Mortgage Servicing Assets - Schedule of Range and Weighted-Average of Significant Unobservable Inputs (Details) - Discounted cash flow - USD ($)	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Real estate — commercial mortgage \| Minimum
Servicing Assets at Fair Value [Line Items]
Expected defaults	1.00%	1.00%
Residual cash flows discount rate	7.72%	7.00%
Escrow earn rate	92.00%	1.46%
Loan assumption rate	0.00%	0.01%
Real estate — commercial mortgage \| Maximum
Servicing Assets at Fair Value [Line Items]
Expected defaults	2.00%	2.00%
Residual cash flows discount rate	10.66%	11.50%
Escrow earn rate	1.16%	2.36%
Loan assumption rate	1.78%	3.37%
Real estate — commercial mortgage \| Weighted Average
Servicing Assets at Fair Value [Line Items]
Expected defaults	1.17%	1.13%
Residual cash flows discount rate	9.30%	9.30%
Escrow earn rate	1.05%	2.02%
Loan assumption rate	1.39%	1.38%
Residential mortgage-backed securities \| Minimum
Servicing Assets at Fair Value [Line Items]
Expected defaults	7.51%	7.50%
Prepayment speed	12.35%	12.06%
Servicing cost	$ 62,000,000.00	$ 62,000,000
Residential mortgage-backed securities \| Maximum
Servicing Assets at Fair Value [Line Items]
Expected defaults	8.80%	10.00%
Prepayment speed	53.36%	62.96%
Servicing cost	$ 5,125,000,000	$ 4,375,000,000
Residential mortgage-backed securities \| Weighted Average
Servicing Assets at Fair Value [Line Items]
Expected defaults	7.57%	7.53%
Prepayment speed	16.89%	14.53%
Servicing cost	$ 81,670,000	$ 67,670,000

Interest rate used to account for mortgage loan at fair value upon assumption.

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- Definition

Servicing Assets And Servicing Liabilities At Fair Value, Assumptions Used To Estimate Fair Value, Escrow Earn Rate

+ References

No definition available.

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- Definition

Servicing Assets And Servicing Liabilities At Fair Value, Assumptions Used To Estimate Fair Value, Servicing Cost

+ References

No definition available.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122596-111746

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- Definition

Percentage of contractually collectible principal associated with a financial asset expected not to be collected due to default by the borrower.

+ References

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- Definition

Estimated rate of prepayments of principal on servicing assets and servicing liabilities.

+ References

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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.

+ Details

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