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Segmented information - Narrative (Details) - CAD ($) | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Disclosure Of Operating Segments [Line Items] |  |
Segment information | Cameco has two reportable segments: uranium and fuel services. Cameco's reportable segments are strategic business units with different products, processes and marketing strategies. |
Uranium [Member] |  |
Disclosure Of Operating Segments [Line Items] |  |
Care and maintenance | $ 195,972,000 | $ 153,924,000
Uranium [Member] | Cigar Lake [Member] |  |
Disclosure Of Operating Segments [Line Items] |  |
COVID-19 care and maintenance | 45,988,000 |
Fuel Service [Member] |  |
Disclosure Of Operating Segments [Line Items] |  |
COVID-19 care and maintenance | $ 8,992,000 |

X
- Definition Costs directly expensed to cost of sales that are incurred to maintain production facilities during suspension of production. + References No definition available. + Details
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Namespace Prefix: | ccj_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Costs directly expensed to cost of sales that are incurred to maintain production facilities during a COVID-19 suspension of production. + References No definition available. + Details
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Namespace Prefix: | ccj_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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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X
- Definition The description of the factors used to identify the entity's reportable segments, including the basis of organisation (for example, whether management has chosen to organise the entity around differences in products and services, geographical areas, regulatory environments or a combination of factors and whether operating segments have been aggregated). [Refer: Geographical areas [member]; Operating segments [member]; Products and services [member]; Reportable segments [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2020-01-01 -Paragraph 22 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2020-en-r&anchor=para_22_a&doctype=Standard -URIDate 2020-01-01 + Details
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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |