Condensed Consolidating Financial Statements (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended
	Apr. 30, 2013	Nov. 30, 2006	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Condensed Consolidating Balance Sheet
Ownership interest in domestic subsidiaries (as a percent)			100.00%
Assets
Cash and cash equivalents			$ 101.6	$ 106.2	$ 113.6	$ 83.6
Accounts receivable, net			1,214.1	1,144.6
Inventories			1,803.3	1,752.1
Other current assets			96.0	118.2
Total current assets			3,215.0	3,121.1
Property, plant and equipment, net			1,643.9	1,656.4
Goodwill			1,730.3	1,736.4
Intangible assets, net			1,220.2	1,241.6
Other assets			78.2	81.1
Total assets			7,887.6	7,836.6
Liabilities & Equity
Accounts payable			417.4	286.5
Accrued compensation and retirement costs			95.1	128.4
Other current liabilities			172.1	154.0
Current maturities of long-term debt and short-term borrowings			100.2	93.9
Total current liabilities			784.8	662.8
Long-term debt			2,268.5	2,222.3
Other long-term liabilities			823.7	823.6
Total Reliance shareholders' equity			3,980.7	4,099.0
Noncontrolling interests			29.9	28.9
Total equity			4,010.6	4,127.9
Total liabilities and equity			7,887.6	7,836.6
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%	100.00%
Reportable legal entities | Parent
Assets
Cash and cash equivalents			26.6	41.9	46.8	19.7
Accounts receivable, net			85.8	72.7
Inventories			59.7	57.6
Income taxes receivable			21.3
Other current assets			118.9	139.3
Total current assets			312.3	311.5
Investments in subsidiaries			5,004.5	4,891.8
Property, plant and equipment, net			103.1	103.8
Goodwill			23.8	23.8
Intangible assets, net			28.9	30.3
Intercompany receivables			1,187.1	1,361.7
Other assets			23.4	22.7
Total assets			6,683.1	6,745.6
Liabilities & Equity
Accounts payable			36.1	29.2
Accrued compensation and retirement costs			13.5	23.9
Other current liabilities			69.1	65.2
Current maturities of long-term debt and short-term borrowings			50.0	43.8
Total current liabilities			168.7	162.1
Long-term debt			2,217.4	2,170.8
Other long-term liabilities			316.3	313.7
Total Reliance shareholders' equity			3,980.7	4,099.0
Total equity			3,980.7	4,099.0
Total liabilities and equity			6,683.1	6,745.6
Reportable legal entities | Guarantor Subsidiaries
Assets
Cash and cash equivalents			(3.5)	(8.3)	(9.5)	(0.8)
Accounts receivable, net			975.9	923.1
Inventories			1,502.1	1,454.2
Other current assets			36.1	38.5
Total current assets			2,510.6	2,407.5
Investments in subsidiaries			286.1	299.9
Property, plant and equipment, net			1,325.6	1,333.7
Goodwill			1,570.9	1,571.0
Intangible assets, net			1,045.6	1,056.7
Intercompany receivables			29.6	26.1
Other assets			49.4	52.5
Total assets			6,817.8	6,747.4
Liabilities & Equity
Accounts payable			323.1	212.3
Accrued compensation and retirement costs			72.7	89.9
Other current liabilities			56.6	26.1
Deferred income taxes			75.2	75.1
Total current liabilities			527.6	403.4
Long-term debt			5.7	5.7
Intercompany borrowings			1,083.5	1,242.5
Other long-term liabilities			455.6	456.2
Total Reliance shareholders' equity			4,738.7	4,633.4
Noncontrolling interests			6.7	6.2
Total equity			4,745.4	4,639.6
Total liabilities and equity			6,817.8	6,747.4
Reportable legal entities | Non-Guarantor Subsidiaries
Assets
Cash and cash equivalents			78.5	72.6	76.3	64.7
Accounts receivable, net			169.9	164.8
Inventories			241.5	240.3
Other current assets			17.6	16.1
Total current assets			507.5	493.8
Property, plant and equipment, net			215.2	218.9
Goodwill			135.6	141.6
Intangible assets, net			145.7	154.6
Intercompany receivables			26.5	18.2
Other assets			5.4	5.9
Total assets			1,035.9	1,033.0
Liabilities & Equity
Accounts payable			75.7	60.6
Accrued compensation and retirement costs			8.9	14.6
Other current liabilities			68.5	62.6
Deferred income taxes			0.6	0.6
Current maturities of long-term debt and short-term borrowings			50.2	50.1
Total current liabilities			203.9	188.5
Long-term debt			45.4	45.8
Intercompany borrowings			159.7	163.5
Other long-term liabilities			51.8	54.1
Total Reliance shareholders' equity			551.9	558.4
Noncontrolling interests			23.2	22.7
Total equity			575.1	581.1
Total liabilities and equity			1,035.9	1,033.0
Consolidating Adjustments
Assets
Accounts receivable, net			(17.5)	(16.0)
Income taxes receivable			(21.3)
Other current assets			(76.6)	(75.7)
Total current assets			(115.4)	(91.7)
Investments in subsidiaries			(5,290.6)	(5,191.7)
Intercompany receivables			(1,243.2)	(1,406.0)
Total assets			(6,649.2)	(6,689.4)
Liabilities & Equity
Accounts payable			(17.5)	(15.6)
Other current liabilities			(22.1)	0.1
Deferred income taxes			(75.8)	(75.7)
Total current liabilities			(115.4)	(91.2)
Intercompany borrowings			(1,243.2)	(1,406.0)
Other long-term liabilities				(0.4)
Total Reliance shareholders' equity			(5,290.6)	(5,191.8)
Total equity			(5,290.6)	(5,191.8)
Total liabilities and equity			$ (6,649.2)	$ (6,689.4)