Fair Values of Assets and Liabilities - Valuation Assumption Ranges for Derivative Commitments (Detail) - Derivative Mortgage Loans Commitments [Member]	Mar. 31, 2021
Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected loan close rate	4.00%
Inherent MSR value (basis points per loan)	53.00%
Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected loan close rate	100.00%
Inherent MSR value (basis points per loan)	201.00%
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)	123.00%