Fair Value Measurement - Fair Value Assets and Liabilities Measured on Recurring Basis with Unobservable Inputs (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014		Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 443		$ 216
Total gains or (losses) (realized or unrealized)
Included in earnings	82		(23)
Included in other comprehensive income	(289)		(143)
Purchases	77		177
Sales	(60)		(169)
Settlements	(5)		(20)
September 30, 2014	84		84
The amount of total gains for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at September 30, 2014	(86)		5
Fuel derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	406		172
Total gains or (losses) (realized or unrealized)
Included in earnings	82		(23)
Included in other comprehensive income	(291)		(147)
Purchases	77	[1]	177	[1]
Sales	(54)	[1]	(154)	[1]
Settlements	(5)		(20)
September 30, 2014	51		51
The amount of total gains for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at September 30, 2014	(86)		5
Auction rate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	32		39
Total gains or (losses) (realized or unrealized)
Included in earnings	0		0
Included in other comprehensive income	2		4
Purchases	0		0
Sales	(6)		(15)
Settlements	0		0
September 30, 2014	28	[2]	28	[2]
The amount of total gains for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at September 30, 2014	0		0
Other securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	5		5
Total gains or (losses) (realized or unrealized)
Included in earnings	0		0
Included in other comprehensive income	0		0
Purchases	0		0
Sales	0		0
Settlements	0		0
September 30, 2014	5		5
The amount of total gains for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at September 30, 2014	$ 0		$ 0

[1] The purchase and sale of fuel derivatives are recorded gross based on the structure of the derivative instrument and whether a contract with multiple derivatives is purchased as a single instrument or separate instruments.

[2] Included in Other assets in the unaudited Condensed Consolidated Balance Sheet.