Financial Derivative Instruments - Offsetting of Derivative Assets (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Offsetting Assets
Asset derivative contracts, net		$ 49	$ 95
Fuel derivatives | Prepaid expenses and other current assets
Offsetting Assets
Gross amounts of recognized assets		48	43
Gross amounts offset in the Balance Sheet		(10)	0
Asset derivative contracts, net		38	43
Fuel derivatives | Other Assets
Offsetting Assets
Gross amounts of recognized assets		62	95
Gross amounts offset in the Balance Sheet		(15)	0
Asset derivative contracts, net	[1]	47	95
Interest rate derivatives | Other Assets
Offsetting Assets
Gross amounts of recognized assets		2	0
Gross amounts offset in the Balance Sheet		0	0
Asset derivative contracts, net	[1]	$ 2	$ 0

[1] The net amounts of derivative assets and liabilities are reconciled to the individual line item amounts presented in the Consolidated Balance Sheet in Note 15.