Fair Value Measurements - Measured on Recurring Basis (Details) - USD ($)		Jun. 30, 2020	Dec. 31, 2019
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	[1]	$ 109,000,000	$ 112,000,000
Fuel derivatives:
Derivative Liability, Fair Value, Gross Liability	[1]	(74,000,000)	(6,000,000)
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Treasury bills		1,649,000,000	1,196,000,000
Interest rate derivatives (see Note 4)			0
Fuel derivatives:
Other available for sale securities		219,000,000	197,000,000
Total assets		13,829,000,000	3,392,000,000
Liabilities
Interest rate derivatives (see Note 4)		0	0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Treasury bills		0	0
Interest rate derivatives (see Note 4)		2,000,000	2,000,000
Fuel derivatives:
Other available for sale securities		0	0
Total assets		849,000,000	879,000,000
Liabilities
Interest rate derivatives (see Note 4)		(74,000,000)	(6,000,000)
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Treasury bills		0	0
Interest rate derivatives (see Note 4)			0
Fuel derivatives:
Other available for sale securities		0	0
Total assets		107,000,000	110,000,000
Liabilities
Interest rate derivatives (see Note 4)		0	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]	107,000,000	110,000,000
Cash Equivalents | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Cash equivalents	[3]	11,961,000,000	1,999,000,000
Cash Equivalents | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Cash equivalents	[3]	0	0
Cash Equivalents | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Cash equivalents	[3]	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		90,000,000	535,000,000
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
Investments		0	0
Certificates of Deposit | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Cash equivalents		19,000,000	14,000,000
Investments		132,000,000	268,000,000
Certificates of Deposit | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Cash equivalents		0	0
Investments		0	0
Time Deposits | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Cash equivalents		0
Investments		0	0
Time Deposits | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Cash equivalents		281,000,000
Investments		325,000,000	60,000,000
Time Deposits | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Cash equivalents		0
Investments		0	0
Estimate of Fair Value Measurement | Fair Value, Measurements, Recurring
Assets
Treasury bills		1,649,000,000	1,196,000,000
Interest rate derivatives (see Note 4)		2,000,000	2,000,000
Fuel derivatives:
Other available for sale securities		219,000,000	197,000,000
Total assets		14,785,000,000	4,381,000,000
Liabilities
Interest rate derivatives (see Note 4)		(74,000,000)	(6,000,000)
Estimate of Fair Value Measurement | Options Held | Fair Value, Measurements, Recurring
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	[2]	107,000,000	110,000,000
Estimate of Fair Value Measurement | Cash Equivalents | Fair Value, Measurements, Recurring
Assets
Cash equivalents	[3]	11,961,000,000	1,999,000,000
Estimate of Fair Value Measurement | Commercial Paper | Fair Value, Measurements, Recurring
Assets
Cash equivalents		90,000,000	535,000,000
Estimate of Fair Value Measurement | Certificates of Deposit | Fair Value, Measurements, Recurring
Assets
Cash equivalents		19,000,000	14,000,000
Investments		132,000,000	268,000,000
Estimate of Fair Value Measurement | Time Deposits | Fair Value, Measurements, Recurring
Assets
Cash equivalents		281,000,000
Investments		$ 325,000,000	$ 60,000,000

[1] Represents the position of each trade before consideration of offsetting positions with each counterparty and does not include the impact of cash collateral deposits provided to or received from counterparties. See discussion of credit risk and collateral following in this Note.

[2] In the unaudited Condensed Consolidated Balance Sheet amounts are presented as a net asset. See Note 4.

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