FAIR VALUE MEASUREMENT - Items Measured at Fair Value on a Nonrecurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Nonrecurring | Level 2
Items Measured at Fair Value on a Nonrecurring Basis
Loans held-for-sale	$ 5,935	$ 6,752
Other real estate owned	16	15
Loans	275	836
Other Assets	3,087	0
Total assets	9,313	7,603
Nonrecurring | Level 3
Items Measured at Fair Value on a Nonrecurring Basis
Loans held-for-sale	2,864	3,574
Other real estate owned	87	92
Loans	712	337
Other Assets	0	0
Total assets	3,663	4,003
Fair value
Items Measured at Fair Value on a Nonrecurring Basis
Other Assets	217,200	186,500
Fair value | Level 2
Items Measured at Fair Value on a Nonrecurring Basis
Other Assets	151,400	126,200
Fair value | Level 3
Items Measured at Fair Value on a Nonrecurring Basis
Other Assets	58,900	53,400
Fair value | Nonrecurring
Items Measured at Fair Value on a Nonrecurring Basis
Loans held-for-sale	8,799	10,326
Other real estate owned	103	107
Loans	987	1,173
Other Assets	3,087	0
Total assets	$ 12,976	$ 11,606