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Pension and other post-retirement benefits - Narrative (Details) - CAD ($) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Disclosure of benefit plans [line items] |  |
Description of Retirement benefit plan | Under the supplemental executive pension plan (SEPP), Cameco provides a lump sum benefit equal to the present value of a lifetime pension benefit based on the executive’s length of service and final average earnings. |
Description of Retirement benefits promised to participants | The plan provides for unreduced benefits to be paid at the normal retirement age of 65, however unreduced benefits could be paid if the executive was at least 60 years of age and had 20 years of service at retirement. This program provides for a benefit determined by a formula based on earnings and service, reduced by the benefits payable under the registered base plan. |
2021 [Member] |  |
Disclosure of benefit plans [line items] |  |
Contributions and fees payable | $ 1,785,000 |
Pension plans [member] |  |
Disclosure of benefit plans [line items] |  |
Description of the refundable tax account held by CRA | equal to half of the sum of the realized investment income plus employer contributions less half of the benefits paid by the plan |
Weighted Average Length Of Time Of Defined Benefit Obligation | 20 years 6 months | 20 years
Pension plans [member] | Increase of one year in the expected lifetime [member] |  |
Disclosure of benefit plans [line items] |  |
Change in defined benefit obligations due to increase in actuarial assumption | $ 2,030,000 |
Other Benefit Plans [Member] |  |
Disclosure of benefit plans [line items] |  |
Weighted Average Length Of Time Of Defined Benefit Obligation | 14 years 2 months 12 days | 15 years 2 months 12 days

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- Definition The description of the retirement benefits promised to participants in retirement benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 26 -IssueDate 2020-01-01 -Paragraph 36 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=26&code=ifrs-tx-2020-en-r&anchor=para_36_e&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The estimate of the expected contributions to be made to a defined benefit plan for the next annual reporting period. [Refer: Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 147 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_147_b&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 148 -Subparagraph d -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_148_d_iii&doctype=Standard -URIDate 2020-01-01 + Details
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