Mortgage Servicing Rights - Additional Information (Details) - USD ($) $ in Billions	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Transfers and Servicing [Abstract]
Mortgage servicing right weighted average life	5 years 8 months 12 days	5 years 1 month 6 days
Unpaid principal balance of mortgage loans serviced	$ 69.2	$ 60.8

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

Name:	us-gaap_AssumptionForFairValueOfAssetsOrLiabilitiesThatRelateToTransferorsContinuingInvolvementWeightedAverageLife1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration