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Pension Plans (Fair Value of Pension Plan Assets by Asset Category) (Parenthetical) (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Japanese Companies Equity Securities    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of pension plan assets ¥ 42 ¥ 30
Japanese Government Bond Securities    
Defined Benefit Plan Disclosure [Line Items]    
Pension plan assets investment allocation in pooled funds 70.00% 70.00%
Japanese Corporate Bonds Securities    
Defined Benefit Plan Disclosure [Line Items]    
Pension plan assets investment allocation in pooled funds 30.00% 30.00%
Fair value of pension plan assets ¥ 6 ¥ 7
Foreign Government Bonds [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Pension plan assets investment allocation in pooled funds 100.00% 100.00%