Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19,20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebtCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebtNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=itw_OtherBorrowingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=itw_A1.95NotesDueMarch12019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_UnsecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=itw_A6.25NotesDueApril12019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=itw_A4.88notesduethruDecember312020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=itw_A3.375notesdueSeptember152021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=itw_A1.75EuroNotesDueMay202022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=itw_A1.25EuroNotesDueMay222023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=itw_A3.5PercentNotesDueMarch12024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=itw_A2.65NotesDueNovember152026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=itw_A2.125EuronotesdueMay223030Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=itw_A3.0EuroNotesDueMay192034Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=itw_A4.875notesdueSeptember152041Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=itw_A3.9notesdueSeptember12042Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Long-term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Nov. 30, 2016	May 31, 2015	May 31, 2014	Feb. 28, 2014	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2009	Dec. 31, 2005
Debt Instrument [Line Items]
Carrying Value	$ 7,379	$ 7,479
Fair Value	7,665	8,052
Less: Current maturities of long-term debt	(1,350)	(1)
Total long-term debt	6,029	7,478
Other borrowings
Debt Instrument [Line Items]
Carrying Value	4	4
Fair Value	$ 4	4
1.95% notes due March 1, 2019
Debt Instrument [Line Items]
Interest rate, stated percentage	1.95%
1.95% notes due March 1, 2019 \| Unsecured debt
Debt Instrument [Line Items]
Interest rate, stated percentage	1.95%					1.95%
Effective interest rate	1.98%
Carrying Value	$ 650	649
Fair Value	$ 649	649
6.25% notes due April 1, 2019
Debt Instrument [Line Items]
Interest rate, stated percentage	6.25%
6.25% notes due April 1, 2019 \| Unsecured debt
Debt Instrument [Line Items]
Interest rate, stated percentage	6.25%								6.25%
Effective interest rate	6.25%
Carrying Value	$ 700	699
Fair Value	$ 706	736
4.88% notes due thru December 31, 2020 \| Unsecured debt
Debt Instrument [Line Items]
Interest rate, stated percentage	4.88%									4.88%
Effective interest rate	4.96%
Carrying Value	$ 4	4
Fair Value	$ 4	4
3.375% notes due September 15, 2021 \| Unsecured debt
Debt Instrument [Line Items]
Interest rate, stated percentage	3.375%							3.375%
Effective interest rate	3.43%
Carrying Value	$ 349	348
Fair Value	$ 354	361
1.75% Euro notes due May 20, 2022 \| Unsecured debt
Debt Instrument [Line Items]
Interest rate, stated percentage	1.75%				1.75%
Effective interest rate	1.86%
Carrying Value	$ 570	595
Fair Value	$ 603	638
1.25% Euro notes due May 22, 2023 \| Unsecured debt
Debt Instrument [Line Items]
Interest rate, stated percentage	1.25%			1.25%
Effective interest rate	1.35%
Carrying Value	$ 569	595
Fair Value	$ 596	624
3.50% notes due March 1, 2024 \| Unsecured debt
Debt Instrument [Line Items]
Interest rate, stated percentage	3.50%					3.50%
Effective interest rate	3.54%
Carrying Value	$ 696	696
Fair Value	$ 712	734
2.65% notes due November 15, 2026 \| Unsecured debt
Debt Instrument [Line Items]
Interest rate, stated percentage	2.65%		2.65%
Effective interest rate	2.69%
Carrying Value	$ 993	992
Fair Value	$ 933	980
2.125% Euro notes due May 22, 2030 \| Unsecured debt
Debt Instrument [Line Items]
Interest rate, stated percentage	2.125%			2.125%
Effective interest rate	2.18%
Carrying Value	$ 567	594
Fair Value	$ 620	646
3.0% Euro notes due May 19, 2034 \| Unsecured debt
Debt Instrument [Line Items]
Interest rate, stated percentage	3.00%				3.00%
Effective interest rate	3.13%
Carrying Value	$ 560	586
Fair Value	$ 678	702
4.875% notes due September 15, 2041 \| Unsecured debt
Debt Instrument [Line Items]
Interest rate, stated percentage	4.875%							4.875%
Effective interest rate	4.97%
Carrying Value	$ 636	636
Fair Value	$ 719	791
3.9% notes due September 1, 2042 \| Unsecured debt
Debt Instrument [Line Items]
Interest rate, stated percentage	3.90%						3.90%
Effective interest rate	3.96%
Carrying Value	$ 1,081	1,081
Fair Value	$ 1,087	$ 1,183