POSTRETIREMENT BENEFIT PLANS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Principal pension plans
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 203	$ 254	$ 435	$ 543
Prior service cost (credit) amortization	36	72	72	145
Expected return on plan assets	(820)	(849)	(1,640)	(1,698)
Interest cost on benefit obligations	667	712	1,333	1,429
Net actuarial loss (gain) amortization	943	697	1,894	1,407
Curtailment loss	0	0	0	43
Pension plans cost (income)	1,029	886	2,094	1,869
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	99	123	194	274
Prior service cost (credit) amortization	(2)	(1)	(2)	(2)
Expected return on plan assets	(359)	(301)	(717)	(595)
Interest cost on benefit obligations	156	145	312	287
Net actuarial loss (gain) amortization	83	107	165	210
Curtailment loss	(6)	0	(6)	0
Pension plans cost (income)	(29)	73	(54)	174
Principal retiree benefit plans
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	16	26	29	52
Prior service cost (credit) amortization	(58)	(43)	(114)	(86)
Expected return on plan assets	(7)	(9)	(14)	(18)
Interest cost on benefit obligations	49	56	98	113
Net actuarial loss (gain) amortization	(20)	(20)	(40)	(41)
Curtailment loss	0	0	0	3
Pension plans cost (income)	$ (20)	$ 10	$ (41)	$ 23