v2.4.0.6
Goodwill and intangible assets (Details Textual) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]      
Amortization charges associated with finite-lived intangible assets $ 397 $ 380 $ 423
Total estimated amortization of finite- lived intangible assets for 2013 464    
Total estimated amortization of finite- lived intangible assets for 2014 446    
Total estimated amortization of finite- lived intangible assets for 2015 434    
Total estimated amortization of finite-lived intangible assets for 2016 413    
Total estimated amortization of finite-lived intangible assets for 2017 $ 271    
Minimum [Member]
      
Goodwill [Line Items]      
Finite-lived intangible asset, useful life 3 years    
Maximum [Member]
      
Goodwill [Line Items]      
Finite-lived intangible asset, useful life 15 years