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, 2013		Sep. 30, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (35)		$ 260
Total gains or (losses) (realized or unrealized)
Included in earnings	(62)		(73)
Included in other comprehensive income	158		(187)
Purchases	26		301
Sales	(88)		(371)
Settlements	0		47
September 30, 2013	123		123
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, 2013	58		92
Fuel derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(76)		219
Total gains or (losses) (realized or unrealized)
Included in earnings	(62)		(73)
Included in other comprehensive income	155		(190)
Purchases	26	[1]	301	[1]
Sales	(88)	[1]	(371)	[1]
Settlements	0		47
September 30, 2013	79		79
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, 2013	58		92
Auction rate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	36		36
Total gains or (losses) (realized or unrealized)
Included in earnings	0		0
Included in other comprehensive income	3		3
Purchases	0		0
Sales	0		0
Settlements	0		0
September 30, 2013	39	[2]	39	[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, 2013	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, 2013	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, 2013	$ 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.