FAIR VALUE MEASUREMENTS - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage banking (expense) income		$ 33,000,000	$ 18,000,000	$ 76,000,000	$ 81,000,000
Transfers from Level 3 to Level 2	$ 5,000,000
Residential loans held for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage banking (expense) income		1,000,000	4,000,000	13,000,000	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		$ 0
Other noninterest income		$ 1,000,000	$ 1,000,000	$ 3,000,000	$ 3,000,000