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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	$ (60,000,000)	$ (63,000,000)	$ (73,000,000)	$ (131,000,000)
Loans held-for-sale
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	10,000,000	(17,000,000)	11,000,000	(15,000,000)
Other real estate owned
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	(4,000,000)	(4,000,000)	(4,000,000)	(6,000,000)
Loans
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	(66,000,000)	$ (42,000,000)	(80,000,000)	$ (110,000,000)
Level 3
Valuation techniques and inputs
Total assets	2,666,000,000		2,666,000,000		$ 3,263,000,000
Level 3 | Loans held-for-sale | Price-based
Valuation techniques and inputs
Total assets	2,114,000,000		2,114,000,000		2,413,000,000
Level 3 | Loans held-for-sale | Price-based | Minimum
Valuation techniques and inputs
Price			87.73		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			98.96		93.08
Level 3 | Other real estate owned, discount to price input | Price-based
Valuation techniques and inputs
Total assets	41,000,000		41,000,000		$ 59,000,000
Level 3 | Other real estate owned, discount to price input | Price-based | Minimum
Valuation techniques and inputs
Appraised value			20,291
Discount to price (as a percent)					0.34%
Level 3 | Other real estate owned, discount to price input | Price-based | Maximum
Valuation techniques and inputs
Appraised value			4,491,044
Discount to price (as a percent)					13.00%
Level 3 | Other real estate owned, discount to price input | Price-based | Weighted Average
Valuation techniques and inputs
Appraised value			$ 1,967,435
Discount to price (as a percent)					3.10%
Level 3 | Other real estate owned | Price-based | Minimum
Valuation techniques and inputs
Discount to price (as a percent)			34.00%
Level 3 | Other real estate owned | Price-based | Maximum
Valuation techniques and inputs
Discount to price (as a percent)			34.00%
Level 3 | Other real estate owned | Price-based | Weighted Average
Valuation techniques and inputs
Discount to price (as a percent)			34.00%
Level 3 | Other real estate owned, price input | Price-based | Minimum
Valuation techniques and inputs
Price			$ 30.00		$ 64.65
Level 3 | Other real estate owned, price input | Price-based | Maximum
Valuation techniques and inputs
Price			54.49		74.39
Level 3 | Other real estate owned, price input | Price-based | Weighted Average
Valuation techniques and inputs
Price			53.48		66.21
Level 3 | Loans | Price-based
Valuation techniques and inputs
Total assets	50,000,000		50,000,000		135,000,000
Level 3 | Loans | Price-based | Minimum
Valuation techniques and inputs
Price			2.75
Appraised value					$ 25.80
Discount to price (as a percent)					0.25%
Level 3 | Loans | Price-based | Maximum
Valuation techniques and inputs
Price			100.00
Appraised value					$ 26,400,000
Discount to price (as a percent)					13.00%
Level 3 | Loans | Price-based | Weighted Average
Valuation techniques and inputs
Price			128.92
Appraised value					$ 6,462,735
Discount to price (as a percent)					8.34%
Level 3 | Loans | Recovery analysis
Valuation techniques and inputs
Total assets	231,000,000		$ 231,000,000		$ 197,000,000
Level 3 | Loans | Recovery analysis | Minimum
Valuation techniques and inputs
Recovery rate (as a percent)			48.00%
Forward price					2.90
Level 3 | Loans | Recovery analysis | Maximum
Valuation techniques and inputs
Recovery rate (as a percent)			91.97%
Forward price					210.00
Level 3 | Loans | Recovery analysis | Weighted Average
Valuation techniques and inputs
Recovery rate (as a percent)			65.20%
Forward price					156.78
Level 3 | Loans | Cash flow
Valuation techniques and inputs
Total assets	$ 155,000,000		$ 155,000,000		431,000,000
Level 3 | Loans | Cash flow | Minimum
Valuation techniques and inputs
Price					3.25
Appraised value			70.00
Level 3 | Loans | Cash flow | Maximum
Valuation techniques and inputs
Price					105.00
Appraised value			88.05
Level 3 | Loans | Cash flow | Weighted Average
Valuation techniques and inputs
Price					$ 59.61
Appraised value			$ 79.61