Condensed Consolidating Financial Statements (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Condensed Consolidating Statement of Comprehensive Income
Net sales	$ 2,614.4us-gaap_SalesRevenueNet	$ 2,553.0us-gaap_SalesRevenueNet
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	1,943.7us-gaap_CostOfGoodsAndServicesSold	1,905.8us-gaap_CostOfGoodsAndServicesSold
Warehouse, delivery, selling, general and administrative	446.1	441.0
Depreciation and amortization	55.3	51.9
Total costs and expenses	2,445.1us-gaap_CostsAndExpenses	2,398.7us-gaap_CostsAndExpenses
Operating (loss) income	169.3us-gaap_OperatingIncomeLoss	154.3us-gaap_OperatingIncomeLoss
Other income (expense):
Interest	(20.6)us-gaap_InterestExpense	(20.2)us-gaap_InterestExpense
Other income, net	1.9us-gaap_OtherNonoperatingIncomeExpense
(Loss) income before equity in earnings of subsidiaries and income taxes	150.6	134.1
Income before income taxes	150.6	134.1
Income tax (benefit) provision	47.7us-gaap_IncomeTaxExpenseBenefit	46.2us-gaap_IncomeTaxExpenseBenefit
Net income	102.9us-gaap_ProfitLoss	87.9us-gaap_ProfitLoss
Less: Net income attributable to noncontrolling interests	1.6	0.7
Net income attributable to Reliance	101.3	87.2
Comprehensive income (loss) attributable to Reliance	76.5us-gaap_ComprehensiveIncomeNetOfTax	78.4us-gaap_ComprehensiveIncomeNetOfTax
Reportable legal entities \| Parent
Condensed Consolidating Statement of Comprehensive Income
Net sales	192.1	182.4
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	155.1	146.1
Warehouse, delivery, selling, general and administrative	39.9	45.1
Depreciation and amortization	5.1	4.5
Total costs and expenses	200.1	195.7
Operating (loss) income	(8.0)	(13.3)
Other income (expense):
Interest	(19.6)	(19.2)
Other income, net	18.9	20.5
(Loss) income before equity in earnings of subsidiaries and income taxes	(8.7)	(12.0)
Equity in earnings of subsidiaries	98.8	84.7
Income before income taxes	90.1	72.7
Income tax (benefit) provision	(11.2)	(14.5)
Net income	101.3	87.2
Net income attributable to Reliance	101.3	87.2
Comprehensive income (loss) attributable to Reliance	76.5	78.4
Reportable legal entities \| Guarantor Subsidiaries
Condensed Consolidating Statement of Comprehensive Income
Net sales	2,237.1	2,244.9
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	1,660.9	1,678.6
Warehouse, delivery, selling, general and administrative	385.4	381.1
Depreciation and amortization	44.5	42.9
Total costs and expenses	2,090.8	2,102.6
Operating (loss) income	146.3	142.3
Other income (expense):
Interest	(5.9)	(6.2)
Other income, net	0.3	(0.2)
(Loss) income before equity in earnings of subsidiaries and income taxes	140.7	135.9
Equity in earnings of subsidiaries	3.5	2.8
Income before income taxes	144.2	138.7
Income tax (benefit) provision	55.0	56.8
Net income	89.2	81.9
Less: Net income attributable to noncontrolling interests	1.4	0.7
Net income attributable to Reliance	87.8	81.2
Comprehensive income (loss) attributable to Reliance	70.1	73.7
Reportable legal entities \| Non-Guarantor Subsidiaries
Condensed Consolidating Statement of Comprehensive Income
Net sales	237.9	187.6
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	180.4	143.0
Warehouse, delivery, selling, general and administrative	37.4	31.2
Depreciation and amortization	5.7	4.5
Total costs and expenses	223.5	178.7
Operating (loss) income	14.4	8.9
Other income (expense):
Interest	(1.5)	(1.2)
Other income, net	5.7	2.5
(Loss) income before equity in earnings of subsidiaries and income taxes	18.6	10.2
Income before income taxes	18.6	10.2
Income tax (benefit) provision	3.9	3.9
Net income	14.7	6.3
Less: Net income attributable to noncontrolling interests	0.2
Net income attributable to Reliance	14.5	6.3
Comprehensive income (loss) attributable to Reliance	(5.8)	(2.8)
Consolidating Adjustments
Condensed Consolidating Statement of Comprehensive Income
Net sales	(52.7)	(61.9)
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	(52.7)	(61.9)
Warehouse, delivery, selling, general and administrative	(16.6)	(16.4)
Total costs and expenses	(69.3)	(78.3)
Operating (loss) income	16.6	16.4
Other income (expense):
Interest	6.4	6.4
Other income, net	(23.0)	(22.8)
Equity in earnings of subsidiaries	(102.3)	(87.5)
Income before income taxes	(102.3)	(87.5)
Net income	(102.3)	(87.5)
Net income attributable to Reliance	(102.3)	(87.5)
Comprehensive income (loss) attributable to Reliance	$ (64.3)	$ (70.9)

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Other Comprehensive Income

-URI http://asc.fasb.org/extlink&oid=6519514

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Comprehensive Income

-URI http://asc.fasb.org/extlink&oid=35737396

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e557-108580

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Net Income

-URI http://asc.fasb.org/extlink&oid=6518256