Related parties transactions - Schedule of related parties transactions (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Apr. 08, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party [Abstract]
Sales to former parent		$ 0	$ 0	$ 4
Contract manufacturing revenues from former parent	$ 47		47	0
Purchases from former parent	$ 19		$ 19	$ 4

Related Party [Abstract]

No definition available.

Name:	alc_RelatedPartyAbstract
Namespace Prefix:	alc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue From Contract Manufacturing, Related Party Transactions

+ References

No definition available.

+ Details

Name:	alc_RevenueFromContractManufacturingRelatedPartyTransactions
Namespace Prefix:	alc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of goods purchased by the entity in related party transactions. [Refer: Related parties [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 24
-IssueDate 2020-01-01
-Paragraph 21
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=24&code=ifrs-tx-2020-en-r&anchor=para_21_a&doctype=Standard
-URIDate 2020-01-01

+ Details

Name:	ifrs-full_PurchasesOfGoodsRelatedPartyTransactions
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of revenue arising from the sale of goods in related party transactions. [Refer: Revenue; Related parties [member]]

+ References

+ Details

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