Shareholder remuneration system and earnings per share - EPS Diluted (Details) - EUR (€) € / shares in Units, € in Millions	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019
Diluted earnings per share [abstract]
Profit attributable to the parent	€ (10,798)	€ 3,231
Remuneration of contingently convertible preference shares (CCP) (million euros)	(278)	(298)
Dilutive effect of changes in profit for the period arising from potential conversion of ordinary shares	0	0
Profit attributable to ordinary equity holders of parent including dilutive effects	(11,076)	2,933
Profit or Loss from discontinued operations (non-controlling interest net) (million euros)	0	0
Profit or Loss from continuing operations (net of non-controlling interests and CCP) (million euros)	€ (11,076)	€ 2,933
Weighted average number of shares outstanding (in shares)	16,598,649,355	16,231,374,256
Dilutive effect of options/rights on shares (in shares)	40,016,222	41,832,881
Adjusted number of shares (in shares)	16,638,665,577	16,273,207,137
Total diluted earnings (loss) per share (eur per share)	€ (0.67)	€ 0.18
Diluted earnings per share from discontinued operations (eur per share)	0	0
Diluted earnings per share from continuing operations (eur per share)	€ (0.67)	€ 0.18

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 2019-01-01
-Paragraph 70
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=33&code=ifrs-tx-2019-en-r&anchor=para_70_b&doctype=Standard
-URIDate 2019-03-27

+ 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 2019-01-01
-Paragraph 66
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=33&code=ifrs-tx-2019-en-r&anchor=para_66&doctype=Standard
-URIDate 2019-03-27

+ Details

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

- Definition

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

+ References

+ Details

Name:	ifrs-full_DilutedEarningsLossPerShareFromContinuingOperations
Namespace Prefix:	ifrs-full_
Data Type:	num: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 2019-01-01
-Paragraph 68
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=33&code=ifrs-tx-2019-en-r&anchor=para_68&doctype=Standard
-URIDate 2019-03-27

+ Details

Name:	ifrs-full_DilutedEarningsLossPerShareFromDiscontinuedOperations
Namespace Prefix:	ifrs-full_
Data Type:	num: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 increase (decrease) in equity resulting from the conversion of convertible instruments.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2019-01-01
-Paragraph 106
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_106_d&doctype=Standard
-URIDate 2019-03-27

+ Details

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

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 33
-IssueDate 2019-01-01
-Paragraph 70
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=33&code=ifrs-tx-2019-en-r&anchor=para_70_a&doctype=Standard
-URIDate 2019-03-27

+ Details

Name:	ifrs-full_ProfitLossAttributableToOrdinaryEquityHoldersOfParentEntityIncludingDilutiveEffects
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
-Name IAS
-Number 1
-IssueDate 2019-01-01
-Paragraph 81B
-Subparagraph a
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_81B_a_ii&doctype=Standard
-URIDate 2019-03-27

+ 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

- Definition

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

+ 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

Dilutive Effect Of Changes In Profit Resulting From Conversion Of Ordinary Shares

+ References

No definition available.

+ Details

Name:	san_DilutiveEffectOfChangesInProfitResultingFromConversionOfOrdinaryShares
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