Condensed Consolidating Financial Statements (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Condensed Consolidating Statement of Comprehensive Income
Net sales	$ 2,553.0	$ 2,025.3
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	1,905.8	1,496.5
Warehouse, delivery, selling, general and administrative	441.0	357.7
Depreciation and amortization	51.9	41.1
Total costs and expenses	2,398.7	1,895.3
Operating (loss) income	154.3	130.0
Other income (expense):
Interest	(20.2)	(13.1)
Other income (expense), net		2.9
(Loss) income before equity in earnings of subsidiaries and income taxes	134.1	119.8
Income before income taxes	134.1	119.8
Income tax (benefit) provision	46.2	35.3
Net income	87.9	84.5
Less: Net income attributable to noncontrolling interests	0.7	0.8
Net income attributable to Reliance	87.2	83.7
Comprehensive income (loss) attributable to Reliance	78.4	73.8
Reportable legal entities | Parent
Condensed Consolidating Statement of Comprehensive Income
Net sales	182.4	179.4
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	146.1	138.1
Warehouse, delivery, selling, general and administrative	45.1	50.9
Depreciation and amortization	4.5	4.0
Total costs and expenses	195.7	193.0
Operating (loss) income	(13.3)	(13.6)
Other income (expense):
Interest	(19.2)	(13.1)
Other income (expense), net	20.5	18.3
(Loss) income before equity in earnings of subsidiaries and income taxes	(12.0)	(8.4)
Equity in earnings of subsidiaries	84.7	82.6
Income before income taxes	72.7	74.2
Income tax (benefit) provision	(14.5)	(9.5)
Net income	87.2	83.7
Net income attributable to Reliance	87.2	83.7
Comprehensive income (loss) attributable to Reliance	87.4	82.2
Reportable legal entities | Guarantor Subsidiaries
Condensed Consolidating Statement of Comprehensive Income
Net sales	2,244.9	1,738.7
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	1,678.6	1,291.4
Warehouse, delivery, selling, general and administrative	381.1	299.6
Depreciation and amortization	42.9	33.6
Total costs and expenses	2,102.6	1,624.6
Operating (loss) income	142.3	114.1
Other income (expense):
Interest	(6.2)	(2.5)
Other income (expense), net	(0.2)	3.9
(Loss) income before equity in earnings of subsidiaries and income taxes	135.9	115.5
Equity in earnings of subsidiaries	2.8	4.8
Income before income taxes	138.7	120.3
Income tax (benefit) provision	56.8	42.2
Net income	81.9	78.1
Less: Net income attributable to noncontrolling interests	0.7	0.8
Net income attributable to Reliance	81.2	77.3
Comprehensive income (loss) attributable to Reliance	81.3	77.5
Reportable legal entities | Non-Guarantor Subsidiaries
Condensed Consolidating Statement of Comprehensive Income
Net sales	187.6	163.7
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	143.0	123.5
Warehouse, delivery, selling, general and administrative	31.2	23.3
Depreciation and amortization	4.5	3.5
Total costs and expenses	178.7	150.3
Operating (loss) income	8.9	13.4
Other income (expense):
Interest	(1.2)	(0.5)
Other income (expense), net	2.5	(0.2)
(Loss) income before equity in earnings of subsidiaries and income taxes	10.2	12.7
Income before income taxes	10.2	12.7
Income tax (benefit) provision	3.9	2.6
Net income	6.3	10.1
Net income attributable to Reliance	6.3	10.1
Comprehensive income (loss) attributable to Reliance	(2.8)	1.5
Consolidating Adjustments
Condensed Consolidating Statement of Comprehensive Income
Net sales	(61.9)	(56.5)
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	(61.9)	(56.5)
Warehouse, delivery, selling, general and administrative	(16.4)	(16.1)
Total costs and expenses	(78.3)	(72.6)
Operating (loss) income	16.4	16.1
Other income (expense):
Interest	6.4	3.0
Other income (expense), net	(22.8)	(19.1)
Equity in earnings of subsidiaries	(87.5)	(87.4)
Income before income taxes	(87.5)	(87.4)
Net income	(87.5)	(87.4)
Net income attributable to Reliance	(87.5)	(87.4)
Comprehensive income (loss) attributable to Reliance	$ (87.5)	$ (87.4)