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Long-Duration Insurance Contracts Relating to Life Insurance Operations - Schedule of Liability For Future Policy Benefit, Weighted Average Discount Rates (Detail)
Sep. 30, 2025
Mar. 31, 2025
Yen-denominated insurance (First Sector)    
Liability for Future Policy Benefit, Activity [Line Items]    
Weighted average of the original discount rates 1.80% 1.80%
Weighted average of the current discount rates 4.50% 2.70%
Yen-denominated insurance (Third Sector)    
Liability for Future Policy Benefit, Activity [Line Items]    
Weighted average of the original discount rates 1.70% 1.70%
Weighted average of the current discount rates 4.50% 2.70%
Foreign currency denominated insurance    
Liability for Future Policy Benefit, Activity [Line Items]    
Weighted average of the original discount rates 3.40% 3.30%
Weighted average of the current discount rates 5.70% 5.90%