Other Assets, Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019
Other assets
Earnest money and refundable deposits	$ 999.8		$ 657.1
Insurance receivables	98.1		81.2	$ 82.4
Other receivables	152.3		143.1
Prepaid assets	54.7		46.0
Margin deposits	20.0		16.2
Contract assets - insurance agency commissions	54.6		47.1
Lease right of use assets	35.0		34.7
Mortgage servicing rights	14.2		17.1
Other	40.2		39.9
Other assets	1,491.0		1,113.7
Accrued expenses and other liabilities
Reserves for legal claims	543.1		473.8	461.3		$ 434.7
Employee compensation and related liabilities	427.8		376.1
Warranty liability	361.5	$ 340.7	310.2	$ 281.3	$ 262.7	$ 247.3
Mortgage hedging instruments and commitments	18.9		16.5
Accrued interest	34.9		35.3
Federal and state income tax liabilities	39.1		42.6
Inventory related accruals	200.5		93.9
Customer deposits	201.3		93.1
Accrued property taxes	37.8		44.1
Lease liabilities	36.5		37.0
Other	99.9		84.4
Accrued expenses and other liabilities	2,001.3		1,607.0
Interest rate lock commitments [Member]
Other assets
Interest rate lock commitments	$ 22.1		$ 31.3