INCOME TAXES - Unrecognized Tax Benefit Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefit at beginning of year	$ 569	$ 623	$ 491
Change attributable to tax positions taken in prior years			37
Change attributable to tax positions taken in prior years	(66)	(13)
Change attributable to tax positions taken during the current period	4	13	148
Decrease attributable to settlements with taxing authorities	(43)	(54)	(53)
Unrecognized tax benefit at end of year	$ 464	$ 569	$ 623