Summary of Significant Accounting Principles - Significant Accounting Principles: Allowance for Credit Losses (Details)	Dec. 31, 2019
Loss severity \| Second Mortgage \| Home equity lines of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Instruments backed by residential real estate assets	1

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.

No definition available.

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration