Fair Value Measurements - Assets Measured on a Nonrecurring Basis (Details) $ in Millions	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale	$ 2,477.5	$ 2,519.9
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	0.14
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	9.5	0.0
Other mortgage loans	1.3	0.0
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	7.0	30.7
Other mortgage loans	9.8	2.2
Restricted cash, fair value	0.4	0.0
Nonrecurring [Member] | Level 3 [Member] | Inventories [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventories	$ 68.1	$ 28.8