Employee Benefit Plans (Changes In Fair Value Of U.S. Pension Plans' Level 3 Assets) (Details) - Pension Plan - USD ($) $ in Millions	12 Months Ended
Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Change in fair value of plan assets:
Fair value of plan assets, beginning of year	$ 455.5	$ 478.5
Unrealized gains	(147.7)	(179.6)
Foreign currency exchange	(2.5)	17.9
Fair value of plan assets, end of year	465.1	455.5	$ 478.5
Non - U.S. Plan
Change in fair value of plan assets:
Fair value of plan assets, beginning of year	158.6
Fair value of plan assets, end of year	161.1	158.6
Non - U.S. Plan \| Level 3
Change in fair value of plan assets:
Fair value of plan assets, beginning of year	31.8	28.2	30.5
Unrealized gains	1.2	2.7	1.3
Foreign currency exchange	1.7	0.3	(5.5)
Purchases	1.0	2.7	2.7
Sales	(1.4)	(2.1)	(0.8)
Fair value of plan assets, end of year	34.3	31.8	$ 28.2
Non - U.S. Plan \| Equity/Fixed Income
Change in fair value of plan assets:
Fair value of plan assets, beginning of year	48.5
Fair value of plan assets, end of year		48.5
Non - U.S. Plan \| Equity/Fixed Income \| Level 3
Change in fair value of plan assets:
Fair value of plan assets, beginning of year	$ 31.8
Fair value of plan assets, end of year		$ 31.8

Level 3 investments of defined benefit plans that were purchased.

No definition available.

Name:	dci_DefinedBenefitPlanPurchases
Namespace Prefix:	dci_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Level 3 investments of defined benefit plans that were sold.

+ References

No definition available.

+ Details

Name:	dci_DefinedBenefitPlanSales
Namespace Prefix:	dci_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (j)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

+ References

+ Details

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

- Definition

Amount of foreign currency translation gain (loss) which increases (decreases) plan assets of defined benefit plan.

+ References

+ Details

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

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=us-gaap_ForeignPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=dci_EquityFixedIncomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: