LOAN SERVICING - Activity in MSR (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Servicing Assets at Fair Value [Line Items]
Mortgage banking operations	$ 8.0	$ 5.0	$ 12.0	$ 11.0
Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Mortgage loans sold with servicing retained	4,333.0		4,333.0		$ 3,968.0
Mortgage loans sold with servicing retained	406.0	283.0	583.0	520.0
Pretax gains resulting from above loan sales	9.0	5.0	13.0	9.0
Mortgage banking operations	3.0	2.0	5.0	4.0
Valuation allowance for servicing rights	3.1		3.1
Valuation allowance for servicing rights, increase			2.6
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Balance at beginning of period	36.4	30.8	36.8	29.1
Additions	4.3	3.3	6.3	6.0
Payoffs and curtailments	(0.8)	(0.5)	(1.3)	(0.9)
Impairment charge	(1.3)	0.0	(2.6)	0.0
Amortization	(0.6)	(0.6)	(1.2)	(1.2)
Balance at end of period	38.0	33.0	38.0	33.0
Loan servicing rights, fair value, start	40.3	36.4	41.1	32.4
Loan servicing rights, fair value, end	$ 39.8	$ 38.6	$ 39.8	$ 38.6

Gain From Sale of Loan, Pretax

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- Definition

Loans Sold With Servicing Retained

+ References

No definition available.

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- Definition

Unpaid Principal Balance For Loans Serviced For Investors

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- Definition

Income from mortgage banking activities (fees and commissions) and servicing real estate mortgages, credit cards, and other financial assets held by others net of any related impairment of capitalized service costs. Also includes any premiums received in lieu of regular servicing fees on such loans only as earned over the life of the loans.

+ References

No definition available.

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- Definition

Amortized amount of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Amount of additions from purchases, assumption or transfer to contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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Amount of amortization of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount conveyed to unrelated parties of contract to contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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Amount of increase (decrease) in the amortized amount from a decrease (increase) in the valuation allowance applied to the servicing asset for a contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
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-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Reflects the estimated amount of impairment as of the balance sheet date of recognized servicing assets that are being amortized in proportion to and over the period of estimated net servicing income or loss.

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The net increase (decrease) in the valuation allowance for servicing assets subsequently measured using the amortization method.

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