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, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 216
Total gains or (losses) (realized or unrealized)
Included in earnings	(69)
Included in other comprehensive income	(20)
Purchases	21
Sales	(36)
Settlements	(7)
March 31, 2014	243
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 March 31, 2014	67
Fuel derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	172
Total gains or (losses) (realized or unrealized)
Included in earnings	(69)
Included in other comprehensive income	(22)
Purchases	21	[1]
Sales	(27)	[1]
Settlements	(7)
March 31, 2014	206
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 March 31, 2014	67
Auction rate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	39
Total gains or (losses) (realized or unrealized)
Included in earnings	0
Included in other comprehensive income	2
Purchases	0
Sales	(9)
Settlements	0
March 31, 2014	32	[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 March 31, 2014	0
Other securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	5
Total gains or (losses) (realized or unrealized)
Included in earnings	0
Included in other comprehensive income	0
Purchases	0
Sales	0
Settlements	0
March 31, 2014	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 March 31, 2014	$ 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.