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Segmented information - Major customers (Details) - CAD ($) | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Disclosure of major customers [line items] |  |
Revenue | $ 1,862,925,000 | $ 2,091,661,000
One customer of Cameco's uranium and fuel services segments [member] |  |
Disclosure of major customers [line items] |  |
Revenue | $ 422,740,000 | $ 204,594,000
Percentage of entity's revenue | 24.00% | 10.00%
Information about major customers | As customers are relatively few in number, accounts receivable from any individual customer may periodically exceed 10% of accounts receivable depending on delivery schedule. |

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- Definition Expiry date 2020-01-01: The income arising in the course of an entity's ordinary activities. Income is increases in economic benefits during the accounting period in the form of inflows or enhancements of assets or decreases of liabilities that result in an increase in equity, other than those relating to contributions from equity participants. Effective 2020-01-01: The income arising in the course of an entity's ordinary activities. Income is increases in assets, or decreases in liabilities, that result in increases in equity, other than those relating to contributions from holders of equity claims. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2019-01-01 -Paragraph 28 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2019-en-r&anchor=para_28_a&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2019-01-01 -Paragraph 23 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2019-en-r&anchor=para_23_a&doctype=Standard -URIDate 2019-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2019-01-01 -Paragraph 32 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2019-en-r&anchor=para_32&doctype=Standard -URIDate 2019-03-27 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2019-01-01 -Paragraph 33 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2019-en-r&anchor=para_33_a&doctype=Standard -URIDate 2019-03-27 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2019-01-01 -Paragraph 34 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2019-en-r&anchor=para_34&doctype=Standard -URIDate 2019-03-27 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 82 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_82_a&doctype=Standard -URIDate 2019-03-27 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 103 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_103&doctype=Standard -URIDate 2019-03-27 Reference 8: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 102 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_102&doctype=Standard -URIDate 2019-03-27 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 5 -IssueDate 2019-01-01 -Paragraph 33 -Subparagraph b -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=5&code=ifrs-tx-2019-en-r&anchor=para_33_b_i&doctype=Standard -URIDate 2019-03-27 Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2019-01-01 -Paragraph B12 -Subparagraph b -Clause v -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2019-en-r&anchor=para_B12_b_v&doctype=Appendix&subtype=B -URIDate 2019-03-27 Reference 11: http://www.xbrl.org/2003/role/exampleRef -Name IFRS -Number 12 -IssueDate 2019-01-01 -Paragraph B10 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2019-en-r&anchor=para_B10_b&doctype=Appendix&subtype=B -URIDate 2019-03-27 + Details
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