POSTRETIREMENT BENEFIT PLANS - Amounts Included in Shareowners' Equity, Pension Plans (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Principal pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	$ 784	$ 1,138
Net actuarial loss	14,326	16,664
Total	15,110	17,802
Other pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	(100)	(88)
Net actuarial loss	3,712	4,800
Total	$ 3,612	$ 4,712