Mortgage Loans - Loan Commitments and Related Derivatives Textual (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Interest rate lock commitments [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 2,700.0	$ 4,000.0
Best-efforts whole loan delivery commitments [Member]
Derivative [Line Items]
Derivative, Notional Amount	18.9	23.5
Hedging Instruments Related To IRLCs [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 2,600.0	$ 3,800.0

Nominal or face amount used to calculate payment on derivative.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-1A

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