PREMISES, EQUIPMENT, AND SOFTWARE - Schedule of Amortization (Details) $ in Millions	Dec. 31, 2017 USD ($)
Capitalized Software, Expected Future Amortization Expense [Abstract]
2018	$ 171
2019	141
2020	109
2021	71
2022	36
Thereafter	92
Total	620	[1]
In-process software	$ 178

[1] Excluded from this balance is $178 million of in-process software at December 31, 2017.