<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.19.3</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>178</ContextCount>
  <ElementCount>315</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>38</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>6</UnitCount>
  <MyReports>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>00090 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>00100 - Statement - CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/StatementConsolidatedBalanceSheets</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>00105 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/StatementConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>00200 - Statement - CONSOLIDATED STATEMENTS OF INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/StatementConsolidatedStatementsOfIncome</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>00300 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/StatementConsolidatedStatementsOfComprehensiveIncome</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>00400 - Statement - CONSOLIDATED STATEMENTS OF EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/StatementConsolidatedStatementsOfEquity</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>00405 - Statement - CONSOLIDATED STATEMENTS OF EQUITY (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/StatementConsolidatedStatementsOfEquityParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF EQUITY (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>00500 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/StatementConsolidatedStatementsOfCashFlows</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>10101 - Disclosure - Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureBasisOfPresentation</Role>
      <ShortName>Basis of Presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>10201 - Disclosure - Impact of Recently Issued Accounting Guidance</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureImpactOfRecentlyIssuedAccountingGuidance</Role>
      <ShortName>Impact of Recently Issued Accounting Guidance</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>10301 - Disclosure - Revenues</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureRevenues</Role>
      <ShortName>Revenues</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>10401 - Disclosure - Goodwill</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureGoodwill</Role>
      <ShortName>Goodwill</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>10501 - Disclosure - Intangible Assets, net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureIntangibleAssetsNet</Role>
      <ShortName>Intangible Assets, net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>10601 - Disclosure - Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureDebt</Role>
      <ShortName>Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>10701 - Disclosure - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureLeases</Role>
      <ShortName>Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>10801 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>10901 - Disclosure - Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureEquity</Role>
      <ShortName>Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>11001 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>11101 - Disclosure - Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureEarningsPerShare</Role>
      <ShortName>Earnings Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>11201 - Disclosure - Impairment and Restructuring Charges</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureImpairmentAndRestructuringCharges</Role>
      <ShortName>Impairment and Restructuring Charges</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>30303 - Disclosure - Revenues (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureRevenuesTables</Role>
      <ShortName>Revenues (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureRevenues</ParentRole>
      <Position>21</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>30403 - Disclosure - Goodwill (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureGoodwillTables</Role>
      <ShortName>Goodwill (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureGoodwill</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>30503 - Disclosure - Intangible Assets, net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureIntangibleAssetsNetTables</Role>
      <ShortName>Intangible Assets, net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureIntangibleAssetsNet</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>30603 - Disclosure - Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureDebtTables</Role>
      <ShortName>Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureDebt</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>30703 - Disclosure - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureLeasesTables</Role>
      <ShortName>Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureLeases</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>30903 - Disclosure - Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureEquityTables</Role>
      <ShortName>Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureEquity</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>31103 - Disclosure - Earnings Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureEarningsPerShareTables</Role>
      <ShortName>Earnings Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureEarningsPerShare</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>31203 - Disclosure - Impairment and Restructuring Charges (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureImpairmentAndRestructuringChargesTables</Role>
      <ShortName>Impairment and Restructuring Charges (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureImpairmentAndRestructuringCharges</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>40201 - Disclosure - Impact of Recently Issued Accounting Guidance (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureImpactOfRecentlyIssuedAccountingGuidanceDetails</Role>
      <ShortName>Impact of Recently Issued Accounting Guidance (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>40301 - Disclosure - Revenues (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureRevenuesDetails</Role>
      <ShortName>Revenues (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureRevenuesTables</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>40401 - Disclosure - Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureGoodwillDetails</Role>
      <ShortName>Goodwill (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureGoodwillTables</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>40501 - Disclosure - Intangible Assets, net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureIntangibleAssetsNetDetails</Role>
      <ShortName>Intangible Assets, net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureIntangibleAssetsNetTables</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>40601 - Disclosure - Debt - Summary (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureDebtSummaryDetails</Role>
      <ShortName>Debt - Summary (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>40602 - Disclosure - Debt - Other (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureDebtOtherDetails</Role>
      <ShortName>Debt - Other (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>40701 - Disclosure - Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureLeasesDetails</Role>
      <ShortName>Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureLeasesTables</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>40801 - Disclosure - Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureIncomeTaxesDetails</Role>
      <ShortName>Income Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureIncomeTaxes</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>40901 - Disclosure - Equity - Share Repurchases, Dividends, Stock-Based Compensation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureEquityShareRepurchasesDividendsStockBasedCompensationDetails</Role>
      <ShortName>Equity - Share Repurchases, Dividends, Stock-Based Compensation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>40902 - Disclosure - Equity - Accumulated Other Comprehensive Loss (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureEquityAccumulatedOtherComprehensiveLossDetails</Role>
      <ShortName>Equity - Accumulated Other Comprehensive Loss (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>41001 - Disclosure - Commitments and Contingencies - (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureCommitmentsAndContingenciesDetails</Role>
      <ShortName>Commitments and Contingencies - (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureCommitmentsAndContingencies</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>41101 - Disclosure - Earnings Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureEarningsPerShareDetails</Role>
      <ShortName>Earnings Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureEarningsPerShareTables</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="rs-20190930x10qb8f28a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>41201 - Disclosure - Impairment and Restructuring Charges (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rsac.com/role/DisclosureImpairmentAndRestructuringChargesDetails</Role>
      <ShortName>Impairment and Restructuring Charges (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rsac.com/role/DisclosureImpairmentAndRestructuringChargesTables</ParentRole>
      <Position>41</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" original="rs-20190930x10qb8f28a.htm">rs-20190930x10qb8f28a.htm</File>
    <File>ex-31d1.htm</File>
    <File>ex-31d2.htm</File>
    <File>ex-32.htm</File>
    <File>rs-20190930.xsd</File>
    <File>rs-20190930_cal.xml</File>
    <File>rs-20190930_def.xml</File>
    <File>rs-20190930_lab.xml</File>
    <File>rs-20190930_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/srt/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
