For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Mortgage Loans Mortgage Loans Held for Sale (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024	Sep. 30, 2024
Mortgage loans held for sale	$ 2,455.0		$ 2,455.0		$ 2,477.5
Mortgage loans held for sale, outstanding principal amount	2,500.0		2,500.0		2,490.0
Payments for Origination of Mortgage Loans Held-for-sale			10,520.0	$ 11,290.0
Proceeds from Sale of Mortgage Loans Held-for-sale			10,480.0	11,130.0
Gain (Loss) on Sales of Loans, Net	$ 151.1	$ 152.7	271.1	$ 281.5
Loans Sold to FNMA, FHLMC or securities backed by GNMA [Member] \| Customer Concentration Risk \| Mortgage Loans
Concentration Risk, Percentage	69.00%
Other Customer [Member] \| Customer Concentration Risk \| Mortgage Loans
Concentration Risk, Percentage	29.00%
Loan Origination Commitments [Member]
Derivative, Notional Amount	$ 1,100.0		1,100.0		637.9
Fair Value, Inputs, Level 3 [Member] \| Interest rate lock commitments [Member]
Derivative, Notional Amount	2,700.0		2,700.0		2,000.0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Loan Origination Commitments [Member]
Interest Rate Derivative Instruments Not Designated as Hedging Instruments at Fair Value, Net	$ (2.6)		$ (2.6)		$ 2.4