Employee separation charges (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Feb. 29, 2012	Sep. 30, 2012	Sep. 30, 2012	Dec. 31, 2011
Employee separation charges [Abstract]
Defined Benefit Plan, net gain due to facility closure	$ 6
Employee Separation Charges [Roll Forward]
Liability balance at beginning of period			90	22
Increase in liability (separation charges)		16	57	112
Reduction in liability (payments and other adjustments)			(123)	(44)
Liability balance at end of period		$ 24	$ 24	$ 90