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Financial instruments - Narrative (Details) - CAD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disclosure of detailed information about financial instruments [line items] |  |  |
Gain (loss) | $ 32,269,000 | $ (81,081,000) |
Cash and cash equivalents | 1,062,431,000 | 711,528,000 | $ 591,620,000
Short-term investments | 0 | $ 391,025,000 |
Pledged cash as security | $ 195,729,000 |  |
Bottom of range [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Quoted market yields | 1.70% | 1.90% |
Top of range [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Quoted market yields | 1.80% | 2.20% |
Interest rate swap contracts [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Gain (loss) | $ 2,068,000 | $ 2,032,000 |
Credit risk [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Cash and cash equivalents | 1,062,431,000 | 711,528,000 |
Short-term investments | $ 0 | $ 391,025,000 |
Interest rate risk [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Proportion of outstanding debt that carries fixed rate | 85.00% | 67.00% |
Interest rate risk [member] | Interest rate swap contracts [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Percentage increase in interest rate | 1.00% |  |
Gain (loss) | $ 1,524,000 |  |
Fair value of Cameco's interest rate swap assets | 2,313,000 | $ 856,000 |
Interest rate risk [member] | Interest rate swap contracts [member] | Series E senior unsecured debenture [Member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Notional amount | $ 150,000,000 |  |
Interest rate risk [member] | Interest rate swap contracts [member] | Series E senior unsecured debenture [Member] | Floating interest rate [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest rate basis | the three-month Canada Dealer Offered Rate |  |
Margin rate | 1.20% |  |
Interest rate risk [member] | Interest rate swap contracts [member] | Series E senior unsecured debenture [Member] | Fixed interest rate [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest rate | 3.75% |  |

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- Definition The adjustment to the basis (reference rate) used for calculation of the interest rate on borrowings. [Refer: Borrowings] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 7 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_7&doctype=Standard -URIDate 2019-03-27 + Details
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