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, 2014		Jun. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 243		$ 216
Total gains or (losses) (realized or unrealized)
Included in earnings	(36)		(105)
Included in other comprehensive income	166		146
Purchases	79		100
Sales	(73)		(109)
Settlements	(8)		(15)
June 30, 2014	443		443
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 June 30, 2014	36		98
Fuel derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	206		172
Total gains or (losses) (realized or unrealized)
Included in earnings	(36)		(105)
Included in other comprehensive income	166		144
Purchases	79	[1]	100	[1]
Sales	(73)	[1]	(100)	[1]
Settlements	(8)		(15)
June 30, 2014	406		406
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 June 30, 2014	36		98
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
Purchases	0		0
Sales	0		(9)
Settlements	0		0
June 30, 2014	32	[2]	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 June 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
June 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 June 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.