FAIR VALUE MEASUREMENT - Valuation Techniques and Inputs for Level 3 Nonrecurring Fair Value Measurements (Details) - Nonrecurring - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	$ (63,000,000)	$ (84,000,000)	$ (131,000,000)	$ (239,000,000)
Loans held-for-sale
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	(17,000,000)	(7,000,000)	(15,000,000)	(7,000,000)
Loans
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	(42,000,000)	(72,000,000)	(110,000,000)	(220,000,000)
Other real estate owned
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	(4,000,000)	$ (5,000,000)	(6,000,000)	$ (12,000,000)
Level 3
Valuation techniques and inputs
Total assets	2,515,000,000		2,515,000,000		$ 4,003,000,000
Level 3 | Loans held-for-sale | Price-based
Valuation techniques and inputs
Total assets	1,988,000,000		1,988,000,000		3,486,000,000
Level 3 | Loans held-for-sale | Price-based | Minimum
Valuation techniques and inputs
Price			0.00		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			93.47		81.05
Level 3 | Other real estate owned, discount to price input | Price-based
Valuation techniques and inputs
Total assets	62,000,000		62,000,000		$ 90,000,000
Level 3 | Other real estate owned, discount to price input | Price-based | Minimum
Valuation techniques and inputs
Price			$ 58.91
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
Price			$ 68.50
Discount to price (as a percent)			13.00%		13.00%
Level 3 | Other real estate owned, discount to price input | Price-based | Weighted Average
Valuation techniques and inputs
Price			$ 59.42
Discount to price (as a percent)			2.96%		2.86%
Level 3 | Other real estate owned, appraised value | Price-based
Valuation techniques and inputs
Total assets					$ 2,000,000
Level 3 | Other real estate owned, appraised value | Price-based | Minimum
Valuation techniques and inputs
Appraised value					0
Level 3 | Other real estate owned, appraised value | Price-based | Maximum
Valuation techniques and inputs
Appraised value					8,518,230
Level 3 | Other real estate owned, appraised value | Price-based | Weighted Average
Valuation techniques and inputs
Appraised value					3,813,045
Level 3 | Loans | Price-based
Valuation techniques and inputs
Total assets	278,000,000		$ 278,000,000		$ 87,000,000
Level 3 | Loans | Price-based | Minimum
Valuation techniques and inputs
Discount to price (as a percent)			13.00%		13.00%
Level 3 | Loans | Price-based | Maximum
Valuation techniques and inputs
Discount to price (as a percent)			13.00%		34.00%
Level 3 | Loans | Price-based | Weighted Average
Valuation techniques and inputs
Discount to price (as a percent)			13.00%		7.99%
Level 3 | Loans | Cash flow
Valuation techniques and inputs
Total assets	$ 347,000,000		$ 347,000,000
Level 3 | Loans | Cash flow | Minimum
Valuation techniques and inputs
Price			3.00
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			$ 55.67
Level 3 | Loans | Recovery Analysis
Valuation techniques and inputs
Total assets					$ 157,000,000
Level 3 | Loans | Recovery Analysis | Minimum
Valuation techniques and inputs
Recovery rate (as a percent)					11.79%
Level 3 | Loans | Recovery Analysis | Maximum
Valuation techniques and inputs
Recovery rate (as a percent)					60.00%
Level 3 | Loans | Recovery Analysis | Weighted Average
Valuation techniques and inputs
Recovery rate (as a percent)					23.49%