Condensed Consolidating Guarantor Financial Statements - Condensed Consolidating Balance Sheet (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
ASSETS
Current assets	$ 1,257.7	$ 1,254.3
Property, plant and equipment net of accumulated depreciation	461.5	483.4
Other noncurrent assets	213.5	226.5
Total assets	1,932.7	1,964.2
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	517.1	456.0
Noncurrent liabilities	1,689.2	1,788.7
Redeemable noncontrolling interest	1.3	1.7
Ryerson Inc. stockholders' equity	(273.1)	(284.9)
Noncontrolling interest	(1.8)	2.7
Total liabilities and equity	1,932.7	1,964.2
Parent [Member]
ASSETS
Current assets	18.4	381.7
Property, plant and equipment net of accumulated depreciation
Other noncurrent assets	978.9	944.2
Total assets	997.3	1,325.9
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	245.4	16.5
Noncurrent liabilities	1,025.0	1,594.3
Redeemable noncontrolling interest
Ryerson Inc. stockholders' equity	(273.1)	(284.9)
Noncontrolling interest
Total liabilities and equity	997.3	1,325.9
Joseph T. Ryerson [Member]
ASSETS
Current assets	1,159.4	2,215.9
Property, plant and equipment net of accumulated depreciation	393.8	410.8
Other noncurrent assets	934.8	319.2
Total assets	2,488.0	2,945.9
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	290.0	254.3
Noncurrent liabilities	1,331.9	1,872.2
Redeemable noncontrolling interest
Ryerson Inc. stockholders' equity	866.1	819.4
Noncontrolling interest
Total liabilities and equity	2,488.0	2,945.9
Guarantor Subsidiaries [Member]
ASSETS
Current assets	121.2	63.0
Property, plant and equipment net of accumulated depreciation	3.2	3.1
Other noncurrent assets	371.8	1,818.6
Total assets	496.2	1,884.7
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	160.7	1,738.3
Noncurrent liabilities	0.8	0.8
Redeemable noncontrolling interest
Ryerson Inc. stockholders' equity	334.7	145.6
Noncontrolling interest
Total liabilities and equity	496.2	1,884.7
Non-Guarantor Subsidiaries [Member]
ASSETS
Current assets	236.5	214.5
Property, plant and equipment net of accumulated depreciation	64.5	69.5
Other noncurrent assets	7.2	14.4
Total assets	308.2	298.4
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	98.9	67.7
Noncurrent liabilities	30.5	32.8
Redeemable noncontrolling interest	1.3	1.7
Ryerson Inc. stockholders' equity	179.3	193.5
Noncontrolling interest	(1.8)	2.7
Total liabilities and equity	308.2	298.4
Eliminations [Member]
ASSETS
Current assets	(277.8)	(1,620.8)
Property, plant and equipment net of accumulated depreciation
Other noncurrent assets	(2,079.2)	(2,869.9)
Total assets	(2,357.0)	(4,490.7)
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	(277.9)	(1,620.8)
Noncurrent liabilities	(699.0)	(1,711.4)
Redeemable noncontrolling interest
Ryerson Inc. stockholders' equity	(1,380.1)	(1,158.5)
Noncontrolling interest
Total liabilities and equity	$ (2,357.0)	$ (4,490.7)