MORTGAGE SERVICING RIGHTS - Fair Value Disclosures (Detail) - MSRs - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Servicing
Fair value of the MSRs	$ 834.5	$ 669.4
Sensitivity Analysis of Fair Value, example 1, impact of percent adverse change in discount rate, percent	1.00%
Decrease in fair value as a result of 100 basis point increase in discount rate	$ 26.3
Sensitivity Analysis of Fair Value, example 2, impact of percent adverse change in discount rate, percent	2.00%
Decrease in fair value as a result of 200 basis point increase in discount rate	$ 50.8

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122739-111746

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=7516967&loc=d3e66267-113978

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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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The hypothetical financial impact of a 1 percent adverse change in the discount rate on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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- Definition

The hypothetical financial impact of a 2 percent adverse change in the discount rate on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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A specified percentage variance in the discount rate assumption in the determination of fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date, sensitivity scenario 1.

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