FAIR VALUE MEASUREMENTS - Schedule of Financial Instruments not Recorded at Fair Value (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Financial Assets:
Securities held to maturity, carrying value		$ 4,685	$ 5,071
Securities held-to-maturity, fair value		4,668	5,058
Other investment securities, at cost, carrying value		722	942
Other investment securities, at cost, estimated fair value		722	942
Other loans held for sale, carrying value		221	42
Other loans held for sale, fair value		221	42
Loans and leases, carrying value	[1],[2]	110,617	107,669
Loans and leases, fair value		111,168	107,537
Financial Liabilities:
Deposits, carrying value		115,089	109,804
Deposits, fair value		115,039	109,796
Federal funds purchased and securities sold under agreements to repurchase, carrying value		815	1,148
Federal funds purchased and securities sold under agreements to repurchase, fair value		815	1,148
Other short-term borrowed funds, carrying value		1,856	3,211
Other short-term borrowed funds, fair value		1,856	3,211
Long-term borrowed funds, carrying value		11,765	12,790
Long-term borrowed funds, fair value		11,891	12,849
Level 1
Financial Assets:
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, estimated 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
Financial Liabilities:
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
Financial Assets:
Securities held to maturity, carrying value		4,685	5,071
Securities held-to-maturity, fair value		4,668	5,058
Other investment securities, at cost, carrying value		722	942
Other investment securities, at cost, estimated fair value		722	942
Other loans held for sale, carrying value		0	0
Other loans held for sale, fair value		0	0
Loans and leases, carrying value		393	355
Loans and leases, fair value		393	355
Financial Liabilities:
Deposits, carrying value		115,089	109,804
Deposits, fair value		115,039	109,796
Federal funds purchased and securities sold under agreements to repurchase, carrying value		815	1,148
Federal funds purchased and securities sold under agreements to repurchase, fair value		815	1,148
Other short-term borrowed funds, carrying value		1,856	3,211
Other short-term borrowed funds, fair value		1,856	3,211
Long-term borrowed funds, carrying value		11,765	12,790
Long-term borrowed funds, fair value		11,891	12,849
Level 3
Financial Assets:
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, estimated fair value		0	0
Other loans held for sale, carrying value		221	42
Other loans held for sale, fair value		221	42
Loans and leases, carrying value		110,224	107,314
Loans and leases, fair value		110,775	107,182
Financial Liabilities:
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 $718 million and $625 million as of December 31, 2017 and 2016, respectively.

[2] Mortgage loans serviced for others by the Company’s subsidiaries are not included above, and amounted to $20.3 billion and $17.3 billion at December 31, 2017 and 2016, respectively.