POSTRETIREMENT BENEFIT PLANS - Schedule of Defined Benefit Plans (Details) - USD ($) $ in Millions	Dec. 31, 2023	Jan. 01, 2023	Dec. 31, 2022
Accumulated Benefit Obligations and Unrecognized Gain
Accumulated benefit obligations	$ 23,841	$ 22,906	$ 687
Unrecognized gain recorded in AOCI		2,481
Net Benefit Liability
Projected benefit obligations		22,953
Fair value of assets		18,908
Net liability		4,045
Pension Plans
Accumulated Benefit Obligations and Unrecognized Gain
Accumulated benefit obligations		21,696
Unrecognized gain recorded in AOCI		1,258
Net Benefit Liability
Projected benefit obligations		21,743
Fair value of assets		18,908
Net liability		2,835
OPEB Plans
Accumulated Benefit Obligations and Unrecognized Gain
Accumulated benefit obligations		1,210
Unrecognized gain recorded in AOCI		1,223
Net Benefit Liability
Projected benefit obligations	1,133	1,210	0
Fair value of assets	0	0	$ 0
Net liability	$ 1,133	$ 1,210