v3.26.1
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, 2026
Mar. 31, 2025
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
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
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
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
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 0.511 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 0.677 0.57