SECURITIES - Schedule of Cumulative Credit Losses Recognized in Earnings (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Reductions for securities sold or matured during the period	$ (21,000,000)	$ 0	$ (25,000,000)	$ 0
Available-for-sale Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Cumulative balance at beginning of period	78,000,000	80,000,000	81,000,000	80,000,000
Credit impairments recognized in earnings on debt securities that have been previously impaired	0	1,000,000	1,000,000	2,000,000
Reductions due to increases in cash flow expectations on impaired debt securities	0	0	0	(1,000,000)
Cumulative balance at end of period	$ 57,000,000	$ 81,000,000	$ 57,000,000	$ 81,000,000