Debt (Details 2) (USD $)			0 Months Ended	3 Months Ended			0 Months Ended	3 Months Ended				1 Months Ended	3 Months Ended		1 Months Ended			1 Months Ended			0 Months Ended			12 Months Ended			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Apr. 04, 2013 Subsequent event Third Amended and Restated Credit Agreement item	Mar. 31, 2013 Unsecured revolving credit facility	Dec. 31, 2012 Unsecured revolving credit facility	Apr. 04, 2013 Unsecured revolving credit facility Subsequent event	Apr. 04, 2013 Unsecured revolving credit facility Maximum Subsequent event Third Amended and Restated Credit Agreement	Mar. 31, 2013 Unsecured revolving credit facility LIBOR	Mar. 31, 2013 Unsecured revolving credit facility Bank prime rate	Mar. 31, 2013 Senior unsecured notes due July 2, 2013	Dec. 31, 2012 Senior unsecured notes due July 2, 2013	Nov. 30, 2006 Senior Unsecured Notes - Publicly Traded item	Mar. 31, 2013 Senior Unsecured Notes - Publicly Traded	Apr. 12, 2013 Senior Unsecured Notes - Publicly Traded	Nov. 30, 2006 Senior unsecured notes due November 15, 2016	Mar. 31, 2013 Senior unsecured notes due November 15, 2016	Dec. 31, 2012 Senior unsecured notes due November 15, 2016	Nov. 30, 2006 Senior unsecured notes due November 15, 2036	Mar. 31, 2013 Senior unsecured notes due November 15, 2036	Dec. 31, 2012 Senior unsecured notes due November 15, 2036	Apr. 12, 2013 Senior unsecured notes due 2023 Subsequent event	Mar. 31, 2013 Revolving Credit Facilities - Foreign Operations	Dec. 31, 2012 Revolving Credit Facilities - Foreign Operations	Mar. 31, 2013 Unsecured Revolving Credit Facility and Senior Unsecured Notes	Mar. 31, 2013 Unsecured Revolving Credit Facility and Senior Unsecured Notes Minimum	Mar. 31, 2013 Unsecured Revolving Credit Facility and Senior Unsecured Notes Maximum	Mar. 31, 2013 Term loan expiring April 4, 2018	Apr. 04, 2013 Term loan expiring April 4, 2018 Subsequent event Third Amended and Restated Credit Agreement
Debt
Number of banks as lenders			26
Borrowing capacity under revolving credit facility						$ 1,500,000,000																$ 20,300,000
Issuance of debt	1,151,900,000	1,208,900,000								75,000,000	75,000,000					350,000,000	350,000,000		250,000,000	250,000,000	500,000,000							500,000,000
Annual amortization of term loan during the first year (as a percent)																											5.00%
Annual amortization of term loan during the second year (as a percent)																											5.00%
Annual amortization of term loan during the third year (as a percent)																											10.00%
Annual amortization of term loan during the fourth year (as a percent)																											10.00%
Annual amortization of term loan during the fifth year (as a percent)																											10.00%
Additional borrowings available under the credit facility							500,000,000
Variable interest rate								LIBOR	Bank prime rate
Interest rate added to base (as a percent)								1.50%	0.50%
Commitment fee on unused portion of revolving credit facility (as a percent)				0.25%
Weighted average fixed rate (as a percent)				1.45%	1.46%
Fixed rate (as a percent)										5.35%
Letters of credit outstanding				31,600,000
Additional amount of letters of credit available to be issued				218,400,000
Combined outstanding balances of revolving credit facilities																						11,300,000	8,300,000
Issuance of debt												600,000,000			350,000,000			250,000,000			500,000,000
Number of tranches comprising the debt issuance												2
Interest rate (as a percent)															6.20%			6.85%			4.50%
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%
Interest coverage ratio, actual																								10.6
Minimum interest coverage ratio required, debt covenant																									3.0
Leverage ratio, actual (as a percent)																								24.50%
Maximum leverage ratio required under financial covenant (as a percent)																										60.00%
Minimum net worth requirement																									1,190,000,000
Reliance shareholders' equity	$ 3,646,800,000	$ 3,558,400,000																						$ 3,650,000,000
Ownership interest in domestic subsidiaries (as a percent)	100.00%													100.00%
Minimum percentage of consolidated EBITDA required for the entity and subsidiary guarantors																									80.00%
Minimum percentage of consolidated tangible assets required for the entity and subsidiary guarantors																									80.00%
Actual percentage of total consolidated EBITDA for the parent and subsidiary guarantors																								91.00%
Actual percentage of consolidated tangible assets owned by the entity and subsidiary guarantors																								89.00%