FAIR VALUE MEASUREMENTS - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage banking (expense) income		$ 18,000,000	$ 21,000,000	$ 81,000,000	$ 55,000,000
Transfers from Level 3 to Level 2	$ 5,000,000
Weighted average life (in years)				5 years 2 months 12 days		5 years 2 months 12 days
Weighted average constant prepayment rate (percent)				12.30%		12.40%
Weighted average discount rate (percent)				9.70%		9.80%
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average life (in years)				2 years 8 months 12 days		2 years 9 months 18 days
Weighted average constant prepayment rate (percent)				11.60%		10.40%
Weighted average discount rate (percent)				9.11%		9.10%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average life (in years)				5 years 9 months 18 days		6 years 7 months 6 days
Weighted average constant prepayment rate (percent)				22.47%		22.60%
Weighted average discount rate (percent)				12.07%		12.10%
Residential loans held for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage banking (expense) income		4,000,000	(2,000,000)	$ 2,000,000	3,000,000
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		0
Other noninterest income		$ 1,000,000	$ 0	$ 3,000,000	$ 0