Represents the number of tranches comprising the debt issuance.

No definition available.

Name:	rs_DebtInstrumentIssuedTranchesNumber
Namespace Prefix:	rs_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the lump sum amount payable at the maturity of the debt instrument.

+ References

No definition available.

+ Details

Name:	rs_DebtInstrumentPaymentAtMaturity
Namespace Prefix:	rs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the percentage of annual amortization of term loan after specified period.

+ References

No definition available.

+ Details

Name:	rs_DebtInstrumentTermLoanAnnualAmortizationPercentageAfterSpecifiedPeriod
Namespace Prefix:	rs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of annual amortization of term loan through specified period.

+ References

No definition available.

+ Details

Name:	rs_DebtInstrumentTermLoanAnnualAmortizationPercentageThroughSpecifiedPeriod
Namespace Prefix:	rs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the redemption price as a percentage of the principal amount at which the debt instrument may be required to be redeemed by the entity in the event of a change of control or downgrade of the entity's credit rating.

+ References

No definition available.

+ Details

Name:	rs_DebtRedemptionPriceDueToChangeOfControlAndDowngradeOfCreditRatingAsPercentageOfPrincipalAmount
Namespace Prefix:	rs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The contingent increase above the maximum borrowing capacity under the credit facility, if any one or more of the existing banks or new banks agree to provide such increased commitment amount.

+ References

No definition available.

+ Details

Name:	rs_LineOfCreditFacilityContingentIncreaseAdditionalBorrowingCapacity
Namespace Prefix:	rs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The number of financial covenants.

+ References

No definition available.

+ Details

Name:	rs_NumberOfFinancialCovenants
Namespace Prefix:	rs_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

+ Details

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

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

No definition available.

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=rs_UnsecuredRevolvingCreditFacilityDueSeptember2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=rs_UnsecuredTermLoanDueSeptember2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=rs_SeniorUnsecuredNotesPubliclyTradedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=rs_SeniorUnsecuredNotesIssuedNovember2006Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=rs_SeniorUnsecuredNotesDueNovember2016Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=rs_SeniorUnsecuredNotesDue2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=rs_SeniorUnsecuredNotesDueNovember2036Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=rs_OtherRevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=rs_IndustrialRevenueBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Other (Details) $ in Millions			1 Months Ended	3 Months Ended
Debt - Other (Details) $ in Millions	Apr. 12, 2013 USD ($)	Nov. 20, 2006 USD ($) tranche	Sep. 30, 2016 USD ($)	Mar. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($)	Nov. 15, 2016 USD ($)
Debt
Total				$ 2,060.7	$ 1,914.5
Number of financial covenants \| item				2
Credit Agreement
Debt
Maximum borrowing capacity			$ 2,100.0
Debt term			5 years
Unsecured revolving credit facility due September 30, 2021
Debt
Maximum borrowing capacity			$ 1,500.0
Total				$ 690.0	$ 538.0
Additional maximum borrowing capacity under the credit agreement subject to approval of the lenders and certain other conditions			500.0
Commitment fee on unused portion of revolving credit facility (as a percent)				0.15%
Weighted average fixed interest rate (as a percent)				3.37%	2.96%
Letters of credit outstanding				$ 52.9
Available on the revolving credit facility				$ 757.1
Unsecured revolving credit facility due September 30, 2021 \| LIBOR
Debt
Variable interest rate				LIBOR
Interest rate added to base (as a percent)				1.25%
Unsecured revolving credit facility due September 30, 2021 \| Bank prime rate
Debt
Variable interest rate				bank prime
Interest rate added to base (as a percent)				0.25%
Unsecured term loan due from June 29, 2018 to September 30, 2021
Debt
Total				$ 555.0	$ 562.5
Debt amount			$ 600.0
Annual amortization of term loan through September 2018 (as a percent)			5.00%
Annual amortization of term loan thereafter until June 2021 (as a percent)			10.00%
Weighted average fixed interest rate (as a percent)				3.13%	2.82%
Unsecured term loan due from June 29, 2018 to September 30, 2021 \| LIBOR
Debt
Variable interest rate				LIBOR
Interest rate added to base (as a percent)				1.25%
Unsecured term loan due from June 29, 2018 to September 30, 2021 \| Bank prime rate
Debt
Variable interest rate				bank prime
Interest rate added to base (as a percent)				0.25%
Senior Unsecured Notes
Debt
Percentage of principal amount at which the notes may be required to be repurchased in event of a change of control and a downgrade of the entity's credit rating				101.00%
Senior unsecured notes issued November 20, 2006
Debt
Issuance of debt		$ 600.0
Number of tranches comprising the debt issuance \| tranche		2
Senior unsecured notes due November 15, 2016
Debt
Total						$ 0.0
Interest rate (as a percent)		6.20%
Lump sum payment on maturity						$ 350.0
Issuance of debt		$ 350.0
Senior unsecured notes due April 15, 2023
Debt
Total				$ 500.0	$ 500.0
Interest rate (as a percent)	4.50%
Issuance of debt	$ 500.0
Senior unsecured notes due November 15, 2036
Debt
Total				250.0	250.0
Interest rate (as a percent)		6.85%
Issuance of debt		$ 250.0
Other notes and revolving credit facilities
Debt
Maximum borrowing capacity				66.5
Total				55.6	53.9
IRB
Debt
Total				$ 10.1	$ 10.1