Mortgage Loans Mortgage Loans Held for Sale (Details) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Sep. 30, 2023
Mortgage loans held for sale	$ 2,044.1		$ 2,519.9
Mortgage loans held for sale, outstanding principal amount	2,000.0		2,600.0
Payments for Origination of Mortgage Loans Held-for-sale	5,100.0	$ 4,600.0
Proceeds from Sale of Mortgage Loans Held-for-sale	5,700.0	5,200.0
Gain (Loss) on Sales of Loans, Net	$ 128.7	$ 79.2
Loans Sold to FNMA or securities backed by GNMA [Member] \| Customer Concentration Risk \| Mortgage Loans
Concentration Risk, Percentage	71.00%
Other Customer [Member] \| Customer Concentration Risk \| Mortgage Loans
Concentration Risk, Percentage	28.00%
Loan Origination Commitments [Member]
Derivative, Notional Amount	$ 765.6		1,100.0
Fair Value, Inputs, Level 3 [Member] \| Interest rate lock commitments [Member]
Derivative, Notional Amount	2,300.0		2,700.0
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	$ (16.5)		$ 15.7

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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The net gain (loss) resulting from a sale of loans, including adjustments to record loans classified as held-for-sale at the lower-of-cost-or-market and fair value adjustments to loan held for investment purposes.

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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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The amount of cash paid for the origination of mortgages that are held for sale.

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The cash inflow from sales of loans that are secured with real estate mortgages and are held with the intention to resell in the near future.

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