v3.26.1
Pension and Other Employee Benefit Plans (Fair Value of Plan Assets by Asset Category) (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets ¥ 1,720,955 ¥ 1,784,082 ¥ 1,956,619
Foreign | Common stocks | Equity securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 117,000 121,000  
Foreign | Pooled funds | Equity securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [1] 14,000 11,000  
Foreign | Pooled funds | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [1] 3,000 4,000  
Foreign | Government bonds | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 167,000 168,000  
Foreign | Other | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 32,000 31,000  
All Other | General account of life insurance companies      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [2] 108,000 118,000  
All Other | Other Invested Assets      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 59,000 44,000  
All Other | Net Asset Value      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [3] 428,000 408  
Japan | Common stocks | Equity securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [4] 672,000 758,000  
Japan | Pooled funds | Equity securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [1] 13,000 12,000  
Japan | Pooled funds | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [1] 10,000 9,000  
Japan | Government bonds | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 84,000 83,000  
Japan | Other | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 15,000 18,000  
Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 1,085,000 1,158,000  
Level 1 | Foreign | Common stocks | Equity securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 117,000 121,000  
Level 1 | Foreign | Pooled funds | Equity securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [1] 2,000 1,000  
Level 1 | Foreign | Government bonds | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 142,000 144,000  
Level 1 | All Other | Other Invested Assets      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [5] 64,000 46,000  
Level 1 | Japan | Common stocks | Equity securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [4] 672,000 758,000  
Level 1 | Japan | Pooled funds | Equity securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [1] 4,000 5,000  
Level 1 | Japan | Government bonds | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 84,000 83,000  
Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 208,000 218,000  
Level 2 | Foreign | Pooled funds | Equity securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [1] 12,000 10,000  
Level 2 | Foreign | Pooled funds | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [1] 3,000 4,000  
Level 2 | Foreign | Government bonds | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 24,000 24,000  
Level 2 | Foreign | Other | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets 32,000 30,000  
Level 2 | All Other | General account of life insurance companies      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [2] 108,000 118,000  
Level 2 | All Other | Other Invested Assets      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets (5,000) (2,000) [1]  
Level 2 | Japan | Pooled funds | Equity securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [1] 9,000 8,000  
Level 2 | Japan | Pooled funds | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets [1] 10,000 9,000  
Level 2 | Japan | Other | Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair values of plan assets ¥ 15,000 ¥ 18,000  
[1] These classes primarily include pension investment fund trusts. Investments in these classes are generally measured at fair value and can be redeemed within a short-term period upon request.
[2] Investments in this class are measured at conversion value, which is equivalent to fair value.
[3] In accordance with ASC 820, certain plan assets that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy.
[4] This class represents equity securities held in the employee retirement benefit trusts of ¥758 billion and ¥672 billion carried at fair value at March 31, 2025 and 2026, respectively, which are well-diversified across industries.
[5] Amounts primarily include cash and short-term assets carried at fair value.