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Pension Plans (Net Pension Cost of Defined Benefit Plans) (Detail) - JPY (¥)
¥ in Millions
 6 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Japanese plans    
Defined Benefit Plan Disclosure [Line Items]    
Service cost ¥ 2,222 ¥ 2,584
Interest cost 975 704
Expected return on plan assets (1,372) (1,397)
Amortization of prior service credit (32) (36)
Amortization of net actuarial loss (69) (49)
Net periodic pension cost 1,724 1,806
Overseas plans    
Defined Benefit Plan Disclosure [Line Items]    
Service cost 1,371 1,654
Interest cost 2,302 2,070
Expected return on plan assets (3,601) (3,535)
Amortization of prior service credit (137) (162)
Amortization of net actuarial loss (2) 2
Amortization of transition obligation 0 1
Net periodic pension cost ¥ (67) ¥ 30