RETIREMENT BENEFITS - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Change in accumulated other comprehensive income (loss)
Change, net of tax	$ (12)	$ (465)
Pension Plans and Postretirement Benefit Plans
Change in accumulated other comprehensive income (loss)
Beginning of period balance, net of tax	(5,164)	$ (5,116)	$ (5,116)
Actuarial assumptions changes and plan experience	(248)		(854)
Net asset gain due to difference between actual and expected returns	253		400
Net amortization	56		232
Prior service (cost) credit	(5)		28
Curtailment/settlement gain	0		17
Foreign exchange impact and other	(58)		99
Change in deferred taxes, net	(10)		30
Change, net of tax	(12)		(48)
End of period balance, net of tax	$ (5,176)		$ (5,164)