Investments - Significant Unobservable Inputs (Details) - Apr. 30, 2014 - USD ($) $ in Millions	Total
Shred-it Partnership
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Equity method investment, recorded at fair value	$ 339.4
Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
EBITDA margin	20.00%
Ratio of capital expenditures to revenues	4.50%
Long-term revenue growth	1.50%
WACC rate	9.00%
Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
EBITDA margin	22.00%
Ratio of capital expenditures to revenues	5.50%
Long-term revenue growth	2.00%
WACC rate	9.00%

Fair Value Inputs, Capital Expenditures to Revenues Ratio

No definition available.

Name:	ctas_FairValueInputsCapitalExpenditurestoRevenuesRatio
Namespace Prefix:	ctas_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair Value Inputs, Earnings before Interest, Taxes, Depreciation, and Amortization Margin

+ References

No definition available.

+ Details

Name:	ctas_FairValueInputsEarningsbeforeInterestTaxesDepreciationandAmortizationMargin
Namespace Prefix:	ctas_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value portion of investments accounted under the equity method.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 25

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=35740979&loc=d3e32014-111567

+ Details

Name:	us-gaap_EquityMethodInvestmentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_FairValueInputsAssetsQuantitativeInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bbb)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueInputsDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of assumed long-term growth in revenues, used as an input to measure fair value.

+ References

+ Details

Name:	us-gaap_FairValueInputsLongTermRevenueGrowthRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ctas_ShreditPartnershipMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: