Capital and funding - Disclosure of Fair Value Reserve (Details) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022
Equity and liabilities [abstract]
Fair value reserve at beginning of period	€ 329	€ 502
Gains/(losses) on equity instruments	(27)	45
Gains/(losses) on cash flow hedges	(27)	(92)
Hedging gains/(losses) transferred to non-financial assets	117	(126)
Fair value reserve at end of period	€ 392	€ 329

A component of equity representing the reserve of gains and losses on financial assets measured at fair value through other comprehensive income. [Refer: Financial assets measured at fair value through other comprehensive income; Other comprehensive income]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2023-01-01
-Paragraph 78
-Subparagraph e
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2023-en-r&anchor=para_78_e&doctype=Standard
-URIDate 2023-03-23

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