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Mortgage Servicing Rights, Net - Additional Information (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Mortgage Servicing Rights [Line Items]
Primary servicing portfolio	$ 58,100.0	$ 57,100.0
Special servicing portfolio	$ 2,700.0	$ 2,900.0
Minimum [Member]
Mortgage Servicing Rights [Line Items]
Discount rate	3.00%	3.00%
Maximum [Member]
Mortgage Servicing Rights [Line Items]
Discount rate	13.50%	13.50%
Discount Rate One [Member]
Mortgage Servicing Rights [Line Items]
Increase in discount rate	1.00%	1.00%
Decrease in fair value of servicing rights	$ (11.7)	$ (12.4)
Discount Rate Two [Member]
Mortgage Servicing Rights [Line Items]
Increase in discount rate	2.00%	2.00%
Decrease in fair value of servicing rights	$ (22.8)	$ (24.4)
Mortgage Servicing Rights [Member]
Mortgage Servicing Rights [Line Items]
Estimated fair value of MSRs	$ 431.5	$ 451.9

X

- Definition

Mortgage servicing rights.

+ References

No definition available.

+ Details

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- Definition

Percentage of increase in discount rate of servicing rights.

+ References

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X

- Definition

Primary servicing portfolio.

+ References

No definition available.

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X

- Definition

Special servicing portfolio.

+ References

No definition available.

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X

- 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
-SubTopic 50
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746

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X

- Definition

The increase (decrease) in the fair value of servicing assets that are subsequently measured at fair value.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746

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- Definition

Discount rate used to estimate the fair value of servicing assets and servicing liabilities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122596-111746

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