprehensive Income \| Fuel derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification to earnings	$ (2)	$ 9

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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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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