FAIR VALUE MEASUREMENTS - Schedule of Financial Instruments not Recorded at Fair Value (Details) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity, carrying value		$ 4,823	$ 5,071
Securities held-to-maturity, fair value		4,839	5,058
Other investment securities, at cost, carrying value		772	942
Other investment securities, at cost, fair value		772	942
Other loans held for sale, carrying value		724	42
Other loans held for sale, fair value		724	42
Loans and leases, carrying value	[1],[2]	110,151	107,669
Loans and leases, fair value		110,710	107,537
Deposits, carrying value		113,235	109,804
Deposits, fair value		113,205	109,796
Federal funds purchased and securities sold under agreements to repurchase, carrying value		453	1,148
Federal funds purchased and securities sold under agreements to repurchase, fair value		453	1,148
Other short-term borrowed funds, carrying value		1,505	3,211
Other short-term borrowed funds, fair value		1,505	3,211
Long-term borrowed funds, carrying value		13,400	12,790
Long-term borrowed funds, fair value		13,543	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		4,823	5,071
Securities held-to-maturity, fair value		4,839	5,058
Other investment securities, at cost, carrying value		772	942
Other investment securities, at cost, fair value		772	942
Other loans held for sale, carrying value		0	0
Other loans held for sale, fair value		0	0
Loans and leases, carrying value		300	355
Loans and leases, fair value		300	355
Deposits, carrying value		113,235	109,804
Deposits, fair value		113,205	109,796
Federal funds purchased and securities sold under agreements to repurchase, carrying value		453	1,148
Federal funds purchased and securities sold under agreements to repurchase, fair value		453	1,148
Other short-term borrowed funds, carrying value		1,505	3,211
Other short-term borrowed funds, fair value		1,505	3,211
Long-term borrowed funds, carrying value		13,400	12,790
Long-term borrowed funds, fair value		13,543	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		724	42
Other loans held for sale, fair value		724	42
Loans and leases, carrying value		109,851	107,314
Loans and leases, fair value		110,410	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

[1] Excluded from the table above are loans held for sale totaling $1.2 billion and $625 million as of September 30, 2017 and December 31, 2016, respectively.

[2] Mortgage loans serviced for others by the Company’s subsidiaries are not included above, and amounted to $17.7 billion and $17.3 billion at September 30, 2017 and December 31, 2016, respectively.