Condensed Consolidating Financial Statements (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Consolidating financial statements, captions
Net sales	$ 2,448.3	$ 2,209.7	$ 4,473.6	$ 4,498.0
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	1,826.7	1,640.3	3,323.2	3,350.8
Warehouse, delivery, selling, general and administrative	426.0	346.7	783.7	704.4
Depreciation and amortization	50.1	36.5	91.2	72.0
Total costs and expenses	2,302.8	2,023.5	4,198.1	4,127.2
Operating (loss) income	145.5	186.2	275.5	370.8
Other income (expense):
Interest	(22.1)	(15.0)	(35.2)	(29.5)
Other income (expense), net	(0.6)	(3.5)	2.3	3.0
(Loss) income before equity in earnings of subsidiaries and income taxes	122.8	167.7	242.6	344.3
Income before income taxes	122.8	167.7	242.6	344.3
Income tax (benefit) provision	40.9	57.5	76.2	116.2
Net income	81.9	110.2	166.4	228.1
Less: Net income attributable to noncontrolling interests	0.9	1.4	1.7	3.1
Net income attributable to Reliance	81.0	108.8	164.7	225.0
Parent
Consolidating financial statements, captions
Net sales	183.6	189.7	363.0	382.4
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	129.3	132.9	267.4	286.6
Warehouse, delivery, selling, general and administrative	58.6	16.2	109.5	31.2
Depreciation and amortization	5.1	3.4	9.1	6.9
Total costs and expenses	193.0	152.5	386.0	324.7
Operating (loss) income	(9.4)	37.2	(23.0)	57.7
Other income (expense):
Interest	(21.2)	(14.8)	(34.3)	(29.2)
Other income (expense), net	18.5	22.8	36.8	56.7
(Loss) income before equity in earnings of subsidiaries and income taxes	(12.1)	45.2	(20.5)	85.2
Equity in earnings of subsidiaries	82.1	60.1	164.7	128.1
Income before income taxes	70.0	105.3	144.2	213.3
Income tax (benefit) provision	(11.0)	(3.5)	(20.5)	(11.7)
Net income	81.0	108.8	164.7	225.0
Net income attributable to Reliance	81.0	108.8	164.7	225.0
Guarantor Subsidiaries
Consolidating financial statements, captions
Net sales	2,139.2	1,924.1	3,877.9	3,896.3
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	1,617.6	1,457.1	2,909.0	2,944.9
Warehouse, delivery, selling, general and administrative	349.8	326.2	649.4	670.7
Depreciation and amortization	40.9	29.8	74.5	59.0
Total costs and expenses	2,008.3	1,813.1	3,632.9	3,674.6
Operating (loss) income	130.9	111.0	245.0	221.7
Other income (expense):
Interest	(4.9)	(4.7)	(7.4)	(8.6)
Other income (expense), net	(0.2)	(0.7)	3.7	2.0
(Loss) income before equity in earnings of subsidiaries and income taxes	125.8	105.6	241.3	215.1
Equity in earnings of subsidiaries	3.2	7.9	8.0	17.8
Income before income taxes	129.0	113.5	249.3	232.9
Income tax (benefit) provision	49.5	57.4	91.7	119.6
Net income	79.5	56.1	157.6	113.3
Less: Net income attributable to noncontrolling interests	0.8	1.4	1.6	2.9
Net income attributable to Reliance	78.7	54.7	156.0	110.4
Non-Guarantor Subsidiaries
Consolidating financial statements, captions
Net sales	177.5	154.3	341.2	345.9
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	131.8	108.7	255.3	245.9
Warehouse, delivery, selling, general and administrative	31.4	24.4	54.7	49.2
Depreciation and amortization	4.1	3.3	7.6	6.1
Total costs and expenses	167.3	136.4	317.6	301.2
Operating (loss) income	10.2	17.9	23.6	44.7
Other income (expense):
Interest	(0.8)	(0.5)	(1.3)	(1.2)
Other income (expense), net	(0.3)	(0.5)	(0.5)	0.5
(Loss) income before equity in earnings of subsidiaries and income taxes	9.1	16.9	21.8	44.0
Income before income taxes	9.1	16.9	21.8	44.0
Income tax (benefit) provision	2.4	3.6	5.0	8.3
Net income	6.7	13.3	16.8	35.7
Less: Net income attributable to noncontrolling interests	0.1		0.1	0.2
Net income attributable to Reliance	6.6	13.3	16.7	35.5
Consolidating Adjustments
Consolidating financial statements, captions
Net sales	(52.0)	(58.4)	(108.5)	(126.6)
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	(52.0)	(58.4)	(108.5)	(126.6)
Warehouse, delivery, selling, general and administrative	(13.8)	(20.1)	(29.9)	(46.7)
Total costs and expenses	(65.8)	(78.5)	(138.4)	(173.3)
Operating (loss) income	13.8	20.1	29.9	46.7
Other income (expense):
Interest	4.8	5.0	7.8	9.5
Other income (expense), net	(18.6)	(25.1)	(37.7)	(56.2)
Equity in earnings of subsidiaries	(85.3)	(68.0)	(172.7)	(145.9)
Income before income taxes	(85.3)	(68.0)	(172.7)	(145.9)
Net income	(85.3)	(68.0)	(172.7)	(145.9)
Net income attributable to Reliance	$ (85.3)	$ (68.0)	$ (172.7)	$ (145.9)