PENSION BENEFITS - Pension Assets (Details) - Pension Plan - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1,152	$ 976	$ 1,074
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	105	55
Time deposits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7	9
Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	120	258
Bond mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	205	464
Real estate trust funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	74	91
Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	625	85
Debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	8
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6	6
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	121	69
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	105	55
Quoted Prices in Active Markets for Identical Assets (Level 1) | Time deposits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Bond mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Real estate trust funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	8
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6	6
Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	852	733
Significant Observable Inputs (Level 2) | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Observable Inputs (Level 2) | Time deposits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7	9
Significant Observable Inputs (Level 2) | Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	120	258
Significant Observable Inputs (Level 2) | Bond mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	205	464
Significant Observable Inputs (Level 2) | Real estate trust funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Observable Inputs (Level 2) | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	520	2
Significant Observable Inputs (Level 2) | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Observable Inputs (Level 2) | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	179	174
Significant Unobservable Inputs (Level 3) | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Time deposits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Bond mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Real estate trust funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	74	91	50
Significant Unobservable Inputs (Level 3) | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	105	83	$ 100
Significant Unobservable Inputs (Level 3) | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0