LOAN SERVICING - Activity in MSR (Detail) - Mortgage Servicing Rights [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Servicing Assets at Fair Value [Line Items]
Mortgage loans sold with servicing retained	$ 4,663.0		$ 4,663.0		$ 4,686.0
Mortgage loans sold with servicing retained	416.0	$ 406.0	676.0	$ 583.0
Pretax net gains resulting from above loan sales	15.0	9.0	22.0	13.0
Mortgage banking operations	3.0	3.0	6.0	5.0
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Balance at beginning of period	34.9	36.4	42.6	36.8
Additions	4.0	4.3	6.5	6.3
Payoffs and curtailments	(4.0)	(0.8)	(5.9)	(1.3)
Impairment charge	(0.3)	(1.3)	(8.0)	(2.6)
Amortization	(0.6)	(0.6)	(1.2)	(1.2)
Balance at end of period	34.0	38.0	34.0	38.0
Loan servicing rights, fair value, start	34.9	40.3	45.0	41.1
Loan servicing rights, fair value, end	34.0	$ 39.8	34.0	$ 39.8
Valuation allowance for servicing rights	$ 9.6		$ 9.6		$ 1.5