Remuneration and other benefits paid to the Bank's directors and senior managers (Details) € in Thousands	6 Months Ended
Jun. 30, 2019 EUR (€) employee item	Jun. 30, 2018 EUR (€) employee item
Remuneration of key personnel
Number of persons \| item	202,398	201,884
Bank's Directors
Remuneration of key personnel
Fixed salary	€ 3,459	€ 3,759
Directors' fees	579	488
Annual emoluments	1,853	1,785
Other remuneration	3,354	691
Total remuneration	9,245	6,723
Contributions to plan	1,001	1,341
Pension rights	77,153	75,804
Contribution to insurance policies	1,069	862
ELEMENTS NOT USED AFTER THIS POINT IN LR
Sub-total from executive functions	9,245	6,723
Former directors of the bank
Remuneration of key personnel
Pension rights	68,201	79,465
Current senior managers
Remuneration of key personnel
Contributions to plan	3,190	2,739
Pension rights	€ 71,237	€ 62,872
Number of persons \| employee	18	18
ELEMENTS NOT USED AFTER THIS POINT IN LR
Sub-total from executive functions	€ 17,690	€ 16,972
Retired senior managers
Remuneration of key personnel
Total remuneration	96	10
Pension rights	166,960	173,819
Loan commitments \| Bank's Directors
Remuneration of key personnel
Total direct risk exposure	€ 121	€ 84

The decrease (increase) in net defined benefit liability (asset) resulting from contributions to a defined benefit plan by the employer. [Refer: Net defined benefit liability (asset); Defined benefit plans [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2018-01-01
-Paragraph 141
-Subparagraph f
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_141_f&doctype=Standard
-URIDate 2018-03-16

+ Details

Name:	ifrs-full_ContributionsToPlanByEmployerNetDefinedBenefitLiabilityAsset
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of exposure to loss resulting from credit risk. [Refer: Credit risk [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Note Expiry date 2021-01-01
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph IG24
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_IG24_a&doctype=Implementation%20Guidance&book=b
-URIDate 2018-03-16

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Note Expiry date 2021-01-01
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph IG25
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_IG25_b&doctype=Implementation%20Guidance&book=b
-URIDate 2018-03-16

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Note Expiry date 2021-01-01
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph 36
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_36_c&doctype=Standard&book=b
-URIDate 2018-03-16

+ Details

Name:	ifrs-full_CreditExposure
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The present value, without deducting any plan assets, of expected future payments required to settle the obligation resulting from employee service in the current and prior periods. [Refer: Plan assets, at fair value]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2018-01-01
-Paragraph 57
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_57_a&doctype=Standard
-URIDate 2018-03-16

+ Details

Name:	ifrs-full_DefinedBenefitObligationAtPresentValue
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of compensation to key management personnel in the form of short-term employee benefits. [Refer: Key management personnel of entity or parent [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 24
-IssueDate 2018-01-01
-Paragraph 17
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=24&date=2018-03-01&anchor=para_17_a&doctype=Standard
-URIDate 2018-03-16

+ Details

Name:	ifrs-full_KeyManagementPersonnelCompensationShorttermEmployeeBenefits
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The number of personnel employed by the entity at a date.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_112_c&doctype=Standard
-URIDate 2018-03-16

+ Details

Name:	ifrs-full_NumberOfEmployees
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

Name:	san_DirectorRemunerationAbstract
Namespace Prefix:	san_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

n/a

+ References

No definition available.

+ Details

Name:	san_ElementsNotUsedAbstract
Namespace Prefix:	san_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of compensation paid to key management personnel for attendance fees.

+ References

No definition available.

+ Details

Name:	san_KeyManagementPersonnelCompensationAttendanceFees
Namespace Prefix:	san_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of annual emolument compensation to key management personnel.

+ References

No definition available.

+ Details

Name:	san_KeyManagementPersonnelCompensationEmoluments
Namespace Prefix:	san_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of key management compensation during the period attributable to executive functions.

+ References

No definition available.

+ Details

Name:	san_KeyManagementPersonnelCompensationFromExecutiveFunctions
Namespace Prefix:	san_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of compensation to key management personnel in the form of other short-term employee benefits.

+ References

No definition available.

+ Details

Name:	san_KeyManagementPersonnelCompensationOtherShortTermEmployeeBenefits
Namespace Prefix:	san_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of fixed compensation to key management personnel in the form of short-term employee benefits.

+ References

No definition available.

+ Details

Name:	san_KeyManagementPersonnelCompensationShortTermEmployeeBenefitsFixed
Namespace Prefix:	san_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of post-employment benefit expense relating to contribution to insurance policies.

+ References

No definition available.

+ Details

Name:	san_PostEmploymentBenefitExpenseContributionToInsurancePolicies
Namespace Prefix:	san_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	ifrs-full_CategoriesOfRelatedPartiesAxis=san_BanksDirectorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_CategoriesOfRelatedPartiesAxis=san_FormerDirectorsOfBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_CategoriesOfRelatedPartiesAxis=san_SeniorManagementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_CategoriesOfRelatedPartiesAxis=san_SeniorManagementRetiredMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfFinancialInstrumentsAxis=ifrs-full_LoanCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: