Fair Value Measurements - Measured on Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Sep. 30, 2014		Dec. 31, 2012	Dec. 31, 2013
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	$ 237	[1]		$ 503	[1]
Fuel derivatives:
Derivative Liability, Fair Value, Gross Liability	(231)	[1]		(380)	[1]
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 | Period end date
Assets
Treasury bills	1,500			1,570
Interest rate derivatives	14			20
Other available for sale securities	67			63
Total assets	3,892			3,757
Liabilities
Interest rate derivatives	(61)			(77)
Deferred Compensation	(162)			(158)
Total Liabilities	(393)			(538)
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Treasury bills	1,500			1,570
Interest rate derivatives	0			0
Other available for sale securities	62			58
Total assets	2,979			2,620
Liabilities
Interest rate derivatives	0			0
Deferred Compensation	(162)			(158)
Total Liabilities	(162)			(158)
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Treasury bills	0			0
Interest rate derivatives	14			20
Other available for sale securities	0			0
Total assets	669			626
Liabilities
Interest rate derivatives	(61)			(77)
Deferred Compensation	0			0
Total Liabilities	(71)			(85)
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Treasury bills	0			0
Interest rate derivatives	0			0
Other available for sale securities	5			5
Total assets	244			511
Liabilities
Interest rate derivatives	0			0
Deferred Compensation	0			0
Total Liabilities	(160)			(295)
Cash Equivalents | Fair Value, Measurements, Recurring | Period end date
Assets
Cash equivalents	1,417	[2]		992	[2]
Cash Equivalents | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Cash equivalents	1,417	[2]		992	[2]
Cash Equivalents | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Cash equivalents	0	[2]		0	[2]
Cash Equivalents | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Cash equivalents	0	[2]		0	[2]
Commercial paper | Fair Value, Measurements, Recurring | Period end date
Assets
Cash equivalents	220			280
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	220			280
Commercial paper | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Cash equivalents	0			0
Certificates of deposit | Fair Value, Measurements, Recurring | Period end date
Assets
Cash equivalents	21			23
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	21			23
Certificates of deposit | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Cash equivalents	0			0
Eurodollar time deposits | Fair Value, Measurements, Recurring | Period end date
Assets
Cash equivalents	174			60
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	174			60
Eurodollar time deposits | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Cash equivalents	0			0
Certificates of deposit | Fair Value, Measurements, Recurring | Period end date
Assets
Investments	228			227
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	228			227
Certificates of deposit | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Investments	0			0
Auction rate securities | Fair Value, Measurements, Recurring | Period end date
Assets
Investments	28	[3]		39	[3]
Auction rate securities | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Investments	0	[3]		0	[3]
Auction rate securities | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Investments	0	[3]		0	[3]
Auction rate securities | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Investments	28	[3]		39	[3]
Swap | Fair Value, Measurements, Recurring | Period end date
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	11	[4]		16	[4]
Derivative Liability, Fair Value, Gross Asset	1	[5]
Fuel derivatives:
Derivative Asset, Fair Value, Gross Liability	(2)	[4]		(8)	[4]
Derivative Liability, Fair Value, Gross Liability	(8)	[5]
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	[4]
Derivative Liability, Fair Value, Gross Asset	0	[5]
Fuel derivatives:
Derivative Asset, Fair Value, Gross Liability		[4]		0	[4]
Derivative Liability, Fair Value, Gross Liability		[5]
Swap | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	11	[4]		16	[4]
Derivative Liability, Fair Value, Gross Asset	1	[5]
Fuel derivatives:
Derivative Asset, Fair Value, Gross Liability	(2)	[4]		(8)	[4]
Derivative Liability, Fair Value, Gross Liability	(8)	[5]
Swap | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	0	[4]		0	[4]
Derivative Liability, Fair Value, Gross Asset	0	[5]
Fuel derivatives:
Derivative Asset, Fair Value, Gross Liability		[4]		0	[4]
Derivative Liability, Fair Value, Gross Liability		[5]
Options Held | Fair Value, Measurements, Recurring | Period end date
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	172	[4]		458	[4]
Derivative Liability, Fair Value, Gross Asset	39	[5]		9	[6]
Fuel derivatives:
Derivative Asset, Fair Value, Gross Liability	(97)	[4]		(274)	[4]
Derivative Liability, Fair Value, Gross Liability	(63)	[5]		(21)	[6]
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	[4]
Derivative Liability, Fair Value, Gross Asset	0	[5]		0	[6]
Fuel derivatives:
Derivative Asset, Fair Value, Gross Liability	0	[4]		0	[4]
Derivative Liability, Fair Value, Gross Liability		[5]		0	[6]
Options Held | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	0	[4]		0	[4]
Derivative Liability, Fair Value, Gross Asset	0	[5]		0	[6]
Fuel derivatives:
Derivative Asset, Fair Value, Gross Liability	0	[4]		0	[4]
Derivative Liability, Fair Value, Gross Liability		[5]		0	[6]
Options Held | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Fuel derivatives:
Derivative Asset, Fair Value, Gross Asset	172	[4]		458	[4]
Derivative Liability, Fair Value, Gross Asset	39	[5]		9	[6]
Fuel derivatives:
Derivative Asset, Fair Value, Gross Liability	(97)	[4]		(274)	[4]
Derivative Liability, Fair Value, Gross Liability	$ (63)	[5]		$ (21)	[6]

[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] Noncurrent investments are included in Other assets in the unaudited Condensed Consolidated Balance Sheet.

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

[5] In the unaudited Condensed Consolidated Balance Sheet amounts are presented as a net liability.

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