Mortgage Loans - Loan Commitments and Related Derivatives Textual (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
Interest rate lock commitments [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 1,500.0	$ 1,800.0
Best-efforts whole loan delivery commitments [Member]
Derivative [Line Items]
Derivative, Notional Amount	88.8	84.6
Hedging Instruments Related To IRLCs [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 1,400.0	$ 1,600.0

Nominal or face amount used to calculate payment on derivative.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5579245-113959

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant