Transfers of Residential Loans - Additional Information (Detail) - USD ($) $ in Billions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Transfer of Financial Assets Accounted for as Sales [Line Items]
Mortgage loans sold and serviced, percent past due	1.30%	0.50%
Reverse Loans And Real Estate Owned [Member]
Transfer of Financial Assets Accounted for as Sales [Line Items]
Unpaid principal balance of assets pledged as collateral to securitization pools	$ 9.9
Carrying value of assets pledged as collateral to securitzation pools	$ 10.4
Residential Loan Transfers Accounted for as Sales [Member]
Transfer of Financial Assets Accounted for as Sales [Line Items]
Mortgage loans sold and serviced, number of days past due threshold	60 days or more
Customer Concentration Risk [Member] \| Mortgage Loans Sold [Member] \| Fannie Mae [Member]
Transfer of Financial Assets Accounted for as Sales [Line Items]
Mortgage loans purchased, concentration percent	47.00%	56.00%
Customer Concentration Risk [Member] \| Mortgage Loans Sold [Member] \| Ginnie Mae [Member]
Transfer of Financial Assets Accounted for as Sales [Line Items]
Mortgage loans purchased, concentration percent	39.00%	35.00%
Customer Concentration Risk [Member] \| Mortgage Loans Sold [Member] \| Freddie Mac [Member]
Transfer of Financial Assets Accounted for as Sales [Line Items]
Mortgage loans purchased, concentration percent	14.00%	9.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611

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- Definition

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.

+ References

No definition available.

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- Definition

Carrying amount of financial assets accounted for as secured borrowings recognized in the transferor's statement of financial position at the end of each period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

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- Definition

This is the amount of the financial instruments that are considered delinquent (past due) at the end of the period expressed as a percent.

+ References

No definition available.

+ Details

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- Definition

The number days past due threshold for mortgage loans sold and serviced by the Company.

+ References

No definition available.

+ Details

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- Definition

Unpaid principal balance of financial assets accounted for as secured borrowings recognized in the transferor's statement of financial position at the end of each period presented.

+ References

No definition available.

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