INVESTMENT SECURITIES - Schedule of Gross Unrealized Losses and Fair Values of Securities (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Investment [Line Items]
Less than 12 months, Fair Value	$ 435	$ 4,326
Less than 12 months, Gross Unrealized Losses	(5)	(84)
12 months or more, Fair Value	505	484
12 months or more, Gross Unrealized Losses	(38)	(42)
Total, Fair Value	940	4,810
Total, Gross Unrealized Losses	(43)	(126)
Debt Securities | Tax-exempt municipal securities
Investment [Line Items]
Less than 12 months, Fair Value	219	843
Less than 12 months, Gross Unrealized Losses	0	(3)
12 months or more, Fair Value	24	52
12 months or more, Gross Unrealized Losses	(1)	(1)
Total, Fair Value	243	895
Total, Gross Unrealized Losses	(1)	(4)
Debt Securities | Residential Mortgage-Backed Securities
Investment [Line Items]
Less than 12 months, Fair Value	2	2
Less than 12 months, Gross Unrealized Losses	0	0
12 months or more, Fair Value	3	4
12 months or more, Gross Unrealized Losses	(1)	0
Total, Fair Value	5	6
Total, Gross Unrealized Losses	(1)	0
Debt Securities | Commercial Mortgage-Backed Securities
Investment [Line Items]
Less than 12 months, Fair Value	115	626
Less than 12 months, Gross Unrealized Losses	(2)	(13)
12 months or more, Fair Value	273	265
12 months or more, Gross Unrealized Losses	(26)	(28)
Total, Fair Value	388	891
Total, Gross Unrealized Losses	(28)	(41)
Debt Securities | Asset-backed securities
Investment [Line Items]
Less than 12 months, Fair Value	26	258
Less than 12 months, Gross Unrealized Losses	0	(2)
12 months or more, Fair Value	70	0
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	96	258
Total, Gross Unrealized Losses	0	(2)
Debt Securities | Corporate debt securities
Investment [Line Items]
Less than 12 months, Fair Value	68	918
Less than 12 months, Gross Unrealized Losses	(3)	(45)
12 months or more, Fair Value	131	63
12 months or more, Gross Unrealized Losses	(10)	(10)
Total, Fair Value	199	981
Total, Gross Unrealized Losses	(13)	(55)
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	3	195
Less than 12 months, Gross Unrealized Losses	0	(1)
12 months or more, Fair Value	0	14
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	3	209
Total, Gross Unrealized Losses	0	(1)
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	2	1,484
Less than 12 months, Gross Unrealized Losses	0	(20)
12 months or more, Fair Value	4	86
12 months or more, Gross Unrealized Losses	0	(3)
Total, Fair Value	6	1,570
Total, Gross Unrealized Losses	$ 0	$ (23)