Condensed Consolidating Guarantor Financial Statements - Condensed Consolidating Statement Of Cash Flows (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Operating activities:
Net income (loss)	$ 8.4	$ 98.1
Non-cash expenses	53.3	38.3
Equity in (earnings) loss of subsidiaries
Changes in working capital	26.3	(50.3)
Net adjustments	79.6	(12.0)
Net cash provided by (used in) operating activities	88.0	86.1
Investing activities:
Net cash provided by (used in) investing activities	(12.9)	(29.5)
Financing activities:
Net cash provided by (used in) financing activities	(62.5)	(65.5)
Net increase (decrease) in cash and cash equivalents	12.6	(8.9)
Effect of exchange rates	(2.7)	1.6
Net change in cash and cash equivalents	9.9	(7.3)
Cash and cash equivalents-beginning of period	70.8	61.3
Cash and cash equivalents-end of period	80.7	54.0
Parent [Member]
Operating activities:
Net income (loss)	13.3	102.3
Non-cash expenses	(0.1)	18.3
Equity in (earnings) loss of subsidiaries	(35.4)	(200.4)
Changes in working capital	616.5	9.8
Net adjustments	581.0	(172.3)
Net cash provided by (used in) operating activities	594.3	(70.0)
Investing activities:
Net cash provided by (used in) investing activities	493.7	(2.2)
Financing activities:
Net cash provided by (used in) financing activities	(1,080.5)	69.5
Net increase (decrease) in cash and cash equivalents	7.5	(2.7)
Effect of exchange rates
Net change in cash and cash equivalents	7.5	(2.7)
Cash and cash equivalents-beginning of period	0.2	3.0
Cash and cash equivalents-end of period	7.7	0.3
Joseph T. Ryerson [Member]
Operating activities:
Net income (loss)	44.2	146.8
Non-cash expenses	37.8	12.3
Equity in (earnings) loss of subsidiaries	(14.3)	(38.0)
Changes in working capital	1,038.0	(83.7)
Net adjustments	1,061.5	(109.4)
Net cash provided by (used in) operating activities	1,105.7	37.4
Investing activities:
Net cash provided by (used in) investing activities	(614.5)	(26.1)
Financing activities:
Net cash provided by (used in) financing activities	(495.9)	(11.0)
Net increase (decrease) in cash and cash equivalents	(4.7)	0.3
Effect of exchange rates		(0.2)
Net change in cash and cash equivalents	(4.7)	0.1
Cash and cash equivalents-beginning of period	15.3	14.5
Cash and cash equivalents-end of period	10.6	14.6
Guarantor Subsidiaries [Member]
Operating activities:
Net income (loss)	14.0	90.0
Non-cash expenses	2.5	2.2
Equity in (earnings) loss of subsidiaries	(0.2)	1.0
Changes in working capital	(1,640.1)	20.3
Net adjustments	(1,637.8)	23.5
Net cash provided by (used in) operating activities	(1,623.8)	113.5
Investing activities:
Net cash provided by (used in) investing activities	1,444.2	(143.1)
Financing activities:
Net cash provided by (used in) financing activities	181.0	29.2
Net increase (decrease) in cash and cash equivalents	1.4	(0.4)
Effect of exchange rates	(0.1)
Net change in cash and cash equivalents	1.3	(0.4)
Cash and cash equivalents-beginning of period	1.9	1.5
Cash and cash equivalents-end of period	3.2	1.1
Non-Guarantor Subsidiaries [Member]
Operating activities:
Net income (loss)	(13.2)	(3.6)
Non-cash expenses	13.1	5.5
Equity in (earnings) loss of subsidiaries
Changes in working capital	11.9	3.3
Net adjustments	25.0	8.8
Net cash provided by (used in) operating activities	11.8	5.2
Investing activities:
Net cash provided by (used in) investing activities	(2.6)	1.9
Financing activities:
Net cash provided by (used in) financing activities	(0.8)	(13.2)
Net increase (decrease) in cash and cash equivalents	8.4	(6.1)
Effect of exchange rates	(2.6)	1.8
Net change in cash and cash equivalents	5.8	(4.3)
Cash and cash equivalents-beginning of period	53.4	42.3
Cash and cash equivalents-end of period	59.2	38.0
Eliminations [Member]
Operating activities:
Net income (loss)	(49.9)	(237.4)
Non-cash expenses
Equity in (earnings) loss of subsidiaries	49.9	237.4
Changes in working capital
Net adjustments	49.9	237.4
Net cash provided by (used in) operating activities
Investing activities:
Net cash provided by (used in) investing activities	(1,333.7)	140.0
Financing activities:
Net cash provided by (used in) financing activities	1,333.7	(140.0)
Net increase (decrease) in cash and cash equivalents
Effect of exchange rates
Net change in cash and cash equivalents
Cash and cash equivalents-beginning of period
Cash and cash equivalents-end of period