LOANS AND LEASES - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	6 Months Ended
	Mar. 31, 2015	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale		$ 397		$ 256
Other loans held for sale		300		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		22,300		22,000
Loans pledged as collateral to support the contingent ability to borrow at the FRB discount window		12,900		11,800
Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale		397		256
Other loans held for sale		0		0
Level 2 | Residential loans held for sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale		318		213
Level 2 | Commercial real estate loans held for sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale		79		43
Commercial loan syndication
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other loans held for sale		260		$ 25
Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other loans held for sale		40
Transfer of portfolio loans and leases to held-for-sale	$ 41
Loans and leases receivable held-for-sale, gross	43
Allowance for Loan and Lease Losses, Sales and Other	$ 2
Residential portfolio segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased during period		636	878
Mortgage loans sold		273	126
Consumer loans auto financing receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased during period		809	759
Student loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased during period		$ 463	59
Loans sold during the period			357
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans sold during the period			$ 132