Condensed Consolidating Financial Statements (Details) (USD $) In Millions, unless otherwise specified					1 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011	Apr. 30, 2013 Senior Unsecured Notes - Publicly Traded	Nov. 30, 2006 Senior Unsecured Notes - Publicly Traded	Mar. 31, 2013 Parent	Dec. 31, 2012 Parent	Mar. 31, 2012 Parent	Dec. 31, 2011 Parent	Mar. 31, 2013 Guarantor Subsidiaries	Dec. 31, 2012 Guarantor Subsidiaries	Mar. 31, 2012 Guarantor Subsidiaries	Dec. 31, 2011 Guarantor Subsidiaries	Mar. 31, 2013 Non-Guarantor Subsidiaries	Dec. 31, 2012 Non-Guarantor Subsidiaries	Mar. 31, 2012 Non-Guarantor Subsidiaries	Dec. 31, 2011 Non-Guarantor Subsidiaries	Mar. 31, 2013 Consolidating Adjustments	Dec. 31, 2012 Consolidating Adjustments
Consolidating financial statements, captions
Aggregate principal amount					$ 1,100.0	$ 1,100.0
Ownership interest in domestic subsidiaries (as a percent)	100.00%				100.00%	100.00%
ASSETS
Cash and cash equivalents	100.1	97.6	70.0	84.6			33.7	28.1	15.0	15.1	13.2	13.1	11.3	10.8	53.2	56.4	43.7	58.7
Accounts receivable, less allowance for doubtful accounts	940.4	807.7					77.4	67.4			767.4	658.3			95.6	82.0
Inventories	1,317.6	1,272.3					58.8	50.3			1,123.4	1,068.4			135.4	153.6
Intercompany receivables							0.5	0.2			18.9	16.7			2.5	2.4			(21.9)	(19.3)
Income taxes receivable	3.2	28.4					38.8	28.2							1.8	0.2			(37.4)
Other current assets	65.1	71.4					103.8	113.3			29.3	26.5			8.8	6.8			(76.8)	(75.2)
Total current assets	2,426.4	2,277.4					313.0	287.5			1,952.2	1,783.0			297.3	301.4			(136.1)	(94.5)
Investments in subsidiaries							3,524.7	3,722.7			257.8	257.8							(3,782.5)	(3,980.5)
Property, plant and equipment, net	1,235.6	1,240.7					100.5	100.8			1,040.5	1,044.1			94.6	95.8
Goodwill	1,312.4	1,314.6					23.8	23.7			1,183.9	1,183.9			104.7	107.0
Intangible assets, net	922.3	936.5					10.3	11.0			785.6	794.6			126.4	130.9
Intercompany receivables							1,186.3	969.7			20.4	26.2			3.5	3.7			(1,210.2)	(999.6)
Other assets	84.4	88.5					18.6	18.3			63.7	68.1			2.1	2.1
Total assets	5,981.1	5,857.7					5,177.2	5,133.7			5,304.1	5,157.7			628.6	640.9			(5,128.8)	(5,074.6)
Liabilities & Equity
Accounts payable	389.5	255.6					39.9	25.7			319.0	195.2			52.5	54.0			(21.9)	(19.3)
Accrued compensation and retirement costs	67.0	112.8					9.4	22.8			53.7	84.0			3.9	6.0
Income taxes payable											37.4								(37.4)
Other current liabilities	128.1	126.2					58.6	48.5			46.7	71.6			24.5	6.1			(1.7)
Deferred income taxes											75.2	75.2							(75.2)	(75.2)
Current maturities of long-term debt and short-term borrowings	86.6	83.6					75.3	75.3							11.3	8.3
Total current liabilities	671.2	578.2					183.2	172.3			532.0	426.0			92.2	74.4			(136.2)	(94.5)
Long-term debt	1,063.8	1,123.8					1,063.8	1,123.8
Intercompany borrowings											1,104.5	864.3			105.7	135.3			(1,210.2)	(999.6)
Other long-term liabilities	590.2	588.3					283.4	279.2			282.4	284.0			24.4	25.1
Total Reliance shareholders' equity	3,646.8	3,558.4					3,646.8	3,558.4			3,379.2	3,577.4			403.2	403.1			(3,782.4)	(3,980.5)
Noncontrolling interests	9.1	9.0									6.0	6.0			3.1	3.0
Total equity	3,655.9	3,567.4					3,646.8	3,558.4			3,385.2	3,583.4			406.3	406.1			(3,782.4)	(3,980.5)
Total liabilities and equity	$ 5,981.1	$ 5,857.7					$ 5,177.2	$ 5,133.7			$ 5,304.1	$ 5,157.7			$ 628.6	$ 640.9			$ (5,128.8)	$ (5,074.6)