FAIR VALUE MEASUREMENTS - Schedule of Gain (Loss) on Assets and Liabilities Measured on Nonrecurring Basis Included in Earnings (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill		$ 6,876	$ 6,876	$ 6,876	$ 11,300
Goodwill impairment		0	0	4,435
Nonrecurring measurement basis | Impaired collateral-dependent loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) included in earnings on assets measured on a nonrecurring basis		(32)	(101)	(83)
Nonrecurring measurement basis | MSRs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) included in earnings on assets measured on a nonrecurring basis		9	5	47
Nonrecurring measurement basis | Foreclosed assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) included in earnings on assets measured on a nonrecurring basis		(3)	(3)	(4)
Nonrecurring measurement basis | Goodwill impairment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) included in earnings on assets measured on a nonrecurring basis	[1]	$ 0	$ 0	$ (4,435)

[1] In the year ended December 31, 2013, Goodwill totaling $11.3 billion was written down to its implied fair value of $6.9 billion, resulting in an impairment charge of $4.4 billion.