FINANCIAL INSTRUMENTS - Marketable Securities (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financial Instruments [Abstract]
Proceeds from sale of marketable securities	$ 7.4	$ 0.0	$ 7.7	$ 0.1
Acquisition date fair value of marketable securities sold	(2.3)	0.0	(2.4)	(2.1)
Gain (loss) on sale of marketable securities recorded in OCI	$ 5.1	$ 0.0	$ 5.3	$ (2.0)

Financial Instruments [Abstract]

No definition available.

Name:	iag_FinancialInstrumentsAbstract
Namespace Prefix:	iag_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The increase (decrease) in the aggregate difference between the fair value at initial recognition and the transaction price of financial instruments yet to be recognised in profit or loss resulting from amounts recognised in profit or loss. [Refer: Aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss; Financial instruments, class [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IFRS
-Number 7
-IssueDate 2016-01-13
-Paragraph IG14
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_IG14&doctype=Implementation%20Guidance
-URIDate 2016-03-31

+ Details

Name:	ifrs-full_IncreaseDecreaseThroughAmountsRecognisedInProfitOrLossAggregateDifferenceBetweenFairValueAtInitialRecognitionAndAmountDeterminedUsingValuationTechniqueYetToBeRecognised
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from the disposal or maturity of available-for-sale financial assets. [Refer: Financial assets available-for-sale]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 7
-IssueDate 2016-01-13
-Paragraph 16
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2016-03-30&anchor=para_16&doctype=Standard
-URIDate 2016-03-31

+ Details

Name:	ifrs-full_ProceedsFromDisposalOrMaturityOfAvailableforsaleFinancialAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of reclassification adjustments related to available-for-sale financial assets, before tax. Reclassification adjustments are amounts reclassified to profit (loss) in the current period that were recognised in other comprehensive income in the current or previous periods. [Refer: Financial assets available-for-sale; Other comprehensive income]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2018-01-01
-Name IFRS
-Number 7
-IssueDate 2016-01-13
-Paragraph 20
-Subparagraph a
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_20_a_ii&doctype=Standard
-URIDate 2016-03-31

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2018-01-01
-Name IAS
-Number 1
-IssueDate 2016-01-13
-Paragraph 92
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_92&doctype=Standard
-URIDate 2016-03-31

+ Details

Name:	ifrs-full_ReclassificationAdjustmentsOnAvailableforsaleFinancialAssetsBeforeTax
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration