Schedule of Effect of Four Quarters Events (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating:
Impairment of assets			$ 412		$ 48	$ 18	$ 11	$ 2	$ 412	$ 79	$ 49
Cleveland airport lease restructuring				$ 74					74
Labor agreement costs and related items	$ (60)	$ 14	10	100	18				64	18
Severance and benefit costs	10	13	6	8	4	28	25	50	37	107	199
(Gains) losses on sale of assets and other special charges	19	18	6	8	61	30	19	12	51	122	195
Special charges	(31)	45	434	190	131	76	55	64	638	326	443
Nonoperating and income taxes:
Losses (gain) on extinguishment of debt and other			(9)	8	7	61	128	6	(1)	202	74
Income tax expense (benefit) related to special charges	12	(16)	(153)	(72)	(11)				(229)	(11)	(10)
Income tax adjustments (Note 6)	180				88	(3,218)			180	(3,130)
Total operating and nonoperating special items, net of income taxes	$ 161	$ 29	$ 272	$ 126	$ 215	$ (3,081)	$ 183	$ 70	$ 588	$ (2,613)	$ 507