Fair Values of Assets and Liabilities - Valuation Assumption Ranges for Derivative Commitments (Detail) - Derivative Mortgage Loans Commitments [Member]	Sep. 30, 2021
Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected loan close rate	1.00%
Inherent MSR value (basis points per loan)	47.00%
Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected loan close rate	100.00%
Inherent MSR value (basis points per loan)	187.00%
Weighted-average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected loan close rate	76.00%
Inherent MSR value (basis points per loan)	121.00%