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Pension Plans (Fair Value of Pension Plan Assets by Asset Category) (Parenthetical) (Detail) - JPY (¥) ¥ in Millions | Mar. 31, 2023 | Mar. 31, 2022
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of pension plan assets | ¥ 1,000,704 | ¥ 978,033
Japanese Companies Equity Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of pension plan assets | ¥ 22 | ¥ 22
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 | ¥ 35 | ¥ 37
Foreign Government Bonds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets investment allocation in pooled funds | 90.00% | 90.00%
Foreign Corporate Bonds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets investment allocation in pooled funds | 10.00% | 10.00%

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