INCOME TAXES - Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income tax expense	$ 260	$ 489	$ 423
Tax effect of changes in OCI	(7)	(168)	(12)
Total comprehensive income tax expense	$ 253	$ 321	$ 411