MORTGAGE BANKING AND OTHER SERVICED LOANS - Economic Assumptions Used to Estimate Value of MSRs (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Fair value	$ 1,564	$ 1,552
Weighted average life (years)	8 years 10 months 24 days	8 years 9 months 18 days
Weighted average constant prepayment rate	7.00%	7.20%
Weighted average option adjusted spread	6.32%	6.30%
Minimum
Servicing Assets at Fair Value [Line Items]
Sensitivity analysis, basis spread	10.00%
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Decline in fair value from 10% adverse change	$ 41	$ 37
Decline in fair value from 10% adverse change	$ 44	43
Maximum
Servicing Assets at Fair Value [Line Items]
Sensitivity analysis, basis spread	20.00%
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Decline in fair value from 20% adverse change	$ 75	71
Decline in fair value from 20% adverse change	$ 87	$ 87