Commitments, Guarantees, and Contingent Liabilities - Additional Information (Detail) - JPY (¥) ¥ in Millions	6 Months Ended	12 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Mar. 31, 2026
Commitments and Contingencies Disclosure [Line Items]
Commitments for purchase of equipment to be leased at cost	¥ 23,263		¥ 23,487
Payments for computer systems under non-cancelable contracts	6,320	¥ 4,646
Estimated construction costs	101,563		144,135
Total unused credit and capital amount available	485,774		475,677
Guarantee Obligations Maximum Exposure	1,247,722		1,247,252
Guarantee Obligations Current Carrying Value	20,326		19,713
Outstanding principal amount of loans transferred under Delegated Underwriting and Servicing program	2,958,789		2,996,771
Investments In Subsidaries Pledged	7,451		7,922
Allowance for off-balance sheet credit exposure	17,175		17,611
Provision for credit losses in the consolidated statements of income	(66)	¥ 2,336
Integrated Resort Development [Member]
Commitments and Contingencies Disclosure [Line Items]
Total unused credit and capital amount available	332,968		335,868
Secured Investments
Commitments and Contingencies Disclosure [Line Items]
Secured debt	387,420		383,753
Secured By Share
Commitments and Contingencies Disclosure [Line Items]
Investment in securities pledged for primarily collateral deposits	204,932		198,764
Secured debt	149,787		149,119
Corporate Loans
Commitments and Contingencies Disclosure [Line Items]
Guarantee Obligations Maximum Exposure	617,180		612,967
Guarantee Obligations Current Carrying Value	6,143		5,953
Performance Guarantee \| Corporate Loans
Commitments and Contingencies Disclosure [Line Items]
Guarantee Obligations Maximum Exposure	466,000		446,000
Guarantee Obligations Current Carrying Value	¥ 2,435		¥ 2,448

Commitments and Contingencies Disclosure [Line Items]

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Deposit liabilitites collateral issued financial instruments one.

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Amount of securities, mortgage loans, or other financial instruments pledged as collateral for deposits.

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The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

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Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

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The minimum amount the entity agreed to spend under the long-term purchase commitment.

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Amount of cash outflow reducing loss contingency liability.

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Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

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Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

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This is the principal amount outstanding for securitized loans only (across all types of loans).

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Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

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Carrying amount of collateralized debt obligations with maturities initially due after one year or beyond the operating cycle, if longer, excluding the current portion. Obligations include, but not limited to, mortgage loans, chattel loans, and other borrowings secured by assets.

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The floor amount as of the balance sheet date that the entity must expend to satisfy the terms of disclosed arrangements (excluding long-term commitments) in which the entity must commit resources to supply goods or services to one or more customers.

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