FAIR VALUE MEASUREMENTS - Schedule of Financial Instruments not Recorded at Fair Value (Details) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset-backed investments included in HTM securities	[1]	$ 9,054	$ 9,184
Fair Value		8,132	8,350
Other loans held for sale, carrying value		50	103
Other loans held for sale, fair value		50	103
Loans pledged as collateral for FHLB borrowed funds	[2]	141,102	143,861
Loans and leases, fair value		137,760	140,504
Other assets, carrying value		791	869
Other assets, fair value		791	869
Deposits, carrying value		176,428	177,342
Deposits, fair value		176,162	177,096
Short-term borrowed funds, carrying value		9	505
Short-term borrowed funds, fair value		9	505
Long-term borrowed funds, carrying value	[2]	13,804	13,467
Long-term borrowed funds, fair value		13,421	13,012
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		8,587	8,696
Fair Value		7,682	7,887
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		881	789
Loans and leases, fair value		881	789
Other assets, carrying value		768	851
Other assets, fair value		768	851
Deposits, carrying value		176,428	177,342
Deposits, fair value		176,162	177,096
Short-term borrowed funds, carrying value		9	505
Short-term borrowed funds, fair value		9	505
Long-term borrowed funds, carrying value		13,804	13,467
Long-term borrowed funds, fair value		13,421	13,012
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset-backed investments included in HTM securities		467	488
Fair Value		450	463
Other loans held for sale, carrying value		50	103
Other loans held for sale, fair value		50	103
Loans pledged as collateral for FHLB borrowed funds		140,221	143,072
Loans and leases, fair value		136,879	139,715
Other assets, carrying value		23	18
Other assets, fair value		23	18
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 6 for additional information.