POSTRETIREMENT BENEFIT PLANS - Amounts Included in Shareowners' Equity, Pension Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Principal pension plans
Defined Benefit Plan Disclosure [Line Items]
Estimated amortization of prior service cost (credits) in 2018	$ 145
Estimated amortization of net actuarial loss in 2018	3,805
Prior service cost (credit) amortization	290	$ 303	$ 205
Amortization of net actuarial loss	2,812	2,449	3,288
Other pension plans
Defined Benefit Plan Disclosure [Line Items]
Estimated amortization of prior service cost (credits) in 2018	(10)
Estimated amortization of net actuarial loss in 2018	310
Prior service cost (credit) amortization	(5)	1	0
Amortization of net actuarial loss	$ 429	$ 256	$ 289