Fair Value Measurements - Nonrecurring Bais (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans held for sale	$ 1,755.8	$ 1,529.0
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Nonrecurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans held for sale	1.0	1.5
Loans Receivable, Fair Value Disclosure	2.4	0.6
Fair Value, Inputs, Level 3 [Member] \| Fair Value, Nonrecurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans held for sale	1.9	2.2
Loans Receivable, Fair Value Disclosure	$ 1.9	$ 2.0

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No definition available.

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

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- Definition

Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=120238483&loc=d3e48678-111004

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