Mortgage Loans Mortgage Loans Held for Sale (Details) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Mortgage loans held for sale	$ 1,438.9		$ 1,529.0
Mortgage loans held for sale, outstanding principal amount	1,370.0		1,460.0
Payments for Origination of Mortgage Loans Held-for-sale	3,500.0	$ 2,300.0
Proceeds from Sale of Mortgage Loans Held-for-sale	3,600.0	2,300.0
Gain (Loss) on Sales of Loans, Net	138.9	$ 73.6
Mortgage servicing rights	$ 9.8		17.1
Loans Sold to FNMA or securities backed by GNMA [Member]
Concentration Risk, Percentage	66.00%
Other Customer [Member]
Concentration Risk, Percentage	27.00%
Loan Origination Commitments [Member]
Derivative, Notional Amount	$ 1,400.0		1,100.0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Mortgage loans held for sale	1,411.6		1,503.2
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	$ (7.5)		$ (5.3)

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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Nominal or face amount used to calculate payment on derivative.

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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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Fair value as of the balance sheet date of all derivatives not designated as hedging instruments.

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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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Aggregate amount of servicing assets that are subsequently measured at fair value and servicing assets that are subsequently measured using the amortization method.

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