SECURITIES - Schedule of Cumulative Credit Losses Recognized in Earnings (Details) - Available-for-sale Securities - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Cumulative balance at beginning of period		$ 81	$ 79	$ 80	$ 75
Credit impairments recognized in earnings on debt securities that have been previously impaired		1	1	3	6
Reductions due to increases in cash flow expectations on impaired securities	[1]	(1)	0	(2)	(1)
Cumulative balance at end of period		$ 81	$ 80	$ 81	$ 80

[1] Reported in interest income from investment securities on the Consolidated Statements of Operations.