Condensed Consolidating Financial Statements (Details 2) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Condensed Consolidating Statement of Comprehensive Income
Net sales	$ 2,423.7	$ 2,616.8	$ 5,038.1	$ 5,169.8
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	1,767.8	1,943.5	3,711.5	3,849.3
Warehouse, delivery, selling, general and administrative	440.8	444.9	886.9	885.9
Depreciation and amortization	54.9	52.7	110.2	104.6
Total costs and expenses	2,263.5	2,441.1	4,708.6	4,839.8
Operating income	160.2	175.7	329.5	330.0
Other expense:
Interest	(21.5)	(20.2)	(42.1)	(40.4)
Other income (expense), net	(2.8)	(1.3)	(0.9)	(1.3)
Income before equity in earnings of subsidiaries and income taxes	135.9	154.2	286.5	288.3
Income before income taxes	135.9	154.2	286.5	288.3
Income tax (benefit) provision	44.3	56.4	92.0	102.6
Net income	91.6	97.8	194.5	185.7
Less: Net income attributable to noncontrolling interests	1.4	1.3	3.0	2.0
Net income attributable to Reliance	90.2	96.5	191.5	183.7
Comprehensive income attributable to Reliance	97.6	110.7	174.1	189.1
Reportable legal entities | Parent
Condensed Consolidating Statement of Comprehensive Income
Net sales	185.6	191.8	377.7	374.2
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	128.4	136.0	283.5	282.1
Warehouse, delivery, selling, general and administrative	41.5	42.6	81.4	87.7
Depreciation and amortization	3.9	5.0	9.0	9.5
Total costs and expenses	173.8	183.6	373.9	379.3
Operating income	11.8	8.2	3.8	(5.1)
Other expense:
Interest	(20.6)	(19.3)	(40.2)	(38.5)
Other income (expense), net	18.5	23.1	37.4	43.6
Income before equity in earnings of subsidiaries and income taxes	9.7	12.0	1.0
Equity in earnings of subsidiaries	74.0	76.5	172.8	161.2
Income before income taxes	83.7	88.5	173.8	161.2
Income tax (benefit) provision	(6.5)	(8.0)	(17.7)	(22.5)
Net income	90.2	96.5	191.5	183.7
Net income attributable to Reliance	90.2	96.5	191.5	183.7
Comprehensive income attributable to Reliance	97.6	110.7	174.1	189.1
Reportable legal entities | Guarantor Subsidiaries
Condensed Consolidating Statement of Comprehensive Income
Net sales	2,069.2	2,311.4	4,306.3	4,556.3
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	1,521.4	1,738.6	3,182.3	3,417.2
Warehouse, delivery, selling, general and administrative	379.9	387.6	765.3	768.7
Depreciation and amortization	45.3	42.9	89.8	85.8
Total costs and expenses	1,946.6	2,169.1	4,037.4	4,271.7
Operating income	122.6	142.3	268.9	284.6
Other expense:
Interest	(5.1)	(7.6)	(11.0)	(13.8)
Other income (expense), net	(0.7)	0.4	(0.4)	0.2
Income before equity in earnings of subsidiaries and income taxes	116.8	135.1	257.5	271.0
Equity in earnings of subsidiaries	2.6	3.8	6.1	6.6
Income before income taxes	119.4	138.9	263.6	277.6
Income tax (benefit) provision	45.7	61.4	100.7	118.2
Net income	73.7	77.5	162.9	159.4
Less: Net income attributable to noncontrolling interests	1.3	1.2	2.7	1.9
Net income attributable to Reliance	72.4	76.3	160.2	157.5
Comprehensive income attributable to Reliance	76.8	84.8	146.9	158.5
Reportable legal entities | Non-Guarantor Subsidiaries
Condensed Consolidating Statement of Comprehensive Income
Net sales	219.4	173.6	457.3	361.2
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	168.6	128.9	349.0	271.9
Warehouse, delivery, selling, general and administrative	37.2	31.1	74.6	62.3
Depreciation and amortization	5.7	4.8	11.4	9.3
Total costs and expenses	211.5	164.8	435.0	343.5
Operating income	7.9	8.8	22.3	17.7
Other expense:
Interest	(1.8)	(1.3)	(3.3)	(2.5)
Other income (expense), net	3.3	(0.4)	9.0	2.1
Income before equity in earnings of subsidiaries and income taxes	9.4	7.1	28.0	17.3
Income before income taxes	9.4	7.1	28.0	17.3
Income tax (benefit) provision	5.1	3.0	9.0	6.9
Net income	4.3	4.1	19.0	10.4
Less: Net income attributable to noncontrolling interests	0.1	0.1	0.3	0.1
Net income attributable to Reliance	4.2	4.0	18.7	10.3
Comprehensive income attributable to Reliance	6.3	17.5	0.5	14.7
Consolidating Adjustments
Condensed Consolidating Statement of Comprehensive Income
Net sales	(50.5)	(60.0)	(103.2)	(121.9)
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	(50.6)	(60.0)	(103.3)	(121.9)
Warehouse, delivery, selling, general and administrative	(17.8)	(16.4)	(34.4)	(32.8)
Total costs and expenses	(68.4)	(76.4)	(137.7)	(154.7)
Operating income	17.9	16.4	34.5	32.8
Other expense:
Interest	6.0	8.0	12.4	14.4
Other income (expense), net	(23.9)	(24.4)	(46.9)	(47.2)
Equity in earnings of subsidiaries	(76.6)	(80.3)	(178.9)	(167.8)
Income before income taxes	(76.6)	(80.3)	(178.9)	(167.8)
Net income	(76.6)	(80.3)	(178.9)	(167.8)
Net income attributable to Reliance	(76.6)	(80.3)	(178.9)	(167.8)
Comprehensive income attributable to Reliance	$ (83.1)	$ (102.3)	$ (147.4)	$ (173.2)