Condensed Consolidating Financial Statements (Details) (USD $) In Millions, unless otherwise specified					1 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011	Apr. 30, 2013 Senior Unsecured Notes - Publicly Traded	Nov. 30, 2006 Senior Unsecured Notes - Publicly Traded	Jun. 30, 2013 Parent	Dec. 31, 2012 Parent	Jun. 30, 2012 Parent	Dec. 31, 2011 Parent	Jun. 30, 2013 Guarantor Subsidiaries	Dec. 31, 2012 Guarantor Subsidiaries	Jun. 30, 2012 Guarantor Subsidiaries	Dec. 31, 2011 Guarantor Subsidiaries	Jun. 30, 2013 Non-Guarantor Subsidiaries	Dec. 31, 2012 Non-Guarantor Subsidiaries	Jun. 30, 2012 Non-Guarantor Subsidiaries	Dec. 31, 2011 Non-Guarantor Subsidiaries	Jun. 30, 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%
Assets
Cash and cash equivalents	100.8	97.6	93.6	84.6			47.7	28.1	30.7	15.1	(7.8)	13.1	13.8	10.8	60.9	56.4	49.1	58.7
Accounts receivable, less allowance for doubtful accounts	1,143.5	807.7					76.6	67.4			967.0	658.3			99.9	82.0
Inventories	1,587.1	1,272.3					58.3	50.3			1,369.5	1,068.4			159.3	153.6
Intercompany receivables							0.6	0.2			18.2	16.7			2.8	2.4			(21.6)	(19.3)
Income taxes receivable	17.6	28.4					57.2	28.2								0.2			(39.6)
Other current assets	83.5	71.4					109.1	113.3			41.2	26.5			11.4	6.8			(78.2)	(75.2)
Total current assets	2,932.5	2,277.4					349.5	287.5			2,388.1	1,783.0			334.3	301.4			(139.4)	(94.5)
Investments in subsidiaries							4,399.0	3,722.7			1,139.3	257.8							(5,538.3)	(3,980.5)
Property, plant and equipment, net	1,586.3	1,240.7					99.9	100.8			1,274.5	1,044.1			211.9	95.8
Goodwill	1,658.8	1,314.6					23.8	23.7			1,525.5	1,183.9			109.5	107.0
Intangible assets, net	1,313.9	936.5					19.0	11.0			1,172.7	794.6			122.2	130.9
Intercompany receivables							1,461.0	969.7			18.1	26.2			871.6	3.7			(2,350.7)	(999.6)
Other assets	84.1	88.5					18.6	18.3			61.8	68.1			3.7	2.1
Total assets	7,575.6	5,857.7					6,370.8	5,133.7			7,580.0	5,157.7			1,653.2	640.9			(8,028.4)	(5,074.6)
Liabilities & Equity
Accounts payable	419.3	255.6					41.6	25.7			305.7	195.2			93.6	54.0			(21.6)	(19.3)
Accrued compensation and retirement costs	98.6	112.8					13.5	22.8			74.3	84.0			10.8	6.0
Income taxes payable											33.5				6.1				(39.6)
Other current liabilities	144.3	126.2					52.2	48.5			133.9	146.8			36.5	6.1			(78.3)	(75.2)
Current maturities of long-term debt and short-term borrowings	114.6	83.6					100.3	75.3							14.3	8.3
Total current liabilities	776.8	578.2					207.6	172.3			547.4	426.0			161.3	74.4			(139.5)	(94.5)
Long-term debt	2,219.9	1,123.8					2,165.6	1,123.8			5.7				48.6
Intercompany borrowings											2,269.4	864.3			81.3	135.3			(2,350.7)	(999.6)
Other long-term liabilities	856.1	588.3					284.1	279.2			526.1	284.0			45.9	25.1
Total Reliance shareholders' equity	3,713.5	3,558.4					3,713.5	3,558.4			4,225.3	3,577.4			1,312.9	403.1			(5,538.2)	(3,980.5)
Noncontrolling interests	9.3	9.0									6.1	6.0			3.2	3.0
Total equity	3,722.8	3,567.4					3,713.5	3,558.4			4,231.4	3,583.4			1,316.1	406.1			(5,538.2)	(3,980.5)
Total liabilities and equity	$ 7,575.6	$ 5,857.7					$ 6,370.8	$ 5,133.7			$ 7,580.0	$ 5,157.7			$ 1,653.2	$ 640.9			$ (8,028.4)	$ (5,074.6)