Fair Values of Assets and Liabilities - Valuation Assumption Ranges for MSRs (Details)	Sep. 30, 2025
Minimum | Expected prepayment
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs measurement inputs	0.06
Minimum | Option adjusted spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs measurement inputs	0.05
Maximum | Expected prepayment
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs measurement inputs	0.21
Maximum | Option adjusted spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs measurement inputs	0.11
Weighted Average | Expected prepayment
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs measurement inputs	0.09
Weighted Average | Option adjusted spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs measurement inputs	0.06