Other assets - Other Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Other Noncurrent Assets [Line Items]
Investment in affiliates	$ 126.1	$ 105.7
Other assets:
Restricted cash	20.9	7.6
Deferred financing costs	7.0	2.0
IBNR receivables	6.7	6.5
Capital lease deposit	6.2	6.2
Assets held for sale	2.6	7.3
Other	46.7	67.9
Total	155.8	164.1
Ti02manufacturing Joint Venture [Member]
Other Noncurrent Assets [Line Items]
Investment in affiliates	109.9	89.2
Basic Management and Landwell [Member]
Other Noncurrent Assets [Line Items]
Investment in affiliates	16.2	16.5
Capitalized Operating Permits [Member]
Other assets:
Waste disposal site operating permits, net	$ 65.7	$ 66.6