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Long-Duration Insurance Contracts Relating to Life Insurance Operations - Schedule of Liability For Future Policy Benefit, Weighted Average Duration (Detail)
Mar. 31, 2025
Mar. 31, 2024
Yen-denominated insurance (First Sector)    
Liability for Future Policy Benefit, Activity [Line Items]    
Liability for future policy benefit weighted average duration 35 years 1 month 6 days 36 years 4 months 24 days
Yen-denominated insurance (Third Sector)    
Liability for Future Policy Benefit, Activity [Line Items]    
Liability for future policy benefit weighted average duration 32 years 6 months 34 years 8 months 12 days
Foreign currency denominated insurance    
Liability for Future Policy Benefit, Activity [Line Items]    
Liability for future policy benefit weighted average duration 33 years 6 months 36 years 10 months 24 days