SECURITIES - Schedule of Cumulative Credit Losses Recognized in Earnings (Details) - Available-for-sale Securities - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Cumulative balance at beginning of period		$ 80	$ 75
Credit impairments recognized in earnings on debt securities that have been previously impaired		1	1
Reductions due to increases in cash flow expectations on impaired securities	[1]	(1)	(1)
Cumulative balance at end of period		$ 80	$ 75

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