BORROWINGS - Schedule of Long-term Borrowings (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 12, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Capital lease obligations	$ 36		$ 15
Total long-term borrowings	$ 37,956		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	$ 350		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%
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	$ 441		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	$ 35,829		$ 35,816