v3.25.2
Financial instruments - Summary of Valuation Techniques Used to Measure the Fair Value of Assets and Liabilities Classified as Level 3 (Detail) - Level 3 of fair value hierarchy [member] - Recurring fair value measurement [member]
Mar. 31, 2025
basispoint
Mar. 31, 2024
basispoint
Credit spread, measurement input [member] | Japanese Corporate Bonds [Member] | Discounted cash flow [member] | Bottom of range [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets [line items]    
Financial assets required to be measured at FVOCI 53 27
Credit spread, measurement input [member] | Japanese Corporate Bonds [Member] | Discounted cash flow [member] | Top of range [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets [line items]    
Financial assets required to be measured at FVOCI 71 72
Credit spread, measurement input [member] | Securitized Products [Member] | Discounted cash flow [member] | Bottom of range [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets [line items]    
Financial assets required to be measured at FVOCI 80 90
Credit spread, measurement input [member] | Securitized Products [Member] | Discounted cash flow [member] | Top of range [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets [line items]    
Financial assets required to be measured at FVOCI 140 170
Volatility Measurement Input [Member] | Equity Contracts [Member] | Option pricing model [member] | Bottom of range [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets [line items]    
Financial assets required to be measured at FVOCI 0.477  
Volatility Measurement Input [Member] | Equity Contracts [Member] | Option pricing model [member] | Top of range [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets [line items]    
Financial assets required to be measured at FVOCI 0.57