Employee benefit plans - Components of Net Periodic Defined Benefit Pension Benefit Cost (Credit) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
U.S. defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 2.7	$ 2.9	$ 3.2
Expected return on plan assets	(4.5)	(4.8)	(4.2)
Amortization of unrecognized: Net actuarial loss	1.6	1.0	1.2
Total	(0.2)	(0.9)	0.2
Foreign Pension Plan Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	10.4	11.2	10.4
Interest cost	22.8	24.1	22.3
Settlement loss		0.5
Expected return on plan assets	(17.4)	(18.0)	(16.8)
Amortization of unrecognized prior service credit	1.1	1.2	0.9
Amortization of unrecognized: Net transition obligations	0.4	0.5	0.5
Amortization of unrecognized: Net actuarial loss	8.0	6.8	5.8
Total	25.3	26.3	23.1
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.3	0.2	0.6
Interest cost	0.8	1.0	1.2
Amortization of unrecognized prior service credit	(1.8)	(2.3)	(0.7)
Total	$ (0.7)	$ (1.1)	$ 1.1