FAIR VALUE MEASUREMENTS - Schedule of Financial Instruments not Recorded at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity, carrying value	$ 4,967	$ 5,071
Securities held-to-maturity, fair value	4,986	5,058
Other investment securities, at cost, carrying value	794	942
Other investment securities, at cost, fair value	794	942
Other loans held for sale, carrying value	187	42
Other loans held for sale, fair value	187	42
Loans and leases, carrying value	109,046	107,669
Loans and leases, fair value	109,323	107,537
Deposits, carrying value	113,613	109,804
Deposits, fair value	113,582	109,796
Federal funds purchased and securities sold under agreements to repurchase, carrying value	429	1,148
Federal funds purchased and securities sold under agreements to repurchase, fair value	429	1,148
Other short-term borrowed funds, carrying value	2,004	3,211
Other short-term borrowed funds, fair value	2,004	3,211
Long-term borrowed funds, carrying value	13,154	12,790
Long-term borrowed funds, fair value	13,275	12,849
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity, carrying value	0	0
Securities held-to-maturity, fair value	0	0
Other investment securities, at cost, carrying value	0	0
Other investment securities, at cost, fair value	0	0
Other loans held for sale, carrying value	0	0
Other loans held for sale, fair value	0	0
Loans and leases, carrying value	0	0
Loans and leases, fair value	0	0
Deposits, carrying value	0	0
Deposits, fair value	0	0
Federal funds purchased and securities sold under agreements to repurchase, carrying value	0	0
Federal funds purchased and securities sold under agreements to repurchase, fair value	0	0
Other short-term borrowed funds, carrying value	0	0
Other short-term borrowed funds, fair value	0	0
Long-term borrowed funds, carrying value	0	0
Long-term borrowed funds, fair value	0	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity, carrying value	4,967	5,071
Securities held-to-maturity, fair value	4,986	5,058
Other investment securities, at cost, carrying value	794	942
Other investment securities, at cost, fair value	794	942
Other loans held for sale, carrying value	0	0
Other loans held for sale, fair value	0	0
Loans and leases, carrying value	341	355
Loans and leases, fair value	341	355
Deposits, carrying value	113,613	109,804
Deposits, fair value	113,582	109,796
Federal funds purchased and securities sold under agreements to repurchase, carrying value	429	1,148
Federal funds purchased and securities sold under agreements to repurchase, fair value	429	1,148
Other short-term borrowed funds, carrying value	2,004	3,211
Other short-term borrowed funds, fair value	2,004	3,211
Long-term borrowed funds, carrying value	13,154	12,790
Long-term borrowed funds, fair value	13,275	12,849
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity, carrying value	0	0
Securities held-to-maturity, fair value	0	0
Other investment securities, at cost, carrying value	0	0
Other investment securities, at cost, fair value	0	0
Other loans held for sale, carrying value	187	42
Other loans held for sale, fair value	187	42
Loans and leases, carrying value	108,705	107,314
Loans and leases, fair value	108,982	107,182
Deposits, carrying value	0	0
Deposits, fair value	0	0
Federal funds purchased and securities sold under agreements to repurchase, carrying value	0	0
Federal funds purchased and securities sold under agreements to repurchase, fair value	0	0
Other short-term borrowed funds, carrying value	0	0
Other short-term borrowed funds, fair value	0	0
Long-term borrowed funds, carrying value	0	0
Long-term borrowed funds, fair value	$ 0	$ 0