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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
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

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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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

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- Definition

Amount of investment in equity method investee and investment in and advance to affiliate.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(18))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

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