Introduction, Presentation and Other Information - Capital Mgmt, Other information (Details)	Mar. 29, 2017
Intro, basis of presentation of the consolidated financial statements and other information
UK Referendum negotiation period	2 years

The period of time over which negotiations are conducted regarding the withdrawal of the United Kingdom from the European Union.

No definition available.

Name:	san_UkReferendumNegotiationPeriod
Namespace Prefix:	san_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration