MORTGAGE BANKING AND OTHER SERVICED LOANS - Economic Assumptions Used to Estimate Value of MSRs (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Fair value	$ 1,620	$ 1,530
Weighted average life (years)	9 years 1 month 6 days	9 years 1 month 6 days
Weighted average constant prepayment rate	6.40%	6.80%
Weighted average option adjusted spread	6.30%	6.29%
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	$ 35	$ 34
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	$ 67	66
Decline in fair value from 20% adverse change	$ 89	$ 86