Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
DEFERRED TAX LIABILITIES:
Accelerated depreciation	$ 4,429	$ 4,277
Other	62	51
Deferred Tax Liabilities, Gross	4,491	4,328
Total deferred tax liabilities	2,490	2,782
DEFERRED TAX ASSETS:
Fuel derivative instruments	750	521
Capital and operating leases	81	125
Deferred tax assets construction obligation	289	209
Accrued engine maintenance	74	83
Accrued employee benefits	541	334
State taxes	62	65
Business partner income	107	90
Other	97	119
Total deferred tax assets	2,001	1,546
CURRENT:
Federal	1,292	203	$ 355
State	114	29	44
Total current	1,406	232	399
DEFERRED:
Federal	(97)	421	62
State	(11)	27	(6)
Total deferred	(108)	448	56
Total	1,298	680	455
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax at statutory U.S. tax rates	1,218	636	423
Nondeductible items	15	9	10
State income taxes, net of federal benefit	66	37	25
Other, net	$ (1)	$ (2)	$ (3)