Condensed Consolidating Financial Statements (Details) - USD ($) $ in Millions	1 Months Ended
	Apr. 30, 2013	Nov. 30, 2006	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Condensed Consolidating Balance Sheet
Ownership interest in domestic subsidiaries (as a percent)			100.00%
Assets
Cash and cash equivalents			$ 131.9	$ 106.2	$ 113.5	$ 83.6
Accounts receivable, net			1,117.1	1,144.6
Inventories			1,672.8	1,752.1
Income taxes receivable			14.7
Other current assets			102.4	118.2
Total current assets			3,038.9	3,121.1
Property, plant and equipment, net			1,648.6	1,656.4
Goodwill			1,732.4	1,736.4
Intangible assets, net			1,195.9	1,227.4
Other assets			75.4	81.1
Total assets			7,691.2	7,822.4
Liabilities & Equity
Accounts payable			371.0	286.5
Accrued compensation and retirement costs			106.8	128.4
Other current liabilities			126.4	154.0
Current maturities of long-term debt and short-term borrowings			107.1	93.9
Total current liabilities			711.3	662.8
Long-term debt			2,094.3	2,208.1
Other long-term liabilities			823.3	823.6
Total Reliance stockholders' equity			4,032.3	4,099.0
Noncontrolling interests			30.0	28.9
Total equity			4,062.3	4,127.9
Total liabilities and equity			7,691.2	7,822.4
Senior Unsecured Notes
Condensed Consolidating Balance Sheet
Aggregate principal amount	$ 1,100.0	$ 1,100.0
Ownership interest in domestic subsidiaries (as a percent)	100.00%	100.00%
Reportable legal entities | Parent
Assets
Cash and cash equivalents			44.1	41.9	49.4	19.7
Accounts receivable, net			79.1	72.7
Inventories			53.6	57.6
Income taxes receivable			63.2
Other current assets			126.7	139.3
Total current assets			366.7	311.5
Investments in subsidiaries			4,895.5	4,891.8
Property, plant and equipment, net			104.0	103.8
Goodwill			23.8	23.8
Intangible assets, net			15.1	16.1
Intercompany receivables			1,120.2	1,361.7
Other assets			25.1	22.7
Total assets			6,550.4	6,731.4
Liabilities & Equity
Accounts payable			36.6	29.2
Accrued compensation and retirement costs			17.8	23.9
Other current liabilities			54.3	65.2
Current maturities of long-term debt and short-term borrowings			50.0	43.8
Total current liabilities			158.7	162.1
Long-term debt			2,043.5	2,156.6
Other long-term liabilities			315.9	313.7
Total Reliance stockholders' equity			4,032.3	4,099.0
Total equity			4,032.3	4,099.0
Total liabilities and equity			6,550.4	6,731.4
Reportable legal entities | Guarantor Subsidiaries
Assets
Cash and cash equivalents			1.7	(8.3)	(11.0)	(0.8)
Accounts receivable, net			887.6	923.1
Inventories			1,367.3	1,454.2
Other current assets			36.1	38.5
Total current assets			2,292.7	2,407.5
Investments in subsidiaries			299.9	299.9
Property, plant and equipment, net			1,330.9	1,333.7
Goodwill			1,570.9	1,571.0
Intangible assets, net			1,034.6	1,056.7
Intercompany receivables			33.7	26.1
Other assets			44.6	52.5
Total assets			6,607.3	6,747.4
Liabilities & Equity
Accounts payable			269.5	212.3
Accrued compensation and retirement costs			79.1	89.9
Other current liabilities			61.7	26.1
Deferred income taxes			75.2	75.1
Total current liabilities			485.5	403.4
Long-term debt			5.7	5.7
Intercompany borrowings			1,023.4	1,242.5
Other long-term liabilities			454.9	456.2
Total Reliance stockholders' equity			4,631.2	4,633.4
Noncontrolling interests			6.6	6.2
Total equity			4,637.8	4,639.6
Total liabilities and equity			6,607.3	6,747.4
Reportable legal entities | Non-Guarantor Subsidiaries
Assets
Cash and cash equivalents			86.1	72.6	$ 75.1	$ 64.7
Accounts receivable, net			170.4	164.8
Inventories			251.9	240.3
Other current assets			16.3	16.1
Total current assets			524.7	493.8
Property, plant and equipment, net			213.7	218.9
Goodwill			137.7	141.6
Intangible assets, net			146.2	154.6
Intercompany receivables			23.2	18.2
Other assets			5.7	5.9
Total assets			1,051.2	1,033.0
Liabilities & Equity
Accounts payable			84.9	60.6
Accrued compensation and retirement costs			9.9	14.6
Other current liabilities			59.8	62.6
Deferred income taxes			0.6	0.6
Current maturities of long-term debt and short-term borrowings			57.1	50.1
Total current liabilities			212.3	188.5
Long-term debt			45.1	45.8
Intercompany borrowings			153.7	163.5
Other long-term liabilities			52.5	54.1
Total Reliance stockholders' equity			564.2	558.4
Noncontrolling interests			23.4	22.7
Total equity			587.6	581.1
Total liabilities and equity			1,051.2	1,033.0
Consolidating Adjustments
Assets
Accounts receivable, net			(20.0)	(16.0)
Income taxes receivable			(48.5)
Other current assets			(76.7)	(75.7)
Total current assets			(145.2)	(91.7)
Investments in subsidiaries			(5,195.4)	(5,191.7)
Intercompany receivables			(1,177.1)	(1,406.0)
Total assets			(6,517.7)	(6,689.4)
Liabilities & Equity
Accounts payable			(20.0)	(15.6)
Other current liabilities			(49.4)	0.1
Deferred income taxes			(75.8)	(75.7)
Total current liabilities			(145.2)	(91.2)
Intercompany borrowings			(1,177.1)	(1,406.0)
Other long-term liabilities				(0.4)
Total Reliance stockholders' equity			(5,195.4)	(5,191.8)
Total equity			(5,195.4)	(5,191.8)
Total liabilities and equity			$ (6,517.7)	$ (6,689.4)