FAIR VALUE MEASUREMENT - Valuation Techniques and Inputs for Level 3 Nonrecurring Fair Value Measurements (Details) - Nonrecurring - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	$ (52,000,000)	$ (324,000,000)
Loans held-for-sale
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	(22,000,000)	3,000,000
Other real estate owned
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	(2,000,000)	(2,000,000)
Loans
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	(28,000,000)	(63,000,000)
Other Assets
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	0	$ (262,000,000)
Level 3
Valuation techniques and inputs
Total assets	2,410,000,000		$ 3,263,000,000
Level 3 | Loans held-for-sale | Price-based
Valuation techniques and inputs
Total assets	1,788,000,000		2,413,000,000
Level 3 | Loans held-for-sale | Price-based | Minimum
Valuation techniques and inputs
Price	77.93		0.00
Level 3 | Loans held-for-sale | Price-based | Maximum
Valuation techniques and inputs
Price	100.00		100.00
Level 3 | Loans held-for-sale | Price-based | Weighted Average
Valuation techniques and inputs
Price	98.03		93.08
Level 3 | Other real estate owned, discount to price input | Price-based
Valuation techniques and inputs
Total assets	$ 57,000,000		$ 59,000,000
Level 3 | Other real estate owned, discount to price input | Price-based | Minimum
Valuation techniques and inputs
Discount to price (as a percent)	0.34%		0.34%
Level 3 | Other real estate owned, discount to price input | Price-based | Maximum
Valuation techniques and inputs
Discount to price (as a percent)	0.34%		13.00%
Level 3 | Other real estate owned, discount to price input | Price-based | Weighted Average
Valuation techniques and inputs
Discount to price (as a percent)	0.34%		3.10%
Level 3 | Other real estate owned | Price-based | Minimum
Valuation techniques and inputs
Appraised value	$ 27,054.05
Level 3 | Other real estate owned | Price-based | Maximum
Valuation techniques and inputs
Appraised value	4,514,806.00
Level 3 | Other real estate owned | Price-based | Weighted Average
Valuation techniques and inputs
Appraised value	2,032,098.00
Level 3 | Other real estate owned, price input | Price-based | Minimum
Valuation techniques and inputs
Price	62.43		$ 64.65
Level 3 | Other real estate owned, price input | Price-based | Maximum
Valuation techniques and inputs
Price	85.81		74.39
Level 3 | Other real estate owned, price input | Price-based | Weighted Average
Valuation techniques and inputs
Price	65.53		66.21
Level 3 | Loans | Price-based
Valuation techniques and inputs
Total assets	345,000,000		$ 135,000,000
Level 3 | Loans | Price-based | Minimum
Valuation techniques and inputs
Price	$ 3.20
Discount to price (as a percent)			0.25%
Appraised value			$ 25.80
Recovery rate (as a percent)	92.68%
Level 3 | Loans | Price-based | Maximum
Valuation techniques and inputs
Price	$ 100.00
Discount to price (as a percent)			13.00%
Appraised value			$ 26,400,000
Recovery rate (as a percent)	92.68%
Level 3 | Loans | Price-based | Weighted Average
Valuation techniques and inputs
Price	$ 23.67
Discount to price (as a percent)			8.34%
Appraised value			$ 6,462,735
Recovery rate (as a percent)	92.68%
Level 3 | Loans | Cash flow
Valuation techniques and inputs
Total assets			431,000,000
Level 3 | Loans | Cash flow | Minimum
Valuation techniques and inputs
Price			3.25
Level 3 | Loans | Cash flow | Maximum
Valuation techniques and inputs
Price			105.00
Level 3 | Loans | Cash flow | Weighted Average
Valuation techniques and inputs
Price			59.61
Level 3 | Loans | Recovery analysis
Valuation techniques and inputs
Total assets	$ 128,000,000		197,000,000
Level 3 | Loans | Recovery analysis | Minimum
Valuation techniques and inputs
Discount to price (as a percent)	18.67%
Forward price			2.90
Level 3 | Loans | Recovery analysis | Maximum
Valuation techniques and inputs
Discount to price (as a percent)	28.39%
Forward price			210.00
Level 3 | Loans | Recovery analysis | Weighted Average
Valuation techniques and inputs
Discount to price (as a percent)	23.57%
Forward price			$ 156.78