AOCI - Differences between Net Income and Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Condensed Statement of Income Captions [Line Items]
Net income (loss)	$ (94)	$ 387
Other, net of deferred taxes	(28)	11
Total other comprehensive income (loss)	(125)	76
Comprehensive income (loss)	(219)	463
Other deferred taxes	(9)	3
Fuel derivatives
Condensed Statement of Income Captions [Line Items]
Unrealized gain (loss) on derivative instruments, net of deferred taxes	(65)	76
Derivative deferred taxes	(19)	22
Interest rate derivatives
Condensed Statement of Income Captions [Line Items]
Unrealized gain (loss) on derivative instruments, net of deferred taxes	(32)	(11)
Derivative deferred taxes	$ (10)	$ (3)