PENSION BENEFITS - Level 3 Defined Benefit Pension Plan Assets (Details) - Pension Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Change in plan assets:
Fair value of plan assets at beginning of year	$ 976	$ 1,074
Actual return on plan assets:
Fair value of plan assets at end of year	1,152	976
Hedge funds
Change in plan assets:
Fair value of plan assets at beginning of year	85
Actual return on plan assets:
Fair value of plan assets at end of year	625	85
Real estate trust funds
Change in plan assets:
Fair value of plan assets at beginning of year	91
Actual return on plan assets:
Fair value of plan assets at end of year	74	91
Significant Unobservable Inputs (Level 3)
Change in plan assets:
Fair value of plan assets at beginning of year	174
Actual return on plan assets:
Fair value of plan assets at end of year	179	174
Significant Unobservable Inputs (Level 3) | Hedge funds
Change in plan assets:
Fair value of plan assets at beginning of year	83	100
Actual return on plan assets:
Relating to assets still held at the reporting date	(1)	(2)
Purchases, sales and settlements	20	(9)
Foreign currency translation and other	3	(6)
Fair value of plan assets at end of year	105	83
Significant Unobservable Inputs (Level 3) | Real estate trust funds
Change in plan assets:
Fair value of plan assets at beginning of year	91	50
Actual return on plan assets:
Relating to assets still held at the reporting date	2	9
Purchases, sales and settlements	(22)	36
Foreign currency translation and other	3	(4)
Fair value of plan assets at end of year	$ 74	$ 91