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Employee Benefits (Details 6) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Debt securities [Member]
   
Summarizes changes for all plan assets measured at fair value using significant unobservable inputs    
Fair value at beginning of measurement period $ 8 $ 7
Unrealized gains (losses) relating to assets still held at end of year 0 3
Purchases, sales, principal payments, issuances, and settlements (1) (2)
Fair value at end of measurement period 7 8
Other plan assets [Member]
   
Summarizes changes for all plan assets measured at fair value using significant unobservable inputs    
Fair value at beginning of measurement period 6 6
Unrealized gains (losses) relating to assets still held at end of year (9) 0
Purchases, sales, principal payments, issuances, and settlements 9 0
Fair value at end of measurement period $ 6 $ 6