FAIR VALUE MEASUREMENTS - Schedule of Financial Instruments not Recorded at Fair Value (Details) - USD ($) $ in Millions		Mar. 31, 2022	Dec. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities held to maturity, carrying value	[1]	$ 2,056	$ 2,242
Debt Securities held-to-maturity, Fair Value		2,011	2,289
Other loans held for sale, carrying value		99	735
Other loans held for sale, fair value		98	735
Loans and leases		131,305	128,163
Loans and leases, fair value		129,134	128,156
Other assets, carrying value		611	624
Other assets, fair value		611	624
Deposits, carrying value		158,776	154,361
Deposits, fair value		158,746	154,366
Short-term borrowed funds, carrying value		25	74
Short-term borrowed funds, fair value		25	74
Long-term borrowed funds, carrying value		5,894	6,932
Long-term borrowed funds, fair value		5,853	7,188
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities held to maturity, carrying value		0	0
Debt 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 assets, carrying value		0	0
Other assets, fair value		0	0
Deposits, carrying value		0	0
Deposits, fair value		0	0
Short-term borrowed funds, carrying value		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
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities held to maturity, carrying value		1,370	1,505
Debt Securities held-to-maturity, Fair Value		1,355	1,557
Other loans held for sale, carrying value		0	0
Other loans held for sale, fair value		0	0
Loans and leases		600	645
Loans and leases, fair value		600	645
Other assets, carrying value		595	609
Other assets, fair value		595	609
Deposits, carrying value		158,776	154,361
Deposits, fair value		158,746	154,366
Short-term borrowed funds, carrying value		25	74
Short-term borrowed funds, fair value		25	74
Long-term borrowed funds, carrying value		5,894	6,932
Long-term borrowed funds, fair value		5,853	7,188
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities held to maturity, carrying value		686	737
Debt Securities held-to-maturity, Fair Value		656	732
Other loans held for sale, carrying value		99	735
Other loans held for sale, fair value		98	735
Loans and leases		130,705	127,518
Loans and leases, fair value		128,534	127,511
Other assets, carrying value		16	15
Other assets, fair value		16	15
Deposits, carrying value		0	0
Deposits, fair value		0	0
Short-term borrowed funds, carrying value		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.