INCOME TAXES - Effective Income Tax Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Amount
U.S. Federal income tax expense (benefit)	$ 442	$ 444	$ (1,214)
Increase (decrease) resulting from:
Goodwill impairment	0	0	1,217
State and local income taxes (net of federal benefit)	27	22	1
Bank-owned life insurance	(20)	(17)	(17)
Tax-exempt interest	(17)	(15)	(13)
Tax credits	(16)	(27)	(11)
Non-deductible expenses	8	0	0
Other	(1)	(4)	(5)
Income tax expense (benefit)	$ 423	$ 403	$ (42)
Rate
Federal income tax rate	35.00%	35.00%	35.00%
Increase (decrease) resulting from:
Goodwill impairment, Tax rate	0.00%	0.00%	(35.10%)
State and local income taxes (net of federal benefit), Tax rate	2.10%	1.70%	0.00%
Bank-owned life insurance, Tax rate	(1.60%)	(1.30%)	0.50%
Tax-exempt interest, Tax rate	(1.30%)	(1.20%)	0.40%
Tax credits, Tax rate	(1.20%)	(2.10%)	0.30%
Non-deductible fines and penalties, Tax rate	0.60%	0.00%	0.00%
Other, Tax rate	(0.10%)	(0.30%)	0.10%
Total income tax expense (benefit) and tax rate, Tax rate	33.50%	31.80%	1.20%