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Securities (Details 1) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2012
Securities
Dec. 31, 2011
Securities
Summary of gross unrealized losses and related fair values    
Number of securities (less than one year) 10 28
Gross unrealized losses (less than one year)   $ (1)
Aggregate fair value of investments (less than one year)   46
Number of securities (greater than one year) 5   
Gross unrealized losses (greater than one year)     
Aggregate fair value investments (greater than one year)     
U.S. Corporate Debt Securities [Member]
   
Summary of gross unrealized losses and related fair values    
Number of securities (less than one year)   17
Gross unrealized losses (less than one year)   (1)
Aggregate fair value of investments (less than one year)   26
Number of securities (greater than one year)     
Gross unrealized losses (greater than one year)     
Aggregate fair value investments (greater than one year)     
Foreign debt securities [Member]
   
Summary of gross unrealized losses and related fair values    
Number of securities (less than one year)   10
Aggregate fair value of investments (less than one year)   15
Number of securities (greater than one year)     
Gross unrealized losses (greater than one year)     
Aggregate fair value investments (greater than one year)     
Equity securities [Member]
   
Summary of gross unrealized losses and related fair values    
Number of securities (less than one year)   1
Aggregate fair value of investments (less than one year)   5
Number of securities (greater than one year)     
Gross unrealized losses (greater than one year)     
Aggregate fair value investments (greater than one year)