BORROWINGS - Schedule of Long-term Borrowings (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2025	Jun. 15, 2025	Mar. 12, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Capital lease obligations	$ 63			$ 15
Total long-term borrowings	$ 37,641			36,684
Parent | Fixed-to-Floating Senior Notes at 5.231% | Senior Notes
Debt Instrument [Line Items]
Debt instrument, stated interest rate	5.231%		5.231%
Long-term debt, gross	$ 497			0
Basis spread on variable rate	1.41%
Parent | Fixed-to-Floating subordinated notes at 3.375% | Subordinated Debt
Debt Instrument [Line Items]
Debt instrument, stated interest rate	3.375%
Long-term debt, gross	$ 0			350
Basis spread on variable rate	2.465%
Parent | Fixed-to-Fixed Subordinated Notes at 6.254% | Subordinated Debt
Debt Instrument [Line Items]
Debt instrument, stated interest rate	6.254%		6.254%
Long-term debt, gross	$ 745			0
Basis spread on variable rate	1.97%
Parent | Fixed-to-Fixed Subordinated Notes At 3.75% | Subordinated Debt
Debt Instrument [Line Items]
Debt instrument, stated interest rate		3.375%
Subsidiaries | Fixed Senior Unsecured Notes at 6.00% | Senior Notes
Debt Instrument [Line Items]
Debt instrument, stated interest rate	6.00%
Long-term debt, gross	$ 58			58
Subsidiaries | Fixed Subordinated Notes at 6.125% | Subordinated Debt
Debt Instrument [Line Items]
Debt instrument, stated interest rate	6.125%
Long-term debt, gross	$ 437			445
Subsidiaries | Purchase Money Note to FDIC fixed at 3.50% | Secured Debt
Debt Instrument [Line Items]
Debt instrument, stated interest rate	3.50%
Long-term debt, gross	$ 35,841			$ 35,816