INVESTMENT SECURITIES - Gross Unrealized Losses and Fair Values of Securities (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Investment [Line Items]
Less than 12 months, Fair Value	$ 5,244	$ 6,758
Less than 12 months, Gross Unrealized Losses	(93)	(187)
12 months or more, Fair Value	114	209
12 months or more, Gross Unrealized Losses	(4)	(9)
Total, Fair Value	5,358	6,967
Total, Gross Unrealized Losses	(97)	(196)
Debt Securities | Tax-exempt municipal securities
Investment [Line Items]
Less than 12 months, Fair Value	1,898	2,756
Less than 12 months, Gross Unrealized Losses	(20)	(67)
12 months or more, Fair Value	39	43
12 months or more, Gross Unrealized Losses	(1)	(1)
Total, Fair Value	1,937	2,799
Total, Gross Unrealized Losses	(21)	(68)
Debt Securities | Residential Mortgage-Backed Securities
Investment [Line Items]
Less than 12 months, Fair Value	0	0
Less than 12 months, Gross Unrealized Losses	0	0
12 months or more, Fair Value	4	4
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	4	4
Total, Gross Unrealized Losses	0	0
Debt Securities | Commercial Mortgage-Backed Securities
Investment [Line Items]
Less than 12 months, Fair Value	99	182
Less than 12 months, Gross Unrealized Losses	(2)	(3)
12 months or more, Fair Value	1	24
12 months or more, Gross Unrealized Losses	0	(1)
Total, Fair Value	100	206
Total, Gross Unrealized Losses	(2)	(4)
Debt Securities | Asset-backed securities
Investment [Line Items]
Less than 12 months, Fair Value	92	51
Less than 12 months, Gross Unrealized Losses	0	0
12 months or more, Fair Value	0	63
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	92	114
Total, Gross Unrealized Losses	0	0
Debt Securities | Corporate debt securities
Investment [Line Items]
Less than 12 months, Fair Value	1,200	1,544
Less than 12 months, Gross Unrealized Losses	(37)	(71)
12 months or more, Fair Value	64	69
12 months or more, Gross Unrealized Losses	(3)	(7)
Total, Fair Value	1,264	1,613
Total, Gross Unrealized Losses	(40)	(78)
Debt Securities | U.S. Treasury and other U.S. government corporations and agencies | U.S. Treasury and agency obligations
Investment [Line Items]
Less than 12 months, Fair Value	645	697
Less than 12 months, Gross Unrealized Losses	(9)	(15)
12 months or more, Fair Value	3	3
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	648	700
Total, Gross Unrealized Losses	(9)	(15)
Debt Securities | U.S. Treasury and other U.S. government corporations and agencies | Mortgage-backed securities
Investment [Line Items]
Less than 12 months, Fair Value	1,310	1,528
Less than 12 months, Gross Unrealized Losses	(25)	(31)
12 months or more, Fair Value	3	3
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	1,313	1,531
Total, Gross Unrealized Losses	$ (25)	$ (31)