INCOME TAXES - Effective Income Tax Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Amount
U.S. Federal income tax expense	$ 537	$ 442	$ 444
Increase (decrease) resulting from:
State and local income taxes (net of federal benefit)	38	27	22
Bank-owned life insurance	(19)	(20)	(17)
Tax-exempt interest	(19)	(17)	(15)
Tax advantaged investments (including related credits)	(31)	(16)	(27)
Other tax credits	(14)	0	0
Non-deductible expenses	0	8	0
Other	(3)	(1)	(4)
Income tax expense (benefit)	$ 489	$ 423	$ 403
Rate
U.S. Federal income tax rate	35.00%	35.00%	35.00%
Increase (decrease) resulting from:
State and local income taxes (net of federal benefit)	2.50%	2.10%	1.70%
Bank-owned life insurance	(1.20%)	(1.60%)	(1.30%)
Tax-exempt interest	(1.30%)	(1.30%)	(1.20%)
Tax advantaged investments (including related credits)	(2.00%)	(1.20%)	(2.10%)
Other tax credits	(0.90%)	(0.00%)	(0.00%)
Non-deductible expenses	0.00%	0.60%	0.00%
Other	(0.20%)	(0.10%)	(0.30%)
Total income tax expense and tax rate	31.90%	33.50%	31.80%