FAIR VALUE MEASUREMENTS - Schedule of Financial Instruments not Recorded at Fair Value (Details) - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020
Financial assets:
Securities held to maturity, carrying value	[1]	$ 2,242	$ 3,235
Securities held-to-maturity, fair value		2,289	3,357
Other loans held for sale, carrying value		735	439
Other loans held for sale, fair value		735	439
Loans and leases		128,163	123,090
Loans and leases, fair value		128,156	123,678
Other investment securities, at cost, carrying value		624	604
Other investment securities, at cost, estimated fair value		624	604
Financial liabilities:
Deposits, carrying value		154,361	147,164
Deposits, fair value		154,366	147,223
Short-term borrowed funds		74	243
Short-term borrowed funds, fair value		74	243
Long-term borrowed funds, carrying value		6,932	8,346
Long-term borrowed funds, fair value		7,188	8,850
Level 1
Financial assets:
Securities held to maturity, carrying value		0	0
Securities held-to-maturity, 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		0	0
Loans and leases, fair value		0	0
Other investment securities, at cost, carrying value		0	0
Other investment securities, at cost, estimated fair value		0	0
Financial liabilities:
Deposits, carrying value		0	0
Deposits, fair value		0	0
Short-term borrowed funds		0	0
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		1,505	2,342
Securities held-to-maturity, fair value		1,557	2,464
Other loans held for sale, carrying value		0	0
Other loans held for sale, fair value		0	0
Loans and leases		645	758
Loans and leases, fair value		645	758
Other investment securities, at cost, carrying value		609	596
Other investment securities, at cost, estimated fair value		609	596
Financial liabilities:
Deposits, carrying value		154,361	147,164
Deposits, fair value		154,366	147,223
Short-term borrowed funds		74	243
Short-term borrowed funds, fair value		74	243
Long-term borrowed funds, carrying value		6,932	8,346
Long-term borrowed funds, fair value		7,188	8,850
Level 3
Financial assets:
Securities held to maturity, carrying value		737	893
Securities held-to-maturity, fair value		732	893
Other loans held for sale, carrying value		735	439
Other loans held for sale, fair value		735	439
Loans and leases		127,518	122,332
Loans and leases, fair value		127,511	122,920
Other investment securities, at cost, carrying value		15	8
Other investment securities, at cost, estimated fair value		15	8
Financial liabilities:
Deposits, carrying value		0	0
Deposits, fair value		0	0
Short-term borrowed funds		0	0
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] Includes only collateral pledged by the Company where counterparties have the right to sell or pledge the collateral.