FAIR VALUE MEASUREMENTS - Schedule of Financial Instruments not Recorded at Fair Value (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Financial Assets:
Securities held to maturity, carrying value		$ 4,165	$ 4,685
Securities held-to-maturity, fair value		4,041	4,668
Other investment securities, at cost, carrying value		834	722
Other investment securities, at cost, estimated fair value		834	722
Other loans held for sale, carrying value		101	221
Other loans held for sale, fair value		101	221
Loans and leases, carrying value	[1],[2]	116,660	110,617
Loans and leases, fair value		116,627	111,168
Financial Liabilities:
Deposits, carrying value		119,575	115,089
Deposits, fair value		119,503	115,039
Federal funds purchased and securities sold under agreements to repurchase, carrying value		1,156	815
Federal funds purchased and securities sold under agreements to repurchase, fair value		1,156	815
Other short-term borrowed funds, carrying value		1,653	1,856
Other short-term borrowed funds, fair value		1,653	1,856
Long-term borrowed funds, carrying value		14,433	11,765
Long-term borrowed funds, fair value		14,390	11,891
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		4,165	4,685
Securities held-to-maturity, fair value		4,041	4,668
Other investment securities, at cost, carrying value		834	722
Other investment securities, at cost, estimated fair value		834	722
Other loans held for sale, carrying value		0	0
Other loans held for sale, fair value		0	0
Loans and leases, carrying value		338	393
Loans and leases, fair value		338	393
Financial Liabilities:
Deposits, carrying value		119,575	115,089
Deposits, fair value		119,503	115,039
Federal funds purchased and securities sold under agreements to repurchase, carrying value		1,156	815
Federal funds purchased and securities sold under agreements to repurchase, fair value		1,156	815
Other short-term borrowed funds, carrying value		1,653	1,856
Other short-term borrowed funds, fair value		1,653	1,856
Long-term borrowed funds, carrying value		14,433	11,765
Long-term borrowed funds, fair value		14,390	11,891
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		101	221
Other loans held for sale, fair value		101	221
Loans and leases, carrying value		116,322	110,224
Loans and leases, fair value		116,289	110,775
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 $1.3 billion and $718 million as of December 31, 2018 and 2017, respectively.

[2] Mortgage loans serviced for others by the Company’s subsidiaries are not included above, and amounted to $69.6 billion and $20.3 billion at December 31, 2018 and 2017, respectively.