Mortgage Loans - Mortgage Loss Reserves (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Loss reserves related to:
Reserve balances	$ 8.9	$ 8.7

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Name:	us-gaap_LoansAndLeasesReceivableAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant