Mortgage Loans Mortgage Loans Held for Sale (Details) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Sep. 30, 2021
Mortgage loans held for sale	$ 1,833.3		$ 2,027.3
Mortgage loans held for sale, outstanding principal amount	1,790.0		1,970.0
Payments for Origination of Mortgage Loans Held-for-sale	3,900.0	$ 3,500.0
Proceeds from Sale of Mortgage Loans Held-for-sale	4,100.0	3,600.0
Gain (Loss) on Sales of Loans, Net	134.1	$ 138.9
Interest rate lock commitments [Member]
Derivative, Notional Amount	$ 1,800.0		1,500.0
Loans Sold to FNMA or securities backed by GNMA [Member] \| Customer Concentration Risk \| Mortgage Loans
Concentration Risk, Percentage	61.00%
Other Customer [Member] \| Customer Concentration Risk \| Mortgage Loans
Concentration Risk, Percentage	30.00%
Loan Origination Commitments [Member]
Derivative, Notional Amount	$ 1,200.0		834.6
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	$ 1.3		$ 1.1

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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This is the principal amount outstanding for loans which are in the process of being securitized as of the date of the statement of financial position (across all types of loans).

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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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