Transfers of financial assets and servicing assets - Key economic assumptions used (Details) - Residential Mortgage	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement
Prepayment speed	9.20%	7.50%	7.50%	6.90%
Weighted average life	8 years 1 month 6 days	9 years 3 months 18 days	9 years	9 years 7 months 6 days
Discount rate (annual rate)	10.70%	11.00%	10.80%	11.00%

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.

No definition available.

+ Details

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- Definition

Discount rate which is used to value residual cash flows generated by financial assets of the securitization, asset-backed financing arrangement, or similar transfer for initial fair value measurement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118948506&loc=d3e107207-111719

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- Definition

Estimated rate of prepayment of principal on financial assets for initial fair value measurement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=118948506&loc=d3e107207-111719

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- Definition

Weighted average life of securitized assets for initial fair value measurement, 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 3
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=118948506&loc=d3e107207-111719

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