BUSINESS COMBINATION - Narrative (Details) - USD ($) $ in Millions		3 Months Ended	6 Months Ended
Sep. 29, 2017	Jun. 30, 2017	Jun. 30, 2017
Business Acquisition [Line Items]
Pro-forma adjustment to increase share-based compensation		$ 11.6	$ 26.3
Pro-forma adjustment to increase amortization of intangibles		$ 11.5	$ 23.1
Angie's List
Business Acquisition [Line Items]
Percentage of interest acquired	100.00%
Purchase price	$ 781.4

Business Acquisition, Pro Forma Information, Adjustment To Increase (Decrease) Amortization Of Intangible Assets

No definition available.

Name:	iac_BusinessAcquisitionProFormaInformationAdjustmentToIncreaseDecreaseAmortizationOfIntangibleAssets
Namespace Prefix:	iac_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Business Acquisition, Pro Forma Information, Adjustment To Increase (Decrease) Share-Based Compensation

+ References

No definition available.

+ Details

Name:	iac_BusinessAcquisitionProFormaInformationAdjustmentToIncreaseDecreaseShareBasedCompensation
Namespace Prefix:	iac_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_BusinessAcquisitionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of voting equity interests acquired at the acquisition date in the business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=109124213&loc=d3e6613-128477

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=109124213&loc=d3e6578-128477

+ Details

Name:	us-gaap_BusinessCombinationConsiderationTransferred1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_BusinessAcquisitionAxis=iac_AngiesListMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: