Employee benefit plans - Schedule of Funded Status (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Noncurrent	$ (202.9)	$ (144.4)
U.S. defined benefit pension plans [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Balance at beginning of the year	65.3	59.8
Interest cost	2.7	2.9	3.2
Actuarial loss	4.9	6.2
Benefits paid	(3.8)	(3.6)
Balance at end of the year	69.1	65.3	59.8
Fair value at beginning of the year	45.4	50.4
Actual return on plan assets	6.9	(1.6)
Employer contributions	2.2	0.2
Benefits paid	(3.8)	(3.6)
Fair value at end of year	50.7	45.4	50.4
Funded status	(18.4)	(19.9)
Current	(0.3)	(0.3)
Noncurrent	(18.1)	(19.6)
Total	(18.4)	(19.9)
Accumulated other comprehensive income (loss) - Net actuarial loss	38.1	37.3
Total amount recognized in balance sheet	19.7	17.4
Accumulated benefit obligations ("ABO")	69.1	65.3
OPEB [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Balance at beginning of the year	22.1	21.4
Service cost	0.3	0.2	0.6
Interest cost	0.8	1.0	1.2
Actuarial loss	0.4	0.9
Change in currency exchange rates	0.3	(0.2)
Benefits paid	(1.2)	(1.2)
Balance at end of the year	22.7	22.1	21.4
Benefits paid	(1.2)	(1.2)
Funded status	(22.7)	(22.1)
Current	(1.5)	(1.7)
Noncurrent	(21.2)	(20.4)
Total	(22.7)	(22.1)
Accumulated other comprehensive income (loss) - Net actuarial loss	3.8	3.4
Accumulated other comprehensive income (loss) - Prior service credit	(10.5)	(12.3)
Accumulated other comprehensive loss, Total	(6.7)	(8.9)
Total amount recognized in balance sheet	(29.4)	(31.0)
Foreign Pension Plan Defined Benefit [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Balance at beginning of the year	469.7	454.8
Service cost	10.4	11.2	10.4
Interest cost	22.8	24.1	22.3
Participants' contributions	1.8	1.9
Actuarial loss	95.9	18.4
Change in currency exchange rates	15.3	(13.4)
Benefits paid	(24.4)	(27.3)
Balance at end of the year	591.5	469.7	454.8
Fair value at beginning of the year	343.7	334.8
Actual return on plan assets	49.0	18.2
Employer contributions	28.2	25.7
Participants' contributions	1.8	1.9
Change in currency exchange rates	11.6	(9.6)
Benefits paid	(24.4)	(27.3)
Fair value at end of year	409.9	343.7	334.8
Funded status	(181.6)	(126.0)
Pension asset	5.1
Current	(1.9)	(1.3)
Noncurrent	(184.8)	(124.7)
Total	(181.6)	(126.0)
Accumulated other comprehensive income (loss) - Net actuarial loss	190.8	133.9
Accumulated other comprehensive income (loss) - Prior service credit	5.4	6.5
Accumulated other comprehensive loss - Net transition obligations	1.3	1.7
Accumulated other comprehensive loss, Total	197.5	142.1
Total amount recognized in balance sheet	15.9	16.1
Accumulated benefit obligations ("ABO")	$ 545.9	$ 437.5