INVESTMENT SECURITIES - Schedule of Estimated Fair Value and Gross Unrealized Losses of Available-For-Sale Investment Securities (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Estimated fair value
Less than 12 months	$ 7,571	$ 9,098
12 months or more	443	663
Gross unrealized losses
Less than 12 months	(90)	(157)
12 months or more	(69)	(111)
U.S. corporate
Estimated fair value
Less than 12 months	957	1,692
12 months or more	233	359
Gross unrealized losses
Less than 12 months	(39)	(55)
12 months or more	(11)	(30)
Non-U.S. corporate
Estimated fair value
Less than 12 months	5,102	5,352
12 months or more	12	14
Gross unrealized losses
Less than 12 months	(15)	(26)
12 months or more	(4)	(1)
State and municipal
Estimated fair value
Less than 12 months	210	674
12 months or more	156	158
Gross unrealized losses
Less than 12 months	(15)	(27)
12 months or more	(52)	(64)
Mortgage and asset-backed
Estimated fair value
Less than 12 months	856	822
12 months or more	42	132
Gross unrealized losses
Less than 12 months	(18)	(21)
12 months or more	(2)	(16)
Government and agencies
Estimated fair value
Less than 12 months	437	549
12 months or more	0	0
Gross unrealized losses
Less than 12 months	(2)	(26)
12 months or more	0	0
Equity
Estimated fair value
Less than 12 months	9	9
12 months or more	0	0
Gross unrealized losses
Less than 12 months	(2)	(1)
12 months or more	$ 0	$ 0