Other Assets, Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019
Other assets
Earnest money and refundable deposits	$ 860.6		$ 657.1
Insurance receivables	90.5		81.2	$ 76.6
Other receivables	166.6		143.1
Prepaid assets	51.7		46.0
Margin deposits	0.2		16.2
Contract assets - insurance agency commissions	51.1		47.1
Lease right of use assets	33.9		34.7
Mortgage servicing rights	6.4		17.1
Other	42.9		39.9
Other assets	1,418.5		1,113.7
Accrued expenses and other liabilities
Reserves for legal claims	524.4		473.8	442.2		$ 434.7
Employee compensation and related liabilities	443.7		376.1
Warranty liability	340.7	$ 324.0	310.2	$ 262.7	$ 251.6	$ 247.3
Mortgage hedging instruments and commitments	49.2		16.5
Additional Collateral, Aggregate Fair Value	72.1		0.0
Accrued interest	36.1		35.3
Federal and state income tax liabilities	241.4		42.6
Inventory related accruals	167.1		93.9
Customer deposits	163.6		93.1
Accrued property taxes	27.0		44.1
Lease liabilities	35.4		37.0
Other	97.4		84.4
Accrued expenses and other liabilities	2,198.1		1,607.0
Interest rate lock commitments [Member]
Other assets
Interest rate lock commitments	26.8		31.3
Interest rate lock commitments [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Other assets
Other	26.8
Accrued expenses and other liabilities
Other	44.1
Interest Rate Derivative Instruments Not Designated as Hedging Instruments at Fair Value, Net	(17.3)		31.3
Forward sales of MBS [Member]
Other assets
Interest rate lock commitments	87.8		0.0
Forward sales of MBS [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Accrued expenses and other liabilities
Interest Rate Derivative Instruments Not Designated as Hedging Instruments at Fair Value, Net	$ 87.8		$ (16.2)