BORROWINGS - Schedule of Long-term Borrowings (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2025	Sep. 05, 2025	Jun. 15, 2025	Mar. 12, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Capital lease obligations	$ 67				$ 15
Total long-term borrowings	$ 38,252				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%		3.375%
Long-term debt, gross	$ 0				350
Basis spread on variable rate	2.465%
Parent | Fixed-to-Fixed Subordinated Notes at 5.600% | Subordinated Debt
Debt Instrument [Line Items]
Debt instrument, stated interest rate	5.60%	5.60%
Long-term debt, gross	$ 597				0
Basis spread on variable rate	1.85%
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 6.000% | 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	$ 434				445
Subsidiaries | Purchase Money Note to FDIC fixed at 3.500% | Secured Debt
Debt Instrument [Line Items]
Debt instrument, stated interest rate	3.50%
Long-term debt, gross	$ 35,854				$ 35,816