Accumulated Other Comprehensive Income (Loss) - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ (3,616)	$ (5,293)	$ (5,763)
Less: Tax Expense	1,298	680	455
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	251
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	378
Less: Tax Expense	140
Net of Tax	238
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	20
Less: Tax Expense	7
Net of Tax	13
Interest rate derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(30)	(45)	(58)
Changes in fair value	(5)	(10)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	20	23
Fuel derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(1,666)	(1,177)	(20)
Changes in fair value	(867)	(1,191)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	378	34
Other
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	6	8	8
Changes in fair value	(2)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Defined benefit plan items
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	22	41	65
Changes in fair value	(19)	(24)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Deferred tax
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	617	435	2
Changes in fair value	329	454
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(147)	(21)
Accumulated other comprehensive income (loss)
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(1,051)	(738)	$ (3)
Changes in fair value	(564)	(771)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 251	$ 36