Fair Value Measurements - Assets Measured on a Nonrecurring Basis (Details) $ in Millions	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale	$ 2,566.5	$ 2,477.5
Inventories [Member] \| Measurement Input, Discount Rate [Member] \| Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Real Estate Owned, Measurement Input	0.16
Inventories [Member] \| Measurement Input, Discount Rate [Member] \| Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Real Estate Owned, Measurement Input	0.10
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash, fair value	$ 0.0	0.0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash, fair value	0.0	0.0
Nonrecurring [Member] \| Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale	8.5	9.5
Other mortgage loans	0.0	1.3
Restricted cash, fair value	0.0	0.0
Nonrecurring [Member] \| Level 2 [Member] \| Inventories [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventories	0.0	0.0
Nonrecurring [Member] \| Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale	19.3	7.0
Other mortgage loans	0.0	9.8
Restricted cash, fair value	0.0	0.4
Nonrecurring [Member] \| Level 3 [Member] \| Inventories [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventories	$ 66.3	$ 68.1

Fair value portion of asset recognized for present right to economic benefit.

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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.

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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.

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Fair value portion of other assets.

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Value of input used to measure real estate owned by financial institution by financial institution which is not directly related to its business.

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