Retirement Benefits - Detailed Information for the Defined Benefit Plans (Detail) - JPY (¥) ¥ in Millions	Mar. 31, 2026	Mar. 31, 2025
Disclosure of net defined benefit liability (asset) [Line Items]
Fair value of plan assets	¥ 2,034,686	¥ 1,804,994
Net retirement benefit assets (liabilities)	593,472	478,072
Of which retirement benefit liabilities included in "Other liabilities"	(35,829)	(34,996)
Of which retirement benefit assets included in "Other assets"	629,301	513,068
Present value of unfunded obligations [member]
Disclosure of net defined benefit liability (asset) [Line Items]
Present value of obligations	(24,054)	(25,972)
Present value of funded obligations [member]
Disclosure of net defined benefit liability (asset) [Line Items]
Present value of obligations	(757,430)	(857,083)
Net retirement benefit assets (liabilities) before the asset ceiling [member]
Disclosure of net defined benefit liability (asset) [Line Items]
Net retirement benefit assets (liabilities)	1,253,202	921,939
Effect of asset ceiling [member]
Disclosure of net defined benefit liability (asset) [Line Items]
Net retirement benefit assets (liabilities)	¥ 659,730	¥ 443,867

The present value, without deducting any plan assets, of expected future payments required to settle the obligation resulting from employee service in the current and prior periods. [Refer: Plan assets, at fair value]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2025-01-01
-Paragraph 57
-Subparagraph a
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-URIDate 2025-03-27

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

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No definition available.

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- Definition

The fair value of defined benefit plan assets. Plan assets comprise assets held by a long-term employee benefit fund and qualifying insurance policies. [Refer: At fair value [member]]

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- Definition

The amount of surplus in a defined benefit plan, adjusted for any effect of limiting a net defined benefit asset to the asset ceiling. [Refer: Defined benefit plans [domain]]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Note Expiry date 2027-01-01
-Name IAS
-Number 1
-IssueDate 2025-01-01
-Paragraph 55
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2025-en-b&anchor=para_55&doctype=Standard
-URIDate 2025-03-27

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The amount of deficit in a defined benefit plan. [Refer: Defined benefit plans [domain]]

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The fair value of any plan assets, less the present value of the defined benefit obligation. [Refer: Plan assets [member]]

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