Deferred Income Tax - Amounts of Deductible Temporary Differences and Tax Losses Carried Forward by Expiration Date (Parenthetical) (Detail) - JPY (¥) ¥ in Millions	Mar. 31, 2026	Mar. 31, 2025
Disclosure of temporary difference, unused tax losses and unused tax credits [abstract]
Deductible temporary differences and tax losses carried forward for which deferred tax assets are recognized	¥ 12,581	¥ 304,322

Deductible temporary differences and tax losses carried forward for which deferred tax assets are recognized.

No definition available.

Name:	smfg_DeductibleTemporaryDifferencesAndTaxLossesCarriedForwardForWhichDeferredTaxAssetsAreRecognized
Namespace Prefix:	smfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant