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		6 Months Ended
	Jun. 30, 2013		Jun. 30, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 242		$ 260
Total gains or (losses) (realized or unrealized)
Included in earnings	16		(11)
Included in other comprehensive income	(301)		(345)
Purchases	86		275
Sales	(70)		(283)
Settlements	24		47
June 30, 2013	(35)		(35)
The amount of total losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at June 30, 2013	(27)		(74)
Fuel derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	199		219
Total gains or (losses) (realized or unrealized)
Included in earnings	16		(11)
Included in other comprehensive income	(299)		(345)
Purchases	86	[1]	275	[1]
Sales	(70)	[1]	(283)	[1]
Settlements	24		47
June 30, 2013	(76)		(76)
The amount of total losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at June 30, 2013	(27)		(74)
Auction rate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	38		36
Total gains or (losses) (realized or unrealized)
Included in earnings	0		0
Included in other comprehensive income	(2)
Purchases	0		0
Sales	0		0
Settlements	0		0
June 30, 2013	36	[2]	36	[2]
The amount of total losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at June 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
June 30, 2013	5		5
The amount of total losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at June 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.