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
	Mar. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at December 31, 2012	$ 260
Total gains or (losses) (realized or unrealized)
Included in earnings	27
Included in other comprehensive income	(44)
Purchases	189
Sales	(213)
Settlements	23
Balance at March 31, 2013	242
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at March 31, 2013	(49)
Fuel derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at December 31, 2012	219
Total gains or (losses) (realized or unrealized)
Included in earnings	27
Included in other comprehensive income	(46)
Purchases	189	[1]
Sales	(213)	[1]
Settlements	23
Balance at March 31, 2013	199
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at March 31, 2013	(49)
Auction rate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at December 31, 2012	36
Total gains or (losses) (realized or unrealized)
Included in earnings	0
Included in other comprehensive income	2
Purchases	0
Sales	0
Settlements	0
Balance at March 31, 2013	38	[2]
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at March 31, 2013	0
Other securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at December 31, 2012	5
Total gains or (losses) (realized or unrealized)
Included in earnings	0
Included in other comprehensive income	0
Purchases	0
Sales	0
Settlements	0
Balance at March 31, 2013	5
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at March 31, 2013	$ 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.