Fair Value Measurements - Measured on Recurring Basis (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Assets
Time Deposits		$ 60
Quoted prices in active markets for identical assets (Level 1)
Assets
Time Deposits		0
Significant other observable inputs (Level 2)
Assets
Time Deposits		60
Significant unobservable inputs (Level 3)
Assets
Time Deposits		0
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Treasury bills		1,196	$ 1,582
Interest rate derivatives (see Note 10)		0
Fuel derivatives:
Other available for sale securities		197	127
Assets, Fair Value Disclosure		3,392	3,101
Fuel derivatives:
Interest rate derivatives (see Note 10)		0	0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Treasury bills		0	0
Interest rate derivatives (see Note 10)		2
Fuel derivatives:
Other available for sale securities		0	0
Assets, Fair Value Disclosure		879	715
Fuel derivatives:
Interest rate derivatives (see Note 10)		(6)	(14)
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Treasury bills		0	0
Interest rate derivatives (see Note 10)		0
Fuel derivatives:
Assets, Fair Value Disclosure		110	138
Fuel derivatives:
Interest rate derivatives (see Note 10)		0	0
Cash Equivalents | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Cash equivalents	[1]	1,999	1,392
Cash Equivalents | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Cash equivalents	[1]	0	0
Cash Equivalents | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Cash equivalents	[1]	0	0
Commercial paper | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Cash equivalents		0	0
Commercial paper | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Cash equivalents		535	454
Commercial paper | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Cash equivalents		0	0
Certificates of deposit | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Cash equivalents		0	0
Certificates of deposit | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Cash equivalents		14	8
Certificates of deposit | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Cash equivalents		0	0
Certificates of deposit | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Investments		0	0
Certificates of deposit | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Investments		268	228
Certificates of deposit | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Investments		0	0
Bank Time Deposits [Member] | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Investments		0
Bank Time Deposits [Member] | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Investments		25
Bank Time Deposits [Member] | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Investments		0
Options Held | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	[2]	0	0
Options Held | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	[2]	0	0
Options Held | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	[2]	110	138
Period end date | Fair Value, Measurements, Recurring
Assets
Treasury bills		1,196	1,582
Interest rate derivatives (see Note 10)		2
Fuel derivatives:
Other available for sale securities		197	127
Assets, Fair Value Disclosure		4,381	3,954
Fuel derivatives:
Interest rate derivatives (see Note 10)		(6)	(14)
Period end date | Cash Equivalents | Fair Value, Measurements, Recurring
Assets
Cash equivalents	[1]	1,999	1,392
Period end date | Commercial paper | Fair Value, Measurements, Recurring
Assets
Cash equivalents		535	454
Period end date | Certificates of deposit | Fair Value, Measurements, Recurring
Assets
Cash equivalents		14	8
Period end date | Certificates of deposit | Fair Value, Measurements, Recurring
Assets
Investments		268	228
Period end date | Bank Time Deposits [Member] | Fair Value, Measurements, Recurring
Assets
Investments		25
Period end date | Options Held | Fair Value, Measurements, Recurring
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	[2]	$ 110	$ 138

[1] Cash equivalents are primarily composed of money market investments.

[2] In the Consolidated Balance Sheet amounts are presented as an asset. See Note 10.