Pension Plans (Significant Assumptions of Japan and Overseas Pension Plans Used to Determine Plan Amounts) (Detail)	12 Months Ended
Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023
Japan
Weighted-average assumptions used to determine benefit obligations at March 31:
Discount rate	2.10%	1.40%	1.10%
Rate of increase in compensation levels	3.40%	4.30%	4.30%
Interest crediting rate for cash balance plans	1.50%	1.50%	1.50%
Weighted-average assumptions used to determine net periodic pension cost for years ended March 31:
Discount rate	1.40%	1.10%	0.60%
Rate of increase in compensation levels	4.30%	4.30%	4.00%
Expected long-term rate of return on plan assets	2.00%	2.00%	2.00%
Interest crediting rate for cash balance plans	1.50%	1.50%	1.50%
Overseas plans
Weighted-average assumptions used to determine benefit obligations at March 31:
Discount rate	3.80%	3.30%	3.30%
Rate of increase in compensation levels	2.30%	2.30%	2.30%
Interest crediting rate for cash balance plans
Weighted-average assumptions used to determine net periodic pension cost for years ended March 31:
Discount rate	3.30%	3.30%	1.70%
Rate of increase in compensation levels	2.30%	2.30%	2.20%
Expected long-term rate of return on plan assets	4.70%	4.60%	4.90%
Interest crediting rate for cash balance plans

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

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- Definition

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

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- Definition

Weighted-average interest crediting rate used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, cash balance and other defined benefit plans with promised interest crediting rate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(4)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

+ References

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- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-8

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

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- Definition

Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

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Weighted-average interest crediting rate used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, cash balance and other defined benefit plans with promised interest crediting rate.

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