Segment information - Additional Information (Details)	Dec. 31, 2020 EUR (€) segment	Dec. 31, 2019 EUR (€)	Dec. 31, 2018 EUR (€)
Disclosure of operating segments [line items]
Number of reportable segment \| segment	2
Property and equipment	€ 313,000,000	€ 291,000,000
Luxembourg
Disclosure of operating segments [line items]
Property and equipment	€ 0	€ 0	€ 0

The amount of tangible assets that: (a) are held for use in the production or supply of goods or services, for rental to others, or for administrative purposes; and (b) are expected to be used during more than one period.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 16
-IssueDate 2020-01-01
-Paragraph 73
-Subparagraph e
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2020-en-r&anchor=para_73_e&doctype=Standard
-URIDate 2020-01-01

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2020-01-01
-Paragraph 54
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_54_a&doctype=Standard
-URIDate 2020-01-01

Name:	ifrs-full_PropertyPlantAndEquipment
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant