LOANS AND LEASES - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	$ 526,000,000		$ 526,000,000		$ 325,000,000
Other loans held for sale	0		0		40,000,000
Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral for FHLB borrowed funds	23,200,000,000		23,200,000,000		23,200,000,000
Loans pledged as collateral to support the contingent ability to borrow at the FRB discount window	16,900,000,000		16,900,000,000		15,900,000,000
Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	526,000,000		526,000,000		325,000,000
Other loans held for sale	0		0		0
Residential loans held for sale | Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	456,000,000		456,000,000		268,000,000
Commercial real estate loans held for sale | Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	70,000,000		70,000,000		$ 57,000,000
TDR Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Pre-tax gain	72,000,000		72,000,000
Mortgage loans sold	310,000,000		310,000,000
Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased during period	200,000,000	$ 326,000,000	534,000,000	$ 1,100,000,000
Student loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased during period	126,000,000	152,000,000	843,000,000	615,000,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans sold during the period	14,000,000	100,000,000	132,000,000	325,000,000
Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans sold during the period		41,000,000		41,000,000
Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased during period	222,000,000	$ 252,000,000	405,000,000	887,000,000
Mortgage loans sold	163,000,000		444,000,000	$ 273,000,000
Residential mortgages | TDR Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans sold	255,000,000		255,000,000
Home equity loans | TDR Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans sold	$ 55,000,000		$ 55,000,000