Derivative financial instruments and hedge accounting - Additional Information (Details) - EUR (€) € in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivative financial instruments and hedge accounting
Bonds	€ 19,172	€ 20,094
Fair value hedges \| USD
Derivative financial instruments and hedge accounting
Exchange rate risk deriving from securities	€ 1,902
Hedging instrument	21
Bonds	€ 1,844

The nominal amount of a hedging instrument. [Refer: Hedging instruments [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2019-01-01
-Paragraph 23B
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_23B_a&doctype=Standard
-URIDate 2019-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2019-01-01
-Paragraph 24A
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24A_d&doctype=Standard
-URIDate 2019-03-27

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