AOCI - Schedule of AOCI Components (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Fuel derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ (170)	$ (125)
Changes in fair value	(21)	(118)
Ending Balance	(151)	(151)
Interest rate derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(74)	(33)
Changes in fair value	3	(39)
Reclassification to earnings	0	1
Ending Balance	(71)	(71)
Defined Benefit Plan Items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	20	20
Changes in fair value	0	0
Reclassification to earnings	0	0
Ending Balance	20	20
Other comprehensive income (loss) other changes net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	55	59
Changes in fair value	14	10
Reclassification to earnings	0	0
Ending Balance	69	69
Deferred Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	39	18
Changes in fair value	1	34
Reclassification to earnings	(9)	(21)
Ending Balance	31	31
AOCI Including Portion Attributable to Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(130)	(61)
Changes in fair value	(3)	(113)
Reclassification to earnings	31	72
Ending Balance	(102)	(102)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Fuel derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification to earnings	$ 40	$ 92