MSR (Servicing Assets and Residual Interests Economic Assumptions) (Detail)	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018
Fixed Rate Residential Mortgage
Servicing Assets
Weighted- Average Life (in years)	6 years 6 months	7 years 7 months 6 days	6 years 7 months 6 days
Prepayment Speed (annual)	11.10%	9.20%	9.10%
OAS spread (bps)	5.17%	4.99%	5.33%
Adjustable Rate Residential Mortgage
Servicing Assets
Weighted- Average Life (in years)	3 years 3 months 18 days	2 years 6 months	3 years 6 months
Prepayment Speed (annual)	23.70%	35.10%	23.20%
OAS spread (bps)	7.00%	6.50%	8.42%

The OAS represents the spread that is added to the discount rate so that the sum of the discounted cash flows equals the market price; therefore, it is a measure of the extra yield over the reference discount factor that the Corporation expects to earn by holding the asset.

No definition available.

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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

Weighted average life of securitized assets regardless of when the transfer occurred, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=109247956&loc=d3e107314-111719

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- Definition

Estimated rate of prepayment of principal on financial assets regardless of when the transfer occurred.

+ References

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