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Pension Plans (Fair Value of Pension Plan Assets by Asset Category) (Parenthetical) (Detail) - JPY (¥) ¥ in Millions | Mar. 31, 2025 | Mar. 31, 2024
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Japanese Companies Equity Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of pension plan assets | ¥ 30 | ¥ 32
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 | ¥ 7 | ¥ 24
Foreign Government Bonds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets investment allocation in pooled funds | 100.00% | 90.00%
Foreign Corporate Bonds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets investment allocation in pooled funds |  | 10.00%

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- Definition Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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