RETIREMENT BENEFITS - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in accumulated other comprehensive income (loss)
Balance, beginning of year		$ 226,143	$ 223,092
Actuarial assumptions changes and plan experience		(760)	(854)	$ 898
Net asset gain (loss) due to difference between actual and expected returns		625	400	(1,457)
Net amortizations		229	232	236
Prior service (cost) credit		(4)	28	(6)
Curtailment/settlement gain		17	17	57
Foreign exchange impact and other		(93)	99	291
Impact of Tax Reform		(3,304)
Change in deferred taxes, net		(13)	30	24
Change, net of tax	[1]	(1,019)	(48)	43
Balance, end of year		201,672	226,143	223,092
Benefit plans
Change in accumulated other comprehensive income (loss)
Balance, beginning of year		(5,164)	(5,116)	(5,159)
Impact of Tax Reform		(1,020)	0	0
Balance, end of year		$ (6,183)	$ (5,164)	$ (5,116)

[1] See Note 8 to the Consolidated Financial Statements.