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Employee Benefits (Details 6)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Weighted average health care cost trend rate assumptions [Abstract]    
Health care cost trend rate for next year 8.10% 8.40%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) 4.50% 4.50%
Year that the rate reaches the ultimate trend rate 2028 2028