Unaudited Pro Forma Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net sales	$ 4,024.7	$ 4,866.8
Net income (loss) attributable to Ryerson Inc.	$ 109.3	$ 27.9

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=7659399&loc=d3e1392-128463

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration