Fair Value Measurements - Measured on Recurring Basis (Details) - USD ($) $ in Millions		3 Months Ended
		Jun. 30, 2016		Dec. 31, 2015
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	[1]	$ 790		$ 1,937
Fuel derivatives:
Derivative Liability, Fair Value, Gross Liability	[1]	(1,770)		(3,465)
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount		0		0
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount		0		0
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount		0		0
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Transfers, Net		0		0
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Treasury bills		1,098		1,248
Interest rate derivatives (see Note 3)		0		0
Fuel derivatives:
Other available for sale securities		78		66
Total assets		2,862		2,651
Liabilities
Interest rate derivatives (see Note 3)		0		0
Total Liabilities		0		0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Treasury bills		0		0
Interest rate derivatives (see Note 3)		21		2
Fuel derivatives:
Other available for sale securities		0		0
Total assets		950		1,437
Liabilities
Interest rate derivatives (see Note 3)		(44)		(49)
Total Liabilities		(392)		(823)
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Treasury bills		0		0
Interest rate derivatives (see Note 3)		0		0
Fuel derivatives:
Other available for sale securities		26		27
Total assets		497		993
Liabilities
Interest rate derivatives (see Note 3)		0		0
Total Liabilities		(1,378)		(2,642)
Cash Equivalents | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Cash equivalents		1,686	[2]	1,337	[3]
Cash Equivalents | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Cash equivalents		0	[2]	0	[3]
Cash Equivalents | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Cash equivalents		0	[2]	0	[3]
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		270		200
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		9		13
Certificates of deposit | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Cash equivalents		0		0
Eurodollar time deposits | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Cash equivalents		0		0
Eurodollar time deposits | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Cash equivalents		75		33
Eurodollar time deposits | 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		277		220
Certificates of deposit | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Investments		0		0
Swap | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset		0	[4]	0	[5]
Derivative Liability, Fair Value, Gross Asset		0	[6]	0	[7]
Fuel derivatives:
Derivative Liability, Fair Value, Gross Liability		0	[6]	0	[7]
Swap | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset		15	[4]	38	[5]
Derivative Liability, Fair Value, Gross Asset		283	[6]	931	[7]
Fuel derivatives:
Derivative Liability, Fair Value, Gross Liability		(348)	[6]	(774)	[7]
Swap | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset		0	[4]	0	[5]
Derivative Liability, Fair Value, Gross Asset		0	[6]	0	[7]
Fuel derivatives:
Derivative Liability, Fair Value, Gross Liability		0	[6]	0	[7]
Options Held | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset		0	[4]	0	[5]
Derivative Liability, Fair Value, Gross Asset		0	[6]	0	[7]
Fuel derivatives:
Derivative Asset, Fair Value, Gross Liability		0	[4]	0	[5]
Derivative Liability, Fair Value, Gross Liability		0	[6]	0	[7]
Options Held | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset		0	[4]	0	[5]
Derivative Liability, Fair Value, Gross Asset		0	[6]	0	[7]
Fuel derivatives:
Derivative Asset, Fair Value, Gross Liability		0	[4]	0	[5]
Derivative Liability, Fair Value, Gross Liability		0	[6]	0	[7]
Options Held | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset		15	[4]	10	[5]
Derivative Liability, Fair Value, Gross Asset		456	[6]	956	[7]
Fuel derivatives:
Derivative Asset, Fair Value, Gross Liability		(10)	[4]	(26)	[5]
Derivative Liability, Fair Value, Gross Liability		(1,368)	[6]	(2,616)	[7]
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring
Assets
Treasury bills		1,098		1,248
Interest rate derivatives (see Note 3)		21		2
Fuel derivatives:
Other available for sale securities		104		93
Total assets		4,309		5,081
Liabilities
Interest rate derivatives (see Note 3)		(44)		(49)
Total Liabilities		(1,770)		(3,465)
Estimate of Fair Value Measurement [Member] | Cash Equivalents | Fair Value, Measurements, Recurring
Assets
Cash equivalents		1,686	[2]	1,337	[3]
Estimate of Fair Value Measurement [Member] | Commercial paper | Fair Value, Measurements, Recurring
Assets
Cash equivalents		270		200
Estimate of Fair Value Measurement [Member] | Certificates of deposit | Fair Value, Measurements, Recurring
Assets
Cash equivalents		9		13
Estimate of Fair Value Measurement [Member] | Eurodollar time deposits | Fair Value, Measurements, Recurring
Assets
Cash equivalents		75		33
Estimate of Fair Value Measurement [Member] | Certificates of deposit | Fair Value, Measurements, Recurring
Assets
Investments		277		220
Estimate of Fair Value Measurement [Member] | Swap | Fair Value, Measurements, Recurring
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset		15	[4]	38	[5]
Derivative Liability, Fair Value, Gross Asset		283	[6]	931	[7]
Fuel derivatives:
Derivative Liability, Fair Value, Gross Liability		(348)	[6]	(774)	[7]
Estimate of Fair Value Measurement [Member] | Options Held | Fair Value, Measurements, Recurring
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset		15	[4]	10	[5]
Derivative Liability, Fair Value, Gross Asset		456	[6]	956	[7]
Fuel derivatives:
Derivative Asset, Fair Value, Gross Liability		(10)	[4]	(26)	[5]
Derivative Liability, Fair Value, Gross Liability		$ (1,368)	[6]	$ (2,616)	[7]

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

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

[4] In the unaudited Condensed Consolidated Balance Sheet amounts are presented as a net asset. See Note 3.

[5] In the unaudited Consolidated Balance Sheet amounts are presented as a net asset. See Note 3.

[6] In the unaudited Condensed Consolidated Balance Sheet amounts are presented as a net liability. See Note 3.

[7] In the unaudited Consolidated Balance Sheet amounts are presented as a net liability. See Note 3.