INCOME TAXES - Deferred Tax Liabilities and Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Deferred Tax Liabilities, Leasing Arrangements	$ (730)	$ (685)
Fixed assets and capitalized software	(5,355)	(4,720)
Other	(501)	(538)
Deferred tax liabilities	(6,586)	(5,943)
Pension and postretirement benefits	3,994	2,522
Loss and credit carryforwards	325	328
Insurance reserves	535	413
Stock compensation	183	249
Accrued employee compensation	583	287
Operating lease liabilities	736	691
Other	357	205
Deferred tax assets	6,713	4,695
Deferred tax assets valuation allowance	(88)	(54)
Deferred tax asset (net of valuation allowance)	6,625	4,641
Net deferred tax asset (liability)	(39)	(1,302)
Deferred income tax assets	527	330
Deferred Income Tax Liabilities, Net	488	1,632
Amounts recognized in the consolidated balance sheets:
Net deferred tax asset (liability)	$ (39)	$ (1,302)