Financial risk management - Summary of Gross Carrying Amount For Loans At Amortized Cost Based On Credit Ratings (Detail) - JPY (¥) ¥ in Millions	Mar. 31, 2025	Mar. 31, 2024
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	¥ 22,435,594	¥ 22,506,844
Banking Business in Financial Services Segment Normal [Member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	3,779,876	3,586,522
Banking Business in Financial Services Segment Normal [Member] \| 12-month expected credit losses [member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	3,779,029	3,585,897
Banking Business in Financial Services Segment Normal [Member] \| Lifetime expected credit losses [member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	847	625
Banking Business In Financial Services Segment Other Than Normal [Member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	5,145	4,805
Banking Business In Financial Services Segment Other Than Normal [Member] \| 12-month expected credit losses [member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	2,400	2,003
Banking Business In Financial Services Segment Other Than Normal [Member] \| Lifetime expected credit losses [member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	2,745	2,802
Housing Loan [Member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	3,763,747	3,575,093
Housing Loan [Member] \| Banking Business in Financial Services Segment Normal [Member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	3,758,693	3,570,389
Housing Loan [Member] \| Banking Business in Financial Services Segment Normal [Member] \| 12-month expected credit losses [member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	3,758,168	3,570,142
Housing Loan [Member] \| Banking Business in Financial Services Segment Normal [Member] \| Lifetime expected credit losses [member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	525	247
Housing Loan [Member] \| Banking Business In Financial Services Segment Other Than Normal [Member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	5,054	4,704
Housing Loan [Member] \| Banking Business In Financial Services Segment Other Than Normal [Member] \| 12-month expected credit losses [member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	2,393	1,998
Housing Loan [Member] \| Banking Business In Financial Services Segment Other Than Normal [Member] \| Lifetime expected credit losses [member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	2,661	2,706
Other Loan [Member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	21,274	16,234
Other Loan [Member] \| Banking Business in Financial Services Segment Normal [Member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	21,183	16,133
Other Loan [Member] \| Banking Business in Financial Services Segment Normal [Member] \| 12-month expected credit losses [member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	20,861	15,755
Other Loan [Member] \| Banking Business in Financial Services Segment Normal [Member] \| Lifetime expected credit losses [member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	322	378
Other Loan [Member] \| Banking Business In Financial Services Segment Other Than Normal [Member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	91	101
Other Loan [Member] \| Banking Business In Financial Services Segment Other Than Normal [Member] \| 12-month expected credit losses [member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	7	5
Other Loan [Member] \| Banking Business In Financial Services Segment Other Than Normal [Member] \| Lifetime expected credit losses [member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	84	96
Total Loans [Member]
Disclosure of credit risk exposure [line items]
Exposure to credit risk of loans	¥ 3,785,021	¥ 3,591,327

- Definition

The amount of assets that are: (a) cash; (b) an equity instrument of another entity; (c) a contractual right: (i) to receive cash or another financial asset from another entity; or (ii) to exchange financial assets or financial liabilities with another entity under conditions that are potentially favourable to the entity; or (d) a contract that will, or may be, settled in the entity’s own equity instruments and is: (i) a non-derivative for which the entity is, or may be, obliged to receive a variable number of the entity’s own equity instruments; or (ii) a derivative that will, or may be, settled other than by the exchange of a fixed amount of cash or another financial asset for a fixed number of the entity’s own equity instruments. For this purpose the entity’s own equity instruments do not include puttable financial instruments classified as equity instruments in accordance with paragraphs 16A-16B of IAS 32, instruments that impose on the entity an obligation to deliver to another party a pro rata share of the net assets of the entity only on liquidation and are classified as equity instruments in accordance with paragraphs 16C-16D of IAS 32, or instruments that are contracts for the future receipt or delivery of the entity’s own equity instruments. [Refer: Classes of financial instruments [domain]; Financial liabilities]

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