LOANS AND LEASES - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	$ 478		$ 478		$ 325
Other loans held for sale	372		372		40
Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral for FHLB borrowed funds	23,200		23,200		23,200
Loans pledged as collateral to support the contingent ability to borrow at the FRB discount window	16,600		16,600		15,900
Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased during period	200	$ 416	334	$ 809
Student loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased during period	348	202	717	463
Residential portfolio segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans purchased during period	63	387	183	636
Mortgage loans sold	108		281	273
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans sold during the period	45	$ 114	118	$ 225
Commercial loan syndication
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other loans held for sale	50		50		40
Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	478		478		325
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	424		424		268
Commercial real estate loans held for sale | Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	54		54		$ 57
TDR Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other loans held for sale	322		322
TDR Loans | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other loans held for sale	60		60
TDR Loans | Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other loans held for sale	$ 262		$ 262