Segment Information - Net sales by region (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure of geographical areas [line items]
Net sales to third parties	$ 6,763	$ 7,362	$ 7,149
Percentage of entity's revenue	100.00%	100.00%	100.00%
Total of selected non-current asset	$ 21,785	$ 22,573
Percentage of entity's non-current asset	100.00%	100.00%
Foreign countries [member] \| United States [member]
Disclosure of geographical areas [line items]
Net sales to third parties	$ 2,975	$ 3,055	$ 2,942
Percentage of entity's revenue	44.00%	41.00%	41.00%
Total of selected non-current asset	$ 10,309	$ 10,559
Percentage of entity's non-current asset	47.00%	47.00%
Foreign countries [member] \| Japan [member]
Disclosure of geographical areas [line items]
Net sales to third parties	$ 650	$ 656	$ 593
Percentage of entity's revenue	10.00%	9.00%	8.00%
Total of selected non-current asset	$ 63	$ 66
Percentage of entity's non-current asset	0.00%	0.00%
Foreign countries [member] \| China [member]
Disclosure of geographical areas [line items]
Net sales to third parties	$ 383	$ 377	$ 341
Percentage of entity's revenue	6.00%	5.00%	5.00%
Total of selected non-current asset	$ 16	$ 18
Percentage of entity's non-current asset	0.00%	0.00%
Foreign countries [member] \| Other [member]
Disclosure of geographical areas [line items]
Net sales to third parties	$ 2,700	$ 3,218	$ 3,216
Percentage of entity's revenue	40.00%	44.00%	45.00%
Total of selected non-current asset	$ 1,660	$ 1,444
Percentage of entity's non-current asset	8.00%	6.00%
International [member]
Disclosure of geographical areas [line items]
Net sales to third parties	$ 3,788	$ 4,307	$ 4,207
Percentage of entity's revenue	56.00%	59.00%	59.00%
Total of selected non-current asset	$ 11,476	$ 12,014
Percentage of entity's non-current asset	53.00%	53.00%
Country of domicile [member] \| Switzerland [member]
Disclosure of geographical areas [line items]
Net sales to third parties	$ 55	$ 56	$ 57
Percentage of entity's revenue	1.00%	1.00%	1.00%
Total of selected non-current asset	$ 9,737	$ 10,486
Percentage of entity's non-current asset	45.00%	46.00%

Non-current Assets Including Property, Plant & Equipment, Right Of Use Assets, Goodwill And Other Intangible Assets

No definition available.

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Namespace Prefix:	alc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of selected non-current assets

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of the entity's revenue. [Refer: Revenue]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IFRS
-Number 8
-IssueDate 2020-01-01
-Paragraph 34
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2020-en-r&anchor=para_34&doctype=Standard
-URIDate 2020-01-01

+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of revenue from contracts with customers. A customer is a party that has contracted with an entity to obtain goods or services that are an output of the entity’s ordinary activities in exchange for consideration.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 15
-IssueDate 2020-01-01
-Paragraph 113
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=15&code=ifrs-tx-2020-en-r&anchor=para_113_a&doctype=Standard
-URIDate 2020-01-01

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 15
-IssueDate 2020-01-01
-Paragraph 114
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=15&code=ifrs-tx-2020-en-r&anchor=para_114&doctype=Standard
-URIDate 2020-01-01

+ Details

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

- Details

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Namespace Prefix:
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- Details

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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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