LOANS AND LEASES - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	$ 369		$ 256
Other loans held for sale	51		25
Retail branches
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans sold during the period		$ 1,100
Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral for FHLB borrowed funds	22,100		22,000
Loans pledged as collateral to support the contingent ability to borrow at the FRB discount window	12,700		11,800
Commercial loan syndication
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other loans held for sale			25
Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased during period	1,100	1,300
Residential portfolio segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased during period	887	1,500
Mortgage loans sold	273	126
Student loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased during period	615	59
Loans sold during the period		357
Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfer of portfolio loans and leases to held-for-sale	41
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans sold during the period		$ 165
Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	369		256
Other loans held for sale	0		0
Residential loans held for sale | Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	269		213
Commercial real estate loans held for sale | Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	$ 100		$ 43