Mortgage Servicing Rights - Summary of Key Unobservable Inputs Used in Determining the Fair Value (Details) - MSR - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Minimum
Servicing Assets at Fair Value [Line Items]
Discount rates	9.00%	9.00%
Annual prepayment speeds	8.20%	8.80%
Cost of servicing	$ 75	$ 75
Minimum \| UNITED WHOLESALE MORTGAGE, LLC
Servicing Assets at Fair Value [Line Items]
Discount rates		9.00%	9.00%
Annual prepayment speeds		8.80%	8.20%
Cost of servicing		$ 75	$ 90
Maximum
Servicing Assets at Fair Value [Line Items]
Discount rates	14.50%	14.50%
Annual prepayment speeds	44.80%	42.20%
Cost of servicing	$ 147	$ 126
Maximum \| UNITED WHOLESALE MORTGAGE, LLC
Servicing Assets at Fair Value [Line Items]
Discount rates		14.50%	14.50%
Annual prepayment speeds		42.20%	30.80%
Cost of servicing		$ 126	$ 138

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

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=125521744&loc=d3e122596-111746

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- Definition

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

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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

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- Definition

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

+ References

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