Shareholder remuneration system and earnings per share - Schedule of diluted earnings per share (Details) - EUR (€) € / shares in Units, € in Millions	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025
Diluted earnings per share [abstract]
Profit attributable to the Parent (EUR million)	€ 8,973	€ 6,833
Remuneration of contingently convertible preferred securities (CCPS) (EUR million)	(318)	(310)
Net profit for the year	8,655	6,523
Profit or Loss from discontinued operations (non controlling interest net) (EUR million)	1,895	454
Profit or Loss from continuing operations (CCPS net) (EUR million)	€ 6,760	€ 6,069
Weighted average number of shares outstanding (in shares)	14,458,003,078	14,995,834,683
Dilutive effect of options/receipt of shares (in shares)	82,062,704	81,043,722
Adjusted number of shares (in shares)	14,540,065,782	15,076,878,405
Diluted earnings per share (in euro per share)	€ 0.60	€ 0.43
Diluted earnings per share from discontinued operations (in euro per share)	0.13	0.03
Diluted earnings per share from continuing operations (in euro per share)	€ 0.47	€ 0.40

The weighted average number of ordinary shares outstanding plus the weighted average number of ordinary shares that would be issued on the conversion of all the dilutive potential ordinary shares into ordinary shares. [Refer: Ordinary shares [member]; Weighted average [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 33
-IssueDate 2025-01-01
-Paragraph 70
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=33&code=ifrs-tx-2025-en-r&anchor=para_70_b&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_AdjustedWeightedAverageShares
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of profit (loss) attributable to ordinary equity holders of the parent entity (the numerator), divided by the weighted average number of ordinary shares outstanding during the period (the denominator), both adjusted for the effects of all dilutive potential ordinary shares. [Refer: Ordinary shares [member]; Weighted average [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 33
-IssueDate 2025-01-01
-Paragraph 66
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=33&code=ifrs-tx-2025-en-r&anchor=para_66&doctype=Standard
-URIDate 2025-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 33
-IssueDate 2025-01-01
-Paragraph 67
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=33&code=ifrs-tx-2025-en-r&anchor=para_67&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_DilutedEarningsLossPerShare
Namespace Prefix:	ifrs-full_
Data Type:	dtr-2022:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Diluted earnings (loss) per share from continuing operations. [Refer: Continuing operations, unless line item indicates otherwise [member]; Diluted earnings (loss) per share]

+ References

+ Details

Name:	ifrs-full_DilutedEarningsLossPerShareFromContinuingOperations
Namespace Prefix:	ifrs-full_
Data Type:	dtr-2022:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Diluted earnings (loss) per share from discontinued operations. [Refer: Diluted earnings (loss) per share; Discontinued operations [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 33
-IssueDate 2025-01-01
-Paragraph 68
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=33&code=ifrs-tx-2025-en-r&anchor=para_68&doctype=Standard
-URIDate 2025-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 33
-IssueDate 2025-01-01
-Paragraph 67
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=33&code=ifrs-tx-2025-en-r&anchor=para_67&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_DilutedEarningsLossPerShareFromDiscontinuedOperations
Namespace Prefix:	ifrs-full_
Data Type:	dtr-2022:perShareItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	ifrs-full_DilutedEarningsPerShareAbstract
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The profit (loss) attributable to ordinary equity holders of the parent entity. [Refer: Profit (loss)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 33
-IssueDate 2025-01-01
-Paragraph 70
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=33&code=ifrs-tx-2025-en-r&anchor=para_70_a&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_ProfitLossAttributableToOrdinaryEquityHoldersOfParentEntity
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The profit (loss) from continuing and discontinued operations attributable to owners of the parent. [Refer: Profit (loss)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2027-01-01
-Name IAS
-Number 1
-IssueDate 2025-01-01
-Paragraph 81B
-Subparagraph a
-Clause ii
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2025-en-b&anchor=para_81B_a_ii&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_ProfitLossAttributableToOwnersOfParent
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The profit (loss) from continuing operations attributable to ordinary equity holders of the parent entity, adjusted for the effects of all dilutive potential ordinary shares. [Refer: Profit (loss) from continuing operations]

+ References

+ Details

Name:	ifrs-full_ProfitLossFromContinuingOperationsAttributableToOrdinaryEquityHoldersOfParentEntityIncludingDilutiveEffects
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

+ Details

Name:	ifrs-full_ProfitLossFromDiscontinuedOperationsAttributableToOrdinaryEquityHoldersOfParentEntityIncludingDilutiveEffects
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The number of ordinary shares outstanding at the beginning of the period, adjusted by the number of ordinary shares bought back or issued during the period multiplied by a time-weighting factor.

+ References

+ Details

Name:	ifrs-full_WeightedAverageShares
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Adjustment To Profit (Loss) For Remuneration Of Contingently Convertible Preferred Securities

+ References

No definition available.

+ Details

Name:	san_AdjustmentToProfitLossForRemunerationOfContingentlyConvertiblePreferredSecurities
Namespace Prefix:	san_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The number of dilutive potential ordinary shares that relate to the assumed exercise of the entity's share options and the effect of share rights.

+ References

No definition available.

+ Details

Name:	san_DilutiveEffectOfShareOptionsAndShareRightsOnNumberOfOrdinaryShares
Namespace Prefix:	san_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration