Restructuring charges - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended							12 Months Ended	36 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Mar. 31, 2012 Operational Excellence Initiatives 2011	Dec. 31, 2011 Operational Excellence Initiatives 2011 Person	Mar. 31, 2012 Global Location Strategy 2009 Person	Mar. 31, 2011 Global Location Strategy 2009	Dec. 31, 2009 Global Location Strategy 2009	Dec. 31, 2011 Global Location Strategy 2009
Restructuring Cost and Reserve [Line Items]
Estimated reduction in workforce due to restructuring, number of positions					1,500	2,400
Estimated reduction in workforce due to restructuring, percentage of positions					3.00%
Restructuring charge, pre-tax	$ (9)	$ 107	$ (6)	$ (2)	$ 107	$ (7)	$ (6)	$ 139
Additional charges/(recovery)				$ (2)		$ (7)			$ 20