POSTRETIREMENT BENEFIT PLANS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Principal pension plans
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 267	$ 307	$ 810	$ 913
Prior service cost (credit) amortization	73	76	218	228
Expected return on plan assets	(847)	(837)	(2,545)	(2,507)
Interest cost on benefit obligations	715	736	2,144	2,205
Net actuarial loss (gain) amortization	702	612	2,109	1,836
Curtailment loss (gain)	0	0	43	(1)
Plans cost	910	894	2,779	2,674
Other pension plans
Defined Benefit Plan Disclosure [Line Items]
Threshold to be included in other pension plans (greater than)	50		50
Service cost for benefits earned	156	106	430	337
Prior service cost (credit) amortization	(2)	0	(4)	(1)
Expected return on plan assets	(324)	(264)	(919)	(786)
Interest cost on benefit obligations	158	172	445	512
Net actuarial loss (gain) amortization	110	68	320	197
Curtailment loss (gain)	11	0	11	0
Plans cost	109	82	283	259
Principal retiree benefit plans
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	25	32	77	84
Prior service cost (credit) amortization	(42)	(41)	(128)	(123)
Expected return on plan assets	(9)	(11)	(27)	(33)
Interest cost on benefit obligations	55	62	168	188
Net actuarial loss (gain) amortization	(20)	(12)	(61)	(39)
Curtailment loss (gain)	0	0	3	0
Plans cost	$ 9	$ 30	$ 32	$ 77