Derivative financial instruments and hedge accounting - Underlying asset or liability by type of risk hedged under cash flow hedge (Details) - Cash flow hedge derivatives - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Cash flow hedges [abstract]
Change of underlying asset used for calculation of hedging ineffectiveness	€ 1,444	€ (389)
CFH reserve	(656)	(13)
Reclassification adjustments on cash flow hedges, before tax	(739)	642
Commodity price risk \| Planned sales
Cash flow hedges [abstract]
Change of underlying asset used for calculation of hedging ineffectiveness	1,444	(389)
CFH reserve	(656)	(13)
Reclassification adjustments on cash flow hedges, before tax	€ (739)	€ 642

The gain (loss) on the change in fair value of the hedged item used as a basis for recognising hedge ineffectiveness. Hedge ineffectiveness is the extent to which the changes in the fair value or the cash flows of the hedging instrument are greater or less than those on the hedged item.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2019-01-01
-Paragraph 24B
-Subparagraph a
-Clause iv
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24B_a_iv&doctype=Standard
-URIDate 2019-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2019-01-01
-Paragraph 24B
-Subparagraph b
-Clause i
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24B_b_i&doctype=Standard
-URIDate 2019-03-27

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