LOAN SERVICING - Activity in MSR (Details) - Mortgage Servicing Rights - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Servicing Assets at Fair Value [Line Items]
Mortgage loans sold with servicing retained	$ 5,638,000,000		$ 5,638,000,000		$ 5,242,000,000
Mortgage loans sold with servicing retained	322,000,000	$ 204,000,000	781,000,000	$ 870,000,000
Pre-tax net gains (losses) resulting from above loan sales	1,000,000	(2,000,000)	1,000,000	(9,000,000)
Mortgage servicing fees	3,000,000	3,000,000	10,000,000	9,000,000
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Balance at beginning of period	55,700,000	50,700,000	52,800,000	44,400,000
Additions	3,800,000	2,400,000	9,000,000.0	10,500,000
Payoffs and curtailments	(1,300,000)	(800,000)	(1,600,000)	(3,800,000)
Impairment (charge) / recovery	0	0	0	2,500,000
Amortization / other	200,000	(600,000)	(1,800,000)	(1,900,000)
Balance at end of period	58,400,000	51,700,000	58,400,000	51,700,000
Fair value, start	72,100,000	64,100,000	68,600,000	46,000,000.0
Fair value, end	75,100,000	$ 69,600,000	75,100,000	$ 69,600,000
Valuation allowance for servicing rights	$ 0		$ 0		$ 0