FAIR VALUE MEASUREMENTS - Schedule of Financial Instruments not Recorded at Fair Value (Details) - USD ($) $ in Millions		Sep. 30, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset-backed investments included in HTM securities	[1]	$ 9,320	$ 9,834
Fair Value		8,054	9,042
Other loans held for sale, carrying value		99	208
Other loans held for sale, fair value		99	208
Loans pledged as collateral for FHLB borrowed funds	[2]	147,666	154,679
Loans and leases, fair value		141,041	151,601
Other assets, carrying value		995	1,058
Other assets, fair value		995	1,058
Deposits, carrying value		178,197	180,724
Deposits, fair value		178,077	180,566
Short-term borrowed funds, carrying value		232	3
Short-term borrowed funds, fair value		232	3
Long-term borrowed funds, carrying value	[2]	17,354	15,887
Long-term borrowed funds, fair value		16,656	15,469
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset-backed investments included in HTM securities		0	0
Fair Value		0	0
Other loans held for sale, carrying value		0	0
Other loans held for sale, fair value		0	0
Loans pledged as collateral for FHLB borrowed funds		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]
Asset-backed investments included in HTM securities		8,810	9,253
Fair Value		7,569	8,506
Other loans held for sale, carrying value		0	0
Other loans held for sale, fair value		0	0
Loans pledged as collateral for FHLB borrowed funds		835	582
Loans and leases, fair value		835	582
Other assets, carrying value		977	1,038
Other assets, fair value		977	1,038
Deposits, carrying value		178,197	180,724
Deposits, fair value		178,077	180,566
Short-term borrowed funds, carrying value		232	3
Short-term borrowed funds, fair value		232	3
Long-term borrowed funds, carrying value		17,354	15,887
Long-term borrowed funds, fair value		16,656	15,469
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset-backed investments included in HTM securities		510	581
Fair Value		485	536
Other loans held for sale, carrying value		99	208
Other loans held for sale, fair value		99	208
Loans pledged as collateral for FHLB borrowed funds		146,831	154,097
Loans and leases, fair value		140,206	151,019
Other assets, carrying value		18	20
Other assets, fair value		18	20
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.

[2] Includes amounts in consolidated VIEs. See Note 7 for additional information.