PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Fair Value and Aggregate Notional Amount of the Derivative Instruments Held by our Pension Trusts (Details) - Pension - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 3,719	$ 4,930	$ 5,514
Foreign currency derivatives, net
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Derivative, notional amount	0	13
Future
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	15
Derivative, notional amount	813	1,073
Total return swaps, net
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	262
Derivative, notional amount	0	558
Derivative instruments, net
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	277
Derivative, notional amount	$ 813	$ 1,644