INCENTIVE PLANS - Incentive Compensation Cost (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Incentive compensation cost	$ 2,251	$ 2,183	$ 2,161
Immediately Vested Stock Award
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Incentive compensation cost	70	73	61
Retirement Eligible Employees | Restricted and Deferred Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Incentive compensation cost	659	555	541
Nonretirement Eligible Employees | Restricted and Deferred Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Incentive compensation cost	474	509	461
Deferred Cash Awards and Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Incentive compensation cost	354	336	325
Variable Incentive Compensation
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Incentive compensation cost	$ 694	$ 710	$ 773
2014 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Number of shares available for grant	39.2