Quarterly results of operations - Schedule of Quarterly Results of Operations (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended					12 Months Ended			3 Months Ended			6 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Sep. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Net of Noncontrolling Interest [Member]	Dec. 31, 2012 Net of Noncontrolling Interest [Member] Sale of TIMET Marketable Securities [Member]	Jun. 30, 2012 NL [Member] Certain Real Property Litigation Settlement [Member]	Jun. 30, 2012 NL [Member] Certain Real Property Litigation Settlement [Member]
Loss on prepayment of debt			$ 3.7		$ 1.7	$ (7.2)	$ (3.1)
Noncontrolling interest gain for insurance settlement				8.7		3.3	16.9	18.8
Noncontrolling interest charges on asset held for sale write-down	0.8			0.9		0.8	1.1	0.5
Net decrease in reserves for uncertain tax positions		11.1		8.4
Litigation settlement gains						14.7		6.3			7.8	14.7
Gain on securities transaction	13.2
Goodwill impairment	5.3					6.4
Gain on sale of excess property	1.7
Incremental tax charge related to sale of TIMET common stock										6.1
Expense related to increase in reserve for uncertain tax positions						11.0	6.0	5.4	2.1
Provision for income taxes									$ 2.7