Summary of significant accounting policies (Details 3) (USD $)	12 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2011 Reporting Units	Dec. 31, 2011 Acquired trade names	Dec. 31, 2010 License agreements	Dec. 31, 2009 License agreements	Dec. 31, 2010 Game engines	Dec. 31, 2009 Game engines	Dec. 31, 2010 Internally developed franchises	Dec. 31, 2009 Internally developed franchises
Definite-Lived and Indefinite Lived Intangible Assets
Estimated fair value in excess of carrying value, low end of the range		$ 4,000,000,000
Estimated fair value in excess of carrying value, low end of the range (percent in hundredths)		40.00%
Discount rate assumed to determine the fair value, low end of range (percent in hundredths)		10.00%	10.00%
Discount rate assumed to determine the fair value, high end of the range (percent in hundredths)		13.00%
Royalty saving rate assumed to determine the fair value (percent in hundredths)			1.50%
Number of trade names that would have an impairment charge in the event of a one percentage point increase in the discount rate			0
Impairment charge				67,000,000	24,000,000	9,000,000	12,000,000	250,000,000	373,000,000
Goodwill impairment	$ (12,000,000)