INVESTMENT SECURITIES - Schedule of Gross Unrealized Losses and Fair Values of Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Investment [Line Items]
Less than 12 months, Fair Value	$ 1,932	$ 4,326
Less than 12 months, Gross Unrealized Losses	(10)	(84)
12 months or more, Fair Value	265	484
12 months or more, Gross Unrealized Losses	(15)	(42)
Total, Fair Value	2,197	4,810
Total, Gross Unrealized Losses	(25)	(126)
Debt Securities | Tax-exempt municipal securities
Investment [Line Items]
Less than 12 months, Fair Value	1,069	843
Less than 12 months, Gross Unrealized Losses	(4)	(3)
12 months or more, Fair Value	24	52
12 months or more, Gross Unrealized Losses	0	(1)
Total, Fair Value	1,093	895
Total, Gross Unrealized Losses	(4)	(4)
Debt Securities | Residential Mortgage-Backed Securities
Investment [Line Items]
Less than 12 months, Fair Value	0	2
Less than 12 months, Gross Unrealized Losses	0	0
12 months or more, Fair Value	5	4
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	5	6
Total, Gross Unrealized Losses	0	0
Debt Securities | Commercial Mortgage-Backed Securities
Investment [Line Items]
Less than 12 months, Fair Value	35	626
Less than 12 months, Gross Unrealized Losses	0	(13)
12 months or more, Fair Value	81	265
12 months or more, Gross Unrealized Losses	(8)	(28)
Total, Fair Value	116	891
Total, Gross Unrealized Losses	(8)	(41)
Debt Securities | Asset-backed securities
Investment [Line Items]
Less than 12 months, Fair Value	35	258
Less than 12 months, Gross Unrealized Losses	0	(2)
12 months or more, Fair Value	68	0
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	103	258
Total, Gross Unrealized Losses	0	(2)
Debt Securities | Corporate debt securities
Investment [Line Items]
Less than 12 months, Fair Value	536	918
Less than 12 months, Gross Unrealized Losses	(6)	(45)
12 months or more, Fair Value	81	63
12 months or more, Gross Unrealized Losses	(6)	(10)
Total, Fair Value	617	981
Total, Gross Unrealized Losses	(12)	(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	190	195
Less than 12 months, Gross Unrealized Losses	0	(1)
12 months or more, Fair Value	3	14
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	193	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	67	1,484
Less than 12 months, Gross Unrealized Losses	0	(20)
12 months or more, Fair Value	3	86
12 months or more, Gross Unrealized Losses	(1)	(3)
Total, Fair Value	70	1,570
Total, Gross Unrealized Losses	$ (1)	$ (23)