FAIR VALUE MEASUREMENTS - Narrative (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average life (in years)	5 years 0 months 6 days		5 years 2 months 12 days
Weighted average constant prepayment rate (percent)	12.80%		12.40%
Weighted average discount rate (percent)	9.80%		9.80%
Transfers between Levels 1, 2, or 3	$ 5,000,000
Mortgage banking noninterest income (loss)	33,000,000	20,000,000
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average life (in years)	2 years 9 months 18 days		2 years 9 months 18 days
Weighted average constant prepayment rate (percent)	11.00%		10.40%
Weighted average discount rate (percent)	9.10%		9.10%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average life (in years)	6 years 3 months 18 days		6 years 7 months 6 days
Weighted average constant prepayment rate (percent)	22.20%		22.60%
Weighted average discount rate (percent)	12.30%		12.10%
Residential loans held for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage banking noninterest income (loss)	1,000,000	1,000,000
Commercial real estate loans held for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans in this portfolio that were 90 days or more past due or nonaccruing	$ 0