Fair Values of Assets and Liabilities - Valuation Assumption Ranges for MSRs (Detail) - Mortgage Servicing Rights [Member]		9 Months Ended	12 Months Ended
		Sep. 30, 2023	Dec. 31, 2022
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected prepayment		8.10%	7.80%
Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected prepayment		6.00%
Option adjusted spread		4.00%
Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected prepayment		16.00%
Option adjusted spread		11.00%
Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected prepayment	[1]	8.00%
Option adjusted spread	[1]	5.00%

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