Financial instruments and fair value measurements - Marketable Securities and Financial Instruments on Fair Value Basis (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Marketable securities:
Current	$ 0.8	$ 22.5
Noncurrent	338.9	354.1
Currency forward contracts	2.2	(0.8)
Contingent consideration		0.7
Quoted Prices in Active Markets (Level 1) [Member]
Marketable securities:
Current		20.9
Noncurrent	83.7	100.3
Currency forward contracts	2.2	(0.8)
Significant Other Observable Inputs (Level 2) [Member]
Marketable securities:
Current	0.8	1.6
Noncurrent	5.2	3.8
Significant Unobservable Inputs (Level 3) [Member]
Marketable securities:
Noncurrent	250.0	250.0
Contingent consideration		$ 0.7