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Acquisitions (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended | 5 Months Ended | 0 Months Ended | 9 Months Ended | 0 Months Ended | 9 Months Ended | 1 Months Ended | 0 Months Ended |  |  |
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Dec. 31, 2014 item | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2014 item | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2014 | Apr. 30, 2013 item | Apr. 12, 2013 | Dec. 31, 2013 | May 16, 2014 | Dec. 31, 2013 | Dec. 31, 2014 | Dec. 31, 2014 | Dec. 31, 2011 | Apr. 04, 2013 | Aug. 01, 2014 country
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales | $ 2,576.7 us-gaap_SalesRevenueNet | $ 2,705.1 us-gaap_SalesRevenueNet | $ 2,616.8 us-gaap_SalesRevenueNet | $ 2,553.0 us-gaap_SalesRevenueNet | $ 2,306.7 us-gaap_SalesRevenueNet | $ 2,443.5 us-gaap_SalesRevenueNet | $ 2,448.3 us-gaap_SalesRevenueNet | $ 2,025.3 us-gaap_SalesRevenueNet | $ 10,451.6 us-gaap_SalesRevenueNet | $ 9,223.8 us-gaap_SalesRevenueNet | $ 8,442.3 us-gaap_SalesRevenueNet |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of business, net |  |  |  |  |  |  |  |  | 26.2 us-gaap_ProceedsFromDivestitureOfBusinesses | 11.9 us-gaap_ProceedsFromDivestitureOfBusinesses | 8.2 us-gaap_ProceedsFromDivestitureOfBusinesses |  |  |  |  |  |  |  |  |  |  |
Number of countries of the acquiree entity | 12 us-gaap_NumberOfCountriesInWhichEntityOperates |  |  |  |  |  |  |  | 12 us-gaap_NumberOfCountriesInWhichEntityOperates |  |  | 12 us-gaap_NumberOfCountriesInWhichEntityOperates |  |  |  |  |  | 12 us-gaap_NumberOfCountriesInWhichEntityOperates | 12 us-gaap_NumberOfCountriesInWhichEntityOperates |  |  |
Allocation of the total purchase price of acquisitions to the fair value of the assets acquired and liabilities assumed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Goodwill | 1,736.4 us-gaap_Goodwill |  |  |  | 1,691.6 us-gaap_Goodwill |  |  |  | 1,736.4 us-gaap_Goodwill | 1,691.6 us-gaap_Goodwill | 1,314.6 us-gaap_Goodwill | 1,736.4 us-gaap_Goodwill |  |  | 1,691.6 us-gaap_Goodwill |  | 1,691.6 us-gaap_Goodwill | 1,736.4 us-gaap_Goodwill | 1,736.4 us-gaap_Goodwill | 1,244.3 us-gaap_Goodwill |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax deductible goodwill amount | 558.6 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount |  |  |  |  |  |  |  | 558.6 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount |  |  | 558.6 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount |  |  |  |  |  | 558.6 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount | 558.6 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount |  |  |
Trade names |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allocation of the total purchase price of acquisitions to the fair value of the assets acquired and liabilities assumed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible assets not subject to amortization | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember |  |  |  | 206.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember |  |  |  | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember | 206.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember | 37.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember |  |  | 206.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember |  | 206.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible assets not subject to amortization | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember |  |  |  | 206.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember |  |  |  | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember | 206.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember | 37.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember |  |  | 206.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember |  | 206.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember |  |  |
Customer relationships |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible assets acquired subject to amortization |  |  |  |  |  |  |  |  | 37.3 us-gaap_FinitelivedIntangibleAssetsAcquired1 / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember | 135.3 us-gaap_FinitelivedIntangibleAssetsAcquired1 / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember | 44.3 us-gaap_FinitelivedIntangibleAssetsAcquired1 / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember |  |  |  |  |  |  |  |  |  |  |
Weighted average lives of identifiable intangible assets |  |  |  |  |  |  |  |  | 13 years 7 months 6 days | 12 years 6 months | 10 years |  |  |  |  |  |  |  |  |  |  |
Unsecured revolving credit facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity of the revolving credit facility, which used to fund the transaction |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,500.0 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_DebtInstrumentAxis = rs_UnsecuredRevolvingCreditFacilityMember |  |  |  |  |  |  | 1,500.0 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_DebtInstrumentAxis = rs_UnsecuredRevolvingCreditFacilityMember |
Term loan expiring April 4, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of debt, proceeds from which is used to fund transaction |  |  |  |  |  |  |  |  |  |  |  |  |  | 500.0 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = rs_TermLoanDueApril2018Member |  |  |  |  |  |  |  |
Senior unsecured notes due April 15, 2023 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of debt, proceeds from which is used to fund transaction |  |  |  |  |  |  |  |  |  |  |  |  |  | 500.0 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = rs_SeniorUnsecuredNotesDue2023Member |  |  |  |  |  |  |  |
NIS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  |  |  |  | 8.9 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_NorthernIllinoisSteelSupplyCoMember |  |  |  |  |  |  |  |  |  |
AMS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  |  |  |  | 105.6 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_AluminiumServicesUkLimitedMember |  |  |  |  |  |  |  |  |  |
Number of countries of the acquiree entity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 us-gaap_NumberOfCountriesInWhichEntityOperates / us-gaap_BusinessAcquisitionAxis = rs_AluminiumServicesUkLimitedMember
AMS | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of countries in which entity's customers operate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 40 rs_NumberOfCountriesInWhichEntityCustomersOperates / us-gaap_BusinessAcquisitionAxis = rs_AluminiumServicesUkLimitedMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Travel Main |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of real estate properties of acquired entity which were leased by subsidiaries of reporting entity |  |  |  |  |  |  |  |  |  |  |  |  | 18 rs_BusinessAcquisitionNumberOfRealEstatePropertiesOfAcquiredEntity / us-gaap_BusinessAcquisitionAxis = rs_TravelMainHoldingsLLCMember |  |  |  |  |  |  |  |  |
Total transaction value |  |  |  |  |  |  |  |  |  |  |  |  | 78.9 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = rs_TravelMainHoldingsLLCMember |  |  |  |  |  |  |  |  |
Value of debt assumed |  |  |  |  |  |  |  |  |  |  |  |  | 43.8 us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred / us-gaap_BusinessAcquisitionAxis = rs_TravelMainHoldingsLLCMember |  |  |  |  |  |  |  |  |
Metals USA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 1,780.0 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 1,240.0 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |
Total transaction value |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,250.0 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  |
Value of debt assumed |  |  |  |  |  |  |  |  |  |  |  |  |  | 486.1 us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  |
Number of service centers acquired |  |  |  |  |  |  |  |  |  |  |  |  |  | 43 rs_BusinessAcquisitionNumberOfServiceCentersAcquired / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  |
Purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  | 766.8 us-gaap_PaymentsToAcquireBusinessesGross / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  |
Acquired debt not refinanced through proceeds from debt |  |  |  |  |  |  |  |  |  |  |  |  |  | 12.3 rs_BusinessAcquisitionAcquiredDebtNotRefinancedThroughProceedsFromDebt / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  |
Transaction costs |  |  |  |  |  |  |  |  |  | 11.4 us-gaap_BusinessCombinationAcquisitionRelatedCosts / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  |  |  |  |  |
Allocation of the total purchase price of acquisitions to the fair value of the assets acquired and liabilities assumed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash | 3.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 3.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 3.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 3.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 3.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Accounts receivable | 206.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 206.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 206.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 206.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 206.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Inventories | 379.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 379.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 379.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 379.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 379.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Property, plant and equipment | 242.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 242.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 242.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 242.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 242.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Goodwill | 382.7 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 382.7 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 382.7 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 382.7 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 382.7 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Intangible assets subject to amortization | 137.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 137.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 137.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 137.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 137.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Intangible assets not subject to amortization | 203.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 203.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 203.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 203.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 203.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Other current and long-term assets | 9.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 9.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 9.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 9.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 9.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Total assets acquired | 1,563.7 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 1,563.7 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 1,563.7 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 1,563.7 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 1,563.7 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Deferred taxes | 184.4 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 184.4 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 184.4 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 184.4 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 184.4 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Current and long-term debt | 486.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 486.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 486.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 486.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 486.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Other current and long-term liabilities | 126.4 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 126.4 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 126.4 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 126.4 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 126.4 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Total liabilities assumed | 796.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 796.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 796.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 796.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 796.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Net assets acquired | 766.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 766.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 766.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 766.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 766.8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible assets not subject to amortization | 203.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  |  |  | 203.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  | 203.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |  |  |  | 203.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember | 203.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember |  |  |
Metals USA | Non-core roofing business |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 25.4 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = rs_BuildingProductsGroupRoofingDivisionMember |  |  |  |  |  |  |  | 9.6 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = rs_BuildingProductsGroupRoofingDivisionMember |  |  |  |  |
Proceeds from sale of business, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 26.2 us-gaap_ProceedsFromDivestitureOfBusinesses / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = rs_BuildingProductsGroupRoofingDivisionMember |  |  |  |  |  |
Pre-tax loss on sale of business |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.1 us-gaap_GainLossOnSaleOfBusiness / us-gaap_BusinessAcquisitionAxis = rs_MetalsUSAHoldingCorpMember / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = rs_BuildingProductsGroupRoofingDivisionMember |  |  |  |  |  |
Fox |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4.2 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_FoxMetalsAndAlloysIncMember |  |  |  |
Haskins Steel Co., Inc. (Haskins Steel) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 29.5 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_HaskinsSteelCoIncMember |  |  |
GH Metal Solutions, Inc |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 64.5 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_GHMetalSolutionsIncMember |  |  |  |  |  |  |  |  |  |  |  |  |
Sunbelt Steel Texas, LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 48.0 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_SunbeltSteelTexasLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |
2014 acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allocation of the total purchase price of acquisitions to the fair value of the assets acquired and liabilities assumed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash | 1.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 1.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 1.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 1.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 1.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Accounts receivable | 67.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 67.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 67.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 67.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 67.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Inventories | 89.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 89.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 89.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 89.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 89.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Property, plant and equipment | 23.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 23.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 23.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 23.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 23.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Goodwill | 51.3 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 51.3 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 51.3 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 51.3 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 51.3 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Intangible assets subject to amortization | 37.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 37.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 37.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 37.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 37.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Intangible assets not subject to amortization | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Other current and long-term assets | 1.5 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 1.5 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 1.5 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 1.5 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 1.5 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Total assets acquired | 310.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 310.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 310.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 310.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 310.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Deferred taxes | 9.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 9.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 9.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 9.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 9.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Current and long-term debt | 39.2 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 39.2 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 39.2 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 39.2 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 39.2 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Other current and long-term liabilities | 53.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 53.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 53.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 53.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 53.1 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Total liabilities assumed | 101.3 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 101.3 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 101.3 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 101.3 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 101.3 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Net assets acquired | 208.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 208.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 208.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 208.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 208.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible assets not subject to amortization | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 39.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
Tax deductible goodwill amount | 20.3 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  |  |  | 20.3 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  | 20.3 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |  |  |  | 20.3 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember | 20.3 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_FoxAluminiumServicesUkNisMember |  |  |
2013 acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax deductible goodwill amount |  |  |  |  | 107.7 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_GHMetalSolutionsIncSunbeltSteelTexasLLCAirportMetalsAustraliaPtyLimitedWorthingtonSteelVonoreNationalSpecialtyAlloysLLCAndMcKeyPerforatedProductsCoIncMember |  |  |  |  | 107.7 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_GHMetalSolutionsIncSunbeltSteelTexasLLCAirportMetalsAustraliaPtyLimitedWorthingtonSteelVonoreNationalSpecialtyAlloysLLCAndMcKeyPerforatedProductsCoIncMember |  |  |  |  | 107.7 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_GHMetalSolutionsIncSunbeltSteelTexasLLCAirportMetalsAustraliaPtyLimitedWorthingtonSteelVonoreNationalSpecialtyAlloysLLCAndMcKeyPerforatedProductsCoIncMember |  | 107.7 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_GHMetalSolutionsIncSunbeltSteelTexasLLCAirportMetalsAustraliaPtyLimitedWorthingtonSteelVonoreNationalSpecialtyAlloysLLCAndMcKeyPerforatedProductsCoIncMember |  |  |  |  |
Airport Metals (Australia) Pty Ltd |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 2.4 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_AirportMetalsAustraliaPtyLimitedMember |  |  |  |  |  |  |  |  |  |  |  |  |
Worthington Steel Vonore |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 2.6 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_WorthingtonSteelVonoreMember |  |  |  |  |  |  |  |  |  |  |  |  |
National Specialty Alloys, LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 78.0 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_NationalSpecialtyAlloysLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |
McKey Perforated Products Co., Inc., |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 19.6 us-gaap_SalesRevenueNet / us-gaap_BusinessAcquisitionAxis = rs_McKeyPerforatedProductsCoIncMember |  |  |  |  |  |  |  |  |  |  |  |  |
2012 acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total transaction value |  |  |  |  |  |  |  |  | 226.5 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  |  |  |  |  |  |
Value of debt assumed |  |  |  |  |  |  |  |  | 59.4 us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  |  |  |  |  |  |
Allocation of the total purchase price of acquisitions to the fair value of the assets acquired and liabilities assumed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash | 0.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 0.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 0.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 0.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 0.2 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Accounts receivable | 32.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 32.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 32.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 32.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 32.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Inventories | 55.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 55.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 55.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 55.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 55.0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Property, plant and equipment | 30.7 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 30.7 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 30.7 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 30.7 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 30.7 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Goodwill | 68.0 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 68.0 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 68.0 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 68.0 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 68.0 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Intangible assets subject to amortization | 45.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 45.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 45.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 45.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 45.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Intangible assets not subject to amortization | 37.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 37.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 37.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 37.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 37.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Other current and long-term assets | 1.2 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 1.2 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 1.2 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 1.2 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 1.2 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Total assets acquired | 270.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 270.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 270.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 270.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 270.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Deferred taxes | 20.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 20.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 20.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 20.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 20.6 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Current and long-term debt | 59.4 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 59.4 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 59.4 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 59.4 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 59.4 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndLongTermDebt / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Other current and long-term liabilities | 23.5 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 23.5 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 23.5 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 23.5 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 23.5 rs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAndNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Total liabilities assumed | 103.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 103.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 103.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 103.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 103.5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Net assets acquired | 167.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 167.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 167.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 167.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 167.1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible assets not subject to amortization | 37.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  | 37.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  | 37.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  | 37.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember | 37.9 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |
Tax deductible goodwill amount |  |  |  |  |  |  |  |  |  |  | 30.3 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_ContinentalAlloysAndServicesIncMember |  |  |  |  |  |  |  |  |  |  |
Businesses Sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary purchase price allocation information for all acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax deductible goodwill amount | $ 17.2 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_BusinessesSoldMember |  |  |  |  |  |  |  | $ 17.2 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_BusinessesSoldMember |  |  | $ 17.2 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_BusinessesSoldMember |  |  |  |  |  | $ 17.2 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_BusinessesSoldMember | $ 17.2 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = rs_BusinessesSoldMember |  |  |

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- Definition Represents the number of real estate properties of the acquired entity, which were leased by subsidiaries of the reporting entity. + References No definition available. + Details
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Namespace Prefix: | rs_
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Balance Type: | na
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- Definition Amount of current and long-term debt assumed at the acquisition date. + References No definition available. + Details
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- Definition Amount of other current and noncurrent liabilities assumed at the acquisition date. + References No definition available. + Details
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Namespace Prefix: | rs_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition The amount of other current and noncurrent assets recognized as of the acquisition date. + References No definition available. + Details
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Namespace Prefix: | rs_
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- Definition The number of countries in which the entity's customers operate as of balance sheet date. + References No definition available. + Details
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Namespace Prefix: | rs_
Data Type: | xbrli:integerItemType
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