FAIR VALUE MEASUREMENTS - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage banking (expense) income		$ 25,000,000	$ 30,000,000	$ 43,000,000	$ 63,000,000
Transfers from Level 3 to Level 2	$ 5,000,000
Weighted average life (in years)				4 years 10 months 24 days		5 years 4 months 24 days
Weighted average constant prepayment rate				13.50%		11.60%
Weighted average discount rate				9.70%		9.70%
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average life (in years)				2 years 6 months		2 years 9 months 18 days
Weighted average constant prepayment rate				13.20%		10.70%
Weighted average discount rate				9.10%		9.10%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average life (in years)				5 years 3 months 18 days		6 years 2 months 12 days
Weighted average constant prepayment rate				24.30%		22.20%
Weighted average discount rate				12.10%		12.10%
Residential loans held for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage banking (expense) income		6,000,000	(3,000,000)	$ 12,000,000	(2,000,000)
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		$ 2,000,000	$ 1,000,000	$ 2,000,000	$ 3,000,000