ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Performance Indicators for Nonperforming Assets (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans and leases as a percentage of total loans and leases	[1]	0.97%	1.07%
Nonperforming assets as a percentage of total assets	[1]	0.73%	0.80%
Loans accruing and 90 days or more past due		$ 26	$ 9
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans and leases as a percentage of total loans and leases	[1]	0.36%	0.15%
Nonperforming assets as a percentage of total assets	[1]	0.26%	0.11%
Loans accruing and 90 days or more past due		$ 2	$ 1
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonperforming loans and leases as a percentage of total loans and leases	[1]	0.61%	0.92%
Nonperforming assets as a percentage of total assets	[1]	0.47%	0.69%
Loans accruing and 90 days or more past due		$ 24	$ 8

[1] December 31, 2015 ratios included loans accruing and 90 days or more past due of $1 million and $8 million for commercial and retail, respectively.