Income Taxes (Details) - USD ($) $ in Millions		9 Months Ended
Feb. 18, 2014	Sep. 30, 2015
Income Tax Examination [Line Items]
Period for unrecognized tax benefits to decrease		12 months
Decrease in unrecognized tax benefits related to intercompany transactions		$ 68
Internal Revenue Service (IRS) [Member] \| Tax Year 2006 [Member]
Income Tax Examination [Line Items]
IRS Notice of Deficiency tax assessment	$ 70

Maximum Period for unrecognized tax benefits.

No definition available.

Name:	itw_MaximumPeriodForUnrecognizedTaxBenefits
Namespace Prefix:	itw_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (d)(3)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319

+ Details

Name:	us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Estimated amount of loss resulting from an adverse tax position.

+ References

+ Details

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

- Details

Name:	us-gaap_IncomeTaxAuthorityNameAxis=us-gaap_InternalRevenueServiceIRSMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TaxPeriodAxis=us-gaap_TaxYear2006Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: