RETIREMENT BENEFITS PLANS - Components of Pension Plans with Accumulated and Projected Benefit Obligation in Excess of Plan Assets (Details) - Pension plans - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
United States
Components of pension plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	$ 4,054	$ 3,883
Fair value of plan assets	3,463	3,433
Components of pension plans with a projected benefit obligation in excess of plan assets
Projected benefit obligation	4,121	4,028
Fair value of plan assets	3,463	3,433
Foreign Plan
Components of pension plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	2,586	1,028
Fair value of plan assets	1,756	242
Components of pension plans with a projected benefit obligation in excess of plan assets
Projected benefit obligation	2,763	2,502
Fair value of plan assets	$ 1,770	$ 1,585