Mortgage Loans - Mortgage Loans Held for Sale (Details) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Loans Receivable [Line Items]
Mortgage loans held for sale	$ 538.2		$ 587.3
Aggregate outstanding principal amounts	521.3		570.8
Mortgage loans originated	1,600.0	$ 1,400.0
Mortgage loans sold	1,600.0	1,500.0
Net gain on sales of loans	$ 57.0	$ 57.4
Percentage of mortgage loans sold to significant purchasers	91.00%
Percentage of mortgage loans sold to one significant purchaser	39.00%
Uncommitted Loans [Member]
Loans Receivable [Line Items]
Mortgage loans held for sale	$ 374.7		330.7
Uncommitted Loans [Member] \| Hedging Instruments related to IRLCs [Member]
Loans Receivable [Line Items]
Notional amounts of hedging instruments, Total	$ 374.6		$ 330.7

The percentage of mortgage loans sold to major purchasers during the period.

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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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.

+ References

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- Definition

Nominal or face amount used to calculate payments on the derivative asset.

+ References

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- Definition

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.

+ References

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- Definition

Amount, after allowance for bad debt, of mortgage loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

+ References

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- Definition

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

+ References

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- Definition

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).

+ References

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- Definition

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.

+ References

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