Fair Values of Assets and Liabilities - Valuation Assumption Ranges for Derivative Commitments (Detail) - Derivative Mortgage Loans Commitments [Member]	Sep. 30, 2023
Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected loan close rate	35.00%
Inherent MSR value (basis points per loan)	58.00%
Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected loan close rate	100.00%
Inherent MSR value (basis points per loan)	194.00%
Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected loan close rate	79.00%	[1]
Inherent MSR value (basis points per loan)	118.00%	[1]

[1] Determined based on the relative fair value of the related mortgage loans.