INVESTMENT SECURITIES - Realized Gains (Losses) Within Investment Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Gross realized gains	$ 10	$ 3	$ 105	$ 34
Gross realized losses	(2)	(3)	(15)	(6)
Net realized capital gains	$ 8	$ 0	$ 90	$ 28