INVESTMENT SECURITIES - Schedule of Contractual Maturities of Investment in Available-For-Sale Debt Securities (Excluding Mortgage and Asset-Backed Securities) (Details) $ in Millions	Jun. 30, 2017 USD ($)
Amortized cost
Within one year	$ 5,902
After one year through five years	4,255
After five years through ten years	5,209
After ten years	17,468
Estimated fair value
Within one year	5,900
After one year through five years	4,449
After five years through ten years	5,704
After ten years	$ 20,890